- Drafting and Permit Document Service.
- Our Solar permit service is available along with our home and business solar packages to help you with the process of obtaining a building permit to install your solar kit. The permit service is custom tailored for your solar system for your local jurisdiction. We guarantee the documents will be approved by your local permit officials or your money back.
- Only: Learn More
Off the Grid Solar Kits, Customized, Ready to be Installed
- Off-Grid Systems:
- Planning, Design & Installation Tips:
- Off-Grid Living; Energy Conservation:
- Resource Documents:
What's On the Truck?
If you click where you see a kit underlined it will open a detail page. You can then scroll down and see "What's On the Truck", which is a list of the parts we supply with the package with optional accessories below that. Optimizing kits typically requires customizing system design beyond the basic design parameters. Mounting on the roof or ground, types of attachment are individual's specific property requirements. Habits, available space, budget and aesthetics does not get more individual than that. As a result there is an absolute requirement for system flexibility beyond the basic package. There are options on the detail pages for racking (roof or ground), and attachment to accommodate nearly every application.
Normally we take the wire to the edge of the array where the transition is usually made to conduit. Here are some additional items that your may need from your local hardware store. The remaining balance of system (BOS) components can be; conduit, ground wire, wire inside the conduit, some minor fasteners and sealants and combiner box (sometimes referred to as "J" box or junction box) which used to combine multiple strings into a single pair of wires. These items are readily available at your local hardware store. How much can you expect to spend? That depends, but the size of the system and other individual site specific variances, but we consistently hear from customers for a 3kW - 5kW kit is about $250 - $300 for BOS locally sourced components.
Planning an Off-Grid Electric System
Off-grid solar systems operate from the stored energy in a battery bank. Solar panels are used to keep a battery bank charged on a daily basis. Some part of the home or cabin electricity loads, during the daytime, will usually end up running directly off the array via the electricity passing across the battery connectors. At night, the inverter is pulling directly off the batteries. Your solar system has to be sized to support your daily loads and replace the stored energy pulled from the batteries on a daily basis.
Defining Your Load
The first step in determining how many solar panels you will need or how big your inverter should be is to figure out how many watts of power you need per day. Since you determine what you are tying to run, and how long each day you want to run the items, the first place you have to start, after reducing your loads, is to determine your daily energy budge or daily loads. You are going to want to reduce your daily energy demands first before you start to calculate your loads because it is cheaper to save energy than to make energy.
All the Parts Needed; Looking at The Whole System
A typical stand-alone system consists of solar panels usually connected in series of 2 or 3 which product DC electricity from the sun. The solar panels are connected to a charge controller which controls the pace at which batteries are recharged which is connected a 24VDC or 48VDC battery bank. You will then need an off-grid inverter to convert the DC (Direct Current) electricity stored in the battery bank to AC (Alternating Current) electricity which is more commonly used in home appliances. (Click on the 2nd sub-tab above "Planning Design & Installation Tips" to learn more.)
Where to Get Started; Cheaper to Save Energy Than to Make Energy
The trick to off-grid living is energy conservation and efficiency. The starting point in planning your system is to first reduce demand. (Need Tips? Click on the 3rd sub-tab above "Off-Grid Living Energy Conservation") Most people in America can easily cut their electricity consumption in half. Reducing your family's energy consumption by conserving and investing in watt saving home lights and efficient appliances means you are putting your money in your pocket and can substantially reduce the amount of off-grid equipment and or battery bank. As you begin your journey towards freedom from the grid, start by conserving as much as possible first. Its always cheaper to save electricity than to generate electricity. Most off-grid generation is used for lighting, appliances like refrigerators and water pumping. Lighting is the easiest to tackle. Don't stop at compact florescent lights, go all the way to LED which can use 1/6th the watt consumption of compact florescent lighting.
The BIG Questions You Need to Answer First:
- List your loads. How many watts per day does your household consume? The most important challenge in an off-grid system is to balance your energy consumption with your supply of energy required. You cannot begin to do that without first knowing how much energy you need each day.
Energy Load Worksheet (Excel)
Energy Load Worksheet
IE: 5 - 13 watt light bulbs X 5 hours per day = 65 watts. 18 CF refrigerator @ 5 amps x 120VAC = 600 watts x 6 hours per day = 3,600 watts. THIS IS IMPORTANT: When we say "list your loads", we mean all your loads. From the cell phone chargers to a hair dryer. Need Help? If you download the Excel worksheet you will only have to indicate how much of each piece of equipment you have and how long your run it.
- Daily energy budget? It is NOT based on a homes sq. ft. It is NOT based on how many people are living in the house. It is based on the equipment or appliances you want to run and how long each day you typically run them. It does not get more individual than that. The amount of energy you and your family consumes each day will vary among individuals habits and personal choices.
- How many days of limited sun do you want to be able to run? (Days of Autonomy) Typical is a minimum of 3 day to 5 days. The more days, the more energy storage required or the bigger the battery bank needed.
- What is the largest load you expect to run (Watts / Amps / Volts IE: 240V Well Pump @ 9.5 Amps)
- Click on the sub-tab above "Planning Design & Installation Tips" directly below the buySafe emblem to learn more.
MidNite Solar Battery Based Off-Grid Micro Kits With DIY Load Center
Micro off-grid living is a lifestyle where less is more. From cabin homes to a simple weekend get-a-way escape, these off-grid kits will provide you just enough power to fit your needs. MidNite Solar designs, manufactures, and sells, advanced electronic devices, combiner boxes, disconnects and installation aids specific to the renewable energy industry. SolarWorld and MidNite Solar, American companies producing products made in America, creating American jobs. We like it... a lot! Listed by ETL for US & Canada
|MidNite Micro Kits||Item #||Voltage DC (Battery) / AC (Optional)||Daily Watts @ 5 Sun Hours /Day STC*||# Solar Panels||Price Per Watt||Price before 30% Federal Tax Credit|
|500 Watt Kit||MIDSW-24-500||24 / 120VAC||2,500 Watts||2 - 250W||$5.54|
|750 Watt Kit||MIDSW-24-750||24 / 120VAC||3,750 Watts||3 - 250W||$4.02|
|1000 Watt Kit||MIDSW-24-1000||24 / 120VAC||5,000 Watts||4 - 250W||$3.26|
|1500 Watt Kit||MIDSW-24-1500||24 / 120VAC||7,500 Watts||6 - 250W||$2.49|
MidNite Solar | Magnum Energy OFF-GRID / ON GRID BATTERY BASED POWER SYSTEMS
These off-grid e-panel kits combine three of the worlds best top brands; Magnum Energy inverter, MidNite Solar Classic charge controller, and Canadian Solar panels. Methodically engineered, every component of this kit has been specially selected to assure the highest performance in a safe and simple-to-install kit. Ideal for applications with medium power requirements such as off-grid cabins, homes and back-up power systems. These pre-wired power systems are ready to hang and connect. Magnum Energy and MidNite Solar, American companies producing products made in America, creating American jobs. We like it... a lot! Listed by ETL for US & Canada
|MidNite / Magnum||Item #||Voltage DC (Battery) / AC||Daily Watts @ 5 Sun Hours /Day STC*||# Solar Panels||Price Per Watt||Price before 30% Federal Tax Credit|
|490W MM1524AE||Mag1524AE-490||24 / 120VAC||2,450 Watts||2 - 245W||$7.79|
|980W MM1524AE||Mag1524AE-980||24 / 120VAC||4,900 Watts||4 - 245W||$4.28|
|1470W MM1524AE||Mag1524AE-1470||24 / 120VAC||7,350 Watts||6 - 245W||$3.14|
|510W Magnum Kit||MNMAG-24-510||24 / 120/240VAC||2,550 Watts||2 - 255W||$10.57|
|765W Magnum Kit||MNMAG-48-765||48 / 120/240VAC||3,825 Watts||3 - 255W||$7.39|
|1020W Magnum Kit||MNMAG-24-1020||24 / 120/240VAC||5,100 Watts||4 - 255W||$5.78|
|1530W Magnum Kit||MNMAG-48-1530||48 / 120/240VAC||7,650 Watts||6 - 255W||$4.20|
|2040W Magnum Kit||MNMAG-24-2040||24 / 120/240VAC||10,200 Watts||8 - 255W||$3.41|
|2295W Magnum Kit||MNMAG-48-2295||48 / 120/240VAC||11,475 Watts||9 - 255W||$3.14|
|2550W Magnum Kit||MNMAG-24-2550||24 / 120/240VAC||12,750 Watts||10 - 255W||$2.93|
|3060W Magnum Kit||MNMAG-48-3060||48 / 120/240VAC||15,300 Watts||12 - 255W||$2.61|
|3828W Magnum Kit||MNMAG-48-3825||48 / 120/240VAC||19,125 Watts||15 - 255W||$2.29|
|4590W Magnum Kit||MNMAG-48-4590||48 / 120/240VAC||22,950 Watts||18 - 255W||$2.08|
|5355W Magnum Kit||MNMAG-48-5355||48 / 120/240VAC||26,775 Watts||21 - 255W||$2.17|
|6120W Magnum Kit||MNMAG-48-6120||48 / 120/240VAC||30,600 Watts||24 - 255W||$2.02|
|6885W Magnum Kit||MNMAG-48-6885||48 / 120/240VAC||34,425 Watts||27 - 255W||$1.91|
|7650W Magnum Kit||MNMAG-48-7650||48 / 120/240VAC||38,250 Watts||30 - 255W||$1.82|
Even a small amount of shade is a bad thing.
When a solar panel is even slightly shaded, it is severely impacted. For example, the module shown to the right has 2% of its cell area shaded. The power output of the panel is reduced by 33% – a 17:1 impact factor! This is true even if a micro inverter or power-optimizer is used. Look out for even small shade factors like overhead power lines or vent pipes in roofs.
If you do not see a standard pre-engineered kit that meets your needs we will custom design one for you. Simply fill out the "Contact Us" form (Top RH Tab), and tell us about the size system you are looking for, what you want it to power per day.
OutBack FlexPower ONE Battery Based Off-Grid Kits
The FlexPower ONE pre-wired power system integrates one inverter/charger, one charge controller, and all the essential breakers and surge controllers in a small space at a low install cost. These pre-configured off-grid kits are ideal for applications with modest power requirements, such as cabins, chalets, homes, remote communication sites, and backup power systems.
|FlexPower ONE||Item #||Voltage DC (Battery) / AC||Daily Watts @ 5 Sun Hours /Day STC*||# Solar Panels||Price Per Watt||Price before 30% Federal Tax Credit|
|500W OutBack Kit||FLEX1-24-500||24 / 120VAC||2,500 Watts||2 - 250W||$11.38|
|1000W OutBack Kit||FLEX1-24-1000||24 / 120VAC||5,000 Watts||4 - 250W||$6.28|
|1500W OutBack Kit||FLEX1-24-1500||24 / 120VAC||7,500 Watts||6 - 250W||$4.53|
|1500W OutBack Kit||FLEX1-48-1500||48 / 120VAC||7,500 Watts||6 - 250W||$4.50|
|2000W OutBack Kit||FLEX1-24-2000||24 / 120VAC||10,000 Watts||8 - 250W||$3.65|
|2250W OutBack Kit||FLEX1-48-2250||48 / 120VAC||11,250 Watts||9 - 250W||$3.33|
|2500W OutBack Kit||FLEX1-24-2500||24 / 120VAC||12,500 Watts||10 - 250W||$3.12|
|3000W OutBack Kit||FLEX1-48-3000||48 / 120VAC||15,000 Watts||12 - 250W||$2.74|
|3500W OutBack Kit||FLEX1-24-3500||24 / 120VAC||17,500 Watts||14 - 250W||$2.52|
|3750W OutBack Kit||FLEX1-48-3750||48 / 120VAC||18,750 Watts||15 - 250W||$2.34|
FP1-3 / FP1-4 - Because few gas generators produce grid quality AC power, when using OutBack grid-interactive products in conjunction with a generator to recharge batteries, Outback only recommends using Honda EU generators. Flexware relay assembly may be necessary for auto start function of a two wire auto start generator.
What Inverter Should Your Choose?
To determine the size of the inverter needed in your application, add up the demand from all your appliances that are likely to operate at the same time (Watts & Amps). The inverter should be sized to handle both the surge (start up) requirements as well as the continuous run or duty demand over extended times for equipment like refrigerators, well pumps and washing machines. Small appliances often times require 2X their amps to turn over the locked rotors of the motors. Deep well pumps can be 3X the continuous run amps.
OutBack FlexPower FP2 Dual Inverter Battery Based Off-Grid Kits
The FLEXpower TWO System is ideal for applications with medium-sized power requirements such as larger homes and business or back-up power systems. FLEXpower systems’ components carry all of the necessary ETL certifications for a code-compliant installation that not only saves time and money, but also retains a fully-customized look.
|FLEXpower FP2||Item #||Voltage DC (Battery) / AC||Daily Watts @ 5 Sun Hours /Day STC*||# Solar Panels||Price Per Watt||Price before 30% Federal Tax Credit|
|3000W OutBack FP2 Kit||FLEX2-48-3000||48 / 120/240VAC||15,000 Watts||12 - 250W||$3.69|
|3750W OutBack FP2 Kit||FLEX2-48-3750||48 / 120/240VAC||18,750 Watts||15 - 250W||$3.15|
|4500W OutBack FP2 Kit||FLEX2-48-4500||48 / 120/240VAC||22,500 Watts||18 - 250W||$2.79|
|5250W OutBack FP2 Kit||FLEX2-48-5250||48 / 120/240VAC||26,250 Watts||21 - 250W||$2.53|
|6000W OutBack FP2 Kit||FLEX2-48-6000||48 / 120/240VAC||30,000 Watts||24 - 250W||$2.34|
|6750W OutBack FP2 Kit||FLEX2-48-6750||48 / 120/240VAC||33,750 Watts||27 - 250W||$2.19|
|7500W OutBack FP2 Kit||FLEX2-48-7500||48 / 120/240VAC||37,500 Watts||30 - 250W||$2.07|
If you want your OutBack FlexPower II kit to have the option to be grid-interactive, you can request in the comment box at checkout to substitute for the OutBack FlexPower II FP2-29 (48V Battery Bank) and your wish is our command, no additional charge.
FP2-28 / FP2-29 - Because few gas generators produce grid quality AC power, when using OutBack grid-interactive products in conjunction with a generator to recharge batteries, Outback only recommends using Honda EU generators. Flexware relay assembly may be necessary for auto start function of a two wire auto start generator.
Tare Losses; Off-Grid Every Watt Counts
Tare loss is energy that is required to run when the system is in idle mode. Every watt is gold in an stand-alone system and conserving energy is critical. The "No Load" or idle mode is a specification to look at very closely. There is wide variance between the quality inverters and cheap imports for tare losses.
OutBack Radian Inverter Battery Based Off-Grid Kits With Prewired GS Load Center
The Radian Series GS8048 Grid/Hybrid™ with GSLC175-PV-120/240 Prewired Load Center (full-flexibility grid-interactive/off-grid) inverter/charger that is engineered toward one goal: making system design and installation easier and faster in grid-interactive and comprehensive off-grid applications. As a leader in off-grid energy systems designed around energy storage, OutBack Power is an innovator in Grid/Hybrid system technology, providing the best of both worlds: grid-tied system savings during normal or daylight operation, and off-grid independence during peak energy times or in the event of a power outage or an emergency. Grid/Hybrid systems have the intelligence, agility and interoperability to operate in multiple energy modes quickly, efficiently, and seamlessly, in order to deliver clean, continuous and reliable power to residential and commercial users while maintaining grid stability.
Radian w/Load Center
/ AC Out
|Daily Watts @ 5 Sun Hours /Day STC*||# Solar Panels||Price Per Watt||Price before 30% Federal Tax Credit|
|3750W Radian 8048A Kit||RADSW-3750||48 / 120/240VAC||18,750 Watts||15 - 250W||$3.20|
|4500W Radian 8048A Kit||RAD80SW-4500||48 / 120/240VAC||22,500 Watts||18 - 250W||$3.02|
|5250W Radian 8048A Kit||RAD80SW-5250||48 / 120/240VAC||26,250 Watts||21 - 250W||$2.75|
|6000W Radian 8048A Kit||RAD80SW-6000||48 / 120/240VAC||30,000 Watts||24 - 250W||$2.75|
|6750W Radian 8048A Kit||RAD80SW-6750||48 / 120/240VAC||33,750 Watts||27 - 250W||$2.36|
|7500W Radian 8048A Kit||RAD80SW-7500||48 / 120/240VAC||37,500 Watts||30 - 250W||$2.22|
|8250W Radian 8048A Kit||RAD80SW-8250||48 / 120/240VAC||41,250 Watts||33 - 250W||$2.93|
|9000W Radian 8048A Kit||RAD80SW-9000||48 / 120/240VAC||45,000 Watts||36 - 250W||$2.79|
|9750W Radian 8048A Kit||RAD80SW-9750||48 / 120/240VAC||48,750 Watts||39 - 250W||$2.67|
Generator - The Radian inverter can work with any “split-phase” generator that delivers reliable AC power at the appropriate voltage and frequency. They cannot work with a single-phase or three-phase generator.
What's the difference between watts and watt hours?
Watt and watt hours are often interchanged, misused and can be just plain confusing. A watt (W) is a measurement of power which is the rate of electricity that is being generated or consumed. A watt hour (wh) is the same energy over a period of time. A light bulb rated at 20 watts, in 1 hour it will consume 20 wh of energy, and in 5 hours the same light bulb will consume 100 wh of energy. 1 watt hour (wh) = 1 watt of power supplied for 1 hour. Think of watts (w) as the speed you’re running and watt-hours (wh) as the distance you ran. Ok professor, need to go deeper? One joule per second is a measurement of the rate of power flowing. 1 watt is a unit of energy equal to the power of one watt operating for one hour or 3,600 joule's.
*STC - To learn more about solar panels and how they are measured you need to know what STC stands for. STC in an acronym for "Standard Test Conditions". All solar panels are rated in Watts. The watt rating is how much power (amps times volts) the panel will produce in full sunlight at 25 degrees C (77F). This is the industry standard (STC) for all PV panel ratings (PV means Photovoltaic which is a fancy word for solar). Solar panel manufactures have long used this test standard which is 1,000 watts per square meter solar irradiance, 1.5 Air Mass and a 25 degrees C. cell temperature.
PTC is an acronym for "PV-USA". The PV-USA test conditions were developed at the PV USA test site at the University of Davis, California for standards established by the California Energy Commission that are considered closer to real world conditions (Real World Vs. STC factory test conditions). The PTC rating test is 1,000 watts per square meter solar irradiance, 1.5 Air Mass, and 20 degrees C. ambient temperature at 10 meters above ground level and wind speed of 1 meter per second. In California, solar panels manufactures must be tested and rated independently at the PV USA test facility at the University of Davis (CA) to be considered for rebates.
The ambient temperature rating (PTC) is generally considered a better real world standard than factory conditions because silicon solar cells average about 20 degrees C. above ambient temperature in the real world, cell voltage drops as temperature increases. A module's power output in real life conditions is lower than the power measured at the panel manufacturing factory where cell temperature is maintained at a controlled 77 degrees F. (25 C).
STC Vs. PTC Cell voltage drops about 0.08 volts per degree C. in environments which exceed 25 degrees C. That means an STC rating of 17 volts can actually become a PTC (PV-USA) rating of 15 or 16 volts. Using Ohm's Law, volts times amps is equal to watts which equals power, so a reduced voltage, means reduced watts.
Neither PTC nor STC account for all "real-world" losses. Actual solar systems will produce lower outputs due to soiling, shading, module mismatch, wire losses, inverter and transformer losses, shortfalls in actual nameplate ratings, panel degradation over time, and high-temperature losses for arrays mounted close to or integrated within a roofline.
• Off-Grid – Utility Grid Power is not available for use.
• On-Grid – Utility Grid power is available for use. Does not imply the ability to sell power back to the utility grid.
• Grid-tie, Grid-interactive, Grid-intertie, Bimodal – Utility Grid Power is available for use and the system is capable of returning (selling) electricity back to the utility grid.
Off-Grid Kit Design; It All Starts With Your Daily Loads
Appliance & Equipment Load List: List and add up your daily electrical equipment load demand in watt hours (wh):
Watt hours (wh) and amp-hours (aH); Watts = Amps X Volts. Watt hours are the most common measure of electricity usage and are the easiest to understand. Amp Hours = Watt hours / System Voltage. Many professional system designers will use amp hours to size a system because amp hours takes into account real world behavior of solar panels and battery banks. Either method will arrive at the same conclusion if done properly. For our purposes here, we will primarily use watt hours (wh) when sizing the number of solar panels (and inverter) and amp hours (aH) for our battery selection.Energy Load Worksheet (Excel) Energy Load Worksheet
TIP; How long each day does a refrigerator run? 120VAC Refrigerators can be a large load for off-grid systems or they can be no draw. How often a refrigerator will run during a 24 hour day depends on many factors and will vary from home to home for the same refrigerator. Some of the variables include; the room temperature throughout the day, how full your refrigerator is (Full refrigerators run less often once the contents are cooled), and how often you open the door throughout the day. You can lower the run time of your refrigerator by turning off the automatic defrost function and keeping your refrigerator full. One off the grid living tricks is to keep full jugs of water in a 1/2 full refrigerator. Once the contents of the refrigerator are cooled, an energy efficient model in your home that is full might be expected to run 24% - 35% of the time with a room temperature of 70 degrees or about 6 hours out of 24.
TIP; Higher battery voltage means less resistance which allows equipment to run cooler. Cooler electrical equipment = longer life. We recommend 48 VDC battery bank especially when you go larger than 8 250 watt panels.
Your system voltage means the nominal voltage you select for your battery bank, charge controller and inverter (if you are planning to use one). Here are some things to consider when choosing your systems voltage:
- The DC system voltage is established by the battery bank in off-grid systems. A major factor in making this decision is how much power will be required from the batteries. As power demands increase it is advisable to raise the battery voltage. This voltage is important because establishes the type of charge controller and inverter that will be selected. The selection of the battery bank voltage affects the currents. A 1200 watt off-grid system operating at 12 volts draws 100 amps. (1200w / 12v = 100A). The same system draws only 25A at 48 volts. Lower amps reduces the size of conductors, over current protection devices, disconnects and charge controllers. Additionally, since voltage drop and power losses are smaller at lower amps, higher voltage off-grid systems are more efficient. As a rule of thumb, off-grid systems up to 1000 watts use a minimum 12 volt battery bank which limits DC currents to less than 84 amps. For 2000 watt systems, often times a 24 volt battery banks is used. For 5000 watt system a 48 volt battery bank should be selected. NOTE: There is nothing wrong with choosing a 48 VDC system for 6 panels and up, however you need to size the array in increments of 3 panel series because your array voltage needs to be at least 20% higher than your battery bank. IE: 9 panels, 3 x 3 in series for 48VDC battery bank. 8 panels, 4 x 2 in series for 24VDC battery bank.
|Panel Mfg. Tolerance||5%|
|Panel PTC (Temp)||12%|
Daily Off-grid System Charge Requirement in Amp Hours:
- Since the energy output to the loads must be balanced by the energy input from your solar panels and or wind turbine, we need to calculate your daily charge requirement in amp hours as that number will come in handy later. Take your total daily watt hours x 50% (rule of thumb derate) to account for losses in inverter, circuits, wire transfer loss, battery efficiency and module temperature (PTC). Now divide by the system voltage you chose based on the previous section and write this number down. This is the charge in amp hours your solar panels will have to provide each day to meet your load requirements you have set. Example 5,000 watts daily load total X 50% = 7,500 watts / 48 volt system = 156 amp hours that will need to be generated. Another way to put it is this means that the daily Ah demand on the batteries will be 156 aH.
Size Your Solar Panel Array; Input Must Equal Output.
Number of Solar Panels = Daily Watt Requirement (1 - 24 hour period (Energy Budget)) X 50% ÷ shortest day sun hours ÷ panel STC rating.
The number of solar panels your will require is a basic off-grid formula that considers your total daily energy requirements X (+) 50% (rule of thumb) to allow for losses in wiring distribution efficiency, panel real world performance Vs. factory STC rating, battery and inverter efficiency. You then take that number and divide the lowest solar irradiance available in the area of the system which is usually the shortest daylight month of the year (December). The last step is to divide that number by the STC watts of the solar panel rating. IE: 8,000 watts per day energy budget X 50% = 12,000 Watt-Hours/Day of energy to be generated. 12,000 Watt-Hours per day div the available sun hours in your area (Solar Irradiance) in December which has the shortest day of the year.
Solar Insolation / Lowest Available “Sun-Hours Per Day”
Off-Grid systems use a sizing methodology than is different from grid-tied systems. Since you are on your own with no utility to back you up, you must consider the shortest day of the year or the amount of available sun in December.
Look up the solar irradiance near your area from our lowest peak sun hour resource map. Find the nearest city to your home and write down the lowest daily sun hours. Divide your daily load calculation (Daily energy budget + 50%) by lowest available sun hours per day from the solar irradiance chart. For example, if the daily load calculation (Daily energy budget + 50%) is 12,000 watts, and the site is near Salt Lake City UT, you would take 12,000 watts / 4 sun hours = 3,000 watt solar array. That means if you choose 250 watt solar panels you would need 12 (EA) - 250 watt solar panels for the size kit you select.
The “peak sun hours” for a location is a measure of the total insolation (solar radiation or amount of sun) available and is usually expressed as an average daily value. It represents the total sunlight an area typically experiences at a given time of year by converting it to the equivalent number of hours per day of 1000W/m2 of irradiance (kWh/ m2/day). For off-grid calculations, we do not want to use average but lowest since we have to take into account the shortest day of the year in Dec.
One more factor comes into play, for 48V battery bank you will need to connect at a minimum panels in series of 3 to provide enough volts during the hot days of summer to top off your 48 VDC battery bank. Your voltage from your panel series should be a minimum of 20% above the battery bank. (If you have a very long DC run from your array you may want to go as high as 4 or 5 in series to use smaller size wire.) In our example above, you would need to use 12, 9 or 6 panels so you have strings of 3.
Your energy budget is a personal choice and an opportunity to aggressively manage your daily energy usage. It is always cheaper to save energy than to make energy. NOTE: No matter how large your system is, you will need to manage your daily energy consumption as it relates to the amount of available sun. IE: a cloudy stretch of days may only produce 50% of your energy requirements. After a many days in a row of heavy cloud cover, you may have to cut back your daily energy consumption until the weather clears a bit.
Evaluating your off-grid site is similar in many ways to grid interactive site evaluations. Key Considerations:
- Check out areas available to install your solar kit. A few things to consider; array dimensions, orientation, tilt and obstructions. For off-grid installations, ground mount systems are the most popular. (Top-of-Pole or Rack Mounted)
- Shading of array location. This is important in any solar installation but a must in off-grid systems.
- Roof type and age.
- TIP; If you plan on re-roofing within 5 years but are not ready yet, some homeowners will replace only the shingles located under the solar array when the panels are installed and leave the rest for later.
- Battery Bank and Inverter Location.
- TIP; Solar cells are activated by visible light not ultra-violet or infra-red. Solar panels produce electricity when exposed to sun light, but plan to keep your inverter and battery bank in the shade and or indoors. Inverter and charge controllers should be located as close to the battery bank as possible.
Battery Sizing and Selection
Choosing your battery:
Battery bank sizing is the part of the off-grid system that has a higher probability of causing you problems that other parts of your system. Use the battery sizing worksheet to help you through this critical stage. Factors such as your budget may tempt you to look to cheaper battery alternatives, but a quality battery will pay off over the years. We recommend you choose a 2V or 6V battery and connect them in series so that the total equals the system voltage you initially selected.
TIP; Match the Number of Solar panels (Derated Output) to the Battery Capacity: After you finish sizing the number of solar panels you need to off-set your load requirements, you will need to consider whether the panels power and your battery bank's capacity are sized to work together, or are matched, within reason. You will want the solar panel array to have the capacity to ideally fully charge your battery bank on the shortest day of the year or be prepared to lower your power needs during the wintertime. If the off-grid array is too large, you waste money and power because your charge controller will not send all the current the solar panels produce because your battery bank will not be capable accepting too much power too quickly. If the solar array is too small, it will not be able to fully charge your battery bank.
To properly design a battery bank, you need to account for the storage capacity required, the maximum discharge rate (the sum of all the loads which might be run simultaneously), the maximum charge rate (the current output from the solar array though the charge controller), and the minimum ambient temperature at which the batteries will be used. Whichever of these factors requires the largest capacity will dictate the size of the battery bank. The storage capacity of a battery the amount of electrical energy it can hold is usually expressed in amp-hours (Ah). Using one amp for 100 hours means 100 Ah have been used. A battery bank in a off-grid solar power system should have sufficient capacity to supply needed power during the longest expected period of cloudy weather. A lead-acid (vented or sealed AGM) battery should be sized 20% to 50% larger than this amount so you do not drain the battery more than 50% on a regular basis.
TIP; Only similar batteries should be connected together in one bank. Do not connect old and new batteries or wet and gel cell batteries together.
Battery Sizing Worksheet
Use this worksheet to determine what size battery bank is required for your system. Battery size, or capacity, is measured in amp-hours. Battery voltage is determined by the number of "cells" in series. All lead-acid battery cells have a nominal output of 2 VDC. Actual cell voltage varies from about 1.7 VDC at full discharge to 2.4 VDC at full charge. 12 VDC lead-acid batteries are made of 6 separate cells in one case. 6 VDC batteries are made of 3 cells in one case. Putting battery cells in parallel increases amp-hour capacity, but does not change voltage.
Tip: An off-grid battery bank should be large enough to deliver about 3 days of power with a discharge of no more than 50% of the battery banks total capacity. Less than 3 days and your charge and discharge number of cycles will shorten the life of the battery bank.
Battery bank sizing is the capacity to store electrons and is expressed in amp hours (AH) and at the rate the battery will charge or discharge not the physical size of the battery. Be careful when you are considering the Ah capacity of a battery and compare batteries that are advertising a 20 Ah discharge and not more (An apples to apple thing). Choose the 20-hour rate when sizing and selecting batteries.
Off-grid or backup battery banks can be made up of many small batteries which are connected in series and or parallel to give you the wattage (Volts X Amps) capacity needed. As a rule of thumb, battery banks with lower voltage (large cells) are going to last longer, take less work to maintain but are going to cost more initially. Keep your battery bank the same age, size and brand. Mismatched batteries will cause the smaller ones to have to work harder and the larger ones to coast and sulfate. (That's a bad thing)
Though both methods of calculations, (watts Vs. Ah), will get you to the same conclusion, here is an example of a battery bank sizing calculation using Ah.
- 6,000 AC Wh Average daily load ÷ 0.9 Inverter Efficiency = 6,667 Wh/day.
- 6,667 Wh/day ÷ 48 DC system volts = 138.9 Ah per day.
- 138.9 Ah per day X 1.11 battery temperature derate multiplier x 3 days of autonomy ÷ 0.5 DOD (Depth of Discharge) = 925.1 total system Ah.
- 925.1 total system Ah ÷ 325 Ah individual battery capacity = 3 parallel battery strings (rounded up from 2.85)
- 48V system voltage ÷ 6V battery voltage = 8 batteries in series
- 3 parallel strings X 8 batteries = 24 total 325 Ah batteries needed for the system.
This Ah battery calculation shows that a battery bank of 24 325 Ah batteries will provide ample energy storage in this example to meet the daily requirements, inverter loss, cold temperature inefficiency and days of autonomy while keeping the DOD above 50%.
Tip: The number of batteries or series strings of batteries connected in parallel should be limited to no more than 3 per charge controller. This minimizes the chance of unequal charging from one battery or string to the next and will increase the life of the batteries all other things being equal.
Battery state-of-charge (SOC) can be measured by an amp-hour meter, voltage or by specific gravity. Some care and knowledge is required to interpret state-of-charge from voltage or specific gravity readings. We recommend amp-hour meters for all systems with batteries. An amp-hour meter is like a fuel gauge for batteries and provides all the information needed to keep batteries charged. At a glance, the user can see system voltage, current, and battery condition.
Power Center = Charge Controller, Inverter, Breakers & More
Choosing your charge controller:
A charge controller is an electronic voltage regulator used in off-grid solar and wind systems with battery banks to properly control the charge from the solar panels or wind turbine keep the voltage to the battery bank within acceptable limits. The charge controller automatically tapers, stops, or diverts power when batteries become fully charged. Without a charge controller your solar panels or wind generator would continue to send electricity to the battery bank and eventually destroy your batteries.
Your charge controller will:
- Provide an optimum charge to the batteries.
- Prevent your battery bank for being overcharged from your solar panels or wind turbine.
- Prevent unwanted discharging.
- Provide information on the state of charge of the battery bank.
|Modified Sine Wave Inverters(Sometimes Called Square Wave)|
|You can save a few dollars by purchasing a modified sine wave over a pure sine wave inverter but consider this first before you buy. Modified sine wave inverters may not run:|
|• Laser printers, photocopiers, and anything with an electrical component called a thyristor|
|• Anything with a silicon-controlled rectifier (SCR), like those used in some washing machine controls|
|• Some laptop computers (Apple Products can be particularly fussy about their energy source)|
|• Some fluorescent lights|
|• Some new furnaces and pellet heaters with microprocessor controls|
|• Digital clocks with radios|
|• Appliances having speed controls|
|• Medical equipment should not be power with modified sine wave inverters.|
|Because the total harmonic distortion is higher in modified sine wave inverters, motors will run hotter and not last as long. You may hear a buzzing from your stereo system and you might see lines on your TV screen.|
The simplest charge controllers cut the power when the battery reaches a set voltage, and turn it on when a low voltage set point is reached. Pulse width modulated (PWM) charge controllers turn on and off very rapidly, maintaining the batteries at full charge with whatever power is available. Maximum power point tracking (MPPT) charge controllers optimize the voltage of the solar panels or wind turbine to maximize total power output then convert that to the correct voltage to charge the battery. This process significantly increases the power from a solar array, particularly in low temperatures when battery voltage is significantly below the solar array voltage. Most MPPT charge controllers work with higher array voltages, enabling the use of larger solar panels, which can be more economical on a cost per watt basis. A higher voltage solar array also minimizes the required wire size between the array and the charge controller. While more expensive than PWM controllers, MPPT charge controllers can boost system performance significantly by up to 30%.
Blue Pacific Solar sells MidNite Solar, Outback Xantrex and Morningstar charge controllers. All these companies have take much of the work out of the technical calculations required for properly sizing a charge controller with their string calculators. On all our off-grid pre-engineered packages, we have matched the right sized charge controller with the package for you.
Choosing your Off-grid Inverter:
Living off the grid means you will be generating, storing and processing every watt your off-grid home or cabin sucks up. If your cabin is going to need AC power, then an off-grid AC inverter is going to be of particular interest to you because you will be depending on it day in and day out.
Off-grid inverters are sold either sine wave or modified sine wave. Sine wave output, which has low total harmonic distortion, will power virtually any type of load, even sensitive audio electronics. Modified sine wave inverters may not run some types of equipment satisfactorily, and some loads won’t run at all.
An off-grid inverter must supply enough power to meet the needs of all the appliances running simultaneously. Before selecting an inverter, you must know the watts your appliances will require and their amp and surge needs. Sizing an inverter for an off-grid system, which is based on instantaneous load, is very different from sizing a grid tied inverter, which is determined by the solar panel array size. A grid tied inverter’s job is simply to convert all the DC electricity from the solar array into AC power, which is fed back into the house electrical system then onto the grid if production exceeds the homes energy consumption. In a grid tied system, the inverter is not responsible for meeting the AC loads, since practically unlimited utility power is available. In the case of an off-grid inverter, the inverter has to provide enough energy to all the AC loads, sometimes at the same time. Say you need to simultaneously power 3,000 Watts from various appliances. For an off-grid system, you’d need an inverter that could supply at least that amount. Note that the solar array size does not enter into this inverter sizing since the inverter pulls its power from the battery bank.
Inverter Surge Capacity
The ability of an off-grid inverter to surge to a higher level than its rated continuous output for a short duration to turn over the locked rotor of large loads like well pumps is critical. The inverter specifications that should be looked at are the Maximum Output Amps and the AC overload capability. If there are large loads a good number to look for is a five second surge capability of at least 1 ½ times the rated output of the inverter. If you have a deep well pump, the minimum requirement may be 3X the continuous run amps.
Blue Pacific Solar only sells inverters that meet Underwriters Laboratories (UL) 1741 standards. So if you are on the fence between two choices of inverters, you might ask and find out if it is UL listed and is it an inverter specifically made for off-grid solar or wind applications.
Lightning and Surge Protection
The funny blue glass like bulbs you see on the power center above are AC and DC surge protectors. Lightning can enter a wiring system by either the DC route or AC or both at the same time. The MidNite Solar Surge Protective Device (MNSPD) is a Type 2 device, designed for indoor and outdoor applications. Engineered for both AC and DC electric systems, it protects both transformer and transformer-less inverters without interfering with the GFP protection circuit, it provides protection to service panels, load centers or where the SPD is directly connected to the electronic device requiring protection.
Combiner / circuit breaker box is a key piece of equipment that begins to bring the pieces of equipment together that allows you to generate electricity. NEC (National Electrical Code) says that each series of strings of panels are to be wired to it's own DC circuit breaker. The combiner box is usually located directly under or near the array
Wire size and breakers are the final items in your off-grid design to consider, but no less important. To have a safe off-grid system, you will need to install breakers and choose the right size wire. If you select one of our pre-wired power systems with your kit, we do all the heavy lifting for you because right size breakers are pre-engineered and pre-wired into each of our power centers. You simply have to hang and connect it following our wire diagram which is supplied with all our kits.
The distance between the combiner box, which is usually located near the solar panels, and the charge controller will be a factor in choosing the best string voltage for the charge controller and battery system. The higher the input voltage the smaller the wire can be for any given amount of power. For example, a system with a 12 volt battery and solar panels consisting of four 6.75 amp 12 volt DC nominal modules located at a distance of 40’ from the batteries could have the modules wired in series, parallel or series and parallel. Input design possibilities in this example are 12, 24, and 48 volts DC. If the panels are configured with the modules wired in parallel, the input voltage would be 12 volts DC with an input current of 26 amps. The same panels wired in series would have an input voltage of 48 volts DC and an input current of 6.5 amps. In this example #1, the 26 amp 12 volts DC panels #1/0 wire, which is prohibitively expensive, would be required to limit voltage drop to 2% which is recommended for 12 volt DC systems. The same panels wired for 48 volts dc would only require a #8 wire. With the #8 AWG wire the 12 volt dc panels would have to be within 7’ of the batteries. The distance that #8 wire can be used is over 5 times greater at 48 volts DC than 12 volts DC.
NOTE: These are just given as examples. At Blue Pacific Solar, we would never recommend you use a 12VDC system in your home or cabin unless you intend to only have 12VDC appliances and lights. 24VDC up to about 8 panels are a common choice, but 48VDC is a better choice for 6 or more panels. Higher voltage = smaller wire and less strain on your equipment.
SAFETY WARNING: Danger to life due to high voltages. Risk of death or serious injury due to electric shock. We strongly recommend you employ the services of a licensed local electrician or other properly trained and qualified persons to complete the final connection and energizing your system.
The amount of current (amps) traveling through any electrical circuit depends on the size of the wire (AWG), the voltage of the array or battery bank, and the one way distance of the wire run. Lower AWG gauge wire has less resistance than larger gauge wire. The longer the distance of your wire run while using lower voltage the larger gauge wire you are going to need. If your solar array consists of 4 or more 90 watt panels and is more than 50' from your battery bank, you should consider using 24V as a minimum with 48V being a better choice.
This chart is useful for finding the correct wire size for any voltage, length, or amperage flow in any AC or DC circuit. For most DC circuits, particularly between the solar panels and the batteries, we try to keep the voltage drop to 3% or less.
TIP; NEC 690.8 CALCULATION of MAXIMUM CIRCUIT CURRENT. (A)1 Solar Source Circuit Currents. The maximum current (Amps) shall be the sum of parallel solar panel rated short circuit currents multiplied by 125 percent.
- Amps = Maximum Number of Amps Through the Circuit
- Feet = One Way Distance of Wire
- % Voltage Drop = Percent of Voltage Drop Desired (2 = 2%)
- Voltage = Voltage Carried by the Wire
|Voltage Drop Index Chart (VDI)|
|AWG Wire Size||Copper Wire||Aluminum Wire|
Personal Solar Consultant & Line Drawing; We Have Your Back
You should not be overly concerned with how or what type of final connection, wire and breaker size because we do the heavy lifting for you. When you make a purchase over $1,000 for a kit, your order gets assigned to your own personal Solar Consultant. Our System Integrators provide polished technical advice on the design and execution of all types of installations. This single point of contact will be there to answer your questions and help walk you through any obstacles you might incur during the process.
When you buy a kit from Blue Pacific Solar, we supply a custom electrical line drawing that shows you exactly how to connect everything. We will specify on our drawing what size and type of wire and breaker you will need to be NEC code compliant. The line drawing can be used for your permit with the local authority having jurisdiction commonly referred to as AHJ (Building Department). If you need help with your full permit documents for your local AHJ anywhere in the country, our permit document service is available to help take the hassle out of your solar purchase.
Off-Grid Living; Appliances and Energy Conservation
If does not make much sense to spend money on an off-grid system without first looking at energy efficient appliances. The use of efficient appliances and lighting, as well as non-electric alternatives, can pay large dividends after designing your off-grid system and its time to plop down the money. Living off the grid using low energy lights and appliances can not only save you money up front, on those dark days when you are trying to save every watt of power you can out of you're battery bank, you will be glad you put a little thought into energy conservation up front. The type of lights and appliances that can be used living off-grid depends on how much sun is available, and the voltage of the off-grid system.
Cooking, Heating and Cooling
Each burner on an electric range uses about 1,500 watts per hour, which is why propane, wood burning stove or natural gas are all better choices for cooking. A microwave oven has about the same power draw, but since food cooks more quickly in a microwave, the amount of watts consumed is usually lower. Propane, wood or solar hot water are generally better alternatives for space heating. Good passive solar design and proper insulation can also reduce the need for winter heating. Swamp coolers are a more reasonable load than air conditioning and in locations with low humidity such as the SW, they are a great alternative.
Lighting requires careful study since type, size, voltage and placement can all significantly impact the power required. In a small home, or off-grid cabin, low voltage DC lighting with LEDs is often the best choice. DC wiring runs can be kept short, allowing the use of fairly small gauge wire. Since an inverter is not required, the system cost is lower. In a large installation or one with many lights, using an inverter to supply AC power for conventional lighting is often more cost-effective. AC compact fluorescent lights are common and efficient, but it is a good idea to have a DC-powered light in the room where the inverter and batteries are in case of an inverter fault. Also, AC light dimmers and overhead fan speed controls will only function properly on AC power from inverters that have sine wave output.
Propane refrigerators can work well in small off-grid systems if propane is available. Modern propane refrigerators consume 5-10 gallons per month. If an electric refrigerator is used for off-grid living DC is usually a better choice than AC refrigerators. A DC refrigerator can cost 2X as much as an AC but they consume less than a quarter of the energy which means less solar or wind and fewer batteries.
Televisions, Washing Machines and Other Appliances
Televisions; look for an efficient DC TV. Power in your television set can vary widely depending on the type. Standard AC electric motors in washing machines, larger shop machinery and tools, swamp coolers, pumps, etc. (usually 1/4 to 3/4 horsepower) consume relatively large amounts of electricity and require a large inverter. Often, a 2,000 watt or larger inverter will be required. These electric motors can also be hard to start on inverter power, due to large surge loads at start-up, and they are very wasteful compared to high-efficiency motors, which use 50% to 75% less electricity.
TIP; Surge is the amount of short term power needed to turn over the locked rotor on an electrical motor.
A standard washing machine uses between 300 and 500 watt-hours per load, but new front-loading models use less than 1/2 as much power. If the appliance is used more than a few hours per week, it is often more economical to pay more for a high-efficiency appliance rather than make the off-grid system larger to support a low efficiency load. Vacuum cleaners usually consume 600 to 1,000 watts, depending on how powerful they are, but most vacuum cleaners will operate on inverters as small as 1,000 watts since they have low-surge motors.
Many small appliances with heating elements such as irons, toasters and hair dryers consume a very large amount of power when they are used but, by their nature, require only short or infrequent use. With a sufficiently large system inverter and batteries, they will operate, but the user may need to schedule those activities with respect to the battery charging cycle – for example, ironing in the morning so that the solar or wind system can recharge the battery bank during the day. Electronic equipment, such as stereos, televisions, VCRs and computers, draw less power than appliances with heating elements, but these loads can add up as well, so opt for more efficient models, such as an LCD TV instead of a plasma or CRT design.
Computers, Music Systems and Cell Phone Chargers
Laptop computers us about 25% of the power a desktop computer uses. You should try and avoid desktop computers altogether. Music systems should be powered using pure sine wave power instead of a modified sine wave inverter. There is nothing that can kill the Zen faster in the evening living off the grid than static from a modified or cheap pure sine wave inverter. Cell phone chargers from the manufacture are usually more efficient than cell phone chargers you buy elsewhere. Every watt you consume by inefficient electrical equipment matters not only to your wallet but also your piece of mind living off-grid.
|Central Air Conditioner||5,000||Electric blanket||200||Hedge trimmer||510|
|Electric Clothes Dryer||3,500||Shaver||15||Weed eater||500|
|Oven||3,000||Water pik||100||1/4” drill||250|
|Hair Dryer||1,538||Well Pump (1/3-1 HP)||480-1200||1/2” drill||750|
|Coffee Machine||1,300||Plasma TV||350||9” disc sander||1200|
||213||3” belt sander||1000|
|Popcorn Popper||1,400||25” color TV||150||12” chain saw||1100|
|Toaster oven||1,200||19” color TV||70||14” band saw||1100|
|Hot Plate||1200||14” color TV||80||7-1/4” circular saw||900|
|Iron||450||Stereo||40||8-1/4” circular saw||1400|
|Toaster||1,100||Satellite dish||30||Refrigerator / Freezer|
|Microwave||1200||Radiotelephone - Receive||5||20 cu. ft. (AC)||1,080|
|Room Air Conditioner NA||1,200||Radiotelephone - Transmit||40-150||16 cu. ft. (AC)||720|
|Water heater (240VAC)||5,500||100 watt incandescent bulb||100||15 cu. ft. (Upright)||500|
|Sink Waste Disposal||450||25 watt CFL||28||15 cu. ft. (Chest)||500|
|Espresso Machine||360||50 watt DC incandescent||50||Cell Phone - recharge||2-4 watts|
|Dehumidifier||350||40 watt DC halogen||40||MP3 Player - recharge||.25-.40 watts|
|Blender||300||20 watt DC CF Light||22|
|Video Game Player||195|
|Portable Fan||60||Engine Block Heater||150-1000|
|Ceiling Fan||100||Portable Heater||1500|
|Can Opener||100||Waterbed Heater||400|
|Curling Iron||90||Stock Tank Heater||100|
|Cable Box||20||Clothes Dryer - Gas Heated||300-400|
|Clock Radio||30||Well Pump (1/3-1HP)||500 - 1200|
|Off-grid Battery Selection / Home Power Magazine|
|Top 10 Battery Blunders / Home Power Magazine|
|Lead Acid Battery Selection Article / Home Power Magazine|
|How to Build a Homemade Battery Box / Home Power Magazine|
|OutBack FlexPower; Power Center|
|Magnum Energy Power Centers|
|IronRidge Solar Rack Brochure (Optional Rack, Not Included in Base Solar Kit)|
off-grid power systems living off the grid with solar
Off-Grid Solar; Here is How it Works
When you hear the term “off the grid,” you may generate a picture in your mind of rustic pioneer-type living with few modern conveniences. In fact, this is not necessarily the case. While it is true that off-grid solar power is usually not sufficient to power an electric heating and cooling system, nearly all other appliances can be adequately powered with a properly configured off-grid system. It’s just a matter of obtaining the right components.
Off the grid living few years ago amounted to only about 1% of the total PV systems installed in America and around 10% world wide. Today there is a much different story brewing being fueled by the economic uncertainty and reliability we are now facing in the US. Since solar can provide power anywhere, there is no shortage of possibilities or limits. Standalone, autonomous or island systems; here are some examples of their common usage.
|Living Off the Grid, Large to Smaller Homes||Fishing or Hunting Cabins|
|Remote Security and Telecommunication Facilities||RV or Marine Vessels|
|Remote Mining and Drilling Operations||Farms, Ranches and Vineyards|
It goes without saying that solar panels are essential for a solar power system. Actually, what you will probably need is known as a solar array. That is because each panel generates a limited amount of electricity. The number of panels included in your solar array depends on how much power you need to generate. Hint; Energy Load Worksheet
Solar Mounts and Solar Trackers
Solar mounts and solar trackers are nearly as important as the panels themselves. Solar mounts provide the stability your panels require to remain in place during high winds and storms protecting your investment. Solar trackers, though expensive, allow you to orient your panels to take maximum advantage of the sun’s rays. Trackers are sometimes used when there is limited available space. A tracker will increase the energy harvest up to about 30% but the cost sometimes does not off-set the advantage. Additionally, a tracker is a mechanical device that has moving parts to break down and requires maintenance.
The function of a DC combiner is bring together different strings from the solar array where they are sometimes connected to fuses or breakers and protected by a DC lighting arrestor. From there the DC electricity travels from he roof or ground mount array to your charge controller usually via the power center.
A charge controller manages the process of charging your deep cycle batteries. The charge controller is an electronic device used to regulate the voltage used in battery based off-grid systems to keep the voltage to the batteries within acceptable limits. The charge controller protects the battery from over-discharge by the use of a low voltage disconnect that shuts down the draw from the loads when the battery bank voltage reaches a certain depth of discharge (DOD). The charge controller also protects the battery from over charging by limiting the battery voltage. This is especially important in AGM and other sealed batteries. Last but not least, a charge controller also prevents reverse current from flowing back into the solar panel array at night. During daylight hours, the charge controller automatically tapers and shuts down the solar or wind power when batteries become fully charged. Charge controller sizes range from 4 amps to 80 amps with many having the ability to connect them in parallel for larger off-grid systems. Some charge controllers offer additional features, like charge status display, data logging, automatic battery equalization charging, generator starting and even control lights on or off.
Deep Cycle Batteries and Battery Monitor
Storage batteries are when an off-grid system gets really interesting. The term battery is a reference to a row of electro-chemical cells connected in series. These are sometimes simply called cells or battery cells. Several batteries connected together are called a battery bank. Another term for a rechargeable battery is an accumulator but that term will not normally be found in most off-grid designers vocabulary. Without a battery system, you will be unable to store the electricity that your solar panel array generates. The battery monitor provides a visual gauge of the electricity generated and stored by your solar power system and is usually included in the power centers Blue Pacific Solar sells.
The type of batteries used in off-grid systems often times flooded lead-acid or AGM batteries. Though there has been a lot of progress in the technology of battery designs being driven by computer and electric vehicles, cost and or low maintenance is ultimately the reason you will see lead-acid batteries in most large off-grid homes or cabins. A lead-acid battery is made up of electrochemical cells that usually have a nominal voltage of 2 volts DC. Six of these electrochemical cells connected by series will provide a 12 volt battery. Lead-acid batteries used in off-grid solar systems are available as 2 volt, 6 volt or 12 volt batteries. By connecting these different types of batteries together, you can produce a variety of increasingly stronger battery banks that will store more energy. Additionally, by connecting the batteries in series and or parallel, you can pump up the power to 12, 24 or the more popular 48 volt systems that are sometimes needed for larger off-grid AC inverters.
Lead acid battery technology has improved over the years but the fundamental electro-chemical reaction in all flooded lead-acid batteries is basically the same. As the flooded lead-acid deep cycle batteries are discharged the lead dioxide positive active material and the sponge lead negative plates creates a chemical reaction with the dilute sulfuric acid electrolyte to form lead sulphate and water, during charging this process is reversed. The efficiency of the charge and discharge process is less than one-hundred percent because during the charge process the voltage from the charge controller and solar panels has to be increased (over the discharge voltage) by about 7.5 to 10.5% to overcome inherent electro-chemical inefficiency and the battery cells internal resistance. Deep cycle lead-acid batteries are widely used in off-grid systems because they are readily available nearly everywhere at a lower initial cost. The life cycle of all lead-acid batteries (flooded, sealed gel cell and AGM) is substantially shortened if operated at high temperatures or the depth of discharge (DOD) is consistently low both of which can be prevented with a properly designed off-grid system. Deep cycle batteries fail through degradation of the plates via sulfation. Elevated temperatures and over charging both create sulfation and becomes the primary reason battery life is shortened
Inverter / Battery Charger, AKA Power Center; The Heart of Your Off-Grid System
The last critical piece of electronic equipment in your off-grid power system is the AC inverter. The electrical current generated by your solar array will be direct current, or DC. However, nearly all indoor electrical appliances run on alternating current, or AC. A power inverter converts the DC power of your solar array into AC power that your appliances can actually use. Without a power inverter, you will be forced to rewire your home and to purchase expensive DC powered appliances. In some cases, DC powered appliances will not be available and you will have to do without certain appliances.
There are a number of things to consider when choosing an off-grid inverter the first of which is tare losses or the energy consumed to operate the inverter itself in standby mode. In each off-grid design, every watt wasted means a larger battery bank and or more solar panels. The second big specification in an off-grid inverter is surge capacity. The ability of an inverter to surge to a higher burst of electricity than its rated output for a short duration to turn over the locked rotors of equipment like well pumps is critical. The specifications that should be looked at are the are the maximum output current (Amps) and the AC surge watt capability. If there are large loads a good number to look for is a five second surge capability of at least 3 times the rated output of the off-grid AC inverter.
Pre-wired power centers come already built and tested with the inverter (s), charge controllers (s) and breakers already installed. You simply have to follow our line diagram, build your array, connect the solar panel DC electricity to the marked bus bar inside the e-panel. You then connect your battery bank via the correctly sized cables, generator if you include one and run your AC out to your main breaker panel. Now it is time to kick back and enjoy the good life in peace and quiet living off-grid in your home or cabin.