Off-grid or Backup Systems with Advanced Solar Power Electronics

 

SolarWorld Solar 285W Kits	SolarWorld 290W Kits	SolarWorld 290W Kits	SolarWorld 290W Kits

 

Planning Required for Off-Grid, Backup or Grid Interactive Electric System

Battery based grid interactive and or stand-alone power, off-grid, backup solar systems operate from the stored energy in a battery bank via an inverter that pulls the DC power [Direct Current] stored in the batteries and converts the electricity into AC power [Alternating Current] to use for your outlets, lights and appliances. Solar panels are used to keep a battery bank charged on a daily basis. Some part of the house, cabin or tiny house 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.

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)
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.

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 trying 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.

 

Additional Hardware That May Be Required

Racks and batteries are site specific options that are not included with the base package. When you click on the detail page of the kit you are interested in, the roof or ground rack and battery options are shown below "What's On The Truck". Normally we take the wire to the edge of the array where the transition is usually made to conduit at the combiner box with breakers which we provide in our kits. In a roof mount application, you may have to supply a junction box to make the transition to the combiner usually located outside on the wall beneath the array. Here are some additional items that you 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. These items are readily available at your local hardware store. How much can you expect to spend? That depends on 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 for BOS locally sourced components.

 

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 as well as the size and types of batteries required are individual's specific property requirements and available on the detail page as options. Habits, energy storage requirements, 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. On our racking and mounts page you can find top of the pole racks.

 

MidNite Solar Micro Battery Based Off-Grid Kits With DIY Load Center

 

Micro off-grid living is a lifestyle where less is more. From your cabin weekend get-a-way escape or tiny houses, 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. MidNite Solar, an American company producing products made in America, creating American jobs. We like it... a lot! Listed by ETL for US & Canada

	Item #	Voltage DC (Battery) / AC (Optional)	Daily Watts @ 4 Sun Hours /Day STC*	# Solar Panels	Price before 30% Federal Tax Credit
0.6 kW MidNite Micro Kit	MIDSW-24-564	24 / 120VAC	2,280 Watts	2 - 285W
1.1 kW MidNite Micro Kit	MIDSW-24-1128	24 / 120VAC	4,560 Watts	4 - 285W
1.7 kW MidNite Micro Kit	MIDSW-24-1692	24 / 120VAC	6,840 Watts	6 - 285W
2.3 kW MidNite Micro Kit	MIDSW-24-2256	24 / 120VAC	9,120 Watts	8 - 285W
2.9 kW MidNite Micro Kit	MIDSW-24-2820	24 / 120VAC	11,400 Watts	10 - 285W
3.4 kW MidNite Micro Kit	MIDSW-24-3384	24 / 120VAC	13,680 Watts	12 - 285W

 

MidNite Solar / Magnum Energy OFF-GRID; ON GRID BATTERY BASED POWER SYSTEMS

 

Methodically engineered with advanced power electronics, every component 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. 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

	Item #	Voltage DC (Battery) / AC	Daily Watts @ 4 Sun Hours /Day STC*	# Solar Panels	Price before 30% Federal Tax Credit
0.9 kW MidNite Magnum Kit	MNMAGSW-48-855	48 / 120/240VAC	3,420 Watts	3 - 285W
1.7 kW MidNite Magnum Kit	MNMAGSW-48-1710	48 / 120/240VAC	6,840 Watts	6 - 285W
2.6 kW MidNite Magnum Kit	MNMAGSW-48-2565	48 / 120/240VAC	10,260 Watts	9 - 285W
3.4 kW MidNite Magnum Kit	MNMAGSW-48-3420	48 / 120/240VAC	13,680 Watts	12 - 285W
4.3 kW MidNite Magnum Kit	MNMAGSW-48-4275	48 / 120/240VAC	17,100 Watts	15 - 285W
5.1 kW MidNite Magnum Kit	MNMAGSW-48-5.1	48 / 120/240VAC	20,520 Watts	18 - 285W
6.0 kW MidNite Magnum Kit	MNMAGSW-48-5985	48 / 120/240VAC	23,940 Watts	21 - 285W
6.8 kW MidNite Magnum Kit	MNMAGSW-48-6840	48 / 120/240VAC	27,360 Watts	24 - 285W
7.7 kW MidNite Magnum Kit	MNMAGSW-48-7695	48 / 120/240VAC	30,780 Watts	27 - 285W
8.6 kW MidNite Magnum Kit	MNMAGSW-48-8550	48 / 120/240VAC	34,200 Watts	30 - 285W
9.4 kW MidNite Magnum Kit	MNMAGSW-48-9405	48 / 120/240VAC	37,620 Watts	33 - 285W

Amps AC Out; Define Your Needs: A Single Magnum inverter's continuous AC output current is limited to 30AAC. The issue here is that the combination of your normal loads (Not Surge Loads) might exceed the inverters output current rating (Amps Out) on larger PV systems. It is critical in the design selection that you make sure the continuous AC load combination of your power requirements is at or below the 30AAC output limit of the single Magnum inverter in these kits.

 

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; OFF-GRID, BACKUP, GRID-TIE

 

 

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.

	Item #	Voltage DC (Battery) / AC	Daily Watts @ 4 Sun Hours /Day STC*	# Solar Panels	Price before 30% Federal Tax Credit
0.9 kW FLEXpower ONE	FLEX1SW-48-870	48 / 120VAC	3,480 Watts	3 - 290W
1.7 kW FLEXpower ONE	FLEX1SW-48-1740	48 / 120VAC	6,960 Watts	6 - 290W
2.6 kW FLEXpower ONE	FLEX1SW-48-2610	48 / 120VAC	10,440 Watts	9 - 290W
3.5 kW FLEXpower ONE	FLEX1SW-48-3480	48 / 120VAC	13,920 Watts	12 - 290W
4.4 kW FLEXpower ONE	FLEX1SW-48-4350	48 / 120VAC	17,400 Watts	15 - 290W

 

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™ TWO; Dual Inverter; OFF-GRID, BACKUP, GRID-TIE

 

 

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™ system 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.

	Item #	Voltage DC (Battery) / AC	Daily Watts @ 4 Sun Hours /Day STC*	# Solar Panels	Price before 30% Federal Tax Credit
1.7 kW FLEXpower TWO	FLEX2SW-48-1740	48 / 120/240VAC	6,960 Watts	6 - 290W
2.6 kW FLEXpower TWO	FLEX2SW-48-2610	48 / 120/240VAC	10,440 Watts	9 - 290W
3.5 kW FLEXpower TWO	FLEX2SW-48-3480	48 / 120/240VAC	13,920 Watts	12 - 290W
4.4 kW FLEXpower TWO	FLEX2SW-48-4350	48 / 120/240VAC	17,400 Watts	15 - 290W
5.2 kW FLEXpower TWO	FLEX2SW-48-5220	48 / 120/240VAC	20,880 Watts	18 - 290W
6.1 kW FLEXpower TWO	FLEX2SW-48-6090	48 / 120/240VAC	24,360 Watts	21 - 290W
7.0 kW FLEXpower TWO	FLEX2SW-48-6960	48 / 120/240VAC	27,840 Watts	24 - 290W
7.8 kW FLEXpower TWO	FLEX2SW-48-7830	48 / 120/240VAC	31,320 Watts	27 - 290W

 

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 PRE-BUNDLED SOLAR KITS; OFF-GRID, BACKUP, GRID-TIE

 

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.

	Item #	Voltage DC (Battery) / AC	Daily Watts @ 4 Sun Hours /Day STC*	# Solar Panels	Price before 30% Federal Tax Credit
3.5 kW Radian	RADSWM-3480	48 / 120/240VAC	13,920 Watts	12 - 290W
4.4 kW Radian	RADSWM-4350	48 / 120/240VAC	17,400 Watts	15 - 290W
5.2 kW Radian	RADSWM-5220	48 / 120/240VAC	20,880 Watts	18 - 290W
6.1 kW Radian	RADSWM-6090	48 / 120/240VAC	24,360 Watts	21 - 290W
7.0 kW Radian	RADSWM-6960	48 / 120/240VAC	27,840 Watts	24 - 290W
7.8 kW Radian	RADSWM-7830	48 / 120/240VAC	31,320 Watts	27 - 290W
8.7 kW Radian	RADSWM-8700	48 / 120/240VAC	34,800 Watts	30 - 290W

Amps AC Out; Define Your Needs: A Single Radian inverter's continuous AC output current is limited to 33.3 AAC. The issue here is that the combination of your normal loads (Not Surge Loads) might exceed the inverters output current rating (Amps Out) on larger PV systems. It is critical in the design selection that you make sure the continuous AC load combination of your power requirements is at or below the 33.3 AAC output limit of a single Radian inverter in these kits. If your AAC out is larger than 33.3 AAC, then for each inverter you add, stacked in parallel, you can increase the AAC out by 33.3 AAC. (Example: 2 Radian Inverters = 66.6 AAC Output)

 

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.

NOTE: 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 Design; EVERYTHING Starts With Your Daily Energy Budget

What is the "Power" required by your electric load?

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.

System Voltage:

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:

Derate Factors
Wire Loss	3%
Panel Mfg. Tolerance	5%
Panel Mismatch	2%
Diodes/Connections	1%
Panel Soiling	5%
Battery Efficiency	15%
Panel PTC (Temp)	12%
Charge Controller	5%
Total	48%

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.

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 48% (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 48% = 7,400 watts / 48 volt system = 154 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 154 Ah.

 

Make the Power; Size Your Solar Panel Array; Input Must Equal Output.

Number of Solar Panels = Daily Watt Requirement (1 - 24 hour period (Energy Budget)) + 48% (Derate Factor) ÷ shortest day sun hours ÷ panel STC rating = number of solar panels needed.

The number of solar panels you will require is a basic off-grid formula that considers your total daily energy requirements X (+) 48% (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 ÷ the lowest solar irradiance available in the area of the system which is the shortest daylight month of the year (December). The last step is to ÷ that number by the STC watts of the solar panel rating. IE: 8,000 watts per day energy budget X 48% = 11,400 Watt-Hours/Day of energy to be generated. 11,400 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 + 48%) ÷ by lowest available sun hours per day from the solar irradiance chart. For example, if the daily load calculation (Daily energy budget + 48%) is 11,400 watts, and the site is near Salt Lake City UT, you would take 11,400 watts / 4 sun hours = 2,850 watt solar array. That means if you choose 270 watt solar panels you would need 10.6 (EA) 270 watt solar panels for the size kit you select (Round Up to 12 or Down to 10 270 Watt Panels.

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 on the hottest day of the summer because during the hottest days of summer panels produce less energy. (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 for a 48VDC battery bank or strings of 2 for a 24VDC battery bank.

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 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. The battery bank should be no further than 10' from the inverter.
• 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.

 

Store The Energy; 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 without drawing your battery bank lower than 50%. 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 or it will dramatically decrease the life cycles of the batteries.

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.

Battery Sizing Worksheet

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

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.

 

Control The System; Power Center = Inverter, Charge Controller & 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 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 MidNite 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.

 

Connect it All; Wire Size & Electrical Distribution Parts

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 12 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

	VDI	Ampacity	VDI	Ampacity
4/0	99	230	62	180
3/0	78	200	49	155
2/0	62	175	39	135
1/0	49	150	31	120
2	31	115	20	94
4	20	85	12	65
6	12	65
8	8	50
10	5	30
12	3	20

 

Technical Resources, 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 $2,000.00 for a kit, your order gets assigned to a Technical Team Captain so your have 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

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.

Refrigeration

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.

Small Appliances

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.

Appliance	Watts	Appliance	Watts	Appliance	Watts
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
Dishwasher	1500	Laptop	60-250	soldering iron	200
Coffee Machine	1,300	Plasma TV	350	9” disc sander	1200
Microwave	1,500	LCD TV	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
Vacuum Cleaner	500	Lights		Freezer
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
Humidifier	700	CFL Bulb	18
Video Game Player	195
Standard TV	188
Monitor	150
Computer (desktop)	150	Heaters
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
Stereo	60	Furnace Blower	1000
Cable Box	20	Clothes Dryer - Gas Heated	300-400
Clock Radio	30	Well Pump (1/3-1HP)	500 - 1200

Helpful Information

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