Solar cells, also known as photovoltaic (PV) cells, capture energy from the sun and turn it into electrical current. Solar energy is clean, renewable, free and always available. This makes it a popular option for home use installing either the Enphase microinverter, SMA or SolarEdge kits. Solar cells are assembled into modules. The modules are formed into arrays that connect the sun-created electricity both to homes and to power grids. Residential solar arrays consist of solar cells, inverters, wiring, electrical panels and protection mechanisms.
Solar Array Electricity Flow
Electricity from the solar array flows through the conduit to the direct current disconnect. From the DC disconnect, it flows through the grounded inverter to the alternating current disconnect. Then, the AC current travels either to the home's electrical panel or to the utility disconnect. From the utility disconnect, the electricity enters the grounded utility service entrance and main load center.
Solar Cell Types
Solar cells generate electricity through the use of silicon semiconductors. Solar cells come in three types: single-crystalline, multi-crystalline and thin film cells. Single-crystalline cells are also referred to as mono-crystalline cells. These are the most efficient kind of photovoltaic cell. They only use one silicon wafer to generate electricity. Multi-crystalline cells, another type of photovoltaic cell, are also very efficient. They use a block formed of many small crystals to create current. They are also called poly-crystalline cells. Thin film cells, or amorphous cells, use a thin semiconductor film attached to glass or plastic. Thin film cells are cheaper, but less efficient, than mono- and multi-crystalline PV cells.
Inverters Used In Kits
Solar cells generate direct current (DC). DC flows in one direction. Enphase microinverters or SMA SolarEdge inverters turn the direct current into alternating current by mimicking the current's wave and rate. Most domestic appliances require AC current. The inverter sends the alternating current to the house or to the power grid, as needed. Inverters are placed near the structure's main electrical panel.
Wiring and Electrical Panels
PV array components are connected with wiring, which must be able to accommodate the strength (the amperage) of the electrical current. Voltage, wire type and temperature determine what size wire should be used. Wires made from copper are great conductors. This makes copper wiring a great choice for solar arrays. PV array wires should be insulated and protected against the elements. Wires can be protected with insulating material and conduit. A circuit breaker transfers electricity from the inverter to the home's electrical panel. The size of the electrical panel determines how much power it can accommodate.
Component Protection Devices
Overly strong electrical currents, electrical interference, lighting strikes and power surges can mean harmful, and even deadly, consequences for residents, service employees, first responders, homes and appliances. Over-current protection, disconnects, and grounding devices help manage electrical loads to keep homes and residents safe.
Over-current protectors safeguard wires from current too strong for the wires to carry. Circuit breakers and fuses help prevent fires caused by hot wires. Disconnects allow a home's power to be easily and quickly shut off in the case of emergency. Disconnects helps emergency responders enter a residence without risk of electrocution or fire. At least one disconnect is needed for every home. Electricity travels through the disconnect before it enters the home. In homes with Enphase, SolarEdge or SMA PV arrays, a disconnect must also be placed between the inverter and the arrays.
All solar array systems must be grounded. Grounding helps to mitigate the effects of lighting strikes and power surges. Grounding also lessens the risk of electrocution and fire. Grounding is important for both equipment and systems. In equipment grounding, exposed metal is connected to a grounding mechanism. In system grounding, the conductor is connected to the grounding electrode. Component protection devices provide big safety benefits for homes and their residents.
Modules have no moving parts so there is no wear and tear on components. However, panels will need cleaning once in a while to keep the surfaces clear of dust and other debris. Dust reduces the efficiency of solar panels and cuts down the amount of electricity generated by around 5 to 7 percent. You don't have to climb up on the roof to clean panels. A hose with a nozzle can be used to spray water over the solar array and cleaning it once every 2-3 months is enough. If you live in a dusty area, then you may have to hose it down more frequently.
Solar Kits creating energy with Enphase microinverters, SolarEdge and SMA DIY grid-tie panel installation packages. First do your homework with the PV information we provide then select the kit that will fit your applications and budget.
To begin the process of sizing your solar system you first need to pull your most recent 12 months utility bills and record the kWh from each month. Then take the total of the 12 months kWh then ÷ by 365 to get your daily average usage. This number is critical to begin the process for a grid-tie system. Don't have 12 months worth of history? Then average what you do have or if you are moving into a different house use the bills from your current home to get an idea of your energy usage.
You can usually find the kWh near the top of the first page of you utility bills. An alternative method would be to go on line and down load the information or call your local utility company to find out your most recent 12 months total.
One thing to note is that at some locations around the country you are charged extra for using electricity during a specific time of the day, usually in the afternoon hours of the summertime. It may be important to understand that peak period of higher charges because that information may help you down the road when you decide on your budget for your project and how best to maximize your return on investment. A smaller solar kit positioned to harvest and create the most energy during these peak tier rate times may be where you want to start.
We talk to hundreds of people a day across the country and often the first thing we hear when we say we need to see how much sun is available in their area is "we have lots of sun so that should not be a problem". The fact is that when sizing a kit, it is not how much sun you have, it is how much sun strikes the earth in your zip code which can sometimes surprise customers. Little considered factors such an high humidity and elevation can play a key role. Example; most of Texas and Florida have latitudes that are farther south than Arizona but have less "sun-hours per day" because Texas and Florida have higher humidity levels and more cloud cover.
The 2nd step in the design process is to look and see what the average amount of solar irradiance is available near your area from our resource map. Find the nearest city to your home and write down the average "sun-hours per day".
You want to go bigger than your last 12 month kWh consumption history? Utility companies are in the business of selling power not buying power. Most local utility companies will allow you to go 10% higher than your last 12 month average with justification, but don't let someone talk you into buying more solar than you need. Even if you are allowed to do it, you will eliminate the best return on investment. Hawaii is one state that in some areas is the exception to that rule.
Mounting your system on the roof, ground or top of a pole; budget, roof dimensions, ground space or setbacks, shading and other site-specific factors call for careful consideration in your design. Compare the sizing results from your calculations in steps 1, 2 and 3 with the location and amount of space available to mount the solar array in order to get a rough idea of the maximum of panels. If you are planning to mount your array on a roof, decide which module best fits into the available roof space, taking into consideration obstructions such as chimneys, plumbing vents and skylights. Many local building codes will not allow a solar system to extend beyond the perimeter of the outside of the house footprint. (You may not be able to utilize your roof overhang or eaves.) A good place to start is to check with your local building department to see what their setback rules are for either a roof or ground mount array.
TIP; Mount your solar panels with at least a 7 degree tilt to avoid "Mud Shading". That's when dirty water washed off the solar panels accumulates across the bottom cells of the panel dammed by the panel frame. When the water dries, the dirt or mud builds up across the bottom which can shade the entire row of lower solar cells on each solar panel.
In most areas of the country you will be required to enter into a "interconnect agreement" with your local utility company. This is a simple form that lets them know you will be producing some of your electricity at your location and the equpment you are proposing is UL listed and approved. Just go to your local utility website to download the document or call your local utility customer service line and have them send one to you.
Wire carries electricity in much the same way as a garden hose carries water. When you turn on a breaker, a electron flows in one direction and knocks another electron which knocks another one until eventually an electron comes out the other end. Voltage is the electrical pressure behind the flow of current or electrons. Current, which is measured in amps, is the measure of quantity of electrons flowing through a wire. The higher the voltage the more current the source can produce. Watts are the measure of power. Volts X Amps = Watts.
Current can be increased by increasing the voltage or by lowering the resistance (IE: Size of Wire or Conductor).
Resistance is the inherent physical opposite to current flow. A good analogy would be to think of it as a dam holding back water. Resistance is created by electrons refusing to be stripped of their atoms and bumped or sent down the wire. The higher the resistance in the wire, the less current will flow. The only way to overcome that resistance, is to increase the pressure (volts) or decrease the resistance (Larger Wire).
National Electrical Code (NEC) 690.64 does not specifically require an AC disconnect however, many if not most utility companies like to have a lockable blade disconnect to protect line workers and fire department officials. An AC disconnect is more likely to be required if the inverter is not close to the main service panel. If an AC disconnect is required, is should not need to be fused unless it is the primary disconnect for the line side connection.
Arrh... power baby, make that meter turn backwards! This is where it all comes together. Your homes main service panel is the heart of your electrical system and how we connect the solar system to this panel using what option is the key to everything we have done so far in the design planning.
Load side connection occurs on the load side of the Main Service Disconnect Breakers via a breaker on the Main Service Panel Busbar. Line side connection occurs between the Utility Meter the Main Service Disconnect Breaker.
Here is why that is important to understand the difference. Before we can go any further in the final connection or exactly where we are going to connect we need to know one rule that we call a biggie in the solar industry. National Electrical Code (NEC) Section 690.64 says that the sum of the rated current for the solar breaker and main breaker amp rating cannot exceed 120% of the bus bar’s rating of the Main Service Panel Busbar Rating
Example: The main service entrance (MSE) breaker box is listed as a 200A bus/200A Main breaker. That means if you have a 200 amp main service panel which is rated for a with a 200 amp buss bar, NEC will only allow a 20% back feed breaker to be added to a 200 amp panel or 40 amp solar breaker. If the size of your system requires a 60A OCPD, this exceeds the maximum allowable backfed current for a load side connection for the given MSE specifications (max. allowable for this service entrance = 40A). To go above that 40 amp back feed solar breaker there are several alternative
One alternative to consider without having to replace your main breaker panel would be to decrease the size of the main buss bar. By lowering a 200 amp main breaker to 150 amps may bring your in compliance if you have to go to a 60 amp backfeed breaker for your solar system. However, before you do that a careful study by a licensed electrician should be conducted to make sure you will not stress the breaker with your existing loads.
On a grid-tie solar system when the utility goes down, the solar system will also go down. What many homeowners fail to realize when they purchase a standard grid tied system is when the grid goes down, so does the power being produced by the solar panels. Why? The IEEE-1547 standard requires that grid-tie inverters cease to export power (Means your meter spinning backwards) if the voltage measured at the Point of Common Coupling (PCC) (That mean your homes electric service meter) exceeds +10% or -12% of nominal. If that were not the case, there could be a utility worker in front of your home who thinks the electricity is off and become injured.
Another alternative is to consider a line side connection. A line side connection or supply-side connections means the connection between the utility company meter and your main breaker box. If you have no room in your existing service panel to add your solar system, see if the number of breakers in your main breaker box can be reduced or consider upgrading the service panel. A line side connection requires a fused blade AC disconnect. If that is required and the solar kit you select states that we will supply the AC disconnect, we will provide the upgrade to a fused AC 60 amp disconnect at no additional cost to you.
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, who is already familiar with your project, is your free life line to answer your questions and help walk you through any obstacles you might incur during the process.
Included with your grid tie package is a full "Instructive Three-Line Diagram of Entire DC Circuit, as Well as AC Lines to Your Metered Service Entrance". When you buy a grid-tie 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 interconnect agreement application with your local utility company and 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.
We often get asked about running wiring in the attics and if it has to be in conduit. With NEC 2011 (National Electric Code), this just got easier. While the industry has rightly focused on 690.11 Arc Fault Circuit Protection, there was a lesser known change regarding running DC wiring inside the building. Section 690.31(E) changed the requirements for running DC inside of a building to enable the use of Metal-clad cable for DC solar source or output circuits. The Metal clad cable needs to comply with 250.118(10) but will enable customers installing wiring an easier alternative to bending conduit in tight spaces.
*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 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 Celsius 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.
NOTE: Neither PTC nor STC account for "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. On the inverse, solar panels may out produce their rated power in cold high altitude locations.
Blue Pacific Solar® permit document service is offered as a value added service for our customers only who purchase our grid-tied or off-grid packages of 18 panels [Minimum] or more. The building permit document permitting service service is available for most states to help you get through your local jurisdiction building permit process. Our team of professional designers can provide the documents, blueprints and expertise needed to work with any building department nationwide.
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! Look out for even small shade factors like overhead power lines or vent pipes in roofs.