A solar electric system is comprised of 4 or 5 main components: solar panels that generate electricity from exposure to the sun, a charge controller to manage the output of the panels, an Inverter which converts DC (Direct Current) from the charge controller to AC (Alternating Current) for your home and, finally, batteries to store the electricity you generate. A system does not need all these components to provide for your electrical needs. Systems may be configured in three primary ways.
Grid Tied systems connect the inverter AC output directly to your home electrical system. When the sun is out and you are using power you use the solar output first followed by power from the grid. When the sun is not out you use power from the grid exclusively. When the sun is out and you are not using power, your solar electricity is sent out to the grid, turning your electric meter backwards.
It is smart to size your grid tied system carefully to produce enough power to run your meter to zero, but not feed excess power to the grid that you will not be compensated for.
Non Grid Tied
Non Grid Tied systems do not have a connection that sends power out to the grid when you are producing more than you are using.
Non Grid tied systems almost always have a battery storage system to store power when you are not consuming, and release power when you are consuming and there is not enough sun.
In general, non grid tied systems also include a generator to charge batteries when the sun fails to appear for days.
Non grid tied systems can be part of a house system that is powered from the grid. For instance, you might pull computers and lighting off your existing electrical panel and run them directly off the solar system. When the power goes out you maintain lighting and computers while the rest of the house systems are down
Grid Tie with battery Backup
Grid tie with battery backup is the most complex and flexible solar electrical system. You can use grid power to charge batteries when there is no sun for days. You can run entirely off solar panels and batteries, drawing from the grid only as a last resort. You can maintain full operation even after the grid has gone down.
Your access to grid power and your power consumption will help determine which of these systems works best for you. Diagrams in this document will help explain these concepts in more detail.
Also known as PV are commonly made from silicon based semi-conductor materials.
When sunlight hits the semi-conductor layer of the panel, electrons travel across the junction of two different materials creating a positive flow of electricity. There are many different types of panels manufactured today. The three most common are crystalline, poly crystalline and amorphous. Each technology has it benefits and negatives. Often location, available space and quantity of sun will determine which technology is best for your needs. Photovoltaic panels can be roof or pole mounted depending on your space and aesthetic requirements.
The gate keepers between the solar panels and the rest of the PV system.
Since output from a set of solar panels can vary wildly throughout any given day, the charge controller is put in place to regulate the flow of electricity between the panels and the system. If, for instance, you had a non grid tied battery backup system and your batteries were fully charged from a good full morning of sun, you do not want to continue to force more power into the batteries running the risk of damaging them. So the charge controller monitors the panel’s output and the battery’s charge condition to determine whether to turn off the panels or let more current flow. A charge controller can also provide a great deal of information about the performance of your system.
Provide a place to store power you are creating with solar panels, that you are not consuming.
It’s great to be able to create solar electricity but you don’t want any of it to go to waste. Batteries for solar usage are generally deep cycle batteries. Deep cycle batteries are designed to release power in small quantities over an extended period of time. In general, deep cycle batteries can be drawn down to 20% of their capacity and be fully recharged thousands of times with no harm done. It is recommended that 50% is a safer number and battery banks should be sized for that target. Your car battery is not a deep cycle battery. It is designed to provide huge output in a short time and then quickly be recharged so its performance does not fit a solar application. There are two common types of batteries used in solar storage systems. Lead acid (or “wet cell”) batteries and gel-cells.
Wet cell batteries are the most common in solar systems because of cost and longevity. A well maintained wet cell battery could provide 10 years or more of good performance with only minor monthly care. Gel-cells on the other hand require no maintenance but they cost more and have a shorter life.
An inverter is a device that converts DC (direct current) from your batteries and or charge controller into AC (alternating current) for your home or business electrical system. The inverter outputs clean stable power from your renewable sources after converting the power from DC to AC. The power is sent into your electrical system to be used or sent out to the grid.
If you are installing a grid tied system the final two components are the automatic disconnect and a new electric meter. The disconnect switch shuts down the power going to the grid in the event of a grid power failure. This insures that a lineman is not injured by power sent out to the grid from your solar system. The new meter will be installed by your power company. This new meter will actually spin backwards when you are producing more power than you are consuming. This meter allows you to sell power back to your provider at the same price that you purchase power. However, most utilities will only allow you to sell as much as you buy, and no more. So your bill could reach zero but no further.
The image below shows one example of an inverter and associated equipment. On the right side of this system is the DC disconnect. The incoming power from the solar panels are connected through the charge controller. The charge controller and batteries are connected there. On the left side is the AC side of the system. Power from the grid and power to systems within your house that are powered directly off the solar system are connected there.