Solar Inverters: What does an Inverter do?
It’s all about compatibility
Solar inverters convert the electricity from your solar panels (DC, or direct current) into power that can be used by the plugs in your house for your TV, computer, and other wired products (AC, or alternating current). Solar panels can’t create AC power by themselves; they need the helping hand of an inverter.
AC vs. DC
In DC power, the current of electricity flows in one direction. In AC power, the current moves in both directions along a wire– both forwards and backwards. Some products, like lightbulbs, can run on either DC or AC power. But because AC power can be sent long distances easily, electricity networks in the U.S. were set up to use AC. (AC electricity can easily change between higher and lower voltage levels, and high voltages allow long-distance transmission).
Doesn’t my laptop actually use DC power?
Yes. Phones, TVs, computers, and many other common products use DC power, and actually have to convert AC power back to DC power. That’s what’s happening in the little black ‘brick’ attached to your laptop’s power cord. Because the U.S. grid is set up for AC power, the things we buy are made to work using AC power. The DC power created by your solar panels is converted into AC power by your inverter in order to be compatible with the grid, and then back to DC by the power supply on your electronics. Ironic? Yes. This isn’t this case in all countries; some use DC networks. Since we live in the U.S., we need inverters.
How efficient is the conversion from DC to AC (and back again)?
Typical inverters are around 95% efficient, so you’ll only have about a 5% loss of power when the electricity is converted from DC to AC. The conversion from AC back to DC in your electronics is less efficient; you may lose 10-40% of the power. That happens whether you’re using ordinary power from the grid or solar power– it’s just part of the way the system is set up. When you feel the black brick on your laptop cord getting hot, that’s a sign of a low-efficiency conversion of AC to DC.
What are the different types of inverters?
Most homes have central inverters, which make the conversion from DC to AC from a box in one location, like your garage wall. A newer type of inverters, called microinverters, work directly and independently under each solar panel. These are a little more expensive and take more time to install.
What other equipment do I need in addition to inverters?
For a complete solar system, you also need solar panels and several smaller components called the “balance of system”– wiring, hardware for attaching panels to the roof, and other small parts. Read more about balance of system parts in the Nitty-Gritty of Solar Roofing.