Ask John

Q: Does Every System Need A Power Inverter? Why?

posted January 28th 2010 at 12:21PM

Yes, a functional DC to AC power inverter is an essential component in any photovoltaic (solar) or wind turbine power generator system. While the complexity, and capacity of your power inverter will vary somewhat depending on the type of system you build, their role is absolutely fundamental in enabling you to generate your own electricity.

Simple power inverters can be bought for as little as $20 but will likely have a limited capacity (IMPORTANT: Your power inverter should have a 20 percent higher capacity than you expect your renewable energy system to produce at its highest output). Larger inverters will cost more, but tend to also be more elaborate – including features such as realtime or web-based power monitoring, and the ability to also act as a charge controller. Expect the size, capacity, and number of features to be reflected in the price whether you buy new or used.

The reason a power inverter is always required is simply this…

In a DC electrical system electrons flow in one direction through a circuit. In an AC system, they travel both ways through a circuit. In the 1800s, a guy named Thomas Edison harnessed the awesome power of electricity using a model based on DC (or ‘direct’) current. DC had the inherent limitation of only being able to flow along a mile of cable before the current diffused and was unusable for significant purposes.

Later, another inventor named George Westinghouse built upon what Edison had done, and introduced ‘high-voltage’ alternating current (or ‘AC power’) that could be transmitted several hundred miles along a properly insulated cable. And so today, for obvious reasons of improved practicality, the American national power grid runs on high voltage AC power. By necessity, the electrical system in your home is configured to run on the same.

But your renewable energy system generates DC power, due to the nature of the materials and technology involved in their most fundamental concepts. This type of power is NOT compatible with the existing electrical system inside your home, and is the only reason that you must use a power inverter, regardless of your setup.

What’s more is that a grid-tie system that enables you to ‘sell’ the excess electricity you generate back to the power company will require a special grid-tie inverter (usually to be approved by your municipal power company). These inverters are ‘smart’ enough to shut down in a blackout so that your system does not continue to send power to the grid that could threaten utiity crews who may be at work trying to bring it back online.

Not to worry, though… Your battery bank will be what you rely upon under these circumstances. It’s the ‘optional’ part of your system that isn’t really optional. And we show you how to get the batteries you need for nothing, or close to it! By keeping a battery backup wired to your system, your grid-tie inverter will first supply your home with power for immediate energy demands, storing any excess in your batteries until they are fully charged. At that point, your grid-tie inverter routes any remaining excess power back to the power company who pay you by the kilowatt hour! The best part of this setup is that you still have the freedom to draw from the grid should your energy needs ever outweigh what you can supply… And in that case, you’re probably not really losing money – you’re just not saving quite as much.

I could go on all day about inverters, but this is all you really need to know to get on your way.

Sincerely,

John Russel

Electrician, Researcher, Inventor, Home Energy Consultant, and Creator
of the Power4Home System