ASK THE EXPERTS: Solar Energy Wasted

A recent New York Times article, “Solar Companies Seek Ways to Build an Oasis of Electricity,” started by saying, “When Hurricane Sandy wiped out the power in areas like coastal Long Island and the Jersey Shore, what should have been beacons of hope—hundreds of solar panels glinting from residential rooftops—became symbols of frustration.”

I read in the article a sense of missed opportunity. I’ve had a grid-tied system for a few years now. I understand that with my current configuration, the essential strategy was to ensure my system wouldn’t energize what would be expected to be powerless grid lines to protect utility repair personnel from electrical shock. However, in situations where restoration of power from the grid may take days or weeks, wouldn’t it be useful for the homeowner, as well as the solar-electricity industry, to have an isolation cut-out device between the grid and the service entrance that would prevent electricity from the PV array from being sent to the grid, but provide electricity to the house and neighboring houses?

Wouldn’t it have been great to read that homes with PV systems were supplying enough electricity to provide a refuge for neighbors who would have been shivering in the dark? Instead, I read about solar energy going to waste.

With all of the gadgets and systems mushrooming in the industry, can’t someone come up with an option that would allow for emergency electricity while protecting the power line workers?

Julius Hayden • Covington, Georgia

There actually is such an option—a grid-tied system with battery backup—but it is significantly more costly, requires more and slightly different equipment, and requires batteries. In HP110, you can find an article on such a system that provides electricity for my office. (Additional articles about grid-tied systems with battery backup can be found in HP139.)

However, the problem is not so much the danger of sending energy back onto the grid when it is down, since there are standard and inexpensive ways of dealing with that. The problem is that a solar-electric array puts out a fixed amount of energy and cannot make up for surges and other quickly changing energy requirements of a home. Plus, sunshine is variable, only available during the day and when there are few or no clouds. That is where either the grid or batteries enter to buffer surges and changes in the solar resource and in usage. 

A good example of the problem is a fridge—something that folks really would like to have energy for during a blackout. That fridge might only take a couple of amps to run, but when its compressor motor tries to start, it might draw 10 to 15 amps for a brief period. And when a cloud skitters over the PV array, without batteries, the fridge—and everything else—would go out.

A battery backup system is more costly—1.5 to two times the cost of a batteryless system—and about 10% less efficient. We usually recommend that people consider batteries only if their homes experience frequent and/or prolonged outages. Of course, with storms occurring with greater frequency due to climate change, more people may be willing to spend the extra money for battery backup.

Michael Welch • Home Power senior editor