Rooftop direct plug-in solar energy

A rooftop solar installation is a type of distributed generation, which is seen in many parts of the country as a way for cities and homeowners to modernize their power system and become more resilient in the face of extreme weather, brought about in part by climate change.

To understand why residential rooftop solar demands a microgrid, you need a bit of background on the electricity distribution grid, how the flow of power on it is managed, the importance of the quality of that power, and how today's residential solar works. Let's start with the grid.

Quite apart from their worries that solar will reduce their ability to pay for grid upkeep, residential rooftop solar has the potential to amplify a problem that already exists in most U.S. homes.

On their own, the effect of a house, or even a whole neighborhood, is minimal. But add in grid-connected rooftop solar and the quality problem has the potential to strain the resources of the local distribution network, as was shown in a 2015 U.S. Department of Energy (DOE) study on integration of renewables in Texas.

If only it were that simple. Rooftop solar seems like it should be straightforward. When the sun shines, you should be able to reduce or eliminate your home's input from the grid and maybe even sell some of your power back to your utility company. With a home battery-storage unit, you should be able to do that even after dark.

When the rooftop panels are producing electricity, the system provides current at the correct 60-Hz fundamental frequency, but it doesn't do anything to cancel out the harmonic distortion from the power supplies running some of the appliances. So the house at times produces more than 100 percent total harmonic distortion at the grid connection.