Solar batteries—are they really green?

I have 10 kilowatts of solar panels on the rooftop of my home in Santa Monica, Calif. — enough to power my energy needs most of the time. Instead of selling excess power to the grid (and buying energy at night when the sun isn't shining) I'd like to install batteries in the garage, storing enough energy in daylight to power my home when it's dark.

Solar panels on house
Mel Stoutsenberger | Getty Images

I'd be off the grid and would also have a great backup system when the inevitable "big one" hits my state and the grid goes down. Taking my home off the grid would also reduce greenhouse gases and other polluting emissions that are created by the grid energy I use today. So this is a good — and green — concept for everyone? Well, not exactly.

Some businesses are being sold battery systems to store energy, but not necessarily from solar or other renewable resources. In many cases, such installations are designed purely to profit from storing grid energy at night, then selling power back to the grid during the day when electricity prices are higher. But even if coupled with some rooftop solar, this won't reduce pollution and may, in fact, increase harmful emissions and dependence on fossil fuels.

The amount of electricity a solar installation can generate depends entirely on its size. Unlike my home, most businesses don't have enough space on their property to generate more than a fraction of the electrical power they actually consume. So during the day, when businesses need the most power, all available solar will be used to keep the doors open and the wheels of industry spinning. Since there will be no excess solar energy to also charge batteries, those will be charged from the grid, with its attendant burning of fossil fuels and pollution emissions.

There is a second fatal weakness with the battery storage strategy if it's used to move electrons back-and-forth to the grid, one that can be blamed on physics. About 10 percent of the power gets lost in the charging and discharging process, so batteries charged by the grid actually increase the work the grid must do, compared to if the solar power was used directly, without any battery intermediary.

These concerns are more than theoretical, because some battery companies are trying to grab a disproportionate share of important incentives that were designed to help commercialize technologies that can help achieve important environmental and energy independence goals. In California, for example, the Self-Generation Incentive Program (SGIP) began in 2001 to provide businesses with incentives to encourage them to generate as much of their own power as possible, thus relieving stress on the grid. Since then, the legislature has added new goals, the most important of these being that new power sources must also reduce greenhouse gasses (actually, those two goals complement each other, since at the moment, most of California's grid power still comes from burning fossil fuels).

Battery companies are lobbying the state Public Utilities Commission (PUC) to grant them the lion's share of the SGIP funding, even though the PUC's own recent annual report on the program showed that battery installations ended up increasing greenhouse gasses by 15 percent. Moreover, a January study by Carnegie-Mellon and the Rochester Institute of Technology concluded that in addition to a "nontrivial" increase in CO2, widespread use of battery storage systems (for storing solar energy) is likely to also lead to increases in emissions of nitrogen oxides and sulfur dioxide, the smog-forming gasses that result in harmful air pollution.

More pollution is not the only outcome of supporting these programs, because any rebates to fund commercial battery installations will come at the expense of other technologies that have been proven to offload demand on the grid and reduce GHGs, including fuel cells, combined heat and power, waste conversion, and other greener power generation technologies. The most recent SGIP evaluation showed the program reduced over 162 thousand metric tons of greenhouse-gas emissions annually, the equivalent of over 33 thousand passenger vehicles, but if battery storage lobbyists have their way, the technologies responsible for achieving these reductions would be excluded from the program.

I welcome storage solutions that can take homes and businesses off the grid entirely, especially when the stored electricity comes from clean renewables (including natural gas, the only fossil fuel that can be produced renewably from waste or landfill gas capture). But scarce government support should be a tide that lifts all clean energy boats, not something that picks single technologies that just don't float in the real world.

Commentary by Terry Tamminen, Secretary of the California Environmental Protection Agency in the Schwarzenegger administration. He has authored numerous books on sustainability, and is a co-founder of the R20 Regions of Climate Action. Follow him on Twitter @terrytamminen.