Navigant Research Blog

Why It’s Still Too Early to Bet on Residential Energy Storage in the United States

Sam Jaffe — April 1, 2014

SolarCity announced recently that it is discontinuing the residential energy storage product that it rolled out in California 2 years ago.  The company put the blame on the shoulders of utilities, which SolarCity said were stalling permitting of its new units.  But, in fact, SolarCity has only itself to blame for the failure of its product.

That’s because the company never stopped to ask why a residential customer would want a battery storage system.  In some cases, such as with off-grid homeowners and homeowners (such as indoor horticulture enthusiasts) with very expensive equipment that needs reserve power, batteries are a requirement.  But the typical homeowner gets no financial advantage from shifting power from one point in the day to another.  Rates that would allow such an advantage, known as time-of-use rates, are rarely offered by utilities to residential ratepayers.  Because residential photovoltaic (PV) power is usually net-metered, meaning that homeowners can receive credit for putting energy back onto the grid, there’s no reason why a solar homeowner would receive a financial advantage from storing energy.

Diesel over Batteries

Meanwhile, SolarCity was trying to sell its residential storage units at an outrageous markup.  I have SolarCity panels on my house in Boulder, Colorado, and when I inquired about the cost of the battery backup system, I was quoted $25,000 for a 20 kilowatt-hour (kWh) system.  That’s despite the fact that Tesla Motors (which makes the battery packs for SolarCity) has told the world that it is able to build its battery packs for less than $300 per kWh.  It’s hard to understand why I should give SolarCity more than 3 times the money it cost the company to buy the battery pack for a system that doesn’t earn me one penny.  The only benefit that such a system could provide me is reserve power when the grid shuts down.  However, a far more reasonable solution to that problem would be an emergency diesel generator.  Yes, it’s dirty, but the carbon and pollutants produced by running a diesel genset during the few hours of a year that I would need it would be far less than that produced from the manufacture of 20 kWh of batteries.

Mind the Wiring

So, is there any merit to SolarCity’s claim that the California utilities are responsible for freezing out the battery system product?  It’s not very likely.  That’s because a battery pack that is situated behind the meter does not require any utility permitting, just as a diesel generator doesn’t.  What does require approval is the capability of an individual building to island itself from the grid (which means that it continues to operate as a nanogrid by itself and shuts itself off entirely from the distribution grid when it does so).  If that’s the case, then the electric utility has every right to deny permitting if it doesn’t feel comfortable with the system.  Improperly set up, islanding can cause a life-threatening situation for an electricity linesman.  The practice of islanding is governed by the IEEE 1547 protocol, which is an extremely complex, difficult to engineer, and expensive set of rules governing an islanded system.

There are ways to do residential energy storage well.  In our upcoming report on the topic, Navigant Research expects that almost 20,000 residential energy storage systems will be installed in Germany, Japan, and South Korea combined in 2014.  All three countries have made concerted efforts to standardize the specifications and permitting process for PV-integrated residential solar systems.  They have also introduced generous subsidies for such systems.  It’s an expensive and politically difficult process, but it’s getting results in those countries.

One Response to “Why It’s Still Too Early to Bet on Residential Energy Storage in the United States”

  1. Len Beyea says:

    If the author is not on a time-of-use rate and has a solar system, SolarCity did not give him the advice he should have gotten. All investor-owned utilities in California and many of the municipal electric utilities offer time-of-use rates for residential customers, which are typically advantageous for solar users, because the power displaced by the solar system is the most expensive (weekday afternoon) power.

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