We also looked at 10 real-world outage events from 2017 to 2020, including hurricanes, wildfires and storms, and modeled building performance for specific locations and real weather patterns during and after the outages.

We found that in seven of the outages, most homes would have been able to maintain critical loads plus heating and cooling using solar with 30 kWh of storage, or just over two Powerwalls.

But the weather around the outage can have a big impact, especially for hurricanes. After Hurricane Florence knocked out power in North Carolina in 2018, cloudy skies hung around for three days, dimming or even stopping solar panels’ output.

Hurricane Harvey, on the other hand, slammed the Texas coast in August 2017 but moved on to cause widespread damage elsewhere in Texas. The skies over Corpus Christi cleared even as it took a week or more to get power restored. Solar and storage would have been a big help in that case, providing virtually all power needs for a typical single-family home, once the skies cleared.

Similarly, we found solar can do well in less cloudy events, like wildfire prevention shutoffs in California, or after the 2020 derecho windstorm in Iowa.

The heat source in a home is also a key factor. In a five-to-10-day outage following an ice storm in Oklahoma in 2020, we found that solar plus a 30-kWh battery could have supplied nearly all the critical power and heat needed for homes with natural gas heaters or heat pumps. But homes with electric resistance heating would have fallen short.

In Texas, over half of homes are heated with electricity, primarily resistance heaters. Energy Star-rated heat pumps – which provide both heating and cooling – use half as much electricity per unit of heat output as electric resistance heaters and are also more efficient at cooling than the average new air conditioner. Converting older resistance heaters to new heat pumps can not only save money and reduce peak demand but also increase resilience during outages.

Setting up solar and storage to provide backup power in a home or building takes extra work and it costs more – just one Powerwall can run from US$12,000 to $16,500 for a full system installation, before incentives and taxes. That’s as much as a fair-sized solar system. Nevertheless, a growing number of homeowners are installing both.

Over 90% of new solar installations in Hawaii in 2021 were paired with batteries after a regulation change. Now these distributed power plants are helping power the grid as coal plants are retired.

California has over 1.5 million rooftop solar systems. A growing number of customers are retrofitting batteries on their systems, or adding new solar plus storage, in part because utilities have resorted to “public safety power shutoffs” to lower the risk of wildfires sparked by power lines during dry, windy days.

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