Home storage batteries coupled with solar panels have a high price tag. Nevertheless, events in the news have made homeowners start to take a serious look.

With its equipment linked to starting some of California’s worst wildfires, PG&E has tried to mitigate risk with rolling blackouts. Since the utility can’t supply reliable electricity during fire season, solar power and home storage batteries seem more attractive than before. The combination seems likely to reduce both wildfires and the necessity of depending on the grid for power.

Solar power seems expensive, and adding batteries makes it more expensive. But more and more people are looking into it in the face of rolling blackouts. As solar companies increase their sales volume, economies of scale will probably drive prices down.

California is hardly alone in experiencing blackouts. Heavy wind and rain knocked out power to 115,000 electricity customers in Vermont in October 2019. But 1,100 homes had battery backup. In one case, the batteries supplied power for 82 hours before grid power was restored.

Alternatives to buying batteries

Internal view of a solar inverter. Note the many large capacitors (blue cylinders), used to store energy briefly and improve the output waveform.

Homeowners who want to install batteries can always buy them, but it’s not necessary.  Leasing or entering a power purchase agreement costs less upfront.  With a power purchase agreement, the company owns and maintains the equipment and sells power to the host at a rate that’s usually lower than what the utility charges.

In Vermont, those 1,100 homes obtained batteries from Green Mountain Power, Vermont’s electric utility.

The homeowners do not own the batteries. The utility, started a pilot project a couple of years ago. It offered customers the chance to pay a monthly fee for the utility to install a Tesla Powerwall on their property. They can use it in the event of a power outage.

Otherwise, the utility uses the batteries to manage the grid. They provide power at peak times and have saved the utility hundreds of thousands of dollars by not having to start expensive peaking plants. The arrangement seems similar to Consolidated Edison’s pilot virtual power plant in New York City.

Vivent, America’s second-largest residential solar company, has recently decided to offer battery backup as part of its power purchase agreement service in California. Up till now, its customers have had to buy the batteries if they want backup. Vivent offered the package only to its customers in Hawaii.

It surveyed 315 homeowners in California, and 40% of them reported interest in purchasing a solar panel/battery backup package. Even before PG&E’s rolling blackouts, most of those homeowners reported having experienced at least one recent outage that lasted more than two hours. Once it establishes its package in California, it will probably extend it to the other states where it operates.

A new alternative product

Eco-house with turf roof and solar panels. By W.L Tarbert – Own work, Public Domain from Wikimedia Commons

Retired Marine Corps Col. Brent Wilson found existing storage solutions unsatisfactory. He thought that Sonnen has a safer and better performing product than Tesla’s Powerwall, but that it’s way too expensive. Could he devise a system as good as Sonnen’s, yet compete with Tesla on price?

He devised a system that satisfied him on both counts and founded NeoVolta to sell it. The company now sells about 50 units a month for about $13,000 each, comparable with Tesla’s price.

With 14.4 kilowatt-hours of storage capacity, NeoVolta’s product has slightly more capacity than the Powerwall. The Resu by LG Chem, another established company in the market, provides only 9.8 kilowatt-hours.

Wilson’s product uses a lithium iron phosphate battery instead of the more common lithium carbon oxide. That chemistry has a lower risk of catching fire.

Solar panels produce direct current, so most solar systems require an inverter to produce the alternating current required by household appliances. NeoVolta’s system can take either AC from an inverter or DC directly from panels. That feature makes it a good choice for retrofitting systems where the inverters reach the end of their useful life. It doesn’t require purchasing a new inverter.

The company took the unusual step of starting with an initial public offering instead of seeking venture capital. With the home storage industry in its infancy, there is plenty of room for new entrants. Success doesn’t come easily to startups, but Col. Wilson managed procurement for $100 billion worth of military helicopters. He considers running a startup much easier.

Is the Powerwall safe?

Installation of Tesla’s PowerWall.

Standard lithium carbon oxide batteries can catch fire. Burning phone or laptop batteries have caused catastrophic damage. Tesla’s Powerwall uses lithium carbon oxide. How safe is it?

To find out, the National Fire Protection Association acquired two Powerpacks from Tesla. A Powerwall has one energy storage pod of about 900 battery cells. A Powerpack has 16 pods. In other words, it amounts to a collection of Powerwall’s in one unit.

The first test wanted to find out if an exploding pod would cause the entire pack to explode. To find out, the team installed a heater cartridge in one of the middle pods. They let the unit run until thermal runaway started.

It took about 12 minutes before the sound of exploding battery cells started. Smoke started to come out of the exhaust vent after about half an hour. The explosions continued for about 15 minutes. The smoke continued but stopped coming out of the vent an hour and a half after the test began. Not only did the other 15 pods not explode, they suffered no damage and could function normally.

The second test entailed mounting a propane torch next to the other Powerpack. It took 45 minutes before anything started to explode. After an hour, they turned off the burner. Thermal runaway had started in the pack by that time. Visible fire appeared after about an hour. The last of more than 14,000 cells exploded after about three hours. The last flames went out about 45 minutes later. While the fire destroyed all the cells within the pack, its outer case remained intact.

With proper installation, therefore, any fire started in one pod a Powerpack will not spread to others. If an external fire destroys a Powerpack, the outer shell will not cause the fire to spread.

Outlook

An overheating Powerwall will not burn down the house, but it can still catch fire itself. Many other companies and researchers are exploring alternatives to lithium-ion batteries.

Regardless of battery chemistry, the cost of solar storage puts outright purchase out of reach for many homeowners. Leases and power purchase agreements reduce upfront costs. Each way of obtaining them has advantages and disadvantages.

New technology is expensive, but the cost always comes down. I can remember when a pocket calculator cost hundreds of dollars. Now, they’re likely to be giveaways at trade shows. Home storage for solar power has only been available since 2015.

Storage, either at home or at grid level, is absolutely essential for renewable energy to replace fossil fuels. Between research into new technology and inevitably falling prices, it’s not a question of whether storage will enable renewables to succeed. It’s only a question of how long it will take.

Sources:

Batteries vs. blackouts: 1,100 homes powered through Vermont outage with storage / Julian Spector, Greentech Media. November 7, 2019
Could solar panels help prevent California wildfires? / Alexandra Kelly, Changing America. November 15, 2019
Marine veteran aims to improve residential storage with startup NeoVolta / Julian Spector, Greentech Media. November 15, 2019
Tesla set fire to a Powerpack to test its safety features – the results are impressive / Fred Lambert, Electrek. December 19, 2016
Vivint launches solar-storage PPA in California, citing wildfire-related demand / Emma Foehringer Merchant, Greentech Media. November 12, 2019

Photo credits:
House with solar panels. Public domain from Wikimedia Commons
Inverter. Public domain from Wikimedia Commons
Eco house. Photo by W.L Tarbert. Public domain from Wikimedia Commons
Powerwall. Some rights reserved by Bryan Alexander