Solar Power Battery Storage

Solar panels are fine in the summer, goes the conventional wisdom. But what about in the winter? And what about those of us who work for a living? Isn’t it a problem that most of our PV generating capacity takes place while we’re at work? How do we take advantage of solar energy when there’s not much sunlight to be had?

That’s where battery storage for solar power plays a big role. These batteries are gaining a lot of attention as solar power becomes more widespread in residential use. They help make solar power viable under less-than-favorable conditions. They enable peak-shifting, where power produced during off-peak hours can be used during periods of peak consumption.

They can even take the place of gasoline and natural gas backup generators, since they produce zero emissions, they’re silent, and they’re clean. Better still, as anyone who’s lived through the aftermath of a hurricane or other natural disaster will attest, it means not waiting on line at a gas station, hoping that supplies hold up amid a massive spike in demand.


A solar-plus system works much the same way a car battery does. Each rely on an outside power source to maintain a charge, and releases it later when needed; your car’s battery is charged off the engine, while your solar backup battery is drawing power from your PV cells and storing it for use later. There are some differences, however. A solar battery backup requires a deep charge in order to last through daily cycles of depletion and recharging. It must also provide steady and sustained output, in contrast to the quick jolt delivered by a car battery.

Ideally, your backup battery should be AC-coupled to the grid via a special inverter, unless your home is entirely off the grid. Traditional permanent gas backup generators use a similar setup to comply with UL regulations meant to ensure the safety of utility workers during power outages, since they keep your solar system from sending power back down the lines during an outage. In the absence of AC coupling, you won’t be able to use solar during a power outage.

Current Solar Power Battery Manufacturers

Tesla Powerwall

The Powerwall generated considerable buzz when it was announced early in 2015, and for good reason. After all, Tesla had succeeded in bringing the electric car to the masses when so many other companies had failed, and analysts are confident that they’re poised to do the same for solar storage with the Li-Ion storage system. Prices are high right now — preorders are running at $3,000 per unit for the base 7kW model — but they are expected to drop considerably once the company’s new battery factory comes online.

Iron Edison LiYFePO4

Iron Edison’s lithium iron batteries start at $7,400 for 48 volt residential use, and increase in price from there. The company offers a number of other products, such as indoor/outdoor enclosures, racks, inverters, and other electronics to augment their core offerings, and also offers nickel iron batteries rated for ~11,000 cycles. Batteries are available on their own, or as part of a complete system.


Alevo is a Swiss startup that has only been in operation since 2014. Currently, the company offers primarily utility-scale backup batteries; there is no word as to whether the company will move into the home Solar-Plus market with the inauguration of a new production facility in North Carolina. If they do, their technology, which promises non-combustible and non-flammable batteries with long life cycles — could be a game-changer.

Eos Energy Storage

Eos’ novel Zynth™ battery is deployed at industrial, commercial and residential scale. The company’s batteries use zinc hybrid cathode technology, which has two advantages: it’s safe, and it’s also considerably cheaper than many alternatives.


Sonnenbatterie originates in Germany, which brings with it certain advantages. Germany is currently the world’s leader in solar power despite having a relatively low insolation. That’s due in part to widespread PV use, but it’s also helped by German innovation in solar storage. This lithium-ion system is compact, lightweight, and AC-coupled.

Stem PowerStore

Stem Incorporated’s signature product is aimed at commercial-scale storage, and is part of a suite of products that includes PowerScope and PowerMonitor, which allow users to better track, monitor, and deploy energy.

Greensmith Energy

Founded in 2008, Greensmith Energy provides grid and microgrid-scale battery solutions for utility and commercial use. Their solutions include both grid and behind-the-meter applications.

Outback Power Inc

Outback engineers solutions of varying sizes, including residential (off-grid and grid-interactive), commercial, and mobile applications. Products include inverters, chargers, communications and monitoring hardware, energy monitoring, and charge controllers.


Younicos provides storage and converter solutions at grid and industrial scale. A company with offices in Germany and the US, it is poised to become a major player as more utilities incorporate renewables into their product mix.

Disadvantages of Solar Storage

Bulk: Until recently, solar backup solutions have been large and ungainly. While that’s improving, the space savings does come at a premium, because the more compact batteries cost more to produce.

Environmental Impact: The high cost of Lithium Ion batteries means that lead acid batteries are still common. While both types cause some degree of pollution, lead acid batteries are by their very nature harder to service and dispose of, as well as being prone to leakage.

Cost: The cost of most solar storage is very high. That’s not only true of innovative systems used by utilities (like the molten salt storage systems in use by some utilities in the Southwest); it’s also the case with many home storage systems. The smallest and most efficient systems tend to be the most costly, especially if you’re wiring your home with an AC coupling system that can draw from the grid but still operate in the event of a power outage.

Advantages of Solar Storage

Ditch the Grid: A good storage system facilitates off-grid living, especially if your energy use is low. Solar storage is one factor behind the success of the Tiny House movement, but it has clear benefits for larger homes trying to transition off the grid as well.

Stretch Your Dollar: Solar is often being generated when we’re not home to use it. Solar storage means storing power during peak production for use later, instead of powering your fridge with the sun during the day, and buying electric to power the TV, microwave, and your laptop at night.

Resiliance: Install the right system and your home can have power regardless of whether the grid is up and running.
Backup the Grid: You can also use backup batteries without solar, charging them from the grid during off-peak hours when electricity is cheaper and then using them in place of a generator during power outages, or to offset the cost of peak power usage.


If solar power has revolutionized the way we think about power generation and environmental stewardship, reliable solar storage is beginning to revolutionize solar. The present state of solar storage is interesting, to be sure, but coming changes in the field — like newer batteries promised by Tesla founder Elon Musk and others working hard to innovate storage cells — are even more exciting. Like solar panels themselves, the industry is finding ways to squeeze more storage out of smaller systems and to do it with less expense. We live in interesting times indeed.


Fran Whittaker-Wood
Home Improvements Expert

Fran loves all things home. She is passionate about finding the best architecture, design and home interior projects from around the world, and has a keen interest in discovering the newest and most exciting design trends.