After debuting in 2015, Tesla’s Powerwall energized the solar industry. The battery’s powerful lithium ion technology, minimalistic design, and integrated inverter inverter made it a favorite among homeowners looking for a solar storage solution. By the time Tesla began producing an improved version in 2016, the Powerwall had become synonymous with solar batteries.
For a long time, the only way to store solar energy was to build your own battery bank. Building a battery bank can be fun if you’re into home improvement projects, but it requires more time and some knowledge of amps, volts, and electrical systems. Most people developing their own battery banks use lead acid batteries like those found in cars. They’re expensive, bulky, and － in the case of so-called “wet cell” or “flooded” batteries －potentially dangerous. Wet cell batteries require regular topping-off with a corrosive sulfuric acid compound. The more you use the battery, the more often you’ll need to refill it. Moreover, the battery corrodes steadily over time because the electrodes within are always reactive.
Of course, you could choose to employ a safer sealed battery that doesn’t require anything additional added to it. But setting up any kind of custom battery bank still requires running the wires, purchasing an inverter, and so on. Installing the Powerwall, on the other hand, is much simpler. And while it’s a bit more expensive, most analyses comparing DIY battery setups with the Powerwall find that Tesla’s product is priced competitively at $5,500 (including the built-in inverter) per 14 kilowatt-hours of storage capacity.
But the Powerwall is far from the only ready-made storage option out there. Unfortunately, for a number of reasons, it’s difficult to compare solar batteries. While a cost-per-kilowatt-hour measure is useful for comparing solar panels, using the same measure to evaluate batteries is spurious because unlike solar panels, batteries have varying product lifetimes, energy densities (the amount of energy they can store per unit of weight), and depth of discharge rates.
With these caveats in mind, comparisons aren’t impossible. One of the other popular battery options is the Iron Edison Lithium Iron Battery. Like the Powerwall, it has a 10-year warranty. The Iron Edison can store 13.7 usable kilowatt-hours of energy, while the Powerwall can store 13.5 usable kilowatt-hours. But since the Powerwall costs $5,500 and the Iron Edison battery costs $14,900, that means that Iron Edison unit costs over $1,000 per kilowatt-hour, while the Powerwall costs just $407 per kilowatt-hour. Tesla’s unit is also far lighter, weighing just 19.7 pounds per kilowatt-hour, while the Iron Edison unit weighs 25.6 pounds per kilowatt-hour.
Another popular battery from a major manufacturer is the LG Chem Residential Storage Energy Unit (RESU). The RESU has less than half the storage capacity (6.5 kilowatt-hours) of the Powerwall and, like the Iron Edison battery, lacks an inverter. Its price isn’t much better: at $4,000 per unit, it hovers around $920 per kilowatt-hour. The RESU does have the Powerwall outmatched in at least one area, however: it has an expected lifetime that’s 50 to 100 percent longer than that of the Tesla unit.
German battery manufacturer sonnenBatterie offers one of the most expensive home battery options on the market. Their four-kilowatt-hour ’s eco compact costs $5,950, or $1,488 per kilowatt-hour. Compared to the Powerwall, it’s also about four times heavier per kilowatt-hour. On the plus side, it has an in-built inverter and a gleaming white exterior similar to that of the Powerwall. Sonnen has plans to expand to Australia and Britain, and opened a factory in the U.S. last year.
The Sunverge Solar Integration System (SIS) is one of the best batteries on the market. Its price is marginally higher than that of the Powerwall and its usable storage capacity of 11.6 kilowatt-hours is not quite on par with Tesla’s product. But the SIS also has a built-in inverter and an expected lifetime of at least 20 years － twice as long as a Powerwall.
There are also a number of smaller solar batteries on the market that provide energy storage for homeowners who don’t need the capacity of a Powerwall. Orison, for instance, offers a 40-pound battery that can store 2.2 kilowatt-hours of electricity. At a cost of $1,600, the Orison unit costs around $727 per kilowatt-hour. Another battery maker, SimpliPhi Power, produces a line of batteries of varying capacities, the largest of which stores 3.4 kilowatt-hours.
In other words, Tesla has some stiff competition. But it will likely maintain its edge for two reasons. First, the Tesla has an aesthetic sensibility that many other solar battery makers do not. The Powerwall is sleek, modern, and clean. Second, the company has a talent for publicity and showmanship. Founder Elon Musk is a household name, and Tesla is associated with a number of impressive technological achievements.
Is battery storage right for you? According to PowerScout, a solar startup, batteries are best for people who are either going off-grid entirely or who live in areas where the grid is unreliable. If you think that you might want a battery at any point in the future, however, it’s best to install it at the same time you install your solar panels. Adding a battery to an existing array at a later date costs about $3,000 to $5,000 more than adding one when you get your panels installed.