Solar Battery Tesla Powerwall and more
If you’re thinking about going solar, or even if you have already, you may be considering installing a solar battery too. How do they work? Why would you want one? How much do they cost? While there’s some good options available, there’s a lot to chew with this one. Let’s see if we can break it down.
The biggest Achilles heel of solar power is that you’re only generating power during the day and that’s not even counting seasonality and weather. There’s an immense amount of power we can generate from the sun, but capturing and then storing overproduction for later use is the challenge.
I’ll be diving into grid scale energy storage solutions in a video later, but for this one I’m going to focus on the most common batteries you can use in your home. These can help to store solar for use at night or to just store energy as a backup system.
Live in an area where the grid can be unreliable? A battery paired with a solar panel system can help you weather grid outages. In fact, depending on the size of the battery and solar panels, you could run indefinitely and not even now there was grid outage in the first place.1
When looking at solar batteries, there are some points of comparison to consider: capacity and power, depth of discharge, and warranty.
Capacity is measured in kilowatt hours (kWh), which is how much energy can be stored in the battery. The power is the flow of energy the battery can output, which limits the number of things you can run at the same time off the battery. This is measured in kilowatts (kW).
Depth of discharge is how low you can run the battery before you need to stop and recharge it.
And warranty is exactly what you think. It’s the manufacturer’s guarantee for how long the battery will last or how many cycles the battery is capable of in its lifetime.
What are the types of batteries for solar?
From my research there are a couple common battery systems you’re looking at when it comes to home use: lead acid and lithium ion. There are some others like saltwater and flow batteries, but they’re still relatively new to the home market.2
Lead acid batteries have been around for well over 100 years, and if you saw my battery recycling video, you know that they can be fully recycled. They come in two flavors: flooded (also known as vented) and sealed. Biggest pro for lead acid in general: they’re super cheap, which makes them a great option for off-grid installations. A big con: they have a very short lifespan and low depth of discharge. The deeper you discharge a lead acid battery, the shorter the lifespan and fewer cycles you’ll get. You’re typically looking at 200 - 1,000 cycles. Each manufacturer will provide details for the recommend depth of discharge. An even bigger con for flooded lead acid batteries: They off-gas hydrogen and require special ventilation ... or ... things can blow up.3 They also require maintenance to monitor water levels and equalize the batteries on a schedule. Sealed lead acid batteries don’t have those downsides, but cost more than flooded batteries.4
Lithium ion is the technology most big name battery systems are using, like Tesla Powerwall. They’re much lighter and more compact than lead acid batteries, and also have a much longer lifespan with deeper discharge cycles. We’re talking about thousands of cycles with the Tesla Powerwall being around 5,000. And no off-gassing or special maintenance to worry about. The big con is the price, which is much more expensive than lead acid, and as of right now they can be more challenging to recycle.
Salt water is still relatively new for solar batteries, but they have no heavy metals which means they are easily recycled. They have a good depth of discharge with cost and lifespan somewhere in between lead acid and lithium ion batteries. And they’re incredibly safe when you consider that they’re non-toxic, non-corrosive, non-flammable ... you get the idea. They’re very safe.5
Flow batteries are still getting started in the home market and are limited where you’re able to buy them. One example is Redflow’s Zcell in Australia, but from my research flow batteries are still primarily large scale energy storage. One big benefit of flow batteries is the 100% depth of discharge, they’re also fully recyclable like salt water batteries.6
So how much?
So how much do they cost? Well, get ready for some sticker shock. Typical solar batteries can cost between $5,000 - $7,000, or about $400 - $750 per kWh of the system. You’ll also need to add installation costs on top of that, so it gets pricey fast. Now, if you know what you’re doing, you can build out your own system for a lot less. I’m not going to get into the DIY angle in this video, but there’s some great resources online.
I'm not going to get into the DIY angle or full off-grid systems in this video. Those deserve their own dedicated deep dives, but there are some great resources online for those.
So with prices like that how can someone justify tacking that onto the expense of a solar panel system? It’s going to really depend on where you live, your energy prices, and what you’re hoping to get out of it. There are three things you’ll have to factor right off the bat: time of use rates, demand charges, and net metering.
If your utility has time of use rates (TOU), you’ll have peak and off peak electricity rates, which means you could be paying very high prices during the day. Then at night you’re paying discounted rates. In California some peak electricity pricing can hit as high as $0.46/kWh in the summer.7
A solar battery takes the excess electricity you generate during the day and stores it for use later. No shock there. And you probably already know that means you’re taking advantage of all of the solar power you’re generating, even at night. But some of these systems can take it a step further by letting you pull electricity for use from the grid while prices are low. Then during peak rate times your system will pull the solar electricity you stored from the battery helping to save money and reduce load on the grid at the same time.
That’s one of the major selling points of Tesla’s Powerwall. It can be set up to take your electricity rates into account to determine the most economical use of your solar and grid electricity.
Does your utility have demand charges? Those types of fees are usually determined by the total amount of electricity you buy during peak hours or the total amount of electricity in a month. If you have a solar battery, it minimizes the amount of electricity you have to pull from the grid, which in turn drops your demand charge.
Where you live may also have feed-in tariffs, which is a rate you’re paid for the amount of electricity you export too the grid. With a solar battery, you’ll most likely see a decrease in those payments because you’re putting less into the grid. But you’ll be using more of your solar generation for yourself, so you’ll need to weigh the difference in savings between those two.8
And finally, net metering. Here in Massachusetts I’m lucky and have full net metering, which means any excess solar that I put into the grid gets erased off of my grid usage. It’s a 1:1 exchange. That actually means a solar battery system is less financially beneficial for me since the grid is acting like a battery for me already. However, there are a lot of areas that have a reduced net metering system, or even no net metering at all. Sometimes electric companies will offer you credits at the wholesale rate for your solar production, but then you’re essentially buying it back later at full consumer rates. That means your solar electricity is more valuable to you if use it at your home. That’s where a solar battery may make sense for net metering situations.
There are quite a few options out there, so I can’t go through all of them ... and I don’t think you’d want me to. But there are a few big ones I thought it would be good to take a quick look at.
The big name that pretty much everyone knows is the Tesla Powerwall. It was originally introduced in 2015 and is currently on it’s second version, which can store 13.5 kWh and sustain a 5kW output. It’s enough to power essential appliances for 24 hours. With a single battery starting at $6,700, supporting hardware at around $1,100, and installation being somewhere between $1,000 - $3,000, it’s pricey. It has a 10 year warranty and is guaranteed to have 70% of it’s capacity still available.
The Powerwall can be configured to hold back a certain percentage of energy for backup purposes, and as I mentioned earlier, will manage all of the energy prioritization automatically for you. The system is designed to be tied to the grid to maximize your solar and take your electricity prices into account. If you’re looking to go off-grid, you’ll need to look elsewhere.
But even being tied to the grid, you still can weather grid outages and refill your battery from your solar production during the day.
Sonnen eco is a 4kWh battery that comes from the German company, sonnenBatterie, and has a continuous power output of 3kW. The battery is a lithium ferrous phosphate battery. Prices start at $9,950 and go up from there. Much like the Tesla Powerwall, it’s software learns and minimizes your grid usage by managing your solar consumption and time of use grid electricity rates. And just like Tesla, the warranty for the system is 10 years and 70% of capacity.
The LG Chem RESU, which is from the South Korean electronics giant, comes in capacities from 2.9 - 12.4kWh and has a 3.5kW continuous power output.9 This is actually one of the most popular batteries for solar panel systems in Australia and Europe. It’s still fairly new to the U.S., so much so I couldn’t find official prices yet, but it’s looking like it will be between $6,000 - $7,000, but you’ll need to tack on an additional $2,000 - $3,000 for equipment costs and $1,500 - $3,000 for installation.
So is it worth it to add a solar battery onto your solar panel system? As you heard from some of those prices, it’s really going to vary depending on where you live and what your electric utility situation is. If I were to add a battery onto my system, I wouldn’t see any kind of return of investment right now because of where I live. In Massachusetts I’ve got full net metering and I don’t have time of use rates, which means I’d see no benefit of any kind. However, that may be changing.
Just this last February the Massachusetts Department of Public Utilities approved a new three-year energy efficiency plan. It’s going to make Massachusetts the first state in the country to make battery storage eligible for energy efficiency incentives. At the end of each year, the utility will reward you by how much you reduced your load on the grid because of the battery. The state wants to increase the amount of behind-the-meter battery storage in the state to 30-34MW.10
There are similar programs around the world that are building out virtual power plants by utilizing home batteries to stabilize the grid. In Germany, Sonnen has received pre-qualification for such a system, which uses all of these batteries to put large amounts of power into the grid during peak usage. A home battery in this case not only benefits the owner, but also everyone else on the grid.11
So there may be different programs available where you are that can offset the addition of a battery to your home. There was a program in Australia that offered interest free loans of up to $10,000 to buy batteries or solar battery systems. The program was such a hit that it was “all but exhausted” two weeks after it was launched.12
But the math is a lot tougher when it comes to batteries than it is for a solar panel system in general. You’ll need to do a little number crunching to see if the math works for you, but you don’t have to do that alone. In my previous video on my solar panel system I strongly suggested using Energysage if you’re in the United States to research solar panels and installers. You can use Energysage to check out information on solar batteries too. They have some great write ups and reviews, which I’ll include in the description.
And be sure to check out my EnergySage portal for researching solar, calculating the costs, payback periods, and any other questions you have. They’re a tremendous resource and completely free. You can plug in your information and request quotes from solar installers, which all get funneled into your EnergySage account, so you don’t have to worry about getting flooded with phone calls. It makes it easy to compare installers, cost estimates and energy production quotes in one place. And installers also have customer rankings and feedback, so you can find a reputable and good quality installer.
To be completely transparent, this is an affiliate program for my channel, so if you research and find an installer using EnergySage, it helps to support the channel. It’s a completely free service, which I’ve used myself and can vouch for how much it helped me through my solar installation process. Whether or not you use my EnergySage portal doesn’t matter, I strongly recommend EnergySage for your research and questions.