It wasn’t 24 hours since Tesla, the Elon Musk led car manufacturer, unveiled the Powerwall home battery that the phone started ringing from interested clients. That just shows you how powerful their marketing machine is, but how powerful is the battery? Before we get into what the battery can and can’t do, let’s make clear what the battery is. It is:
- Lightweight
- Attractive
- Elegant
- Energy-dense
- Fun to look at and talk about
If it sounds like I’m describing Hope Solo (or insert your energy packed small athlete here), I am not. The Tesla Powerwall battery can be described the same way.
So let’s explore the physics behind the battery to see how powerful it is. At 10kWh of rated capacity, the battery can theoretically discharge 100 watts for 100 hours, 1,000 watts for 10 hours, or 10,000 watts for one hour. In reality there are inefficiencies involved and the actual output would be much less, and the faster it is discharged, the greater the losses. The “average” home uses about 30kWh of electricity per day, which equates to an electric bill of about $100 per month. Most single-family homes in Florida use substantially more energy that that, especially pool homes. Doing some quick math shows that the battery would have enough energy to get you through about 8 hours of power loss from the utility company.
What? Just 8 hours? Really?
Really.
Side note: the “average” residential electric bill includes apartments, condos, and every single meter, even garages and out buildings. People we meet rarely have an “average” electric bill.
Now in reality, you wouldn’t power your whole house with this battery. You would probably carve out “critical loads” like refrigeration, lighting, and maybe a circuit for a TV or radio and mobile device charging. You aren’t going to power your air conditioner, water heater, or pool pump with just one battery. 10kWh is not a lot of energy storage, and if your utility bill is higher than “average,” 10kWh may be a drop in the ocean. It could be scaled up with several batteries to do the job, but it’s going to get expensive quickly.
Speaking of price, the reported $3,500 price is extremely misleading. The price of the battery itself may be $3,500, but the required electronics and wiring will substantially increase the price. You can expect to pay at least as much for the required inverter that converts the battery’s DC electricity to AC electricity that is usable in your home. The installation labor and rewiring of your critical loads will set you back a few thousand more. And then there is dealer overhead and profit. In the end, it would likely cost about $12,000-$15,000 to have this battery installed. There would be an economy of scale when installing multiple batteries, making the investment more viable.
Don’t expect a $3,500 battery to power your whole home and solve your energy woes.
Make no mistake – the Tesla Powerwall is a step in the right direction. It makes batteries consumer friendly, the energy density (energy per cubic foot) is excellent, and it has the chance to be cost effective at the right scale. It will appeal to early adopters, and it will likely be a well-performing, long-lasting, quality product.
However, there are already cheaper options on the market that do the exact same thing, albeit in a less elegant package. You can buy traditional off-grid lead acid batteries at a fraction of the price, even considering the expected lifetime and maintenance required. If you want a whole-home battery backup system, it has been available for many years – decades even. People have been living off the grid for a long time (I did it as far back as 2000). There is nothing revolutionary about the Tesla Powerwall in terms of price. It does not make it more affordable to cut the cord to the utility company.
There is some good news. There have been big strides in terms of off-grid and grid-interconnected solar energy systems affordability. Solar panel prices have plummeted in recent years. The solar panels themselves account for a fraction of the installed price of a system now. Similar to the battery pricing above, solar panels account for just 25% of the installed price of a grid-interconnected solar energy system today. Solar panels can account for less than 15% of an off-grid solar energy system.
While the Powerwall battery is not revolutionary in terms of function or price, it give us hope that a consumer oriented mainstream battery solution will soon be available. New products will likely follow that complete the consumer friendly package required for a true whole-home solar energy system with battery backup. The dream of a single box that you hang on the wall to power your house is within reach, and Tesla is on the leading edge of delivering what consumers want. Thousands of people drive Tesla automobiles, and there is hardly a financial argument to be made for owning one. But they are amazing products, and very, very cool!