Tesla chief technology officer, JB Straubel, is a pretty smart fellow. When it comes to being an authority on electric cars and battery technology, he may be one of the top three experts in the world today. So when he speaks, people listen — even E.F. Hutton. In a presentation last May, he was asked to give his opinion on vehicle to grid technology — often abbreviated as V2G — and on re-purposing used EV batteries for grid storage duty. Sadly, Straubel was quite negative about both ideas.
The V2G model goes like this. Soon there will be lots and lots of electric cars on the road. Each one is essentially a battery on wheels. Wouldn’t it be swell if all those batteries could be connected to the grid? Then they could soak up any excess electrical power, which would help balance the grid. Later when demand for electricity is high, they could give some of that stored energy back. eliminating the need for utilities to fire up so-called “peaker plants.” Those plants usually run for only a few hours a day during that 5 pm to 8 pm period when the demand for electricity is highest.
Not so fast, says Straubel. He agrees that using EVs to absorb some of the excess energy on the grid makes sense, but only under carefully controlled circumstances. “Using vehicles as a buffer for renewable energy, this is definitely something that’s coming, and I think there’s two ways to implement this. “The first is to use dynamic charging. This is essentially intelligently commanding when the vehicles absorb their energy from the grid to match up with when you have renewable energy available. This is something we can do very easily with just essentially software and controls. We don’t have to change any hardware and there’s no additional regulatory or certification work needed. It’s just essentially controlling the timing of when something otherwise would happen.
“If we want to actually send energy back from the car to the electricity grid, this gets much more complex. That’s something that I don’t see being a very economic or viable solution — perhaps ever, but certainly not in the near term. The additional wear and tear and degradation on your vehicle battery has a fairly high cost. Many of the people and small businesses looking at this today don’t take into account fully that degradation cost, and also the additional interconnection cost. Because if you interconnect your vehicle, you do have regulations that play a part. It has to interconnect in the same way that a solar system would on someone’s home or on a business, which have different standards so that they can protect line operators and people on the grid.”
Straubel’s explanation does not address the situation where someone already has a solar system installed that is capable of sending power back to the grid. In that case, it may be feasible to do so technically, but will still have a negative impact on the life of the battery.
On the subject of using an EV battery to store electricity, I have actually been considering this over the past several days. The Tesla Powerwall costs about $7,000, after you figure in an inverter and the services of an electrician to install it. When you’re done, you have a battery with a fairly modest capacity of roughly 7 kWh.
Why not, I asked myself, buy a used 2011 Nisan LEAF for about $5,000 (or less)? Then I could take the 24 kWh battery out of it and junk the rest of the car. More than 3 times the storage capacity for about the same price. That’s a no brainer, huh? Maybe not, says Straubel. “We’ve looked at reuse or kind of the second life of automotive batteries for grid applications very closely ultimately, every time we’ve studied this, we’ve come to the conclusion that it’s not a very economical or very good use of those assets.
“By the time they come out of a vehicle that’s lived its life, the technology will be quite old. We expect 10, maybe 15 year life at a minimum from these batteries. And the degradation is not entirely linear. By the end of their life, the efficiency has degraded on every cycle. You see lower efficiency, the capacity will have somewhat degraded, and for a lot of reasons it makes it very difficult to deploy those efficiently back into a grid setting, where you want high reliability and you do want predictability.
“So, my view is that we’ll see new batteries dedicated to that market, that also have slightly different characteristics. They should have higher cycle life. In an electric vehicle that has 200+ miles of range, you don’t need as many cycles as you do on a battery that’s designed to charge and discharge every single day on the grid. There’s perhaps a factor of about 4 or 5 difference in the cycle life — so that’s one aspect.”
Dang. There goes my dream of an inexpensive home battery storage system. You can watch the entire video at your leisure if you want to hear more of Straubel’s remarks.