Vehicle-to-Grid (V2G)
Posted by Max Dunn Thu, 31 Jan 2008 00:20:00 GMT
What is with this vehicle-to-grid (V2G) stuff? Why is everyone so excited about it? I already showed how using batteries to store energy at night when it is cheap and then use it during the day doesn’t make sense economically1.
However, this is only part of the picture. It turns out that electricity generation is very complicated, in large part because there is no real storage on the electrical grid. Think about this: what happens when the power plants on the grid don’t produce enough electricity? There will be brownouts or blackouts, both of which are bad. But what happens when they produce too much electricity? Where does it go? Well, actually, since there is no real storage on the grid, it can’t go anywhere, so this is bad.
Electricity usage also changes a lot during a day. In California during the summer time, demand for power peaks about 50 GW and then goes down to 26 GW at night2. Also during the day there are wiggles in the usage as people wake up, go to work, then come home, etc3. It is the job of the ISO to match power product to power demand very precisely.
But this is not easy. A large coal-fired power plant can take several hours to come up to full power. It is also not easy or quick to adjust the amount of power it produces, and producing anything less than the maximum amount of power is not efficient. Gas fired power plants can come up more quickly, usually within 30 minutes and are more easily controlled. So in order to smooth out the power produced by these “base” power plants, the ISO uses peak power reserves, spinning reserves and regulation4.
Peak power is used for just a few hundred hours in the summer months when it is really hot and everyone has the air-conditioner on. This can be anticipated fairly well so coal and other slow starting power plants will have time to come up to speed. For faster response, spinning reserves are plants that are running but essentially idling (usually natural gas) that can be turned up or down within 10 minutes. But this is still to long to adjust for all the little corrections needed throughout the day. For this, they use regulations services.
Regulations services are those power sources that can be adjusted up or down within seconds. It is used to smooth out all the little bumps and valleys in the demand-supply curve and usually is needed for just a few minutes at a time, and is sometimes called for 400 times per day4. And here is the kicker: for just standing by to provide regulation services, the ISO will pay $0.02 per kW-h (that is a kW capacity that is standing by for 1 hour) for up-regulation and the same for down-regulation5_8. So for most houses that have a 15kW electrical drop and use their car only 10% of the time, you have the potential to make almost $390 per month by providing regulation services7! Also, unlike using batteries for backup power that will deep discharge them, the short energy discharges that regulation services require allow batteries to last much longer. So there is some depreciation cost from this, but not too much. So the overall income that can be expected from providing vehicle-to-grid servers is about $2,500 per year6. Not bad!
1 Can Battery Backups Make Money?
3 California ISO: Today’s Outlook
5 Vehicle-to-grid power fundamentals: Calculating capacity and net revenue (Table 2)
6 Above, Section 6.3
7 15 kW x $0.4/kW x 24 hours * 30 days/month x 90% = ~$390/month
8 Frequency Regulation Basics and Trends (Page 7)
This is very interesting stuff. So what are the barriers to making this happen? Is it difficult to engineer a way for the individual batteries to start outputting when necessary (I wouldn’t think so)? Or is it simply chicken and egg – there are no battery banks available, so there’s no energy program to encourageit.
Also, I’d be interested in seeing your math for this. How do you get $390 month? And how does this impact the cost of the batteries – like your earlier analysis?
There are several barriers to making V2G happen:
When a battery is only lightly discharged, it’s life is extended, sometimes greatly. For instance in a typical battery, discharging to 80% gives 500 cycles, discharging to 50% gives 1000 cycles, gives 5000 cycles. Put another way, a 10kWh battery pack would produce a total lifetime energy output of 4,000kWh at 80% depth of discharge (DoD), 5,000kWh at a 50% DoD, and 10,000kWh at 10%.
1 Battery Life