My previous blogpost noted that some utilities argue that the real value of unpredictable power—power that varies with the wind or the sun, regardless of demand—is negative. That is, it’s like someone forcing you to take a gift “right now,” when your hands are full. The gift might be something you’d like under different circumstances, but you just can’t take it “right now.” Let me explain why that’s so.
A working electrical network has little “give” to it. There’s not much capacity to store energy. Each time a user shuts off a light or flushes the toilet, the energy input to the network must be changed. To accommodate this quivering demand, the network must always have some “spinning reserve”—generators that can instantaneously increase or decrease their output as required.
Once you have that spinning reserve in place—a nuclear or coal-fired plant that can reliably deliver power when needed, even to replace a large generator that may suddenly drop off the line unexpectedly—once that capability is in place, then the “gift” of unreliable power is of no value.
The wind or solar plant cannot provide that spinning reserve; reliability is the key requirement there. Spinning reserve is like insurance. Would you accept an insurance policy from a company that says it may not be able to pay you when you need it? The typical wind farm operates at only 20-30% of nameplate capacity. That’s not like saying there may be occasional extraordinary circumstances when they cannot pay. It’s saying that there are only occasional times when it can deliver rated power and even those times will be short-lived.
There is talk of plans to decrease this unavailability through the use of hydrogen, or pumped storage, or fuel cells or other untested stratagems. But wouldn’t it make more sense to just build another nuclear plant? We know how to do that.