A little while ago California signed into law SB-1 which was labeled the “million solar roofs” legislation. That bill calls for California based utilities and policy to encourage home owners to install solar photovoltaic systems to generate power they can use but also which can be fed back to the state’s utility grid at times when the home owner makes more power than they are using at that time.
Now that sounds like a serious effort and, in fact, there is nothing else like it around the USA. But there was a similar effort started earlier in Germany and now practically everywhere you drive you in Germany you see solar panels on the roof. Such programs tend to succeed in focusing citizens to do their part in helping change the dynamics of a problem.
But how much will that really impact California’s electrical grid? Below is a picture of today’s power usage for a typical spring (not hot or cold) day – one where little air conditioning or heating is required.
Now this is a very typical day. In the middle of the night around 3 am you find we use the least energy and around noon to 3 or 4 pm we use the most. On this day there is a secondary peak of needed power around 9 pm at night. Guess what we are doing then – Yes, you can actually see us all watching TV.
This graph also shows how much power California has in reserve to meet unexpected needs. This is the green jagged line at the top of the graph. You can find this type of graph daily here.
Interestingly enough, a couple of days after this one we had a weekend day where there was particularly low overall demand. The weekend helps because businesses are closed. But it also helped that the weather was not too warm nor too cold and the day was “long” so that we needed less inside lights. Here is what that day looked like on the same graph –
On very hot summer days, the mid-afternoon peak will rise as high as 50 GW or more than 2x what we need at night. And on such days this demand exceeds all the power that we can generate in the state. So we have to purchase additional power from our neighbors if they have surplus.
So now you can see the point of the million roof bill. At precisely the times when California is shortest on power, the solar panels on those 1,000,000 roofs will be generating the most power … on hot sunny summer days. And if they generate about 5 KW per roof (a typical installation) then 1,000,000 roofs will generate 5 GW of power which is about 10% of all of the power required by the system. In such a case the top of the peak in the curve, will flatten off just a little bit. But that little bit is pretty important because it provides relief at just the right time.
What if we were able to have Californians put up not 1,000,000 solar roofs but instead 10,000,000 would be built over some period of time. What would be the impact then? Well then these roofs would potentially generate 50 GW of power and this would be all that the system requires. Wow. Why not set that as the target right now and help us drive towards energy independence? Great question.
Some answers have to do with the politics of it all. But some of the answers also have to do with how the overall electrical power grid will perform when so much of our power is generated from these sources. What happens if the sun goes behind a cloud in a change of weather over large parts of the state? How will that be handled, for example?
Still more relate to how will people be compensated for the power they generate. Today, you are not paid at all but you can receive credits against your electric bill and power you use at night. But if you make more power than you need, you do not get an additional compensation. So that has to be reconciled.
There are many questions like that where we will need to build up experience and make adjustments over time and based on real world learning, I suspect. So even if we could “flip the solar switch” on quickly, it is probably best if we do it at a little slower pace.