The biggest problem that needs to be solved with renewable energy is the fact that production fluctuates massivly thru out the day for most types of renewables. At least for solar we can be certain that PV panels will not produce any energy for 50% of the day. The graph below is now famously known as the “duck chart”—released from the California Independent System Operator (CAISO) in a report released late last year. A quote from the Rocky Mountain Institute:
The duck chart shows the net load CAISO’s central thermal power plants would need to supply when you combine hour-by-hour expected customer electricity demand with the offsetting output from variable renewables (especially solar) over the course of a typical spring day. As the forecast goes to 2015 and beyond, the curve shifts as growing shares of renewable generation are added to the grid, with the belly of the duck sinking deeper and the neck rising more steeply.
The “belly of the duck” sinks during the middle of the day, when solar output is at its peak, minimizing demand for the grid’s coal/nuclear/gas plants. But these thermal power plants can not be varied in energy output, they basically always run full throttle to be efficient.
So what can we do with this surplus supply of energy?
- It can be exported to surrounding regions – this might work for a while but if we all go renewable there is no surrounding region with demand any more.
- Use demand-side resources – these are for example smart appliances which can be turned on or off by the utility company to balance the lack or excess of energy
- It can be stored – Storage holds a great deal of promise. Storage can come in all shapes and sizes: It could be pumped hydroelectric, compressed air, batteries, or electric vehicles. Especially hydrogen battery are seen as most promising.
The conclusion is that it will require a lot of work, ideas and investments to address the problems of the “belly of the duck” which are caused by renewable energy sources. Additionally, the utility business model will have to evolve.