How to Maximize Renewable Energy in California

by Emil Morhardt

The looming problem with renewable energy—especially in California where there is potential for a great deal of solar energy—is finding the right balance between attractive new, but intermittent, solar and wind power plants, and some other source of generation large enough that dispatching it will meet any energy demand, even if the wind isn’t blowing and the sun isn’t shining. A new paper by Abebe Solomon, Dan Kammen, and Duncan Callaway, researchers in the Energy & Resources Group at the University of California Berkeley, calculates that if energy dumping doesn’t occur, the best we can hope for in California without energy storage, is meeting 29% of our energy needs with solar and wind. No energy dumping means that all of the energy generated by solar and wind facilities gets used, just what the investors in those technologies would hope. But there are two ways to dramatically increase the penetration of solar and wind: put some energy storage in place so that excess energy generated by wind and solar (or by any other source) can be saved for a rainy day (so to speak…or a cloudy, still day), or get more solar and wind power plants in place than are usually needed, and tolerate not using or storing (or as they say, dumping) some of the electricity they generate. This paper doesn’t go into the economics of these prospects—maybe government subsidies would be required to entice generators to overbuild—just the question of what would need to be done to make sure that more of our energy comes from wind and solar.

The models conclude that the best mix would be 90% centralized photovoltaic power plants and 10% wind, without any of the somewhat less efficient distributed generation that most of us would like to see on more rooftops. There’s a big jump in renewable penetration if even 5% energy dumping is allowed, and a fairly linear increase after 10% energy dumping. It also turns out that we won’t be needing new large transmission lines for the purposes of moving renewable energy from one part of the state to another, but new lines will obviously be needed to connect new energy to the grid. Adding a little storage also helps, but not as much as the researchers initially anticipated. Energy storage use will peak out in usefulness at about 22% of peak daily demand. If this amount of storage were present, and the operators could tolerate dumping 20% of the electricity generated (remember, no fuel is involved, just the economics of trying to get a payback on the investment), renewables could provide 85% of California’s annual demand.

It occurs to me that somebody might then find a use for this excess energy anyway, if the price were much reduced, so the initial dumping might not need to be continued.

Solomon, A., Kammen, D.M., Callaway, D., 2014. The role of large-scale energy storage design and dispatch in the power grid: A study of very high grid penetration of variable renewable resources. Applied Energy 134, 75-89. Abstract at:

2 thoughts on “How to Maximize Renewable Energy in California

  1. From Soloman Abebe:
    For a very high penetration of intermittent renewable, energy dumping does not mean “mere” waste of energy as it was shown to significantly reduce the conventional backup capacity requirement. Thus, its economic valuation will require developing some arithmetic’s that accounts for the anticipated energy dumping during planning (so the builders could receive some prior incentives for their commitment) OR a proper model that would value the cost of the curtailed energy during operation. The latter may allow accounting for deferrable loads that could use the excess energy.


    • Yes. It will be papers like yours that get the regulators thinking about what they might do to encourage more penetration of renewables and protecting their investors. Is energy dumping in PV just a matter of short-circuiting the panels?


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s