Solar has grown dramatically in California over the last few years, but is still only about 5% of generation and growing fast. Its generally accepted that without energy storage, renewables with fossil fuel backup cannot exceed a penetration of more than their capacity factor. Depending on how you measure it, Solar's capacity factor in California is 25% at best, so it would seem a long way from having problems at only 5% penetration. However as solar grows, the article points out an emerging problem that is called the duck curve after the shape of the graph of daily electricity generation from sources other than solar when solar is added to the grid. The issue is the rate at which fossil fuel generation needs to ramp up as the sun goes down and solar generation ceases, particularly around the spring equinox in late march. Most of current grid generation cannot ramp quickly and what can, is very inefficient. This highlights that incorporating growing percentages of renewable energy into the grid exposes new problems all along the way. Even at these low penetration levels, storage is starting to be a necessary element.
In Europe, high renewables penetration in local markets is possible because Europe is geographically small and connected and majority areas with low renewables penetration balance the overall small renewables penetration. The California grid is relatively isolated and cannot avail of this help.
The NREL report further highlights the longer-term problem of California achieving its goal of 50% renewables by 2030. If renewables have an average capacity factor of 25%, 50% is way beyond their achievable penetration without storage. NREL conclude that 50% is only achievable with high levels of storage in the region of 19GW to 30GW depending on assumptions. For perspective, this is for a grid that maximally demands 60GW. Even at $1/W, that is a lot of money by 2030. There is no large scale deployable storage today. Todays batteries are expensive and cannot handle the deep daily cycling for 20 or 30 years required of a viable electricity storage technology. Even when they can meet a $1/W cost and adequate reliability, they are still an additional cost of at least as much as the cost of generation. To address long term outages that cannot be handled by storage, it is proposed to build a large amount of long distance transmission (an issue not covered by NREL). This would cost at least the cost of generation. The true cost of a 100% fossil fuel free electricity SYSTEM on the path being pursued by California is then at least three times the cost of already expensive PV generation which NREL assumes will fall to $0.03/kWh by 2030. California is rich and its consumers already pay twice the national average for electricity. This cost will inevitably rise.
These costly realities have not yet penetrated the broad consciousness of alternative energy supporters.
By Edmund Kelly