Grid Integration: Juggling Surplus Grid Power from Wind and Solar is Currently Expensive Any Way You Look at It

Grid Integration: Juggling Surplus Grid Power from Wind and Solar is Currently Expensive Any Way You Look at It

The cheapest way to deal with temporary excess grid power, particularly from solar, is simply to curtail it.  This delays payback for a solar project. This can be done with solar plants owned by utilities but not so easily with rooftop solar owned by people and business who sell their excess to the grid. Surplus power can also be exported but this is often at a loss – due to supply/demand and subsequent immediate pricing a utility might have to pay to export its power. Grid integration issues with renewables increase as more intermittent renewables - wind and solar - penetrate the grid. At around 20-25% penetration the issues exacerbate and get more expensive. This has happened in Germany and is now beginning to occur in earnest in California.

Even though utilities like PG&E in California have a hierarchy of preferred energy sources from efficiency to renewables to conventional sources they still have to balance the grid to prevent blackouts and brownouts. California utility-generated energy was 15% renewables in 2010 and increased to 27% now with nearly 80% of the increase being solar. That does not include about 4% from rooftop solar. The utility solar is what gets curtailed. There was 15% curtailment in 2015, 21% in 2016, and 31% in the first few months of 2017. Part of the increased curtailment is due to increased river flows to hydro plants as rains relieved the drought. More rooftop solar will increase the surpluses with which utilities must deal. The drop in price of solar power due mainly to better panel efficiency has made rooftop solar more affordable and that along with continued government subsidies encourages more people and businesses to install solar. Utility models in California reward energy efficiency which helps the utilities decouple energy sales from profits and pair efficiency and energy services with profits but this is partial as they still benefit from build-outs and sales. Currently, Californians pay 50% higher electricity costs than other states. If renewables mandates continue to go higher those costs will increase further. The state also has aggressive mandates for energy storage which helps to balance the grid but again cost is the main issue. California is a massive energy user and currently burns about an eighth of the natural gas burned in the U.S. No doubt the renewables push will continue but so too will the grid integration challenges. The system operator Cal-ISO noted that for the first two months of 2017 18% of sales involved negative pricing (ie. losses) while for the same period in 2014 it was 2.5%. Another issue in California is that the big solar farms and solar thermal plants are in the desert hundreds of miles from populated cities and power line congestion can be problematic during peak demand times. That is one argument in favor of redundancy, of building more gas plants close to the cities. Currently, there are disagreements about how much redundancy is needed as many gas plants run at low capacity due to solar availability and so the cost of building newer and better ones to replace old less efficient ones, though more useful, would add significantly to ratepayer costs and may not be necessary anyway.

To summarize, the current alternatives to dealing with excess grid power are:

1)      Curtail solar (and possibly some wind)

2)      Export power, most often at a loss – the importer benefits but often needs to curtail its own solar power to accommodate the imported power which reduces the cost benefit

3)      Curtail natural gas plant power output which can be wasteful/inefficient and hard on the plants

4)      Employ battery storage and other energy storage

5)      Convert to heat for some applicable process (this is popular in Germany)

6)      Power EVs – dynamic pricing could be an incentive to charging during high solar generation time – this would require many more EVs than currently and more charging infrastructure – if there were enough EVs the reverse could happen, that is vehicle-to-grid (V2G) where EVs sell power back to the grid at high prices during peak demand times, effectively acting as battery storage to balance the grid. This scenario, however, is far off – it is not likely for a decade or two.

References:

Energy Goes to Waste as State Power Glut Grows – by Ivan Penn, in LA Times, June 2017