There’s no longer any doubt that wind and solar (call it RE for renewable energy) can deliver affordable and clean power — but there’s a great deal of skepticism surrounding RE’s ability to deliver reliable power all year around — that a grid dominated by these resources will develop a duck curve and won’t be able to stay balanced.
Detractors of RE seized upon the duck curve as proof that RE could never be more than a supporting actor on the grid. Some technology promoters use the duck curve as an excuse to hawk their wares. These duck hunters have everything:
- Hydrogen and/or Power to X
- Pumped hydro
- Compressed and liquid air
- Blocks that get stacked in the air by cranes
- Blocks that get pulled uphill by trains
- MTV’s Dan Cortese
Fortunately it turns out the duck curve is largely a manifestation of conventional thinking. An appreciation for both supply and demand side technologies reveals there are far more affordable ways to deal with the duck curve. The demand side needs to learn how to dance to the rhythm of the supply side.
Jim Lazaar, formerly of the Regulatory Assistance Project, put together a handy list of strategies that can be used to manage the impact of the duck curve. With his permission, I’ve modified the original list slightly.
- Electric rates designed with controllable loads in mind
- Inter-regional trading
- Peak-oriented renewables
- Coal retirements
- Targeted efficiency
While RE isn’t going to deliver power that’s too cheap to meter, as nuclear once promised, it’s likely to produce power that’s too cheap to keep.
Throw power away
When I say throw power away, I literally mean throw power away. Perez and Rabago were the first to spell this out. Others had suggested some spill, but these guys recommended upwards of 30% to 35% spill. The modeling community hasn’t fully embraced the idea yet but we’re getting there. The recent Berkeley study for example only spilled about 10%. It’s counter-intuitive but this is arguably a shortcoming of that modeling.
Don’t store the spill. Figure out how to use it in real time.
- Build lots of RE. Plan on overbuilding it such that eventually you’re spilling 30% to 40% of total production.
- Trade electricity regionally. See EIM or EDAM. This is a software over hardware solution.
- Use price signals that drive demand response. There’s a feedback loop between RE and price signals that allows you to reduce spill. This is another software over hardware solution that has quietly saved scads of power from being spilled.
- Deploy heat pumps and EVs and make things like pool pumps controllable.
- Get rid of coal every which way you can and then some. Coal is King of the monsters, so far as carbon and particulate matter go. Don’t let up.
- Use gas as a bridge. Squeeze it out over time and slowly but surely transition over to a clean gas. In the meantime, stop making a false equivalence between coal and gas.
Where possible we should use software over hardware. For example, don’t build a battery that costs a billion dollars, only works 2% of the time and only moves around 100 GWh of electricity. Build an energy imbalance market or an extended day ahead market for $50 million or $100 million that moves around hundreds of gigawatts of electricity. Don’t subsidize batteries so a few rich people can have Powerwalls. Give all consumers price signals and then watch the flexible consumers adapt to those price signals using software to manage existing loads.
The cheapest form of flexibility we have on the power system is price signals combined with demand response. The California Department of Water Resources pumps in California are a good example of this. Ten years ago these pumps operated in the middle of the night but today they operate in the middle of the day when solar is plentiful. This is around 1 GW of water-pumping load that behaves in a totally different way — thanks to new price signals.
The shift in costs is approximately nothing.
This is a wonderful example of solving a problem without installing new hardware. We know price signals work at the industrial level (these are the most price sensitive customers) and the commercial level (second-most price sensitive customers) but we haven’t yet done a good job of extending price signals down to residential customers.
Residential load has historically been stiff, but you have to realize once upon a time we went to Blockbuster to get movies. Things change.
The Missing Power Problem
There’s another beast hiding in the shadows. This beast is known as the missing power problem. The missing power problem is caused by continental-sized weather events which lower the production of RE down to a fraction of rated output. These events occur multiple times a year and can stretch out for multiple days in a row.
The duck hunters and some newcomers have used the missing power problem as yet another opportunity to promote their favored flavors.
- HVDC (See NREL’s SEAMs study)
- Overbuilding RE
Analysts have estimated it would cost $2.5 trillion to use batteries to cover the missing power problem. My money is on some combination of Power-to-X, biogas and overbuilding RE.
A recent grid study by a team from Berkeley put things in perspective by suggesting that it would take around 300 GW to 360 GW of gas capacity to solve the missing power problem. It just so happens that we have 300 GW of gas capacity in the U.S. Fueling these plants with a clean and renewable fuel looks to be the most affordable option on the table for solving the missing power problem and getting us to a reliable, affordable and clean grid.
The Big Spill
If we fast forward to a world where 30% to 35% of RE generation is spilled — what does that look like? What does the pattern of the spill look like? At first thought it may seem like we’re spilling a third of our power on a daily basis but this isn’t the case at all. It’s more likely we’ll have multiple spill patterns:
- Heavy seasonal spills in the fall/spring
- Medium weekly spills on the weekends and holidays
- Daily spills in the middle of the night when load troughs and the middle of the day when solar peaks.
In an RE dominated grid, the frequency and duration of the spill is all over the map, but it’s likely going to be dominated by the seasonal spills (the spring in particular). Liebreich points out that building a hydrogen infrastructure around utilizing RE spill to generate hydrogen is a fool’s errand because the pattern of the spill results in low utilization factors.
I think this same argument can be applied to batteries. The idea of utilizing spill at low utilization factors is actually a far bigger problem for batteries than electrolyzers because storing electricity with batteries is far more expensive than storing hydrogen.
Don’t build energy infrastructure to solve today’s problems if they don’t solve tomorrow’s problems. Skip the temporary solutions and build stuff that solves the problems of today and tomorrow.
The author is a WECC-based power system operator.
The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.
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