Thursday, August 20, 2020

Dispatchable hydropower versus pumped storage, Round 2

I've been meaning to return to this concept of dispatchable hydropower and distinguishing it from pumped hydropower storage. The tweet above shows how one example of it being used in practice. We could do much more, somewhat to help in energy crises similar to what's happening now in California, and more to smooth out renewable power-based systems generally.

Sammy Roth publishes some great work about climate and energy, and recently published eight low-carbon solutions to variability in renewable power. Pumped hydro was one of them, while dispatchable hydro was not. Glen Canyon Dam suggests it should've been.

Dispatchable hydropower is (mostly) distinguishable from pumped hydro storage in that it makes use of existing dams and reservoirs, and (mostly) doesn't build new infrastructure like pumped hydro does. Its focus is a change in how hydropower is used and released from baseload power that's used constantly, first in line to satisfy demand, to dispatchable power that - subject to other constraints that require release - is conserved and then released when needed.

I previously had some documents that I'll try to dig up from my local Community Choice Energy Aggregator that showed essentially no 24-hour variation in the hydropower they received, and that's the type of baseline use that could be saved, somewhat, for the late afternoon and evening hours when demand is up and solar is down.

I also want to distinguish this from Mark Jacobson's Wind Water Solar system for replacing all fossil fuels. He's proposing something gigantic, I'm discussing something much smaller and therefore able to be implemented much sooner. In particular, what I had read a while back was that he wants to quadruple the dispatchable power from existing dams by rebuilding their outlets. I don't know how well that would work, but I do know it would require dewatering and then mostly or entirely rebuilding the dams themselves. I'm not talking about that.

These ideas do shade into each other a bit. You can't fully turn off and turn on water from dams, they have ecological and water supply reasons for running as well. Some construction might also be helpful for dispatchable hydropower, particularly an afterbay below a dam that stores a tiny percent of the total water, maybe a day's worth or more, and can modulate the downstream releases from the main dam. The expense would be small though compared to other massive projects, or you can just not do it and still use some limited flexibility in water releases to time them for dispatchability.

Using that power in this manner could help in the shortages California is facing now, and maybe elsewhere too, along with batteries and everything else we can do to reach 100% carbon free economies.


Ken Fabian said...

Seems like conversion of existing flow through hydro to backup for solar and wind is simpler than dedicated pumped hydro - and wholesale time of use pricing will favour such conversion by inducing higher pricing during periods of low solar and wind availability. I would think conversion would involve increasing the peak output capability to better optimise for varying output with the same water flow - bigger or more downhill pipes and associated turbines mostly. But existing plant could tap into such market opportunities. How that market is structured and regulated may be more crucial than the specific technologies.

As an aside I think the "failures" of solar thermal with thermal storage may have had the absence of clear market arrangements as a contributing factor - with power plants simply turned down (and no carbon pricing) then turning them back up was cheaper than turning to stored energy. Without markets that price dispatchable, fast response backup power higher than "baseload" there was no financial benefit to including storage.

In places with significant amounts of wind and solar the economics of storage have changed and the real value - as worth significantly more than an average daily price - becomes more obvious.

Old_salt said...

There is a significant problem on the river itself, where flow variability can be extreme. This can have significant impacts on the river ecology. Of course, there is no such thing as a free lunch.

Ben McMillan said...

Many of the conventional hydro schemes were also built partly for irrigation purposes, so release may be tied in to needs of water users.

Pumped hydro is less disruptive from that point of view: the impact there depends on whether the upper/lower reservoirs already exist and how problematic it is for the water level to change.

But the main market opportunity seems to be for four hours of storage or less; hard to see how new pumped hydro could compete with batteries.


Does hydro reservoir evaporation control come under the heading of

" and everything else we can do "?

Or is the moral hazard of actually mitigating AGW impacts too 'orrible to contemplate?

Brian said...

Ken - I think you're right, and we'll see larger price signals for stored power as renewables increase their share. Maybe solar thermal storage will have a comeback.

Ben - some pumped hydro is very cheap. The advantage of my proposal though is that you don't have to construct anything.

Climate Wars - evaporation from reservoirs is a problem, although my sense is that it's a second-order problem compared to say leakage in transmission. Floatovoltaics will somewhat reduce evaporation. Groundwater storage does have an advantage of no evaporation compared to reservoirs. Still, it's not the biggest issue IMO.


Please run some numbers comparing

"leakage in transmission".

with evaoration from delivey canals -

A watershed evaprates all the way fron the headwaters down, and the area of a fractally branched fluvial system must be measured before it can be compared to leakage,

Brian said...

TCW - watershed-wide evaporation isn't relevant - you can't control it and wouldn't want to. The issue I'm responding to is whether evaporation from reservoirs constitutes a significant problem with reservoirs.

I highly doubt reservoirs lose more than few percent of their water to evaporation, maybe much less than that. Water delivery systems routinely lose 10-25% to leakage.