The round trip efficiency of storage technologies are of great interest and discussion. Some are concerned about "wasting energy" when storing
electricity. "Losing" 30% of the electricity going into a storage facility is a "non-starter" for them. However, others counter by pointing out the greater value of electricity delivered on-peak, even if some energy is lost by storing off-peak power.The number one storage technology in use today is pumped hydro. These are, usually, massive projects, where water is pumped up to a reservoir at night, when power is cheaper, and allowed to flow downhill during the day. The turbine used to pump the water uphill is then spun backwards by the water coming downhill, generating electricity. Whenever energy storage is discussed, pumped hydro is held up as the ideal answer due to it's large storage capacity, low emissions (although some have begun to be concerned about the amount of methane released from underwater biomass), fast response (although only when generating electricity) and high efficiency. However, your humble blogger has had a difficult time finding authoritative literature on pumped hydro efficiency, and I'm hoping to tap the resources of other, more knowledable members of the industry, by tempting them with fame and fortune.
As an example of what appears to be unsupported but accepted wisdom, NREL recently published their technical report on energy storage, and said this about pumped hydro:
"PHS plants can achieve round-trip efficiencies that exceed 75% and may have capacities that exceed 20 hours of discharge capacity. (pg 43)" However, even though this is supposed to be a technical report, no citation was offered.
Again, the Electricty Storage Association indicates efficiencies in the 70 - 85% range, but no authorities or links are provided.
I would tend to accept these statements as accurate, not knowing any better, but I have been at conferences where such claims have been hooted at by participants, with counter claims of less than 65%. This has piqued my interest in getting some authoritative answers, especially since the VRB-ESS achieves efficiencies in the 70 - 75% range when used for the same purposes as PHS. Obviously, if efficiencies of 70% or less are not a problem when applied to PHS, then higher efficiencies from a flow battery, like the VRB-ESS, would be even more desireable. If, however, PHS is much less than 70%, then alternative storage systems become even more attractive. But we need to know the facts before we can have an informed discussion.
Hence my contest. We will award prizes and fame to those that provide the most useful resources discussing PHS efficiency. Unless you wish to remain anonymous, we will announce the three commentators that provide the best citations or other authoritative resources. And, the winners will receive their choice of the Enerdynamics publications, "Understanding Today's Electricity Business" or "Understanding Today's Natural Gas Business". Both publications are valued over $60!
As a bonus, anyone that also provides authoritative analysis resources on the actual per kWhr cost of PHS will receive both books = $120!
I'm having a little bit of fun with this, but it looks like a good project given the dearth of information, or so it seems to me, on pumped hydro storage efficiency. Your comments will be posted below, therefore contributing to the general store of knowledge, unless you prefer to email your offerings to ctoca@utility-savings.com. I will be the sole judge of the winners - since it's my contest - and we will close the contest on Thursday, April 15th, so we won't continue to "tax" your patience!
Please click the "Post a Comment" link below or email your replies. Thanks for the help!
2 comments:
This is a very good contest. Let us know your finding too. Will give our 2 cents of thoughts to the research too.
Interesting...I always took EPRI and ESA figures at face value and didn't think twice. If you can reference better numbers I'd be happy to know.
Here's what I can tell you:
I have a technical report which I cannot share which estimates the round-trip eff of a facility yet to be built to be 80%. (not helpful, I know)
I also have a technical feasibility study for the Lake Hodges pumped hydro facility near San Diego. This report was produced in 2000 by the engineering consulting company HESI, which has now been absorbed into Ventyx. It has the following statement: "We investigated the implications for reasonable expectations for both lower (70 percent) and upper (80 percent) bound, set based on experience with other hydroelectric generation facilities". I do not know the performance of the facility that was actually eventually built.
Hope that helps.
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