Contest! Prizes! Discover Efficiency of Pumped Hydro!

Please help us ferret out (apologies to mink and weasel lovers!) information on what appears to be a great mystery - the round trip efficiency of Pumped Hydro Energy Storage. Prizes will be awarded!

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!

CAISO Postpones Entry of Energy Storage

The California Independent System Operator (CAISO), the state agency running the transmission system, has postponed the entry of limited energy storage resources (LESRs) into their ancillary services markets.

CAISO is bound by the Federal Energy Regulatory Commission (FERC) Order Nos. 719 and 890 to allow Non-Generator Resources to participate "on a comparable basis to services provided by generation resources in meeting mandatory reliability standards, providing ancillary services and planning the expansion fo the transmission grid".

To that end, CAISO began a stakeholder proceeding in September, 2009. LESR technology providers, like the Beacon flywheel, Altarinano and A123 lithium ion batteries, saw this as an opportunity to open these markets to their short term energy storage systems, as they have been able in other ISO markets. Many saw this as a continuation of the various energy storage proceedings that have started and stopped without resolution at CAISO since 2008.

However, the existing CAISO markets require greater energy resources than the above technologies can provide. Although CAISO reduced their requirements from up to 2 hours of energy, to as little as 30 minutes in the course of this proceeding, the LESR technologies are limited to 15 minutes of energy in one direction - charging or discharging. In fact, they want to be paid for providing service in both directions, requiring them to operate in the middle of their capacity, which only allows them to provide 7 minutes of energy - more or less.

The final decision of CAISO, after months of meetings and stakeholder comments, was the determination that new ancillary services markets would need to be created for these technologies because, "...energy storage and other resource have different operating characteristics and different implementation issues." (Draft Final Proposal, page 3)

CAISO proposes to take up the issue of LESR participation in future proceedings, although the timing is uncertain. This is understandably disappointing for the LESR companies, who have seen some success in other ISO territories, either with full participation or through pilot programs. However, for the foreseeable future, limited energy storage will not be able to participate in CAISO markets.

However, nothing in this decision or other proceedings prevents other energy storage technologies, with longer energy capability, from participating in CAISO markets. For example, the VRB flow battery, with the ability to store hours of energy, qulifies to provide spinning reserve, frequency regulation and other ancillary services. The VRB Energy Storage System (VRB-ESS), sited in conjuction with a solar PV, could shift generation, maintain peak output for the solar generator, and could then provide services to CAISO when not needed for solar energy.