Friday, September 17, 2010

CAISO Report - Integration of Renewable Resources

CAISO - the California Independent System Operator - is constantly worrying about the impact of renewable wind and solar generation on the California grid. It's their job as the grid operator - gotta keep the grid stable and the lights on. The problem with intermittent - oops, sorry, variable generation - "variable" is the new PC term for intermittent - it just sounds so much better - the problem with variable generation is that it is "variable". The grid can't dispatch it when it is needed, like a natural gas peaker plant. It just happens when it wants to happen, whether it is convenient or useful or not.

As a result, CAISO is always studying the problem, and the latest report just came out. Here are some of the highlights:
  • First, you'll be happy to know, is that the California grid can handle 20% penetration of renewable resources. Of course, there are some caveats. For example, the increased production of solar and wind energy will displace traditional thermal generators, so their revenue will decrease. In other words, we are likely to put the current generators out of business. Hope you are not invested in one!
  • At the same time, we are going to need to keep those plants that are now uneconomic, because we need them to balance out the rapidly changing wind / solar PV generation.
"The integration of variable energy resources will require increased operational flexibility—notably capability to provide load-following and regulation in wider operating ranges and at ramp rates that are faster and of longer sustained duration than are currently experienced. Forecast uncertainty associated with wind and solar production will increase the need for reservation of resource capacity to ensure that these requirements are met in real-time operations...In providing these capabilities, the existing and planned generation fleet will likely need to operate longer at lower minimum operating levels and provide more frequent starts, stops and cycling over the operating day."
Exec. Sumary, pg. iii.

Again, the existing fleet of generators is going to loose money, "The lower capacity factors combined with the reduced energy prices under 20 percent RPS may result in a significant drop in energy market revenues for the gas fleet in all hours of the day and in all seasons." - pg xiv, but we need the entire fleet to keep renewables from crashing the grid, "The additional regulation requirements appear to be well within the capabilities of the existing generation fleet."

So, as long as we keep the current, money - loosing generators, and work them harder, for less money, we can add variable wind and solar without black-outs. Of course, ramping them up and down so much will increase their cost - for less revenue - and increase their emissions - adding pollution when the renewables are supposed to be reducing emissions.

The trade-off on emissions is supposed to come from lower over-all energy generation. Since they will produce less energy, the increased emissions from inefficient ramping will still be less than if they were at full production, although the impact from this type of operation was not calculated."The table also shows a reduction in CO2 emissions from combined cycle generators due to the reduction in operations, although this was calculated using a single emissions factor multiplied by energy output, and did not consider the potential for higher emissions at less efficient levels of operations." pg.86.

And the report made certain assumptions about the status of this generation fleet, that it will increase in capacity, not decrease:
  • "Table 2.10 shows the new and planned thermal resources that were included in the analysis. These resources were included as they are currently under construction and have little or no risk of not being available in the 2012 timeframe. No resource retirements were modeled, nor were sensitivities conducted for the status of once-through cooling (OTC) plants. OTC plants are slated to be retrofitted or shut down after 2013 and are not expected to affect the 20 percent RPS integration. However, they could affect renewable integration after 2013, and hence are being examined in the ISO’s 33 percent RPS operational study."
So, the bottom-line seems to be that we should be okay until 2012, because we can thrash our current peaker plants up and down and avoid grid collapse. But all bets are off for any increase over that.

We think increased penetration of energy storage is a better balancing strategy then building more natural gas peaker plants. Using energy storage, like the VRB-ESS™, allows variable resources to be fully integrated without increasing emissions. As we plan for 2020, we hope the regulatory agencies will continue to look toward clean technology resources to integrate renewables, and keep clean energy "clean".

Friday, June 18, 2010

Efficiency of Pumped Hydro Contest - Dud!

My contest to try and get some real figures on the round-trip efficiency of pumped hydro was a dud! No studies, no real world numbers. I heard from a few helpful readers that had projected efficiency numbers based on new turbines from Japan, but no information on existing projects. I find this highly interesting because new advanced energy storage systems, like the VRB-ESS(tm), are being compared, sometimes unfavorably, against pumped hydro. If PH is the gold standard for highly efficient time-shifting power generation, then one would think there would be substantial and easily accessed information on real-world experience.

I may try this again. In the meantime, if any reader has any resources on the subject, please leave a comment.

While we're on the subject, here are a couple of interesting points on the electricity in - electricity out efficiency of the VRB. The standard metric is 65% - 75%, AC-AC. However, the actual round-trip efficiency depends on the application.

For example, the lithium battery providers, like A123 and Altairnano, and flywheel providers, like Beacon Power, are advertising 90% efficiency. However, this is for a very limited pulse of power in the middle of their state of charge (SOS). The application is used for balancing the 60Hz frequency of the grid by pulsing to full capacity - in megawatt size - for only 15 minutes. Apparently, just about any battery system, including lead acid, could pulse like this, in the middle of their SOC, with high efficiency and many cycles.

This applies to the VRB-ESS as well. The greatest efficiency loss occurs at the end of the charge cycle, as it takes more work to find "uncharged" vanadium ions to "fill up the tank". In other words, if a facility had installed enough tanks of electrolyte to store 8 hours of energy, but only used the first 6 hours, then the round-trip efficiency would be closer to 80% than 70%, and if the VRB-ESS was used for the same application as the lithium systems, the efficiency would be the same - in the 90% range. However, one of the key distinctives of the VRB is the ability to fully cycle a nearly unlimited number of times without loss of capacity. Capacity is dependent on the amount of electrolyte. So, an application could chose 30 minutes of storage or 8 hours; it's simply a function of how much electrolyte is stored in the tank. After thousands of full cycles, whether on a 30 minute tank of electrolyte, or an 8 hour tank, the VRB is still able to provide full capacity and for the same amount of energy.

Wednesday, March 31, 2010

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 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!

Monday, March 15, 2010

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, " 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.