The State of our (energy) Storage

Storage-Based Generation

Last week, on October 10th, the EIA released its finalized 2012 utility/generator dataset. In their words, this release covers:

generator-level specific information about existing and planned generators and associated environmental equipment at electric power plants with 1 megawatt or greater of combined nameplate capacity.

making it a rich resource for information on the current state of America's power generation systems. For this post, I am going to focus on storage technologies: their place in our energy system, where they are now, and their future. There are a lot of fun little metrics to work through, although some explanation first is useful.

In reporting generator data, the EIA recognizes 23 "prime movers" and 42 "energy sources." Prime movers are the method of generation, and energy sources are the feedstock or fuel for each generation process.

Prime Movers*

There are a few ways to break down these generation methods into more useful categories. The first is to differentiate between storage and ongoing or direct generation. The storage technologies are extremely useful, because they turn the inefficiencies of traditional generation and demand patterns into usable and highly dispatchable energy. There are 5  somewhat novel energy storage technologies listed (compressed air is listed twice), and 1 traditional technique (reversible hydrokinetic turbines) that can operate in reverse and act as a storage technology. Growth in storage technologies is the key for integrating larger amounts of renewable resources which can vary daily (wind and solar), seasonally (hydro, or even over the course of decades (geothermal, dependent on regeneration of via heat flow rates). With growth in these storage technologies so important, let's take a look at their implementation in the US.**

Out of 19,023 generators in the United States, 172 are storage technologies. In terms of total numbers, storage-based generation accounts for less than 1% of US generators, 0.90%. Despite the vanishingly low number of storage-generators, it's a misleading statistic. There will always be a smaller number of storage generation units than primary generation, a more illuminating factor is to compare the generation capacity totals.  Form EIA-860 reports a nameplate capacity, winter capacity, and summer capacity. While true capacity factors would be the most useful, I took the average of winter and summer capacities for each generator, rather than the larger nameplate capacity.

The total direct generation, and remember, this is an average of winter and summer capacities, which is not taking true capacity factors into account, is 1076 GW. To compare, storage accounts for a measly 22.8 GW. 2.12% of generating capacity could potentially come from storage right now.

Honestly, this sounds a little better than I expected when I started digging into this data, however, there is one major factor that makes the current situation look a bit worse. The cheapest and most well known storage is simply pumped water, or reversible hydro if it's available. Unfortunately, areas with the greatest potential for solar technologies often have less water availability than more temperate regions, and the cost of installing large pumped-hydro storage in the plains dotted with wind turbines could be prohibitive. Removing pumped storage from the storage technologies produces a nameplate capacity of only 0.2916 GW. In fact, with pumped storage excluded, only 16 generating units out of the 19,000+ reporting units were storage technologies. Here's a summary table:

So most of our storage technologies are pumped storage. But how old are these systems?

The first storage generator was constructed in the late 1920's (2 pumped storage generators in 1928 in Connecticut on the Rocky River), most of them were constructed from the 1960's and through the 1970's, then we experienced a large drop going into the 1990's, with a resurgence in the late 2000's. I wouldn't be surprised if this trend was political in nature, but I'll keep that speculation closer to my chest for now.

Again, I'm going to remove pumped storage from the figure. While considerably fewer data points will remain, upcoming technologies should be more apparent.

Because there are so few examples, here's a table describing these installations.

Unsurprisingly, the trend is towards batteries, with a little experimentation in flywheels. Considering the trend towards renewable generation, and the relatively known commodity of pumped storage, it would be reasonable to assume that recent pumped storage installations easily eclipsed those of more esoteric or untested technologies. However, this is not the case.

Surprisingly, despite the maturity of the technology, pumped storage installations have been surpassed by other technologies in installation numbers since the early 2000's. One potential explanation for this phenomenon is that the existing hydro installations that could be retrofitted with this technology are saturated. If that is truly the case, then perhaps investing in new technologies is seen as potentially less capital-intense. Another simple explanation, is that our grid has only begun to feel the strain of variable, renewable generation in the past 10 years, and installations of storage-based generation simply haven't caught up. This also makes sense given the availability of subsidies for investing in green generation, rather than figuring out how to utilize it most effectively.

Finally, let's take a look at why storage generation technologies are so important, through the curtailment of wind generation.

Of the renewable energy technologies, land-based wind is the most variable, and therefore would benefit most from increased utilization of energy technologies. The amount which would be useful is easily to visualize using 2012's curtailment data. Curtailment is the practice of shutting down wind turbines, which can be forced or voluntary. Voluntary curtailment is the process of following the market and determining that running the turbine isn't worth it, and forced curtailment is non-market based, but could be due to grid concerns.  Only ERCOT reports both forced and voluntary curtailment, the other regions only report forced curtailment.

Unfortunately, curtailment information is not as widely disseminated as other generation data. Even going from 2011 to 2012, the DoE experienced different level of participation from utilities in reporting curtailment, shown below***.

This gap in data requires some back-of-the-envelope calculations, something I'm certainly not averse to, although I wish there were more data points to work with. Given the somewhat extreme variability in curtailment losses over the past 5 years, any method I employ will certainly have gaping holes. In the face of these limitations, I'm just going to keep it simple. The average % lost over the 5 reporting groups is 2.36%.

While the EIA's wind data page is several years out of date, an estimation as to installed capacity can be made from the recently released generation report. Summing the nameplate capacity of the operating on-shore wind turbines gives 59.62 GW of capacity. If wind operated 100% of the time, the annual generation would represent the hours in a year (8760) times this capacity: (8760hours) x (59.62GW) = 522,271.2 GWh. This isn't the case, as that figure would need to be reduced by the turbines' capacity figure, and the actual electricity onto the grid would be drop further due to conversion and efficiency losses.

A fairly wide range of capacity factors for wind turbines exists, from 20-40%, but the average reported in the 2012 Wind Technologies Market Report was 32.1%. So,

(522,271.2GWh) x (0.321) x (0.0236) = 3956.51 GWh.

To put that in perspective, the 2011 total electricity sales were 3,749,846 GWh, so the amount of wind potentially curtailed was about 0.105% of our total electricity consumption (reported as sales). That doesn't sound like much, but with an average price of 9.9 cents per kWh it can quickly add up.

($0.099) x (3656.51 GWH) x (1000 MWh/GWh) x (1000 kWh/MWh) = $391,695,252.57

Nearly $400 million dollars of generating capacity left on the table is not an insignificant amount of money, and these calculations are somewhat tip of the iceberg. It might be tempting to compare this "lost" cash to the costs of peaking plants, which have to be maintained, but run relatively rarely. This is a poor comparison because a utility knows the peaking plant will only be run occasionally, and charges accordingly during peak hours. Curtailment of wind generation can be voluntary, but much of what is reported is not, and speaks to the larger issues of reliability and maintenance in our grid.

There are certainly other inefficiencies in electricity generation, and I have seen wind curtailment figures ranking from 25-40 TWh. Although I couldn't find any data or sources to back up those claims, my 2.36% figure is a very conservative estimate.

Hopefully this sheds a little light on the state of our storage deployment, and provides a bit of a backbone for why this is such an important topic. I didn't even discuss the mismatch between wind and solar generation vs. peak demand, but hope to in a future post.


I'm still feeling out this whole posting-independent-thoughts-and-research-online thing, so feel free to call me out on some perceived bullshit, or ask questions about my methodology or sources. I tried to keep this post to a length that would prevent too many eyeballs from glazing over, but I guess I'll just have to wait and see.

*Unless otherwise noted, all information in this post is sourced from the form EIA-860 for 2012, found here.

**Note: I'm only looking at operable plants, the EIA also reports on proposed and retired plants.

*** 2012 Wind Technologies Market Report. US Department of Energy.

3 thoughts on “The State of our (energy) Storage

  1. So - storage sans pumped hydro is about 1% of current hydro storage. This would be very interesting to see demonstrated in .... well, let me count ... chart 4 rather than (or in addition to!) total number of installations. What are the total capacities, rather than number, of the installations?
    Also - my pet point: ANY hydro can count as storage most of the time; it's very easy to dial back in times of excess generation, unless reservoirs are at blessed capacity AND inflows to reservoirs are so high that shutting off turbines would cause a bottle-neck. Of course, this type of storage is also constrained by minimum in-flow rules, water rights, and navigation needs, but it can be substantial.

    1. Right, I didn't chart the capacities because I was getting a little graph heavy at the time, these installations did account for more, and I'll come back to here with another graph later, illustrating that. Tried to avoid graph fatigue haha.

      As to your point about hydro, you slightly of missed the point I was making, and/or got me on a little technicality. The idea is that this isn't storage that's just sitting around, but something we have to put excess energy into. Dialing back hydro isn't exactly the same, and ix a luxury only a certain portion of the country enjoys. I tried to express this in my comment explaining why wind curtailment wasn't the same as the low low capacity factor on peaking plants, but that was probably a bit abstract of an explanation.

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