Tag Archives: generation

The State of our Solar Generation

After the last post on coal generation, I thought it would be nice to cut a few steps out of the photon processing, avoiding all the dirty gunk that gets picked up along the way, and talk about straight-up sunlight. You probably know by now (also the title's a total spoiler), but this post is going to be about solar generation.


So, I think a small discussion of technologies is useful to get some background before diving into the delicious numbers. First, 4 prime movers are represented in the data: PV, ST, OT, CP.

  • PV - You were probably able to guess this one, it's photovoltaic. Photovoltaic installations are the typical depiction of solar panels on roofs. Slabs of silicon that directly convert photons into electricity. This property that is unique to this form of generation, not just amongst solar technology, but all of our generation techniques for any fuel source. What I find particularly amazing is that the photovoltaic effect was first noted in 1839. It's fun to think about an alternate history in which we were able to produce workable solar panels in the 1800s.
  • ST - Steam turbines. Steam turbines + solar can also be referred to as solar steam. This is probably the other technology you've heard of, at least in passing. The general idea is to concentrate heat using reflective plates. This heat is then used to drive a traditional steam turbine.
  • OT - Other. There's only one of these, and it's not listed explicitly in the data, but thankfully the operating utility and year is, and a little googling turned up this article. Based on that piece, I believe this 1 MW installation to be a concentrated solar power demonstration plant utilizing parabolic troughs.
  • CP - Energy storage, concentrated solar power. Like OT, there's only one of these in the EIA's data. This generator is one of the Solar Energy Generating Systems (SEGS) in California. Specifically, I believe it is SEGS I. Fun fact, a nearby solar installation inspired a side-mission in the video game Fallout: New Vegas.

With a little bit of background, let's get into the number. As always, I'm rocking the data off of that October-fresh EIA-860 form. A lot of the data in this post would have been wildly different a year ago, so it's really nice to have the updated numbers. Let's start with a basic breakdown of the generation types I just discussed.

Now, how about a breakdown of the PV and ST installations. If you're curious, the capacity of the CP generator is 13.8 WM, and the OT generator is 1 MW.

And finally, the same breakdown, but for all the solar installations together.

If PV's dominance wasn't terribly obvious from the first table in this post, it should be now. The sheer number of PV installations compared to ST and the others allows it to define all of the operation date categories, and maintain a statistical stranglehold on the capacity values as well. Before moving away from the basic information I'd like to throw 2 maps at you to get an idea of the spatial distribution in solar generation.

A glance at some basic histograms illustrates the capacity values and installation ages above. 

Unsurprisingly, most solar generators are under 5MW, with the bulk of those actually at 1MW or less.

Mirroring the capacity graph, the number of annual installations show a sharp rise that began less than 10 years ago. As I mentioned at the beginning of this post, the 2012 numbers are dramatic, and reaffirm the trend of solar as a growing energy source in terms of installations. However, due to solar's capacity factor, conversion losses, and lack of storage available 1000 1MW generators could produce less useful energy than a 600MW coal power plant. In its current state, solar isn't all the great for peak power, so it generally is going to be contributing to baseload. But why would what appears to be 1000MW of solar generation produce less energy than a 600MW nameplate coal power plant?

I mentioned a few factors above, but the major one with solar is capacity factor. I've mentioned it several times before, but it still might not be clear exactly what a cpacity factor is. Lots of people get confused by it (as I recently found on reddit), but it's a simple, albeit very useful, metric. Essentially, capacity factor is the actual energy production over the theoretical energy production.

Let's take our theoretical 1000MW of solar, and 600MW of coal. Typical capacity factors for coal and solar are around 80% and 20% respectively.

8760 = Number of Hours in a Year

Coal: 600MW×8760 = 5256000MWh

Solar: 1000MW×8760 = 8760000MWh

20% Capacity Factor means you only operate for 20% of the theoretical max time

80% Capacity Factor means you only operate for 80% of the theoretical max time

Solar Actual Production →  8760000MWh×0.2 = 1752000MWh

Coal Actual Production →  5256000MWh×0.8 = 4204800MWh

4,204,800MWh > 1,752,000MWh

The idea of a capacity factor is a nice as an easy metric for industry folks to make quick assessments with. It's important to note that some generation technologies have low capacity factors by design because they just aren't used all that often. Natural gas peaking turbines occupy this niche, and I'll discuss that further when I get to the natural gas post. Coal and solar are not a part of that same niche. Both of these technologies either are already run as close to 24/7 as possible (coal), or that is the eventual goal (solar, some sort of satellite-based microwave solar could achieve a pretty high capacity factor[hell, with the cost of one of those systems, it better]).

So solar's capacity factor isn't great, but there have been a huge number of installations in the past few years, which should add up. Right?

Good news, the recent uptick in installations wasn't all itty bitty generators, but enough large ones to blow most other years' capacity installed out of the water. I also plotted capacity in terms of its rate of change from year-to-year and against the average. But this produced really absurd graphs with minimal usefulness. Which makes sense given how extreme the changes are in the past several years

At this point it might be interesting to look at maps of just the 2012 installations. Perhaps California is installing loads of capacity in a handful of installations, while states further back on the solar uptake curve are experienced spurts of growth in smaller generators?


So, overall, the answer is "not really." California's pace of installation and the relative capacity of those outstrips almost every state by a huge degree. However, there are two other visualizations that may present a different picture. One has to do with Renewable Portfolio Standards (RPSs), which I will save for a future post.  The other has to do with population.

California's a big state. It has 12 million more people than the 2nd most populous state, Texas. Only 6 states even have 12 million people altogether. So, what if I rolled back to the original 2 maps, but did everything in terms of a state's population?


So California gets dethroned on installations per 100k people, but the more dramatic drop is in its capacity, which isn't surprising given its population. Here are the top 10 states, sorted by capacity, then installations. This list might have been surprising 6 maps ago, but I bet you could guess most of them right now. Also, because I can't help myself, I've labeled each state with how they voted in the last election, and the political affiliation of their governor. I believe that a state's standards on renewable energy are a product of both their government and the people.


Immediately, I want to say that I feel bad about Hawaii, because I've kept it and Alaska off of all the maps I've made so far. The reason is partially for ease of aesthetics, but also because each of those states is highly anomalous compared to the contiguous states. I'll try to mix them in sometime, maybe they'll each get their own post (Alaska and Hawaii both have completely different, largely uncharted, and totally intriguing resource bases), but for now they'll just occasionally pop up in tables. Hawaii aside, there are a few things I find very interesting about this. Foremost is the myth that solar only works in the Southwest. Realistically, solar can work anywhere, it just depends on what kind of installations are being considered, and what output you expect. The Southwest is almost certainly the best bet for huge multi-gigawatt plants, but New jersey and Vermont, neither of which is notoriously sunny, make it clear that with the will to do so solar installations can happen. As for the political spectrum, I was largely thinking ahead when I added those, as I'll be doing some kind of political post in the future. For now though, I think it's interesting that the state's general populations seem to be more Democratic than the average, while the governorship is more split between Democrats and Republicans.

This post was a bit light on text, as my brain seems to be running out of fuel as it near 10pm on a Saturday, but hopefully the cavalcade of figures was enough to keep at least a few people amused. As always, if you have any questions about methods, data sources, or simply want to rant at me, hit up the comments.


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. http://www1.eere.energy.gov/wind/pdfs/2012_wind_technologies_market_report.pdf