Media Misinforms Public About Solar Power Again

I am an engineer, a scientist, and an optimist.  I find enjoyment in the silliest of science experiments, like the pitch drop experiment taking place in Australia and Ireland.  I am sure humans will one day be able to travel the stars to new worlds, and even go to other galaxies.  I am also confident that humans will be able to curb their greenhouse gas emissions without reverting back to pre-industrial times.

Society and nature can exist side-by-side in harmony, and technology is going to provide the solutions.  I am a supporter of any plan that has a goal of cleaning up the environment, provided the benefits outweigh the costs, including solar and wind power projects.  That being said, I am disappointed with the media yet again for failing (either inadvertently or intentionally) to report the facts about a new solar power plant that is in the final stages of construction in the Mojave Desert.

The Ivanpah Solar Electric Generating Station Will Come Online This Year

The Ivanpah Solar Power Facility is a solar thermal power plant under construction near the border of California and Nevada in the Mojave Desert.  It consists of three units with a total peak power output of 377 Megawatts (MW), slated to be brought online sometime in 2013.  The technology behind this project is different than the photovoltaic panels most people think of when you mention solar power.  Instead a large array of dark panels, each generating small amounts of electricity, this plant is a giant field of mirrors, each directing sunlight onto a single point at the top of a large tower.  This tower heats up water inside to around 1000 degrees Fahrenheit (540 degrees Celsius) converting it to steam, runs it through a standard steam turbine, which spins a generator to generate electricity.  This steam cycle (Rankine cycle) is the standard way we have been making electricity for over 100 years.  Coal and nuclear plants both use this cycle to create their electricity, with the only difference being where the heat comes from.  This old technology, combined with the power of the sun, provides some very cool visuals.

Ivanpah Solar Electric Generating Station Units 1, 2, and 3.
CC Image courtesy of DiverDave on Wikipedia.

One of the Ivanpah units online.
CC Image courtesy of Aioannides on Wikipedia.

Having glanced at the website promoting this project, it appears that most, if not all, media outlets have just grabbed the important facts out of the press releases and did not bother to do any of their own math.  Many recent articles have been pushing many facts supplied by the owner, most of which are mostly accurate, but one two in particular are very misleading, especially when it comes to renewable power.  Those are peak output and homes served.

A Crash Course in Electricity Production

CORRECTION: Based on reader input and some research of my own, the energy consumption of an average household is closer to 1.3 KWh per hour, or just 1.3 KW.  It appears the 140,000 homes does assume the plant only generates power during the day.  Using the same 30% capacity factor, the Ivanpah plant generates power for around 86,000 homes on average, though most of that generation still occurs during the day.

These units are directly related, with the homes served calculated by taking the peak output (377 MW) and dividing by the average power consumption per home.  Working backwards, that means the assumed home power consumption is 377 MW / 140,000 homes = 0.00269 MW or 2.69 KW per home on average.  That seems like a reasonable average, except there is an important point to note.  All these numbers are in power (Watts), NOT energy (Joules).

When we talk about energy, we are talking in an amount, in Joules, or in the case of food, in Calories.  This is useful when talking about power plants, but notice they are called power plants, not energy plants.  Power is a rate (Joules per second), like the speed of your car.  Energy is like the distance from point A to point B.  If you drive at 60 miles per hour (~100 kilometers per hour) for one hour, you have traveled 60 miles.  Likewise, if a 377 MW power plant operates for one hour, it has produced about 1.36 million megajoules, or 1.36 terajoules.  Follow so far?  Good.

This is especially important because we are talking about a solar power plant.  If the Ivanpah Solar Electric Generating Station (SEGS) generated 377 MW all the time, twenty-four hours a day, seven days a week, it would produce 11,889,072,000 megajoules, or 11,889 terajoules or 11.89 petajoules.  That also means in one year 140,000 homes, using an average of 2.69 KW each, use 11.89 petajoules of energy.  That's what the claim states.  The amount of energy the power plant produces is the same as the amount of energy 140,000 homes use.

Reality is a Far More Complicated Beast

Well that's great, but if you are familiar with the workings of the Earth and Sun, you will know that the sun isn't out all the time.  The value changes depending on the latitude you are at on the planet, but the sun is out around twelve hours a day.  Assuming the power plant is able to generate 377 MW even when the sun has just risen all the way until the sun completely sets, that is only half the day.  In the electrical generation industry, you would say the plant has a capacity factor of 50%, or the stated power generating capacity (377 MW) can be generated 50% of the time.  Right there you have cut the amount of homes the power plant actually supplies to 70,000 on average.

The Truth About Solar Power Capacity Factors

This also assumes all the mirrors are functioning all the time, the steam cycle portion of the plant never needs to shutdown for maintenance, and there is never any inclement weather (though being in the Mojave Desert the amount of cloud cover is probably very low).  Adding on top the original assumption that the sun supplies noon-time heat the entire day and you are looking at a real capacity factor of 30%.  So the plant doesn't power 140,000 homes or 70,000 homes, but 42,000 homes.  That is not insignificant, but it isn't 140,000 either.

Every Energy Source Has a Capacity Factor

I don't mean to single out solar power, because peak output is used the same way for every type of power plant.  It really isn't a very useful number on its own, except for electricity grid operators who have to put the right amount of power onto the grid all the time.  The reason this simplification is so apparent in renewable power is because the capacity factors are so low.  A coal power plant averages around a 70% capacity factor, while a nuclear power plant averages around a 90% capacity factor.  Wind and solar, meanwhile, average between a 20% and 40% capacity factor.  That means a 1000 MW nuclear plant, on average, generates 900 MW, while a 1000 MW solar thermal plant generates, on average, 300 MW.  The nuclear plant with the same capacity generates three times the amount of energy as the solar plant.  Check out page 56 from the US Energy Information Administration's Electric Power Annual Report from 2009 (latest currently available data) for more details on capacity factor by fuel source.

While I do not think the media does it on purpose, reporting the numbers like this without any context is misleading.  It implies that this $2 billion solar power plant generates a lot more energy than it really does.  People will read this and come to the conclusion that 1000 of these plants would power every home in the US, when in reality (assuming we also invested in massive battery storage to keep the juice flowing at night) we would need 3,300.  I get the feeling that the media doesn't think the average person can follow this logic, so they just report the "facts" and don't bother with explaining the finer details.

Like I wrote earlier, I am still a fan of solar and wind power projects.  I think they will play an important role in power generation in the future, but there is no reason to stretch the truth in order to make them look better.  The people actually investing their money in these projects know better, so it isn't like they are getting swindled.  The public, however, is getting swindled into believing a technology is further along than it really is.  I support solar power and I support the Ivanpah SEGS project.  In many ways this is a test facility, because a solar thermal power plant of this size has never been built before.  The industry will learn a lot from operating these three units and hopefully will apply that knowledge to future projects to make them more efficient.  This plant may not be cheap, and may seem much more expensive now that I have put it in a new light (pun intended), but I still think it is worth every cent.