Is solar energy really renewable? Is it free?
The answers to these questions are, except in the most trivial sense, no and no.
Solar energy is said to be renewable because, as one source puts it, it is “naturally replenished.” A different source states it in a slightly different way: Solar power is renewable because “there is an endless supply.”
But the truth of the matter is that in any meaningful technological, economic, or practical sense solar is anything but renewable.
For any unit of usable energy generated by the sun, often expressed in terms of British thermal units, it is highly unlikely that, as it is used, it will be — or even can be — renewed by another BTU of energy also generated by the sun. This is because, unlike the claim above that “there is an endless supply” of solar power, on any given day there is a very finite supply. On some days there is no supply at all of sunlight that is usable for conversion to electricity.
The extent to which a megawatt of electricity that is generated by solar power actually can be renewed by another megawatt of electricity that is also generated by solar power is completely dependent on the time of day that the electricity is used to light a lamp, run an air conditioner, or heat a hot water tank. If I generate electricity from the solar panels on the roof of my house at 2 p.m. to run my air conditioner, to renew that used electricity at 6 p.m. to cook my dinner would be impossible.
In fact, I would have to turn to an entirely different source of energy with renewability that does not depend on whether the sun is shining — a source such as coal, natural gas, or nuclear power.
It is meaningless to refer to an energy source as “renewable” if it can’t be renewed as needed. If my solar energy does not allow me to renew the electricity that I use at 4 p.m. until 10 a.m. the following day, in what practical sense can that energy source be called renewable? The answer is none.
Of course, this is true not only for the household with panels on its roof but also of solar-generated electricity being put onto the electrical grid, and for all the same reasons. It seems to be a dead giveaway that there is not “an endless supply” of an energy source or that it is not “naturally replenished” if for most hours of any given day it needs backup generation from a supposedly nonrenewable conventional energy source.
Indeed, in a practical or even meaningful technological sense, which are the truly renewable energy sources (i.e., those which are renewable on command for the purpose of generating electricity): the sun, coal, or natural gas? Clearly it must be the latter two. In fact, it is solar power’s lack of renewability when actually needed that makes it so expensive as compared to these other sources.
So what does this imply for the claim that the sun is a “free” source of energy? If the word “free” refers to price in the economic sense, then the claim is misleading at best.
The price of the sun as an energy source is completely bifurcated. Energy from the sun has two prices: zero and infinity. On a clear day at noon, it’s free. On that same day at midnight, it’s infinite. That is, it cannot be obtained at any price.
The same is true for sunny versus cloudy days. It is typically argued that, on average, given that many days will be cloudy with no “usable sun” at all, a solar-based power plant can generate electricity for about five hours. This means that for an average of 19 hours out of every day the price of solar as a usable energy source is infinity.
It is time to stop referring to solar power as “renewable” or “free.” The reality is that these descriptions have no practical meaning and serve only to obfuscate the true nature of solar energy as a source of electricity.
Ultimately these are propaganda words invoked by special interests in the renewable energy industry. Their purpose is to color the political debate about energy policy in favor of subsidies and special privileges with costs foisted upon taxpayers and utility customers.
Dr. Roy Cordato (@RoyCordato) is Vice President for Research and Resident Scholar at the John Locke Foundation.