The sun delivers about 1000 Watts for every square meter of land. This is why we burn fossil fuels. These substances (peat, coal, petroleum, natural gas) store ancient—and concentrated—solar energy. This energy density makes them desirable as they can be transported from their source of origin and exploited elsewhere.

Pipelines are inherently safer than railroads and highways when it comes to the transport of these fuels, but pipelines are no longer politically popular. Resistance to things like LNG facilities is no longer the province of environmentalists. Cities are even banning natural gas from new construction, citing its climate impacts.

Of course the burning of fossil fuels is replete with ecological consequences, well-known and well-documented consequences, I should point out. This point is not arguable.

There is a great deal of enthusiasm for solar power and other renewable sources like wind. But there’s a limit to what these can do.

Let’s start with 1000.

A square meter of land can collect, in theory, 1000 watts worth of the sun’s energy. Imagine a plot of land one square kilometer in size, that is, one thousand meters by one thousand meters. That’s one million square meters. One million times 1000 watts is one billion watts or one gigawatt (GW).

That’s about power-plant size. The Palo Verde Nuclear Station in Arizona is the biggest power plant in the US and is rated about 3 GW.

A square kilometer, with a perfect collector, is limited to one GW. But there is no such thing as a perfect collector. Modern single-junction solar panels are about 25% efficient. There is a physical limit, called the Shockley-Queisser, that says it can’t get better than 33.7%. That’s physics, not economics.

Multi-layered (multi-junction) solar cells can bypass this limit and achieve up to 68.7% in normal sunlight. Right now such cells are imaginary, the best we can do is about 40% efficiency in specialized applications.

The sun is capricious, too. It doesn’t shine all day. And if varies from place to place and day to day. That 1000 watts per square meter is an average. It’s not a steady stream. So you have to store the electricity for the lean times. Fossil fuels are the first storage devices. Plants collected solar energy and photosynthesized carbohydrates. When they died and were buried that carbon was preserved and later ingenious humans learned to burn it.

But nature’s storage devices come at a cost. All that carbon gets released and messes with the atmosphere and the climate. So ingenious humans are inventing new storage devices (like batteries) to capture sunlight that won’t release carbon by-products when the energy is used.

And these storage devices come with a cost, mostly the mining of the materials needed to make them. And they are just a link in the chain. Sun –> PV panel –> battery –> wires –> end user. Another limit is the Second Law of Thermodynamics. In effect, it says that at each step you’ll lose some of the energy. You can’t convert it perfectly.

We already cut our 1000 down to 400 with our ideal (past the Shockley-Quiesser Limit) solar cell, by the time we get to the end we’ll have even less. And this is true of EVERY energy transition, whether you use coal or nuclear or hydro- or whatever.

Two things are competing. One is the continuing increase in energy demand and energy use. The other is the need to conserve, to prevent continuing environmental degradation.

We need to figure out how to do both. People in poor countries want to gain the benefits of the modern world and the only way to do that is to use energy. People in rich (high energy use) countries want to maintain their wealth and comfort. It takes energy to do that.

Nature sets the limits. 1000 watts per square meter, for example. It’s up to us to live within them.

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