How much energy can I get from the sun?

This is not a new topic. The purpose of this article is simply to condense a lot of material into a straightforward answer. Whether you want to save the world by closing down the toxic, gas-spewing power plants, blow off society and live “off-grid,” or just stick it to the power companies by generating your own energy, everyone has basically the same question: “How much energy can I get from the magic yellow orb in the sky?”

How much energy is there?

According to NASA, the sun belts out somewhere around 380 septillion watts (or “yotta-watts” if you want to sound cool). Now, that is the amount of sunlight blasting off in all directions, and while there are some radical theories about harnessing the full yotta-wattage of a star-battery (for example, a Dyson sphere or, slightly more practically, a Dyson swarm), we currently can only harness the power that exists here on earth.

So, how much energy hits earth?

If you calculate the average distance from the sun, along with the diameter of the earth at the exosphere, allowing for angular exposure and the rotation of the earth, you can get a rough approximation of the percentage of solar energy that would, on average, be available for our use. That number is approximately 127 watts per square foot. Unfortunately, one must also take into consideration that not all of the energy that hits the atmosphere is going to reach earth. Accounting for the 6% loss from lensing, reflection, and light that misses the ground through the edges, the 17% blocked by clouds, the 8% that is backscattered into the thermosphere and the 19% that is absorbed by water and dust particles in the sky, that calculation yields a rather unimpressive 15.3 watts at the earth’s surface (on average) per square foot. Note that 15.3 is just the number that I have calculated, based on statistics pulled from NASA, GE and a few other organizations around the web. I have seen other numbers that vary anywhere from 9 to 100 Watts, but I think that 15 is fairly reasonable.

How much energy do we use?

Even though we are only hit by about .00000022% of the sun’s energy here on the surface of earth, that still adds up to a lot of energy. If we could wallpaper 29% of the earth’s surface with energy-capturing devices, that adds up to over 238 quadrillion watts! How much do we really need? According to the US Energy Information Administration, the United States averages about 4 billion watts in energy usage. China, the world’s biggest energy consumer, uses 616 billion watts. That’s according to the Chinese National Energy Administration. In fact, according to Wikipedia, the entire world only consumes about 2 trillion watts.

By these rough numbers, we could capture enough energy to feed the entire world’s demands with a solar farm that covered 6,777 square miles. Right? That’s smaller than the state of New Jersey! Well, that’s not the whole story. If we could capture all of the energy that makes its way from the sun to the surface of Earth over that 6,777 square miles, and convert it to electricity, then we could supply the entire world’s energy demands. But the conversion of solar energy to electricity is far from 100% efficient, which gives rise to our next question.

How efficiently can we convert solar energy to electricity?

When people think of solar energy, they most commonly associate the thought with Photovoltaic cells, or “Solar panels” (those beautiful blue grid-like contraptions that are going up everywhere). This is because, currently, the most efficient way to convert solar energy into electrical energy is via the famed solar panel. In fact, in May of 2016, engineers from the Australian University of South Wales created the most efficient solar panel ever. This record-breaking 11 inch Solar Panel has a 34.5% efficiency rating under laboratory conditions. Assuming that we could use these hyper-efficient cells, our solar farm would need to grow 233,807 square miles… a bit smaller than Texas.

In addition to the problem of the panels having efficiency losses by design, the Texas prairie is a far different place than a laboratory. Dust sticks to the flat surface of a solar panel, rain leaves streaks and birds drop… well… let’s just say that there are real world contaminates that reduce the efficiencies of real world solar farms. For example, the 550 MW Topaz Solar Farm in California uses panels that were rated at about 22% are actually only producing power at 19% to 20% efficiency due to environmental factors even with regularly scheduled cleaning. As a side note, photocatalytic “self-cleaning” glass could dramatically reduce this problem, but the energy consumed by the glass cleaning itself would reduce the overall energy efficiency of the unit.

A further problem with the efficiency of solar cells is that they decay. Solar panels lose efficiency over time. Most solar panel manufacturers only promise about 80% of the original efficiency after 25 years. According to a study by the National Renewable Energy Laboratory in Colorado, solar panels loose the bulk of this efficiency (7% to 12%) in the first two years. Also, the most efficient types of solar panels loose efficiency the fastest. In short, it is this drastically inefficient conversion between solar power and electricity that is currently preventing us from powering our civilization with solar energy. The sun puts out plenty of energy, more than enough for our needs, but we need to find a way to capture and convert that energy for our use.

Summary

Currently, even though the sun produces plenty of energy to solar power the world, there is no technology that mankind possesses that can realistically utilize this power to replace traditional energy production methods. However, this is a growing space, and the standard photovoltaic cells are not the only way that we have to produce energy from the sun (I am playing with some concepts myself in this area… more on that later). I remain firm in my conviction that there is no limit to what we can accomplish through science and engineering.