# How Much Solar Energy Hits Earth?

If solar power is the purest form of renewable energy known, then how much solar power have we got? The answer to this question, when considered alongside how efficiently we can convert raw sunshine into usable power, helps determine whether or not it is realistic to consider solar energy as a viable alternative to conventional energy sources.

In full sun, you can safely assume about 100 watts of solar energy per square foot. If you assume 12 hours of sun per day, this equates to 438,000 watt-hours per square foot per year. Based on 27,878,400 square feet per square mile, sunlight bestows a whopping 12.2 trillion watt-hours per square mile per year.

With these assumptions, figuring out how much solar energy hits the entire planet is relatively simple. 12.2 trillion watt-hours converts to 12,211 gigawatt-hours, and based on 8,760 hours per year, and 197 million square miles of earth’s surface (including the oceans), the earth receives about 274 million gigawatt-years of solar energy, which translates to an astonishing 8.2 million “quads” of Btu energy per year.

In case you haven’t heard, a “quad Btu” refers to one quadrillion British Thermal Units of energy, a common term used by energy economists. The entire human race currently uses about 400 quads of energy (in all forms) per year. Put another way, the solar energy hitting the earth exceeds the total energy consumed by humanity by a factor of over 20,000 times.

Clearly there is enough solar energy available to fulfill all the human race’s energy requirements now, and for all practical purposes, forever. The key is developing technologies that efficiently convert solar power into usable energy in a cost-effective manner.

For energy conversion constants a good website is Energy Conversion, to help elucidate this data.

Categorized | Energy, Energy & Fuels, Solar
12 Responses to “How Much Solar Energy Hits Earth?”
1. fireofenergy says:

The above math has got to be wrong because only at noon is it possible to get 1,000 watts per square meter (divide by 10.75 for sq ft), Thus I would roughly estimate that the sun shines 10,000 times what we use at any given time.
No need to give up on solar! Infact, promote the millions of large mirrors and molten salt concept (solar power towers)

2. Mike Parks says:

The above math must be right because it is noon somewhere every minute of the day as our planet spins in the path of the constant energy from the sun. Clouds, pollution, shade, angel, atmosphere, reflection… all reduce the 1383 watts per square meter that is just outside our atmosphere trying to get here 24 hours a day, 7 days a week, 365 days a year.

3. tony says:

Assuming. 20% efficient solar thermal and 10,000 times more energy than we use hitting the earth, that suggests we only need to cover 1/2000 of the Earth’s surface with mirrors. Doable?

4. Jesse says:

If Tony is correct. Covering the entire state of Indiana with mirrors would supply the entire world with power.

5. S. Martipanz says:

Covering Indiana with mirrors would definitley tick off the Indianians. Since it would then be dark in the entire state 24 hours a day, crime rates in Indiana would likely increase making them even madder. This would touch off a race to install more and more artificial light there to stem increasing Indiana crime wave. (a bright note here is that this would probably make for some good reality TV police episodes) Before we knew what happened there would be run on light bulbs, street lamps, glow sticks and even candles. I say don’t cover Indiana! If we have to cover a state with mirrors make it Florida. Hell, Florida probably won’t even notice the increase in crime.

6. 4ndy says:

Truly, no renewable energy source is necessarily ‘better’ than another for meeting mankind’s needs, and it would be best if we harness all that are available while respecting nature as much as we can.
Funnily enough though, if we put a single geothermal powerplant on top of mount kilauea, it could harness energy thousands of times what the whole of humanity currently consumes. People seem so ignorant to the fact that they are standing on top of a 12,700km-wide nuclear reactor that will keep ticking for millenia without needing maintenance or disposal of heavily radioactive waste.

7. no mans land says:

fireofenergy the math seems right. doesnt really matter anyways. your only safely assuming, so a factor of two considering the suns energy is not too bad.

8. Ponderous Fool says:

I bet our power usage figure would drop dramatically if we replaced all our HIDs with LED and induction lighting.

9. theWHO says:

if you had a belt of solar cells 1 mile wide going around the Equator, than at a given point in time (24hrsx365day/yr) you’d have near maximum effect per square mile of sunlight at full power BUT the output from solar panels diminish below 80% in just 10 years. And there lies the problem of ROI (return on investment).

You also need to maintain the solar panels and keep them clean, make sure birds don’t poop over it and dust and dirt and leaves and branches don’t blanket it…. All this is extra cost. If a crow decides to drop a walnut over it, forget about your investment.

Also, we’re not taking political motives and human nature into consideration. Man kind tend to fight for power and control.

10. Sam Mecham says:

It sounds/looks like there is a potential for another Bill Gates type (or perhaps many) but in the solar energy field instead of OS/computer world. Look at the possibilities. What effect would a PV cell of 40% to 50% efficiency have on the world? What about 60% to 70%? Why does it have to be PVs or even focused sunlight producing heat which drives generators. Is there something else that could be powered by the sun and produce a form of energy that is useful and not near as wastefull as electricity? Sam

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