# Geothermal vs Solar Power

#### lgw (121541) writes | more than 2 years ago

1

Here are the basic numbers on aailable geothermal vs solar power (since this has come up in discussion more than once).

The surface area of the Earth is about 5.1 x 10^14 m^2. The cross sectional area is about 1.3 x 10^14 m^2 (one quarter of the surface area, of course).

Here are the basic numbers on aailable geothermal vs solar power (since this has come up in discussion more than once).

The surface area of the Earth is about 5.1 x 10^14 m^2. The cross sectional area is about 1.3 x 10^14 m^2 (one quarter of the surface area, of course).

Per this paper found as a cite on wikipedia, the total heat flow out from the Earth's interior is 4.42 x 10^13 W, or 0.0867 W/m^2. Of course, the available power is much less because it's only the subsurface-surface temperature difference that's available.

Total solar irradience is 1361 W/m^2 by NASA's latest estimate (so about 1.7 x 10^17 W across the entire cross section), or about 1000 W/m^2 on the surface at noon on a cloudless day. Averaged over the day-night cycle (surface area vs cross-section, so 250 W/m^2), and taking clouds into account that's about 180 W/m^2 (I can't find a solid source on that yet, but it looks close).

So, total solar power flow is about 4000 times as large as total geothermal flow. I'm not quite sure how to estimate the (ideal) available power as a percentage of the total geothermal power flow, but if we use a WAG of 50%, then the available power from solar is also about 4000 times per square meter more than geothermal - significantly more if we average solar power only across populated latitudes.

## More harm than good? (1)

## sznupi (719324) | more than 2 years ago | (#37356230)

There are worse and better places for both geothermal and solar. I can think of a few which are fabulous for one, but quite poor for the other. There's no reason for them to not coexist (especially since they have different characteristics, geothermal being very suitable for base load for example), choosing one which is more suitable for the place

PS. Plus, that total solar irradience drives the atmosphere and essentially

the whole planetary biosphere, on which we also greatly depend - though, admittedly, we already use more than is available... [wikipedia.org] (temporarily thanks to the fossil fuels, which simply store past solar energy collected by the biosphere - last I've heard, we now use ~3 million years worth of production in 1 year - and when spoilingfuturehectares)Of course, the last laugh might still be on us... [wikipedia.org]