23

After watching Elon Musk's presentation regarding the Tesla Powerwall, I had a question.

On his diagram of the USA, he claims that a "tiny blue square" on the top of Texas that consists of solar farms would be enough energy to power the united states. I've watched documentaries, that claim it should be 10 times that size. This seems absurd right?

That blue square there is the land area that's needed to transition the United States to a zero-carbon electricity situation

enter image description here

  • 8
    Keep in mind that Musk never said that this area is needed to power the entire US - it is the area needed to remove fossil fuels. You would still be using hydro, nuclear and wind power, in addition to solar power. – T. Sar May 7 '15 at 19:28
  • 2
    It's on the first moments of his speech, right on when he tells about the blue square. He never talks about going full solar. I will do that in a moment. Just let me pick the correct second. – T. Sar May 7 '15 at 19:52
  • 4
    @EnergyNumbers It's on the 3:24 mark: "The blue square there is the land area that's needed to transition the united states to a zero carbon electricity situation". Zero carbon is different from Solar-only - Nuclear Power, Hydro Power and Wind power are all "zero-carbon", since they don't burn fossil fuels. – T. Sar May 7 '15 at 19:55
  • 1
    @JPhi1618 you could pack it at 100% fill, but almost no one does for utility-scale, because it's not the most economical solution (except on rooftops). A 1:3 ratio is more likely for a typical commercial installation, but it will of course depend on cabling costs, land costs, location, and installation & maintenance techniques – EnergyNumbers Sep 10 '15 at 19:22
  • 1
    That tiny blue square is still VERY big. If you want to get to the centre of it to do some maintenance, you need a car. You need to connect your solar panels to HV lines to transport the power, and these will shade large areas. Sure, these wires COULD be underground if reducing land area is the goal, but it isn't, reducing cost is. There are a lot of reasons that space on a solar farm of this size would need to be bigger than the size of the panels. – Scott Jun 6 '16 at 2:28
35
+50

Summary: yes, the area shown is reasonable, as a visualisation of the surface area of panels required to generate electricity equal to total US electricity consumption, on a multi-year average: that area of panels would generate 500 GW, which is above the current US annual average electricity consumption of 425 GW

Calculations below are taken from this blogpost at the Energy Institute, University College London.

As Thales Pereira has pointed out in the comments on the question, the claim could be taken to mean that that area of PV would displace fossil fuel, and supplement the existing zero-carbon options on the US grid (hydro, nuclear, wind). That would make it an slightly weaker claim. I've assumed that it's the strong version of the claim: that that area would be the same amount of power as total US demand, even before considering existing hydro, nuclear and wind generation. If the stronger claim is valid, then the weaker claim automatically follows.


  • US electricity consumption is about 425 GW on average
  • The area shown is 10,000 km2, in NW Texas
    Eyeballing this google map and comparing with the graphic in the question: using the scale in the bottom-right corner, the square is about 100km along the side
  • Table 2 of Green et al's Solar cell efficiency tables (Version 45) gives the best module as being 24% efficient, giving a PV capacity per unit area of 0.24 GW/km2
  • PVWatts gives a capacity factor for Amarillo, Texas, of 21%

10,000 km2 x 0.24 GW/km2 x 21% = 500 GW

Which is more than current US electricity consumption of 425 GW.

So yes, the area shown is reasonable, as a visualisation of the surface area of panels required to generate electricity equal to total US electricity consumption, on a multi-year average.

  • Is solar thermal energy (such as California Solar One or Nevada Solar One) more or less efficient than PV panels? – vartec May 7 '15 at 21:00
  • 2
    @vartec It would be worth asking that question on Sustainable Living There's little data to go on that I could find: AFAICT it looks like those (CSP) plants are less land-efficient than PV. They may have similar energy efficiency (~20%, before storage losses). Cost-efficiency is harder to compare: CSP's potential storage will have different values depending on what the rest of the grid looks like; and we don't really have enough experience to calculate a meaningful learning curve for CSP capital costs. – EnergyNumbers May 8 '15 at 2:03
  • For the sake of this question I guess only land-efficiency matters. – vartec May 8 '15 at 16:43
1

Firstly, the northern 55 km of the square is the Oklahoma Panhandle, while the remainder is the Texas Panhandle, which is 270km east to west.

The blue square is therefore about 123km on each side, 15,000 sq. km. or 3,700,000 acres.

A great resource for evaluating whether this is sufficient is Land-Use Requirements for Solar Power Plants in the United States by the National Renewable Energy Lab.

According to table 4 (which considers only direct land use) the most efficient use is by 2-axis concentrating PV systems, which need only 2 acres to produce a GWh per year.

So with 3,700,000 acres, 1,850,000 GWh can be produced per year.

This compares to 4,686,400 GWh per year in electricity consumption for the USA as of 2013.

So, no, even considering the best current technology and only direct land use, it is not a large enough area.

  • This answer does not answer the question - 'electricity consumption for USA' != energy needed to transition to zero carbon electricity. – NPSF3000 Jun 6 '16 at 22:14
  • @NPSF3000 67% is currently from fossil fuels eia.gov/tools/faqs/faq.cfm?id=427&t=3 – DavePhD Jun 7 '16 at 0:42
  • so taking that into account, the difference between 4,686,400GWh*67% and 1,850,000GWh within a factor of 2 (70%), you may want to change answer to 'possibly' or firm up the math. – NPSF3000 Jun 7 '16 at 1:03
  • For example estimates for 2016 are only 4,088,000 GWh of electricity will be generated, 64.5% of which will be gas and coal - significantly different than the numbers you use. eia.gov/forecasts/steo/report/electricity.cfm – NPSF3000 Jun 7 '16 at 1:09
  • @NPSF3000 maybe the Wikipedia number is wrong. I'll investigate more. – DavePhD Jun 7 '16 at 2:03

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .