Industrial energy costs are $1 per million BTU (MMBTU) or 300kWh, or $3*10^-6 per watt hour (Wh).


Solar has 1 kg of 9n silicon per 100W, at $20/kg. Since raw material prices are mainly energy costs, this is:

($20/kg)/($3e-6/Wh) = 6MWh/kg

Kg per watt solar is:

1kg/100W = 0.01kg/W

That means energy use to build a watt of capacity is:

0.01kg/W * 6MWh/kg = 0.06 mwh = 60kWh

Let's say a 1 watt cell operates for 20 years:

8760*1W*20=180 kWh

At 20% capacity this is:

0.2 * 180kWh = 36kWh

Is this correct?

This is a specific new question and not a dupe of the above.

  • 1
    "Raw material costs are mainly energy costs" is probably an excessive assumption - do you have a citation for that (specifically for silicon)? Where do your other assumptions come from (e.g. 20% capacity, industrial energy costs)?
    – Chris H
    May 25, 2016 at 9:45
  • The other assumptions are based on what I've seen on this site. Feel free to refute them. Raw material costs reflecting energy costs is a widely used assumption eg wsj.com/articles/copper-prices-slide-on-oil-dip-1461581413
    – D J Sims
    May 25, 2016 at 10:12
  • I would welcome other sources if they disprove my assumptions
    – D J Sims
    May 25, 2016 at 10:14
  • 3
    Your figure of 8760 seems to be made up of 24hrs times 365 days. The sun doesn't shine 24hrs/day so I think you want something like 10 times 365. The effective number of hours will vary depending on the location, the weather, and whether the panel tracks the sun. Or was the 20% capacity supposed to cover that difference? May 25, 2016 at 10:48
  • 4
    better duplicate (closed as dupe of same target, but has PV specific answer sustainability.stackexchange.com/questions/2968/… May 26, 2016 at 15:22

1 Answer 1


Yes, PV is viable.

That's why somewhere around a billion solar panels have been connected to the grid - about 200 GW of capacity, with another 50 GW or so coming online in 2016.

I'm afraid that the costs you have are quite wrong.

Remember, PV generates electricity - that's a higher-quality (high exergy) energy than heat from gas. To get electricity from gas, you get about half the energy out that you put in, and you'll need to buy and manage a power plant.

And most of gas's costs are hidden - there's the externality of pollution.

Total electricity costs from fossil fuels are around us$100-300 / MWh, depending on where you put the marginal social cost of carbon - (somewhere between $100-200 / tCO2e)

Whereas total electricity costs from PV are around us$30-120 / MWh and trending downwards.

  • 2
    While I'm personally pro solar, the argument that it's viable because lots of it has been installed doesn't really hold water, since government subsidies are in many cases the largest motivator for installing solar.
    – LShaver
    May 25, 2016 at 22:01
  • I am asking about energy costs not monetary costs. Monetary costs are only used in the absence of data for silicon manufacturing energy use
    – D J Sims
    May 25, 2016 at 23:01
  • 2
    @NeilTyson yes, it really does - the answer there completely answers your question here. Your question is whether there's more energy out than in. The other question completely answers that. Your calculations are based on incorrect assumptions, and comments have already pointed that out. If you want to have an open discussion about the numbers, please do so in Sustainable Living Chat, not in comments.
    – 410 gone
    May 26, 2016 at 8:07
  • 1
    @NeilTyson if you'd like to see better answers there, then please do consider putting a bounty on that question.
    – 410 gone
    May 26, 2016 at 12:52
  • 2
    @LShaver The argument wasn't that solar is viable because there are lots of panels installed. Rather that lots of panels are installed because it's viable. (Implications are reversed.)
    – Earthliŋ
    May 28, 2016 at 5:51

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