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What is the typical embodied energy of a solar photovoltaic panel, in terms of nominal power output or panel area? The ideal answer would be in kWh/WP, but kWh/m2 would also be acceptable.

I understand there is probably a range of answers to this question, so here are some simplifying assumptions:

  • If the manufacturing process is more efficient for larger panels, then the answer for large panels (best case scenario) is preferred.
  • If the manufacturing process has become more efficient over time, then an answer for the most modern and efficient process (best case scenario) is prefered.
  • If different manufacture technologies (monocrystal, polycrystal, thin film) have different amounts of embodied energy, then the lowest answer (best case scenario) is preferred.
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  • With such a significant positive return on energy investment, what's to stop solar panels taking over the world? Sure, there are not enough of them to meet our energy needs at the moment, but if a large proportion of energy output from solar panels is allocated to making new solar panels, the total number of panels can just keep growing exponentially with surplus electricity to spare. It's not like the world is going to run out of the raw materials (basically silicon & silicon dioxide) within any meaningful time frame. Am I missing something?
    – Snorlax
    Oct 14 at 12:58
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According to the Wikipedia article on EROI, 585 kWh/m2 is a median value for the embodied energy of a photovoltaic panel, rated based on surface area.

The "energy invested" critically depends on technology, methodology, and system boundary assumptions, resulting in a range from a maximum of 2000 kWh/m² of module area down to a minimum of 300 kWh/m² with a median value of 585 kWh/m² according to a meta-study. [9]

Assuming a panel efficiency of 20% (typical of commercially available panels) and solar irradiance of 1000 W/m2, 1.0 m2 of panel would have a peak power output (WP) of about 200 W/m2. Or stated differently, it would take about 50 cm2 of panel to deliver 1 Watt, and manufacturing that panel would use about 2.9 kWh of energy.

So as a rough back-of-the-napkin calculation, the embodied energy of a solar panel, normalized for peak power output, is about 2.9 kWh/WP.

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If the "embodied energy" of photo-voltaic tech is ~585kWh/m^2 and it generates ~0.2 kW/m^2 then; the answer to the question seems to be that the photo-voltaic tech will need to run for:

~(585kWh/m^2)/(0.2kW/m^2) hours = 2925 hours to generate it's embodied energy; yes ?

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  • Yes, 3000 hours at nameplate capacity (in full sun). Of course, the panel doesn't generate much power at dusk/dark/dawn so estimating the number of days/years for EROI depends on more variables.
    – Nic
    Feb 13 at 17:48
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Energy payback in 1-6 years

Taking manufacturing variables into account basically gives you a range of time from 1.25 - 6.5 years based on 5 sunny days out of seven and an average of 6-8 hours of sun per day.

But in reality none of this matters, here’s why...

Fossil fuels never reach energy payback

Electricity as a commodity has been in use for over a century, it isn’t going away in our lifetime. A better question is, “What’s the best way to produce it?”

If you look at the embodied energy of a coal plant, or even a modern high efficiency natural gas generator, how long does it take to earn back their embodied energy? The answer is they never do. We forget, or more accurately ignore the fact that once you build a coal plant, or gas fired turbine, you then have to feed it fuel the rest of its life which it converts to electricity at a rate somewhere less than 100%. So they keep digging themselves a deeper and deeper embodied energy hole they can never crawl out of.

At least the solar panel, water wheel and wind turbine can one day get even. This is why renewable energy as a whole is better for us environmentally and economically than any form of fossil based fuel source.

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  • I disagree that fossil fuel plants wouldn't pay back the embodied energy. For example, the major oil and gas company Eni is planning that in 2050 the production is 90% natural gas, and emissions are net zero. Yes, that even includes emissions from the use of the produced fuels, not just emissions from extracting the gas. So they are planning to pump back the carbon dioxide back where the natural gas came from. One mole (/ cubic meter) of natural gas produces one mole (/ cubic meter) of carbon dioxide. So if there was room for natural gas under ground, you can fit the carbon dioxide there.
    – juhist
    Oct 14 at 15:25
  • We will need either natural gas or hydrogen for generating electricity when intermittent renewables have zero or low production. There is not enough rainfall in the world to create all adjustable power as hydropower, and no battery is big enough to store energy for use during calm winter periods with no winds for example (and during winter in areas that have real winter, solar production is practically zero). The only competitor to natural gas is hydrogen. We won't know if green hydrogen will ever be cheap enough. Natural gas might be needed.
    – juhist
    Oct 14 at 15:27

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