How many solar panels can you make from one ton of sand?

September 5, 2024 2:48 PM

Assuming high grade sand. I came across an article that said sand was now $55 per ton. That compares to roughly $140 per ton of thermal coal. Then I was wondering how one ton of sand compares to one ton of coal when they are used to generate energy. How much better is solar energy on this per ton basis?
posted by storybored to Technology (4 answers total)

In practice, silicon is manufactured from mined quartzite, not sand.

It looks like coal can produce 0.88 kWh/pound. So 1760 kWh/ton.

I found this source saying that solar panels produce about 0.5 W per g of silicon. Keeping to short tons... that gives us like 450 kW per ton of silicon. Assuming 10 h/day of operation over 1 year, that's 1.6e6 kWh. If you have a solar cell lifetime of 15 years, we're at about 25 million (2.5e7) kWh, or about 14,000 times the energy produced by the ton of coal.

Sand and quartzite are both basically silicon dioxide. So a little more than half of their mass is oxygen; you need to mine about two tons of quartzite to get one ton of silicon. So ton of sand produces about 7,000 times as much energy as a ton of coal.

This is simply tracking the masses of the elements and leaves out all techno-economic and lifecycle calculations that would be necessary to make a comparison between the total process costs of the two energy sources.
posted by mr_roboto at 4:59 PM on September 5 [6 favorites]

There is more than just sand in a solar panel (By weight, the typical crystalline silicon solar panel is made of about 76% glass, 10% plastic polymer, 8% aluminum, 5% silicon, 1% copper, and less than 0.1% silver and other metals) Note that the silver alone may be less than 0.1 % of the weight but 10% of the cost.

But you can just burn coal as is. Sand needs turned into pure metallurgical grade silicon which taxes 14-16 kWh per 1k of silicon and then purified again using hydrochloric acid and hydrogen gas. and then melt down again with the addition of boron, phosphorous, silver and more in the processes of turning the silicon wafer into a usable solar panel. (citation)
posted by metahawk at 5:00 PM on September 5 [3 favorites]

Bear in mind that there is much more sand in the form of glass in a solar panel than there is sand in the form of silicon for PV cells.
posted by ssg at 7:55 PM on September 5 [1 favorite]

But you can just burn coal as is.

Bear in mind about 60% of the energy from coal is wasted in typical electricity generation.
posted by biffa at 4:08 AM on September 7