Solar Panels on Half the World’s Roofs Would Power the Planet | Hacker News Reader

Solar Panels on Half the World’s Roofs Would Power the Planet

thedailybeast.com

It's interesting just how little rooftop area needs to be covered with panels to provide power for a house. Modern solar panels have gotten a lot more efficient than they used to be.

Our whole house is powered by 12 solar panels, covering < 20% of total roof surface. Each block of 4 is about 7x10 ft. The house next door had panels installed ~2014. They have 20 of them, covering maybe 30-40% of the roof's surface. In 6 years, efficiency basically doubled and price fell by about 3-4x.

Solar panels are on the new Moore's Law.

Can't we just set up an orbital solar panel array beyond the space debris field, have it always rotate to point at the sun 24/7, and just get a really big extension cord to connect back to earth, and call it a day?

Look, if we're gonna spend a gorgillion dollars we don't have, let's at least be efficient with it. We're engineers, damnit!

I know you're being sarcastic, but please don't use the "just" word to talk about trillion dollar infrastructure projects that require product-ionizing thus-far theoretical technologies.

If you had superconducting power cables that could carry power from the side where the sun shines to the side that doesn't.

Something I have been curious about for a while: How thick of a cable would you need to implement this strategy with traditional cables? I’m imagining something like a large oil pipeline, with a diameter of a couple feet. Is this viable?

The usual method is to increase the voltage, rather than the wire gauge. That's why we have 1.1 million volt transmission wires.

To handle half the world's avg electricity use, I estimate it would take a ~3ft thick copper cable at 1.1Mv hvdc. This ignores the heating of cable which might become a problem. Also you might need two of these unless you want do earth return.

global_consumption_joules = 22848E12 * 3600

seconds_per_year = 365.25*24*3600

avg_power = global_consumption_joules/seconds_per_year

hvdc_voltage = 1100E3

amps = (avg_power*.5)/hvdc_voltage # assume shiping half the power to dark side of planet

sq_in_copper = amps/1000 # 1000A/sq in of copper

dia_in = (4*sq_in_copper/3.14)**.5

print(dia_in/12) # 3.23ft dia of cable

This seems very thin. The planned Sunrise Australian Singapore cable, ~5000km, ~5GW, this is 1/1000th of the power, so a cable 1/30th as thick? Under 2 inches???

Anyway - can you maybe lend a quick hand for a more practical calculation?

How do we move 10MW DC, from a battery pack, to a motor 200m away? Can i just hook the batteries in parallel and get to 10Kv ?!

Obviously a liquid cooled cable.

Area increases as a square of diameter, and the square root of 1000 is 31, so 1/30th as thick seems about right.

Current state of the art battery packs run at 800V. Making a 10kV pack would be difficult. 10MW is about the size of the largest wind turbines so maybe a wind turbine engineer could help you.

Batteries and price-aware appliances seem dramatically more practical than a superconducting electric power infrastructure

Interesting article. My current household of two people consumes less power than the average one person household and this is with myself working a remote job. Where is the incentive for someone like me to get solar power if I'm already really low consumption?

From the subtitle of the article:

Prices are dropping, but not enough to make this is a reality—yet.

What is the enough point? Anyone know?

In the United States, the majority of the cost isn't the panels. Install needs to get more affordable. More modular, with roofs made to accept them. But, as I said in another comment, I expect most solar to go to big solar farms, where install costs are negligible.

Its also the issue of housing affordability, if you have young families moving into small dwellings that they have to upgrade out of in <5 years time then most solar installations are not going to repay themselves in that timeframe. Therefore its logical to not install solar until you are in your forever home.

Yeah, just not in Europe, clouds are a serious problem.

At the rate panel prices are dropping, they'll be cheap enough it won't matter. But, while I'd prefer them on homes, I think most solar will go to big, commercial solar fields.

Would there be unintended consequences of half the world’s roofs being black?

Largely it cools the house, which is usually a desirable byproduct. Instead of solar energy being converted into thermal energy by the roof and then radiating into (and off of) the house, it's converted into electrical energy by the panels. We had a home energy audit guy come into our house and point an infrared camera at the roof, and you could very clearly see the outline of the panels as a detectable cool spot in the ceilings.

Half of the world's roofs are probably already black or at least dark brown - asphalt shingles, slate, vinyl, many wood varieties.

So more heating energy will be required in the winter?

Yeah, but incident solar radiation is rarely a large component of the energy used to heat a home. If it were, we could just live in greenhouses and forget the whole fireplace vs. gas vs. oil vs. electric vs. heat pump debate. You get a much bigger boost to heating efficiency by having new windows installed or cleaning your ductwork than by keeping your roof sunny.

Also, heat pumps can be up to 400% efficient, so the electrical energy that comes from a solar panel could actually turn a profit thermally if used to run a heat pump.

> Largely it cools the house, which is usually a desirable byproduct. ... you could very clearly see the outline of the panels as a detectable cool spot in the ceilings.

Based on my cursory googling, it seems that this is indeed the case, since the solar panels absorb the sun's energy, rather than the roof. I'm having a hard time finding reliable sources, but my sense is that those black solar panels may warm the surrounding environment.

e.g. https://e360.yale.edu/features/urban-heat-can-white-roofs-he... (2018)

" Urban Heat: Can White Roofs Help Cool World’s Warming Cities?

It has long been known that installing white roofs helps reduce heat buildup in cities. But new research indicates that making surfaces more light-reflecting can have a significant impact on lowering extreme temperatures – not just in cities, but in rural areas as well. "

> Half of the world's roofs are probably already black or at least dark brown - asphalt shingles, slate, vinyl, many wood varieties.

Fair point. So... Would there be unintended consequences of an increase in the world’s number of black roofs? ;)

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