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Comment by Analemma_ | Hacker News Reader

People can get weird about solar panel placement and constantly come up with terrible ideas like putting them on cars (not enough surface area for any real power) or roadways (no!). Does anyone know if this idea is one of those terrible ones or is genuinely feasible?

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The proximity to water cools the the panels which increases their efficiency, there's a lot of sq ft available, and the government already owns the land. It also decreases the amount of water lost to evaporation, and the amount of weeds/plant growth around the canals since there's less sunlight for them.

if you use water to cool down the panels then you should not expect to lower the evaporation. I would say that this would increase evaporation as solar panels reflect less light than water. but this is just speculatio from my side.

water underneath the panels will still evaporate to an extent, and cool the panels compared to panels above dry earth.

The panels will shade the water and reduce evaporation compared to unshaded water.

but doesn't this ignore that a lot of the light now absorbed is become electricity instead of heat?

You can't cheat thermodynamics! If it's being absorbed by the panels (rather than reflected) then it's absolutely becoming waste heat. Solar panels look dark blue/black because they're absorbing most of the light that hits them. This is why them overheating is a problem that can affect performance. If they were mirrors they wouldn't overheat at all, but they also wouldn't be able to produce any electricity.

Thermodyamics says that a solar panel is cooler than an equivalent black panel. Some solar energy gets converted to electricity. All of that converted energy does not end up as waste heat. A 100% efficient solar panel would not get hot. Only the inefficiency ends up as waste heat.

The portion of incoming light that becomes electricity is dissipated as heat primarily where it is used (e.g. in an appliance attached to the grid fed by the solar panels), not in the cells themselves. So it's true that a cell connected to an external load will be cooler at equilibrium than one that is disconnected.

Maybe I'm missing something obvious, but by conservation of energy if all of the energy of the sun was converted to heat then no electricity would be produced? Conversely, that fact that panels do produce electricity means that not all of the sun's energy is heating the panel?

solar panels are only partially efficient. if the solar -> electric conversion efficiency is 21%, then 79% of the incoming solar radiation is converted to heat.

Catching the light before it hits the water does reduce evaporation. It does not eliminate it. The water is not used for active cooling. Water has high specific heat and liquid to gas is endothermic. Which is why the water temperature is lower than the ambient air temperature.

Putting the panels over the canals reduces evaporation while cooling the panels. This is proven.

In this case there's a desire to cover the canals anyway for evaporation reasons. There's a reason you see a lot of solar covered parking: once you're already building the structure to support a cover, it doesn't drive up the structure cost that much to make it racking for solar panels. So this kind of thing can produce a real cost savings, by installing solar in situations where the supporting structure is desirable for independent reasons.

Yeah, solar panels have become really cheap. I am looking into covering a flat roof with solar. The support structure (nothing super fancy) will probably turn out to be more expensive than the panels themselves.

I can’t see anything obviously terrible. Its not small segregated mobile areas like cars, and its something people drive on like roads.

Canals are naturally fairly linear and remote, which seems to imply maintenance is likely to be less efficient than if you had a single compact site with similar area, but it also isn't competing with other land uses, whereas a compact installation would be.

One concern is CA has lots of solar and supply problems are most acute outside of peak solar production times as a result, so without robust storage, massive additional solar capacity may not be as useful as the peak capacity makes it seem. (Though, that also means more off-peak capacity, too, which is useful.)

It has nothing to do with science or even power generation. This is about regulatory compliance. They put them over canals because a canal is not private land. Either they are owned by government or the government has easements for their maintenance and improvement. Canals are also readily accessible for light construction, most all of them having a dirt road alongside. The same principals apply to roads. Governments face all sorts of issues acquiring and building upon new land. But placing something beside, on top, or even within the road surface can normally be done without new permits let along environmental impact statements.

> Does anyone know if this idea is one of those terrible ones or is genuinely feasible?

They've done it India, a country notorious for red tape. Which begs the question: how long will it take California's bureaucratic ineptitude take to screw this up.

The cost of solar panels is less than the cost of installing them on a roof in California. I guess the real question is whether it is more expensive to install the panels over a canal or over a roof.

Also, what happens when the canal floods?

> what happens when the canal floods?

Nothing. The panels aren't intended to contain the water within the canals, they're installed above the water on racks. Aside from catastrophic flooding that might compromise the solar panels' supports, the panels wouldn't be impacted by flooding.

Solar over canals and reservoirs is a great idea, and the catchy name is floatovoltacis for floating installs on reservoirs. Solar roadways are an absolutely terrible idea.

I think that car placement is still mostly bad idea but it shouldn't be thrown out yet. As PV gets cheaper and cheaper, the financial impediment disappears and it starts to make a small bit of sense.

For a regular sedan, solar panels won't make a car completely autonomous, but one could fit at least 600W of cells, and if parked in the sun all day, that could generate 2-3kWh of power, which is 8-12 miles of range.

Plug in charging would still be needed, but that extra bit of power could be used for temperature control of the battery pack or interior too, while the car is sitting in extreme heat in Phoenix, or outside a garage in North Dakota.

Pros: Reduces evaporation Cools the panes so they’re more efficient Uses otherwise unused space

Cons: More difficult to install and maintain Less efficient for management since the panels are in long thin tracts rather than square ones

Pros seem to outweigh cons in initial pilot deployments

Additional critical benefit: somewhere to run the transmission lines. Tautologically where the water goes so too can the transmission, certainly to connect to the nearest convenient substation.

Stupid question but why not above roadways?

There are already light fixtures and usually power lines going around there. It would block some sun from the black road and that's also a good thing. Sending a maintenance vehicle would be easy as it would be accessible.

The only downsides I can see are:

* It needs to be tall enough so trucks won't hit it. So that might make it more expensive. * It might be stretched over a long distance creating logistic problems with the delivery and efficiencies.

Is there anything basic that I'm missing here?

Above roadways is fine. The bad idea is making the road surface out of solar panels that vehicles drive on top of.

Yes. I don't get the "road surface" stuff. Doesn't make much sense.

But if it's so viable above road then why aren't all interstate roads like that already?

It seems like "free money" for the municipality or an entrepreneur that can build it as a "BOT" project. No?

I've always wondered just how awful the run off from rain landing on solar panels is as far as those nasty sort of chemicals that we then find out are terribly carcinogenic or disruptive to human health. Same would apply to water condensation forming below the panels and dripping back into the canal.

Given the materials that go into solar panels and the proximity to water that will end up in either the food supply, or inside people; I would hope they at least run some tests.

Solar panels are fully encased in glass enclosures, so I'm pretty sure there is no runoff, but yeah putting them above water ways like this does make you think.

The heavy metals in solar panel waste you typically hear of is for discarded and broken cells in landfills iirc.

No - any toxic materials in a solar panel are bound up in the silicon and unable to leech out. Rain is generally good, as it cleans dust off and increases efficiency. Pollution is not a concern at all with solar.

There's a concerted disinformation campaign out there to try to insinuate that solar panels break and then poison the ground. Here's a podcast covering some of it and the funding mechanisms that help push it:

https://overcast.fm/+0-PqLPM34

People will believe anything with the right confusing language. Throw in "rare earth minerals" and everybody gets as scared as if you call water "dihydrogen monoxide."

https://dhmo.org/facts.html

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