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Comment by bruce511 | Hacker News Reader

As someone who has acquired rather too much information about solar over the past few years (in preparation for a largish system) I can say this is a good overall primary.

One irrelevant detail not mentioned, which I like repeating, is that despite being made to literally sun-bathe all day long, solar panels don't like being hot. (Effeciency drops with heat, gains with cold.)

There's not a whole lot you can do about this, except allow for passive air cooling. There are some water cooled panels available, but costs make them uneconomic for now.

I was interested to learn though that on a cold summers day, the panel output can exceed the nominal rating got the panel. Something to consider if you are at high altitude.

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solar panels don't like being hot

Indeed, and this touches on the 'Regular cleaning of PV panels is important for ensuring maximum energy production' statement in a funny way. First of all, while the statement is accurate, I'd say is not too important practically depending on where you live. As our isntallation guys also told us. Our panels seem to do just fine with occasional heavy rainfall to clean them and the loss when they're covered in a thin layer of dust is not worth spending time on. On the other hand, the PV cleaning companies will say that it's super important to clean them. So when my mum got her panels cleaned it went like this: sunny day, panels get hot, efficiency drops. Panels were cleaned with water, temperature drops, cleaners told her 'look how much better it is now'. But after they were gone temperature rose again and efficiency was essentially back to where it was before.

Had to get a home PV system out of necessity due to our national power company being up a shitcreek with an aging fleet of badly maintained coal power plants.

3.7 Kw solar panels and 2 x 5KW LifePO batteries and a 5Kw SunSynk inverter tied to the grid - solar geyser and it does not power our electric oven - the only issue is the management system is dumb as bricks - there is no intelligence and difference charge settings or profiles for our cold winters and hot summers or using the weather forecast for the day.

It just averages out.

If it can be controlled via RS485 you might be able to add some smarts to it, like lowering charge level if weather is supposed to be good next few days.

There are third party solutions running on a Rasberry Pi that connects to WiFi port but it means "hacking" and it bad enough maintaining my own office I.T infrastructure.

Yep, I live in Southern Europe and my panels have the biggest output end of April/May, while one would expect it to be end of June.

> solar panels don't like being hot.

For boats there's flexible panels that in many cases you can even walk on.

But the sun's power not turned into electricity, heats both panel & roof of the boat (and in turn, its interior). Not something you want on a hot sunny day.

A rack-mounted panel otoh, allows for airflow underneath, and -if roof mounted- separates (potentially hot) panel from the boat's roof.

So, cool(er) vs. aesthetics. Definitely a pitfall to be aware of for boat owners installing PV.

>> solar panels don't like being hot

that's why in tropical countries people should aim for photothermical systems instead, collecting sun energy with parabolical mirrors heating up water, moving steam engine thus generating energy

"There are some water cooled panels available, but costs make them uneconomic for now."

Couldn't you just use that warm water and so make it economic? Are there any combined systems that try this?

You can, but the problem is that warm water isn't that useful.

Unless your system can regularly heat up to >60C to kill legionella then it will need external heating.

Secondly, when the external temperatures are high there's very little need for warm water. Perhaps a few dozen litres for washing. No one is taking a hot bath on a summer's day!

If you have the space, you can store the hot water underground and then pump it back up in winter for heating. But that's expensive.

"You can, but the problem is that warm water isn't that useful."

Depends on your other systems. Dishwater wants hot water(but usually has no input for hot water), washing machine(some do). And if you have a house with 4+ people who like to shower a lot .. it adds up very quickly. And yes, heating. Now are already the days (in europe), with cold nights and mild but sunny days.

So .. it makes sense in theory, but not so easy to economically make use of as of now.

There are but you just won't be able to use all that water if you have more than a few panels.

Like if you need enough water for shower you might just need heat of like... one or two solar panel sized heaters, anything extra means water will be permanently hot and so any benefits from cooling would be minimal unless you had some heat dump to pump the excess heat out. So more cost

There is probably some use for heating house in the spring/autumn, but system that can put the heat from panels either to heat the water or heat the house is additional extra complexity and cost.

I'm not sure where you could use it. At least in the UK:

- water for heating your home is in a closed loop, and you wouldn't want to add this cooling to that closed loop as it would heat up your solar panels on cold days

- water for drinking/washing comes from the same cold feed, and you don't want to heat that up as you can't get cold water then

- bisecting the water supply into hot taps and cold taps, and running the hot one under the PV cells could work, but it would only flow the water when something is pulling water, e.g. running a tap, which might be a hindrance to cooling

There are solutions in the market for this. The heat recovery system is filled with glycol solution, which means it doesn't freeze over even if left unpowered during sub-zero outside temperature. Then there's a temperature sensor and a control unit that only runs the pump when the fluid in the panels is warmer than the warm water accumulator of the home heating system.

The heat collectors are vacuum insulated, so provided with enough solar radiation, they will work even when it's very cold outside. These systems work okay for example here in Finland. Of course it's a limiting factor that you normally need the heating most when the solar radiation is at the minimum. If you've got a swimming pool or some other use for the hot water during the summer, it's a good deal.

> the warm water accumulator of the home heating system

I'm not sure how this would work in a modern UK heating system - there is no warm water accumulator to my knowledge.

I suppose a modern gas or oil burner doesn't need one. But this sort of solar based heater as well as ground-source heat pumps typically would need it. They are not very expensive however, as they are just heat-insulated tanks of water. Of course space requirements and such might rule out adding one in many cases.

I think it's more - how do you hook it up with the rest of your water?

The gas boiler has a small tank where the radiator circuit's water is heated. Warm water accumulator is analogous to making this tank larger. The radiator connections would be moved to the big tank and the boiler would be made to warm that tank. Perhaps typical combination boiler isn't optimal for this setup, so incorporating other heat sources might be best timed when the boiler is due for replacement anyway.

There are lots of houses in the UK that have hot water tanks. The water in these is heated by effectively a radiator inside the water tank. We have one here and the my tank has a 'secondary loop' designed to be driven by a water-filled solar panel. Typical kind of tank: https://www.screwfix.com/p/heatrae-sadia-megaflo-eco-solar-p...

True, but those are often older. I know some new builds also have them (I lived in one of said new builds a few years ago) but my impression is they are often older heating systems that don't have a combi boiler yet.

From:

> 59% of dwellings in 2019 used their central heating system to provide hot water without a separate cylinder. Around a third (32%) used their central heating system to provide hot water through a separate hot water cylinder, 7% had a hot water cylinder and immersion heater as the primary means of water heating and less than two percent had an instantaneous water heater or dedicated boiler (1% and 0.2%, respectively)

So about 40% have hot water tanks, though I guess the number is falling.

its not the running of them thats uneconomical, is the added infrastructure and component cost.

Off-topic: The most practical alternative energy seems to nuclear

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