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 Post subject: Solar hot water panels and a power cut...
PostPosted: Tue Jul 19, 2016 10:14 am 
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So, we have solar panels on the roof for hot water. It's a De Dietrich system installed by a registered firm. We had a power cut for a couple of hours last week which got us to thinking what would happen if this was longer than 2/3 hours, as no, we are not climbing on the roof to cover the panels up!

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 Post subject: Re: Solar hot water panels and a power cut...
PostPosted: Tue Jul 19, 2016 10:47 am 
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Hardworkinghippy is the person to ask, Datz - she's very knowledgeable about living with solar panels !
Don't forget that in winter, if the panels get covered with snow ....

But power cuts affect anyone who has electricity, even gas, if it's to run a pump or switch ! We had a back boiler in our wood-fired cuisinière which meant we never had a problem.


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 Post subject: Re: Solar hot water panels and a power cut...
PostPosted: Tue Jul 19, 2016 8:59 pm 
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Location: Between Bergerac and Périgueux in the Dordogne 24
Blaze,

It's true, snow can be a problem in flat plate collectors - solar photovoltaic panels have the same drawback but in the Dordogne the snow doesn't last long. We've 450 watts of photovoltaic panels on top of the terrace which can be cleared of snow from the upstairs windows and they're enough keep us supplied with electricity for lights, music and a bit of internet for a couple of days after a snowfall until the other panels are clear.

In the newer evacuated heat pipe tubes the gaps between the tubes normally allow snow to fall and for ice to slide through the collector even though the tubes may only be a few degrees above the surrounding temperature.

Datz,

As they're on the roof, I'd imagine your panels are run by a 220v pump which obviously stops when there's no electricity.

I'm sure a respectable firm would supply panels which are built to withstand the heat build up in the manifold on a sunny day and I expect that they're guaranteed to withstand extreme conditions.

The problem is that if there's a power cut, you've no hot water. (I always it's a good idea to think about things like that when you install a system.)

If you have regular power cuts and your panels suffer as a result, you could, depending on your guarantee (And the after sales service), suggest that the company supplies you with a DC pump and installs a small solar panel next to the tubes to run the pump independently of the electricity supply.

A DC pump can be connected to the differential sensors in the system (Which operate it when the temperature of your hot water is lower than the temperature of the water coming from the collectors) in exactly the same way as an AC pump.

Irene

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 Post subject: Re: Solar hot water panels and a power cut...
PostPosted: Tue Jul 19, 2016 10:56 pm 
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hardworkinghippy wrote:
1. I'm sure a respectable firm would supply panels which are built to withstand the heat build up in the manifold on a sunny day and I expect that they're guaranteed to withstand extreme conditions.

2. A DC pump can be connected to the differential sensors in the system (Which operate it when the temperature of your hot water is lower than the temperature of the water coming from the collectors) in exactly the same way as an AC pump.

Irene


1. Not always, some need a solar cover/roller blind to lower the heating effect.

2. An AC pump could still be powered from a DC supply via an inverter, at least for a short while but a low voltage DC pump is probably the preferable option.

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 Post subject: Re: Solar hot water panels and a power cut...
PostPosted: Fri Jul 22, 2016 9:23 pm 
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When looking at solar panel installations, 40 odd years ago, the company fitting them said , that the temperature could reach 250°c in a panel without water/heat transfer fluid being circulated, I thought that it was a bit of a Mickey Mouse company, half inch copper tubes being hard soldered to a sheet copper backing plate, mat black painted, and no proper cylinder heat probe, just a couple of different metallic wires twisted together and taped to the cylinder, for the heat sensing device

When I asked my son, who does install solar heating panels, what would happen if the sun was out and there was a power cut, his first words were, "your a bit bolloxed then"

Now days the set up is a bit more sophisticated, whilst the vase d'expansion will take up a bit of the expansion of the fluid, if there is a power outage, there is also, or should be an over pressure valve, set at 6 bar, close to the cylinder and control panel, which will or should let the over pressurised fluid run into a container

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 Post subject: Re: Solar hot water panels and a power cut...
PostPosted: Fri Jul 22, 2016 9:36 pm 
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That's true Peake, the evacuated tube problem is that as you said the solar collectors get so hot many of the manifold parts degrade/melt.
I roller blind as a sun shade can easily stop that happening and the roller blinds als protect the tubes in a hailstone situation.

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 Post subject: Re: Solar hot water panels and a power cut...
PostPosted: Fri Jul 22, 2016 10:42 pm 
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Our hot water has flat plate solar collectors and so far this summer we have been away 3 times. OK, no power cuts so far, but all we do as we drive out of the gate is to turn off the water main to the house. The system is left as it is when we are here. when we return and I turn the water back on there is almost always some water shoot through into the hot tank. that means that the over pressure valve has blown and let water out of the system.

The panels were installed some 30 years back. They are at ground level and I do not bother to cover them as I don't believe it necessary.

Our pool is a different matter. We have solar tubes, 50 of them, on it and when we go away I have a cover for each frame. Dead simple to use and I fitted caravan awning channel along the collector box and had covers made from the same stuff used on the truck sides. That heavy weight plastic material and it works a treat. The reason for that is because one time we had a power failure in one summer and the heat generated by the tubes built up so much it softened the pool 50mm plastic tubing to an extent where it loosened the fittings and would have started to empty the pool. It also warped that plastic tubing!

These are the covers

Image

And the tubes before they were expanded from 30 to 50 tubes

Image

I forgot to say that the manifold on our tube system is all braised copper and compression fittings on the pipe work to the heat exchanger. It's the pool side we have to be careful about. The plastic bits!!

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 Post subject: Re: Solar hot water panels and a power cut...
PostPosted: Sat Jul 30, 2016 4:43 pm 
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Thanks for all the great advice. We do have a pipe coming off into an empty jerrican so I guess we are covered!

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