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Discussion Starter · #1 ·
Sorry if this has been discussed before but we have decided to have a solar panel on our new roof.

Our old system uses a Vaillant gas-fired instantaneous water heater. Obviously, even here in Spain, there is not enough heat in the sun for the water to heat above warm or even tepid between October and March so we will need to switch to the old system during that time.

My memory from my school days says that the new system is a closed loop so, in theory, the pressure is constant in the system until a tap is opened. So, in the winter, the warmed water from the solar heater could be used as the feed to the water heater (i.e. the solar panel acts as a pre-heater) thus reducing the gas demand. HOWEVER, the fontanero who installed the solar panel says there won't be enough pressure to operate the water heater. I think that there should be, but before I get him to revise his pipework, has anybody any thoughts on this?
 

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I think that there should be, but before I get him to revise his pipework, has anybody any thoughts on this?
Not enough heat from the sun? Surely the solar panel itself is being used to generate electricity to heat the water? Are you saying there isn't enough light from the sun to produce sufficient electricity to heat the water in winter?
 

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Discussion Starter · #4 ·
Not enough heat from the sun? Surely the solar panel itself is being used to generate electricity to heat the water? Are you saying there isn't enough light from the sun to produce sufficient electricity to heat the water in winter?
I think you have your technologies confused. This solar water heater not a PV panel
 
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I've thought a bit about your plumber's remark. And although I installed solar hot water heating systems in California, the systems there & here are vastly different.

In your case the only thing that comes to mind is that if the water is running directly from the solar panel to a hot water heater, there might be a shutoff valve at the solar panel that is activated by a sunlight sensor... it's purpose would be to not allow water to pass thru the panel at night as cooler evening temperatures would lower the water's temperature before entering the water heater and thus more energy would be needed to heat the cooler water.

I hoping to read more on how this plays out for you.
 

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Discussion Starter · #6 ·
I've thought a bit about your plumber's remark. And although I installed solar hot water heating systems in California, the systems there & here are vastly different.

In your case the only thing that comes to mind is that if the water is running directly from the solar panel to a hot water heater, there might be a shutoff valve at the solar panel that is activated by a sunlight sensor... it's purpose would be to not allow water to pass thru the panel at night as cooler evening temperatures would lower the water's temperature before entering the water heater and thus more energy would be needed to heat the cooler water.

I hoping to read more on how this plays out for you.
The solar system is indirect (we get frosts here so the primary needs to carry anti-freeze). It has no pump and therefore if there is no heat input to the panel, there is no flow. The tank (160 litres) appears to be very well insulated so heat losses should be minimal. On the day it was set up, it was operational only from about 5.00 pm and there was still very warm water from the tank at 8.00 am the next morning.

What I would like to try is to take the secondary (warmed) output from the tank to the water heater in winter so that there is less gas used to heat the water to a reasonable temperature (e.g.40° C, i.e. suitable for a shave or shower) at the point of use.
 
G

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The solar system is indirect (we get frosts here so the primary needs to carry anti-freeze). It has no pump and therefore if there is no heat input to the panel, there is no flow. The tank (160 litres) appears to be very well insulated so heat losses should be minimal. On the day it was set up, it was operational only from about 5.00 pm and there was still very warm water from the tank at 8.00 am the next morning.

What I would like to try is to take the secondary (warmed) output from the tank to the water heater in winter so that there is less gas used to heat the water to a reasonable temperature (e.g.40° C, i.e. suitable for a shave or shower) at the point of use.
If you can send me a PM with a diagram of the system I might be able to sort this out for you. Do you have a "user's manual" that you could scan and send?
 

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If you can send me a PM with a diagram of the system I might be able to sort this out for you. Do you have a "user's manual" that you could scan and send?
Actually I would like to see a diagram as well.

Two thoughts; the water will have to run through a heat exchanger which might well reduce its flow rate sufficiently to stop an on-demand heater working and also there might be issues with quite hot water flowing into the heater.
 

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I have a friend with an indirect system & he has to bypass it in winter using the gas heater alone. It was installed like that by a reputable spanish plumbing firm.
I've never taken the time to have a good look at it though.
 
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