Solar Power and Combi boiler

[Clark]

Hi there,

I want to know how I can use combi boiler with my solar PVs. Will my heating elements be affected?

Thanks

[vtsnowedin]

Hi there,

I want to know how I can use combi boiler with my solar PVs. Will my heating elements be affected?

Thanks

If your solar PV system is set up right the power heading out to any light or appliance will be the right voltage and cycle for the country you live in. just a matter of having the correct inverter between the batteries if you have them or the panels and your circuit breaker panel.

[nicknel]

Hi

There is another way to resolve this. However it would involve additional work and money which is worth. You can have a storage tank at the inlet of the combi-boiler which actually takes in cold water. To this you could have a power diversion switch like solarimmersion installed. This device heats up the water with the immersion heater and supplies it to the boiler. As the water is already hot the boiler need not turn on.

[briantodd]

Here are two diagrams and some advice to solar plumbers considering fitting a solar water heating system to a combi boiler. I hope so it will be helpful for you.





ADVERT DELETED

[emordnilap]

Thanks briantodd.

One thing that's missing is the pump to bring the thermal store water back up to mains pressure.

We have one on our system but rarely use it - it's far too powerful for normal use. Even for the shower, we rely on gravity feed.

[vtsnowedin]

Thanks briantodd.

One thing that's missing is the pump to bring the thermal store water back up to mains pressure.

We have one on our system but rarely use it - it's far too powerful for normal use. Even for the shower, we rely on gravity feed.

If I'm reading those diagrams right the solar water in the panels is isolated from the mains supply and the heat is transferred to the domestic supply via a coil inside the storage tank. Therefor there is no need for that water to ever be brought up to the mains pressure.
If I was installing this I would seek to have the storage tank as high or higher then the top of the panels to allow thermo-syphon circulation and not try to pump hot water down to the tank or at least reduce the energy needed to achieve circulation. Note also that pressure relief valves are not shown which are more essential then the tempering valve.

[adam2]

Be aware that most of this thread consisted of adverts. Note the 3 contributions made by members each having just one post, and each originally trying to sell something.

[emordnilap]

Be aware that most of this thread consisted of adverts. Note the 3 contributions made by members each having just one post, and each originally trying to sell something.

True but the diagram is interesting and relevant.

[emordnilap]

If I'm reading those diagrams right the solar water in the panels is isolated from the mains supply and the heat is transferred to the domestic supply via a coil inside the storage tank. Therefor there is no need for that water to ever be brought up to the mains pressure.

vt, it's a Solartwin - we have one, the water you heat is the water you use; water is taken from the bottom of the tank, heated and returned to the top of the tank. A solar-powered pump moves the water. It all works without mains power.

It suits our way of life and (so far, 7 years on) maintenance/intervention free.

If I was installing this I would seek to have the storage tank as high or higher then the top of the panels to allow thermo-syphon circulation and not try to pump hot water down to the tank or at least reduce the energy needed to achieve circulation.

It works here in Ireland because many houses are single-storey, meaning getting the tank higher is difficult; hence the 5 volt solar pump. Also, the water only needs to move very slowly. The stronger the sun, the faster the pump runs.

Note also that pressure relief valves are not shown which are more essential then the tempering valve.

A pressure relief valve is not needed in the solar system - perhaps you're thinking of some other part. The Solartwin system allows very high and extremely low temperatures and no draining in winter. You can let it freeze, in fact.

It doesn't suit everyone and is a less efficient system than many but as I say, it fits in perfectly with our requirements. The aluminium is produced using hydro power too, a small bonus.

[vtsnowedin]

I'm just going by what is drawn so cannot argue with or about your actual system. What is drawn shows a boiler or water heater of some sort on the right. That part needs a temperature/ pressure relief valve on it at the point where water would be hottest.
The zig zag line in the thermal storage tank indicates an interior coil that keeps the water in that tank from mixing with the domestic mains supply. I have one of these tanks in my hot water system (80 gallons). As drawn you could have non toxic antifreeze in the solar collector water which is what is needed here in cold climates.
Remove the zig zag line or coil and let the water intermix and you have what you describe. One would assume that the vent for the thermal storage tank would be at the highest point in the system and would be combined with an automatic air release to preclude the solar loop from getting air locked, another PRV should be located next to it. Also A cold feed refill line would need to be run from the mains to the solar collector but that could be accomplished with a garden hose and tap.
And yes the roof is where it is and the water tanks and boiler are usually in the basement so a pump is usually required.

[emordnilap]

Yes, the zig-zag line is confusing me too. It looks like it's a mistake, it shouldn't be there at all and the exit pipe to the hot tap should be at the top. I see now what you were referring to with the relief valve.

As for anti-freeze, the Solartwin (as shown and in my system, that's the real way it works) doesn't use it. The water in the panel and pipes is allowed to freeze in winter, if it's that cold. It does no harm.

[vtsnowedin]

Yes, the zig-zag line is confusing me too. It looks like it's a mistake, it shouldn't be there at all and the exit pipe to the hot tap should be at the top. I see now what you were referring to with the relief valve.

As for anti-freeze, the Solartwin (as shown and in my system, that's the real way it works) doesn't use it. The water in the panel and pipes is allowed to freeze in winter, if it's that cold. It does no harm.

I've fixed more then my share of burst from freezing water pipes. Even with the most flexible plastic I would avoid it if possible or protect the pipes with antifreeze. The non toxic type they use in Caravans (RVs to me) works fine.

[emordnilap]

No, it's not plastic, it's food-grade silicon rubber piping throughout the whole system and can expand up to 100% - water typically expands a few percent (5%?) when frozen. The water heated is the water you use.

[Tarrel]

Nothing wrong with the zig zag line. Water under mains pressure would normally feed into the combi-boiler and be heated instantaneously as it flows through to the taps. The system as shown is merely pre-heating the water before it enters the combi-boiler so the boiler has less work to do, if any.

I doubt it would be beneficial to have mains-pressure water intermixing with the solar-heated water in the tank. I doubt that the Solartwin system would be designed to take that sort of pressure, though I may be wrong and, of course, it depends how high the mains water pressure is.

Our domestic hot water is heated in the same way. Water under mains pressure passes through a coil in our thermal store (big, stratified hot water tank) when called by the bath, shower, basin or kitchen sink. We keep the thermal store at 70-80 degrees C, and the hot water is hot and plentiful. Our thermal store is heated by three potential sources; the solid fuel Rayburn, an oil boiler and an electric immersion heater. The oil boiler is a combi boiler, but we elected to disconnect the hot water side and have the thermal store fed by the "central heating" side. The boiler kicks in automatically if it senses that the temperature in the store has dropped below 70 degrees. This can happen if either:
- The Rayburn is not lit, or is not hot enough, or
- There has been high demand for hot water and / or radiators.

The Rayburn can't keep up if we have everything running flat out - radiators turned up and using lots of hot water.

We have an additional coil ready and waiting in the thermal store for solar collectors should we wish to add them at some point.

ETA: none of this is relevant to the OP, who was asking about solar PV, not solar thermal.

[vtsnowedin]

Nothing wrong with the zig zag line. Water under mains pressure would normally feed into the combi-boiler and be heated instantaneously as it flows through to the taps. The system as shown is merely pre-heating the water before it enters the combi-boiler so the boiler has less work to do, if any.

Yes there is nothing "wrong" with the zig zag line it is just how they depict a coil inside a tank that's contents are isolated from mixing with the contents of the tank and can be at a separate pressure. I merely pointed it out as the written description of the system did not agree with the drawing.
Even if your solar collectors could work at your mains pressure you might want to maintain the separation as it would guard against a leak in your system leading to a major loss of metered/billed mains water. Here in Vermont solar thermal panels usually have non toxic antifreeze in them and that of course needs to be kept isolated from your consumable water supply.