# Solar water heating



## Strontium

I am looking at the options of installing Solar water heating of the passive direct type where the tap water is in pipes/panels laid on a roof and heated by the sun directly. Has anyone got this system and any data on the water temperature, time of year and flow? 

Thanks


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## MrBife

I have had Solar Hot Water and indeed Solar Heating power Heating (UFH) through the house and have had for a while. We definitely have a more comfortable life because of it I am not sure whether in hindsight we shouldn't have gone for Solar Photovoltaic power and use it when required to heat hot water with an immersion heating coil and the rest of the time for cooling (Running A/C equipment) and running pool pumps etc.

I don't think there is much value in storing PV Power or selling it back to the grid but if you can generate 4kw or even 5 and use it correctly then that has to be one of the most efficient options.


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## In 2 bikes

love our solar hot water system but its the type that has a closed circuit and heats a large tank of water, a bit like an immersion tank or huge kettle. It supports the same hot water / central heating as the pellet burner. If the sun doesn't get the water hot enough the burner kicks in. Brilliant..


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## Strontium

MrBife said:


> I have had Solar Hot Water and indeed Solar Heating power Heating (UFH) through the house and have had for a while. We definitely have a more comfortable life because of it I am not sure whether in hindsight we shouldn't have gone for Solar Photovoltaic power and use it when required to heat hot water with an immersion heating coil and the rest of the time for cooling (Running A/C equipment) and running pool pumps etc.
> 
> I don't think there is much value in storing PV Power or selling it back to the grid but if you can generate 4kw or even 5 and use it correctly then that has to be one of the most efficient options.


PV has the problem of matching supply to demand and you'd struggle to get PV working at 10% efficiency (though this is slowly getting better) as it can only uses a select range of frequencies of the incident solar energy and then there are conversion losses which will make it even less efficient for heating water whereas direct solar hot water uses a larger amount of the incident solar energy so is a lot more efficient at heating water. This make the installation smaller and it can be simply used as a direct water input to existing gas/oil/wood hot water systems with no modifications. And then there is the cost.


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## MrBife

To clarify a little ...

PV is only inefficient if you are saving it to batteries but in my book that is a complete waste of time and resources (unless you have no mains connection or other option).

The latest generations of Photo Voltaic panel are much more efficient and much cheaper than they ever were. As a guide the installation cost is less than 1 euro per watt. So to put up an array to provide 4kwh is €4000. Efficiency does drop by around 10% over the lifetime of the panels which all being well is 20 years. Just add another panel to ensure you achieve design output.

The newest variety generate 320w each so close to 4kw from just twelve panels which keeps the installation a lot smaller. 

Main consumption of power in the standard Portuguese Home is not domestic hot water. I used to run a gas water heater for that and only ever used five or six small size gas bottles a year - at current cost that would still be under 160 euros a year.

Buying a solar water heater is going to cost at least 3500 euros and you will probably still need to leave the gas heater in place as a top up during winter cloud. So a payback time of around 20 years.

The main energy requirements in Portugal are for 

Cooling in Summer
Pumps (pool circulation, house water pressure, borehole)
Domestic Appliances (Washing Machine, Dishwasher etc)

4 Kw carefully managed will run all those things for nothing and still leave enough to power an immersion heater.

With 3000 hours of sunshine each year the potential is there to generate up to 3000 x 4kw = 2000 euros worth of free power.

Much faster payback time of two or three years and a lot more flexibility.

Personally I am not worried about using a room full of expensive batteries to store power, I can use all I generate. The buyback tariff has been eroded to parity and may go down further so there is no point in selling any back to EDP. A user would plan to buy power at night to run low energy/LED lights and to top up any peak requirements.


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## Strontium

No, I am asking about Solar water heating of the passive direct type which are ubiquitous in Asia and sold here for 150 -250 euro and absorb a greater proportion of the solar spectrum than PV so are inherently more efficient at solar energy conversion. So I am looking for information about the collector size/type and temperature of inlet and outlet and usage in a real world Portuguese installation. PV typically uses a maximum of 35% of the solar spectrum and only a minor proportion of that is converted as most of the useful incident photons have to loose energy as heat during the PV process.


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## Centralbound

Strontium said:


> 150 -250 euro etc etc more efficient etc etc real world Portuguese installation


A couple of your electrons may be failing to tunnel. 

If you put €250 of solar thermal on your roof, buy a nice ladder as well cos you will be up there a fair bit fixing it. A small stainless number with european quality valves, fittings and mountings would cost close to €1500. That buys a lot of butane. They don't last well either.

The point of PV without batteries made by MrBife is economics. Hot and cold daytime AC most of the year is worth the investment, solar thermal HW is not. Plus once you have a couple of kWh going spare you can start to get all Heath-Robinson. Storage heaters, remember them...?


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## Strontium

A passive direct type solar water heater has no valves or pumps and is often plumbed between the rising main and a gas water heater. It works by thermo-siphon with cold water entering at the lowest point and a water tank at the highest point all under mains water pressure. I don't understand which parts you think will need constant maintenance. We have installed many of these over the years elsewhere and just want information about the two types, pipe or plate and their size from anyone who uses them here in Portugal. Nothing to do with PV nor Air Cons.


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