# Electric water heater versus solar panels



## p9cbs

Hi all,
We recently purchased a house just outside Tomar. We are renovating the property and have lots to do (no surprise there). We are learning as we go and thankfully have received lots of help and support on this forum- thanks so much.

My next mission is to get some hot water at the house (amongst other things). We are having no gas no boiler and no heating (except a wood burner). It is just a holiday home and we will use it mainly in the spring and summer months.

I had planned to buy a large 200L basic water tank approx 300 euros BUT a friend who lives out there has suggested we buy a thermo water tank 1000 euros that we can later rig up to a solar panel to save on electricity. We do intend to have a small pool in the future.

Does anyone have any useful experiences or advice? How much extra will it cost to rig up a solar panel in the future. I have to consider the overall cost of materials and installation against the money we might save on electricity if we only use the house for a max of 12 weeks a year. Also what happens to all the energy generated by the solar panel when we are not at the house??

Any thoughts/suggestions/ideas gratefully received.


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## p9cbs

I have just been reading through lots of past posts about solar power. Apart from it all being very complicated it also sounds very expensive to get it all installed in the first place.


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## Verinia

Solar is extremely useful to heat water, it saves us huge amounts on our gas bil every year and it's free! Also, if you're getting a log burner stove, I'd get one with a back boiler connecting into the storage tank for the water so it tops it up on days when there is no sun. All free heat . You could even run a radiator off it to raise the ambient temperature.


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## oronero

Are you after solar heated water or solar generated electricity?

Do not confuse yourself between the two as they are quite different things and each operates in a different way.


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## travelling-man

We looked at solar hot water & I just can't see how it's financially viable........ gas it as cheap as chips & works year round without worries.


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## oronero

My grandfather had solar hot water at his house in Portugal, this was in the 70's, it was great....consisted of coils of black water pipe lying on the roof. It worked!

Solar water heating does not generally get the water hot enough to heat a house during a UK winter, though it will get water hot enough to wash with and certainly heat a pool during the summer.


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## Strontium

The simpler way is to use a passive direct solar water heater, this consists of a collector plate with a water tank above it in one unit, no pumps no electricity, water main input at the bottom and hot water out the top and is know as thermosyphon. This preheated hot water is used as the input for bottle gas powered direct water heater. The system is simple and effective, when you don't use hot water it doesn't cost anything to run, the gas only heats the hot water you use if the temperature of the water from the solar collector is below the set point.


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## p9cbs

Thank-you all for your replies and interesting information and experiences. After much debating, we are going for a simple electric water heater for now with a view to look at solar energy in the future once the house is up and running.


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## MrBife

I am a disbeliever in the local version of Solar Water heating ideas as local suppliers charge way too much - usually 1000's and the payback time calculations just don't stack up. 

However there is a lot to be said for spending a couple of hundred or less on something like this and bringing it in yourself ..

Evacuated Tube Panels - Solar Panels (Water Heating) | Navitron Green Energy

Then just incorporating it into a simple system with an electric immersion heater or gas heater as a secondary source/backup.


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## Deithrian

If you're using the house for only 12 weeks, I'm not sure how much worth you will get out of installing systems that need years of constant use to return on investment.
Isn't it more important to have systems that are more maintenance free and dependable, so you can enjoy your holiday when you get there?

I have a friend with both solar water heater and a burning "stove" connected with radiators to heat the house.
Both systems use water as means of transporting the heat.
It all sounded like a fairy tale when they first installed those systems and had huge decrease in electrical bills.
Then came things like "the chimney caught on fire and I had to climb the roof to poor water in it with a garden hose", and "the temperature sensor for the solar panel broke and the water pump didn't work and ....".

I'm not saying those systems are bad, but they're not for everyone. 
As far as I know electric solar panels are expensive and need converters and batteries to store power, all of these components go bad and need replacement with time.

I'm not against solar heating or solar electricity, but for a 12 weeks in a year are they worth it?

All things said, I absolutely love my small Goal Zero solar panel, I can charge my phone anywhere I go in about 20 minutes, but I have it for "just in case" (definitely get one of these!). 

What I'm trying to say is, is it worth it?
Initial cost?
Installation cost?
Maintenance cost?
Replacement of components cost?

I'm not sure I would bother with all that for a 12 weeks in a year place 
just my personal (not so well informed) opinion :wave:


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## Strontium

MrBife said:


> I am a disbeliever in the local version of Solar Water heating ideas as local suppliers charge way too much - usually 1000's and the payback time calculations just don't stack up.
> 
> However there is a lot to be said for spending a couple of hundred or less on something like this and bringing it in yourself ..
> 
> Evacuated Tube Panels - Solar Panels (Water Heating) | Navitron Green Energy
> 
> Then just incorporating it into a simple system with an electric immersion heater or gas heater as a secondary source/backup.


Be careful with that idea, the evacuated tube collectors are highly efficient and usually used as part of indirect sealed system with pumps/ controller and heat exchanger all filled with antifreeze/summer coolant like an automobile's engine. The heat exchanger is inside aa hot water tank They can produce internal heated liquid over 100C and are not suitable for the un-initiated to install due to structural roof mounts + electrics + water + scolding heat.


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## HeyBubbles

I have to agree with the last post.

We lived just north of Tomar and we installed solar panels with an esse woodburning stove and an electric immersion heater, all connected into one storage tank. Very efficient all year round but for just 12 weeks not worth it. Only used the immersion heater once. 

I would still consider gas over electric as for water heating electric is the most expensive method in Portugal. A simple wall mounted gas boiler that produced direct hot water would be my recommendation.


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## MrBife

Fully agree with the last two posts - definitely a project for an experienced pro plumber that knows his stuff. Not recommended for a DIY first timer.


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## longbow

I have read the above with interest and if your interested in solar then why not research 12v immersion heater, basic principle is you wire the immersion to your dump switch and excess energy is diverted to water heating. A cheaper option, most people would require two heaters I think


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## baldilocks

Instead of all the theory and speculation that seems to be going on in this thread.

Forget the solar panel for electricity that some have mentioned, that is not what you need and is very costly.

A simple water heating solar panel is passive and doesn't need any electricity to run. Avoid the type that has the hot water storage tank on the outside of the roof - that's a lot of extra weight on the roof. A simple tank inside the roof is far better, it is protected from freezing in the winter when you may not get much hot water from the panel. 

The panel itself and the primary coil of the tank (this is the tube from the panel) carry a mixture of water and antifreeze) are protected by antifreeze. The primary coils carrying hot water from the panel heat the water in the tank and this secondary water is what you use (no antifreeze!) For those times when there is not enough heat in the sun to heat your water, you need another heat source and the cheapest is to use a gas fired instantaneous water heater that only heats the water that you need and when you need it. It is like an Ascot and can feed several outlets in the house (basins, showers, baths, sinks - but not all at once) and because it only heats the water that you use, it is economical. If you are not on mains gas, they will run off the 15kg gas bottles and in fact when I lived in Wales I ran central heating off the 45kg bottles. If you can get a water heater that will accept heated water and only fire up if the water is below a certain temperature, great but they can be a lot more expensive. The system we use is changeover valves which we turn over manually to either panel or boiler.

Forget immersion heaters - they are probably the most expensive way to heat water because not only do they heat the water using the most expensive fuel they keep the water in the tank hot whether you are using it or not. You do not need any pump to move the water from the panel to the tank as has been suggested, hot water rises and will flow through the panel to the tank by itself, provided you have a well thought out system.

If you are able to use a log-burner with a back boiler for heating as well as the primary source for hot water, all well and good but bear in mind that you will have to have the log burner going when, perhaps, you wouldn't otherwise use it. 

What we have, as you may have gathered from the foregoing is a solar panel and an instantaneous water heater. The water heater has a couple of U2 (D) size batteries which supply all the electrics that the water heater needs and last about 5 years. This set up supplies two bathrooms (1 on the lower ground floor, 1 on the first floor) and the kitchen on the ground floor and a secondary kitchen plus washing machine on the lower ground floor. The tank is in the attic (second floor) under the roof. We also have a log burner which heats about half the house using hot air ducts and also the attic by drawing heated air from the chimney void.


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## SpiggyTopes

baldilocks said:


> What we have, as you may have gathered from the foregoing is a solar panel and an instantaneous water heater. The water heater has a couple of U2 (D) size batteries which supply all the electrics that the water heater needs and last about 5 years. This set up supplies two bathrooms (1 on the lower ground floor, 1 on the first floor) and the kitchen on the ground floor and a secondary kitchen plus washing machine on the lower ground floor. The tank is in the attic (second floor) under the roof. We also have a log burner which heats about half the house using hot air ducts and also the attic by drawing heated air from the chimney void.


Hi,

The system you describe is exactly what we are thinking about. Simplicity is important here!

We have an ancient lpg water heater (no electronics) which works well and we have been advised not to replace it with modern, even if the new ones are more efficient.

If I understand correctly, the solar panel only heats the water in the tank and you switch over to the water heater when the tank is too cold. The panel water feeds a heating coil in the tank

Is the heating water from the panel pumped to heat the tank storage?

Cheers.


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## baldilocks

SpiggyTopes said:


> Hi,
> 
> The system you describe is exactly what we are thinking about. Simplicity is important here!
> 
> We have an ancient lpg water heater (no electronics) which works well and we have been advised not to replace it with modern, even if the new ones are more efficient.
> 
> If I understand correctly, the solar panel only heats the water in the tank and you switch over to the water heater when the tank is too cold. The panel water feeds a heating coil in the tank
> 
> Is the heating water from the panel pumped to heat the tank storage?
> 
> Cheers.


Not on ours which operates on the thermosyphon principle. The tank is a little higher than the panel so the fluid* from the panel rises to the inlet at the top of the storage tank where it cools as it transfers heat to the water in the storage tank, then exits from the lower connection on the storage tank back to the bottom of the panel where the heat imparted to the fluid (from the sun) starts the fluid on its journey again.

* I have used the word fluid which in this case consists of water + antifreeze to avoid confusion with the potable water in the storage tank which you are going to use.

https://en.wikipedia.org/wiki/Thermosiphon
The picture shows the hot water being drawn off the primary supply (i.e. direct from the panel) which is not the case where you have antifreeze in the primary circuit to prevent damage to the panel in the event of a frost. Freezing may be rare where you live but on the odd occasion, it could be very expensive if you didn't have a system with anti-freeze in the primary circuit (panel + primary coil of the tank.)


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## Strontium

SpiggyTopes said:


> Hi,
> 
> The system you describe is exactly what we are thinking about. Simplicity is important here!
> 
> We have an ancient lpg water heater (no electronics) which works well and we have been advised not to replace it with modern, even if the new ones are more efficient.
> 
> If I understand correctly, the solar panel only heats the water in the tank and you switch over to the water heater when the tank is too cold. The panel water feeds a heating coil in the tank
> 
> Is the heating water from the panel pumped to heat the tank storage?
> 
> Cheers.



The usual way is to use the rising main solar heated water as the water supply to your lpg water heater with pre-heated water at rising main pressure. The lpg water heater, even an old one with bi-metallic strip heating control, should regulate on demand the temperature of the hot water to a set point (maybe 50C) supplied to your taps. If your solar heated water temperature is high enough the water will pass through the lpg water heater without it firing up. If you solar water is below 50C it will fire up but still only heat the water to the taps to 50C. This is all flow and lpg boiler heat output dependant. Find a local plumber or two and they will go through it with you and give you a price .


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## SpiggyTopes

Strontium said:


> The usual way is to use the rising main solar heated water as the water supply to your lpg water heater with pre-heated water at rising main pressure. The lpg water heater, even an old one with bi-metallic strip heating control, should regulate on demand the temperature of the hot water to a set point (maybe 50C) supplied to your taps. If your solar heated water temperature is high enough the water will pass through the lpg water heater without it firing up. If you solar water is below 50C it will fire up but still only heat the water to the taps to 50C. This is all flow and lpg boiler heat output dependant. Find a local plumber or two and they will go through it with you and give you a price .


Thanks, that would be less costly than a storage tank.

There is a control on the heater but I thought it just reduced the gas supply to the burner. At present, I adjust this control so that we shower only using the hot tap (that is, not adding any cold and having to fiddle with the cold tap).

I'll try to find a good plumber .... I would love to find one I could have a sensible, technical discussion with!

Cheers.


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## Strontium

SpiggyTopes said:


> Thanks, that would be less costly than a storage tank.
> 
> There is a control on the heater but I thought it just reduced the gas supply to the burner. At present, I adjust this control so that we shower only using the hot tap (that is, not adding any cold and having to fiddle with the cold tap).
> 
> I'll try to find a good plumber .... I would love to find one I could have a sensible, technical discussion with!
> 
> Cheers.


Without seeing your installation this may not apply. On an lpg water heater there is often a set point control to vary output water temperature which works by changing the amount of gas supplied for the heating flame and the set point should have a range from tepid to very hot but not scolding . This is a safety thing so should be part of the lpg heater design. If the water coming into the lpg heater is already preheated then less gas will be used to bring the water to the set point. If you had solar perheated water at rising main pressure going into your lpg water heater then the only difference you would notice would be using less gas to get hot water from shower or tap. I don't know your area but if you see a passive solar water system, heater plate with integrated tank, locally to you then just go and talk to the house holder about it, the system does not need to be on a roof but can be ground level in many cases in Portugal.


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## SpiggyTopes

Thanks so much ..... it is a lot clearer now.


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## baldilocks

SpiggyTopes said:


> Thanks, that would be less costly than a storage tank.
> 
> There is a control on the heater but I thought it just reduced the gas supply to the burner. At present, I adjust this control so that we shower only using the hot tap (that is, not adding any cold and having to fiddle with the cold tap).
> 
> I'll try to find a good plumber .... I would love to find one I could have a sensible, technical discussion with!
> 
> Cheers.


You would still need the storage tank - a solar panel doesn't heat the water to 40° or more instantaneously.

To save fiddling with the taps to get the temperature right for the shower just fit a thermostatic control - this is what we have and it automatically adjusts the amount of hot or cold needed to achieve the desired temperature.


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## SpiggyTopes

I do think, on reflection, that we should have a storage tank as we have an annex which we're going to let out for holidays, and a tank would give a more balanced supply to us and our guests.

So, it would be:

+ flat solar panel on roof (that is the type without the tank)

+ solar panel and gas water heater connected to heating coil in storage tank

+ storage tank in roof space, supplying house and annex through discrete pipes.

The only slight problem is that the heating of the water would be manually switched for solar or gas, unless the storage tank had 2 coils.

Is that about it?


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## baldilocks

SpiggyTopes said:


> I do think, on reflection, that we should have a storage tank as we have an annex which we're going to let out for holidays, and a tank would give a more balanced supply to us and our guests.
> 
> So, it would be:
> 
> + flat solar panel on roof (that is the type without the tank)
> 
> + solar panel and gas water heater connected to heating coil in storage tank
> 
> + storage tank in roof space, supplying house and annex through discrete pipes.
> 
> The only slight problem is that the heating of the water would be manually switched for solar or gas, unless the storage tank had 2 coils.
> 
> Is that about it?


NO. 

The gas water heater supplies hot water direct to the taps and only comes on when the tap is turned on. 

The tank will be heated by the solar panel. The water supply to the boiler will come from the tank so that when the water in the tank is already hot, the boiler will not light and the hot water will just pass through. In the event that it has been cloudy for a few days or there has been extravagant overuse of the hot water so that what is in the tank is cold or cooler than the setting on the boiler, then the boiler will fire and heat the water.


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## Strontium

I have not drawn any safety devices, isolators etc to simplify it.

For places where the water doesn't freeze outside.











For places where water does freeze outside.


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## stevensuf

I would agree with other who say forget about roof mounted solar hot water and immerser tanks, a simple gas boiler (esquentador) 150 euro for a cheap one will do the job just fine.

I am against others who say forget about solar electric, just now the payback on it is very short and you say you may add a pool which will require a pump which will eat up a fair amount for electricity when you are not there. 

A simple 250w panel with a cheap inverter (and you can now self install (autoconsumo)) should cost you about 250 euros, this will generate around 70 euros of electricity a year , pay back just over 3 years if you are capable of installing yourself.


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## christopherdouglas

This is such a brilliant thread ?
Can I ask how this would work on a gravity fed water system?
Cheers, Chris


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## VinhoVerde

Can I ask about heating possibilities without using circulating fluids, trombe wall for example?


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## MrBife

VinhoVerde said:


> Can I ask about heating possibilities without using circulating fluids, trombe wall for example?


There are plenty of these (search Youtube for 'Soda Can Heater' and you will see a hundred videos showing ideas being slowly perfected over the last 8 or 10 years). Trombe wall never really seemed to catch on at least in Iberia but that is probably because upcoming Architects and Engineers never explored it but more importantly its not ideal for the type of heating requirements here and by my calculations the recently newer available technology supersedes it.

Residents of Portugal need energy as much (maybe more) for cooling as for heating and if you add in 1kw of pool pump then the calculations make more sense to generate power and use it yourself (no batteries or grid tie to worry about).

Passive air heating or solar water heating functions when solar (Photo Voltaic) panels would also work best. Sadly the former are a bit 'old tech' now.


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## VinhoVerde

MrBife said:


> There are plenty of these (search Youtube for 'Soda Can Heater' and you will see a hundred videos showing ideas being slowly perfected over the last 8 or 10 years). Trombe wall never really seemed to catch on at least in Iberia but that is probably because upcoming Architects and Engineers never explored it but more importantly its not ideal for the type of heating requirements here and by my calculations the recently newer available technology supersedes it.
> 
> Residents of Portugal need energy as much (maybe more) for cooling as for heating and if you add in 1kw of pool pump then the calculations make more sense to generate power and use it yourself (no batteries or grid tie to worry about).
> 
> Passive air heating or solar water heating functions when solar (Photo Voltaic) panels would also work best. Sadly the former are a bit 'old tech' now.


Thanks. I'm thinking to avoid wires and pipes and provide some heating of the house in winter without worrying about short circuits, leaks, and toxic substances. Seems to me that some careful planning might work, perhaps.


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## Strontium

christopherdouglas said:


> This is such a brilliant thread ?
> Can I ask how this would work on a gravity fed water system?
> Cheers, Chris


Hi,

Most water systems are gravity fed from a local or district water tower header tank but I suspect you mean something else. Please explain the situation, do you mean a house with a cold water header tank in/on the roof or in/on a nearby roof?


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## baldilocks

stevensuf said:


> I would agree with other who say forget about roof mounted solar hot water and immerser tanks, a simple gas boiler (esquentador) 150 euro for a cheap one will do the job just fine.
> 
> I am against others who say forget about solar electric, just now the payback on it is very short and you say you may add a pool which will require a pump which will eat up a fair amount for electricity when you are not there.
> 
> A simple 250w panel with a cheap inverter (and you can now self install (autoconsumo)) should cost you about 250 euros, this will generate around 70 euros of electricity a year , pay back just over 3 years if you are capable of installing yourself.


Agreed, generating the stuff is easy peasy but what do you do when you've got more than you need (such as during the day) and not enough at a different time (such as evening and night? It is the storage that costs the money.


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## MrBife

baldilocks said:


> Agreed, generating the stuff is easy peasy but what do you do when you've got more than you need (such as during the day) and not enough at a different time (such as evening and night? It is the storage that costs the money.


You use it to heat an insulated tank full of water that will stay hot for 12 hours, you run your pool pump, you run your air conditioning system, you run your borehole pump, you put on the washing machine or dishwasher. No problem to make use of 'free power'. No storage needed

If you want to sit and watch TV with the (low energy LED) lights on at night then just buy in that small amount of energy whenever you need it.


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## baldilocks

MrBife said:


> You use it to heat an insulated tank full of water that will stay hot for 12 hours, you run your pool pump, you run your air conditioning system, you run your borehole pump, you put on the washing machine or dishwasher. No problem to make use of 'free power'. No storage needed
> 
> If you want to sit and watch TV with the (low energy LED) lights on at night then just buy in that small amount of energy whenever you need it.


I just heat my tank full of water using a solar panel and it keeps hot for several days, no need for any electricity. Using any form of electricity to heat water and then keep it hot is so wasteful. If you follow the Moorish way, you don't need air-conditioning.


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## Strontium

MrBife said:


> You use it to heat an insulated tank full of water that will stay hot for 12 hours, you run your pool pump, you run your air conditioning system, you run your borehole pump, you put on the washing machine or dishwasher. No problem to make use of 'free power'. No storage needed
> 
> If you want to sit and watch TV with the (low energy LED) lights on at night then just buy in that small amount of energy whenever you need it.


Hi, Have you any numbers to go with this system, number of panels, size of panels rated max output, actual output, inverter rating etc?? If you are looking at running Aircon or white goods directly from panels with water heating etc. involved then that's quite a power drain the panels need to supply and keep running without an interruption so usually some electrical storage would be used to cover reduced power periods. PV panels struggle to 15% efficiency and this drops off with temperature where as directly heated solar hot water is more efficient (less flexible) simpler and cheaper and doesn't need a licenced electrician to hook it up. Here are some quite old but still working solar hotwater amateurish installations we inspected last week. We are trying to find a few "typical" passive systems to hook data loggers to get a fuller picture of available energy vs area vs useage vs time.


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