Midgo

Hi
We have a gas 'on demand' water heater
Its 17 lpm IIRC, but we only ever use one shower at once and I think the water pressure at street is usually the bottleneck anyway (whatever the Camara is legally obliged to supply ...)

I'd like to install a solar water heater (i.e. not electro-voltaic panels)

I have seen (what I presume is) these on roofs with a silver cylinder
I am guessing that the silver cylinder holds the warmed water that is then fed into the inlet of whatever water heater you have, so depending on the season / sunlight, the heater has to do more or less work?
Or I could be wrong

Anyone know how much to install and work required etc, in Portugal (and recommendations for suppliers &/or installers near Costa Caprica?)

Our house heating is totally sorted, I'd just like to use solar for hot water (and not for electricity)

We are just 3 at home, (although that includes two Alfacinhas, one of which is now a teenager )

Thanks

Dafty

I recently had a quotation for the installation of a system as you describe, with a view to moving away from gas.
The whole job, including an electrical heating element to compensate for solar shortfall, with a 200ltr tank, was 2500€.

Midgo

Thanks @ Dafty
Presumably if I wouldnt need the electric element if I just fed it into the gas heater (I like gas cooking)?
I lied - I hate cooking with gas less than I hate cooking with electricity

Also, where are you, and who gave the quote?

Cheers

Alan PT

We have one, two panels plus a 300l tank and a gas heater as backup. Don't know the cost I'm afraid since it came with the house, but it is great!

The backup almost never kicks in and we find that (even up here, in less sunny climes) we go through one of those little 30 euro gas cylinders in about 9-12 months

Midgo

Thanks Alan

I'm regretting not having one put in when we renovated the house

I am looking into it more and seems there are two options: passive (convective ) or active (pumped) circulation.

Passive is more attractive fro me - less parts to wear out, elec pump costs, dont need top efficiency - Presumably the downside of passive is you have to have the tank on the roof, which could be bad aesthetically (my wife) &/or structurally given 200l water is 200 kg plus weight of panels and tank etc (me)

Midgo

wow! if its 2.5 k and we use 2 bottles per month and a half and can go down to one per 6 months (to be conservative) then that's a simplistic payback in approx 5 years, at current gas prices!
Gas bottle savings per 6 months = (6*(2/1.5)) -1 = 7, i.e 14 bottles per year
Current price here (propane) ~ €35/ bottle
Gives yearly saving of approx €500

macliam

You'll find it difficult to get anyone to quote you for such systems..... there is a huge "blind eye" to the costs of the electrical backup as well as huge ignorance about the installation of panels. Supposedly "in the know" Portuguese I have spoken to just fit a panel at a fixed 30 degrees and let the back-up do it's thing. Usually they have absolutely no idea whether or not they are payiing for electrical backup or how much. They also have no idea that the panel angle should vary with Winter/Summer for efficiency, no idea that the angle should depend onyour latitude and an absolute belief that only a south-facing panel will work. It's like talking about magic beans......

The systems you have observed are gravity-feed systems, but they are designed to replace, not augment a gas system.... and they have an electrical element as a back-up (obviously you can disable that). There are also gas boilers sold specifically to accept hot-water input (as you would need), but honestly, I can't see why any gas heater would not accept a pre-heated input (unless it's purely a physical problem). It may be that the thermostats are more designed for the augmentation of already heated water, I really don't know.... Like you, I prefer the idea of a system that pre-heats water and that it can be boosted to the correct temperature by gas, if required, but we seem to be the minority!

If you check the installation suggestions for panels, you will find that everything is a matter of efficiency. If you have a south-facing panel, angled for maximum efficiency, that is the ideal - but, many people have issues with panels over-heating in summer and needing the water temperature boosted in winter. It seems that setting the panel to your "winter" angle would give you the best boost in winter and the dropped efficiency in summer might help avert over-heating. Equally, many people have to face their panels away from South and accept the drop in efficiency.... but, of course, you can increase the panel size to offset that.. The point is, don't be constrained by "efficiency".... work out what you need in terms of water capacity and temperature and then the best way to achieve that year-round.

Good luck!

wellinever

Hi
I recently built my house and had to include Solar Water by law. (I had already pre installed the house to accept Solar water)
and had already installed a Vulcano Sensor Ventilado 11ltr gas `on demand` boiler,
That one is equipped to accept water from a Solar source. (so do others, just look at the specs, it will say Solar accepted)
I wasn`t aware that I had to install solar and because there was only me, and for a shower a day, solar hardly seemed worthwhile. But having had to install it I chose the cheapest 300 litr with twin panel I could find.....From Leroy Merlin, brand Aelios (Greek I think).....used the recommended installer from Leroy (to make sure any warranty would be honoured).....(it had to be 300 litre cause its a 3 bedroom house, thats the law !!) Did not have an electrical immersion heater put in tank !!!
Well after 3 winters the original large gas bottle is still in use, and still feels like plenty still in there, as and when the boiler senses the solar water is not hot enough (42deg C) it will keep running on gas.
(this works on the principal that if it is turned on, it fires up as normal, and will then stop when it senses the water is at or above the temp set, if not it just keeps running) It does actually save water that was as otherwise it takes almost a full sink full before the water from the solar comes through at 40deg !!!!)
I am not sure that all boilers will accept solar water and turn off automatically, but I think not.
But with this system, and only me using one shower a day (dont bother with washing up as its quicker and cheaper just to use a kettle of hot water) if its cloudy for more than 3 days the water is below 40deg (considerably).......not surprising of course as for every litre you take out a litr of cold water goes in, and average quickish shower uses about 50litrs of water.
These are all very well but as said above there are issues, as in I go back to UK for July/August/Sept and house is empty, so I have to cover with insulation boards to ensure it doesn`t overheat. And again as said the angle they put these at is not ideal for winter sun, just when you need hot water the most..
However it is a nice feeling onece its all working, that you can shower for nothing
If only now washing machine manufacturers would include hot fill so advantage can be taken of solar water.......
Cost 3 years ago.....Solar Equipment €1300
Installation € 300 (but the house was pre installed with fully flat roof with easy access)
Solar Boiler € 350

Midgo

Thanks

I can see that efficiency can be a problem in both senses, too little in winter and too much in summer
Getting the right angle (azimuth and Elevation) wouldnt be that critical, as you can just vary the area &/or accept that it wont heat at the optimum for that size, wouldnt it?
Probly there are only a few distinct sizes available to buy so you cant optimise the Area very finely
Between N & S Portugal the elevation wouldnt change much surely, for a given season?
You could have tracking panels tho

Good point about heater inlet, probly the temperature control system (AKA thermostat, but prob with various sensors, PID, feedback &/or forward these days?) is optimised on a gas water heater for the usual inlet temperature range of cold water (prob between 10 & 20 °C?) so if you start feeding it warmer/hotter water might confuse it
https://www.earth.org.uk/note-on-dat...mperature.html not published science but good guide perhaps
For sure, if the inlet water temperature is higher than the temp set on the gas heater (we have it set at 44 °C) , it cant cool it down (although it could by mixing with cold water ...)

The thing is, if it involves replacing our pretty new (4yrs) water heater then it wont be an option (would be like buying a brand new electric SUV after selling your near new Diesel SUV to parade your green credentials )
Mind you those gas water heaters dont have an extremely long life expectancy IIRC

The thing is, immersion heaters are so inefficient as you are just burning money keeping up with the heat losses even when not using the water, which will be pretty bad in winter with a holding tank mounted outside on the roof, and the ones I have seen, despite being silver dont seem to be particularly well insulated.

Alan PT

Ours is passive and is on the roof, but ours is a flat roof, so I was concerned that we would only have 3m at most of head which would be OK but not great for pressure. But the plumber told us that the water stays at mains pressure in the system and that appears to be true, the hot pressure is distinctly better than I'd expect just from gravity. The passive just refers to the fact that the water rises up into the tank as it is heated, rather than having to be pumped into the tank

So, in theory I think you could fit a passive system at gound level, assuming you have an area which gets sufficient sunlight. Not sure that would make it any less ugly though

Midgo

Thanks!
That seems like what I neeed
I will have to look into solar source accepting heaters then
I didnt realise Leroy did them - although Leroy are expensive, it can be a god option - we got our pellet burners from there and used their installers for the guarantee too
Will have to look at the laws too - does this apply for old houses?
I have also asked a PT Engenheiro Civil friend with a construction company about this so I'll see what he says too

Alan PT

This is the angle of ours, seems fairly steep so I'm guessing it is set more for Winter efficiency?

It is almost due South facing and doesn't get much shading. Our gas heater is set to kick in if the water temp is below 50C and it very rarely does (apart from the first 30sec before the hot water reaches it!). I never heard anything about having to shade the panel to avoid overheating, but then temperatures here are not quite at Algarve level

Midgo

Yes!
My water heater (Junkers miniMAXX Excellence WTD 17 KME) has Solar capacity

In the instructions there is even an installation guide and it says:



From what I remember from my studies, the symbol for 5 is just some sort of release valve isnt it?

macliam

The difference Winter /Summer is far more than you think - 24-30 degrees! If I remember correctly, the incline should equal the latitude, minus 12-15 degrees for Summer and minus 12-15 degrees for Winter. In Portugal, the best is to set the panel for the winter and only change it is you have problems in the summer. So, for me in the Alentejo, that would mean an angle of 37.5 +15 in the Winter, or 52.5 degrees and 37.5- 15 degrees in Summer, 22.5 degrees. As you'll see, the typical 30 degrees is nothing like correct!

A panel facing 90 degrees off South would lose 15-20% oif peak efficiency..... so as I said, you can make up the loss by more panel area of a more efficient panel.

dingg

5 is a pressure relief valve