Hi all. Recently bought a townhouse in Mora and thinking that simple gravity fed Solar Water Heating from a rooftop unit might be practical. Has anyone any experience or recommendations in this respect?
P.S. Most impressed with the forum setup and content.
Cheers, Ray.

Hello Ray.
We have had solar hot water for 7 years. The make is SolaHart.
It is made in Australia. I suppose there are spanish equivalents.
The panel and tank sit on the roof. The water is gravity fed.
It provides all the hot water we need most of the year. Perhaps a few times in winter after a sequence of dull days, we need to use the immersion heater which is built into the tank.
I believe it is now a law in spain that all new builds must have solar hot water heating.
It has saved me a lot of money. I think the pay back is in the order of 5 years but that depends on how much you use it etc. Money well spent in my view. 

I have solar hot water (a self built system) and have installed a few systems. All work extremely well, the best solar investment you can make!

One customer of mine has a system he also uses to heat his house - I only installed it this spring so as yet we don't know the results.

I'm currently working on a project to install a hybrid solar/heat pump heating system for my house, again a home made system hopefully I'll have it installed soon and will know how well it works this winter. I had the heat pump working last winter and saved in the order of 1500 euros in heating oil by running it.

I must admit to not being a fan of the gravity fed systems as I've seen problems such as boiling/calcium build up etc. with them. The system I prefer is a closed solar circuit with circulating pump and an indirect heated tank.

Mine, for example, is a single panel (about 2.4m x 1.2m) and a 160 litre water tank. We have hot water from this pretty much from late February to November. Outside of this I use a combination of a heat pump or immersion heater to heat the water, the former being the most efficient. The pump and control runs from solar so effectively costs nothing to run.

Nigel did you make the panel yourself -15mm -22mm tube or is it a bought evacuated tube type, and is the cylinder a single coil or a dual coil,  these are dear !!!!! been looking for a while now for one of these to work with a wood burner.
I have just won 2 x ultra violet filters from work this week, and will hope in time ;D to be using 1 of these in a collected rainwater system,I have a bit of a query that might be in your line, as I have also collected a few 24dc shurflow pumps which I was going to incorporate in this system.
, but not sure about flow rate going through filters ? I know there is a max but cannot find info on minimum? any advise appreciated.
Thanks Phil

Hi Nigel, could you provide a plan for your 160l system?  :)

The panel(s) are repaired solar water panels I have been lucky to obtain. All 3 that I have had suffered bursts (probably from freezing) and needed brazing. One had shattered glass and the others were repaired from behind, cutting out the aluminium panel and then repaired with aluminium strips pop-riveted down the cuts.

The 160L tank is a conventional indirect heated tank (Roca) but used with solar instead of from a boiler.

You can read all about the system and how it works with a combination of solar and heat pump here:
http://ecorenovator.org/forum/solar-heating/3123-combined-solar-heat-pump-water-heater.html

Wow they were a good find Nigel, never seen any of them in a skip ;D
And thanks for the link, bookmarked them, useful site for us with an eye for cutting costs.

Nigel, thanks for the link. :)

Thanks all for input. Gravity system still looks simplest (and probably cheapest) to me..acknowledged that I'm only going on reading stuff and that there might be some longer term issues. Seems difficult to find a spanish supplier quoting prices, but I have found some in Malaga via ebay uk site if anyone is interested.
Cheers, Ray.

I might be talking carp here but if the water from my green hose pipe is anything to go by, would it not be feasible to just lay out a coil of about 100m of 32mm black irrigation pipe ?  Either on a flat roof or the deck (if you could fit it into the typically tiny "gardens" here)  :D
If one end was fed from the cold supply and the other to a typical butane water heater via a thermostatically controlled mixer valve, the heater should only cut in if it's input drops below 65C ?

I see lots of this type of system around - it seems an obvious solution but does have limits, some of which are below:

1. The pipe radiates heat and as it is not enclosed in a panel the heat escapes so reducing the efficiency. Also wind will cool the pipe if not enclosed in some form of panel.
   
2. The quantity of water is limited to the amount that will fit in the pipe.
   
3. The surface area of the pipe in contact with the water is small. The bigger the pipe the less contact.
   
4. The surface area of the pipe exposed to the sun is small as large parts of the pipe are in the shade.
   
5. Plastic pipe is not a good conductor of heat.
   
6. At night the heat will be lost due to lack of insulation.
   

When I first came over and had no bathroom in my chicken shed, I used a black plastic expansion tank with a hose out of it. Worked brilliantly so long as I had my shower before the sun went down.  Sometimes it was too hot.
I am thinking of putting a hose back up on the roof and preheating the water for the gas heater.
If it goes cold at night it doesn't make any difference as the current feed is cold anyway. If it freezes then I'll have ice for my G&T :)

Hi Nigel,
I hear what you say but :-
1.  I'm thinking that if a 30m green hose pipe gives me about 10 litres of water hot enough for washing up (and too hot for showering) then 100m of black 32mm pipe would give a lot more (i.e about 300 litres).  More than enough for general houshold use at any one time as once you've done the washing up or showered (or whatever) the residue in the pipe would carry on heating up.  It wouldn't be difficult to locate the pipe in the lee of the wind ?
2.  See above.
3.  Don't get that ?
4.  Ratio mentioned in 1. still applies.
5.  Ratio mentioned in 1. still applies.
6.  How much washing up etc. do you do at night ?
I'm not trying to deliberately contradict you and your laws of physics are correct but it seems to me that it would be very cheap and simple to construct.  I'd give it a try if I had nowt else to do and a 15€ bottle of gas lasts about three months on the water heater.
Could an insulated storage tank not be included in the circuit so that there was a resevoir of pre-heated water to feed the boiler in the morning ?

I got through two insulated hot water copper tanks in four years. The water I have from a well at the bottom of the mountain is very corrosive. I gave up on the tanks and just use a gas water heater.
I also used to use a vacuum tubes  system but the pumps used to fail on a regular basis :(
Where can you buy gas at €15 a bottle? I paid 17.50 last week

Nigel what is your opinion on 3/400 ft. of 32mm black pipe coiled flat on 8x4 ply base painted black enclosed on top with uv grade polycarbonate. placed on a frame on the ground facing the sun. The hot water from the coil thermosyphons up through insulated pipe to a heavly insulated 1000l tank on the roof with either a second coil or just direct feed from the tank back to the coil gaining heat during each cycle.  :)
A DC pump with panel could be used for circulation if the thermosyphon is not enough.

Copper tanks are not a good solution as they are very thin and not designed to be used in a pressurised system. The water here is also extremely high in calcium in some places and iron in others. The tanks here tend to be steel with an enamel coating but they do still suffer.

I've seen several of the gravity type systems totally furred up with lime scale and am not a fan of them. I have a stainless steel one that I acquired from a job and it has been totally eaten through where the joints were made.

I've just been using regular run of the mill central heating circulating pumps in my systems and haven't had any problems with them at all.

Re the thermosyphon - would it work in a coil as you will have hot water at the top and cooler at the bottom of each coil?  A better layout would be a continuous S shape so the hot water would rise and pull the cooler into the tube at the bottom.  Beware that if it is in a box it will get hot and if it is under any sort of pressure then the plastic may burst. If it is a closed circuit then it will develop pressure and you will need a pressure vessel but this may produce more pressure than the pipe is capable of sustaining.

If you have an open system with the 1000l then this isn't a problem but then your hot water will be at the pressure related to the height you locate your cube at which, unless it is on the roof of a tall building, is unlikely to be enough to fire a gas water heater should you decide to put one in line as a backup (they normally need a minimum of 0.5 bar to fire and more to get a decent flame for heating). It will also take an awful lot of sun to heat up 1000L of water!

If you use a pump then because of the extremely poor conductivity of heat through plastic don't expect to get a very high temperature increase. You would be much better off using copper pipe however for 1000L you would need an extremely large panel - or panels. One large panel would probably end up with the water boiling in it so you would need more than one to achieve the desired result. If it was a closed system you could pressurise it to avoid boiling (look up Boyles law) but then you are definitely going to need copper.

Ah, it's a minefield.. but don't be put off and don't take my word for it - if you have time then try it out, the learning is as much fun as the doing and if it works you'll have the satisfaction of knowing that you built it.  :)

Nigel thanks, very helpful, especially the bit on the gas boiler i had not thought that through and you are correct it is an open system and there would be/is a gas boiler backup..5 bar requires 17 feet height  I have approx 20ft.  to the bottom of the storage cube which would work.  :)

A little warning for the creative DIY cheap water-heater builders. Beware of the risk of legionnaires disease. Expecially systems where the water stays in the system for several days (like when used 1000 liter cubes or 100m irregation pipe in the system) are at risk.

Also it is not a good idea to connect this type of water heating system directly to the cold water supply. The bacteria will grow in the heated up pipes and can contaminate the cold water supply if there is a direct connection. If you use water without chlorine (like from a well) the risk is even higher. Don't kill yourself out here.

Mark

If you are worried about LD. gardeners beware. :)

http://www.telegraph.co.uk/gardening/10347803/Hygiene-warning-to-gardeners-after-study-finds-Legionella-bacteria-in-compost.html#

I get a tanker full delivered every couple of days. I don't need it I just like the delivery driver.  ;) ;) ;)

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That's hot water  :)