Just a quick question,

As my house is listed and in Dartmoor, solar thermal or PV on the roof is a big no no. I am planning an approx 4kw pv array on one the outbuildings - direct south aspect.

Question is can I do the same with solar thermal? Would too much heat be lost over pipe run outside - estimate approx 10 - 15m from outbuilding to proposed location of thermal store. Obviously would propose to highly insulate the pipe run, even bury it 4ft underground it recommended? I assume the solar thermal doesn't "have" to be higher than the store as its pumped round isn't it?

Perhaps daft questions but would be useful to know the answer.

Thanks!

How much room is there on the outbuilding. The reason I ask is that you could always put a bigger area of ST on it to counteract the losses, but may pay for it in the summer when all the losses not so signifcant and the insolence is higher.
Alternatively, you could up the amount of PV you install, you could put 4.5 kWp (15 x 300Wp modules) through the inverter and off to the grid (get your FIT payments increased on that too) and then have a secondary system feeding an ordinary E7 water tank (say a 2.1 kWp, 7 module and separate inverter). That would be 22 identical modules of 1m by 1.6m (ish). You may have to get a 2 kW heating element made, but that is probably not that hard or expensive.
Just make sure that the cables are thick as there is only a 1% volt drop allowed between the inverter and the main consumer unit.
Much easier to fiddle with cables than pipes.

thanks for your replies, ive been looking at this forums discussion:

http://singletrackworld.com/forum/topic/solar-water-thermal-panels-the-installation-w-pics

who has run solar thermal from ground array and looks interesting.

Question, over a year do you think the energy produced and FIT payments from a larger PV array would ultimately be a cheaper/ more efficient solution than solar thermal for hot water. I assume by E7 water tank you mean heating a hwc up each night with e7 for the next days use, offset by the money and energy generated by the array?

I have alot of outbuilding roof space orientated direct south by luck - at least 25m * 3m and more if need be.

Noted about thermosyphon and potential loses, panels would probably be similar level but pipe runs would have to drop to underground ground (5m) and then rise again in house .

Thanks.

thanks, will have a read through your links!

Posted By: SteamyTeaAlternatively, you could up the amount of PV you install, you could put 4.5 kWp (15 x 300Wp modules) through the inverter and off to the grid (get your FIT payments increased on that too) and then have a secondary system feeding an ordinary E7 water tank (say a 2.1 kWp, 7 module and separate inverter).

Why 4.5 kWp? I thought the price break for FITs was 4 kWp - or has that gone away with the new pricing?

Anyway, another consideration is the limit of 16 A/phase on your feed in unless you can get the DNO (local electricity network) to agree to allow you more. If you had a total of 6.6 kW then, the moment your water tank thermostat dropped out in bright sunshine you'd be over the 16 A limit.

Still, the idea of having more than 4 kW of PV, only claiming FITs for 4 kW worth, but being able to use the output of more without importing has some attraction. E.g., a 6 kW array with 4 kW through the total-generation meter on a less than fully bright day so it's only producing half output could run a 3 kW immersion while still claiming 2 kW of FITs.

Something like this might help:

http://www.immersun.co.uk/

Posted By: SteamyTeaI have been told, though not 100% sure, that you can do this under the MCS/FIT rules.

IIRC it's complicated, and not necessarily logical...
e.g.
http://www.navitron.org.uk/forum/index.php/topic,17718.msg202525.html#msg202525

Hi Steamy - I think the 4kW rule is set in the FIT legislation, or I would have gone for a higher figure to produce more on dull days. The only case I can think of for an exception might be that the power figure is taken at the inverter after losses, but I am pretty sure it is the headline power rating on the panels that count.

The DNO limit of 16A is locally set and is fixed on my inverter. The actual max output in kW going to the grid is determined by the local line voltage, and can go over the theoretical limit of ~3.7kW, if the line voltage is nearer 250 than 230. Mine is usually around 240 - 244v

I have seen 4.3kW on my 4kWp system - that seems like a long time ago, when the sun was shining!

Hi Noodle - could you use smaller diameter pipes for your ST. Greater pumping effort but less water content to lose heat when switched off

When I did the research in to making a block of flats that could run as economically as possible. Solar water heating was one of the things researched. The investors who asked to look into this introduced me to a German marine engineer who had put in a system for his parents in the North of Germany, there house did not sit at the right angle for the panel’s to go on the roof but the outbuilding’s did. He altered the angle of the south face to the right incline for the panel to gain maximum sun, also they were built in their own little green house (so as to speak), and this was backed with reflective panels. The pipes were lagged to slightly over 100 mm all round and this was put inside a large plastic pipe which had glued collars and buried in the yard. The run across the yard was just under 15meters and the house was two story, he used a hydraulic type of pipe that can withstand a lot of heat this took expansion out of the equation. In the house he used a heat exchanger similar to a marine engine, this kept the mixture in the solar panels separate from the central heating system, and the cold water supply to the tank went through the exchanger. He told me that in the summer you could cook on this it was so hot, the pump was a standard central heating pump and it was thermostatically controlled so as not to pump cold water.

"CASAFLEX is a flexible, self-compensating, endless production, monitorable and heat-insulated pipe system with a special steel medium pipe.

Operational data
Excellent heat insulation at high temperatures
The diffusion barrier and the structure of the CASAFLEX pipe system guarantee minimal heat losses as well as resistance to high temperatures. Operational temperatures up to 160 °C, peak temperatures up to 180 °C, PN 16/25, DN 20-100."

Shame it says nothing about the thermal properties apart from maximum temperature.

Brilliant

So taking a worse case scenario of 70°C source and 60°C return that will be 15m x (9.4 + 7.8)W/m loss, or 260 W loss.
I would stick to PV and 6mm cable.

It is probably the easiest and cheapest to fit, performance is a bit harder to work out as depends on how much water you want to heat and how much sunlight you get. You would have to contact an inverter expert to see how well they can cope with a 3kW resistance load when the panels are producing less than that, I am sure someone will know.
Would also be worth looking at cable losses and working out if you are better having an AC or a DC run to the house, not sure how much difference it would make, but easy enough to work out. There are a few online cable loss calculators and the Carbon Trust/EST solar calculator will give you an idea of PV outputs (as will PVGIS).