Thermal Solar Power - worthwhile under the upcoming RHI scheme?

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  • penrhynpenrhyn Forumite
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    For what its worth and I have nothing to do with these people, but the system offered by SolarTwin, uses a small secondary solar PV panel to power its circulation pump.
    That gum you like is coming back in style.
  • Ken68Ken68 Forumite
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    Often wondered what happens to these things in a scorching hot summer. Say when you're away on holiday.
    Do they have an off switch ?
  • frozen_wastesfrozen_wastes Forumite
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    For the Vaillant cylinders at least, there's a thermal cut out for the solar pump when the temperature exceeds 90 degrees. Failing that, there's a pressure/temperature relief valve on the cylinder. Failing that, there's a rather good mythbusters episode worth watching:
    http://www.youtube.com/watch?v=pu3FwgIHsQA

    230 Watts for a solar pump sounds like a lot of power. I know the Grundfos CH pumps use around 60-100 Watts, and their flow rates are much higher. Solar pumps typically pump around 0.4litres/square metre of panel. Mine barely registers on my energy monitor.
    8.9kw solar.  12 panels ESE,  16 panels SSW.  JA solar 320watt smart panels.   Solar Edge 8KW HD wave inverter.  Located Aberdeenshire
  • Ken68Ken68 Forumite
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    So in addition there must be a relief valve in the solar unit itself.
  • frozen_wastesfrozen_wastes Forumite
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    There's at least three mechanical pressure / temperature relief valves on sealed circuits (not required for open vent systems)

    There's one for your pressurised drinking hot water - located on the cylinder
    There's one for your sealed central heating - usually located on your gas boiler (if it's a system type boiler)
    There's one for your solar glycol antifreeze circuit. This should drain out into a collection vessel in the event of overpressurisation.

    Older systems often have these valves vent out without any pipework attached (meaning boiling water all over your cupboard floor). Newer systems are required to have discharge pipework to carry away the boiling water to somewhere safe (like a external drain for example). If all the other safety features work, these relief valves should never have to do their jobs.

    However I'm guessing that if you're away from your house for prolonged periods in the summer, your solar circuit will just get hotter and hotter during the summer without any means of dumping that surplus heat. So I guess you could well find yourself with all the glycol dumped back into your collection vessel if you don't do anything else.
    8.9kw solar.  12 panels ESE,  16 panels SSW.  JA solar 320watt smart panels.   Solar Edge 8KW HD wave inverter.  Located Aberdeenshire
  • Ken68Ken68 Forumite
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    Thanks Frozen, just as well I abandoned this DIY (copper pipe) project. Realised I only used about two kettles of hot water per day anyway .
    What with everything being electric, dishwasher/washing machine/shower.
  • frozen_wastesfrozen_wastes Forumite
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    Aye, I leave all my plumbing to the plumber. I'm just a backseat plumber with a youtube qualification myself!
    8.9kw solar.  12 panels ESE,  16 panels SSW.  JA solar 320watt smart panels.   Solar Edge 8KW HD wave inverter.  Located Aberdeenshire
  • edited 16 February 2011 at 5:50PM
    frozen_wastesfrozen_wastes Forumite
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    edited 16 February 2011 at 5:50PM
    I've now also seen a supplier called "Navitron". They are considerably cheaper than the likes of Vaillant.
    http://www.navitron.org.uk/product.php?proID=115

    They seem to have a loyal and enthusiastic DIY fan base, but has anyone heard of their reputation? The assembly videos I've seen make the units look like rather cheap quality. So I'd have doubts if their performance is even a large fraction of what pricier panels can achieve. For one thing, they don't have reflective mirrors behind each tube, and the fixings to the roof top look somewhat amateurish.

    If their panel performance is good however, maybe these can be genuine hot water money savers...
    8.9kw solar.  12 panels ESE,  16 panels SSW.  JA solar 320watt smart panels.   Solar Edge 8KW HD wave inverter.  Located Aberdeenshire
  • edited 16 February 2011 at 7:53PM
    Ken68Ken68 Forumite
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    edited 16 February 2011 at 7:53PM
    Frequently asked questions on http://www.decc.gov.uk/en/content/cms/consultations/rhi/rhi.aspx
    is interesting.
    £400pa RHI mentioned in above link and £500 in this link
    http://www.solarthermalworld.org/node/1166
  • zeupaterzeupater Forumite
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    Ken68 wrote: »
    Frequently asked questions on http://www.decc.gov.uk/en/content/cms/consultations/rhi/rhi.aspx
    is interesting.
    £400pa RHI mentioned in above link and £500 in this link
    http://www.solarthermalworld.org/node/1166
    Hi

    You do need to consider that although the industry is tending to push the £400 annual return, it is likely that this would only apply to reasonably large installations.

    The DECC consultation documents referenced above actually raise the possibility of the scheme being based on a 6% return. Considering that a typical professional installation is currently likely to be £3k - £4k, then the annual return is more likely to be between £180 & £240.

    To support this range of figures a series of solar thermal field tests produced results which describe a number of various system types as producing around 1000kWh of usable thermal per year. Apply the anticipated 18p/kWh RHI payment to this and you would also get to an annual return of £180.

    Don't be sold a package based on hyping the return on investment based on the value of an as yet unconfirmed RHI payment.

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
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