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    • CommentAuthorowlman
    • CommentTimeApr 1st 2016
     
    Questions of using most of your PV production yourself aside. Has anyone got one? Most seem to be aimed at immersion heater input but any resistive load should suffice. I was thinking of electric underfloor cables. The most expensive and sophisticated are £500 plus, plus the cable etc., total can easily be in excess of £1- 1.5K, so one has to question, is it worth it?
    Opinions, models, reliability, etc. ??
  1.  
    i boost+ gets my some what late vote
    • CommentAuthorbillt
    • CommentTimeApr 13th 2016
     
    I use a customised version of Robin Emley's PV Router http://www.mk2pvrouter.co.uk/.

    It has 10 switched outputs, the first three heat water the others just waste energy.

    N.B. this is for a non subsidised system, so the energy wasted wouldn't go to the grid anyway.
    •  
      CommentAuthordjh
    • CommentTimeApr 13th 2016
     
    I use Robin Emley's PV Router too, but I believe he can only supply kits at present thanks to EU red tape.
    • CommentAuthorowlman
    • CommentTimeApr 13th 2016
     
    Thanks guys. What prompted the question was the fact that I'm doing floor tiling at the moment and the thought of putting in UFH cable to take advantage of my 10 Kw array in early spring and late autumn, to supplement CH.
    I'd looked at a few systems, at a glance this seems to be the most sophisticated.

    http://www.powerflowenergy.com/company/
    • CommentAuthortony
    • CommentTimeApr 13th 2016
     
    10kW
    •  
      CommentAuthordjh
    • CommentTimeApr 13th 2016
     
    Posted By: owlmanI'd looked at a few systems, at a glance this seems to be the most sophisticated.

    http://www.powerflowenergy.com/company/

    Hmm, not cheap though. I especially like immersion heaters at £200 a pop!
    • CommentAuthorEd Davies
    • CommentTimeApr 13th 2016 edited
     
    Posted By: owlman…at a glance this seems to be the most sophisticated.
    What particular sophistication of these is good in your case?

    It's really difficult to work out how much useful energy you'd get out of something like this. Say your panels generate 10 kW for the equivalent of 800 hours a year with 400 hours of that in the summer when you don't want much or any heat anyway, except to a towel rail and, perhaps, the bathroom floor. So that leaves 400 hours of generation. A bit of that will be lost, even outside the summer months, when you're generating more than 6 kW so the remainder gets exported (if you don't self-consume it some other way). On the other hand, 10 kW into 6 kW will give a slightly higher number of effective hours at 6 kW - say 500.

    500 hours at 6 kW is 3000 kWh. If that directly replaces gas at 5p/kWh that's £150/year so that's a 10% return on your £1500 invested. After 10 years or so the box might go phut but a) you'll still have your cables and b) a replacement might well be cheaper then. So overall, it doesn't look like a silly deal.

    Still, I wonder if being able to switch where the power goes to might be a good plan. In the summer you might still want to send it to the hot water tank - maybe a second immersion at the bottom - and to a towel rail. Late spring and early autumn you might also want to heat the bathroom floor. Later in the autumn, through the winter and for the early part of the spring more general heating when it's available. Dunno, it depends very much on other aspects of your house.

    Perhaps wire the output of the box to a small consumer unit then just flip the breakers for things you don't want running at any time.
  2.  
    Hi,
    Looks expensive to install the under floor heating. Why not just a simple electric heater(s) to use the extra power ?. They are very reliable and cheap - £20 with thermostat and can be wall mounted. They are also a good backup if the main heating is down for aany reason.

    Richard
    • CommentAuthorowlman
    • CommentTimeApr 14th 2016
     
    You're right on with the price Richard , I guess it was just the invisibility of the UFH cables and the fact that I was tiling at the same time.

    Ed: it was the ability to automatically switch/prioritise the loads, especially smaller UFH cable areas, according to need, that I thought neat, and the device I linked to did seem to have the greatest range of options. I still need to do more research though.
  3.  
    If it costs £1500 and saves you £150 for 10 years, you'd be left at the end with £1500, so that's 0% simple return on your investment. .

    If you did want a 10% simple return over 10 years, you'll need to save £1500 x (1.10^10) = £3890 over 10 years, eg £389 each year.

    Your real-terms return could be a bit more or a bit less, depending on future inflation and energy prices, and on where you reinvested your savings each year.

    My view is these diverter boxes are only economic to enable one to play games with the FIT and lack of export metering, at the expense of all other bill payers. I am interested if the cost of self consumption can be driven down such that it will payback on 'real' energy cost savings, another thread on diy pv-direct-to-resistive-heat.
    • CommentAuthorEd Davies
    • CommentTimeApr 14th 2016
     
    Posted By: owlmanEd: it was the ability to automatically switch/prioritise the loads, especially smaller UFH cable areas, according to need, that I thought neat,
    Ah, that makes sense. I read the main pages on each of the units but didn't dig into the detailed specifications. You'd have thought they'd have emphasized that up front, or did I miss it in their waffle?

    Posted By: WillInAberdeenIf it costs £1500 and saves you £150 for 10 years, you'd be left at the end with £1500, so that's 0% simple return on your investment.
    You'd also be left with £1000 worth of cables in the floor for use during the next ten years, one hopes.

    My view is these diverter boxes are only economic to enable one to play games with the FIT and lack of export metering, at the expense of all other bill payers.
    Diverters are irrelevant to FiT. Unless this is a quite recent installation the export rate is also not large so the presence or otherwise of export metering doesn't make a huge difference but, yes, if there was an export meter you'd need to subtract the lost export payment from the price of gas saved if really counting the pennies.
    • CommentAuthorowlman
    • CommentTimeApr 14th 2016
     
    Yes Ed the upfront stuff is a bit lacking in detail, there's more in the download section. With UFH cables maxed out @ 200W per M2 I thought matching load to the diverter load ports would be a good plan, but that means you need a good sized floor area which isn't always possible in an existing building. These diverters can, I understand, cope with many smaller diverse loads, others often can't.
    Or maybe I'm talkin' crap?
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