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    •  
      CommentAuthordjh
    • CommentTimeFeb 26th 2016
     
    Posted By: Ed DaviesBut then you need an inverter as well. And you're probably limited to 16 amps at mains voltage. And definitely need an electrician.

    Sorry Ed, I didn't realize this was an off-grid thread!? The OP has an electric cooker. So of course he'd have an inverter with the PV. And what's the problem with electricians? The OP has already as much as stated he'll need a plumber so why wouldn't he need an electrician! And what's with a 16 A limit, where does that come from?
    • CommentAuthoran02ew
    • CommentTimeFeb 26th 2016
     
    80 tubes on our roof into 225l cylinder. Boy she heats up quick Evan this week full tank of hot water by 12 then diverts into user floor heating. Would like to see pv do that! Tubes cost £1800 3 years ago when pv was £12000 +
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 26th 2016
     
    an02ew
    Do you have a heat meter on your system, then we can compare it to local weather conditions.
    How does the system cope in the summer, any over heating/reliability issues yet?
    What service regime do you do?
    • CommentAuthoran02ew
    • CommentTimeFeb 26th 2016
     
    My solar controller has some data that says

    1170 operating days
    10647 kWh of heat
    ( iPhone photo won't upload)

    My 350mm concrete slabs nicely absorb surplus heat till around May when I manually divert surplus into under slab AGS (solar dump)

    The summer recharge is amazing tank hot by around 10am

    No service as yet the system is design around a PAW drain block unit which is a low pressure water filled system
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 27th 2016
     
    So about 9 kWh/day delivered, what area does the complete system take?

    At current E7 prices it would cost about 63p/day, so £735 for the last 1170 days.
    • CommentAuthoran02ew
    • CommentTimeFeb 27th 2016
     
    <blockquote><cite>Posted By: SteamyTea</cite>So about 9 kWh/day delivered, what area does the complete system take?

    At current E7 prices it would cost about 63p/day, so £735 for the last 1170 days.</blockquote>

    I assume you mean area on the roof? Which is 4 banks of 20 tubes. Say 7m x 1.6m = 11m2


    But 9kwh per day would be more like 126p/day at a more realistic 14p/kWh so £1474 a lot nearer my initial investment, after only little over 3 years
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 27th 2016
     
    A quick look at PVGIS and assuming that you can fit 2 kWp system in the same area would yield 1890 kWh a year (in the middle of Devon).
    So over that same 1170 day period you could have generated 6060 kWh, so 40% less.

    So on basic numbers it looks like your ST system is performing better.

    What did it produce yesterday?
    • CommentAuthoran02ew
    • CommentTimeFeb 27th 2016
     
    5kWh yesterday
    15kWh the day before
    16kWh day before that
    • CommentAuthorEd Davies
    • CommentTimeFeb 27th 2016 edited
     
    Posted By: djhSorry Ed, I didn't realize this was an off-grid thread!?
    Yeah, but I was answering an02ew's “Solar thermal, its cheaper, can be self installed by competent person” so a direct comparison wouldn't necessarily be (all) grid connected. With the 16 A limit you might want at least some PV which isn't if you're serious about replacing solar thermal.

    Posted By: an02ewMy solar controller has some data that says

    1170 operating days
    10647 kWh of heat
    Right, but how much in December and January? Or even November and February?

    [Cross-posted with Steamy and An02ew's last two.]
    • CommentAuthoran02ew
    • CommentTimeFeb 27th 2016
     
    That depends to the amount of sun? Listening to bbc yesterday it's been the warmest winter on record? February has been a great month for solar

    And although a little mean to hijack this thread for a solar debate it is all born out of the feasibility of the OP. In my opinion solar thermal or PV is a must for anyone trying to run a home on a tight budget if for no other reason than its free and don't need chopping first
    • CommentAuthorEd Davies
    • CommentTimeFeb 27th 2016
     
    Posted By: SteamyTeaA quick look at PVGIS and assuming that you can fit 2 kWp system in the same area would yield 1890 kWh a year (in the middle of Devon).
    So over that same 1170 day period you could have generated 6060 kWh, so 40% less.
    1) You often need to compare on cost, not area. Of course, sometimes it is area that matters.

    2) There's no doubt that solar thermal can produce oodles of heat in the right circumstances and will almost certainly beat PV on cost as well as area for total annual production.

    However, weak sunshine and high output temperatures for DHW are not the right circumstances. In that case ST will basically produce nothing whereas PV will at least give you a trickle of heat. If you have enough of it that could be a very useful trickle.

    We're moving (very slowly) towards an energy system where prices, particularly of electricity, are very much more variable (more renewable energy plus smart metering (not a coincidence)) so electricity is very likely to cost a lot more just at the time when solar thermal isn't doing anything useful for your DHW.

    I have 8 panels of 20 47 mm tubes to go on my house. I'm planning to do a lot of experimentation but the expectation is that in the winter they'll contribute mostly to space heating and not much to DHW; maybe as a preheat which gets topped off by resistance heating from the PV.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 27th 2016 edited
     
    ST can give you some very cheap storage though.

    My initial interest in renewable was via ST, but when I eventually got around to studying it properly, 22 years later, I did my first project on ST for house heating. I then moved onto PV because of the versatility.

    I don't think February was particularly good for insolation/irradiation, the higher than normal temperatures were caused by the weather patterns and the higher global temperatures, in part because we have a large El Nino happening.

    Anyone got any PV figures for last few days? Preferably in Mid Devon (not quite sure where you are Andrew).

    Sidmouth College has this online, just need to dig about to find out what size the system is to do adjustments.
    https://web.sidmouthcollege.devon.sch.uk/ictblog/solarpower/

    They seem to be using 56 BP-4175N modules. They are 175Wp ones. 790mm by 1593mm, so 140W/m^2.
    So 11 m^2 is 1.53 kWp.
    Yesterday the who system produced about 12 kWh from 70 m^2.
    So around 0.24 kWh/m^2
    11m^2 should produce about 2.67 kWh.

    Wednesday, 24th, Feb, it produced about 32 kWh
    0.45 kWh/m^2
    or 5 kWh of the 11 m^2.
    • CommentAuthoran02ew
    • CommentTimeFeb 27th 2016
     
    I'm in Somerset. Near taunton

    My comment" PV is dead long live solar thermal" was aimed at every decreasing funding available for pv(FITs) I'm assuming that without the government hand out sence will provail and people will choose, based on what is actually required not on a payment return?
    • CommentAuthorbillt
    • CommentTimeFeb 27th 2016
     
    But the funding has disappeared because the cost of PV has dropped like a stone in the 5 years since FITs were introduced. Solar thermal has increased in price.

    For instance, I use a couple of Economical ET collectors. The 30 tube variant now cost £713, to which you need to add a controller, a pump, copper pipe, insulation and various fittings. So you'ld probably spend about £1200 on parts for a small system which has a maximum output in ideal conditions of 1500W.

    A few months ago I bought some B grade but new 230W solar panels for £100 each; last week I bought a brand new SMA SB1600TL inverter new for £240. You would need an isolating switch and a bit of cable, so a 1500W system would cost about £1000 for materials.

    So for less money you have a PV system with equivalent peak output but which would actually harvest much more energy and in a much more versatile and useful form.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 27th 2016
     
    I agree that subsidies skew a market, but there are places where subsidies are not available, or hard to claim, that are choosing PV over ST, Sub Saharan Africa and rural India.
    These places, which have a need for thermal energy, have opted to get that via electricity.

    In an ideal world every building would have a combination of ST, PV, Wind and Hydro that feeds into heat pumps, thermal storage and chemical storage.
    Now that would be an interesting project to see if such a plot could be found and how much it would cost to just buy and self install the kit without bothering with all the legalities.
    • CommentAuthorEd Davies
    • CommentTimeFeb 27th 2016 edited
     
    An02ew - all my calculations on this have been on the assumption of no FITs, RHI or whatever but focusing on minimum cost for near-year-round useful generation rather than maximizing annual production. If you think you can get more useful energy at DHW temperatures out of, to use Billt's example numbers, £1500 worth of solar thermal than £1500 worth of PV in December and January, or even November and February, then show us your numbers.
    • CommentAuthorGarethC
    • CommentTimeFeb 27th 2016
     
    Bit tangential and left field (as usual...) but can excess heat in summer from solar thermal be used to generate electricity, perhaps via a Stirling engine?
    •  
      CommentAuthordjh
    • CommentTimeFeb 27th 2016
     
    Posted By: GarethCBit tangential and left field (as usual...) but can excess heat in summer from solar thermal be used to generate electricity, perhaps via a Stirling engine?

    In principle, yes, but in practice the efiiciency is so low because of the relatively small temperature differential that nobody bothers. Solar thermal power stations use concentrating collectors to increase the temperature differential until it becomes worthwhile. But even then, more concentrating PV stations are built, I believe.
    • CommentAuthorskyewright
    • CommentTimeFeb 27th 2016
     
    Posted By: an02ewThat depends to the amount of sun? Listening to bbc yesterday it's been the warmest winter on record? February has been a great month for solar

    In this area at least 'cold' winter weather is usually better for solar gain! 'Warm" winter weather usually means cloud.

    For much of this week the mean 24hr temp has been between 2 & 3C but we seen more sun than for for a good while. In the last 7 days the PV has generated more than the whole of December 2015 (mean 6.8C) & January 2016 (mean 4.8C) combined (days are longer of course, but the difference in solar is far greater).
    • CommentAuthorbxman
    • CommentTimeFeb 27th 2016
     
    my question is will a thermal store be likely to answer our demands for morning luxury after an evenings burn of the rayburn?

    A definite No in my opinion

    I think you will find that both Rayburn's and Aga's are designed for 24/7 operation .

    The Rayburn will never heat a thermal store so that you can run even a couple of radiators in the morning to take the chill of the bathroom and kitchen in the bungalow

    I am sure you will find the firebox is to small to get sufficient heat from wood for what you want to do .

    As for cooking they have a thermal mass that will take a couple of hours to build up before you can start cooking.

    If you can manage keep it in overnight you might be OK. But serious timber will be required more than a match for a crosscut saw I suspect.

    Stop the Drafts and get the insulation in place would be my recommendation.

    sorry to rain on your parade but good luck with your project.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 27th 2016
     
    I can usually get two baths out of my 200 lt 'thermal store' (usually called a DHW cylinder) and I only run it at 50°C.
    Not unusual for me to have a bath in morning (an hour or so after last charge up) and one 14 hours later.
    So there is not really an issue with the store 'holding the temperature' as that is just about usage and insulation.
    More about the best way to get the energy into the store.
    • CommentAuthoran02ew
    • CommentTimeFeb 27th 2016
     
    The principle is ok in as much as a biomass boiler a thermal store and radiator. But not with a Rayburn. You need a dedicated appliance just for the store if you are only using one input

    And I agree seal her up as tight as a submarine insulate well and notice I don't say as much as in my opinion insulation installed well is better than more installed poorly.
  1.  
    We are totally wood fired for cooking heating and DHW using an Esse for cooking and DHW and a Dunsley Yorkshire for the central heating. It works reasonably well but if I was redoing the system then I would run the whole system off a Lohberger stove which also has the wood pellet option so that it can auto ignite at a preset time in the morning. Would not even consider the Rayburn when compared to a Lohberger but the difference is reflected in the price.
    • CommentAuthorTriassic
    • CommentTimeFeb 28th 2016
     
    Fabric first?

    EWI on exterior walls to help keep the place warm and the heat in?

    Discuss...
    • CommentAuthortorrent99
    • CommentTimeFeb 29th 2016
     
    Posted By: TriassicFabric first?

    EWI on exterior walls to help keep the place warm and the heat in?

    Discuss...



    Indeed. Being able to collect almost free wood is all very good (and laudable) now, when you're young fit and willing. But what about when you're older with failing joints? Or just don't feel like it? Insulate now and it'll pay you back in many ways later....
    • CommentAuthorCliff Pope
    • CommentTimeFeb 29th 2016
     
    We use a Rayburn for cooking, heating and hot water, burning free firewood, and it produces easily more than enough heat. We dump excess by switching in radiators in the downstairs rooms. Once the hot water cylinder is hot the radiators can be left running indefinitely as long as the stove is alight.
    We basically live in the kitchen, which is large and hot, and if wanting more than background radiator heat in the sitting room we light the open fire.

    It takes 20 minutes from stone cold to heat the hob enough to cook or boil a kettle, but obviously a few hours to get the oven hot enough for baking. It's just a matter of planning requirements in advance.
    We don't normally try and keep the stove in overnight, but it will do so with a shovelfull of anthracite on top of the wood.
    • CommentAuthorbxman
    • CommentTimeFeb 29th 2016
     
    Seems I was wrong at least it has flushed out someone with first hand experience .

    which was what was needed.

    How much does a modern Rayburn weigh? the old ones weighed several hundredweight.

    However I would still insulate as a priority it will make best use of all that hard won wood you have gathered .
    • CommentAuthoran02ew
    • CommentTimeMar 1st 2016
     
    But is does prove that pushing residual heat around a few radiators once HW demand has been met probably wouldnt be enough to provide a charge to a thermal store, how much wood has has to burnt before the radiators engage? how long a burn before hot water demand is met?
  2.  
    Thanks for all of the comments as usual. Please don't feel the need to apologise for going off on tangents - I have found this very useful when looking through other threads.
    I've not got to grips with the quote thing yet but in response to a few posts - I don't intend keeping a fire in all night and I just use the hand tools to make the timber small enough to haul back to my van or trailer, I process the firewood with a chainsaw after that. When I'm no longer enthusiastic or able to cut wood I hope to hire a young, enthusiastic, able person to chop it for me - I feel it is something I'd like to invest my pension in. Also I should mention that I'm not opposed to buying in a load of logs now and again, many of my neighbours do, I just like having the option to do it myself. This also puts me off pellet boilers- always in thrall to the supplier.
    As for solar, we have a PV array thanks to the previous owner taking advantage of the very high initial FIT which we now benefit from. I hoped to tie this into the system by having three immersion heaters at different levels in the thermal store.
    I've taken on board the advice that it is asking too much of the rayburn to do everything and currently favour the idea of having the living room stove feed the TS from a backboiler and have a split system for DHW and CH. I'll try to draw myself some schematics to get my head around a couple of different options (mainly to ensure that both summer and winter needs can be met and that the solar element can be utilised effectively).
    Reports of the timescale for cooking on the rayburn are in line with my expectations.
    Thanks everyone for the helpful advice.
  3.  
    Dont pass off the Lohberger because it uses pellets it is actual a very clever dual fuel burner so that it can automatically light itself at a preset time using pellets but then once you get up you can feed it logs all day and the pellet feed automatically turns off.
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