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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    Hi Guys I have not contributed for a while as often feel out of my depth and so content to read along!

    Anyway at long last we are about to build an extension to the factory/workshop. We have a 10 kW Turbine and a 10 kW Solar PV installation. When we paid for line upgrade to Western Power we requested they leave provision for 30 kW however they said not possible and gave us 25 kW max. Having spoken to Western Power they are now saying 20 kW is now our maximum export they will allow (without silly money going their way). Our installers are saying if we stick another 10 kW of PV on the new roof the odds are that most of the time we would not be able to go over the 20 kW limit as Sun and wind in perfect harmony a rare event, and if we get close there are gizmos that can be fitted to prevent us going over. We use electricity for light, office, machinery etc. and Kerosene for the boiler. Cost wise we spend not far off £10k a year on kerosene but electricity is down to around £2k so my questions are:

    Would, Western Power would allow this?

    Is this the best way for us to reduce our energy import? (we did undertake quite a big insulation exercise a year or so back, thanks for the help ST!) but running the kerosene boiler that melts the wax (we make candles) is still our biggest energy user by a mile. I have been advised that Solar would not be hot enough for our needs (boiler runs at around 75C ) but PV could power heating elements to help heat the water system that the kerosene boiler heats.

    Are we missing a trick here should we be looking at heat pumps, a new pellet boiler etc?

    Any thoughts gratefully received
    • CommentAuthormarkocosic
    • CommentTimeMar 24th 2014
    You can purchase export limiting devices that'll ensure you're never exporting more than 20kW and Western Power will allow this.

    (other brands are available)

    75C is well within reach of solar thermal but needs thoughtful collector specification. (low performance flat panels won't cut the mustard) The commercial tariff is attractive.

    Do you have photos/videos/diagrams of your candle making process?

    What is the return temperature to the boiler? If there's a heating tank and a cooling tank for the candles you can probably run a modified ground source heat pump (water to water heat pump) between the cooling and heating tanks more cheaply than you can burn kero and dump the heat. Running large tanks and night rate certainly.

    Coal (or pellets if claiming subsidies) are also cheap compared to kero. If you're burning £10k worth a year it could be worth the palaver of running a solid fuel boiler.

    Have you exhausted the options for process improvement? Most industrial processes waste oodles of energy, especially those more artisanal processes where energy was historically a minor part of the bill.
    • CommentAuthorSteveZ
    • CommentTimeMar 24th 2014
    New pellet boiler - comment. Our local swimming pool installed a pellet boiler, replacing their oil boiler. According to the latest accounts, the non-domestic RHI payments actually cover all the running costs for heating, so that may apply to your situation as a business user. If this does apply, it would seem to be worth checking the figures. We had better leave out any arguments about the sustainability of using wood pellets or we'll be here all day!

    More PV panels? If you can mount the new panels to take advantage of early and/or late sunshine, rather than trying for the noon peak, you could find the even spread through the day more useful. I would imagine that using electric heaters to heat the wax, with a boost from the oil boiler when necessary, might be the way to go. I have an inverter with a programmed cut-off at the 16A limit, although my own 4kWp array rarely reaches 4kW output as it is split 3:2 East:South, but it does produce electricity over a large part of the day. If I had known the that large Beech in the back garden would have to come down, I might have installed more panels facing West as well :bigsmile:

    Hope this is useful
    • CommentTimeMar 24th 2014 edited
    I am surprised that your RE supplier (who I know) have not already sorted out an electric boiler to heat the water that heats the wax (though heating the wax directly uses less energy overall).
    Do you have figures for your electricity production? Some inverters have this facility built in as standard, and an adjustable relay (though making a device for your needs would not be that hard). From these you can create a supply profile and see how well it fits into your demand profile. I have a spare logger at the moment that I could put on your RE installation that might help.
    For the price of some modules, fixing kit and inverters you can by pass the expense of the MCS/FITS (which you cannot claim as your supply is too small) and get your builders/electrician to fit an independent system. Probably do a 10 kWp system for £10,000.
    Thanks Mark
    I will PM a link for our promo video under 3 mins dont worry (as it in effect promotes a product not sure if I should post it up) not a lot of help but gives you a feel of just how low tech we are! you are right energy was not a real headache 10 years ago but costs I guess have given us all a well deserved wake call.

    interesting that we can in effect over install on the PV.

    The boiler at nearly 18 years old must I guess be a contender for retirement. as budget is limited we could not fit PV or Solar and a new boiler basically the boiler heats the water which runs round in water jackets round the stainless tanks, 7 tanks each can hold 500 kilos of wax water temp return depends on how much solid wax we are melting down over the day, busy times big drop on tick over very little drop.

    Honestly we are very very low tech, our main drawing machine is pre war (and East German) but it is all part of our rustic charm :)
    • CommentAuthorEd Davies
    • CommentTimeMar 24th 2014 edited
    Posted By: markocosic: “75C is well within reach of solar thermal but needs thoughtful collector specification. (low performance flat panels won't cut the mustard)”

    Indeed. However, it's very likely that in practice PV will turn out to be about the same cost or a bit cheaper at these sorts of temperatures.

    Here's my calculator page for comparison of solar thermal against PV set up for 65 K temperature difference (e.g, 75 °C water temperature, 10 °C outdoor air temperature) with current prices for Navitron 200 W Kinve PV panels vs their 20 tube 47 mm evacuated tube panels:


    As you can see in the first graph, when the sunlight gets less than about 400 W/m² the PV gets progressively a lot cheaper than the evacuated tubes. Above 400 W/m² the solar thermal gets a bit cheaper, but not a lot.

    Much below 300 W/m² these ETs essentially cease useful production (all the received heat gets lost to the outside) whereas the PV is producing something of use down to about half that input. (Note that this is because of the high output temperatures - these panels are much more useful for producing lower grade heat in poor light. I have 8 of these panels which which will be used primarily for space heating in less than ideal conditions.)

    There are ET panels around which perform significantly better than the Navitron ones but I think they're also significantly more expensive. Anybody fancy researching and plugging the numbers in?
    Thanks all, some really useful input. all our roofs are pretty much exactly North/South facing so spreading the angles of new PV not an easy option. right off to try and get my head round Ed's calculator...
    • CommentAuthorbxman
    • CommentTimeMar 24th 2014
    Naive Question
    could you use a heat pump to remove the heat from your solidifying candles and transfer it to the wax needed for the next batch of same ?
    • CommentAuthorrhamdu
    • CommentTimeMar 25th 2014
    Some people would call it a big tub of wax.

    Others would call it a phase-change thermal storage installation.

    1kg of beeswax absorbs about 150kJ between 40C when it starts to soften, and the melting point of 62-64C. It releases the same amount when it solidifies again. The figure 200-220kJ/kg for paraffin wax, described by Wikipedia as 'an excellent material for storing heat' http://en.wikipedia.org/wiki/Paraffin_wax

    Put that another way: you need 24kg beeswax or 18kg paraffin wax to store 1kWh. A ton of wax could absorb 4-5 hours output of your 10kW PV. You have tanks for 7x500kg=3.5 tons wax. If I have done the sums right, the idea is not totally crazy (SteamyTea, I *know* you will check my calcs.)

    I don't know what tariff you are on, but if you get paid for generation rather than export, PV might be more economical than solar thermal as a source of process heat. You might need a few more tanks if you seriously intend to pursue a policy of 'melt wax while the sun shines'. They would, of course, need to be well insulated.

    Hey, this stuff could make sense even for people who don't make candles :bigsmile:
    excellent thanks! yes best for us to use rather than export. lots of ideas the other blindingly obvious (Now! and thanks bxman) thing is that having melted the wax and poured it into containers we then want to cool it so end up putting fans on them to speed production. if we used Heat source pumps we could use the heat reclaimed to heat offices, melt wax maybe?
    • CommentAuthorrhamdu
    • CommentTimeMar 25th 2014
    I now have this Willy Wonka vision of an office heating system consisting of a long conveyor belt which carries freshly-made candles, still radiating heat, past every desk.

    But seriously, folks. Certainly there is heat to be reclaimed from the candles. I am not sure a heat pump would be economic, or necessary, for this. When you use fans to cool the candles, what do you currently do with the resulting warm air? Is it laden with VOCs or could it be ducted direct to the office? If you need to transfer the heat to fresh air, a simple heat exchanger might be OK. Exhaust-air heat-pumps are used mainly in places like commercial kitchens where they have a big supply of hot air and a demand for hot water - you might qualify, I guess.

    Better stop. This is all getting a bit beyond my expertise...

    What your trying to do is perfectly feasible using thermal solar but you will need to use thermal oil instead of water. Your max temperature then goes upto 230C which you can regulate down to your boiler temperature. The process is well established for large bakery ovens where temperature control is critical.
    • CommentTimeMar 25th 2014 edited
    John, have you seen the cloud cover in Cornwall!!

    Posted By: rhamduIs it laden with VOCs
    Having been to the factory I can tell you it does smell a bit, not unpleasant, but not what you want it your office/showroom.
    The main problem would be transferring the the low grade energy between buildings. I like the idea of an A2WHP taking the energy out of the production area and piping it to the office. It is a big production area compared to the current office area.

    You don't need a lot of sun to keep the kettle boiling

    • CommentAuthorEd Davies
    • CommentTimeMar 25th 2014
    Really? Any examples of running solar thermal at 230 °C in the UK?

    It might make sense with concentrated solar (probably in a sunny country) but for a setup like Candlemaker's this seems, to this humble correspondent, not a very good idea.

    A quick calculation shows that with insolation below 900 W/m² the standard Navitron 47 mm panels will not produce any output at all at 210 °C above ambient - the losses from the panel exceed the input.

    Of course, this isn't a terribly realistic calculation because it's extrapolating the performance figures way out of the range they're intended to be used in. Still, I suspect it gives a rough idea that really not a lot can be expected. Of course, there are better ETs available but still…

    Even at 1000 W/m² they produce very little:


    with the cost per watt being 10 times that of PV. If you actually wanted to heat thermal oil to 230 °C in the UK from solar your best bet would be to do most or all of the job with an immersion heater run off PV.

    Last summer I left one of my Navitron tubes out in bright sunshine (with the heat pipe in) with the top wrapped in some impromptu insulation (work gloves then some other bits of cloth then a bin liner as a wind-tightness layer). It got to 195 °C and the plastic bung at the top of the tube browned a bit.

    Solar tubes for high temperature are normally spaced 1 in 3 with reflectors where the other 2 tubes would be and thermal oil instead of heat pipes.
    I love the Willy Wonka mental picture not sure the guys would like to be known as Umpalumpa's! just fascinated now with how much heat we waste in production, the fans we use at the moment literally are just big desk fans so they are only stirring up the air not really cooling at all. to give you an idea of just how Willy Wonka we are here is a link to a very short video on how we make them


    Really hope this will not fall foul of advertising rules there are loads of other great candles out there not just ours and candles probably not high on a list of green building products, but if you see what/how we make our candles you can see how low tech we really are!

    We are also trying to get a handle on the energy mix of what we use and what we generate as we have a supply meter and two export meters not easy. All are with Scottish Power and when I spoke to them asking if we could have a smart meter fitted the answer was no they are not installing them until they have to.
    • CommentTimeMar 26th 2014
    Anyone have experience of CO2 Heatpumps as they can heat water up to 90°C.
    Mitsubishi make a 30 kW unit.
    • CommentTimeMar 27th 2014
    Just to give you an idea of how sunny it is down here this is a view of the clouds from my window.

    Still it stops the shadows hitting the PV.
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