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    • CommentAuthorEd Davies
    • CommentTimeJan 8th 2014 edited
     
    Thanks billt, always nice to see real numbers. Supports figures I've seen elsewhere which indicate about 45 minutes generation per day.

    But, where? What inclination?

    The ET figures are less useful without understanding what they're feeding.

    Posted By: billt3.8kW PV … array is larger than it would be possible to install on any reasonably sized house.
    3.8 kW is pretty much the standard installation often set by the 16 amp DNO limit rather than by roof size. It really doesn't take a lot of forethought to design your roof to be able to take considerably more.
    •  
      CommentAuthordjh
    • CommentTimeJan 8th 2014
     
    Posted By: billt
    People seem to be missing the fact that it's cold in winter largely because there is very little solar energy. If there's no solar energy you can't harvest it, no matter how much wishful thinking is applied.

    Agreed. They also tend to look just at space heating and ignore the DHW elephant in the room.

    ST, as you no doubt know, there is no best. If you have a PH, then mains electricity is undoubtedly best. Low capital cost and running costs should be trivial, as not much energy will be needed.

    Are you thinking of resistance heating or heat pumps? What do you mean by 'best'? Lowest cost? Lowest carbon? Most reliable/least fuss? And what about discount rates for comparing capital against running costs etc. You may yet persuade me not to install a gas boiler, though it would be more difficult to persuade SWMBO to do without her gas hob (she's not convinced by new-fangled induction yet).

    Self generation is silly if you have a mains connection, so there isn't a "best".

    It would certainly be silly if PV wasn't subsidised but why is it silly in the crazy real world that we have?
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014 edited
     
    Posted By: SteamyTea(by best I really mean most appropriate)
    I did add this.

    You just have to work out what is going to be your most effective method of supplying your HP.

    This time of year I use about twice as much for space heating as I do for water heating. One disadvantage of E7 resistance heating is that HDDs mean little as you draw energy from the grid for the same amount of time.
    This year I have decided to change track and limit the E7 times even more with additional timers. This does mean a slightly colder house, but that can be supplemented with a fan heater for a few minutes (very really more than an hour but has been very mild so far). I am trying to keep overall usage to below 20 kWh/day.
    If I compare the last week with same week last year I have saved 19 kWh, but the temperature is 1.2°C cooler this year (still mild though). Does not sound much of a saving but when it comes to price that is probably a saving as I have swapped day rate for night rate (think I had the fan heater on for 10 minutes all week).
    If I look up a week with similar weather then the 30/01/2012 to 5/02/2012 is within 0.2°C and I used 180 kWh. So I was possibly using about 40 kWh on heating during the day (as opposed to extra in the storage heaters).

    So rather than just look at the technologies for heating and generating, it may be worth looking at the management of your heating. I bought 3 battery backed up 16A timers (about £100). If I can save 30 kWh/week, but that saving is at £0.17 then over the 4 months heating season I have saved £82.
    So 'best' for me seems to be better control of resistance storage heaters as it has a payback in just over a year (on space heating, there is also some water heating savings too). It is all a matter of scale though, I only use 5.5 MWh/year all in.

    If I was going to go down the RE route then I would go for PV because of the reliability and simplicity of the system and the generous FITs. Trouble is with my small roof area that is angled in the wrong direction my £/W price is prohibitive (£3.5 to £4/W installed). I would not worry about my generation matching my demand though.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 9th 2014 edited
     
    Billit, the paltry figures in your RH col, av 2.0, are what you'd expect for a standard ET (or flat panel) wet collector system in Dec - hopeless. As you say, just oversizing the hopeless is still hopeless. Did you see
    Posted By: fostertomMaybe you guys are thinking of standard set-ups that are optimised for whole-year maximum production, or at least you're thinking of the dregs of production that still remain in mild-weather. A whole system (incl but not only the collectors) that's optimised in several ways for cold-weather production, storage and input is a different animal - talking 60% end-to-end capture/conversion efficiency.

    The fact that your mid column, av 3.2, for PV in Dec, is higher than the ST figure, splendidly proves (part of) Ed's point - despite PV's nominally much lower efficiency than ST, in deep winter PV maintains its conversion efficiency while conventional ET or flat panel ST bombs.

    But a cold-optimised ST whole-system would maintain its conversion efficiency - whether a bit better or bit worse than PV - that's the question. If you re-worked your RH col assuming 60% conversion efficiency, how wd it look then?

    Ed's suggestion of PV instead of cold-optimised ST, for space-heating, does imply a v large installation, way above 'normal'. He's saying that tho super-large it's still cheaper £/kW than a smaller ST installation.

    If you had one large PV for space heating you'd still need a 'normal' one for electricity, so makes no sense to say
    Posted By: billitnot enough generation to meet the demand for electrical power, let alone any heating requirements
    • CommentAuthorMikel
    • CommentTimeJan 9th 2014
     
    We have had our GSHP (10KW) and Solar thermal (3 FP, 5.28kW, 305L dual coil hot water tank) system in since 20th March 2013 (oil-fired boiler prior to that). So have yet to have a complete year with this so far.

    We didn't need to heat any hot water from May through to mid-Oct. Since then we have had only the odd day when we didn't have to heat the hot water (normally to 50C). A sunny day in Dec will heat the tank to 50C but you are lucky to get 20C out of any other day.

    These are our average daily electricity metered consumption figures, kWh, (we have 3.84kW ground mounted array, which kept the roof free for SSE facing solar thermal).

    Oct 2011 10.9
    Oct 2012 9.7
    Oct 2013 7.6

    Nov 2011 11.3
    Nov 2012 10.1
    Nov 2013 18.6

    Dec 2011 15.8
    Dec 2012 11.7
    Dec 2013 23.2

    We have had more visitors this last year and a particularly busy Dec, so not all the increase can be put down to the heat pump. The cooker and tumble dryer has taken a bashing!

    We took a long term view with all this investment, so the payback is correspondingly long term. The basic idea was to invest capital and reduce recurrent costs including much lower maintenance costs.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014 edited
     
    Posted By: MikelA sunny day in Dec will heat the tank to 50C but you are lucky to get 20C out of any other day.
    My WH cylinder rarely goes below 35°C, if it does then apart from dish washing we don't use hot water (too cold to use). So if that 20°C is the temperature coming out the collector then it is of no use. Though I know you know that:bigsmile:

    Posted By: fostertomBut a cold-optimised ST whole-system would maintain its conversion efficiency
    Efficiency is the wrong measure here. What you need is kWh above a set temperature point. It is no good just raising a few kgs of water from 1°C to 3°C, what you have to do is raise a few tonnes from 30°C to 40°C to heat even a small house. And that will take a large collector area regardless of ST technology.
    Right now it seems quite sunny compared to what we have had the last few days, but the eye can deceive you. I just looked at my local solar meter and it has peaked at 84W/m^2 (10AM 09/01/2014), so probably get nothing from ST and maybe 5W from a PV system. So not a lot of use for space heating.
    Things have to be kept in perspective.
    • CommentAuthorMikel
    • CommentTimeJan 9th 2014
     
    ST wrote: "

    My WH cylinder rarely goes below 35°C, if it does then apart from dish washing we don't use hot water (too cold to use). So if that 20°C is the temperature coming out the collector then it is of no use. Though I know you know that."

    You've just sent me off to get the readings now that the sun is out here!

    Solar panel temp: 30.1C
    Hot water temp (top part of tank) 44.5C
    Bottom of tank (where the solar thermal feeds in) 19.7C

    So we might get something out of even a dull day if the cold water feed is 10C.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014 edited
     
    :cool:

    I really should put some sensors on my tank, I just measure the temp coming out the tank (cause that is what I want hot).

    So if your tank has a mean of 33°C, you can get some energy into the 'bottom' third. Do you know the mass flow rate of your ST system and the size of your tank?

    At 10:10 it was 105 W/m^2 then dropped again
    •  
      CommentAuthorfostertom
    • CommentTimeJan 9th 2014 edited
     
    I know that the ASHP in the topic title is supposed to cover both space heating and DHW, but my part in this thread has been specifically about space heating, and specifically about deep winter.
    I agree with comments above that in deep winter, no 'standard' solar collection system, whether PV or ST, and whether or not multiplied-up by a heat pump, ASHP or GSHP, will help significantly with either space heating or DHW. Particularly so DHW, which demands higher flow temp, ruling ST out completely, tho PV might help slightly.
    However, if deep-winter DHW is out, for deep-winter space-heating there is a possibility - but it won't be a 'standard' system, whether PV or ST.
    If it's to be 'non-standard' PV, that means a huge collector area - and Ed's suggesting it will still be cheaper £/kW than a smaller 'non-standard' ST system. And it could help a little bit with DHW.
    If it's to be 'non-standard' ST, that means a whole-system that's optimised for cold, integrates collection, storage and delivery, and consequently gets about 60% end-to-end conversion efficiency. That v high conversion efficiency means that weak deep-winter insolation is enough to satisfy space heating in a near-PH, or even a significantly 'relaxed' PH!
    However it achieves that by providing a flow temp abs no higher than it needs to be for large-emitter radiant space heating - only 23C or so. Therefore such a non-standard ST system wd offer nothing for DHW.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 9th 2014
     
    Posted By: SteamyTeaWhat you need is kWh above a set temperature point. It is no good just raising a few kgs of water from 1°C to 3°C, what you have to do is raise a few tonnes from 30°C to 40°C to heat even a small house.
    As per my last post, what you have to do is raise many tonnes of masonry (the outside walls, inside EWI 'tea cosy') to 19C (outside surface) so its inside surface is 18C, which as a large-emitter radiant heater will provide 17C internal comfort temp. Yes, there's many sophisticated questions around that simplistic outline, and I've discussed those here many times, and will have to do so again no doubt.
    • CommentAuthorMikel
    • CommentTimeJan 9th 2014
     
    ST: tank size is 305L. The solar thermal system has a flow meter pumps at 4L/min.

    Latest readings at 12.05pm

    Col temp: 35C
    Bottom of tank: 30.1C
    Top part of tank: 40.0C

    As the sun rises in the sky, so the cloud starts to bubble up. Sunnier down by the coast but nearer the floods!
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014
     
    Sunny in Porthleven at 12:40. No flooding or other unpleasant things today thankfully. :bigsmile:
    • CommentAuthorMikel
    • CommentTimeJan 9th 2014 edited
     
    Just taken a series of readings to capture the peak output today for the solar thermal.

    2.00pm. 2.15pm. 2.35pm. 2.55pm

    Panel temp. 38.0C. 40.4C. 44.4C. 34.4C
    Bottom of tank. 34.7C. 35.3C. 35.8C. 36.0C
    Top of tank. 36.6C 37.2C. 37.6C. 37.8C

    Total PV production to 3pm (3.84kWp array): 5.3 kWh, peak output today 1.79kW
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014
     
    If your PV actually a 3.48kWp system or is that just what the G83 inverter limits to? From your peak figure you could have had a 5 kWp system (ish) and stayed within the G83 limit.
    If it is 16 240Wp panels have you thought of adding a few more, or changing the ones you have to higher capacity?

    This is what the clouds has been doing, though probably not directly over yours.
    • CommentAuthorMikel
    • CommentTimeJan 9th 2014
     
    3.84kW is the system.

    PV output today to 3pm, from the datalogger which reads 4% higher than the generation meter (as an attachment, I'll work out how to get it to display when I have a bit more time).
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014 edited
     
    Similar to my chart :cool:
    • CommentAuthorSprocket
    • CommentTimeJan 9th 2014
     
    Just adding a "me too" :-)
    Scaled, it's a pretty close match from the 20kWp here. We had 24.9 kWh today. Peak was over 12kW.
    Our 10am peak looks just a little bit brighter. We had a couple of hours with over 5kW available in the middle of the day.

    It *was* nice weather though. I seem to remember this time last year was 'orrible.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014 edited
     
    Posted By: SprocketIt *was* nice weather though. I seem to remember this time last year was 'orrible.
    Let's have a look, first chart was last year:
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014
     
    Yes, lot cloudier last year
    • CommentAuthorEd Davies
    • CommentTimeJan 9th 2014
     
    We seem to have a conundrum, do we not? Both Mikel and Sprocket's systems have peaked at around 50% of their rated powers today from which we might infer insolation of around 500 W/m² yet Steamy's readings show a considerably lower peak. I'd speculate it's because Steamy's readings are in the horizontal plane whereas the PV panels, by some strange coincidence, point somewhere in the general direction of the Sun. Any other suggested resolution?
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 9th 2014
     
    Probably right at around Noon this time of year, and there is a 25 to 30km distance between the weather station and Mike's location.
    I think the sun got to about 27° altitude at noon, so I think that implies a 10% difference, (cos of 27 = 0.9), still leaves a 100W difference.

    (I hate geometry, it is all over the place)
    • CommentAuthorEd Davies
    • CommentTimeJan 9th 2014
     
    For direct rays (i.e., ones straight from the Sun, not scattered by dust, molecules or clouds) the W/m² that a flat surface will get compared with one perpendicular to the rays is proportional to the sin, not cos, of the elevation. (Consider that when the Sun is directly overhead the ground receives the full insolation with sin 90° being 1, when the Sun is on the horizon sin 0° = 0 giving no direct power on the ground.)

    So 500 W/m² in the direct ray for 30° (cos(30) = 0.5) would be 250 W/m². ST's data shows a peak of 350 W/m² so that's probably 100 W/m² of scattered light.

    In reality, the panels will be seeing some proportion of the scattered light, too, so the direct rays will be less than 500 W/m² and the scattered component greater than 100 W/m².
    • CommentAuthorskyewright
    • CommentTimeJan 10th 2014 edited
     
    Posted By: SteamyTea
    I think the sun got to about 27° altitude at noon

    At tad over 11° at solar noon[1] here at 57N at present according to
    http://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html

    Winter sun can be quite effective here through a window or on a near vertical panel.

    Mind you, this year in December & so far in January we've seen very little sun at all - December's PV production was just 40% of the PVGIS figure at 18kWh in total, that's the poorest monthly figure by far (both as a total and as a percentage of PVGIS) in over 3 years.


    [1] About 1230 at our longitude.
    • CommentAuthorEd Davies
    • CommentTimeJan 10th 2014 edited
     
    Posted By: skyewrightAt tad over 11° at solar noon[1] here at 57N at present according to
    Yes, should have mentioned in my post above that the difference between horizontal and perpendicular-to-the-rays panels is greater the further you get, in the UK, from Steamy.

    Mind you, this year in December & so far in January we've seen very little sun at all
    Funny, it's been very bright quite a few days over this side (Caithness). Probably chillier this way but I think I made the right choice avoiding the we[s]t coast.

    [1] About 1230 at our longitude.
    That depends, plus or minus about a quarter of an hour, on the time of year as well as the longitude.

    http://en.wikipedia.org/wiki/Equation_of_time
    •  
      CommentAuthorfostertom
    • CommentTimeJan 10th 2014
     
    Posted By: Ed Daviesthe difference ... is greater the further you get, in the UK, from Steamy
    Even when he's off on holiday?
    • CommentAuthorSeret
    • CommentTimeJan 10th 2014 edited
     
    I've got a PV system and a little air-to-air heat pump. The days when I can run the heat from the PV are pretty few and far between.

    Besides total output you need to consider timings. In my case the PV is optimised to catch morning sun, which is idea IMO as that's a more useful time to produce heat. However there's a big chunk of winter in which the sun is too low to be hitting my roof until after about 09:00, which is a bit late IMO. It does work well on spring and autumn days where the array is producing a useful amount of power by about 07:30, which is when I'm wanting heat.

    For me, it's a nice bonus to be able to use my PV to run the heat pump, but in general I just run the heat pump when it's needed. It's very rare that I'll switch it on just to take advantage of available solar power and even then getting more than an hour or two is pretty unheard of.
    • CommentAuthorEd Davies
    • CommentTimeJan 10th 2014
     
    Seret's points are good but do assume it matters when you run the heat pump. If the house is massive and tight it doesn't so much.
    • CommentAuthorSeret
    • CommentTimeJan 10th 2014
     
    Indeed, I was going to mention that. Same goes for heat stores I suppose.
    • CommentAuthorSprocket
    • CommentTimeJan 11th 2014 edited
     
    Yes, PV here doesn't kick in usefully until about 10am.

    GSHP is on a timer to start at 10am.
    Large thermal mass and air tightness means internal temp this morning with no heating was still 21.5C
    But it has no useful solar aspect, it's a big old stone barn facing east/west.
    Right now we are generating over 8kW PV which is plenty enough to run the 12kW GSHP for space heating and DHW. It will be done topping up heat in a couple of hours.

    If we had only 10kWp PV then there still would be enough this morning.
    I don't know what proportion of days would then not be covered by the PV though.

    An interesting thought... this is a twin compressor GSHP. So it is actually 2x 6kW heat pumps. So if there was less PV available you could pretty easily run just one compressor to try to match the lower PV power available.

    An inverter heat pump (like most modern ASHP) could presumably do a better-fit if it were controlled appropriately.
    • CommentAuthorcrusoe
    • CommentTimeJan 11th 2014
     
    Been watching this with interest. Especially Tom's solar wall. If all objections must first be overcome, nothing will ever be attempted. So bravo for trying. A few points...

    Got a call from son-in-law of a customer at lunchtime today who was 'watching' his father-in-law's ST-fed, (oversize) system gain heat (mid winter Jan sunshine) and expressed incredulity at the heat generated. Because we get so little sun is, to my mind, a better case for oversizing ST than not....grab 3 days' hot water in one day, why not?

    FWIW, as far as HP and self-gen electric goes, I have one customer in Wales and one in Cornwall generating enough from hydro to run a HP comfortably. I have never been asked about to design a PV-powered HP system. Not saying there aren't any, just that they appear as thin on the ground as the old rocking horse stools.
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