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Renewable Energy: Solar Payback

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  1.  
    I have an EWI'd Victorian mid terrace with ASHP.

    Is it worthwhile going solar next or or wait for prices to come down further again?

    I have a SSW facing roof

    What sort of payback period in realistic terms not what salesman would give you?
    • CommentAuthorowlman
    • CommentTimeOct 25th 2017
     
    Personally I think the hardware price has more or less bottomed out. The rest is labour, and that'll only increase.

    When you talk of payback are you referring to a grid tied FIT eligible system, or, a home supply system whereby you use and or store all of which you produce. if the latter you also need to factor in the cost of home storage or power diverters. You then need to think of where you'll put the generated electricity. Water immersions are the obvious first place, but you'll not be able to use it with your ASHP without a storage/home management interface.
    The costs for something sophisticated soon start racking up, and in answer to you payback question I'd guess you'll never get payback.
  3.  
    If you ask someone to come and give you a quote they will include a payback calculation. This obviously isn't perfect, but gives an indication to start working with.

    What you'll earn (generation + assumed export) should be relatively easy to model. The opportunity saving of replacing the energy you would otherwise import with energy you have generated yourself would be much harder. Although I am sure the boffins on here will tell me I'm wrong!
    • CommentAuthorJamster
    • CommentTimeOct 25th 2017
     
    Jumping on this and tell me to move it if inappropriate, but this ties in with something else I have been thinking about:

    We're a relatively well insulated home, without a gas supply so all heating and DHW is provided through an ASHP installed under and getting cash back for a FIT (c 3 years in);
    Our mortgage is up for renegotiation at the moment and we would have some margin to increase the loan without affecting the loan to value based percentage rate;
    South facing to within about 10 degrees roof, no obstructions.
    PVGIS suggests 1900kWh yearly generation; our total electrical consumption (all electric remember) is approx 11500 kWh.
    Most recent tarif is 4.00 pence / kWh - is this only going to give me £76 / year? (1900 x 4)/100? Our current tarrif charge on the bill is 11p / kWh by comparison.

    Yes, we would also reduce our demand but obviously the demand vs supply curves don't allign that well so only a proportion would come off our usage - does anyone have any data around a correction factor for how much generated power is used at source rather than being exported?

    Has anyone else done this recently, specifically borrowed to install PV) or have we likely missed the boat? Borrowing rate looks like 2.24%, likely subject to imminent change...

    I'm getting a few quotes for 4 and 8 kW systems - we're rurally located so there isn't a lot of use of our supply so worth looking at I think with the DNO for a larger system, given installation costs will be a lower proportion of any fitting...

    I've rambled on enough for now, but would be interested in your (non-binding, I know the risks!) opinions...

    Cheers,
    Jamie
    • CommentAuthorgoodevans
    • CommentTimeOct 25th 2017 edited
     
    Ball park figures - yes generation payment at 4p / kWh but also...

    50% of generated is expected to be exported which is another payment at 4p /kWh.
    (lumped together that's 6p/kWh generated).

    Regardless of whether you actually use or export the electricity the 50% is fixed.

    But if you do use generated electricity yourself for something you would have had powered up regardless of solar (e.g. a computer), fridge, ASHP etc you save the cost of buying from the electricity company at say 15p /kWh.

    And for all the excess solar dump it into heating even more water (or making the water hotter) to save the heating/DHW costs (depends of cost of heating fuel or COP of ASHP).

    It's better for the environment/country for you to export rather than use excess to heat - but the tarrif system is set up so it's better for you to use the energy in an inefficient way to heat things up.
    • CommentAuthortony
    • CommentTimeOct 25th 2017
     
    You factor in electricity saved through using your own and export at 50% at I reckon 5p per kWh
  7.  
    jamster 1900kWh/yr sounds a bit low, what size system was this for and whats your location
  8.  
    generally it near 1000kWh per year per kW installed in south england
    lets say you use all generated with ashp and or immersion dump
    4kW install £4000
    4000kWh/yr x 15p (grid imported kW price) £600 per yr

    6.5 years to pay for itself then you're saving £600 per year til it stops working
    • CommentAuthorJamster
    • CommentTimeOct 25th 2017
     
    James, we're in Durham and this data is via PVGIS using their default technology and a 4 kW array:

    Location: 54°48'47" North, 1°37'45" West, Elevation: 157 m a.s.l.,

    Solar radiation database used: PVGIS-CMSAF

    Nominal power of the PV system: 4.0 kW (crystalline silicon)
    Estimated losses due to temperature and low irradiance: 10.5% (using local ambient temperature)
    Estimated loss due to angular reflectance effects: 6.9%
    Other losses (cables, inverter etc.): 14.0%
    Combined PV system losses: 28.3%

    I've also done a run with the classic PV-GIS model and that returned 1820 kWh so I'm not sure. Pretty sure our roof pitch is 35 degrees too.

    Tony and Goodevans - thanks for your replies, I'll look at a few numbers. The most crucial bit looks to be around how much of our power consumption I can schedule for when the PV is producing...
  10.  
    Running an ASHP for the central heating would use imported electric overnight so no benefit there.

    Not sure much electric would be used in the day other than at the weekend...

    So the amount exported would have to be decent to make any money?

    6.5yrs payback isn't the best in my opinion as an investment, be better to invest in stocks and shares surely? Particularly as I'd imagine things do and will go wrong?
  11.  
    just run Durham through PVGIS im getting 3480kWh per year for 4kWpower due south
    try it out again
    http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php
  12.  
    victorianeco , I brought some stocks and shares, half of them are now worthless the other half are worth what I brought them for quite a while ago :-)
    My pv panels have already paid for themselves and the FITs I get pay all my household bills
    I know which investment I prefer ( im on the high FITs tariff so very lucky)
    also my back of a fag calc was without any FIT or export payment.

    I dont have my heating on during the night ,
    ASHP with a buffer tank can store heat energy for later use
    Pv immersion dump will sort your water needs.
    timer on washing machines etc to run at peak generation can help use that solar.
    electric car charging during the day another possible use
  13.  
    Ah okay. A tracker fund is a bit more reliable..

    But anyway, can you provide me with a link to where you are making these calcs?

    And what sort of kit or spec do I need to specify?

    How much are buffer tanks? Soon adds to the cost...

    Are battery storage worthwhile if so what type?

    Is 4kw fine or is it better to fill the roof space? I may consider a dormer at a later point mind

    So many questions as I've always thought the installers are ripoffs, promising stuff that is too good to be true
    • CommentAuthorowlman
    • CommentTimeOct 25th 2017
     
    As other have said your fitter will work out standard payback and it'll be part of the quote, but if you are thinking of using all of the electricity yourself and then possibly decreasing the payback time, you'll need somewhere to put the energy.
    AFAIK with power diverters, (more expense), you can only divert solar energy alone, without mains backup, into "resistive" loads, immersions, UFH cable, storage rads. ASHPs are an inductive load and I don't think power diverters can directly alone handle that. So, you are going to need more equipment/storage/management system, to survive on solar alone, all of which will impact on your total payback. There may be more sophisticated diverters on the market since I last looked, but the principle is it will add to your overall costs to fit one.
    • CommentAuthorFred56
    • CommentTimeOct 25th 2017
     
    Jamster. Like others I doubt your 1900kWh from a 4kWp system in Durham. I lived in Ripon, North Yorks (briefly) and installed a 2kWp system. In the three years I owned it I got 1600kWh per year. the roof was south west facing and 45 degree pitch. There is something wrong in your numbers.
    Everyone. Don't forget to account for failed inverters and hardware manufacturers and agents going bust leaving a warranty disappearing in a puff of limited liability.
  16.  
    Is there a preferred brand or kit?
    •  
      CommentAuthordjh
    • CommentTimeOct 25th 2017
     
    Posted By: owlmanPersonally I think the hardware price has more or less bottomed out.

    That isn't what I've been reading in the press lately. They seem to think the downward price trend will continue.

    Posted By: richardelliotIf you ask someone to come and give you a quote they will include a payback calculation. This obviously isn't perfect, but gives an indication to start working with.

    Specifically, they're required to give you an estimate according to a specific set of rules that are deliberately pessimistic. So you're pretty much sure that you'll do better than the estimate. The rules were brought in after early cowboys gave estimating a bad name, I believe.
  18.  
    Going back to the question of "how much of the energy"can I use myself"? I just had a look at my system and in the last two months we exported 24% of what we generated. I suspect our power diverter is the main reason for this as we are out at work during the day so can't really consume when we generate.
    •  
      CommentAuthordjh
    • CommentTimeOct 25th 2017
     
    Posted By: richardelliotI just had a look at my system and in the last two months we exported 24% of what we generated.

    The proportion exported tends to vary a lot over the course of a year, since the amount generated each month is a lot more in summer than in winter. Do you know whether your last two months' figures are a good estimate of your annual figure?
  20.  
    Folks, the Feed In Tariff is funded by all bill payers including the least well off, in exchange for the public good of getting PV Fed In to the grid. They also ultimately pay the cost of the Export tariff to purchase 50% of the PV.

    It's legal for home-owners to play clever tricks using an immersion diverter device to claim the public subsidy without Feeding In or Exporting, instead dumping the PV into resistive heat. This is I think the only way to make PV payback financially and make a personal profit from all the other bill payers and the subsidy system encourages that.

    I chose not to do that and so I don't have PV myself. I don't tell others how to live, we all make our own choices. If a return on investment is required (nothing wrong with that) then I speak to an investment advisor along the lines VE suggested, maybe a green investment fund? Or more insulation?
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 25th 2017
     
    Posted By: owlmanAFAIK with power diverters, (more expense), you can only divert solar energy alone, without mains backup, into "resistive" loads, immersions, UFH cable, storage rads
    Not sure that is correct.
    Electricity is a lazy thing and will take the shortest path.
    So if you run a load of say 3 kW, your PV is supply a variable amount between say 200W and 3 kW, al that will go to your local load (minus a few general cable and system losses). The rest of the load will be topped up from the grid.

    So say your ASHP can supply all your thermal needs in 4 hours, you can just use a timer set between 10AM and 2 PM every day on the ASHP.
    That way any PV generation will get used by the ASHP (assuming no short cycling, defrost setting etc).



    Posted By: WillInAberdeenIt's legal for home-owners to play clever tricks using an immersion diverter device to claim the public subsidy
    I agree 100%, but I have never liked the FiT system, it stifled the industry in the end.


    Posted By: djhThat isn't what I've been reading in the press lately. They seem to think the downward price trend will continue.
    What press? Do you have a reference.
    • CommentAuthorJamster
    • CommentTimeOct 26th 2017
     
    Fred and James - I've re-run this and you are right - I'm getting around 3700 kWh as a yearly figure so a significant operator error there at some point!

    I'll work out what this will return vs additional borrowing costs; I'll post any quotes and specifications I get given too. Any significant reductions in usage I'll leave out of my calculations in the first instance I think and I can look at automatic scheduling as a seperate project... Makes me wonder if the old nightstore radiators could make a comeback...

    Thanks again everyone.
  23.  
    My ASHP takes no longer than 20mins to get up to 50c from whatever is used previously. I guess it would be even better to top it up to say 65c in the day and use the COP of the pump to the advantage.

    It all gets confusing when you start adding certain scenarios and so forth...
  24.  
    Posted By: djhDo you know whether your last two months' figures are a good estimate of your annual figure?


    Sadly I don't. I have a generation meter made by Geo Solar and the display in my kitchen only stores two months of data. A longer time series of data would be stored on their website, but I need to re-register my device on their portal and I haven't got round to doing that yet...
    • CommentAuthorowlman
    • CommentTimeOct 26th 2017
     
    Steamy: I did say without mains backup.:wink:
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 26th 2017
     
    Owlman
    See what you mean now.

    Victoria, if you run your ASHP up to 65°C, your CoP will be crippled and it will almost certainly be using a built in resistance heater. Not that it matter if you are using PV.
    • CommentAuthorJamster
    • CommentTimeNov 2nd 2017
     
    Hi again,

    Have kicked this around a little bit more and my outline conclusions:

    Assuming £5000 for installing 4 kW of capacity and generating 3500 kWh / year (see above), also assuming the deemed 50% export rate and that I use 50% of what I generate and save that against my bill...

    Income from FIT and export tarrif is around £228 a year and electricity-use savings would be £193, a total of £421 vs a borrowing cost on the mortgage of £252 a year so £170 better off at current rates.

    Scaling it up to 8kW of panels, income would be £457, savings £386 with a total of £843. No quotes for this yet, but assuming £10,000 would be £576 in repayments, so I'd be £267 better off.

    I've spoken to a couple of installers and also done some modelling for using powerwalls or similar so essentially all generated electricity is used at home. That changes the outlook slightly and means the savings are more significant than the FIT. I don't have any reliable powerwall prices yet but it suggests to me that its possibly economical to do this now, partially because the FIT-system will stay pay the deemed export rate of 50% until a decent smart meter design is agreed.

    Will in Aberdeen, you're right, this is a flaw so I imagine a smart meter rollout will be manadated for powerwall schemes at some point?

    Anyway, hope this helps someone...
  28.  
    I recently went to a lecture by a Imperial PHD student who had been modelling the costs of various renewable technologies including storage. Part of his analysis looked at the cost projections of home storage, and the conclusion was that they wouldn't be cost effective until around 2030. There was a caveat in the presentation on how complex this was to model and an acknowledgement that his model was simplified - aka take '2030' with a pinch of salt.

    I did some vague looking at home batteries when we installed our PV system and I also concluded that they were very expensive compared with the cost savings of importing electricity. It would be very interesting to hear what prices you are quoted.

    Their research is published here (subscription required):
    https://www.nature.com/articles/nenergy2017110
    • CommentAuthorJamster
    • CommentTimeNov 2nd 2017
     
    Posted By: richardelliotI did some vague looking at home batteries when we installed our PV system and I also concluded that they were very expensive compared with the cost savings of importing electricity. It would be very interesting to hear what prices you are quoted.


    I will let you know. I hope its earlier than 2030!
  30.  
    there's always the DIY powerwall option :-)

    https://www.youtube.com/watch?v=dGXIRGJdbHc

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