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Saving money with solar?

  • 03-06-2008 5:25pm
    #1
    MickLimk
    Closed Accounts Posts: 188 ✭✭


    Can someone have a look over what I've calculated below and see if I'm way off the mark on this? I've taken official figures almost exclusively but want to be certain that I've not missed out on something big here. Unless I'm mistaken, current standard ESB prices are 13.24c/kWh + 13.5% VAT = 15.03c/kWh. Using data from the SEI website and a quote I just got for oil for my central heating (92.79c/litre !), this gives a cost of €0.101/kWh from kerosene with a 90% efficient boiler.

    Evacuated Tube A: Figure of 631kWh/m2 for domestic hot water given in EN-12975 certification document. 1 panel (2.135m2, 20 tubes) gives 1347kWh. 2 panels, 40 tubes (4.27m2) = 2694kWh. Allowing 10% loss for pipework, non-ideal orientation etc. gives 2425kWh.
    At current prices this equates to ESB cost of €364 per year or an equivalent oil saving of €245/yr. This setup should also qualify for an SEI grant of €1281.

    Evacuated Tube B: Figure of 1058kWh per panel of 18 tubes given by supplier. 2 panels, 36 tubes (3.42m2) gives 2116kWh -10% loss = 1904kWh equating to €292/yr ESB saving or €192/yr oil saving. This should qualify for a grant of €1026 based on the total panel (aperture) size.

    Flat Plate A: 517kWh/m2 from EN-12975 cert. Panel size of 4.92m2 gives an output of 2543kWh, less 10% loss gives 2289kWh, equivalent ESB cost of €357/yr ESB saving or €231/yr oil saving and an SEI grant of €1230.

    Flat Plate B: 505kWh/m2 from EN-12975 cert. Two panels of 2.4m2 (total 4.8m2) gives an output of 2020kWh, less 10% loss = 1818kWh, equivalent ESB cost of €284/yr or oil saving of €184, SEI grant of €1200.

    If anyone can point out a mistake in these calculations I'd be most grateful as trying to find this info to calculate wasn't easy! None of these figures take into account the cost of running a pump circulating the fluid through the panels/tubes but this is small in comparison with the potential savings. If you took a 50W pump running for 20 hours, it would only cost 15.03 cent. Average at 6hours/day (complete guess) gives a cost of about €16.50/yr.

    Thanks!


Comments

  • #2
    boots1
    Closed Accounts Posts: 31 ✭boots1


    Mick...very good exercise. Is it possible for you to also post the capital costs of each solution to enable posters calculate the ROI for each option?


  • #3
    MickLimk
    Closed Accounts Posts: 188 ✭✭MickLimk


    boots1 wrote: »
    Mick...very good exercise. Is it possible for you to also post the capital costs of each solution to enable posters calculate the ROI for each option?

    I thought about it but I'm not so sure how good an idea that would be for a couple of reasons:
    1. There's no such thing as a standard install. There are so many variables that will have a large bearing on the final cost that I'd run a mile from anyone who was able to give you a detailed quote without an on-site survey. Cylinder requirements are an expensive variable as is pipework these days so it would be impossible to come up with a complete capital cost for an installation.

    2. Prices paid even for the same equipment can vary greatly depending on the relationship between the supplier and the contractor.

    3. I just picked some examples of tubes/plates that were on the SEI list and had data easily available on. I don't know what the policy on naming specific products on here is. The kWh figures for almost identical looking systems made by different manufacturers can vary greatly so to assume all 40 tube systems would perform the same would be incorrect.

    4. Could be seen as me advertising a service by the mods.

    However, if the mods were ok with it and I could get prices from suppliers for supply of the panels only (including 21% vat), then I could probably post them with the caveat that your installation is certainly going to cost a lot more than the prices posted for the panels.

    Bear in mind that a cylinder could cost anywhere from about €600 for a small twin coil copper one (not even be suitable for all but the smallest solar installations) to about €2k for a larger stainless steel one depending on the manufacturer. Flexible, insulated, stainless steel pipework can potentially cost €40 per metre hence the reason I say it impossible to give an accurate quote without a site visit and next to impossible to provide a capital cost for a 'standard' installation!


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