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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorjamesingram
    • CommentTimeMay 25th 2012 edited
    1 Sold , 2 left , thanks

    Just found this on Ebay , got me thinking about a Pv direct feed DC immersion again .

    Any way of calculating potential output of say 2x250W panel direct DC feed to immersion via Pvgis and then finding potential input to immersion and HW
    eg how long would it take to heat my 150l tank up :confused:
    • CommentTimeJun 7th 2012
    Work on 10% of the kWh.m^-2 for your area and you won't be far out.

    150 kg of water raised by 40°C will take 7 kWh.
    So your going to struggle with a 50 W input.
    • CommentAuthorjamesingram
    • CommentTimeJun 7th 2012 edited
    if i had 2x250W panel at NOCT (nominal operating temp. irr.800W/m2,amb.temp20C)
    on a good day.
    Vmp = 76V Imp=6.9
    so would that be 524.4W of power output under these conditons?
    pvgis for 500W of panels for inverter type sys. give average daily output of 0.742kWh and best 1.48kwh in june
    • CommentTimeJun 7th 2012 edited
    Posted By: jamesingramirr.800W/m2

    That is the problem

    Posted By: jamesingram0.742kWh and best 1.48kwh

    So about 10 days and 5 days.
    back to solar thermal then :sad:
    • CommentTimeJun 7th 2012
    When it comes to water heating you can't get better, apart from a gallon of diesel.
    or a gas boiler :bigsmile:
    mines been using approx 120kwh/week for HW and cooking ( any idea the est. for cooking use of gas)
    • CommentTimeJun 7th 2012
    Posted By: jamesingramany idea the est. for cooking use of gas

    Plot the gas usage against the HDD data, where it crosses the y-axis is about what the non-heating usage is.
    ow , that sounds to complicated for me. anyway i was just thinking cooking, not HW/cooking
    I think Damons est. was 6-7kWh/day for cook/HW
    my old flat with a A rated combi was around 40kWh/week so fit Damons est.
    The new place has got a G rated floor boiler, gravity feed sys. with HW tank so not good but,

    Haven't had the heating on for a month and still 100+kWh/w gas ( most this year in winters with heating on been 340kwh)

    Seems something is not right ??
    • CommentTimeJun 7th 2012
    One way would be to boil a couple of kilos of water in a pan and time it. Assume 50% losses. Take meter readings before and after and see how much it has used.

    100 kWh is enough to heat about 2 tonnes of water, so if your boiler is about 50% efficient it will do a tonne, or about 13 baths.
    Or a shower that uses 10 lt/min running for 100 minutes (1 hour 40 minutes).
    I shall try your experiment , thanks
    • CommentTimeJun 7th 2012
    Experiments are always good You can compare it to using an electric kettle.
    • CommentAuthorjamesingram
    • CommentTimeJun 7th 2012 edited
    no luck there, didn't reg. on my old ft3 meter.

    1l water raised 80 degC
    575 sec. via gas hob in pan with lid on , small burner so probably 1kW
    In electric kettle 0.12kWh (via plug in meter)

    back to the 13 baths for 1 tonne of water , 70l bath
    at most 6 baths (460l) a week and 28 washing up bowls (112l) = 572l HW

    so at best 25% HW sys. efficiency ?
    so if I take 3/17 % for HW/cook then for current average use 120kWh = 102/18, HW/cook
    • CommentAuthorEd Davies
    • CommentTimeJun 7th 2012
    Posted By: jamesingram: “Haven't had the heating on for a month and still 100+kWh/w gas...”

    At least 25 kWh of that could be the pilot light:


    Worth investigating (watching the meter closely).
    • CommentTimeJun 7th 2012
    I think I heard my name mentioned: I didn't do it, I wasn't there!

    Gas use over the last 2 months has been ~5kWh/d for cooking and DHW: heating went off at the end of March.



    • CommentAuthorSeret
    • CommentTimeJun 8th 2012
    I use about 10kWh per day myself, with an ineffcient old boiler, kids bathing every day and a wife who likes long showers, so if you take mine as somewhere near the upper bound and Damon typically likely to be the lower one, it should give you an idea of which a ballpark you should be in.

    Reading the meter over summer when you've got the heating off is the easy way, but if you've got weekly data already then plugging it into iMeasure will generate the graph SteamyTea was referring to. Obviously the more data you have the more accurate it's likely to be.
    • CommentAuthorjamesingram
    • CommentTimeJun 8th 2012 edited
    Thanks Seret , sound like I should be closer to your use with my current setup , so my gas use seems to high at 100+kwh/week.
    what you boiler , a potterton kingfisher flor standing type ?
    Starting to wonder if my meters miss reading , I'll monitor it for a few more weeks
    i've lots of imeasure data for my last place and getting close to a year on the new place , re.HDD it usually slightly above the expected line in our new place as there's still plenty to do
    some info on the project here http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6234&page=1#Item_29 needs an update if I can find the time.
    • CommentAuthormark_s
    • CommentTimeAug 27th 2018
    Just wanted to ask if you did apply resin to your panels or bin them?
    There are some available locally with cracks and I'm pondering having a play
    • CommentAuthorjamesingram
    • CommentTimeSep 19th 2018 edited
    I flogged them in all in the end.
    But.. 6 years later I've 23 panels up on my roof and one got damaged some how about 2 years ago, looks like an air rifle shot or a stone perhaps and the toughened glass has all shattered It's actually only noticable on very sunny day and It points NW so only gets evening sun.
    anyway its hard to get to, was an end of line product and working fine so I've left it til it fails.
    Its on a solaredge inverter so acts individually.
    You may find they are fine even with cracks in as the bonding compound will protect the cells below the glass
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