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Housing - New Build: Viking's new Micro 91°C AE Digester

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  1.  
    @Viking House,

    How much is the total cost for the AE Digester, including installation? Do you have any payback figures/estimates?
    • CommentAuthorRobL
    • CommentTimeApr 26th 2015
     
    I've just spent a happy hour cutting, drying, measuring and calculating our grass clippings...
    The front lawn was last cut 2 weeks ago. It's around 50m^2, and I cut it with the same mower set to the same height. I weighed the clippings using bathroom scales (me+lawnmower boxfull - me+emptybox), then I took a small sample of the grass to calculate it's moisture percentage. Did this by leaving it in an oven at 50degC, and repeatedly weighing it until I got bored.

    Results:
    "Wet" grass mass: 2.5Kg
    Area cut 50m^2
    growing time: 2 weeks (+/-1week of 20th April)
    Moisture level: 60% by mass (even tho when I cut it, it felt dry ish)

    How much dry grass will I get per year per m^2 ?
    2.5Kg * (52/2) * 0.4 /50 = 0.52Kg

    What yearly energy could I get from our 440m^2 garden ? (this time I measured it, last time I guessed badly)
    0.52Kg * 3.6KWh/Kg * 440 = 823KWh

    What average power will I get per m^2 ?
    0.52Kg * 3.6KWh/Kg * 1000 / (365*24) = 0.213 W/m^2

    Let's call Mid April an average month for now. I took 3.6KWh/Kg from here, for "elephant grass" - good description of our lawn sometimes, which is grown as an energy crop:
    http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,20041&_dad=portal&_schema=PORTAL

    There would also be externally added stuff, which at the moment goes into our green bin - uneaten/waste stuff. Don't worry, I'll be measuring that too...

    Had a go at making a "hot" compost too, which seems mostly about the shape & size of it. My heap had been flat, low, and cool before - now I made it more of a pyramid it & covered it (reduce moisture cooling loss), it's warmed up to ~40degC from ambient in a few days.
  3.  
    How much petrol/energy was used to cut the grass?
    • CommentAuthorwoodgnome
    • CommentTimeApr 26th 2015
     
    Have you assumed the grass will grow 52 weeks per year?
    I might be missing something in your calcs.
    • CommentAuthorRobL
    • CommentTimeApr 26th 2015
     
    I refill a 5litre petrol tank for the petrol mower aprox every other year, so 25KWhr/year used on petrol.

    And yes, you're right woodgnome - I made a pretty dodgy assumption that April grass growth is a good average for the entire year.

    I've now left the grass drying for longer still, and it's got even lighter, suggesting now I had 75% moisture content originally (not the 60% my calcs were based on), so I have even less dry matter than I thought, effectively dropping the yield somewhat. But then the 3.6KWh/Kg I quoted for for Miscanthen assumed 20% moisture content, so in this case 2 wrongs almost make a right, so I won't bother edit it.
  6.  
    <blockquote><cite>Posted By: woodgnome</cite>Have you assumed the grass will grow 52 weeks per year?
    I might be missing something in your calcs.</blockquote>

    If you cover the grass with a cloche it will grow all year round.
    • CommentAuthorwoodgnome
    • CommentTimeApr 26th 2015 edited
     
    You would be lucky to get much grass growth between Nov and Feb, if any.
    I like the idea of a 440m2 cloche!
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 26th 2015
     
    Posted By: RobLHad a go at making a "hot" compost too, which seems mostly about the shape & size of it. My heap had been flat, low, and cool before - now I made it more of a pyramid it & covered it (reduce moisture cooling loss), it's warmed up to ~40degC from ambient in a few days.
    If you know how much moisture you loose in the composting, and the average temperature and how long it takes till it stops composting, then you can work out the thermal energy generated.

    It is good to collect real data isn't it :bigsmile:
  9.  
    Posted By: woodgnomeYou would be lucky to get much grass growth between Nov and Feb, if any.
    I like the idea of a 440m2 cloche!


    How do you think they keep the grass growing through the winter on football pitches if your not a top flight club with undersoil heating.
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 27th 2015
     
    Here is the link to the grass growing rates that I linked to somewhere else:
    http://www.dardni.gov.uk/grasscheck-13apr15.pdf
    • CommentAuthorRobL
    • CommentTimeApr 29th 2015
     
    Green bin day today, so out came the scales. Madness confirmed in eyes of family.

    2 weeks worth of compostable kitchen material came to 7.9Kg. If I assume the same 60% moisture content as the grass, then this represents around 82Kg dry material/year, giving perhaps 300KWh/year of energy when composted.

    So if I collect all the compostable material, both from our garden, and from the kitchen, I could get a theoretical 1.1MWh of heat/year.

    Whilst this doesn't sound that much, it's more than we get out of woodburner - being ocaissional weekend users. Getting, cutting, storing wood is actually a load of effort, so maybe there's something in this ?
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 29th 2015
     
    Keep measuring as you are coming into the best growing period for grass.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 6th 2015
     
    Any news on how the digester is working, other than what I have heard.
    • CommentAuthorbxman
    • CommentTimeSep 2nd 2015
     
    ST you were going to see this and I was hoping you would be giving us the benefit of your observations .

    Is anything happening ?

    It all seemed to good to be true .

    What is the News on the project ?
    ST VH or anyone else
    Thanks Patrick
    • CommentAuthorconverse
    • CommentTimeApr 25th 2016
     
    There are details of big Ireland project up on the Viking website now - but I don't know if this is up and running yet or just projections.

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