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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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    • CommentAuthorPhill
    • CommentTimeApr 30th 2007
    Hi all

    This is my first post here on this forum, I’ve been looking around for a few days and have found the whole site very informative and the input from the forum users is excellent.
    So please excuse me if I pick your brains!

    I’ll give you an idea of what were planning so it might help with the “bigger picture”, we have decided to build a new house again (just completed first one!) but we do want to really push for a more eco friendly house especially on the energy use side of things.
    I would really like to live off grid but I don’t think that may not be viable for us as I don’t fancy a huge array of batteries for when the wind doesn’t blow and the sun isn’t shining. We live in Caithness and very exposed on a hillside so I do think a wind turbine should be pretty successful for the majority of power required and I have been doing a lot of research into this and getting accurate data for local windspeeds etc. Heating will be from a GSHP coupled to a solar PV to run the system and a solar heat panel to help boost the hot water etc.

    Now my first question relates to an alternate or backup for power on a calm day, this particular thought only really came to me last night.
    We have plenty of land and we are on a hill so if I were to dig two reservoirs, on at the top and one at the bottom, how large a volume of water would we need over what ratio of fall to produce a useable supply of power through a water turbine?

    Now I know that question actually is quite vague but hydro power is something I know nothing about and despite a quick search of the net this morning I’m not finding much useful information, in short would it be feasible to have the two reservoirs and when power is required on a calm day a valve on the upper reservoir can be opened to release the water to turn the turbine and then once the wind turbine is running, and ideally using the power dumps, pump the water back up.

    Does this seem feasible?

    Many thanks
    Your own pumped storage facility eh? I like the idea. Why not build your house out of the earth you dig from the holes? The ponds might also have uses for aquaculture, encouraging wildlife or fresh water swimming. I think it would be a costly thing to do just for the power storage but if incorporated into a permaculture design where the ponds have multiple uses then sounds like a great idea to me. No idea about the technical aspects.
    • CommentAuthorPhill
    • CommentTimeApr 30th 2007
    I do think on the practical side with the construction it would be pretty costly if the idea was workable, however I suspect the actual size and volume of water required is going to be the deciding factor to write off my theory!:shocked:
    We do want a sizeable pond anyhow so this is where the idea stemmed from, I thought it may have had a possible use as a standby power supply.

    • CommentAuthorJane Smith
    • CommentTimeApr 30th 2007
    This bit worries me for two reasons:

    "Heating will be from a GSHP coupled to a solar PV to run the system"

    First reason: you'll get most of your PV electricity in the summer, when you least need heat. Our neighbour, who has a 2kW PV array, gets nothing from his PVs from November to February, which is when you'll need the most heat.

    Second reason: not sure if the PVs will be able to power the heat pump directly. We're off-grid, and have a wind turbine plus batteries and inverter for our electricity. We can't have a heat pump here because heat pumps use electric compressors. The compressor stops and starts periodically through each day, and each time the compressor starts it sucks up a huge peak of electricity, which would overwhelm our system. Within a split second that peak dies away and the consumption becomes manageable: but that peak makes it impossible for us to run a heat pump off-grid without installing a generator dedicated to the heat pump, as we understand it. Unless anyone here knows different?

    Onto the hydro scheme:

    "if I were to dig two reservoirs, on at the top and one at the bottom, how large a volume of water would we need over what ratio of fall to produce a useable supply of power through a water turbine?"

    I'm assuming that you have a stream or something that you're planning to dam up to create these two reservoirs? You might have a lot of trouble getting planning permission to do that. If you're near any agricultural land then I suspect the farmer wouldn't be too happy with you.

    We looked into hydro a while ago and I found quite a lot of information about power available. Drop and volume are both important, but you need a lot of both to get a useable amount of power. The information is out there, try looking for installers' websites.
    • CommentTimeApr 30th 2007
    Posted By: Phillhow large a volume of water would we need over what ratio of fall to produce a useable supply of power through a water turbine?
    It's all in http://www.british-hydro.org/mini-hydro/index.asp
    One of our schemes included similar concepts but we prioritised the renewables for electricity production ratehr than heating.
    You have correctly identified that having a water source / store opens up many more sustainable advantages.

    There are a number of high head / low head and no head hydro power units available. For your domestic application I would suggest a budget of 3K for the new techno bits although it is fairly easy to convert certain water pumps into hydro units.
    The main problems relate to intake screens and the maintenance thereof.

    If you can get a fall of over 6ft I would recommend a down draught unit. They are very efficient and require low volumes of water. We Selected a load profile of 4 to 8 hours as we didn't want to effect the water level at the head too much. By combining the techniques of a dew pond and maximising your rainwater collection area coupled with abstraction it is practicable to install a micro turbine installation to a volume of water as little as 5m3. The advantages include;oxygenating the water (useful for any grey black water downstream applications) for wildlife, Utilisation of heavy rain for power, pumped storage instead of dump loads.
    We are active in the pico and micro hydro areas and can probably help youy with the detail. If you need any assistance or links contact me directly.
    Good luck and recommend you go for it if you have the space and resource.
    • CommentAuthorPhill
    • CommentTimeApr 30th 2007
    Hi Jane, thanks for your comments.
    The GSHP + PV is, so I’m led to believe, a system whereby a solar panel or panels on a motorised system which will track the sun and run the pump and charge a small battery system for darkness use. I’m not sure how this fits in with the compressor though. Apparently if left to run it is nearly 100% self powered this way, still waiting on techie info for details.

    We’re in a rural location and are surrounded by drainage ditches/burns and these drain off the fields and run off into larger burns down to the sea and over the winter will soon fill up a quite a large volume. The drop could be 8 – 10 metres.

    fostertom, thanks for the link!

    Hi Paul
    Thanks for your input too, just looking through your website now – I will be in touch!

    Thanks all
    Phil, could you give me details of who is providing the PV + GSHP system? I'm doubtful it will work for you year-round, but if it does I want one!

    You can email me at info at peafowl dot freeserve dot co dot uk if you'd rather not put a name up here--I'd be grateful.
    • CommentAuthorGBP-Keith
    • CommentTimeMay 1st 2007
    I've actually got a hydro setup similar to what you are asking about Phil - top ponds - big ones and a 24 metre drop . I've not had chance to read the whole thread so excuse me if I'm off the mark here.

    My, currently burnt out hysro system is AC because the turbine had to be placeed some way from the house. It has been a money pit and I could have installed a good few more PV's had I not embarked on the hydro.

    Advice from an old hand at hydro failure would be do at least one year (probably two) of water flow testing first, plan on a drying climate and don't try to rely on top ponds, they don't hold as much water as you think. if the stream cannot be proven suitable as a steady supply then don't bother UNLESS you can run the system as DC close to the buildings.
    • CommentAuthorGuest
    • CommentTimeMay 2nd 2007
    Hi, as a rough ready reckoner, the total amount of storage that you can

    Potential Energy = mass x height x force of gravity

    Height is the "head availiable"
    Assume force due to gravity to be 9.81
    Now mass is the amount of water you can store in your reservoir. You find mass by multiplying volume by density (1000kg per cubic meter is the density of water).

    So that's the "potential" stored in your reservoir.

    The power availiable at any one time depends on how fast you can release (and capture) that power. That requires a lot more calculation, but at least the above is a not-too heavy answer to "how much can I store in my reserviour".

    Hope it helps,

    Gavin Harper
    I might to guessing but a DC drive for a compressor is variable, so it can start slowly (as PV generates) and therefore eleminates high start up loads or spikes!

    Like most projects it is important to calculate the load and then see how much it costs to reduce it and then compare the cost of different generation methods. My guess is super insulation is cheaper then digging reservoirs!
    Given that you like the idea of having your own bodies of water and want to install a heat pump why not a water source heat pump (more efficient).
    What about using the ponds further for even a heat dump (bathing) as well as all the other possibilities.
    As a start we initially use 12 as the magic number to size things. ie Each of your renewable energy systems say heat generation first (solar thermal 6 hours/WSHP 6 hours) and electricity generation second (PV 6 hours / hydro 6 hours) perhaps even adding a wind turbine (to improve resilience) all total 12 hours operation.
    Allow for 12 starts every day and 6 hours normal running as the basis for the HP electrical load.
    The starting load for the compressor could be provided by a seperate battery system easily.
    You probably wont need a dual mode (ie cooling heat pump) in this lifetime for your location but hey...
    Contact me if you need some pointers to 500W - 2kW micro Hydro units.
    • CommentAuthorPhill
    • CommentTimeMay 3rd 2007
    Hi Gavin

    Thanks for that, am I being a dit dimm by asking what is the potential? i.e. watts, joules etc.

    Hi Keith, your comments are noted! I've not thought about AC or DC, I guess DC as I was thinking of a low power backup.

    The whole idea was a bit of a brainstorm that may never come to fruition however I might try a small scale version just for curiosity!


    • CommentAuthorGBP-Keith
    • CommentTimeMay 3rd 2007 edited
    Posted By: paul johannsen
    By combining the techniques of a dew pond and maximising your rainwater collection area coupled with abstraction it is practicable to install a micro turbine installation to a volume of water as little as 5m3.

    I find this very hard to believe Paul. It must be pica-pica. Give us some data please.

    I've got storage of about 10,000 M3 of of water and I can push it through my turbine in 12 -15 hours or so (10 ltres per sec). When my AC system was working, it produced 1.3kw per hours. BUT without a LOT of inflow (rain) there is little point in 12 hours of electricity every few weeks (the time it might take to refill the ponds between April and September) My alternator actually burnt out from being turned on and off a lot during cold weather.

    Now If I can replace the system with DC I could take less flow on a continuous basis. perhaps 1 litre per sec would do. The hamstring is the distance from the house to the turbine. I am investigating some kind of inversion at the turbine house to send up the wire as wild AC.
    Where are the lines between macro / micro / pico ? Can confirm my micro pelton at 3gpm (15 litres/minute) lasts for just about 6 hours with the output gracefully reducing for the last hour on just over 5m3.
    As you well know there are so many ways to connect things and reviewing your installation (again) appears to have a lot of potential.
    Perhaps alternative spinner would give you better performance what are you using?.
    Have you considered running a multiple set with your shunt load being pumped storage / batteries (to save your alternator).
    Another way round the distance between load and generator is to specify a generator with higher voltage windings.
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