Solar hot water?, too many trees, solar pv likewise, GSHP? only using 4.5KWH per day at the moment and don't want to use more leccy, but we have got a nice little woodburner.

The new house (80 sq m) is to be built 2009, so planning ahead!

I sit and watch the kettle lid lifting as it boils on the stove, (ring any bells?). New electricity supply £15k or so! Watch miniature steam engines pull 20+ people along a track, mighty powerful.

Why can't I boil a bit of water and trickle generate electricity for my needs? Nothing huge, just maybe 500 watts per hour?

Everyone simply laughs at the idea, but I don't get the joke. It must have been done somewhere before!

I agree with Ted the big problem is the amount of heat you need to generate enough steam/hot air to do 'real' work and thus the scale of the woodpile.

Stirling engines big enough to do real work are mighty expensive and you would need a specially constructed firebox as well (to burn all that wood).

In terms of steam you would need a bigger boiler & water feed pump arrangement to keep it all going unless you were prepared to shovel in small amounts of coal avery few seconds and sit next to it pumping water in with a trigger spray (as per garden railway engines). If you are in a hard water area you also need a supply of distilled/reverse osmosis water to stop your small boiler from furring up in short order. I've never seen anyone running model steam on wood - the thought of all that 'scale' chopping is enough to put me off!

Bear in mind that garden railway engines run at proper steam pressures (80+ PSI) so you really do need a proper boiler. As the boiler would not be a 'toy' you would probably need a regular boiler check/commercial boiler certificate as it is nice to know that the boiler probably won't kill you (garden railway enthusiasts put their nether regions at risk so tend to have a certificate!). Also steam models do wear out quite quickly in extended use so you wil need to factor in quite a bit of maintenance.

All that said you could rig something up, if you know a freindly model engineer, using a large Stuart Turner engine (a number 4 or 5A should do the trick) with a small second hand launch boiler (although nearly all need to run on coal or gas fou you would need to fabricate a firebox) and an alternator/dynamo. It would be costly (probably in excess of £5000 all told), probably not that effective and fill your house with the smell of steam oil but also huge FUN.

Oh and you will need a lot of really dry wood.

Let me know if you do it in steam; it would be a must see as far as I am concerned.

S

Hi Skywalker,

Yeah, you need a lot of fuel, but as our heating comes from a lot of dry wood already, surely I can nick some of that heat to generate with? I understand the limitations re safety etc but am aware, for instance, that you can get a sterling fan to sit on your stove and blow air about, a bigger version making DC surely is worth a go?.

£5000.00 versus £15000.00 for a boring old electricity cable? Not a problem. People are willing, of course, to spend an awful lot more on PV etc.

Boiler etc mounted externally, methinks!

Even though we're in whacky territory, when you look at all the odd stuff people come up with to be self sufficient, I'm still very surprised that there seems to be nothing out there at all. The only thing I found was a parobolic reflector generating steam at its focal point, fantastic....except that it screamed like a banshee.

Thanks for your input.

Any sterling engineers out there?

The only people I know of who are doing this type of thing even semi-seriously are doing it the opposite way around though. Using old Lister diesel generators running on veg oil to generate electricity and using the waste heat to suplement CH and DHW.

As for stirling engines these are what is being built into the small gas boiler micro-CHP units. They are available but only in quantity and not as retail one-offs.

You can get small one-off 1 stroke steam engines from the USA for about £2000

There is a 1 hp (1 stroke) and a 3 hp (2 stroke) version. efficient at lower steam temperatures (if you consider about 5% to be efficient): I don't think you'll be able to get the right steam temperature from wood using a Stirling (from memory they require at least 800C so that micro-droplets don't form.. but I may be wrong)

You need vast amounts of fuel

Probably only bought by the survivalist movement

Low temperature differential stirling engines are available that run on the hot air above a cup of coffee or a PC monitor. Stirling engines are good for no boilers or water but poor for manufacturing costs - need to be precision made. The efficiency of any heat engine (stirling / steam or other) = Temp in - temp exhaust all over temp in. All measured in degrees K (like deg C but +273). This leads to the low temperature differential engines running at 300 - 293= 7/300 = 2 % nearer 1 to allow for mechanical inefficiencies. With some thing like a wood burner, what you want is to have one on top of your stack instead of a pot. This could run on the smoke as the hot side and the prevailing wind as the cold side. A lot of thought would have to be given to stop the actual engine getting sooted up!!
Frank

Apparently CAT is just installing a wood burning generator, a mole told me it was 250kw, not to sure about that !.
a route I've been toying with is a flash boiler, driven generator, instead of a pressure vessel etc. you wrap a copper pipe around the flue, you then pump water in and get steam out, needs a bit of control, someone might have more info.
Its always seemed a waste to me generating heat (whatever the fuel) and not getting some electric as well.... all energy ends up as heat, might as well get some motive force during the process.

tom

You wont get enough heat out of your flue to drive a flash boiler - needs superheat (in steam terms) they work at high temperatures and very high pressures not to be played with. They are reliant on a carefully controlled supply of water (again scaling from a pop pop engines to a steam plant that does usefull work is a steep curve).

I love the Idea of stirlings on chimneys - very steam punk.

As andytk says I've never seen a small boiler let go but I have heard of a Stuart Turner sight glass stattering under steam which was described as 'very exciting' and the quickest way to strip wall paper ever witnessed!

It is legal to build you own boiler (a new design may be different), model steam types do all the time, but it must be tested if used in a public arena and in any case for your own peace of mind. I cannot be overstated that playng with steam at 80+PSI is not to be undertaken lightly.

s.

Slight deviation...
Considering 'CHP' and the crux what to do with 'H' in the summertime.. could it be used in these ways?
Or could the heat be compressed by an "uprated heat pump' and turn a turbine in some way?

just to confim CAT are installing a 100kw wood fired electical generator giving 250kw peek !!! as neil points out what do you do with the 200-500kw of heat in the summer, I've asked the question and will post the answer asap

Niggle

Here is more info

http://www.stationroadsteam.com/archive/1995.htm

turns out to a Stuart Turner Sirius also used for a 'small' charging unit for covert ops radios.

S.

Thanks everybody for your input on this topic, which still leaves me feeling that there might be a way....

I guess the only way to stop this niggle deep down inside is for a clever person to do an equation for me. Let's say I've spent 5K+ on having a certified steam generator built especially for me. How much wood would I need to burn to get 100w/hr out of it?

Anyone?

BedZed has a biomass CHP unit, 110kW(e) and 180kW(t) I believe, it's not worked for years. I've heard various stories as to why, one reason was because the council insisted that they had to switch it off at night, and as a result it suffered from gunging up as the resins/tars in the wood cooled. Whatever the reason, nobody seems to be able to make it work reliably. In terms of the time and effort involved and the energy generated I'd say you'd be much better off with an exercise bike with a dynamo or possibly a team of highly trained hamsters in wheels.

Everyone I've spoken to on this subject agrees that biomass CHP is completely unproven on a small scale, at a seminar I attended recently the senior technical manager of Dalkia said it's not viable on anything under 5MW(e). Dalkia burn 1 million tonnes of biomass a year in their plants, many of which are biomass CHP.

Whether you opt for biomass or gas fuelled CHP it's really best suited to large scale projects with some diversity of demand, I've looked at including CHP on new housing projects and generally it's ruled out as the electrical and heating load profiles are so poorly matched. For example your heating normally comes on well before you get up and so electrical demand is still peanuts. In mixed use developments, such as with swimming pools and offices it works much better.

Bite the bullet, pay the £15k and then spend your time and energy on all the other green measures you can include on your house.

Olly you could fit a large thermal store to give your rads a boost in the morning "no rocket science involved"

Dickster, heres a good link for a bit of DIY
http://www.firedragon.com/~kap/Educator/

tom

Posted By: skywalker
If you really want to be off grid you may be better off with a big wind turbine although you would probably benefit from a grid connection to export your surplus/import when you need it and save all the tedious mucking about with batteries.

Whilst I'm generally against the use of small scale wind turbines I think they are sometimes a good solution in off grid applications. however, given the fact that his roof is overshadowed it probably means there are some fairly high trees in the local vicinity so it may not be ideal.

Posted By: howdytom
Olly you could fit a large thermal store to give your rads a boost in the morning "no rocket science involved"

A thermal store will certainly help flatten the load, but the larger it is, the higher your heat losses (although the increase is not linear) and the more space you require. The other issue is that many CHP units have a low electrical to thermal output ratio, so if you size for the electrical load you simply end up throwing away heat, no point storing heat if you can't use it!