OT - Anaerobic Digestion - Does it make much sense to put crops in it?

[TimW]

Trying to get some reliable, factual information about AD in the wider scheme of things. I am somewhat involved in opposition to larger rural AD plants on a very local basis - so we are unhappy about the smell, the tractor movements, the lorries bringing in stuff from miles away, the visual impact, the concreting over of farmland, the pollution risks, the sq mile after mile of the worst kind of intensive agriculture... etc and on and on.

What I don't know about and want to know is does it actually make any sense for national energy generation? I can see the benefit of dealing with waste this way, producing a bit of gas/energy and fertiliser while avoiding the greenhouse emissions of the normal decay of organic matter, that's fine, but the subsidies appear to be so stacked that farmers are abandoning 'agriculture' in the sense of food production to grow beet and maize which is chucked directly in the AD plant. They are subsidised to grow the stuff and then the gas is bought at a subsidised price so they stop complaining about the price of milk and get rich quickly. I was reading somewhere that to supply gas to the whole of Dorset you would need two Dorsets to grow the crops - can that be true? I guess the same would apply to electrical generation - is there any sense in it?

Tim W

[Tim Lamb]

In message , TimW writes

Don't have any detail, Tim. You could do a topic search on *the farming forum*.

They will get the basic claim for the land whether the crop is used for AD or other purposes.

There is something enormous just North of Baldock.

Big rush to get the land up that way covered in solar panels before the cut off.

[Tim Lamb]

In message , Tim Lamb writes

Something here..

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[Tim Streater]

Doesn't David MacKay's book/ebook "Sustainable Energy without the Hot Air" cover this? I seem to recall that bio-fuel production for Brazil only works because they have shitloads of land. In the UK you'd have to grow e.g. maize over an area the size of Wales to replace our fossil fuel consumption in the UK. Can't remember if he said anything specifically about AD for gas, though.

[michael adams]

Seems fair enough. Instead of having to go down the mines and possibly contracting all sorts of respiratory diseases in mining coal, they can all drive around in the open air on tractors instead.

Sound like a win, win situation to me.

michael adams

...

[newshound]

Need a suitably green tractor first! (And I don't mean a John Deere).

[Bill Wright]

Those days are long gone.

Bill

[The Natural Philosopher]

Doesn't really matter.

Conversion of sunlight to biomass is about 0.1W/sq meter. (check that in DMS book)

PV is a lot better.

[Tim Lamb]

Point of order... is that sq. metre flat or would tall plants grown on one m^2 give more incident area?

:-) I hope Harry doesn't spot that!

I think the AD concept works best where crop residues (sugar cane) or animal waste from intensive agriculture are available.

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[The Natural Philosopher]

flat.

yes. growing crops for fuel is about the worst way to generate electricity there is

[harry]

We have a local one

You can put shit in them but then a large proportion of the gas generated is CO2 which has to be removed.

Using say corn, mostly methane is generated.

Using straw.wood chippings, again mostly methane is generated but it takes longer for the straw/wood to break down so the plant is bigger & costs more.

You don't get anything for nothing.

Any smells come not from the gas plant but from the shit store (if that's what they're using).

Re the economics, no-one can say. The price of fossil fuel is all over the place, so making any comparison is difficult.

But in the long term we probably need it for transport. Big business in Brasil, most cars there run on "alco ol".

I've seen interesting theories about the cost of tractor fuel used v. the bio-fuel created.

[Tim Streater]

We'll leave it to you, then, shall we, to tell all the Welsh to f*ck off? Perhaps Syria will take them in.

[764hho]

Irrelevant. It's basic physics, stupid.

[Brian Gaff]

Since when was sense required to make money? Brian

[Brian Gaff]

Yes a local reservoir in Walto just got a floating solar farm in under the cut off date, though they did say with the falling costs of cells and the better efficiency, in a couple of years this would still be viable with no subsidies at all. Brian

[news]

If you remember Stephen Temple: his digester deals with all the effluent from the cheese making business and the dairy herd, he also buffers this with sugar beet and maize silage to keep the fermentation consistent and stable (cow shit has lower volatile solids on account that the cow has metabolised them and whey has very high and immediately available volatile solids).

AJH

[Tim Lamb]

In message , [e-mail] writes

Yes. I bumped into some Mrs. Temples *Binham Blue* cheese in Suffolk:-)

I also noticed the diagonal cattle barriers I sold him in a photo in Farmers Weekly!

[TimW]

According to Farmers' Guardian, a biogas plant with a capacity of one megawatt, "requires 20,000-25,000 tonnes [of maize] a year, accounting for 450-500 hectares of land. I don't know but I assume they are talking electricity, not watts of heat from biogas.

But what we need is a figure for MWh. If a plant has a 1MW capacity does that mean it produces 1MW for most of 24hrs x 7 days x 52 weeks?, so say

8000 MWh ? or what?

4,000 kWh is the amount of electricity consumed by an average household. which is 4MWh?

So something like 2000 households per 500 Ha of land. which is 0.25Ha of land required for AD sourced electricity for an average household

UK has 260 persons per sq km so 2.6 persons per Ha, and an average household is 2.3 persons and only 70% of land is agricultural So we have around 0.6Ha of agricultural land per household in the uk.

We produce less than 60% of the food we eat already. I haven't accounted for agricultural land which couldn't be used to grow energy crops (eg hill pasture and marginal land) I think I wildly overestimated the MWh you might get from a MW capacity But on this basis growing energy crops in the uk is fairly bonkers

Have I made any obvious big mistakes?

Tim W

[TimW]

That was meant to be a new thread, so ignore pls.

[The Natural Philosopher]

If your conclusion is that biomass is totally useless for generating energy on the scale we require, no.

Frankly only 'renewables' that make any sense are solar PV and hydro, and they are pathetic by comparison with any fossil, or nuclear.

For better or for worse we have constructed a society where billions of peoples lives depend on a massive excess of energy consumption over that which the sun alone can supply, at any reasonable cost - and the cost in any case would put their lives at risk if we tried.

Ultimately we have to use fossil or nuclear, and if you think fossil will get too expensive or is damaging the environment, the *only choice we have is nuclear*.

Or watch a helluva bigger death rate than the Holocaust. Or be part of it.

If you read David Mackays book, and this introduction to intermittency

you will see the rationale. Coal is probably dead beyond resurrection in this counytry.

Its gas or nuclear.