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Author Topic: Biogas FITs  (Read 17926 times)
Ivan
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« on: November 21, 2015, 09:11:20 PM »

I was looking at the various FIT options this evening, to see if there are any new potential markets that Navitron, when I noticed that the Anaerobic Digestion FIT tariff (presumably for running an engine-based generator from the gas) is availanle for non-MCS accredited products, in a similar manner to water turbines. I hadn't realised this before - I had previously assumed that all systems claiming FITs were large capacity and therefore fell outside MCS on the basis of the kW rating.

So it looks like it would be possible to build a DIY biogas digester and run a generator from it, claiming FITs using the ROO-FIT process, which is relatively straightforward, if a little long-winded. Has anyone done this, or considered this?

I doubt it would be profitable, but on a small hobby-scale, it would allow you to generate for your own purposes, and get paid a little towards the cost of your hobby. A quick calculation revealed that if you were to use a high-yielding substrate - such as tree leaves, you should be able to generate about £50 per ton of leaves processed (taking into account the losses). I would certainly consider coupling this with a solar thermal heating system - which would provide higher yields, and additional RHI income if it were run as a small-scale commercial setup.

I can't remember the retention time inside the digester - from memory I think it's about 45days.
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Justme
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« Reply #1 on: November 22, 2015, 09:52:21 PM »

This could be good for us, however the time we would need it would be for the colder months & I am not sure that small home digesters work well then.
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Ivan
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« Reply #2 on: November 22, 2015, 10:24:52 PM »

Yes, they do work in the winter - I know someone who runs his rayburn from biogas throughout the winter months, but output slows unless you heat them. The best option is to build it below ground level, and/or insulate the walls. Also, you get a significant increase in output by putting a little solar thermal energy into the system.

There is also RHI available for biogas - 7.5p/kWh. I'm guessing that you could claim RHI and FITs for a CHP system, but I haven't actually checked that. If you can, then your income for digesting a ton of leaves would be £50 for the electricity (plus £12 for deemed export - assuming it's deemed at 50%) plus £150 for the RHI for metered heat recovered from the exhaust and cooling system. Total income per ton = £212....which doesn't sound too bad.

Did a bit more reading - for kitchen waste, the retention time is around 30days. Assuming you wanted to put 1 ton per month of dead leaves into the digester (or equivalent substrate), you'd need a digester of around 2m3 (according to calculations in this paper - http://www.theijes.com/papers/v2-i11/Part.2/J021102070076.pdf. If my income calculations are correct, and you ran the plant continually throughout the year, it could potentially generate £2500 annually. Scale it up, and it could be quite lucrative.
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readiescards
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« Reply #3 on: November 23, 2015, 07:35:09 AM »

Quote
digesting a ton of leaves would be £50

Dry or wet? 

With a good mornings effort I could probably gather 1 ton of very wet mushy leaves in late autumn (certainly yesterdays green wheelie bin was darn heavy).

1 ton of dry leaves gathered in the late summer and stored until needed, would be quite a task

Is it worth it?
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jotec
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« Reply #4 on: November 23, 2015, 09:41:40 AM »

Mind there is not something that stops you claiming small amounts. My WVO CHP system is registered for ROCs and generated about £500 worth a year. Fine year 1 then a requirement to audit the fuel came in which would cost £1000 a year, despite the WVO being exempt there is no way round it!
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Ted
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« Reply #5 on: November 23, 2015, 10:20:18 AM »

DECC do have longer-term changes planned for AD FiTs on the sustainability aspect of the fuel - this was in the most recent consultation.

Quote
Proposal
137. While we are not proposing any immediate measures, we are considering implementing sustainability criteria for solid and gaseous biomass for new AD installations under the FITs scheme and are seeking stakeholders’ feedback on how such criteria could work.

138. This would provide a consistent application of sustainability across incentive schemes, to further encourage the use of waste and avoid the risk that AD operators gravitate to the FITs if their feedstock is not likely to pass sustainability criteria in the RO or RHI. Sustainability criteria under FITs would provide standards consistent with the RHI and RO sustainability criteria, whilst taking into account the fact that under FITs these measures are likely to apply largely to crops as opposed to woody biomass under the RO and RHI.

Criteria
145. We intend for the measures to apply at all scales to newly accredited schemes. FITs payments will be conditional on generators demonstrating:
- A lifecycle greenhouse gas emission saving of at least 60%.
- That biomass was not sourced from land with a high biodiversity value, including primary forests, grasslands and of areas designed by law for nature conservation purposes.
- That biomass was not sourced from land with a high carbon stock value, including wetlands, continuously forested areas or peatlands.

Reporting
149. We consider that sustainability criteria should be underpinned by a robust reporting system. It is also clear, however, that additional reporting requirements create administrative burden for generators, suppliers and Ofgem. In line with the RO and RHI, we propose that generators over 1MW will be required to submit an independent audit report verifying that feedstock consignments have met the criteria or are exempt from meeting them.

150. We will not require generators of under 1MW to conduct an independent audit, but they may be subject to audits already undertaken by Ofgem. A greenhouse gas calculator is already available to help generators calculate their greenhouse gas savings, along with a user guide. Reporting will take place on a quarterly basis, following the same consignment and mass balance rules as the RHI.

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Ivan
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« Reply #6 on: November 23, 2015, 10:33:03 PM »

I don't think there is anything fundamentally wrong with the sustainability criteria. The only drawback is the fact that it involves a lot more record-keeping and reporting - similar to the biomass requirements are currently, I guess.

I wonder if Jotec's requirement for external auditing may have evaporated now? I think OFGEM are quite keen of self-assessment for this kind of thing now, unless you are a BIG producer. Have you checked this recently? It might be that by now, a paper trail of waste-collection notes equating to the number of kWh generated would suffice as a record of sustainability?

Not sure if the figures relate to wet or dry - I couldn't see, at a quick glance. I suspect they are referring to wet, as most of the tables I saw included 'cattle slurry' - which can hardly be dry. It would make more sense to talk about dry weight, but given the materials and quantities involved, I don't think anyone is going to be measuring dry weight! I only mentioned leaves, as they are a reasonably high producer of gas, and ubiquitous. Even higher was cereal grains - but clearly this is going to be a complete waste of a foodstuff, unless it is a production by-product -eg from brewing.
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jotec
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« Reply #7 on: November 23, 2015, 10:44:43 PM »

Thanks Ivan but it is no longer grid tied as we have solar PV now. It is still in use though for direct power. I am also experimenting with a UPS attached to it for backup power when we have power cuts.
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brackwell
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« Reply #8 on: November 24, 2015, 09:03:29 PM »

http://www.treehugger.com/clean-technology/home-sized-biogas-unit-turns-organic-waste-cooking-fuel-and-fertilizer-under-900.html
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« Reply #9 on: November 26, 2015, 05:38:25 PM »

HomeBioGas
"Warm climate: The system works optimally in places with average day/night temperatures above 17 °C (64 F). Under this temperature the system will decrease its productivity. Our system is not suited for cold or freezing temperatures."

Well that rules out rural Lincolnshire, UK
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Ivan
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« Reply #10 on: November 26, 2015, 09:22:40 PM »

Not necessarily. First, you bury it in the ground - the ambient temperature of the ground is more or less 10C, if you ignore the first half metre or so. Then you insulate the walls. Then you add a little heating (eg solar thermal or ASHP). Even without the heating, you'll see only a drop-off in production in cold weather. It won't actually stop.
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Justme
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« Reply #11 on: November 27, 2015, 06:56:57 PM »

If your going to insulate & heat it would you not be better off not putting it in the ground?

The ground would be a huge heat sink even if it was at 10c rather than air temp.

Heat transfer to air would be slower than it would to soil.

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Navitron solar thermal system
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1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
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24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
Ivan
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« Reply #12 on: November 27, 2015, 09:02:50 PM »

Ground at 10C is warmer than air at 0C. Ground doesn't tend to have convection or wind.
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Justme
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« Reply #13 on: November 28, 2015, 03:10:42 PM »

Ground at 10C is warmer than air at 0C. Ground doesn't tend to have convection or wind.


You are prob right its just does not feel right.

It has unlimited mass & conduction which is more efficient at transferring heat.

IE if I put a 2kw heater in the ground I bet that 2m away It would not affect the ground temp as the heat would be lost quicker than it was made. 2m away in air you can feel the heat.

Would the unit be better off in a very thickly insulated box with little mass than buried?

I know that the heat differential across the insulation is important so that the unit at 17C & the ground at 10c is in theory better than air at 0c. Yet air has little mass & lower conductivity. Would one balance out the other?

I know if I put my cuppa on a lump of metal (tractor, digger, house stove thats off ect) it cools down much quicker than if I put it on a bit of wood in the same place. So the cuppa in the house (24c air temp & stove should be close to that too) on the stove cools quicker than the cuppa outside on the wood with the air at sub 10c. The stove sucks the heat out quickly & its only touching at the base.

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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
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