Electricity from wood heat

[Cynnergy]

Can anyone point me to any projects that are looking into small-scale (i.e. a few homes - 10-15 kW system) electricity generation from biomass? I'm trying to find some renewable alternatives to the massive fuel bill for our off-grid island generator (currently 15 kW) which runs 24/7.

Solar and wind are probably more realistic options, but it would be interesting to see if wood could be added in to the mix.

 

[Ehouse]

Do you have battery storage and an inverter? By adding these you could probably save a ton of $ in fuel and downsize the genset.

 

[peakbagger]

There really isnt any proven technology out there to generate electricity from wood on a small scale. If you want to be on the "bleeding edge" there are several technologies that are not ready for prime time (and have been this way for a long time).

Wood Gas generators get a lot of press and there are firms that will sell you a system. What they dont tell you is you need to have a large supply of dry chipped wood which requires a lot of horsepower to convert trees into chips. Generally it really only makes sense to generate power if you have a use for the large amount of waste heat that the generator produces. To generate useable power you have to think in the terms of tons of wood.

Sterling Cycle generators are intriguing but the concept has been around for 200 plus years and no one has built one that will run for any period of time.

Organic Rakine Cycle generators are sort of in production but the initical cost is high. I personally think this tech has a chance as they use the same technology that a heat pump uses.

Super Critical Carbon Dioxide generators are similar to Organic Rankine Cycle. There are some 100 KW units in commercial stage.

Realistically the best investment is a properly designed battery storage system augmented with solar. Odds are the generator is vastly oversized most of the time and is bascially idling. By installing a large battery bank, with solar, the generator only is run when the batteries are low or every month or so to equalize the batteries. If you are on an island, you may have reliable wind and you can use that to also charge the batteries.

You may want ot get a subscription to Home Power Magazine as they have a lot of info on renewables in general, They usually have a deal on the scubscription that gives you access to back issues. One of their editors, Ian Woofeden (something like that) lives off grid on an island in the NW and does occasion articles on his systems which are mostly wind.

 

[Ehouse]

Google "New England Solar Electric" and peruse their site, Lots of good info. They are very helpful over the phone as well.

 

[EatenByLimestone]

Running the generator only when you need it is probably the easiest way to lower the fuel bill.

You can also use the generator to charge batteries. Batteries don't do well in cold weather so they may not be a very good choice since you might completely shut your cabin down when you aren't there in the winter. A small solar system can keep the batteries charged when you aren't there.

Figuring out ways to lower usage is probably the easiest way to lower the fuel bill.

 

[Cynnergy]

My dad currently does all of the maintenance on the generator and he's worried that adding in a battery system would increase the maintenance costs and decrease the life of the generator with all of the stopping and starting. Personally, I think that's a false economy (use the fuel savings to hire somebody to fix it), but he's kind of old school. Do you know of any sort of calculator where I can size a system and calculate fuel savings and capital/maintenance costs?

He pointed out a short blurb in 'Canadian Biomass' magazine where they said that Pratt & Whitney had an Organic Rakine Cycle generator that was 10 kW, but I looked on their website and I can't find anything - it might have been a typo. I thought that if he was interested though that I'd try to do a bit more research.

We have lots of wood and we could buy a chipper, but I'm not sure about chipping and drying tons of chips. Could we use the waste heat from a wood gas generator to do that? How much fuel do you think we'd need to run the chipper for that many chips?

 

[Ehouse]

After rereading your initial post I think you're talking about a whole island generator serving several homes . Is that right? I missed that part at first. How far apart are the homes? It might be cheaper (with incentives) for each home to have it's own solar/wind/generator hybrid set up. Is there any potential for hydro on the island?

 

[begreen]

I'm intrigued by using solar to create hydrogen as the storage medium. It's a good fuel for fuel cells and the process is relatively simple.

 

[EatenByLimestone]

How about a small generator for normal usage and then you turn the big generator on when you need it? I can't imagine that you need all that power, all the time. Try completing a generator sizing worksheet. Figure out how many lights you have on at one time and which appliances you will use together.

 

[begreen]

That's similar to the way a sailboat is run on the ocean Matt. Run off the batteries for small loads, run the genset for larger loads like charging, desalinizing water, A/C, etc..

 

[brian89gp]

It would probably be cheaper to directly use the heat from wood to reduce the need for electricity (heating, heat powered chillers, etc), reduce the electrical load as much as possible, then go solar/wind with a battery bank and keep the generator as backup. Trying to generate 15kw with wood would probably be a full time job.

 

[Circus]

Soon (not yet) it'll be easier to produce electricity. With parallel ready generators, solar and batteries using inverters you'll be able to combine small sources instead of a single large source of power.
Can't see how you could use the wood short of constantly feeding a boiler for a steam engine. Biodigesters usually collect methane from animal waste.
In a way your fortunate. You don't have a hostile money grubbing utility putting the kibosh on your schemes. Once your problems are solved we'll be envious

 

[peakbagger]

If her father is worried about maintenance on a diesel, any of the other technologies are order of magnitude more costly intitially and will require far more time. Basically plan on someone prepping and feeding the wood full time 24 hours per day.

 

[pdf27]

What is the daily energy consumption? Running the generator at half load/less is liable to do it more damage than running it at full load for a couple of hours then switching it off for the rest of the day. If you've got a bit battery bank that becomes possible, and you can link in other energy sources quite easily which may mean the generator doesn't fire at all.

In terms of alternatives, wood is a pretty poor choice - you might be able to set up a gasifier and run a petrol generator off the wood gas (think all the cars with big bags on the roof from WW2), but that's about it. If you have any streams that can be used, reasonable amounts of sun or fairly consistent wind (in order of how good they are - hydro is by far the best) then they're by far the best ways to generate.

 

[GaryGary]

Can anyone point me to any projects that are looking into small-scale (i.e. a few homes - 10-15 kW system) electricity generation from biomass? I'm trying to find some renewable alternatives to the massive fuel bill for our off-grid island generator (currently 15 kW) which runs 24/7.

Solar and wind are probably more realistic options, but it would be interesting to see if wood could be added in to the mix.

I know zero about this area, but these guys seem to be pretty active, and they offer 10 and 20KW wood gasifier generators packaged on a pallet for about $20K.
(broken link removed)

Gary

 

[Cynnergy]

Wow thanks all!

As mentioned, the generator doesn't run anywhere near full load most of the time, but it is sized to serve everyone (if we're careful). Most of the houses are only vacation homes now (although back in the island's heydey there was a proper community and there was even a one-room schoolhouse with 25 kids).

Given the usage pattern, I think it makes the most sense for the full-timers (2 houses full-time plus 2 houses that are weekend homes) to get a renewable system sized for their needs. The generator could be used full-time when there are a lot of people around and as backup for the renewable systems as mentioned above. There are an additional 4 vacation houses hooked up to the generator, plus 6 more houses that are not hooked up but that have ancient fridges and freezers running in the old logging camp using the 'excess' generator power. I have reno'd our cabin with minimal electricity usage in mind because I can see the way this is going in the future - but it sure has been nice to be able to run lots of power tools and shop-vacs for the past couple of months!

It's just frustrating because change does not come easily. It's also a case of what to do first - I suppose getting a battery system makes the most sense, and then adding in renewable pieces as we go along. There is potential for solar in the summer, possibly microhydro in the winter, and wind intermittently all year. Maybe wood if small-scale systems ever come to commercial fruition (or if anyone wants to do a pilot project - hello P&W and Nexterra ). That's also more things to break down though I guess, and I have no idea which one will get the most bang for the buck. At least by getting the battery system, the link between 24/7 power and the fuel bill will be broken, and we can start to talk about things like how many freezers are running, because those will suddenly start to 'cost' money whereas now they're just using the excess power for 'free'.

As a side note: the houses are spread out over about 1.5 km, so using waste heat from a wood power plant probably isn't feasible. Also, I believe the fuel bill for the generator is currently running at ~$30k/year, so I imagine the payback period for whatever system we put in should be quite attractive.

 

[Badfish740]

Contact this guy:

(broken link removed to http://hydrogenhouseproject.org/the-hydrogen-house.html)

I know that he's built some systems for small off grid islands in the Carribean.

 

[begreen]

Very interesting. Thanks for the link badfish. That's more what I had in mind. This guy is inspiring.

 

[pdf27]

Is there anything in the old fridges/freezers? If not turning them off will save you money on your fuel bill right away, even if you do nothing to the generator. It's more efficient at full load, but adding load will still require more fuel even if the efficiency goes up, so nothing is "free".

I'd strongly suggest getting a handful of cheap, secondhand electricity meters and datalogging them before you do anything else. You really need to know what your actual consumption is (ideally in each house) by time of day before you design a system. I suspect it's likely to be <2kW for most of the day (overnight, for instance), rising rapidly in the morning and evening. That suits **some** battery systems very well (be careful here - the cheaper battery systems like lead-acid are very finicky about how much you can discharge them and how many charge/discharge cycles you can have. More expensive ones like Nickel Iron are more robust but much more expensive), but you do need to know a bit about your usage patterns before you design a system.
Once you are using the diesel engine as a battery charger, rather than base load power, then assuming the battery pack is large enough the engine should be happier and need less maintenance. Fuel bills should drop, although probably not by enough to pay for the battery pack all that fast - diesel engines are relatively good at part load efficiency, and there are some losses in the batteries. As a rectal extraction, you're looking at saving maybe 10% that way, perhaps more if the overnight power demand is down to ~1kW. If you can log the generator power consumption over the course of a typical day and put the model number up on here we may be able to come up with a better number than that. However, once you've got renewables hooked in the numbers change a bit - every 10 kWh or so of renewable electricity saves you about a gallon of diesel.
Incidentally, is that $30k figure about right? Unless you're paying quite a lot for your diesel, a quick back of the envelope calculation suggests that the generator is **REALLY** inefficient. How old is it, and do you have any figures for volume of diesel used per year rather than cost?

If you have an available stream with a reasonable amount of drop (at least 10ft, preferably several hundred in an ideal world) that plus a battery system could probably drive everything - it's surprising how little water you need for one of those. It does need to be sized to match the water supply though...
The big advantage to solar in your particular situation is that the peak generation matches the peak load on the system (the vacation houses being full), and oversizing a solar system is pretty cheap and doesn't really have any problems with it.
Wind is a little more obtrusive and does need fairly good wind speeds to work, plus requires about as much maintenance as hydro (greasing the bearings occasionally - both are much better than a diesel engine!). Again, oversizing it is fairly cheap but you will need a safe way to dump the excess power - classically an immersion heater set to pour hot water down the drain if you have too much power.

 

[Ehouse]

If you do go to the "New England solar Electric" site, they have a small booklet titled " PV generator Hybrid system for your PV home" which gives an over view of options.

 

[Ehouse]

I'm with pdf27 on using the generator part time. One line of thought is not to use the genny for charging batts directly but only run it for large sustained loads and charge while it is already in use. As an example, you could run for 2 or 3 hours in the morning and 2 or 3 in the evening. Every one knows that is the time to do laundry, and any other high draw uses. You can piggy back other loads onto the same gen/run time, for example a water holding tank in each home could be filled by the well pump(s) at this time with a booster pump for the pressure tank (or perhaps gravity storage). Each home has a battery bank and an inverter (with a DC panel box), for lite loads when the genny is down. PV/wjnd/hydro can be added if needed. Simply getting everyone on the same page can have significant energy savings.

 

[Jags]

Badfish - that is a very interesting link. Thank you.

 

[Badfish740]

Badfish - that is a very interesting link. Thank you.

The guy lives about 20 minutes away from me. I've spoken with him a few times and have been meaning to get down to see his house but haven't had the time. He caused quite a stir when he first proposed storing all of that hydrogen on his property with the local building inspector, but luckily common sense prevailed and folks realized that tanks full of hydrogen were no more dangerous than the 500lb tanks of propane folks have on their property in that part of the state (rural area). If I had the cash I'd definitely spring for it. Obviously he's using conventional fuel cells, but I wonder how hydrogen would work with one of those Bloom Boxes?

 

[Jags]

I am waiting to see the day that stuff like this is sold in "kit" form with financing options like a car. Walk into a dealership with your energy bills in hand and bingo - you need kit 3B. Sign here and we will have it delivered next Wednesday.

 

[pdf27]

Incidentally, is that $30k figure about right? Unless you're paying quite a lot for your diesel, a quick back of the envelope calculation suggests that the generator is **REALLY** inefficient. How old is it, and do you have any figures for volume of diesel used per year rather than cost?

Just realised I got my units mixed up. Assuming about $1.30/litre, that's 23,000 litres. Diesel Gensets seem to do about 3 kWh/litre, so that's 69,000 kWh/year. 365 x 24 = 8760 hours/year, so you're averaging a 7.9 kW load. If I had to guess, I'd say you've got 3-4 hours per day of peak load or close to it (15kW), and the rest of the time at a base load of ~6kW. Over 14 houses, that's about 500W/house. Assuming that's evenly distributed (it won't be, but if the unused houses really are inefficient it might not be that bad an assumption) then the six empty houses with the ancient fridges are using ~3kW between them. If that's an accurate assumption, you're spending ~$10,000/year on diesel to keep those fridges going.

http://www.google.co.uk/url?sa=t&rc...JI0WMyiKY_ItAXHEoMgHMLA&bvm=bv.45645796,d.d2k is probably a better estimate - that suggests between 1500 and 2000 kWh/year per fridge from about 1960-1980. For 6 houses, I'll assume 6 refrigerators and 3 freezers, all at 1750 kWh/year - ~16,000 kWh/year, or about $7,000! I'd say turning those off is the very first thing to do before you even think about other energy sources.

For a PV system, I'll take a quick stab and assume that summer demand is ~20% higher than average after taking out the demand from the old fridges. 69,000 - 16,000 = 53,000 kWh/year or 145 kWh/day, so assume the summer load is ~175 kWh/day. That's a BIG solar array - getting on for 40kW if your climate is similar to Vancouver. However, it will also give you ~39,500 kWh/year (PVWatts data), worth around $17,000/year at your current diesel price. Not sure what local solar prices are like where you are, but I suspect that's a pretty rapid payback time. As a rough cut, that would leave the generator normally only running from October-March, and even in January it's only going to be running for ~6 hours/day (always assuming a suitably sized battery pack).