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Electricity from wood heat

Post in 'The Green Room' started by Cynnergy, Apr 23, 2013.

  1. Cynnergy

    Cynnergy Feeling the Heat

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    Wow pdf27 and Ehouse, that is AWESOME. Thank you!

    Your assumptions seem to be about right too - I got my dad an Efergy meter in the UK a few years ago, and his house averages ~25kWh/day, with peaks normally under 3kW. When both of my sisters are on the island with their young kids all bets are off though - I've seen the meter logging over 7kW at Christmas with the microwave, washing machine, electric heaters, 2 fridges & a freezer going all at once plus who knows what else. I have no idea about the consumption of the other houses or the average load on the generator, but I can try to find out more this weekend when I'm up there.

    $7000 for those empty fridges/freezers?!? OMG!!! I had no idea - I'm not mechanical, and I always had been told that although they were adding a little bit of load, it wouldn't add up to much more fuel because the generator was already running all of the time anyway. Time to get some meters for sure! Or the alternative I suppose - just unplug them. Although I may not be the most popular person on the island for doing that - guess I'll need some solid numbers first.

    Behaviour is a major issue to deal with - we use electricity on the island like we're connected to the grid, but it's even worse because no one wants to spend the money or have the hassle of upgrading their appliances and disposing of the old ones. Make do and mend is the mantra, but sometimes replacing something that's old (even if it works) is much better for many reasons. I guess the money spent on fuel isn't a problem for most of them, but it is for me. Plus the whole carbon footprint thing...

    Right, you have inspired me to get this sorted out. There is a better way. Time to do an energy inventory and start having some serious talks with people.

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  2. Redbarn

    Redbarn Burning Hunk

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  3. Ehouse

    Ehouse Minister of Fire

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    I'd suggest you start researching because it's not going to be simple. For example, you'll need an electrical plan that sequences load surges (such as well pumps), so everything doesn't come on at once. Learn about DC power. You may find you can create a layered system one step at a time starting with a small battery bank in each home with some DC emergency lighting and maybe a DC fridge and well pump. Then install an inverter for AC. You may find savings to be enough at this point that you don't need to go further, But you could also add solar/wind/hydro/fuel cell/ treadle/hamsterwheel etc. at any point. You'll come up with a much better system if you educate your self and your community rather than plopping down a huge wad of cash for someone else 's design and install.

    I'd find some sympathetic individuals with good skill sets (plumbing, electrical, grant writing) to help set up a tentative plan, starting with your dad. Then, a community roll out with a couple o' boxes of pizza...(oops, fish fry then!). Getting everyone on board's going to be the toughest nut to crack, but with a layered approach and gradual cash outlay, you might pull it off.

    I forgot to mention that individual homes could add a small genset (with proper disconnect) if they need or want to run larger loads when the main generator is off line.

    Where's your island? sounds beautiful!
  4. peakbagger

    peakbagger Minister of Fire

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    This article may be of interest, I used to work for Northern Power but they were done with the project by the time I went to work for them. Northern Power is no longer in this business but will sell you a 100 KW wind turbine which is used extensively in severe condtions like yours. but the price tag of typically $600,000 installed is probably far too priced for most. There is a offshoot of Northern that does still do off grid power but

    http://www.distributedenergy.com/DE/Editorial/Sounds_a_ProblemEven_on_an_Island_1830.aspx The people who worked on the project said the prior electrcal system was a nightmare, with household cable laid in ditches with no real ground fault protection and splices just twisted together and wrapped with electrcial tape.

    http://mlcalliance.org/2013/02/20/monhegan-island-gets-a-little-slice-of-the-sun/ The island is near the proposed site of a large floating wind farm so I expect they are hoping that they can get power off the turbines.

    The best chance for your island is too look for a university that wants to work on a project. The system size is manageable and the location hopefully nice to visit, so some professor may be able to fund a grant to take this on as a project as its the perfect type of project that college students could work on to come up with a design.
  5. pdf27

    pdf27 Member

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    No problem. Rather embarrassingly, I actually find this sort of thing fascinating.

    25kWh/day is about 5 times my average electricity consumption (2 of us in a ~1000 Sq ft house heated with natural gas), so you can probably get that down quite a long way. At the moment you're using about 3 Jerry cans of diesel a week to power the house.
    Don't worry too much about peak loads - batteries are actually quite good for short term peak loads, and just about any conceivable system will have the generator still there as a backup for just that sort of occasion.

    You may be able to get agreement to turn them off for say a day or week and compare diesel use with and without them on. Bit difficult as electricity consumption will vary, but probably easier to get agreement for than just turning them off completely.

    With the generator, there are two sources of torque on the drive shaft - internal resistance of the engine itself, and the electrical load on the dynamo. Since generators run at constant speed, the internal resistance of the engine is absolutely constant - the mechanical movements are identical, as is the resistance to air being pumped through the engine. That means adding load to the dynamo will directly increase the amount of fuel it needs to keep turning at the same speed.
    The reason efficiency goes up at higher loads is simple - at no load you will be consuming say 5kW to keep the engine ticking over, and with no useful work the maximum possible efficiency is 0%. At full power you will be consuming the same 5kW to keep the engine turning, plus 15kW of electricity and ~25kW of extra hot exhaust gas. The efficiency has gone up to ~30%, but you're burning 40kW more diesel to do it. That means reducing the electrical load will always reduce the amount of diesel burnt. Just for diesel alone - not counting maintenance, human time, etc. you're paying something like $0.40/kWh for your electricity.
    This should be a fairly convincing way of showing it - the engine burns about a litre per hour with no load on it, going up to around 10 litres per hour at full load. Increasing the load ALWAYS increases the diesel consumption. If you let me have the generator details I can probably come up with a similar curve for it.

    How do people pay for their electricity? It sounds to me like you're experiencing a classic Tragedy of the Commons - the costs of reducing their electricity consumption falls to the individual, but the cost of higher electricity bills are paid by everybody.

    Sounds to me like the actual problem isn't really so much one of technology as of incentives. Nobody is paying a penalty for their own higher consumption, and indeed don't seem to be aware that they are directly paying for consumption. Realistically, if you put every house on an electricity meter plus one on the generator and share the fuel costs accordingly I suspect consumption will probably almost halve in a few months. Once you've done that you're looking at technological solutions, but when you can point to say a solar setup and tell people with confidence that it'll cost $50,000 and save $17,000/year from their electricity bill they'll start listening. If you don't have the data - and they don't believe it through not paying the bill directly - then I think you're on to a loser unless you can self-fund the whole thing.

    Incidentally, if you can you might be on to a nice little earner if you offer to take over the power grid for the island and sell it to people at the rate they're currently paying. You'd have to do it per kWh rather than as a flat rate to stop them doing something stupid, but you're looking at potentially a 30%+ ROI for a solar system and something obscene like 100% for a hydro system if there is a suitable site.
  6. Ehouse

    Ehouse Minister of Fire

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    pdf27, you know way more about Generators than I do; I'm seeing lots of references to variable speed units. Honda and Yamaha for example. Whats the scoop on these?
  7. pdf27

    pdf27 Member

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    A synchronous/fixed speed generator connects the engine to an AC generator. That means the engine HAS to turn at 50/60Hz, depending on what country you're in (or some fraction of it - you can turn it at 1500 RPM and use a four-pole generator) to give the right AC waveform. That means when you're away from their design load they're pretty inefficient, and they tend to be a bit on the big and heavy side. However, they're really cheap and simple to build - diesel engine, governor, dynamo.

    A variable speed generator connects the engine to a DC generator, which then feeds an inverter to create AC power at whatever frequency you want. That has a fair few advantages - at idle, the engine can slow right down to minimum speed and hence minimum losses, you can to some extent reduce throttling losses in a petrol generator (if your ECU is smart enough), and you can use a smaller engine. The latter is the main reason manufacturers do it - a synchronous 15kW generator needs to be able to produce max power at say 1500 RPM to keep the part load losses down. A variable speed generator will have the same part load losses but be able to rev to say 3000 RPM at max load. Everything else being equal you have an engine of half the size, which gives lower throttling and general running losses.
    The downside is that until recently inverters were pretty expensive, so variable speed generators were more expensive. Now they've come down a long way in price, they're arguably cheaper to build to the same quality than a fixed speed unit (much smaller engine). The quality of the power (noise, etc.) is also liable to be higher from a decent variable speed unit.

    For most situations and people, variable speed will be the most appropriate. I have some reservations about them, but they're minor ones:
    - At full load they're liable to use more fuel, so if you have a completely fixed electrical load a synchronous generator is probably more suitable. Once you start varying the load even a bit this advantage goes though.
    - If you really, really need high reliability then a synchronous generator is the way to go - less to go wrong. This only really applies to places it's safety or process critical not to lose power at all though - if you really rely on generator power it's probably cheaper to buy a spare and keep it mothballed in case the generator dies, and if not don't worry about it.

    Incidentally, I'm an engineer, I deal with various similar components (inverters, etc.) at work but I don't have any real hands-on experience of running generators so the above should be taken as a theoretical explanation only - I'm sure I'm missing the real life bits...
  8. Circus

    Circus Member

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    Wonder how much line loss you have. Maybe the first thing to do is to get a couple step/up and step/down transformers. (Out of my expertise.)
    First graph the load. Then you'll have an idea what's possible.
  9. renewablejohn

    renewablejohn Member

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    Have a look at what is happening on the Isle of Mull off the UK coast.

    http://haunnblackhouse.blogspot.co.uk/2009/08/woodchip-story.html

    They have a successful woodchip industry with various woodchip biomass boilers and have even got a woodchip fired thermal oil bakery on the island.
    Once you have a woodchip fired thermal oil system, producing steam and generating electricity is relatively simple.
  10. renewablejohn

    renewablejohn Member

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  11. pdf27

    pdf27 Member

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    I think the real issue here is size, rather than cost - that system seems to be designed for at least a 35kW electrical load, and they seem to be averaging about 7kW with potential to drop it a bit quite easily. As I understand it, the capital cost isn't likely to go down all that much for a smaller system, and it's liable to be pretty unhappy if underused, so unless they can set up something that really needs electricity and will give that electricity an economic value then I think it's poorly suited to their specific application.

    I think there is certainly potential to use something like that (gasifying boiler + Stirling engine), I just struggle to see it not being massively more expensive than a PV + Diesel genset alternative...
  12. renewablejohn

    renewablejohn Member

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  13. pdf27

    pdf27 Member

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    That would be the way to do it for a one-off, or building from scratch. Problem is, the only way I can see it being economical is if they already heat with wood and are willing to go for some sort of mini combined heat & power scheme. Otherwise, the fact that they already have a generator is going to give them problems with the capital costs.
  14. renewablejohn

    renewablejohn Member

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    Whats the problem with capital costs. Current annual spend on generator fuel $30k quote for 10kw wood generator £12k seems to me to be a no brainer if you have a source of logs and the ability to run a small steam engine. (ie unlike larger systems which can be automatic small systems require continuous adjustment)
  15. renewablejohn

    renewablejohn Member

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    The reference to Pratt & Whitney and an Organic Rankine Cycle generator will be a thermal oil system manufactured by Turboden in Italy who Pratt & Whitney purchased and is now part of there energy division. Unfortunately the 10kw is a typo I think the smallest unit they do is 500kw and the largest 2MW.

    http://www.turboden.eu/en/applications/applications-overview.php
  16. jharkin

    jharkin Minister of Fire

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    Im no expert but you got a lot of good advice and Id add another vote to look into adding batteries and an inverter. To begin with you will lower the load on the genset and over time you can incrementially add other sources like solar/wind as budget allow.

    The maintenance headache sounds like the old argument against start stop systems on cars. Paying hundreds more on extra fuel over years to avoid paying $50 for a new starter motor. ;)


    Lead acid is still the battery of choice in 95% of alternative energy and backup systems AFAIK. Basically anything where weight and size is not a constraint. Even thought the energy density is low its still one of the most efficient charge/discharge chemistries (you get 90%+ of the energy back) and even when oversize to account for 40% or less average DoD (the typical cost break even point for capacity vs. cycle life) it tends to be the cheapest option.

    NiFe main advantage over lead is long service life - 40 or 50 years compared to 10-20. The drawback is very low efficiency (you only get back 60% of the charging energy) and a high self discharge rate. I beleive they used to be used as Telco float batteries a lot but are not very common these days.

    There is some solar outfit experimenting with using Lithium Ion as solar storage batteries in a partnership with Tesla. Interesting idea as LiIon has potentially the greatest charge efficiency of all but still is much more expensive and short lived (2-5yr) than Lead so I don't know how far it will get.
  17. Highbeam

    Highbeam Minister of Fire

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    What a great thread buried over here in the green forum. Sorry I'm so late so my thoughts may repeat those above. I am a utility engineer and part of my business is figuring out how and how much to bill for service.

    You have a situation where it is human nature for each resident to abuse the system. They will be wasteful since there is no direct relationship between consumption and cost. Worse yet, if they think the bill is high they will purposely overuse to "get their money's worth". The only way for this system to work is to meter each service. The meters will reduce consumption overall and encourage folks to conserve. In addition to metered consumption charges you will have a base rate where the customer pays even if they use nothing, because they could have used something and you had to be ready.

    A lot of the advice has been for off-grid houses and individual solutions. Well, you're running a small utility here. There are rules and methods. What if some yahoo decided he had to have some sort of machine to support his life and moved to his cabin? You would not interrupt power or he dies. What sort of obligation do you have to provide this power? What legal ramifications if the power goes out or if you tell the cabins to get their own?

    Doing it right means meters. Only then can you know your electricity demands. The folks that live there part time are getting a smoking deal. You have to pay for and keep up equipment capable of handling their needs year round while they only demand it and pay for it while they live there in the summer. This means you will have a base rate and a consumption charge.

    Honestly, I would break up the system and let everyone take care of their own intermittent and variable needs. I can't believe you've been wasting so much energy for so long running a 15kw set 24/7.
  18. begreen

    begreen Mooderator Staff Member

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  19. Bad Wolf

    Bad Wolf Minister of Fire

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  20. Jags

    Jags Moderate Moderator Staff Member

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    They really need a better PR program. Statements like this:
    Leave Lemmingville and live like James Bond… Disruptive Top Secret technology gives ordinary men “Super Spy-like” powers.

    Will make some people automatically classify these folks a nutters.
  21. Highbeam

    Highbeam Minister of Fire

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    Wow, quite a site to stroll around on. Lot's of crap like that. "space age" and "fellas".
  22. Corey

    Corey Minister of Fire

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    They do have a lot of data, but also a good point. You are probably much better off getting low grade heat as a byproduct from high grade electricity generation than trying to generate high grade electricity from low grade heat.
  23. renewablejohn

    renewablejohn Member

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    Low grade heat upto 230C is ideal for use with thermal oil. Conversion from hot thermal oil to conventional steam is straightforward and very safe.

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