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CHP/home Cogen

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philba

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I while ago I stumbled upon this concept. It makes total sense to me after a cursory view however, I wonder if others here have more experience with it. I'd also like to hear people's opinions (like I could prevent that, huh?).

Basically the idea is that when you burn fuel for heat, you are wasting a lot of the energy of the combustion. Why not use it to generate electricity. This is the idea behind industrial cogeneration but why not apply it to residential generation as well?

CHP stands for combined heat and power. There are a number of companies doing this. The claims seem good and not inflated but there is really no way to judge. They are claiming up to 90% efficiency but I've heard that bull before. There is no way for me to even guestimate what my savings would be. Still, I'm considering getting one for my pool which sucks large amounts of natural gas to heat the water.

thoughts?

some links
**broken link removed**
https://www.whispergen.com/
**broken link removed**
 
Obviously if you can use the waste heat, then you are improving efficiency, but generally it costs quote a bit to do! - and you only recover a percentage of it, on a small scale it may not be cost effective?.

There's a small woodyard a couple of miles from where I work, and they burn the sawdust they create - the heat is piped to the owners house a fair distance away, I believe there are a number of other houses heated from it as well?.
 
Nigel Goodwin said:
Obviously if you can use the waste heat, then you are improving efficiency, but generally it costs quote a bit to do! - and you only recover a percentage of it, on a small scale it may not be cost effective?.

There's a small woodyard a couple of miles from where I work, and they burn the sawdust they create - the heat is piped to the owners house a fair distance away, I believe there are a number of other houses heated from it as well?.

it may not pan out but is definitely worth looking into. I've got emails into several outfits, hopefully, I can get in touch with some one who can answer my questions. the big issue for me is payback period.

the sawdust thing is a good idea but technically not cogeneration which mean generating useful heat and electricity at the same time.
 
I already know who you need to talk to.
Capstone Microturbine makes some very reliable, flexible, low maintenance, low noise turbines which are specifically designed for cogen. They are better than a quality piston engine for shaft power efficiency but not remarkably so, but they do well with cogen and get about 80% efficiency in the end.

Your house would need to have a radiator system in some way. It makes hot water, not hot air, although it's not rocket science to turn hot water into hot air.

Nobody wants a generator puttering away next door. The Microturbine is supposed to be a lot like a box fan, it's not like a jet engine.

Microturbine comes with an integrated DC generator head. You do need a serious inverter to use it to power your house or tie it into the grid.
 
BTW, you may think a Microturbine is expensive, and it is, but they're going on the surplus market and eBay occasionally. Few thousand dollars maybe. One can only hope the turbine, electronic controls, and generator head electronics are in good shape. Capstone should be able to provide information on how to operate it. I think it requires a blast of compressed air to get started too, but don't quote me on that.
 
thanks for the lead, I'll take a look. My house uses hot water for heating and the pool has a seperate furnace for heating the pool water. I'll probably convert that first. The main house has a 6 year old furnace that I'm reluctant to junk.

On cost, I'm not concerned about the initial outlay, even more than $10K is not out of the picture. It's the payback period that's key. I'm in the process of building a payback calculator spreadsheet. Plug in installation costs, maint costs, gas usage over time and util buy back prices to get a reasonable estimate of payback period. My wife is definitely on-board for this - hell, she wants to start a company selling them. I think it makes a huge amount of sense and is potentially good for the environment.
 
I seem to recall running numbers once and found generating electricity off of the city's nat gas was similar to the cost of electricity. At least I seem to remember concluding that. Depends a lot on nat gas and electrical rates though.

So you'd lose something like 30% of the heat due to conversion to electricity, but most of the energy still goes to heat water you were planning to heat anyways. If that's true the power payback just about doubles the value of what you get outta that nat gas. So, maybe a rough idea- if you spend $50/mo on nat gas now, you might spend $65 with the cogen but get $50 of electricity out of the deal.

Not too shabby! But if that turbine and grid-tie inverter costs $10,000, wow that'll take nearly 17 years of trouble-free service to break even.
 
Wouldn't the only real way to recover heat from a combustion process be to have an overall lower exaust temperature, or decrease thermal losses in the system the enegry is going into? Maybe if you did something simpler, like feed your exaust air into a heat pump you'd recover more of the thermal energy released. Or used a better pool cover or increasing the insulation to the pool itself. Every conversion stage of the energy being generated is going to introduce it's own losses. Increasing the existing systems overall energy effciency is going to be more cost effective in the long run.
The total cost to run the system sounds like it completly ruins the point.
The first link you left says the service schedual is twice a year, and the complete overall period is every 5 years or so. If the systems cost that much you're talking a net loss over time.
These kinds of systems generally only work on a very large scale and still work out economically.
In my opinion an additional heat exchanger and better insulation would end up saving your more money.
 
the breakthrough being claimed is that small scale chp units are cost effective.

By the way, I wish it was just $50/mo for natural gas, we wouldn't be having this discussion. my pool is 75' x 20' and has a greenhouse structure over it. It costs a bundle to heat even during the summer months. we shut it down for the winter. I'll have to run the numbers but if I can sell an average of $200 worth of electricity back to the power company, a 10K investment will pay for itself in less than 10 years.
 
The waste energy from your pool heater probably isn't even the primary energy drain itself, it's the lack of pool insulation and building insulation, if you invested that money into directly combating energy loss in the first place it would pay for itself in reduced energy consumtion instantly, without complicated mechanical overhead and hoopla.
 
philba said:
I'll have to run the numbers but if I can sell an average of $200 worth of electricity back to the power company, a 10K investment will pay for itself in less than 10 years.

Man you do spend a lot on nat gas!
Yeah if you could generate $200/mo, actually you're gonna break even at a little over 4 yrs making it a very reasonable solution!

Power companies vary at their "buyback" policy. I've heard it said that at least one guy ran into this thing where they'll give you credit but not cash, and that credit expired at the end of the year (hopefully not month).

There is a big concern due to the power feeding back through the line, so called "island" power. So they need to work on the 7200V feeder line and cut it off from the power station but not your home. Well, your home is propping up the 220V power and transformers work both ways, so the transformer is keeping that line at 7200V which would kill the lineman. Might even be a situation where you turned this thing on and energized the line after they already checked that the line was dead. But then, all solar etc guys have dealt with this problem.

Actually, I don't know how they handle it now but I've seen lots of lines being worked on from day to day yet almost never see my own power go out. So either they reroute both ends then cut off the connection from both ends, or they just work on it live. I think they do a lot of working in it live nowadays.
 
I've got a cover. actually, 2 covers - a greenhouse over the pool which actually has a fair amount of solar gain and a regular pool cover. The reality is that short of tearing down the structure and building a new one, I'm not going to get much improvement on the insulation side.

I am pretty sure that I will get significant benefit from microCHP but, as I have stated, the payback period is key.
 
oznog, payback will take longer because I only operate it for about 8 months. Also, I am assuming some amount of annual maint.

and, yes, I spend way too much on gas.

I'm pretty sure the power couplers know when the power grid is dead and don't feed into it. It maybe a side effect of syncing with the 60 hz cycle.
 
Well don't look at it just as money. I feel that's a mistake a lot of experimenters make.

I mean, you write into an alternative energy magazine, or have the guys who want to build "off-the-grid" houses to learn how to "build green" or live in remote locations and show them what you did and what real-world results you got- this stuff means a lot to a lot of people.
 
True and potentially a business to get into. If it works on a smaller scale (say 3K sqft homes) then there is a huge opportunity out there. If we can increase the energy conversion by even 20% then it is a huge win.
 
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