This thread should discuss the economics, leave the technical discussion in the "selling listeroid power back to the grid" thread.
The following is based on my situation in Connecticut, each state has different rates and rules.
In Connecticut my electric rate is currently .18/kwh inclusive of commodity charge and delivery. As of 1/1/06 the rate will increase to .192/kwh. My state allows me to net meter up to 100kw/hour various incentives are available including grants.
My project is in progress and the intention is to burn veg oil in my 12/1 turning a 10hp induction motor above sync speed pushing back about 7kw/hour back to the grid at full output. Many months ago I started this process, and it is quite a process, the most challenging part is dealing with the hoops the utility makes you jump through. But before you lay out any cash it makes sense to run the numbers, below is a review of some of the numbers I considered prior to embarking on this process
The costs add up quickly
Electrical Engineer $2000 Strongly suggested by the utility
Protective equipment $1200 required by the utility
Install $1200 suggested by the utility
Misc materials $800
Engine $0*
Gen head/ Motor $0*
Total $5200
*I brought a load of gen heads and engines in to the NY area last summer; I resold those with enough margin to pay for my gen head and engine.
I ran an unscientific test a few months ago to get an idea of how long my 12/1 would run on a gallons of wvo. The gen was loaded at abput 6800 watts, as this was the max load I could create with the materials/ appliances I had on hand.
I measured the wattage draw of various heaters and other appliances using a Kill a Watt meter. The sum of these items came to 6800, I understand there may be some variance after they heat up, it still gives me a good idea of load vs. consumption. The exhaust was clear to slight white/grey and the engine was loud but seemed to run fine. I believe I could coax a little more power out of it, so I am using 7kw as an output number.
I have a 1 gallon auxiliary tank that I filled with 1 gallon of vo. The engine was run on diesel and warmed up to 220 deg f as measured at the upper coolant outlet. I then switched over to the Vo, the engine ran for 88 minuets before I saw air in the clear plastic fuel line from the small 1 gallon tank just prior to the exhaust heat exchanger. At the point of injection the fuel is at least 230 def f, per the fuel temp sensor just before the injector. The engine consumed more fuel than I had expected. It works out to .68 gal/hour consumption, I was expecting under .5/hour. Perhaps this number will improve as the engine breaks in. The engine has < 100hrs on it
The engine runs for 88 min and I produce 10.22kw
28 min = .46hr 28min/60=.467
7kw *1.467hrs=10.269kw per hour on WVO
.192(retail rate)*10.269kw= $1.97 worth of avoided retail electricity
So each gallon of free WVO can be converted into $1.97 using the 12/1 Lister type engine
Now I need to make a lot of electricity to cover those costs. At .192/kw I need to make 27083 kw to break even. This equates to about 3870 running hours for my 12/1
3870hrs*7kw=27090kw
That equates to about 11hrs a day 30 days per month.
27090*.192=$5201…. payback in one year.
The above is not reality though, as this assumes I receive the full retail rate for all of my production, sadly this is not the case. Once I produce in excess of my consumption I am compensated at the avoided or spot rate as determined by ISO New England auction. Over the last 3 years the monthly rate averages .07/kw This is a far cry from the .192 retail rate I pay as of 1.1.07
My annual consumption for the last 3 years has been pretty steady, averaging just under 16500kw at the old rate it is about $3000/year. The rate will be a little higher starting 1/1/07.
Any production above 16500kw will be paid out at about .07/kw (This is not really the case, in high demand months the rate is higher, in June, July, August and Sept the rate is .089. So if I really want to optimize my electric production I would skew production to the months where the payout is highest. It may even possible to sign up for “by the hour pricing” where I would be paid based on the actual rate during the actual hours I produce excess electricity.) I expect that there is a pretty strong correlation between air temp and the spot price during these months, with this in mind it should be relatively simple to “predict” when the rates are highest and adjust gen run time accordingly.
……..But for the sake of simplicity I have assumed a flat .07 spot rate.
16500(annual consumption)*.192(retail rate)= $3168 avoided usage charges
$5200cap cost - $3168= $2032 this amount needs to be recouped.
$2032/.07=29028kw at a rate of .07 I would need to produce 29028kw which means running the engine another 4146 hours. This rate schedule makes it impractical to run the engine due to the low amount paid for the incremental output above my domestic usage. It makes more sense to run it only enough to cover my actual kw consumption.
If you really want to look at the true value of these numbers you must acknowledge that this production is worth more than production in excess of usage, because the savings flows directly to my household bottom line. Any production over my domestic usage is paid to me by the utility and as such is taxed at my income tax rate. A dollar saved is worth more than a dollar earned!
It makes more sense to just run the engine just enough to cover my domestic usage.
16500kw domestic usage /7kw (1hr output) = 2357 hours *7kw * .192 = $3134
Cap cost $5200
Production yr 1 $3134
Shortfall $20366
So in year 2 I run the engine 2357 hours and I am at the break even point
2357 hrs *7kw = 16500kw* .192= $3134
Total run time year one: 10 hrs a day 20 days a month =16794 kw
Total run time year two: 6.5 hrs a day 20 days a month = 10916 kw
Run time is variable, run it longer per day for less days per month.
Below is theory not many hard numbers used:
Now I have not mentioned using the coolant or exhaust heat. Someone made mention of high and low value heat. High value heat I define as useable heat that had a much higher temp than the ambient temp where it is to be applied. This can be from the exhaust and or the coolant. The low value heat would be the heat radiating from the mass of the engine. This heat is hard to recover.
Capture the heat which is easiest to work with first then move on to more difficult sources. Take the “low hanging fruit” this would be from the coolant loop, run it through copper finned baseboard heating sections. Add a circulating pump and the baseboard heat becomes your radiator. I am sure the HVAC guys in the group could do a heat loss analysis to best size the baseboard sections. With the right data you would also be able to fine tune the flow to optimize heat gain to the room while leaving enough heat for the return line to keep the coolant in the block hot enough for efficient combustion. (As for the consumption of electricity of the circulation pump, the Taco model 005-f2 draws .53 amps at 115v so about 61 watts are consumed by the pump. Even at 24hrs run time it only costs 28 cents a day to run.)
This is a balancing act, and with creative use of valves and or variable flow rate pumps it could be done.
Harvesting the exhaust heat will require fabrication or purchase of a gas to liquid heat exchanger. The principals are pretty straight forward, increase surface area and increase heat transfer. I am sure there are other factors at play such as dwell time and materials used, but sometimes common sense is enough to get a simple project done. Have a downward slope to the heat exchanger and put it after your muffler if one is used, this will reduce the acids from a cool exhaust from eating everything. Plumb it to your house, pool , hot tub or greenhouse.
Calculate how many BTUs you can take out of the exhaust. Take that btu content and add it to the BTUs you captured from the coolant loop. The dollar value of those BTUs are determined by the price paid currently for your home heating fuel, as they will displace BTUs you would have purchased normally for your domestic heating requirements.
I have done the real world math for the electric generation, the numbers work. Part of the reasons my numbers work is because CT has the 2nd highest electric rates in the country, second only to NY. I have not done the math for the cogen, but any heat I can use is a bonus. For my project to make economic sense I don’t need to do cogen. I can further accelerate the payback time if I use cogen.
Interesting info I found along the way:
Each gallon of free vo is converted to $1.97 in electricity up to my domestic usage.
Each KW of electricity is equivalent to 3412 BTUs
A BTU of electricity at my retail rate costs me just $0.0000562 .192/3412btus= .0000562
A cubic foot of nat gas has 1031BTUs
Using last months nat gas bill, my cost per BTU of nat gas is .00158 when converted to BTUs, the cost of nat gas is much higher than electricity.
There are also losses involved with burning nat gas, using a resistance heater there are negligible losses converting each kw to 3412 BTUs. I would have expected the reverse, It seems it would be cheaper to heat my house with electric vs. nat gas. The cost per BTU of nat gas vs electricity is so far apart I fear there is a calculation error somewhere.
A gallon of soy oil (my WVO is soy) has about 118000btu per gallon.
1kw = 3412 BTUs
10.269kw*3412=35037 BTUs extracted from a gallon of soy based WVO
35037/118000=29% efficiency which is higher than I expected, and causes me to question the real output I was seeing out of the generator. I will run the test again once additional ammeter and volt meters are hard wired into the gen panel.
So the economics for my particular situation are:
Cap cost of about $5200
Payback period <2yrs with no cogen
The state offers grants for this type of project, I was awarded a grant of $3300. I will receive the money when it is operational and deemed in compliance by the utility. This makes my project pay back in less than one year. They also offer a separate grant of $250 per kw for backup generators. If you are called upon by the utility you must take your self off the grid, this can happen if there is a power emergency where rolling brownouts may be required. I have a ST head, so I also have a backup generator. Because I am using an induction setup if the grid fails I have a source of power. This grant or grants will make for a very quick payback period of far less than one year.
I have also been looking into using a UL listed off the shelf grid tied inverter, these are common for solar and wind applications. If this works out, utility approval will be easier and less expensive. There is still a lot of research to do into this option, I have contacted several manufacturers with limited success so far. I have 3 years from the date of the grant award to get something installed, so I am in no great hurry.
Bottom line, under the right circumstances and with enough research and hard work it can work, but it is by no means anything close to easy.
Best regards
Scott