I am in the process of planning an alternative energy system for my home and I am trying to do something that is a bit out of the ordinary. Thoughts and suggestions are invited ....

I have a generator that I would like to use for co-generation. The waste heat will heat my house. I would like to utilize the electrical output of the generator as well but the generator is not large enough to run my entire house. I would like to avoid net metering.
What I have in mind is to take the generator output, convert it to DC (the generator may not track frequency that well) and feed it to something like a Sunny Boy (or any of the other inverters). It would be pushed out to the grid at that stage which is a problem (as I am trying to avoid net metering). To avoid the net metering hassles, I am thinking of installing current sensors on the split phase AC line coming into my house. A dedicated microprocessor of some variety would measure the power entering the house and would adjust the output of the inverter to minimize power purchased from the utility. When power demand is low, I should be able to provide all needs from my generator and if power needs are high than the utility company provides all the power that my generator can't produce.

For any of this to work, the grid tie inverter that is used must be dynamically adjustable in regards to power sent to the grid.

When I read the Xantrex XW specs, I noticed that it does allow this kind of operation for loads hooked up to it but I don't think this will work for me because all power used by the house would have to flow through the XW unit. I have a 200 amp service. In the setup that I have in mind, the house power never actually flows through the inverter - only the power injected by the generator runs through the inverter and that will be in the 6 kw area max.

I hope this makes some sense.

BTW, when grid power fails and the inverter shuts down, the plan would be to isolate the house from the grid with a transfer switch and then feeding the AC from the generator directly to my house (bypassing the inverter circuitry)

Anyway, I am hoping for suggestions, especially as to what grid tie inverter could be dynamically controlled in regard to the amount of power that is injected into the house grid.

So many questions .......

Jens

Honda has been selling a co-generation system for a few years now (presumably, in the North East of the USA too--may need to contact them directly for details).

http://world.honda.com/news/2007/c07040 ... werSystem/

If you don't go grid tied--I am not sure that it would be cost effective (cost of fuel, batteries, loss of efficiency, etc.) to do what you are thinking of...

If you are in the US and have utility power--more than likely you will have to conform to building codes, get permits, and have inspections performed. Bypassing any of this will probably let your insurance company deny claims in the future if any cause of action can be tied back to non-conforming electrical/power/fuel/heating/etc. work.

I guess the short question is "...does your local electric utility allow grid tied systems/inverters/co-generation devices or not?"

If you are in the US--I would suspect that you could get a one time approval from the utility to tie in a "green system" of some sort...

If not, anything electrical power system (off-grid type system) will be so expensive (installation and replacement of batteries) will be really cost prohibitive (and--by extension a waste of resources--fuel/batteries/etc.).

Since you don't mention solar--I am guessing that you don't have good sun available (climate, trees, other buildings, etc.)? If you cannot do grid tie solar PV--and have sun available--solar thermal system of some sort (domestic hot water, space heating) would not be a bad place to invest your time and money.

In any case, energy conservation (including insulation, lighting, energy star appliances, replacement of heating/AC systems with more efficient units, etc.) is probably where your first monies should go... If you don't need/use the energy in the first place--then you don't have to spend money making the energy.

-Bill

Thanks for your reply Bill. I was not aware that Honda had such a system - very interesting !
In my case I use a slow speed diesel engine fueled by waste veggy oil so the economics are quite different than the Honda system.
In reply to your questions - I am aware that bypassing permits and inspections is risky and IF that is the way I end up I am aware that insurance issues might arise. At this point I have not decided on how that aspect will be handled. In any case, my utility allows net metering but I would like to avoid the actual Net Metering part because this requires a contract that allows the utility company to pretty well show up at my door step and demand to inspect my system. Not something I would like to put up with.
I am located in Canada (Victoria, BC) and sun is an issue in the winter time when I need to run my plant to heat the house. Because fuel will be more or less free, going the way I plan to makes economic sense to me. I currently use a fireplace to heat the house in the winter but veggy oil is easier to store and you don't have to chop it .
I have future ambitions for PV energy but IMHO with the costs of solar cells being what they are at the moment and seeing that I can purchase energy from the utility grid at something like 8 cents/kwh, it doesn't make sense to go that way. The only reason that the generator makes sense is because I use it as a heat source and electricity is a by-product. There is currently no subsidy for installing PV systems and any power sold to the grid is reimbursed at the buy price or 8 cents/kwh.
I hope that explains my situation a bit better.

Jens

As long as you have free waste veggie oil....

Hmmmm.....

There is one very interesting way of generating electricity without any fancy equipment... I am not sure that it is legal--but it is certainly easy and difficult to call illegal...

Take your low speed generator and belt/gear up a good quality induction motor to run at approximately 6% over 1,800 RPM (or whatever the 60Hz nameplate rating would be based on the number of field poles)...

Turns out, that you can "drive" a straight induction motor at faster than rated RPM and turn it into a generator.... Hook up a servo+controller to the generator that reads current (going out your meter for example) and adjust the throttle for the amount of current you wish to output (output current should be roughly equivalent to torque input)...

Of course, you would have to have to setup a safety circuit to drop the AC motor power--or it would drive your diesel motor if no fuel was available...

Does not give you emergency power (unless you connect an off-grid inverter and back drive it the same way)... Technically feasible...

Easy enough to setup and run some tests (for fuel / electrical conversion efficiency, stability with the injector controller, coupling issues between the diesel and electric motor).

-Bill

Technically feasible but highly illegal ... and, as you say, won't give me power when the grid is down. Whatever I do has got to be legal. If the utility company ever found a setup like that they would immediately lock out the meter. At least if I have a UL/CSA/whatever certified appliance sitting there which is rated for direct interconnect, they can slap my wrist but that's about it. They are assured that I won't fry a line repair man. Anything that I 'cobble up' that is home brewed may even land me in prison.

The setup that I have in mind won't do any net metering so not having a contract with the utility is perfectly fine. The setup also would satisfy any legal requirements for interconnection so I think it would be totally kosher.

I will pass on the synchronous generator idea

Jens

I am not sure the "induction motor generator" is illegal by itself... We used to do similar things in electric shop some 35 years ago (two motors connected together--AC/DC motor generator set) and run experiments where one motor would drive the other motor... The intent/capability to drive the motor/generator and turn the meter backwards would certainly make it illegal in most places.

In the end, just using the genset as a AC generator and use a standard Inverter with AC Mains/Generator/Battery input... The generator would run your home, if it drops out it could fall back to AC mains. If both failed, then you can draw from the batteries (if you want three levels of backup)...

Or, since your genset is not frequency stable--then converting to DC and charging batteries and used with a Xantrex or Outback inverter is probably your only solution (and I don't believe that any of them have the capability to do "zero out the meter" grid tied). The Xantrex XW has the ability to do grid tie or not (as I understand).

If your local utility allows grid tie--and you go through all of the permits required... I don't think they would come out once a year to "inspect" your installation. If you can install the grid tied inverter system in an outbuilding--perhaps you can then keep them out of your home (at least here in California, in the last three years, there have been no knocks at my door to reinspect my GT system).

Pure GT is so much more efficient (and less costly--I have 3.5kW of solar panels)--that I chose to go that way, and just get a small generator for my emergency usage (mine is the "big one"--the next large San Francisco California earthquake). For me, my loads are small and a little eu2000i generator and 28 gallons of gas will keep me going for two weeks (or I have extra gasoline to bug-out).

I have seen a few people ask for such systems ("almost but not quite" grid tied)--but I have not seen anything like that out there... Such a system would still be "grid tied" -- just does not have the ability to turn the meter backwards (which would also require further electronics to monitor the amount and direction of energy flow at the meter)... I don't foresee that anyone will sell such a system as (it would seem) still require all of the Grid Tied safety/permits, more components, more complexity (place to dump excess power, how to manage power generation/throttling, etc.) and about the only thing lacking would be the "net metering" billing agreement with the utility.

I would find out more about the "utility inspection requirements" and see if you can get an agreeable definition for you... Otherwise, you would be left with just powering part of your home with your genset via the equivalent of a large UPS system... Even then, it seems that your power costs (cost of equipment/batteries/etc.) will still be more than your current utility charges (probably something like $0.50 per kWhr--although, the heating from the genset will offset some costs--maybe 1/3 energy to electricity, 2/3rds to heating)...

-Bill

Running any diesel, even a listeroid, on straight veggie oil, will cause cokeing of the injector and cylinder head. Overhauls to de-carbon at 200 - 500 hours become mandatory. If you process the glycerin out of the oil, and make bio-diesel, then the cokeing issue goes away, and you are fine to go, until the sand painted into the crankcase comes loose.
http://www.otherpower.com/listeraxialflux.shtml
check out all of the listeroid stuff at otherpower.com before jumping in.

As a matter of fact, that is exactly the setup I have. A 20/2 listeroid (with an unpainted crankcase).
De-coking intervals can be substantially increased by heating the fuel just prior to injection. I also plan on adding some regular gasoline to get fuel viscosity in line with regular diesel (15% ought to do it).
Biodiesel is not an option since the end product is almost as expensive as pump diesel.
I anticipate de-coking once a year during summer. The engine will only run in the winter when there is a requirement for the waste heat. De-coking a Listeroid is an easy thing to do unlike in a current technology engine.

One of my issues is that I need to put a decent load on the engine in order to reduce coking. Running the engine at variable speed was the thought when I concocted the idea of rectifying the generator output and feeding it to a grid tie inverter. The engine is stable down to about 500-600 rpm (rated at 1000 rpm) at which point rated power would be close to 10 hp. That's roughly 5 kw. I figure a 3 kw load ought to give me enough load to reduce coking. Any power requirements past 5 kw would result in an engine rpm increase. I could control inverter output strictly by engine RPM but that is not responsive and accurate enough IMHO. This is why I would like to control the inverter output dynamically.

Technically this is quite feasible but the trick is to somehow do it without modifying the grid tie inverter.
The Xantrex XW apparently has the capability of doing this out of the box but the problem is that all house power has to flow through the XW which becomes an issue if you have a 200 amp house service. I guess what I am trying to do is the same as what the XW does but using external sensors. The XW has it's current sensors internally so the current has to flow through the unit. By mounting the sensors externally, I eliminate the need to run the entire house power requirements through the inverter. The inverter can then be sized based on the generator (or battery) capacity.

Jens

Going under the assumption that no commercial solution to my problem exists, here is a concept solution (maybe) ....

Generator >> SCR bank >> Filter >> Sunny Boy >> Main distribution panel >> Current sensors >> Utility meter

The generator produces 220 V Ac. The generator output flows through an SCR bank which is controlled by an error signal from the current sensors. The output of the SCR bank is filtered to present DC to the Sunny Boy. The Sunny Boy is set to run in constant voltage mode and it's output feeds the main distribution panel on the house.
The current sensors measure net current flowing in or out of the grid, the signal is used to control the SCR bank and possibly the generator throttle.

The scenario would go something like this:

Let's say the house has a 1 kw power requirement and it is happily drawing that from the grid. I start up my generator and the Sunny Boy. The current sensors measure a power flow from the grid and signal the SCR bank to build up power to the Sunny Boy. The voltage set point for the Sunny Boy is reached and the Sunny Boy produces AC and feeds it to the main house panel. The power drawn from the utility reduces and the current sensors note that fact and send appropriate control messages back to the SCR bank. Eventually, a steady state is achieved with the net power drawn from the grid being zero.
Let's say my water heater comes on and adds 5 kw to the base 1 kw load. Since my generator can only produce 3 kw in my example here, the current sensors will always see power being drawn by the utility and in an attempt to reach steady state, the SCR bank is turned fully on. The generator will produce it's maximum of 3 kw and the utility will supply 3 kw to the house as well to make up the total 6 kw power requirements.
Let's say the water heater turns off. The current sensors will see an attempt to back-feed the grid and shut down the SCR bank which reduces the DC supplied to the Sunny Boy and it reduces it's output in response. Eventually a steady state of zero grid power draw is achieved again.

Should the grid fail, the Sunny Boy's internal electronics will sense this and automatically shut down.

Now before anyone jumps up and down to tell me that this might be illegal, we are talking 'concept' here folks !

Would anyone care to shoot some holes in this concept ?

Jens

Seems like a lot to just get around a net metering agreement with the utility... A pure grid tied system (using solar PV panels) is roughly 77% of name plate rating... When you add batteries, inverters, and such, you get down to 52-54% of name plate rating (the difference goes into heating inverters, batteries, and making hydrogen and oxygen from your batteries during charging/equalization).

One other issue is that a simple current clamp cannot measure the direction of the current flow... So you will need a more complex method of measuring the direction of current flow (I think you need to measure both current and voltage phase, plus amplitude--Solar Guppy would know more).

-Bill