Cogenerators and grid tie?

[Number21]

I've wanted to setup a cogenerator for a very long time, but one of the biggest hurdles are permits and other rules from my power company. They of course allow standard net metering with solar panels, and other renewable energy sources, but they tell me specifically natural gas, propane, and diesel fuel are NOT included.

I would like to have a standard net metering setup with a generator instead of a solar panel. I can understand they don't want a homebrewed system connected to the grid. But what if I had a million bucks to spend and I bought a commercial natural gas cogenerator system? Maybe one of the ones made by Marathon, or Honda. I find it hard to believe something like that would not be allowed. I have a "smart" meter so I can't just run the meter backwards without permission like you could in the old days.

What I'm wondering is, are there any ways to grid tie a generator, WITHOUT ever feeding power back into the grid?

For example:
I have a 5kw generator and a 7kw power consumption. I can run the generator all day and still pull 2kw from the grid. If I turn off the load, I need the generator to automatically disconnect from the grid so as not to feed power back. Is this possible?

Also, is there any way to momentarily tie a generator to the grid, while you switch from one power source to the other? This way there is no loss in power for electronics.

I suppose I could generate DC power and use a grid tie inverter, but I'd like to generate AC power directly.

[focodiesel]

No easy answer for you sorry. You could split up your panel into two, one utility, and one generator. Or use a battery bank and inverter to feed your main panel, then charge the bank with your generator, and a grid tied charger. Yes you will have expensive batteries to maintain and replace, but you gain all of the benefits of uninterruptible power. Without being grid tied (back feeding), it is my opinion that a dc link is the best option. You don't necessarily need a ton of battery capacity, just a dc link, I plan on doing this using ultra capacitors, to see if I can avoid chemical batteries. If you plan on having your generator running constantly you don't need batteries or caps, just rectify dc then straight to your inverter.

[Number21]

My biggest issue with converting to DC is the loss in efficiency. Basically I'm just wondering if there is any equipment out there that is actually designed for this? (Even if super expensive, and unavailable)

I think I found a loop hole that allows me to run a generator as a small "commercial" power plant under 25 kilowatts. They will buy my electricity at the "avoided cost", which works out to about 3 cents/kilowatt hour. I am not allowed to simply turn my meter backwards, but this could give me an excuse to grid tie for a moment while I switch circuits over to the generator, without ever losing power. It still may be cheaper to go DC and use an inverter, depending on the switch gear requirements.

I wonder if an automatic transfer switch could be modified to sense the load and switch over when generator output exceeds local demand?

[mike90045]

The XW series of Hybrid Inverters can take local DC, invert it, but NOT sell to the grid, and use the grid to supplement or be your backup power when the generator is off.  Inverter output is about 95% efficient.

Supposedly, Outback & Radian can do this too. 

[Number21]

The XW series of Hybrid Inverters can take local DC, invert it, but NOT sell to the grid, and use the grid to supplement or be your backup power when the generator is off.  Inverter output is about 95% efficient.

Supposedly, Outback & Radian can do this too. 

Interesting, that's more efficient than I thought. Could I get the same efficiency generating 48v DC as I could generating 120v AC?

[mobile_bob]

can you get the same efficiency generating 48vdc as you can generating 120vac?

yes, no, and maybe!

generally speaking the answer is going to be a no, reason being all things being equal
you will lose some efficiency due to losses in rectification, however

there are some very efficient alternators systems out there, at least as efficient at making DC as an st head is at making AC power,  however

the key word is "some"

generally speaking most alternators are going to come in less efficient than the typical ST generator head.

bottom line is you are not going to make DC power anywhere close to as efficient using the typical automotive alternator, such as those small case jobs that are rewound or reworked to make 48vdc and sold as the next best thing to sliced bread.

how much power do you envision wanting to generate (DC)?  and do you want to not use batteries at all?

i can relate a design wherein a set of batteries of modest size/cost could be used as a buffer, in order to provide brown out protection, so that a seamless transfer of power could take place should either the grid and/or the generator drop out.

bottom line answer is yes, you can do what it is you want to do, however it will take a bit of forethought, and a significant investment to get the job done, at least if you want to do it and be both safe and reasonably efficient.

as for grid tie and being paid deferred cost (3cents/kw/hr) in my opinion it is a huge waste of effort... you can't even make that work out even if the fuel is free and we all know that is never truly the case.

so there is no way i would grid tie to try and get an offset of check from the power company.

personally i am all about cogeneration,   most especially during the cold/cooler months where i know i could effectively use the generated heat from all sources (exhaust, coolant, oil, and radiant) and to somewhat of a lessor extent during the warmer/hotter months, "unless" i had a "real" use for this generated heat (some sort of plant process needing the heat, hot tub or heating a swimming pool that i ordinarily would have to pay to heat anyway etc.

under which conditions i would design a system that would use the grid only for peaking, or for black/brown out conditions with the cogenerator.  in other words i would use the grid as my back up source.

all this providing i had a fuel source that was sufficiently cost effective so that i could make the power and the useable heat for significantly less that what i could simply by it from the power company for?   therein is the rub!

my design is predicated on natural gas cyclic pricing being such that sometimes it is cheap enough so that the math works in favor of generating power via the cogen, and other times when the pendulum swings to disfavor i simply switch back over to grid power.

under so circumstance can i foresee even an excellently engineered system ever being a real money maker,  actually if it saved me 20 bucks a month at best i would be surprised.

if on the other hand the design also incorporates design elements of the house too, and maybe other alternative energy sources might be included?  then maybe it would start to make enough sense to at least be somewhat interesting, if not a moneymaker.

if you can start from scratch and pare back your electrical needs to something very low by modern standards, then it starts to be even more viable.  reason being those first few kw/hrs from the power company are the most expensive owing to the addition of all those added surcharges.  in some cases 50cents per kw/hr is not unheard of and i suspect there are also cases where a buck per kw/hr for the low amounts of power might also be the reality for some folks.

if you can get your  loads down to very low numbers the whole design thing becomes dramatically easier.

fwiw
bob g

[Number21]

how much power do you envision wanting to generate (DC)?  and do you want to not use batteries at all?

Right now I'm thinking around 5kw for a rough number. I haven't settled on an engine yet. I've gone back and forth trying to make it pay for itself for years, it's time I just throw that out the window and call it an experiment in efficiency. I probably won't save money but I think I can save overall fuel input and be close to the cost of utility power. (Not counting initial investments) I could use a lot more than that but I don't think I can source enough fuel. (Want to use WVO) I have some unusual loads in a big industrial building. I'd like to avoid using batteries except maybe just a small one if needed for an inverter.

Seems like I remember reading about rewiring an ST head for 48(60) volt output. Would that be less efficient than making 120v with the same head? Does the rectifier really use a lot of power?

I'm thinking using a transfer switch to switch between grid/generator would work best. Is there any way I can make the switch without loosing power momentarily? (And without plugging everything into a UPS) One option might be to switch over to a time of use power plan and use the generator only during peak cost.

[glort]

Here's a long shot at a suggestion bearing in mind I'm not 100% sure what you want and I'm also thick and have a cold atm which doesn't exactly sharpen my senses.

I set up an induction motor Generator and ran it through a solar controller as a NON net metered grid feed. I have a regular meter and just run this back to the mains wiring on the outlet circuit.

The wvo powered engine turns an induction motor.  The motor has caps to turn it into a generator. The output is fed through some bridge rectifiers and converted back to DC and fed into the solar inverter. This Brings the power from the genny up to spec and feeds it into the mains circuit.  Being a proper solar inverter, this is approved for connection to the grid and has all the saftey  disconects etc.

The one in the vid of the test setup https://www.youtube.com/watch?v=HUE1RQRAXlg&list=UUEfdKGemqGDvpn2hSuJl2Nw is a 5Kw unit.

Noting your requirement not to back feed, I'm wondering if the inverter could be connected directly to the load side of what you want to drive behind the appliances on/off switch?  These inverters take a couple of minutes to do various checks before they actually feed power, 2 of them being the frequency and voltage of the mains. If they were in fact connected to the load behind the on off switch, they would not feed any power to it till after the mains power was switched to the load and it was running. Once it was happy with what it saw, it would start feeding the load and offset the consumption from the mains.  If you have a load you switch on and run for a good length of time or all day, this would be ideal as you'd offset all but a few minutes of mains power cost.
When you switched the mains off, the inverter would detect what it assumed to be a power failure and also switch off therefore preventing backfeeding. As these units also respond to voltage fluctuations, you should be fine with varing loads and consumption.

If your load is in the form of a circuit with many loads connected, then you may have to switch the inverter in and out if it could go less than the inverters rating and there was nothing else on that side of your smart meter to use it up, or maybe work something through a relay or the like for the inverter      . Can't suggest much more as I'm not sure of what you want to drive or what form the load is.

I don't know about smart meters but if the inverter is in fact over feeding, what happens?  If it's back feeding and making the meter count backwards, great. If it does nothing, also in this case not a big problem.

PURELY  Hypothetically, I'm -thinking- Of setting this up in my fathers wrecking yard. I have a Mercedes diesel I can drive the 3 phase motor with (Plus enough engine power and 2x 32A Circuits to run a lot more) and connect it to the 5 Kw solar inverter plus another 2 I have.
I would wire it back to the mains which may also help with the voltage drop problem he continualy suffers with the shitty country power supplier. He has plenty of used oil from the cars he wrecks plus I can bring him plenty of veg to run the engine on. As where he is get's too cold in winter, I could just put the engine radiator inside the shed and get additional benifit that way.
The thing with this would be it would offset his stupid high power costs at the rate charged instead of getting the lousy tarrif the power company offer for solar feed which makes the idea far more worth while.
It would work the same for you where you were paying yourself the current grid use tarrif through savings on your bill instead of the insulting .3C kw/h.

Anyway, hope that is of some help in figureing something out.

[mike90045]

Meters.  standard programming = any power through them, is counted on your bill.   Several folks in the solar community "jumped the gun" and activated their system before the electric company re-programmed/swapped their meter, and their generated power fed into the grid, was counted as "consumed" and they were billed.....

Ain't that special !

[LowGear]

glort:  Wow!

I chased this wild pony for a couple of years and have surrendered,  Yup!  Surrendered.

Mentioning diesel engines and net-metering is the surest way to start a stampede at a regulators convention.  I'm sure Mike's works and SMA has a Sunny Island that will make it work as well.  It's the diesel generator thing that seems to get them nostrils flared all open, the heavy breathing and the stammering feet.  Just the fuel storage part has at least 5 regulations by unheard of agencies.  So I said Screw It and have started shopping for another 4 KW of solar.  The meter box being 250 feet away is one of the very expensive or impossible problems to solve at our farm.

Casey

[Number21]

Great information! Thanks for all the replies everyone. Very interesting idea about putting the inverter after the switch. That just might work.

The one in the vid of the test setup https://www.youtube.com/watch?v=HUE1RQRAXlg&list=UUEfdKGemqGDvpn2hSuJl2Nw is a 5Kw unit.

I really like this. Anyone care to guess what the output efficiency into the grid would be with a setup like that, compared to a standard ST head?

I'm starting to wonder if I can't just build a diesel powered "solar panel". Is the power company actually going to go on my roof and check to see that I have 5kw of solar panels?  I could get an inverter installed and permitted with a bidirectional meter, and say I'm installing the solar panels in the future.  I would be happiest if I could just spin the meter backwards and not worry about load balancing.

[Jens]

It's been quite a while since I experimented but for what it's worth, here is my 2 cents ....

You do not want to run an engine on old motor oil unless you intend to replace the engine on a regular basis.
You can make good money (by avoiding paying for electricity) running a co-gen setup if you do not count your time or the money spent on equipment (ie it's strictly a hobby)
Our electrical rates are going up something like 25% in the next 3 or 5 years so yes, it can be cost effective.
It is only cost effective if you collect the waste heat and make use of it. For my area (Vancouver Island, BC, Canada) that is ideal because we have sun in the summer but not in the winter and I need heat for the house in the winter. I heated totally with electricity this last winter as compared to wood heat or diesel generator heat and a couple of bills during the coldest time were close to giving me heart attacks!
Backfeeding the grid which I was initially planning on is a no go. Too many permits and rules about what you can or can't do. In my case I opted to not only recover the waste heat from my setup but I also converted the generated electricity to heat. It was the simplest way to go but it was not the best way. If I was to carry on with my experiments, I would have two options: Number one, if I was strictly generating heat, then there would be no need to run an engine. An oil burning boiler of some kind would make a lot more sense as the fuel requirements would be much more liberal and waste oil could be used (but be aware, a minor environmental spill of waste engine oil and you are toast!)
Number two, if I had set my heart on generating electricity, I would run the generator based on demand. This would be set up like the Honda Generators in that you adjust the rpm / power output of the engine. The output is then rectified and stored in Lithium Ion batteries (they can accept and deliver very high power rates and have a much longer cycle life compared to flooded lead acid. An inverter then runs the house.
Incoming electricity from the grid will be converted to DC and charge the batteries when the generator is out of action for some reason or other.
With this setup, there is no grid tie arrangement, no permits, no meddlesome officials, nothing. You do your own thing and only use power from the grid when your system is having problems keeping up. The generator doesn't need to be sized for peak power which is inherently bad. Instead, you size the generator for average power demands over 24 hrs and you size the batteries for 2 or 3 days of power demand (or whatever you feel comfortable with). You will want to capture waste heat to make this worthwhile.
You can augment or replace a generator with solar power if you live in an area that gets enough sun.
Here is the catch 22 .... the electronics will be very expensive (including batteries, solar panels, inverters (multiple in case of a failure) and on and on. If you have cheap fuel available (WVO) then a generator makes sense but keep in mind the interval for oil changes, the amount of oil required for each change and the amount of diesel needed to purge the WVO out of the system before you shut down and for startup. It's amazing how those things add up. With a 200 hr oil change requirement you will be doing an oil change every 8 or 9 days if you run the engine 24/7. Of course you can go for more generation capacity and only run the engine for shorter periods but the oil changes still get bothersome after a while. Multiple generators would also be advisable for redundancy. There are millions of little things that need to be dealt with and if it starts out as a hobby it will feel like a job within a year (it did for me).

[Number21]

Here is the catch 22 .... the electronics will be very expensive (including batteries, solar panels, inverters (multiple in case of a failure) and on and on. If you have cheap fuel available (WVO) then a generator makes sense but keep in mind the interval for oil changes, the amount of oil required for each change and the amount of diesel needed to purge the WVO out of the system before you shut down and for startup.

Yep, that's the real deal killer for me, equipment costs. (Though grid tie inverters are getting much cheaper) I would love to take advantage of all the various state and federal tax and other incentives for installing wind/solar power, but to get the incentives you have to use a special contractor for the install and they eat all the savings and then some! I'm trying to negotiate a deal right now for ~300 gallons/month of WVO for $0.75/gallon. At that price diesel engine power should be about the same as utility power. I plan on converting my truck to run on WVO also, the only question is how much can I get. If I can get "free" heat that's enough profit for me to bother with.

If I had my way, I'd have an old 500kw diesel generator that I only run for a few hours/month to spin the meter backwards, but that's illegal in so many different ways. Our total power bill is around 8,000KWH per month.

[glort]

I chased this wild pony for a couple of years and have surrendered,  Yup!  Surrendered.

Mentioning diesel engines and net-metering is the surest way to start a stampede at a regulators convention.  I'm sure Mike's works and SMA has a Sunny Island that will make it work as well.  It's the diesel generator thing that seems to get them nostrils flared all open, the heavy breathing and the stammering feet.  Just the fuel storage part has at least 5 regulations by unheard of agencies.  So I said Screw It and have started shopping for another 4 KW of solar.  The meter box being 250 feet away is one of the very expensive or impossible problems to solve at our farm.

Casey

I guess it's a cultural thing in a lot of ways. Here in the wild west ( or any other direction) of  Oz, we have a mentality of don't tell anyone anything you don't have to.  We also don't have the fear of being fined out of house and home if anything isn't by the book because firstly, unless you are dobbed in for something or do something really stupid, no ones going to find out, and 2ndly, if they do you pleade ignorance and apoligise profusely and get away with a slap on the wrist.
We have lots of over regulations and stupidity, Largely taken from US models, but there is still a culture of over looking the stupid rules and concerntrating on those which pose reals risks such as public safety etc.

I can't imagine anyone here telling the aurthourities they set up their own genny to offset the power bills. IT would be taklen as stupid because we'd get the same amount of over bearing red tape as you guys.
Only difference seems few people are silly enough to try and do things by the book because the book is stupid and we don't have this  fear of fire and brimstone if something is discovered.  Guess we are less honest and bigger gamblers than you guys. 

I'm starting to wonder if I can't just build a diesel powered "solar panel". Is the power company actually going to go on my roof and check to see that I have 5kw of solar panels?  Shocked I could get an inverter installed and permitted with a bidirectional meter, and say I'm installing the solar panels in the future.  Wink I would be happiest if I could just spin the meter backwards and not worry about load balancing.

That's exactly what a mate of mine has done.
He has the most efficent 2KW solar system in the world!  It produces about  10 hours a day on average of the full 2KW output. Month in Month out.
He's done pretty much what you say except he is on a solar tarrif that gives him back what is ATM double what he is charged for what he uses.  He has a WVO fired generator which is a Hatz Diesel and alternator from a mobile Road sign. That goes to a good inverter, to a rectifier bridge and then into another solar controller and into the solar metered circuit.  He runs the setup sometimes in the evenings and on weekends.  The engine has a controller board with low oil pressure, over temp, low fuel, and output monitoring shutdowns so it can be run as a stand alone.  He supplements the solar feed with the genny feed.

At his power rate, (.63C Kwh)  he has paid the cost of the genny back he bought used ( $350) long ago and as I gave him the inverter for nothing, he's well ahead.  His power bill is usually a cheque. He only gets it every so often though because they wait till he's $10 or $20 whatever it is in credit before they issue it. He has monitoring on his computer through and interface on the smart meter for inbound and outbound power so can balance them out very closely.
He's been doing this a couple of years now and much against his expectation and planning in design of the system, hasn't been quired on it at all.  I don't think they actually note the size of the system here, just the in and out. They might well think he has a 10KW system so don't think twice about it.

[glort]

I plan on converting my truck to run on WVO also, the only question is how much can I get. If I can get "free" heat that's enough profit for me to bother with.

When you want to convert it, message me and I'll tell you how to do it without getting carried away with all the useless and idiotic hype people on veg forums go on with.
Don't tell anyone how you are doing it though. They have been telling my system won't work and will kill my engins for 10 years now. Funnily enough, I have never had a failure in any of my engines but I have read about a heap and seen 3 personally from conversions that " Were done by the book".   

If I had my way, I'd have an old 500kw diesel generator that I only run for a few hours/month to spin the meter backwards, but that's illegal in so many different ways. Our total power bill is around 8,000KWH per month.

80000 Kwh would be at least a $2500 bill here... every month? WOW!
With that sort of money on the line, I'd certainly be bending a few rules to offset the consumption by generating my own power!

Do you have or is it normal/ customary/ usual to have inspections done at residences or businesses by the power authurities? I'm just trying to get a realistic feel for what your chances of getting done for having your own DIY power offset actually are?

Here, I have certainly never had nor heard of any such inspection. It's hard enough to get the electrical suppliers out when you want them let alone them dropping in for spot checks.
The only time they would drop in unannonced here was when a home suddenly started using $2K worth of power a month.  They would no doubt arrive with with the TRG ( SWAT) police to bust a drug growing operation.
Other than that, I can't see any way you would get busted for doing back feeding or supplementing your power here unless you did something stupid that caused a fire, lines to be hot when they shouldn't, drove the neighbours nuts with the noise of a genny  etc.
Do they have regular inspections or some sort of mnonitoring in the US to catch people out like this?