Converter/Inverter to Marry Synychronous AC Generation to Solar Inverter Grid Tie


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I've found that continuously generating 75KVA power basically problem free from a Kokler 100KW standby generator over 35,000 hours continuous production is the smallest part of an electrical generation project. More free fuel is available, but the ideas max out at a variable 5 KW to 50 KW so far. I could, would and do willing tell interested people how good quality flare gas from associated gas off the oil well casing of even a marginal well can produce more power than any ordinary farm can utilize on a continuous basis. Perhaps someone can comment on what would solve the requirements of the grid authority and in the least complicated and costly way in order to sell the excess to an electrical utility.

Despite several years of researching grid tying to a provincial power utility and searching the internet, I have yet to come up with a relatively simply grid connection for synchronous power production...outside the control units equivalent to the power companies commissioning of a new unit at their large generating sites.

The solar industry has a wide selection of grid tied solar inverters that accept high voltage (max 1000Vdc) DC bus sources. (most usual from conventional strings of photovoltaic solar panels). Those inverters are considered and accepted for near immediate connection to electrical grids such as I was and am interested in applying to access.

What pitfalls and oversights would there be in connecting 480VAC synchronous generation to an Allen Bradley Variable Frequency Drive (3ph 480V) input? Then using the) accessible DC bus running at close to 670 VDC ( and which could be parallelled with other similar VFD's in a common bus system.) In any case the VFD DC+ bus would feed the solar inverter instead of the solar panel string.

Any hints on DC amperage control etc that would be essential to feeding this into an Allen Bradley (Yaskawa) PVI23L-480 grid tied solar inverter to hopefully output about 23 KW of 3 phase 480VAC power approved into the power company infrastructure would be deeply appreciated and maybe even reciprocated.

Alternatively; any other suggestions about mechanically connecting induction motor/induction generation would be appreciated. I've tried a 20 HP test unit which works; but the required relays and certification appears to make that a non-starter.

I've come to the conclusion that the least resistance with inspection might come with the proven solar grid tied inverters; and feeding them with appropriate; but consistent and fixed BC bus required voltages from VFD(s); and hope that any required current control to protect the solar inverter is a simple matter.

There's a market for this (which I'm not particularly interested in being involved in); but the testing and commissioning aspects are right down my alley.

Hope to hear from anyone interested in these ideas My email address is [email protected]
Interesting thoughts....

Where I live a LOT of oil well casing gas is just flared--in large diameter "stacks" that hide the flame; one only sees the heat waves at really cold ambients or when the sun is just right. It's a real waster of energy. There were (maybe still pending) lawsuits by investors who were suing the production companies for flaring well gas and even natural gas from oil wells because that was energy they were not getting paid for. (There was no easy way to ship the gases to places where it could be used or added to a gas pipeline.)

I would imagine some farming operations could definitely use waste gases to generate electricity--I'm thinking particularly of dairy operations, and cheese-making factories, of which there are a lot where I live--and are pretty close to wells, which are being drilled at an unbelievable rate, many of which are just being capped right now.

But, you raise the biggest problem: Connecting electricity from turning that waste gas/natural gas into electricity to a grid. I recall when wind turbines were all the rage in the USA in the 1980's--and everyone was trying to put up a wind turbine at their home and connect it to the utility's grid and get paid or offset their power consumption/bill. A very few were successful--until the utilities lobbied for and got laws passed to require even homeowners to put up multi-million dollar bonds and install what were, at the time, very expensive protective relays (digital relays are MUCH cheaper now), and pay for very expensive power system studies before being allowed to connect their 10-25 kW wind turbines to the utility grid. (I remember reading about one poor soul who's wind turbine at his home blew over in a very bad storm, and struck some nearby power lines in the neighborhood, and knocked out power to about 7,000 homes and businesses for about 24 hours.)

I would imagine it's still a pretty stiff requirement--and bill--for connection, that only well-funded enterprises could support. And, one can understand the reasoning, too--the utilities do have to protect their transmission and distribution assets, for everyone's benefit, not just theirs! And, many rural or even suburban transmission lines are not designed for power "input", or power distribution. I hear people saying all the time that it's the big generator utilities who don't want small power utilities (or home solar) on the line--and the relative sizes don't really frighten the bigger utilities. It's who's going to pay for maintenance, and upkeep, and interconnection?

In writing this, I guess people connect their solar panels on their home's roofs to the utility all the time without much in the way of protective relays.... Hmmm .....

It really is a big dilemma--and a very wasteful one at the present time, too.

In my personal opinion, it's storage that's going to be the big game changer for farming operations and other operations who could benefit from using waste gases from wells and flares in rural areas. When it can be beneficial to generate power and store it for use in a rural application, that's when it will become economically viable. Trying to connect small "distributed" generation to a utility grid, or a rural electric co-operative, is not really going to be feasible--until such time as someone comes up with a reliable and safe method to do what you are describing, with a single "black box" which is approved by the utilities and co-op's. THEN, putting power on the grid might really be good for everyone.

But, when that happens, there's going to be an outcry about emissions from the generator prime movers.

As I sit and write, it's really probably going to require fuel cells, and even fuel cells that convert methane (which is available in MANY forms of "gas" (think cattle!)) into hydrogen, which can then be converted into electricity. I think I have seen small-scale wind- and solar-powered hydrogen-producing "stations", though most of the ones I have seen or read about have been in Europe. When the primary output of the hydrogen "converter" is water vapour, and nothing else, well, that's going to be the holy grail. (I don't recall what environment impact the process of converting methane into hydrogen is ... need to do some more research on that.)

BUT, it's still going to require the connection equipment approved by the utilities, and they are still going to want the power studies (paid for by the people/firms wanting to connect their power to the transmission and distribution grid). (But will it--think again to the millions of homes connecting their roof-top solar to the utility...!)

Nope; unless there's a need for power at the local area where the waste gas is being burned, and it's fairly constant, I don't see how the utilities are going to be "persuaded" to allow small generators to put their power on the grid. (Or is it just going to take the right legal arguments, and laws? Gosh, I hate thinking about more laws. Sometimes it's the answer, though.)

Comments? Ideas? Alternative thoughts? It's all great fun to speculate, and who knows, someone or some group may have the answer already if the problem is presented in the proper way. But, there's always going to be that utility connection issue....
In Sask; the provincial Power Corp is somewhat committed to individual customer net metering. No money ever gets returned to the generator and the best possible scenario is that over a three year period you get credit for the amount you drew from the grid.

But those flare gas wastes are 24 hr/day 365 day per year sources of tens of kilowatts of typically currently wasted energy. We're talking supplying handfuls of other electrical customers on a continuous basis; and getting the benefots of cogeneration (CHP)

You and I are in complete agreement that what is needed is a utility accepted "black box" UL (C or US or any other Can or US) or other approval standard)

Anyway is it feasible to use the DC+ bus of a VFD connected to a grid tied "solar" inverter.

I've got a call into ABB (Allen Bradley) to inquire if they have any such combination to do the trick.

Thanks for the comments. Just for info; maybe 15,000 standard cubic feet per day of flare gas (has to be free of H2S or you want no part of such an operation) is probably capable of heating 10 houses just from the waste heat off the generator radiator and exhaust system....not to mention 50 or so KVA of electricity. There's propane, butane and condensate in some associated gas from oil production providing an extra 50% energy content than in processed natural gas. And it can be burned with a stock natural gas motor (without adjustment) and few spark plug changes (if any) in a few tens of thousands of continuous running. Oil changes on more than a month's intervals.

But where is the lead to that grid connection box costing say $10,000???
Are there any trusty way to program a VFD for input current limiting, that wouldn't automatically trip a fault when an absolute maximum value of current is exceeded?

Something like a 3ph motor "Soft starter" that is programmed for an extended acceleration to full motor speed.