Feeding the Grid

I recon you are smarter than you think.

I think you are right...you have to match phase, and to get the current to flow you will need to raise your voltage.
There are units which do all this complex stuff.
I too am willing to get shot at on this a power electrics isn't my field..
I'll stand right behind you.
Del

Ahh, I do feel better with backup!

but raise my voltage? Really?

Well if you use the good old water analogy....
You won't get it to flow uphill.
Presumably it is just raised enough to get the current to flow, e.g. without exceeding the tollerance of the supply which is probably +/- 5% or so.
Del

Good thread Edignan.

GA sb,

Although the first link wouldn't open for me, the second did and was good info.

Thanx

Sure I'd appreciate that. shadetree@rcabletv.com

Excellent links!

Sir, You have given excellent links .Very nice information to Our Electrical Engineers.

thanks

Might want to check FERC (Federal Energy Regulatory Commission) Regulations for cogeneration. Here is a link to their search results for "cogeneration."

I think you were looking for another term, rather than cogeneration, which is ordinarily used to mean combined heat and power. Although is possible cogenerate at home, (using waste engine heat to heat domestic hot water) Th OP's questions are related mainly to other issues, I think -- mainly the electrical phasing issues, grid tie, etc, rather than the thermodynamics of generating power.

Some terms to look up: grid tie inverter, generator synchronizing, generator phasing, VTG (vehicle to grid -- a hot topic, which I think is nearly nuts in the days of incredibly expensive, limited life batteries ) net metering.

Good point, but I thought the information may be helpful anyway. I figured, "What the heck, if anyone is thinking about producing electricity and selling it back to the grid, they may as well think about cogeneration." Note that the FERC governs all wholesale electricity transactions, even those involving systems connected at the distribution level.

Duke Energy has a link or two to FERC documents for qualifying to produce power. American Wind Energy Association also has information. US Dept of Energy also has information on PURPA (Public Utilities Regulatory Policies Act), as well as EERE (Energy Efficiency and Renewable Energy) about connecting to the grid. Connecting Solar Panels to the grid is covered by the "Better Building Series" folks at the National Renewable Energy Lab. Cogeneration is covered well at this site by Renewable Energy Technologies. IREC covers a host of issues regarding connecting to the power grid.

Wikipedia also has a good list of references and links on the power grid.

Anyway, I hope this helps.

While there are many many people involved in regulating electricity's generation and sale, for the finances for the tiny production - one should resort to the local state and specific utility websites.

The state is going to specify your incentives, and it is the utility who has been tasked to come up with a plan to accommodate you.

Point well taken, but I also figured that anyone interested in "connecting to the grid" may get some use out of the links I posted, and although I did not assume that anyone ingenious enough to undertake such a project would also have enough sense to contact their local electric utility, I reckoned they would eventually find out they need to do so.

great post thanks for sharing.

Gave the Thread a 5 star. First time to rate a Thread same as a GA.

I know if I want to feed the house from a 5000 watt generator, I better cut the Bull Switch to the house before I plug the cross wired 220 plug out the generator to the Dryer socket, or the draw from the Grid will blow the Generator up.

How exactly the Inverters convert DC to AC and then give Watts to the Grid for credit, is not fully understood by me either.

Hence Good Thread Vote!

P.S. Gottah make the 220 plug put 110 to the house, so you have to drop a phase in the plug, from what I remember. I thought it was all interfaced by Watts, and not voltage for Grid supply, and demand. Since I learned all my electricity in the streets just adding up what was on line demands for phases, to keep lights running, I am not a fully realized expert, as is Sparkstation.

They way I was taught, the small daughter genset will always sync to the mother. That would be the reason we use a synchronizing method to engage a genset into a grid. Picture your 5 k genset at 180 degrees out of sync with the grid, trying to be pulled into sync at the speed of light.

This is one of the reasons I question a news cast that is displaying a home system and saying its making the owner money because he is selling power back to the utilities. Knowing that utilities require you to have certain protective devices in place before they are going to allow you to tie into their system. I can't speak for the present but it used to be a fairly expensive thing to do.

Don't get me wrong I am a big supporter of home grown energy and I am always looking for ways to produce it, but it will always get back to cost and payback before it becomes a viable option. Right now I think in the lines of producing power for the private sector off the grid through the use of transfer switching and separation.

Fortunately several firms have stepped into the void selling isolation units, frequently remote controlled for safety. And to their credit, the utilities out west have sort of embraced the whole thing so between the equipment improving and the utilities dropping the bar a bit, selling your power back is actually possible.

Now I haven't seen a model that works without subsidies yet, or necessarily even cover the capital costs. But that is a different discussion.

Here is a crude analogy. Imagine a tandem bicycle. The pedal motion is analogous to current and the force you put into it is voltage. You have to stay in phase with the other person. If you supply force (voltage) in phase with the motion (current) you will be supplying power to the bicycle (grid).

So then effectively within the limits of my current capacity, the amount of overvoltage between the grid local and my supply determines how much I am *capable* of feeding, and the rate I feed at?

Guest's analogy (#17) is fine for DC, but is fatally flawed for AC. If you increase the generator's output voltage in a synchronized (not stand-alone) AC system, you will increase the reactive output (in which voltage and current are out of phase with each other), but not the active output (voltage & current in-phase). Even in jurisdictions where the utility is required to take and pay for your power, you get paid for active power, not reactive.

To maximize your return, the voltage of your machine should be matched to the utility voltage; then, as sb said, raise the power output of your prime mover (increase fuel flow, tighten the clutch, or whatever causes more torque on the generator shaft). Since your generator is sync-locked with the utility system, it will not speed up; it will, however, supply a larger portion of the total active power demanded by the loads connected to the utility.

You are absolutely right. Speed up the generator (within a limit). As you try to speed up, the rotor poles starts leading the stator and the resultant braking action will transmit the active power to the grid/load.

The point here is to supply the extra torque to the generator without actually speeding up. This is to be limited within the field excitation limits, else, simply the rotor may break free (ie loose sync)- not likely case.

These are usually taken care by the governors.

I think you have a pretty good understanding already.

As you probably know, transformers are bidirectional, so the 120 or 240 v current you send back to the power company gets stepped up in your local transformer. Power distribution is really three phases -- in fact, you can see the three wires (each separated from the other by some feet, all around the country).

I think you can imagine the problems in lack of synchronization -- if the two systems are 180 degrees out of phase, the currents between one and the other could be very high. If you look up manual generator synchronizing, you will see that you can do it with a light bulb -- just wait for the bulb to go out and tie the generators together at that instant. Once tied together, then the two will stay locked, with the "lagging" one being immediately motored back up to speed by the leading one. See generator phasing, generator synchronizing, grid tie inverters, three phase motor operation.

You can probably envision a problem with single phase sources feeding the three phase grid. If all the single phase sources fed the same phase of the grid, there would be a lot of unbalance in the grid. But in fact, this problem is essentially self-correcting, because every single phase tap from the grid cannot all be on the same phase either, for the same reason. Therefore the power company wires things up to balance the supply, and if the distribution of people feeding the grid is fairly random, the balance remains. It all evens out.

The majority of states are at least net metering, meaning that you can spin your meter backwards, selling power back to the company at the price you pay for it (seemingly a bad deal for the company -- what company would want to buy their product at retail?). In some cases, you can sell the power back at higher rates than you paid for it, on average. (Solar cells can be good for this, because they produce their power when rates are high.) The power companies save some money by not having to provide so much excess capacity for peaks, so are more or less willing to buy power during peaks.

If you had an electric car, you would naturally charge it at night, when rates are low (depending where you live and how you are billed) and you would generate solar power in the day, selling it back to the company at a higher rate. This can make driving very cheap, depending upon solar cell cost, state and federal subsidies, etc. In some places, with self-installation of solar cells, you can pay back the cost of the cells in as little as 7-10 years or so, even without the subsidies. Our church is putting in a large solar installation, and the payback is very short.

meaning that you can spin your meter backwards, selling power back to the company at the price you pay for it

Just a little nit on this--net metering [better, net-zero metering] refers to the forward/backward spin on the meter, with the idea that the consumer, w/solar or whatever, ends up with a net-zero bill--not quite the same as the utility buying your generation--While I admit I haven't looked at every permutation across the country, those I've looked at in the West and Southwest do NOT buy excess generation, but do offer multiple avenues to subsidize consumer installations of renewable generation [here in central Texas the Pedernales co-op gives a 20% discount on electricity used over net-zero, 0.08/kWh vs 0.10/kWh]--But net-zero metering just means you end up with a zero electricity bill [after connection charges--you still pay those, and Pedernales charges $30/month]--my direct experience has been that, if my metered usage over a year is greater than when I started, I'm billed for that use--if my metered usage is LOWER than when I started, that becomes my new BASELINE, I'm not credited or paid for the excess generation [beyond my own use] I've contributed--However, being grid-tied essentially makes the grid your back-up system, like a set of batteries.

Yes, it would be cool to collect energy at off-peak rates to sell back at peak rates, which is sort of like Cosmo Kraemer collecting five-cent recyclables in New York and taking them to Michigan where they're worth ten cents.

As for the phase thing, the inverter pretty much takes care of issues in connecting to the grid, and most residential applications are single-phase anyway

edignan,

Be careful! I am not sure who you have your electrical service with in AZ. It is imperative that you contact whomever is your provider and obtain written guidelines as well as a written agreement with all constraints, requirements, and legal ramifications clearly "spelled out". In my area, one of the neighbors spent a small fortune on a sizeable Solar-Voltaic system only to find out the local utility company is not required to accept nor re-imburse any generation facility owner or company unless a legal, binding agreement has been entered into. He has been generating surplus power for over a year and despite his concentrated legal efforts, the utility has not yet been forced to re-imburse him for any generated power accepted by the grid. The only way he can keep the utility company from using the excess power generated by his site is to disconnect from the grid which eliminates his having a "backup" power supply. Needless to say, he has spent a "ton of money" and is very frustrated with the protection allowed Arizona utility companies.

Jim

SHOCKISCAN, good advice in general, but missing the point.

That's kind of like going over to the neighbors' yard, putting gas in his tank, then asking to be paid at retail rates without ever checking with him or getting any understanding about your expectations.

There are also major safety concerns for the linemen who may work on the grid he is connected to, since he could very well kill an unsuspecting worker who did not know of his generation into the grid. The man you speak of did not use his intelligence to it's full extent though his intention may have been good.

Also, once he ignores the rules and safety, he should expect the power company to be a lot less inclined to expect better from him. They have a legal obligation to treat all customers equally, which is not what would be the case if this guy gets such a major exception to the rules all the others followed. As for getting paid, he is also neglecting (or purposely trying to avoid) the cost of maintaining and installing the grid system he has been using without permission, along with expecting to be paid without proper metering.

Bravo to his being willing to help generate power for his neighbors, but shame on his intelligence for not asking some simple questions before acting on his intentions. All the more so if he spent time and money engineering the system, when the local utility would have guided him for free.

I can't help but wonder why this story is not about him suing the installer and seller of the system, since they had to be well aware that he was heading for a lot of problems by not going to the power company first. Also he must have avoided the cost of a permit for the work(which is there to save him the trouble he has gotten himself into) since that process would also have saved him.

sorry if I sound less than sorry for such a foolish man, but he tried to skirt the costs of doing this project correctly. The system is in place to provide protection and safety to everyone he affects with his generation, and he skipped steps thinking it would save him money, regardless of the potential negative effects on his neighbors or the utility.

Regards, CJM

Right on target CJM! Excellent points!

My intent without getting too deep into the subject, was that anyone planning to go on line with a small generating unit is required to meet all of the local utility grid requirements "up front". You cannot just go out and purchase any power generating system, install that system, and then try to "force" the utility company to accept you as a provider. The requirements are there to protect both sides and it is suicidal (physically & finiancially) for anyone (home owner or small business owner) not to follow the rules when connecting to a power grid.

As evidenced in the many responses, most do not have adequate knowledge to make the connection safely to their local power grid without competent advice/guidance. The technical side is a major concern but the safety side for the utility is even more important.

edignan, to be more informative in the specifics of your query, you can put power into the grid at EXACTLY the same voltage as the grid or even slightly lower. Power flowing into the grid is not dependent on your voltage being slightly higher than the grid.

The short answer is, it's all in the timing shift caused by the addition of energy, not the voltage difference.

What is required is related to a concept that has been well discussed on the forum, but not taken in this direction - Power Factor.

When we discuss power factor, we use terminology about the vectors. For the power factor discussion we are concerned with values between 0⁰ and 90⁰ lagging current in relation to the voltage, 0⁰ lag being 1.0 (100⁰/₀) PF and 90⁰ being 0.0 (0⁰/₀) PF.

Ever consider what happens if another force, say the force of a flywheel or the physical load that the motor is driving, perhaps an elevator or an oil pumping set-up adds to that CEMF and pushes the timing past 90⁰? That's right - generation back into the grid.

I have used the term CEMF, counter-electro-motive force, to explain the reason the current lags. As long as the reverse force is supplied by the inductive effects of the coils involved, the angles will remain in the 0-90⁰ range.

Generation in the reverse direction almost always occurs, that is how a transformer with no connected load can be connected to the line and nothing happens. That is why the inrush current for starting a motor goes down as the motor comes up to speed - it generates more CEMF as it goes faster. Usually the phase angle is under 90⁰ in normal energy using situations since the loads tend to slow down the motor, using energy.

Sometimes however, such as with an elevator for instance, being pulled up uses energy, but when it goes down it actually reverses the direction of a mechanical electric meter because it pushes the current timing past 90⁰ which is the definition of positive generation in the reverse direction.

OK, the timing we are discussing is pretty minute, but as in the example of pedalling a bicycle uphill, our legs put all their energy into the pedals due to the good timing. When then crossing to the downhill side, if our feet are in stirrups to hold our feet to the pedals, the gravity adds energy and advances the timing of feet/pedals minutely, and energy is pushed into our legs.

I know we compare electricity to water in order to explain some features, but this feature doesn't compare in the way you have suggested. In this case it is the direction of flow for reasons other than the pressure of the water that is at issue.

Regards, CJM

I had a feeling this was going to get complicated!

Thanks, now I know where to go read.

In fact it is not complicated

a) Check How you are going o get back power from the company

b) take their help in installing the equipments

c) If found OK, I would have preferred the inverter to feed to the line (check the other thread running by miik999) so you don't much bother about synch or voltage.