Optimizing AC Household Generators for Consistent 60 Hz Frequency at Varying RPM

[deckart]

I'm only familiar with a gas powered generator that I use at home when the power is out. But I'm designing a contraption that will be able to spin a generator with considerable torque. But the RPM will not be consistent. I can limit the upper end but it will often be below max RPM.

Am I correct in assuming that lower RPM will affect the 60 Hz frequency generation? If so, are there ways to maintain 60 Hz with a varying input RPM?

 

[berkeman]

I'm only familiar with a gas powered generator that I use at home when the power is out. But I'm designing a contraption that will be able to spin a generator with considerable torque. But the RPM will not be consistent. I can limit the upper end but it will often be below max RPM.

Am I correct in assuming that lower RPM will affect the 60 Hz frequency generation? If so, are there ways to maintain 60 Hz with a varying input RPM?

Generate a DC voltage and use an inverter to make the appropriate 60Hz AC Mains output voltage.

 

[deckart]

Aha, that's the way to do it! Thanks.

 

[CWatters]

How will your "contraption" regulate it's output power?

My understanding is that when the load on a generator increases (because someone turned on a light) they open the throttle to increase power/torque and maintain rpm. If your contraption can't do this then perhaps consider using a battery to decouple the load from the generator?

 

[deckart]

From what I understand, excess power can be put back into the grid. This is one of the benefits of household solar. If the home owner isn't using the excess his meter actually begins to go backwards.

 

[dlgoff]

From what I understand, excess power can be put back into the grid. This is one of the benefits of household solar. If the home owner isn't using the excess his meter actually begins to go backwards.

I wouldn't consider selling power back due to the equipment cost. As it is, here in the US, you'll need a Automatic Transfer Switch (ATS).

• A[/PLAIN] transfer switch is the only safe way to directly connect the generator to your home.
  A transfer switch isolates selected circuits your home from the power lines. This prevents back-feed, which occurs when power goes back down the utility lines.
  Back-feed can not only damage the generator, but has the potential to cause a fire.
  Even worse, back-feed could electrocute any technicians who are working on the lines - causing injury or even death.
  A transfer switch eliminates the risk of back-feed. It is the only safe way to connect your generator directly to your home.

 

[deckart]

"But why would utilities go through the trouble of purchasing this energy?
Well, because the government says so. In the U.S., the Public Utility Regulatory Policy Act (PURPA)dictates that electric utilities on the traditional power grid must purchase the excess electricity that renewable energy systems generate. It's a way of encouraging renewable energy production without requiring utilities to invest in expensive renewable systems themselves." http://science.howstuffworks.com/environmental/energy/sell-electricity-back-grid.htm

I don't believe I need to purchase an ATS.

 

[dlgoff]

"But why would utilities go through the trouble of purchasing this energy?
Well, because the government says so. In the U.S., the Public Utility Regulatory Policy Act (PURPA)dictates that electric utilities on the traditional power grid must purchase the excess electricity that renewable energy systems generate. It's a way of encouraging renewable energy production without requiring utilities to invest in expensive renewable systems themselves." http://science.howstuffworks.com/environmental/energy/sell-electricity-back-grid.htm

I don't believe I need to purchase an ATS.

I don't think you can get around this. Yes utilities are required to purchase excess when the equipment is properly attached to the grid; that and they're not going to pay you at the same rate as they are selling it for and usually for quite a bit less than selling price.

 

[deckart]

I understand that you get paid at a lesser rate, but there are also rebates, tax incentives, etc.
As far as the hardware required, I'm asking a buddy who is an electrical contractor. He installs solar array systems and knows details. I'll post what he has to say on it.

 

[Drakkith]

I understand that you get paid at a lesser rate, but there are also rebates, tax incentives, etc.

Caution: Be SURE to check the 'fine print' in your local power companies regulations or rules or whatnot regarding what you actually have to do to sell power back to them. I looked into this once but decided not to go this route because not only did they pay very little per kWh, they also charged a $75 monthly fee for this service. I'd have had to generate several times my homes power consumption just to break even with that fee.

 

[deckart]

Ok, so if I sell power back to the grid, it could cost me more than if I didn't?

 

[Drakkith]

Ok, so if I sell power back to the grid, it could cost me more than if I didn't?

It's possible, yes. Like I said, check with your power company.

 

[CWatters]

From what I understand, excess power can be put back into the grid. This is one of the benefits of household solar. If the home owner isn't using the excess his meter actually begins to go backwards.

That's certainly possible here in the UK. The meter doesn't go backwards (most are digital these days) you either have a separate export meter or they assume that 50% of what you generate will be exported.

 

[Nugatory]

I don't believe I need to purchase an ATS.

The ATS requirement is a bit of a red herring here. An ATS automatically and completely disconnects your house from the grid whenever your generator is working, so it's not part of the solution if you're planning to return excess power to the grid.

To connect your generator to the grid, you need the power conditioning equipment to ensure that not only are you generating at 60 Hz (North America), but also that it is in phase (the peaks and valleys of your 60 Hz power match up with those of the grid) and the waveform is at least vaguely sinusoidal and spike-free (the output of some light-duty farm/home/shop generators can be amazingly dirty). There also has to be an automatic lockout so that the power company can shut you down whenever they need to work on the power lines in your neighborhood. This equipment is becoming increasingly available and affordable when you're starting with the DC output of photovoltaic cells, but I'm not sure that there's a commercially available solution for a repurposed home generator, let alone one that would be acceptable to the local power company.

 

[russ_watters]

Ok, so if I sell power back to the grid, it could cost me more than if I didn't?

It might. Have you calculated how much it will cost for you to generate your own electricity? It shouldn't be hard to find out the price per kWh the utility will pay you and compare with what it is costing you to make it. There's a reason people don't do this very often and I'm not sure you understand what you are getting yourself into (or even what it is that you are going to be doing).

In general though, when you buy electricity, you are paying for three separate things: the generation at the plant, the transmission from the plant to the local grid and the distribution of the power from the local grid to your house. Each of those is about a third of the cost, so if, for example, you pay 15 cents for your electricity, you'd only be able to sell it back for about 5 cents because the only thing you are doing for the utility is the generation.

 

[anorlunda]

There also has to be an automatic lockout so that the power company can shut you down whenever they need to work on the power lines in your neighborhood.

Phrasing it that way makes it sound like there must be a back channel communication from the utility to your house. That's not reliable enough for safety purposes.

It also sounds like disconnect is used only when the utility truck is in your neighborhood. That's insufficient In addition to protecting utility workers you must not attempt to power your whole neighborhood, because that could put neighbors at risk.

The same disconnect must also protect you from galvanic DC currents that could fry all your stuff when an unbalanced fault exists. That means ground fault detection on the customer side.

For safety purposes, the disconnect automation must use only local information, and it must act instantaneously when the grid point you connect to loses voltage. Only devices certified to meet applicable standards may be used to interconnect a home to the grid.

 

[deckart]

It might. Have you calculated how much it will cost for you to generate your own electricity? It shouldn't be hard to find out the price per kWh the utility will pay you and compare with what it is costing you to make it. There's a reason people don't do this very often and I'm not sure you understand what you are getting yourself into (or even what it is that you are going to be doing).

In general though, when you buy electricity, you are paying for three separate things: the generation at the plant, the transmission from the plant to the local grid and the distribution of the power from the local grid to your house. Each of those is about a third of the cost, so if, for example, you pay 15 cents for your electricity, you'd only be able to sell it back for about 5 cents because the only thing you are doing for the utility is the generation.

It may cost an excess of $20-30k USD to get this project up fired up. And that's just a very early estimation. It's a prototype and there will be a lot of refinements to be worked out after it is already up and running. I don't expect it to pay for itself, actually, if it does it will likely be more than a decade of use before it does. But, it will be capable of generating far more power than your typical home based solar array.

The generator will be DC and convert to AC using an appropriate inverter.

I'm researching the details with my local utility company and there is a limit to the amount of power you are allowed to put back on the grid. But you do get a good rate from them: "If your system generates more electricity than you use, the excess power delivered to the PUD’s distribution system is credited to your account at the same rate class at which you would buy power from the PUD. Other requirements of the rate schedule apply, including the daily system charge. Unused credits carry over each month until April 30 of each year. If any net metering credits remain, they will be granted to the PUD as described in Washington State Law. (RCW 80.60)"

 

[deckart]

However, at this utility company you only receive a credit. No money to be made from this power company out of a home based generator. But there are other incentives.

 

[dlgoff]

The ATS requirement is a bit of a red herring here. An ATS automatically and completely disconnects your house from the grid whenever your generator is working, so it's not part of the solution if you're planning to return excess power to the grid.

My thought concerning the need for the ATS was: During power outages, times when you start the generator, you certainly don't want it attached to the grid. This is what's dangerous for anyone working to restore the power.

 

[deckart]

My thought concerning the need for the ATS was: During power outages, times when you start the generator, you certainly don't want it attached to the grid. This is what's dangerous for anyone working to restore the power.

It's required and would be part of the system.

• A disconnect switch with a lockout function, allowing PUD 3 linemen to disconnect your solar array from the electric grid so that they can work on utility lines without fear of energy back-feeding from your system into the grid.

The electric company has complete access to shut it down without notice.

 

[dlgoff]

Well, using a generator during outages and a solar array are two different animals.

 

[deckart]

Well, using a generator during outages and a solar array are two different animals.

They are animals of the same species and are under similar renewable energy guidelines when working with the electrical grid.

 

[Averagesupernova]

There are companies that offer products/services to set you up with this sort of thing. A lot of time it is wind. But solar is not unheard of. There is switching involved, but it is not the typical double pole double throw transfer switch, manual or automatic.
-

Well, using a generator during outages and a solar array are two different animals.

This is correct. They are not the same thing. Both systems generate power, but that is about where they end. Tying in with the grid is a completely new operation. I would suggest getting more info directly from those who offer such services instead of asking around here. I would like to see how it turns out for you though.

 

[deckart]

There are companies that offer products/services to set you up with this sort of thing. A lot of time it is wind. But solar is not unheard of. There is switching involved, but it is not the typical double pole double throw transfer switch, manual or automatic.
-

This is correct. They are not the same thing. Both systems generate power, but that is about where they end. Tying in with the grid is a completely new operation. I would suggest getting more info directly from those who offer such services instead of asking around here. I would like to see how it turns out for you though.

I'll keep you in the loop if you are interested. I'm soliciting help from people interested in the participating in the project.

 

[anorlunda]

Deckart, you haven't said anything about the kind of contraption you intend.

 

[deckart]

Deckart, you haven't said anything about the kind of contraption you intend.

I apologize, I have another part of this on another thread. I'm designing a wave powered generation system.

 

[davenn]

That's certainly possible here in the UK. The meter doesn't go backwards (most are digital these days) you either have a separate export meter or they assume that 50% of what you generate will be exported.

I think you will find things have advanced a bit ( hopefully for you in the UK also) Digital readout "Smart" meters are used in homes these days
These measure power flow in BOTH directions. There is no need for 2 meters

"Smart" meters were rolled out across Australia over a several years from around 2012 - 2015
The installation did not cost the homeowner. Dave

 

[davenn]

It's required and would be part of the system.

• A disconnect switch with a lockout function, allowing PUD 3 linemen to disconnect your solar array from the electric grid so that they can work on utility lines without fear of energy back-feeding from your system into the grid.

The electric company has complete access to shut it down without notice.

In Australia, as least, the system has to be fully automatic and failsafe ... as in, when grid power fails, the home generation system is automatically disconnected and is unable to feed back into the grid till grid voltage is detected
D

 

[dlgoff]

I would suggest getting more info directly from those who offer such services instead of asking around here.

I'm glad to see this. Thanks, as it makes me feel better knowing that someone somewhere may NOT get injured.

 

[Averagesupernova]

In Australia, as least, the system has to be fully automatic and failsafe ... as in, when grid power fails, the home generation system is automatically disconnected and is unable to feed back into the grid till grid voltage is detected
D

So I wonder what happens when enough locals are feeding power back into the grid and there is a power failure such that a section of the neighborhood becomes an island. Do the individual co-generation units know the difference?

 

[dlgoff]

So I wonder what happens when enough locals are feeding power back into the grid and there is a power failure such that a section of the neighborhood becomes an island. Do the individual co-generation units know the difference?

Except for wanting to sell power being the main objective, probably wouldn't ever happen. If you can make enough energy to take care of your own needs, you probably wouldn't be connected to the grid. Just sayin'

 

[anorlunda]

So I wonder what happens when enough locals are feeding power back into the grid and there is a power failure such that a section of the neighborhood becomes an island. Do the individual co-generation units know the difference?

That's an interesting speculation. The answer would depend on the technical details of how each unit detects grid presence. I don't know.

Except for wanting to sell power being the main objective, probably wouldn't ever happen. If you can make enough energy to take care of your own needs, you probably wouldn't be connected to the grid. Just sayin'

Even if the neighborhood (or individual homeowner) makes all its own energy, it would be hard for them to provide their own backup and repair service for less money than a grid connection. It has to do with the very high availability numbers we have become accustomed to for electricity. I think any such neighborhood (or individual) would demand backups and 24x7 repair service.

Remember that with wind and solar, a long period with no wind no sun means relying on the backup. Batteries can not get you through a week long snow storm. To be really self sufficient, you need wind power and/or solar plus batteries plus a backup that can run a week or so. The grid connection alternative has to compete economically with that.

 

[dlgoff]

... it would be hard for them to provide their own backup and repair service for less money than a grid connection.

No. I'd bet that most people having these kinds of set-ups are very knowledgeably of them and would prefer to maintain them. But maybe that's just me ... No.

 

[anorlunda]

No. I'd bet that most people having these kinds of set-ups are very knowledgeably of them and would prefer to maintain them. But maybe that's just me ... No.

I agree, but only if we distinguish most people (early adopters) from most people (general population). Much miscommunication has occurred because posters use both of those definitions interchangeably in the same conversation. Averagesupernova seemed to talking about the general population (i.e. a neighborhood of Aunt Millys) while you seem to project people like yourself.

 

[jim hardy]

It's required and would be part of the system.

Good.

I comment here only to encourage other readers of this thread -
jury-rigged generators will backfeed the transformer on your utility pole, energizing its high voltage side. and you don't know how far that goes. In Florida we lost a couple linemen during every hurricane restoration from jury rigged household generators.

If you're not a pretty good electrician - hire one, or stay the **** out of your house wiring and use extension cords

old jim