Full-time generator with grid backup?

[tebish]

I've searched and searched and cannot figure this out.  Is it possible to run a generator as your main AC source while having the utility grid there to support any power requirements over the generator capacity and for when the generator isn't running?  I've seen the kits for solar and wind plants but haven't seen one for a generator setup.  Has anybody done this setup or have objections to running something like this?  Any links or ideas would be greatly appreciated.

[phaedrus]

The short answer is “yes”.  However, the local utility would probably have a fit if you just paralleled the generator. There are considerable safety questions, I think.  I doubt that it would be economic in any case. Using available inverter-grid-tie setups might be kosher in an engineering sense, but the lower efficiencies involved would seem to make such a setup even less economic.

Frankly I would shy away from the project.

[Procrustes]

There are lots of possibilities here.

With an adequate battery bank and inverters, you could power huge loads with a relatively small generator.  You could have the generator producing DC to charge the batteries, and get all your power from the batteries.  If you want grid for backup you'd need an inverter that will switch to grid when battery reserves fall below n amp hours.  Safe grid intertie requires inverters that are made for this; they have protections against powering dead power lines and getting out of phase with the grid.  DC generators are somewhat problematic.  The efficient ones are expensive.  Some folks just use a battery charger running off of AC.  Also if you go this route you can replace your lighting appliances, etc with DC counterparts, thus lowering the load on your inverter.

I presume you are going to be burning WVO or WMO.  Someone on this forum who is offgrid calculated that he is paying $0.35/kWH with diesel IIRC, so you are almost guaranteed to pay more for electricity by burning premium fuel.

If you want to sell electricity back to the utility, or keep your electric meter at zero, check with your utility.  The regulations vary quite a bit by utility.  If you go this route you can spare yourself the expense and maintenance of a battery bank.

[fireram]

Our "cheap" hydro costs one third of what it costs for fuel oil alone.  After our taxes and delivery charges, and even a debt retirment charge, yes, thats right, we pay a fee cause the last management of our hydro network rang up a huge debt. but i digress,   Our total is still only 11 cents per Kw/H.

However, Our area, my house included, is now getting "smart" meters. they wil determine how much you use, and when.. During Peak hours we will pay around 9 c/Kw/H just for the juice, plus tax, delivery, etc... During off time, 11pm to 6am it drops to 3c/Kw/H.

So a feller with some batteries, large enough to handle just a days worth of usage, mine is around 30Kw/h per day, cause i have an outdoor hot tub, soon to be heated with an oil boiler instead of electricity.  You can use the batteries to run your house through the day, and charge them at night when the rate is low with the utility power.

This can all be done with an expensive trace inverter charger.. Of course we all have listers here, and well you may as well have it feed the grid, even if its through an approved inverter.  But they must provide utility grade hydro, wich means no square wave stuff, or in some areas, not even modified sine.  Only Pure sine, quallifies in my area, acording to the utility.

Intresting though.  here in Ontario, If you produce your electricity By Solar panels, under contract with the provincial government. You will be paid 42 cents per Kw/H, gauranteed for 20 years.. with other renewables like Hydro, or wind, or even maybe veggi, Just 11c per Kw/H.

Big push on solar in Ontario, I would say so.. Or is the predicted price of electricity here to rise past 42c in 20 years??

[captfred]

For almost 3 years now we've run a non grid-tied  outback inverter with t-105 battery banks  instead of a generator for backup power during frequent power outages.  With power now at 22 cents /kwh for the first 500 kwh and 32 cents/kwh above we've decided to set up a lister based generator (hopefully it's on the boat from india as I write) and go off the grid, (hopefully with wvo).
 
Our intention is to run the generator 4 to 5 hours per day during the work week for battery charging and running a 2 ton a/c unit, additional hours during weekends.   Our issue here on saipan isn't heating but cooling, mostly in the early evening hours. 

Quality inverter/chargers and batteries are expensive, but they are quiet, easy maintenance, and don't need to be started when the power grid fails.   If you feel you occationally need additional power than  your inverter/batteries/generator system can provide, why not include an appropriate transfer switch which will allow you to transfer to grid supply when necessary. 

[buffdownunder]

It may be absolutely stupid because electrical engineering is not my friend but why not make a solution like this:

Put the generator in parallel to the grid but ad a device after your meters and before the parallel connection that no power can go into the grid and that the grid is disconnected as soon as it fails. This way you shouldn't have any security issues with the utility. Then you would probably also need a load limiter on your generator so that the lister isn't forced to go over say 70-80% load or what every you like to put as an upper load limit.

Cheers,
Edward

[SCOTT]

Tebish

What you have described is a grid interconnection.  Most states mandate that the local utilities allow a customer to interconnect with the grid for the purpose of net metering.  Net metering in its pure form sums all the electricity you produce and subtracts the amount you have consumed.  The result being a credit if you produced more than you consume and a bill if you consume more than you consume.  Take a look at the below link and see if your state offers a net metering program:

http://www.dsireusa.org/

The most common application of this is, as others said solar, but the upfront costs of solar are pretty steep.  It would be very nice if you  could do as you described and use your generator as your main source of power and the grid as a backup or a supplemental source.  You also want to get as much out of your generator as possible, and that usually means running it at close to the max rated continuous load.  If you have a generator large enough to run your entire house without having to schedule loads, you are not likely to run it most of the time with a large enough load to achieve max efficiency.  Ideally you would undersize the generator and run it for a set number of hours a month, near its max continuous rating, to offset your usage.

The problem is that interconnection with the grid is that it can be complicated, and dangerous if done wrong.  Utilities have rules in place to protect their equipment and people.  The only way to do this is by the book, following the utilities rules, they will not allow an interconnection otherwise.

Solar is easy because there are inverters that are already UL approved, all the safety requirements are met.  Using a generator is another story, and no you cant just connect a generator to a solar inverter, they expect clean, usually high voltage low current source of DC.  A car or truck alternator will not work either, it may be possible to find a high quality permanent magnet DC generator but they are very expensive and negate the whole concept. 

Another way to net meter is by running an induction motor above its sync speed, for example 1800rpm.  When the motor is running below 1800rpm it consumes power, but when it is above 1800rpm (to a point) it will act as a generator.  There are still all the safety requirements to be met, but it is another way to use a generator to provide your power without having to give up the grid.

Keep an eye on the forum, a solution is not that far off.
 
Best regards
Scott