ECN Forum Forums General Topics of the Trade Alternative Energy Grid tie inverter question

The main advantage of grid tie inverters is you do away with all of that battery stuff.

Hmmm...not a bad idea...maybe an auxiliary load bank for when there is more PV power than needed?

Greg, is your inverter currently in place and selling power back to the POCO? If not, an off grid inverter is your answer. It still connects to the power, just doesn't back feed the grid

I have not bought anything yet. I was interested when we still had the rebate. Without it I am trying to come up with a reason to do it.

"where will the excess power go if the loads are less than Solar production?" Is that an actual problem? I am under the impression that you can open circuit PV panels. The inverter will only draw the power that it can use. I agree that backfeeding a small generator is not a good idea, especially the new inverter style.

Even if you could put a generator on the line side, running a generator is inefficient. You'd be better off just putting the generator on the load side of the inverter via a transfer switch but then you run into the gambit of dealing with transfer switch sizing, generator panel, etc. Trying it tie I'm a generator with a grid tie system can be more trouble then it's worth

I can't speak for the rest of the nation...

But out my way, if the AHJ ever find out that you've gotten tricky with field engineering...

Your tax subsidies are TOAST.

Here's the problem. Trust.

The Poco has already decided that it doesn't trust contractors to engineer failure proof systems.

As for economics...

If the grid is actually down... who wants their power to be backed up ONLY during daylight hours? Around my house, power NEED (as againt use -- we'll bear up under a hot day) is at a maximum after dusk... unless it's an insanely hot day.

True back-up power has to be available right through the night. In which case, the cost per kWHr is trivial. The money is all expended by the capital budget. (the shear cost of installation)

The ding to one's wallet from diesel/ natural gas/ gasoline use is utterly trivial. It's only ever going to happen on a very occasional basis.

No.

The Poco has it right: the sole economic value of PV arrays is to displace retail demand during ordinary operations. There is no merit to messing around with even the slightest mistakes -- backfeeding the grid -- from an errant installation. The threat to their line crews is way to high vs the trivial -- and imagined -- gains from using PV to power the home during outages. They're just too rare, too brief. You'll NEVER recover the expense of the complications -- in a century of use.

It flat out doesn't pencil out.

It was more of a theoretical question but in any serious emergency, "feeding the monster" (fuel) is far from a trivial task.
Proper transfer equipment is going to be needed for the generator anyway so any "field engineering" will not be attached to the grid. This would be used in lieu of the generator during the day.

I have this response from others...

The generator is a demand source, i.e., a voltage source, that keeps the AC bus at a constant voltage by delivering whatever current is necessary to do that. A GT inverter, on the other hand, cannot regulate its current output to maintain line voltage - it behaves as a current source. If you have a generator running on an AC bus alongside a GT inverter and the demand from the loads on the bus falls below the output of the GT inverter, the only way that the generator can regulate the line voltage is to sync rather than source current, which most generators cannot do without sustaining damage.

Here is some more...

The GTI will try to drive the generator as a motor. Depending on the design of the generator this might drive the voltage higher or increase the speed of the generator. If you are fortunate this will just cause the generator voltage or frequency to go out of range and shut the GTI down.
In the worst case the reverse current will interact with the speed and voltage regulation of the generator to cause damage.
A normal GTI's anti islanding circuitry will simply never see the generator as a low enough network impedance and will not run in the first place.

shortcircuit

Is there an inverter available that can operate in grid tie OR island mode? That would solve the issue. Even if you had to turn the inverter off and then back on to switch between modes.