panels, inverters and generators

[farmerdoug]

My solar panels will be hooked to the grid using an inverter. When the grid goes down, I would like to use a generator as back up and to run the inverter as well. It seems to me I should be able to do it. Any suggestions how?

[russ]

Hi Farmerdoug - Welcome to Solar Panel Talk!

I see no benefit in using the inverter when running the gen set?

What are you trying to gain?

Russ

[Sunking]

Well you you can certainly use a generator as emergency power, but yu will not be able to use your GTI when commercial power is off as they are not designed to work with a generator or high impedance source.

[farmerdoug]

GTI?

It's been a while since I took an electronics course isn't a transformer used to match impedances?

[Sunking]

GTI?

It's been a while since I took an electronics course isn't a transformer used to match impedances?

GTI = Grid Tied Inverter.. No power transformers are used to convert AC voltages either up or down within their impedance limits. You might be thinking of impedence matching transformer like they used in tube amplifier days to match the high impedance of the tube amplifiers to low impedance speakers.

GTI's are current sources, not voltage sources like a generator or battery. They are made to operate into the extremely low impedance and frequency precision of the grid. An emergency generator like those used at a residence or commercial application are very low power (high impedance) and have horrible frequency regulation compared to the national grid. Well unless your home generator happens to be a few Terra Watts.(That means 1 Trillion Watts or more, enough to run a small country)

[farmerdoug]

So I need something more sophisticated. I need to take some power from the generator to run the inverter ( or one of new design); and when the generator is in use, I need somewhere to dump the extra power that would normally go back to the grid. In fact, since the generator is not meant to replace the grid, there may never be any extra pump. I could insure that by what I ask the generator to power in the house.

[Sunking]

So I need something more sophisticated. I need to take some power from the generator to run the inverter ( or one of new design); and when the generator is in use, I need somewhere to dump the extra power that would normally go back to the grid.

No when power is lost and you have an emergency generator, you have what is called a Transfer Switch that isolates you home from the grid and the GTI. Once the generator is running the GTI is completely shut down, turned off, isolated, and disconnected completely from your homes electrical system. In other words it is not doing squat.

[farmerdoug]

Ok. Forget the grid for a moment. I could build a circuit that allows me to use solar panels and a generator. Right?

[Sunking]

Ok. Forget the grid for a moment. I could build a circuit that allows me to use solar panels and a generator. Right?

Not that I know of unless you have a degree in electrical and mechanical engineering.

With that said there are what is called Hybrid GTI's. They use batteries to take over when the grid fails for a short period of time until the generator starts up and takes over. But they have very limited power output, still require two transfer switches one to isolate you from the grid, and another to limit what has power in your home like cutting off your air conditioner, electric hot water heater, stove, oven, etc.. IMO they are not worth the expense, time or trouble.

Best option with a grid tied system if you want emergency power is a generator. It is th eleat expensive option and you do not have to suffer with power limitations if sized correctly.

[farmerdoug]

So let me rephrase that: One could hook up a generator and solar panels.
Regarding your other comment: What happens when the grid goes down for days or weeks?

[russ]

If the grid is down for a couple of weeks you run the generator a lot.

The preferred method here is to have a grid tie PV system with a generator for emergency power. It is by far the cheapest option available for most folks.

[farmerdoug]

If I have a propane generator, the price of propane may stay reasonable for a while but if I use diesel then the price will get very high. If the grid goes down for a week or two, it would be silly to let the panels go used. No?

[Sunking]

If I have a propane generator, the price of propane may stay reasonable for a while but if I use diesel then the price will get very high.

Depends on what country you live in, but in the USA diesel is the least expensive generator fuel because of its energy content and efficiency

If the grid goes down for a week or two, it would be silly to let the panels go used. No?

I understand what you are trying to say and think, but it just does not work that way with grid tied inverters. Like i said you can buy a hybrid gti inverter with batteries, plus the generator if you are dead set if using solar panels for emergency standby power. However if you think the gen fuel is expensive wait until you pay for the batteries and replacing them every 5 years or so on top of the generator and fuel.

[farmerdoug]

That's why I am investigating the use of solar panels and generators.

[Sunking]

That's why I am investigating the use of solar panels and generators.

Good luck as it has already been developed. You can have it as long as money is no object.