# Making grid tied solar panels and a genset coexist



## cbcansurvive (Jan 29, 2009)

Does anybody have a schematic or something I can look at to give me some idea of what a grid tied solar panel system with a permanently installed genset would look like? Basically what I'm hoping to do is this:

-Solar panels on the roof would supply/supplement power during the day and sell excess power back to the grid. 

-During the night/extended cloudy periods the house would operate on grid power, but hopefully this would mostly consist of using credits built up during sunny periods.

Here's where it gets tricky. The catch with grid tied solar is of course that when the grid power fails, you're still in the dark. This is why we'd like to install a permanent diesel (Lister) genset capable of powering the entire house during outages, and I'd like to it start/shut down automatically. I understand that there are automatic switches that can switch between grid and genset power, but will these work with a solar system? Also, can these switches be operated manually if, say I wanted to run the genset at night rather than take power in from the grid?


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## SolarGary (Sep 8, 2005)

Hi,
Don't really know for sure, but a couple things to bear in mind.

You have to be certain that when the grid is down, that nothing you do can energize the grid. The generator transfer switch takes care of the generator not energizing the grid, but if the generator looks like the grid to the solar grid tie PV, then it will start producing power -- you would have to be certain that this is kept on your side of the transfer switch and does not go out over the grid.

The inverters on grid tie systems check both the grid voltage and frequency. They are required to shut down immediately if either of those go out of a fairly narrow range. So, your generator would have to produce power with both voltage and frequency that is close to what the grid does, or the grid-tie inverter would shut down. 

If the power has failed, and your genset comes on. Then the PV would come back on line if the genset looked like the grid to it. Now if the electrical load in the house is low, is the grid-tie PV system (or generator) going to get upset because the PV system is producing more power than can be used. In the regular grid-tie setup, the grid would absorb whatever of the PV output cannot be used by the house.

Seems a bit iffy to me? Not sure I would risk all this expensive equipment to save manually flipping a few switches?

Gary


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## Jim-mi (May 15, 2002)

Setting up a Lister with electric start . . . . . . . . .
That should be interesting . . . . . . .


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## farminghandyman (Mar 4, 2005)

you would probably be better off to switch off the solar when using the generator, 
but you may want to add some deep cycle batteries and have a way to charge them to provide some minimal power for lighting and some other low use devices, 
off the lister you could hook up a generator to charge the batter that way, (keep the batteries charged via grid when no on generator power), the battery system could be completely DC LED lights and 12 volt, auto type devices (CD player) or what ever, 
make a long night shorter, with some lights and entertainment.


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## TnAndy (Sep 15, 2005)

cbcansurvive said:


> Here's where it gets tricky. The catch with grid tied solar is of course that when the grid power fails, you're still in the dark.



Not if you put in the RIGHT grid tied system for this application. 

Outback GTFX series inverters are grid tie, but when the grid goes down, they have a set of extra contact in them that close, allowing your solar power ( and battery back up at night ) to flow to where ever you want. In my case, it flows to a manual transfer switch, which I flip from "grid" to "solar" and life goes on.

The "best" way to use a generator, IMHO, is to keep a battery bank charged, not to tie it directly to the house. That way, when the bank is full, the generator can stop. Otherwise, you have to run a generator even to pull the smallest load you have....say even a single light.....whereas you could draw off a battery bank perhaps for many hours, even days ( if you design the bank and load correctly ) before you'd even need to fire up a generator.....and THEN you would use it a full capacity until the bank was recharged....and so on....

Besides the obvious savings in fuel, you can get by with a smaller generator this way, since your battery bank will handle your short time peak loads rather than having to size a generator UP to the peak you might have.


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## mightybooboo (Feb 10, 2004)

Agree with Andy,thats the way to go.


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## davel745 (Feb 2, 2009)

To grid tie a panel and or a generator you need a meter that will go both ways LOL not that way. And most importantly is a device that will synchronize the electricity to the line phase. Or things will come to a screeching halt. And the generator will be broken. 

These are the two most important things. The rest is about how much you will feed to the grid.

Best Regards

Dave


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## texican (Oct 4, 2003)

What Andy said.... get a battery backup addition to your system... otherwise you only have a feel good system, that's reliant upon the grid, and how much fuel you can store for your genny. In a prolonged shtf situation, or TEOTWAWKI, you _Will _run out of fuel. At least with a battery system, you'll have some after hours electricity available. Otherwise, you'd only have power available when the sun shines.


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## cbcansurvive (Jan 29, 2009)

This raises a good point about the batteries. What is the average life of a battery? What practices can prolong the lives of batteries? Finally, are they something I can "stock up" on? In other words, could I put some new batteries into storage (under proper conditions-whatever those might be) and put them into service perhaps years down the road when the original batteries fail?


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## TnAndy (Sep 15, 2005)

"Average" life of batteries is a function of the quality of the battery to start with, and then, how the battery is used/abused.

You can ruin a set of batteries in a VERY short time, ( weeks/months even ) or they can last decades.

All batteries are rated for the number of times you use them and how deeply you discharge them. If, for example, you don't discharge them more than 50%, they will often give three times the number of cycles than if you discharge them 80% every time....so "average" is a pretty wide ballpark.

As to setting aside batteries, you'd have to find a seller that will sell you dry ones ( without acid ) and also sell you the acid to fill them. I have a couple set up like that for my tractor.....I find I go thru a battery about every 4 years, so by setting 2 of them aside, dry, and a jug of acid, I figure I will always have at least 8 years worth of tractor starts around.


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