Help with inverter setup

Cobra_Phil

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Aug 17, 2019
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I work on a small college campus in Papua New Guineawhere a solar system will be installed. The grid tied system is small enough that it will never supply all the power needed to cover the power demands of the campus, probably in the 10-12kw range,but it will help with the electric bill. We will also be installing a li-ion battery system, possibly in the 10kWh range. What we would like to do is during the day, power generated from the panels will be tied to the grid to lower the power bill and charge the battery, but at night power inverted from the batteries only go to a certain location, like the computer lab and security lights, not the whole campus because the battery would be discharged in a matter of a couple of hours. The only way I can think that this will work is by having two inverters. One connected to the PV array, grid, and batteryto charge it and then another inverter connected to the battery with the AC output going to computer lab and security lights. But this means that during the day the lab and lights can still only receive power from the battery which may be ok, I just don't know. Can someone shed some light if this is possible or if there is a correct way of doing it.

Thanks.
 
Hybrid system wheres the Gear you want from battery is hooked to load out. As you where thinking.
Depending on manufacturer its One, 2 or even 3 units.

Depends on what you can get hold of in your area
 
I guess my biggest question is can it be done with 1 inverter. I've looked at the MPP Hybrids but can't figure out if it will work in my scenario by itself. I can get any inverter I want, I just have to pay for shipping and wait forever. For a 1-inverter setup, itseems like I would need an inverter with an auxiliary output, if that exists.
 
You'll need more PV, preferably DC coupled (directly charging the battery) - your existing grid tied installation can remain as is.

https://www.victronenergy.com/live/ess:design-installation-manual


image_qjdmef.jpg
 
This may seem a little too simple, but instead of buying another inverter, what about using a couple appropriately rated SSR's controlled by a Raspberry pi or arduino? At 4pm everyday I disconnect the A/C output from inverter from the grid but leave it connected to the security lights and lab. At 9am everyday I connect the inverter back to the grid. That way during the day the lab is still being powered by either the PV array or the grid, and the battery is getting charged. And at night the lab and lights are being powered by the battery. In this scenario, I think I would still have to use a hybrid inverter so that the battery side will work without the grid being connected. Any issues you see with this setup. Unless I am missing something, it would be a 1 inverter solution for very little extra money.
 
Cobra_Phil said:
The grid tied system is small enough that it will never supply all the power needed to cover the power demands of the campus, probably in the 10-12kw range ....

assuming you mean 12kWh ?

It would appear that your existing PV isnt generating enough surplus, over and above what the campus is using instantaneously such that the surplus can be used to charge a battery ?

How/when will the battery be charged ?
 
The battery will have higher priority than the grid and get charged first in the morning.
 
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