Grid-Tied Hybrid System with Generator

[barnabyrees-jones]

I am designing my first hybrid solar system (in South Africa where their grid often has blackouts) and need some advice.

A grid tied solar hybrid inverter coupled to a 5kW solar PV system (could be bigger) for general energy use, coupled to a Li-ion battery. I have been looking at the LG chem, but open to suggestions based on other peoples advice/experience? Any other brands that are reliable/good value?

First question is, does the solar inverter only output the power from the battery pack during a blackout to the max power output of the battery pack, not the inverters rated power output. For example if I had a 7kW Solar PV system and hybrid inverter connected to a LG Chem 6.4kWh battery pack, would the backup power output be 7kW, or the LG Chem batteries 5kW peak?

I also would like to know what happens during a blackout should it occur during the day time. Does the Hybrid inverter continue to feed loads from the solar array, or just from the batteries, and will the solar continue to charge the batteries when they become depleted even during a grid outage or are they completely redundant?

If I was to integrate a generator into the grid tied hybrid, will that take up any increased peak loads, or again is it throttled by the inverter power? Does the battery charge off the generator, and then the loads run off of the battery, or does the inverter direct the power direct from the generator to the loads. What size generator is recommended? And also what happens if the inverter packs in, is it recommended to run the generator into the hybrid inverter through a manual 3-way switch that can be manually switched to bypass the inverter so that some loads will work? What happens if the generator is overloaded, do things just not turn on, or would the generator switch off?

All help will be greatly appreciated. Any hybrid inverter, battery brands and generator sizing/brands that can be recommended would be greatly appreciated.

Thanks

[inetdog]

The result depends on whether the battery pack has protective circuitry to enforce the output current limit.
if it does not, you will just reduce your battery life a bit and have a less efficient operation because of the internal resistance of the battery pack.
if the battery pack tries to limit the output current by reducing the voltage, the inverter will just try to compensate by drawing more current and the system will crash.
If the battery packs cuts off completely at the current limit, then the inverter will shut down, your loads will lose power and you may have to do a manual reset (and reduce the load) to get started again.

A hybrid inverter with a "generator support" feature (some Xantrex and some Outback models among others) will allow you to run the generator and the inverter at the same time, sharing the high power loads.

[jflorey2]

I also would like to know what happens during a blackout should it occur during the day time. Does the Hybrid inverter continue to feed loads from the solar array, or just from the batteries, and will the solar continue to charge the batteries when they become depleted even during a grid outage or are they completely redundant?

Using the old water-tank analogy, the solar power system keeps trying to "fill the tank" while the inverter keeps emptying it. If you fill it faster than you empty it, you charge the batteries. If you empty faster than you fill, you discharge them.

And also what happens if the inverter packs in, is it recommended to run the generator into the hybrid inverter through a manual 3-way switch that can be manually switched to bypass the inverter so that some loads will work?

Most people recommend having an "essential loads" panel that contains all the loads you want to back up. (i.e. all your loads except the big ones.)

[Graycenphil]

I defer to the solar experts on all the other questions, but I do know about generators. Your first decision is what fuel you want or can use. Is natural gas available? How long will your outages be, and, if extended, what type of fuel will be available? Can you store fuel?

I also don't much about South Africa, but here during natural disasters, gasoline is often hard to get. Diesel is usually easier to come by, and also easier and safer to store. Natural gas is wonderful as long as it keeps flowing, which it usually does. But if it stops, you're pretty much out of luck.

In general, you want the smallest generator that you can live with. Bigger ones cost more, and use more fuel. Fuel is expensive, and may be hard to get depending on the reason for the power outage.