Radian and AC coupling in non Grid Tie mode

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Radian and AC coupling in non Grid Tie mode

Postby Beechigby on Sat Oct 28, 2017 11:45 am

im going to use a 8 Kw Radian 240Vac 60Hz and AC couple a SkyStream 3.7 (1800watts?)
I am tryuing to get a handle on the varius choices for preventing overcharge to the batteries.
one way, (correct me if Im wrong) is to use a Diversion Load Control (a C40 would work) to send the power to a dump load, like a 48 volt water heater element.
what other diversion loads are there to be had? Space heaters? light bulbs? whos sells this stuff?
Where can I buy a solid state relay of 48 Vdc to use on a FM 80 control's AUX channel? (I assume that I can still use the FM 80 as a charge control for PV panels?
Would you say its true that the SSR that MidNite uses a 24VDC Triac? relay to open a PV/GridTie AC circuit and stop the Power output of the grid tie inverter?
I want to stick with my 48Vdc battery
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Re: Radian and AC coupling in non Grid Tie mode

Postby Farlander on Thu Nov 02, 2017 6:34 pm

Hire a pro
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Re: Radian and AC coupling in non Grid Tie mode

Postby pss on Sat Nov 04, 2017 9:25 am

Let me ask some questions please?
Are you saying you are going to use a Radian inverter and a second Skystream inverter in your system. I am assuming that both inverters have the capability to charge batteries from an AC source. You produce solar power via an FM80 into the battery bank. Both the Radian inverter, and the Skystream inverter derives their power, from this one battery bank. You would only need to charge the batteries when solar is not available. The FM80 would be in sleep mode. A Mate3 connected to your Radian inverter would allow you to easily program the charger of the Radian inverter as well as set the time of use of the inverter's charger. Power would be drawn from the grid or generator in this case. The Radian inverter can provide close to 10 kWh of power into a battery bank. So for example, if your battery bank is 48V and 1000 amps, and you discharge 40% overnight, that means you need to replace 400 amps at 48V = 19200 watts. Add 10% to this for battery loss and you are at 21,210 watts. The Radian inverter could replace this in 2-3 hours with it's onboard charger. There would be no reason to use your other inverter to do any charging at all. And you can set the time and parameters when you want the Radian inverter's charge to start charging.

In my case, I have my Radian inverter programmed to go into "support" mode at 1800 hours until 0100 hours. So 7 hours total. The rest of the time, it is in "gridzero" mode. During the gridzero time, the batteries are charged by available solar, and during the time in support mode, the batteries are charged from the grid via the inverter's charger. Sometimes my batteries need a 10% charge, other times a 40% charge if very cloudy for a couple of days. Batteries supply all loads from 1 AM until solar charging kicks in in the morning.

Using the Mate 3, you program the parameters of the battery bank into the system, same as for an FM80 and this prevents the batteries from overcharging via a three stage software program. If you also install a Flexnet DC monitor, you can then see the "state of charge" and battery voltages online.

I hope this helps you to find a solution to your question that was posted.
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Re: Radian and AC coupling in non Grid Tie mode

Postby Beechigby on Thu Nov 09, 2017 8:01 pm

the skystream 1800 watt is a gridtie inverter only. It needs a sine wave (like the grid or the radian) to connect to, like any grid tie inverter needs. This is to be an AC coupled system. the problem with AC coupled systems is controlleing the output to the batteries fromt the gird tie source (wind or solar) thru the Radian that is charging the bats when the house loads are not using all the power. I know of one way to dump the load and keep the bats from beeing overcharged. I am wondering what the other options are.
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Re: Radian and AC coupling in non Grid Tie mode

Postby Farlander on Thu Nov 09, 2017 8:58 pm

Other options are frequency shift (the master battery inverter adjusts the AC output frequency far enough away from 60hz that the GT inverter does not like it and turns off)
Remote operated circuit breaker. ROCB (outback makes it)
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Re: Radian and AC coupling in non Grid Tie mode

Postby Mike Curran on Thu Nov 09, 2017 9:17 pm

You could run the Radian in mini-grid mode. From the manual:

"Mini Grid
The Radian inverter can be programmed to automatically reject an AC source and run solely from battery (and renewable) energy. In Mini Grid mode, the inverter only connects to the AC source (usually the utility grid - in your case would be your Skystream) when the batteries run too low. In this mode, the Radian inverter runs on battery-supplied power for as long as the batteries can be sustained. It is expected that the batteries will also be charged from renewable sources such as PV. When the batteries become depleted, the system reconnects to the utility grid (Skystream) to operate the loads."

On the downside this means whenever your battery is full your wind genny might be spinning but no energy harvest from it.

I'm no expert, just my 2 cents' worth.

Edit: On second thought, this probably won't work because your Skystream will never detect voltage on the grid side of your Radian (assuming you're off grid).
Last edited by Mike Curran on Fri Nov 10, 2017 5:57 am, edited 1 time in total.
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Re: Radian and AC coupling in non Grid Tie mode

Postby Farlander on Thu Nov 09, 2017 11:20 pm

In AC coupled mode can't you control the max charge rate to the batteries by adjusting the radian max charge rate setting? Or will it try to invert all the PV power into the battery bank? I guess it has no where else to go, and if there's no load present to simulate the vastness of the grid, the battery inverter has no choice but to invert all the power to the batts, or the PV system will power down.
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Re: Radian and AC coupling in non Grid Tie mode

Postby Farlander on Fri Nov 10, 2017 8:53 am

Just got off the phone with Outback, the AC coupled solution for radians is no longer being supported. Main issues were installers sizing systems incorrectly, reliability issues the ROCB, and poor charging performance due to lack of sophistication in the aux relays ability to control the ac-coupled inverter's output. Basically you can only charge up to the float voltage, than the PV system would turn off, likely not providing a sufficient charge.
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