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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Re: Radian and AC coupling in non Grid Tie mode

Postby Beechigby on Sat Dec 30, 2017 6:43 pm

sorry its takken so long to respond. Hurricanes have really screwed up my broadband
Will the 8 Kw Radian at least perform a frequency shift to drive the 1800 watt Skystream windmill offline?
As is the case in all AC coupled systems I know off, the GT inverter output connects to the Bat based (Radian) inverters output, so the Radian uses the "extra" energy not used by the loads to go backwards and send power to the batteries (8 Concorde 8D AGM, 4 series, 2 parallel, 516Amphr total , and yes the parallel cables are exactly the same length). Where can I get a 48Vdc relay that will cut the 1800 watt Skystream out?
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Re: Radian and AC coupling in non Grid Tie mode

Postby EMCF on Sun Dec 31, 2017 12:30 am

As in the previous comment, I think Outback is quietly staying away from AC coupling, as evidenced by non-availability of parts like ROCB.
Anyways, who needs an AC coupled system when OB inverters like the Radians and FXRs are already fully interactive? Being battery based inverters, as contrast to battery less grid-tie inverters, Outback inverters can function with or without the presence of grid. The battery less grid tie inverters, together with the solar panels serve as dead weights with the loss of grid power, even on daylight with plenty of sun.
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Re: Radian and AC coupling in non Grid Tie mode

Postby Beechigby on Sun Dec 31, 2017 5:16 am

Yes, all true. and exactly why working out the details for AC coupling is important. Here especialy, we have theese events that destroy power for months. and people that have the useless grid tie solar systems want batteries and inverters for power, as generators are giveing people generatoridis. the Magnum solution seems to work well enough with there frequency dithering, and I hope I am correct in believing the Radian will also change the frequency to knock the Grid Tie inverter off lineThe advantage the Radian has over the Mannum is people can use the abilty of the Radian to parallel the grid (not selling) to reduce power consumption from the grid by using the avail;able solar not beiing used to charge bats to power the home (Grid Zero)
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Re: Radian and AC coupling in non Grid Tie mode

Postby EMCF on Sun Dec 31, 2017 2:55 pm

in my sometimes fallible world view, AC coupling Outback style was just the company's solution/concession/workaround with the customers who had invested initially in battery less grid tie inverters, then made the decision to acquire a Radian inverter. In order to not totally "retire" the non-outback grid-tie inverters, they offered this AC coupling solution to have the merging of this non-Outback grid-tie inverter and a Radian inverter.
But, the thing is, the fully interactive Radian can function with or without the aid of grid power, or a third party grid-tie inverter.
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Re: Radian and AC coupling in non Grid Tie mode

Postby Beechigby on Mon Jan 01, 2018 8:04 am

In my REAL world situation, I have an 8 Kw Radian arrived here for a client who has a 518Ahr Concorde AGM battery, 3060 watt solar array, and a Skystream 1800watt GT windmill, (that I did not install), and they are not grid Tied to the utility. they do have a GVFX3648 on a power panel that I did install, along with the bats and solar. They want to run more of the house, and they want to be able to include the power from the windmill. I sold them the Radian. Now I need some assitance controlling the power flowing backward thru the Radian to the Inverter Subpanel loads, (which will soon be cha nged to 240Vac) and the Batteries.
I only have a small water heater available to convert to DC. It may not be enough. i guess (I wish I was wrong) the Radian does not "dither" the 60 cycle frequency to knock the Skystream 240Vac GT windmill off line. I need to find and buy a soliution. (ROCB?) can and will you porvide any ideas or sources. I have been to Carling website, but I geuss I still need a relay?
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Re: Radian and AC coupling in non Grid Tie mode

Postby Kurt Lundquist on Tue Jan 02, 2018 1:56 pm

I wonder why components designed for on grid use have been installed for an off grid application but I'll leave that question in my pocket for now. Off Grid AC coupling will certainly lead to power quality issues such as flickering lights. You should verify your customers are okay with this before proceeding. If they are not down with the power quality issues you could still AC couple the turbine but use the GVFX (or another 48V FX) as a dedicated rectifier for the wind output (nothing connected to GVFX output other than Skystream). Either way I'd look to install both a diversion circuit and a disconnect relay. The diversion circuit would have lower DC voltage set points while the relay should be at a slightly higher battery voltage. If the diversion circuit fails you still have a backup method to cut off the turbine to protect the batteries. For diversion I'd go for a solid state relay with a 12Vdc coil rated at <300mA, and contacts rated at 60Vdc+ and 50A minimum. Make sure to get a big heat sink for the relay. For the disconnect relay you could use a standard mechanical relay such as the OutBack OBR-16-DIN. At this time the Radian does not dither the frequency to kick the AC coupled inverter offline.

Here are a few resources:

http://solarhomestead.com/charge-batteries-with-skystream/

http://solarhomestead.com/skystream-auto-disconnect/

http://solarhomestead.com/diversion-load-for-skystream/

Also this article covers the considerations for using AC rated heating elements with DC instead of AC. Since you need >1800W of diversion it may be cheaper/easier to just by a DC rated element (search online for 48V 2000W water heater element).

http://solarhomestead.com/ac-elements-as-dump-loads/
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