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Author Topic: AC coupling with a Voltacon inverter  (Read 783 times)
bobbybaz
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« Reply #15 on: October 15, 2020, 12:12:03 PM »

Update after some good generation.

Observations :
We have been able to send up to 25 amps at 240v to the car, so the AC coupling and load sharing sems to work as we hoped. If we couple a full set of panels to the Solis GTI we should be able to provide the full 32 amps that the EVSE car charger can deliver.

In low light levels the GTI does backfeed power to the battery. We see an increase in the amps to the battery when the GTI is generating, but there is no AC load connected. There is no charge regulation, so we only allow that when the light is very minimal.

In full sun on all the PV, the power to the car is increased to the max available. The GTI making 1200 watts, and the main array making 4.5 Kw. When the sun goes in there is a brief time before the power demand to the car decreases to match the available power. The system draws from the 48v battery, but it only takes a second or two so the battery can cope. (200 Ah at 48 volts.) I have yet to discover if the car is OK with these variations in power, but it seems to be happy to adjust the charge rate.

When the car is full or not connected, the only load available is 4.4 Kw immersion heater. In full sun there is not enough load to absorb all the available PV power. In that situation, as predicted, the AC bus voltage was pushed up, and the Conversol flagged an alarm. We now have a relay in place to disconnest the GTI when that happens. The Conversol was not apparently damaged, and returned to normal operation.

I was interested in the comment about MPPT charge regulator compared with PWM.  I can see the logic of connecting panels direct and using a dump load controller to regulate over charging. My understanding of the benefit of MPPT is that we get some charging in low light level, when the PV volts are lower. Until the PV volts are higher than battery volts, no charging will happen.  Series connection results in higher volts, so you get some useful output. Trade off being the higher self consumption of the MPPT controllers. Are MPPT controllers really very inefficient ?
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4 kw PV. on FIT scheme from 2010.
EV charging : 5 Kw PV on car port, with Conversol inverter, not grid connected. 
3 Kw additional PV with Solis Grid Tie inverter AC coupled to Conversol inverter for additional EV charge power. 
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Ecotech pellet range.
camillitech
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« Reply #16 on: October 15, 2020, 12:37:38 PM »

Nice one BB, you could use a PWM controller or two in 'diversion mode' to take of your batteries. Never been a fan of MPPT charge controllers myself but they do seem to have improved reliability no end in the last few years. With PV being so cheap these days I would just buy more panels if you have the roof space nearby.

Cheers, P
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'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SMA SI6.OH, 800ah Rolls, 9kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
bobbybaz
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« Reply #17 on: October 15, 2020, 01:00:14 PM »

PS. I will post some pics and a description of the whole setup when we have finished playing with it. Happy to share the Arduino code if anyone is interested. It is getting quite involved because it has to take into account if the car is connected and charging, and has two control programs, one for the car and one for the immersion. Now we are adding a short one to limit the GTI power. My original plan was to investigate what you could do for EV charging fully off grid. My conclusion is that you need at least 8 Kw of PV to enable charging in poor light, and ideally about 10 Kw. As a person who has spent up to 3k a year on diesel, the effort seems worthwhile. Of course the car has to be on the car charger in the day, so wouldn't work for many people.
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4 kw PV. on FIT scheme from 2010.
EV charging : 5 Kw PV on car port, with Conversol inverter, not grid connected. 
3 Kw additional PV with Solis Grid Tie inverter AC coupled to Conversol inverter for additional EV charge power. 
Okofen pellet boiler.
Ecotech pellet range.
bobbybaz
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« Reply #18 on: October 27, 2020, 12:14:08 PM »

We put a voltage control in the Arduino to cut the 240 supply to the GTI when the voltage exceeds limits. The Conversol specifications give quite wide range for overvolts. Initially we put the limit 2 volts above the set point, but we found that tripped under normal operating conditions. We now have that set to 247 volts, with the operating voltage at 240.  We have 4.4 Kw of immersion heaters as a dump load, but the total PV input can exceed that in optimum conditions. Not seeing any over volts conditions since. System is working quite well, but of course we need to observe under a whole range of conditions to see if we are getting the best out of it. Recently the skies have been so grey there has been very little to get excited about. We realise that to charge the car from an overcast sky we need about 14 Kw of PV.
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4 kw PV. on FIT scheme from 2010.
EV charging : 5 Kw PV on car port, with Conversol inverter, not grid connected. 
3 Kw additional PV with Solis Grid Tie inverter AC coupled to Conversol inverter for additional EV charge power. 
Okofen pellet boiler.
Ecotech pellet range.
Iain
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« Reply #19 on: October 27, 2020, 04:41:00 PM »

Hi

Quote
We put a voltage control in the Arduino to cut the 240 supply to the GTI when the voltage exceeds limits.

Could you alter the settings in the GTI to do the same? ie set the max AC volts

Not sure if it would just stop producing at that voltage or if it would bring up a fault and trip? Just a thought

Iain
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