Blue Sky Thinking.
Hi All,
Firstly my apologies for my poor writing skills, but here goes…….
As you know I have built and I am running a 6kW to15kW OzInverter, 48vdc to 230vac, 50HZ. This replaces the SMA Sunny Island that I bought which cannot AC couple & DC couple and sends the HZ frequency up to 60HZ.
I have in all honesty thoroughly enjoyed the OzInverter build and the challenge, especially ‘oztules’ great hands on assistance and real life understandable instructions/info.
And yes I am doing another OzInverter, bigger torroid, 230mm OD X 100mm core hole and at 140mm thick and a 75mm/2 Primary.
Background Info, here.
We have a small community of buildings here in Rural Normandy, France. I am doing, (20 year project) 3 Gites, Passive House standards, (holiday cottages), lecture Theatre, pool 12m x 5m etc. We have 3 boys so if all else fails each could have a home to raise their own families if need be.
We are self sufficient but our RE is the Key. Friends Course & Holiday folk, in this unspoilt tranquil valley, still require Electricity, all our heating here is underfloor electric heating.
Having a huge Battery bank, or generators, or having to fit all equipment from a particular expensive manufacturer, is against our philosophy of simplicity, sustainability and cost effectiveness, so we have gone down the route of AC coupling………..
(AC coupling, we create a 230vac 50HZ Mini Grid, all our buildings are connected in. On that grid is Grid tie Inverters that our using PV on roof installations and this feeds into the created mini Grid. This way we can directly use the grid tie generation on our created Mini Grid without the power going in and out of the batteries, and hence saving the battery bank)………..
Our Battery bank is 48vdc 1300ah and we still have 5kW of PV on trackers and 3off 3.7m diameter Hugh Piggott design wind turbines, that direct charge the battery bank with DC controllers such as Midnite Classic 200, Tristar MPPT, and Tristar diversion controllers for the wind turbines.
The Issue.
At present I only have 2.75kW of PV on a separate static array that is AC coupled, its winter here so no real problems with back charging the Mini Grid back through the OzInverter, and yes it can back charge up to 8kw, says ‘oztules’, which is neat.
I use the slight voltage rise on the OzInverter, when it has nowhere to put its excess generation and the batteries are full, to bang off the PV SB3000 grid tie Inverter, GTI. I can alter the voltage settings on the GTI.
Some of my PV installations can be up to 500 meters away from the battery bank, and I did promise Mrs that I will not dig any more trenches, ( I didn’t fit any control cables in the the original trenches, sigh). But in this case I may have to……….
So, it’s a sunny day and I have 8kW of PV coming into the OzInverter, no power being used, so its back feeding about 140a DC at 60volts of raw power back into the batteries. Gulp! Great if the batteries want a Bulk Charge, but what about a float charge?
Basically, I want a Backcharging battery charging regime.
Do I……..
Set the GTI’s to bang off sequentially on the voltage rise?, but its still 60vdc coming into the batteries. Remember that a holiday person could put on an electric kettle and uses a hair drier so the GTI needs to come alive reasonably quickly to take over from the batteries/OzInverter.
No back charging ? or Just Divert/dump excess GTI generation into the pool and Allow the DC charging sources to finish/float the battery?
Use my Midnite classic Aux relay settable control to somehow control the AC backfeeding.?
Use a Zero Export Device, ZED, (Australia seem to be doing these) that allows the Grid to be there but stops backfeeding of GTI’s. But not sure how this works in practice.
Use a radio frequency, fail safe wired, that can switch off a Isolation relay of each GTI that follows the Midnite classic charging parameters. Need some sort of controller and hard wiring.
Any other Suggestions ?
Here is my RE layout.......
