The last couple of weeks have seen our renewable energy setup almost completed, as the wind turbine was commissioned, although we quickly realised that we would need some additional capacity to deal with all the power coming in. Our Victron Multiplus 24/3000/50 inverter was frequently overloaded, and the worry was that a strong wind coming after a sunny day (not too unlikely, it happened a week after the turbine went up) could cause mayhem.
The reason? The wind turbine is a grid tied model, designed to be connected directly to the mains grid, which will provide a constant load on the turbine. This is needed to prevent the turbine free-wheeling, which is never a Good Thing. Our Inverter/Charger creates a local micro-grid, which the Aurora 3600 GTI (Grid tied inverter) that is fed by the turbine, is happy to connect to – a process known as AC Coupling. Trouble is, if our batteries are full, there is little power demand, and the wind blows, there is only one way for the power to go – into the batteries. This is potentially a Bad Thing, and they will boil.
So, in these circumstances, the system has to do something with the excess power. In our case, send it to a couple of storage heaters that come on in sequence, as the battery voltage rises. Between them they are enough to soak up all the power the wind turbine can generate if necessary.
This is all pretty cunning. We had to install a second Victron Multiplus to be able to deal with it all, and it works in parallel with the existing one to provide a single 6kva inverter. We have each Multi programmed to switch a relay on and off at given battery voltages, and thus connect and disconnect the storage heaters as needed.
So far it all works well, our Multiplus’s are getting along fine, the batteries are kept well charged, and when the wind blows, we get warm rooms. This will be extended to providing an immersion heater in the hot water tank of the little cottage fairly soon.
We’ve also added an AC current sensor to the output of the Aurora, so that we can measure what is coming out of the wind turbine at any given time, and feed that data to the monitoring software. A couple more panels on the little cottage roof, and I think we will be there. Looking at my picture there’s probably a case for a bit of wire tidying too, and then I can leave it all alone for a while.