Direct drive shed ventilation (not strictly dust but uses the sort of the same kit)

Guys,

I’m upgrading my house solar. This leaves me with a perfectly fine, but older system that is to be junked by the new installers.

I’m told they don’t have to junk it if I (my sparky technically) disconnects it from the grid. This can be as simple as have the sparky unwire it from the board and sign it decommissioned or similar so the grid supply guys don’t get the grumps. It’s never to be grid connected again as it’s older SMA inverter doesn’t meet the newer standards.

So to continue it’s useful life for a decade or two more I’m hoping I can use the power to force vent my shed with a fan using free power when the sun is out.

Does anyone now of a fan type that moves lots of volume but doesn’t need large inrush currents to start up? I could simply hard wire this to the inverter (well my sparky could) and I’d hope the fan might come on when there’s enough sun, and this would cool the shed a little.

Power supply specs would be:
240 volt,
500 watt reliable power for the next decade at least. Peaks at 900w now at mid day. Browns our to nil at dark.


Alternately I could run a fountain pump in a pond or something, but I don’t know of any pumps that have low enough startup currents at 240v that aren’t crazy expensive.. (not sure if a 12v pump with a transformer down from 240v would work)

Thoughts?

I'm not sure if this feasible but what DC volts does each panel output, You may be able to reconfigure their connections so as to completely by pass the inverter and use a DC motor driven a fan(s). Then starting currents won't matter as fan speed will just vary with the DC V.

Strongly recommend getting sparky advice on this - High DC voltages are deadly.

I'm not sure what you can find in Australia but here the fans used for HVAC are often speed controlled. A fan has a nonlinear load curve and a motor designed for it can have it's speed controlled with different winding taps or even different voltages. The motor operates as a torque device rather than a speed device. The motor is sort of operating in start up mode all of the time. This kind of motor doesn't have the huge start current of the induction motors you are probably familiar with.

If you can scrounge around for such a blower (here they are usually three speed) check it's start current, it may be low enough for your inverter.

You have two problems that I can see.

The first is that for the inverter to work it requires a 240v supply to deliver an output. So unless you connect it to the grid it wont work.

The second is that when the sun is at partial or reduced brightness the output of the inverter may not be sufficient the actually start the fan spinning and it may burn out the motor (the spinning fan cools the motor).

Your only realistic solution is to get an off grid inverter and a battery and then run the fan off the battery storage (not cheap).

Another solution would be to see if you can get a 12v battery charger and battery to suit your panels and then use a DC fan, like a car radiator cooling fan.

Great advice all.
The lack of grid voltage crippling the inverter is something I knew about but had just not thought about. . It’s a bummer. So the inverter is scrap.


I think converting to a low voltage system with tiny battery system might be best. (The panels are 48v open circuit) It’s just going to need a huge mppt controller though.. there’s 1000w of panels.

I’ve used one to run a little system opening my chook shed doors, but don’t really need 6 more automated chooksheds!