Running a mini-split HV/AC unit from pv panels

[rich@prg-llc]

Hello,

I have installed 16 panels I have access to, which are generating 210 volts and 1150 watts, according to my meter.

I want to install a mini-split HVAC system to condition a very small shack--about 350 sq. ft. I have found this system: http://heatingandairconditioningdeal...t-heat-pump-ac According to this, my panels will supply this load most of the day (the building is not occupied at night, so the load should only exceed on cloudy days.)

My questions:

1. Is there a way with these systems to have the pv power run it primarily, but have the grid make up when the current is less than the load? It's my understanding they are running on DC which is inverted from the grid AC, so I'd like to just provide the DC first, if at all possible.
2. For permitting reasons, I don't want to hook up to the main panel of the building....just want to connect to a control apparatus--perhaps which is also connected to an AC outlet?-- and the mini-split itself.
3. If this isn't possible because of the way this mini-split is manufactured/set-up, can anyone recommend one that is more friendly to solar?

I would appreciate any advise, or pointing me to good resources, for this.

Thanks!!

[Sunking]

You are going to need batteries, and a lot of them. Smart money is let your neighbors help pay for a grid tied system.

[Amy@altE]

You still need a lot of expensive equipment to make this work. The A/C uses Alternating Current, AC, and the panels are generating Direct Current, DC. You need an inverter to convert the DC to AC. Before that, you need a battery bank to store the DC power you are making. Before that, you need a charge controller to manage storing the power into the batteries.

You can get an off-grid inverter that would use the power from the grid to charge the batteries when solar is not available. This would be 1 directional coming from the grid, you would not sell any extra back into the grid.

I think what you are trying to accomplish is much bigger of a project than you anticipate. Do you know how much power the A/C uses?

[inetdog]

1. Is there a way with these systems to have the pv power run it primarily, but have the grid make up when the current is less than the load? It's my understanding they are running on DC which is inverted from the grid AC, so I'd like to just provide the DC first, if at all possible.

Since the units are UL listed and tested exactly as built, I think the chances of the manufacturer supporting your efforts in any way are so close to zero as to be indistinguishable from it.

Some mini-split and window shaker units are specifically designed for DC input, in which case you could just connect up your AC powered battery charger to kick in when the battery voltage dropped below a preset threshold.
But without batteries the DC would not be stable enough to operate the A/C properly and reliably.

[bcroe]

Hello,

I have installed 16 panels I have access to, which are generating 210 volts and 1150 watts, according to my meter.

I want to install a mini-split HVAC system to condition a very small shack--about 350 sq. ft. I have found this system: http://heatingandairconditioningdeal...t-heat-pump-ac According to this, my panels will supply this load most of the day (the building is not occupied at night, so the load should only exceed on cloudy days.)

My questions:

1. Is there a way with these systems to have the pv power run it primarily, but have the grid make up when the current is less than the load? It's my understanding they are running on DC which is inverted from the grid AC, so I'd like to just provide the DC first, if at all possible.
2. For permitting reasons, I don't want to hook up to the main panel of the building....just want to connect to a control apparatus--perhaps which is also connected to an AC outlet?-- and the mini-split itself.
3. If this isn't possible because of the way this mini-split is manufactured/set-up, can
anyone recommend one that is more friendly to solar?

I would appreciate any advise, or pointing me to good resources, for this. Thanks!!

That is a pretty interesting idea, but the mini-split people won't support it. If you found the
mini-split has a fairly constant DC operating voltage, you could set up your panels to supply
the high range of that voltage. Maybe use a simple regulator to limit voltage when no load
is applied. Feed that into a big filter cap with a diode. Then build an AC to DC supply feeding
through another diode to the same big cap, but at the low end of the operating range. When
the panels couldn't supply enough current, the voltage would sag and the AC would pick up
the difference.

You will of course get no support from the equipment source and void the warranty. A
nice project for someone into building regulated DC power supplies. Bruce Roe

[RedDenver]

You could look at a DC powered heat pump like this one: http://www.hotspotenergy.com/DC-air-conditioner/

But that's a lot of money just to heat/cool a shack.

[inetdog]

You could look at a DC powered heat pump like this one: http://www.hotspotenergy.com/DC-air-conditioner/

But that's a lot of money just to heat/cool a shack.

And you still need batteries and a Charge Controller:

Due to solar voltage fluctuations the unit cannot connect directly to solar
panels and must have a stable source of power such as batteries.

The other thing that they do not mention in the specs is what the starting surges for the compressor and fan motors are. In general even a current limited source like panels that is large enough to provide running current will not be able, unassisted, to start the motors.
The unit may in fact have some soft start capability if it uses a pulse drive DC motor, but the specs do not give us any assurance on that point.

[RedDenver]

And you still need batteries and a Charge Controller:

The other thing that they do not mention in the specs is what the starting surges for the compressor and fan motors are. In general even a current limited source like panels that is large enough to provide running current will not be able, unassisted, to start the motors.
The unit may in fact have some soft start capability if it uses a pulse drive DC motor, but the specs do not give us any assurance on that point.

I assumed they were using VFD for the compressor, which allows soft starting, but they don't actually say that anywhere.

[bcroe]

I assumed they were using VFD for the compressor, which allows
soft starting, but they don't actually say that anywhere.

If you build what I said above, you don't need any batteries. And the AC line will pick up any
part of the starting surge the panels can't supply.

Bruce Roe