Off-Grid Mini-Split, no Batteries?

I thought this may have been discussed somewhere before, but I can't seem to find it. Anyone have any experience running a mini-split offgrid without a battery bank? I currently power my cabin 100% with panels/battery bank/inverter. I got ahold of some extra panels and want to install a mini-split at my offgrid vacation cabin for the days that I'm there in the summer when it's really hot. Since those days are only when the sun is shining, I thought it would be easier/cheaper to set it up without a battery bank. I don't want to run it off my existing system, because I would have to upsize my battery bank (and I'd fear that my wife and kids would drain my batteries with the AC on high all day). My thought is to wire the new panel bank in series (up to 300+ volts), and run them straight to a separate grid-tie inverter (which is not wired to any AC input) that would be isolated to run the min-split. When the sun is out, it should power up the inverter (when panel voltage output is >220V) and then run the mini-split. When the sun is not out, the inverter would shut off (as well as the mini-split), but that's fine because I wouldn't need to run the AC when the sun is not out. This would only work if the inverter and mini-split auto turn on when DC power is present (I would want it to be self-sufficient, not requiring a manual "power-on" on the inverter and mini-split each morning when the inverter has DC input). What are your thoughts? Would this work? I'd like to figure out a way to do this without a battery bank (1/2 the cost, and no ongoing battery maintenance/replacement needed).
Comments
BUT... there may be an exception... some SMA grid-tie inverters have a new feature that allows them to make some power when the grid is down. I don't know how suitable that feature will be for a mini-split. Also, it is not an automatic system.
--vtMaps
http://www.solar-electric.com/inverters-controllers-accessories/gridtiesolar/sma-sunnyboy-grid-tie-inverters/sma-sunny-boy-transformerless-inverters/sma-sunny-boy-3000tl-us-22-grid-tie-inverter.html
I do think this idea is ill conceived. It would be better to just use the existing system or make it better. You should be able set the low voltage disconnect on the inverter to protect the batteries from being discharged.
http://members.sti.net/offgridsolar/
E-mail [email protected]
http://www.solairworld.com/100-off-grid
Every time I see s statement like;
I want to buy one, set the battery outside, not connected to anything and send it back after it discharges, saying the sun never recharged it...
Dave, do you see any ill effect on the mini split from cutting the AC power?
--vtMaps
http://members.sti.net/offgridsolar/
E-mail [email protected]
Hi, can you tell us what size mini split you have or are going to get? A 12,000 BTU mini split will require about 1 KW while running, some are inverted so will not use the 10X's that to start but the older models where not. You can install an adjustable time delay relay somewhere in the circuit to prevent short cycling, they come in many voltages and configurations.
Stillchillin
Probably going with the LG 21000 btu model at 22 seer.
Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor
21 SW280 panels on Schletter ground mount
48v Rolls 6CS 27P
SEER is simply a formula that is described by the outcome of the following.
Divide the system's rated Btu's by it's stated SEER rating to determine how many watts it consumes per hour
So, assuming I'm looking at a 21000 btu unit at 22 seer.
21000 / 22 = 954 watts when the compressor is running full blast.
The same 21000 btu unit at 16 seer would use 1312 watts when running at full power.
Keep in mind that this is when your compressor is running at full power and will often be much less.
I believe this only accounts for the energy the compressor unit uses. The inside blowers on a mini split will probably add an additional 40-120 watts depending on fan speed and how many indoor blower boxes you have. In addition I think minisplits have a parasitic load of about 30-40 watts when not running as they "watch" for the remote controller ect.
Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor
21 SW280 panels on Schletter ground mount
48v Rolls 6CS 27P
http://theenergydetective.com/
-Bill