Off-Grid Mini-Split, no Batteries?

mjp24coho

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).

vtmaps

mjp24coho said:

 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.

That will not work.  A grid-tie inverter can only use the solar panels when there is a grid for it to synchronize with.  It is a very important safety feature... if the grid goes down you can't have inverters (or generators or anything else) feeding into it.

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

mjp24coho

I thought the same thing, and then saw the specs on the SMA inverter you mentioned (link below).  It looks like it can power one 1500W circuit without grid input - not sure if that is 110V or 220V.  By automatic system, do you mean that it will not power on (begin inverting) on its own when voltage input is present?

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

vtmaps

mjp24coho said:

By automatic system, do you mean that it will not power on (begin inverting) on its own when voltage input is present?

yes... from what I've read...  I have no hands on experience with them.  --vtMaps

Dave Angelini

The new SMA secure supply is 2KW BTW . I have installed a few now.
 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.

cgserrant

I have been checking these out but not ordered one yet.

http://www.solairworld.com/100-off-grid

Photowhit

cgserrant said:

I have been checking these out but not ordered one yet.

http://www.solairworld.com/100-off-grid

Every time I see s statement like;

• "...battery through out the night, which is charged FREE by the Sun!"

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...

mjp24coho

Thanks all for the feedback

Desert Rat

I just installed a mini split, and I'm planning on installing a relay which will be controlled by the AUX function on my inverter. The relay will cut power to the air conditioner when the batteries reach a preset voltage. This will prevent over-discharge in the event of sudden cloudiness (or forgetfulness).
Dave, do you see any ill effect on the mini split from cutting the AC power?

Desert Rat

I also meant to say that this might be a good solution for mjp24coho.

vtmaps

Desert Rat said:

I just installed a mini split, and I'm planning on installing a relay which will be controlled by the AUX function on my inverter. The relay will cut power to the air conditioner when the batteries reach a preset voltage. This will prevent over-discharge in the event of sudden cloudiness (or forgetfulness).

When the power is shut off, the battery voltage will rebound.  What will the aux function do then?  You probably don't want to be turning the minisplit on and off too frequently.

--vtMaps

Dave Angelini

There are lot's of strategies for doing this correctly, along with the incorrect ones. I think I have done most of them for my clients and they want it done right.

Desert Rat

vtmaps said:

  You probably don't want to be turning the minisplit on and off too frequently.
--vtMaps

Right, I've been thinking about that, and I want to avoid short-cycling. I think it's possible with the right AUX settings. I'm going to be setting this up with my old Trace inverter as well as my girlfriend's Outback, and the two inverters are different in the programming of the AUX functions. I'll post up my results after I have experimented with this.

stillchillin

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

Desert Rat

My mini split is a Pioneer 12,000 BTU inverter air conditioner/heat pump. 115 VAC, 15 SEER. I'll try to get some readings tomorrow with my Kill A Watt meter and post the results.

Desert Rat

OK, I ran the mini split through my Kill A Watt meter today, and here are the results. I turned on the mini split at 10 AM, when the outside temperature was 81 degrees.The compressor came on at around 12:30 PM when the outside temperature was 88 and the inside temperature reached 80. When the compressor first came on the meter showed a draw of ~1000 watts, Each subsequent time the compressor cycled on during the day it showed a draw of ~460 watts. The outside temperature reached 93 at around 1:00 PM, and the afternoon high was 97. At around 6:00 PM the sun was blocked by clouds and my battery voltage dropped to 25 at which point I turned off the mini split. Total usage during the 8 hour run time was 2.59 kWh. The inside temperature in the room with the mini split never exceeded 80. Note that it could have been lower, but that's where I had it set. It may seem odd to some, but after living here for 13 years with no A/C, anything cooler than 80 degrees in the house would have been too cold. So far I'm happy with the new unit. I have no intention of using it after sundown. It cools off drastically here in the desert at that point, and I always open doors and windows at sunset.

WaterWheel

I'm installing a 230v minisplit in the next few weeks.       Is there a Kill A Watt type meter I can wire inline for 230v so I can monitor the mini split's power consumption? 


Probably going with the LG 21000 btu model at 22 seer.

WaterWheel

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.

BB.

There are "whole house" monitors (and branch circuit options too)--Such as this family:

http://theenergydetective.com/

-Bill

Jlasater

The EG4 mini splits seem to work just fine direct off the solar pv with the correct wattage.