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Old 01-28-18, 10:34 AM   #1
NeilTheCop
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Default Solar A/C, again

Need a little bit of advice.
I have just ordered my 2nd split system to put in our 400 sq ft living room and would like to run it off solar. I know that itís normally a non starter due to the size and cost of the battery bank, but I want to use a different approach. Here in southern New Mexico we have the maximum 5.5 hours of direct sunlight a day in the summer, seems more but thatís what my calculations are based on. My roof faces due south, is at the perfect angle, about 1000 sq ft and is unobstructed, so I have the potential to fit plenty of panels.
So hereís the plan. The split system is a 17.5 SEER with a digital inverter. The manufacturer says itís a soft start and does not have the normal A/C start up current draw, has no problem with using a modified square wave inverter, and the absolute maximum running power draw will be 1430 watts. I want to run the system directly from the solar panels during the day which will not only cool the room but take heat out of the 1200 cubic feet of concrete the room is built on therefore using it as a thermal storage for the evening. There will also be a manual switch to use grid power if anything goes wrong with the solar set up.
Now the question. I know that I will need to use batteries as a buffer between the panels and inverter, but how much capacity? Every on line calculator assumes battery capacity will be needed at night or when cloudy, but none can calculate as a buffer for running direct from panels. Any input?

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Old 01-28-18, 11:59 AM   #2
NiHaoMike
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Perhaps it would be better to use an evaporative cooler with the motor replaced with a BLDC?
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Old 01-28-18, 04:01 PM   #3
oil pan 4
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Well, there are air conditioning units designed to use direct wired solar panels to help power them.
For use where the power companies are anti grid tie solar.
Typically an inverter drive is going to want to use between 170 and around 330 volts DC. But solar panels put off widely varying voltage and the inverter would have to be designed around this. Normal inverter drives can't handle the wide voltage range put off by panels.
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Old 02-01-18, 11:06 AM   #4
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Quote:
Originally Posted by NiHaoMike View Post
Perhaps it would be better to use an evaporative cooler with the motor replaced with a BLDC?
Thought of that but to use the local water (PPM over 600) in a swamp cooler plugs the pads up within days and to use distilled water would be too expensive.
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Old 02-01-18, 11:07 AM   #5
NeilTheCop
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Quote:
Originally Posted by oil pan 4 View Post
Well, there are air conditioning units designed to use direct wired solar panels to help power them.
For use where the power companies are anti grid tie solar.
Typically an inverter drive is going to want to use between 170 and around 330 volts DC. But solar panels put off widely varying voltage and the inverter would have to be designed around this. Normal inverter drives can't handle the wide voltage range put off by panels.
Thanks for the reply. could you link to a site for the direct driven A/C units please?
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Old 02-01-18, 09:24 PM   #6
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You want to look at the Lennox sunsource A/C units.
I also saw some solar assist mini splits on ebay, but they are expensive.

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