Run an air con unit off solar

[driver52]

let's say I have 3 solar panels of 375w each so that's 1125 watts total

Could I run a small air con unit say 500-750watt from them (or can I get one even lower consumption?) to cool a room say 3meters x 4meters and what battery capacity would I need to run it overnight too?

Thanks!

[Crossy]

OK, quick and dirty calculation.

 

I'm going to assume 7500 BTU (750W consumption) inverter aircon (to minimise the size of the solar inverter).

 

That's going to use about 250Wh (0.25kWh) per hour of use, assuming it's correctly sized for the room (10m² ish room a bit more if well insulated). For 24 hours thats 6kWh.

 

Our 345W panels produce on average 1.2kWh per day each so you will need 6 panels to generate your 6kWh.

 

To store that energy you will need 4kWh of battery (if the A/C is running during the day it will use some of the solar directly), at 12V that's 350Ah of usable storage, say 400Ah of LiFePO4 or 700Ah of lead-acid.

 

Since the panels will make rather more energy on good days and a lot less on bad days, unless you have grid power available for backup I'd be looking at a minimum of 50% more battery.

 

Couple up a suitably sized charge controller or two (at 12V you're looking at 172A charge, maybe consider a 24V or 48V system) and a 2kW inverter and you're good to go.

 

You might be able to find a DC aircon (look at the RV world) and lose the inverter.

[driver52]

@Crossythanks for the reply!

so are you saying a 750w air con unit is actually only pulling about 250watts? if so that's ace!!!

SO if I run em direct from panels during the day and only use the batteries at night, I could get away with needing circa 3kWh battery capacity?

Which would be say 6kWh of lead acid but say 4kWh for those new fangled funky batteries cos they can be drained a lot more?

 

[Crossy]

A 7500 BTU A/C will pull around 750W at full chat, but it will throttle to around 30% of that once the room is down to temperature, I'm assuming no penguins or polar bears as pets here.

 

I've already taken account of the A/C using solar directly during the day, that 4kWh is really the MINIMUM capacity, you are going to need a bit more to cover those dull days (of which we have had rather too many recently).

 

The new-fangled funky batteries can be had for very competitive prices if you don't mind recycling EV batteries.

 

I'm assuming an enthusiastic DIYer here of course.

 

 

[connda]

Ice Ice Baby!

[driver52]

1 minute ago, connda said:

Ice Ice Baby!

cool! has it got a block of ice in it? how does it work?

If I do get around to building something out there I don't mind cycling to the local corner shop for a block of ice every day lol BUT are they that readily available?

 

[connda]

4 minutes ago, driver52 said:

cool! has it got a block of ice in it? how does it work?

If I do get around to building something out there I don't mind cycling to the local corner shop for a block of ice every day lol BUT are they that readily available?

 

DYI.  Internet search.  Ice is readily available and inexpensive in Thailand. 

[sucit]

Yes, it would work flawlessly. This is why you see so many solar panels in Thailand. 

[Crossy]

The ice "powered" units certainly work, it's how early aircon worked and what lead to A/C being rated in "tons" (that's tons of ice https://gulfcoastairsystems.com/air-conditioner-capacity-measured-tons/). Obviously you have to pay for the energy to make the ice at some point. They also tend to put moisture into the air unless you keep the ice isolated from the air (put it in a bag), but that will reduce the efficiency.

 

For some perspective, melting 1kg of ice will absorb about 334000 Joules of heat which equates to 316 BTU.

 

When running in a cooled room your 7500 BTU/h A/C will absorb about 2,500 BTU of heat each hour.

 

So to get the equivalent cooling you need to melt about 8kg of ice each hour!