# 12 Volt Solar Air conditionair

I saw a post on YouTube where somebody was able to make ice with a 90 watt solar panel, two 12 volt batteries, an ice maker (800 watt spikes) and 1000 watt DC-AC inverter.

In another post, somebody else uses a 12 volt fan and cooler of ice to make a 12 volt air conditioner that cools a small space nicely for about 4 hours until the ice melts.

Two separate systems, both DIY experiments riddled with apparent inefficiencies I'm sure.

Made me wonder if it might be possible under the footprint of a 90 watt solar panel to silently cool a 10x10 room for 8 hours overnight? Is Ice the most efficient to store cold air? Possible to create cold air more efficiently from stored power? If ice is still the best way, the system would need to reuse the same water and I wonder if a 90 watt solar panel could both charge batteries for the fan and somehow freeze a single block of ice for the system.

• Depends on the insulation of the room. A floor figure for HVAC is that one human produces at least 200 W, so you might keep one person cool with 50 W of power. But the usual figure for a room that size would be a small aircon consuming perhaps 1 or 2 kW. The fans alone will be several hundred watts. So the guy melting a cooler of ice is kidding himself. Aug 9, 2015 at 16:54
• It's called a swamp cooler. Aug 9, 2015 at 17:02
• I'm in South Florida with very high humidity. Aug 9, 2015 at 17:39
• Water has an exceptionally high heat capacity, and also ice has a very high capacity. The transition between ice and water also contains a remarkable amount of energy. So yes, if you need to store heat or cold, water is usually the best choice. Aug 9, 2015 at 17:40
• @tomnexus I cannot find my source now, but I have stuck in mind that 1human=~100W, not 200W. Can you provide a source for that figure? Thanks. Aug 10, 2015 at 13:08

Ice is a great way to store "coolth" (the opposite of warmth) because (1) the phase change from ice to water absorbs a lot of energy per unit volume without changing the temperature, (2) the melting temp of ice (32F) is a pretty good temperature for cooling and dehumidifying air for human comfort, and (3) as ice turns to water, the liquid flows so you can easily keep melting more and more ice by just circulating the water around it.

Here is a product designed to move cooling loads from daytime (when air is hot and electricity is typically more expensive) to night...

http://www.ice-energy.com/

12 volt DC air conditioners are available for use on boats and RVs, although the ones I've seen are expensive and inefficient.

Sharp recently announced that it will be making DC-driven air conditioning units...

http://hardware.slashdot.org/story/15/07/30/0221235/sharp-announces-sales-of-dc-powered-air-conditioner-other-products-to-follow

...so hopefully options will improve soon.

As to weather you would be able to cool your 10x10 room overnight from a 900 watt solar panel, that depends on a lot of factors including the insulation value and the air tightness of the walls, what heat sources are going to be inside the room while you are trying to cool it, and the temperature and humidity of the outside air.

If, for example, you made a 10x10 room located in Seattle out of Vacuum Insulated Panels, and only wanted to keep a single bottle of beer in there, then I think it would definitely be possible. If you are trying to cool a 10x10 stick hut in Mumbai with a family inside, then almost certainly not. In between - maybe... :)

Great question, BTW. I have been working on a project called Bed Box to bring the joy of air conditioned sleeping to the developing world. The Bed Box is basically a semi-insulated tent that you sleep inside and has a hyper-efficient and silent AC unit attached to it. By reducing the load on the system (mostly by reducing the volume to be cooled), it would be possible to operate a system like this on a small 900 watt panel, and by using a phase-changing gel pad inside the BedBox, you could store a lot of "coolth" during the day and then be able to hold much of the cool temp throughout the night.