# solar powered cooling unit

#### Hassan Wahaj Malik

Joined Oct 15, 2017
45
Hi everybody,
I need a little help with choosing the right solar panel to run my miniature cooling unit. The total power required for it would be 74 watts and it's supposed to run for a good 5 hours. so that's around 0.35kWh worth of energy required. any recommendation on which solar panel i should use? also if need to run it on the battery what battery back it up for 5 hours? My size requirement for the solar panel is small as-well I do not need a panel bigger than 3 inches. I have attached the power budget in the thread

thanks!

#### Attachments

• 22.6 KB Views: 15

#### Alec_t

Joined Sep 17, 2013
10,355
As for the battery, your energy demand is 370Wh. For a 12V battery that would require a theoretical capacity of 370/12=~31Ah. In practical terms you would probably need ~50Ah capacity as a minimum. That's going to be quite chunky; for example a mobility scooter battery.

#### oz93666

Joined Sep 7, 2010
668
yes ...I agree with eric ...100W is the minimum size panel you need it delivers an average of about 0.35KwHrs /day

But what will you do for those times when it's cloudy for a week ? very little power coming in so you will need a big battery if it's essential for your cooler to run ....

I would start with a 100W panel and perhaps just a 30Ahr 12 car battery , since you don't need to run the cooler at night I guess.
You can always increase the number of panels or the number of batteries latter ... it's better to have lots of panels then it's possible to have a smaller size battery ,since even on cloudy days , many panels will produce enough .... Panels are cheap and last over 25 years .... batteries need topping up and need replacing often .

#### Hassan Wahaj Malik

Joined Oct 15, 2017
45
so the area I am aiming for it receives around 6 kWh/m^2/day so I want a panel good enough to provide for my cooling unit. the cooling unit is supposed to be a mini portable unit therefore, i am restricted on the panel size. The system can directly run from the panel as it just needs to work when there is sunlight available and for at least 5 hours, I am not counting for cloudy days. It's basically aimed to cool down on a really hot day.

thanks, everybody for the help.

#### ericgibbs

Joined Jan 29, 2010
8,723
hi Hassan,
If you require to have the cooling unit unit working during sunlight hours, you have to calculate for a solar panel rating that is capable of charging the standby batteries as well as powering the cooling unit at the same time.
During the hours of darkness or insufficient sunlight how long do you want to run the cooling unit.?
E

#### Hassan Wahaj Malik

Joined Oct 15, 2017
45
Hi Eric,
So I currently do not want it to work in hours of darkness or even on a cloudy day as I want to minimize the panel size and cost. it's basically supposed to provide a relief in scorching heat.

that is the reason why I am having difficulty in deciding what panel I should use.
what would you recommend keeping in mind the size constraint?

#### ericgibbs

Joined Jan 29, 2010
8,723
hi H,
For your original estimate of 75Watts, the Solar panel size will be at least approx 500mm * 800mm.
Could you test your 3 inch panel, measure the output voltage and current when driving just the fan.?
Update:
I would estimate your 3inch panel will be 5V at ~100mA
E
EDIT:

Watch this video

Last edited:

#### wayneh

Joined Sep 9, 2010
16,102
To be blunt, you cannot do what you want. Either change the goal or accept reality and stop now.

I agree with the other assessments that you need a panel of about 100W rating, give or take. Any such panel will be many times larger than what you’ve stated as your goal, like almost 100X larger. No fudging around will close that gap.

A small panel might be able to power a mister, which can provide a significant cooling effect under dry conditions.

#### Hassan Wahaj Malik

Joined Oct 15, 2017
45
hey, so what I gather from this is that it is almost impossible to use a solar panel that small to power the cooling unit? What size panel would you recommend then?

#### Hassan Wahaj Malik

Joined Oct 15, 2017
45
hi H,
For your original estimate of 75Watts, the Solar panel size will be at least approx 500mm * 800mm.
Could you test your 3 inch panel, measure the output voltage and current when driving just the fan.?
Update:
I would estimate your 3inch panel will be 5V at ~100mA
E
EDIT:

Watch this video

I do now have such a panel the one i had doesn't really fit the criteria. I need 12 volts and 5 amps

#### ericgibbs

Joined Jan 29, 2010
8,723
hi Hassan,
Let us know when you have the Solar panel for the project.
If you do decide to have a rechargeable battery backup, you will also need a control unit.
E

#### Hassan Wahaj Malik

Joined Oct 15, 2017
45
hi Hassan,
Let us know when you have the Solar panel for the project.
If you do decide to have a rechargeable battery backup, you will also need a control unit.
E

Hi Eric,

That’s the thing I do not know what solar panel to buy which would fit the criteria. That’s where I needed your help.
Thanks

#### Hassan Wahaj Malik

Joined Oct 15, 2017
45
The total would be under $400. I have a budget of around$1000. The size constraints are killing me though. I think i might need to change the plan. thanks for the help though.

#### ArakelTheDragon

Joined Nov 18, 2016
1,265
hi Hassan,
A 3 inch square solar panel rated at 75W. ?
You must allow for a bigger area panel, I would suggest at least 100W.
Is it a 12v or 24v system.?

Look thru this link for panel sizing.
https://www.theecoexperts.co.uk/solar-panels/what-size-do-i-need

E
350w/h is not a little. On top of that it depends how much light per day the sun will give. You will need at least a double power battery of 700w/h, in case you have 1 cloudy day and 1 sunny day. If you have 2 clody days,....... The a suggestions up are good.

#### Hassan Wahaj Malik

Joined Oct 15, 2017
45
6 kWh/m^2/day of energy sun gives out in this area.
I am not counting for cloudy days as of now.

#### ArakelTheDragon

Joined Nov 18, 2016
1,265
6 kWh/m^2/day of energy sun gives out in this area.
I am not counting for cloudy days as of now.
The standard method is test for 1 year. What happens if the weather is bad for a week, or the device is used somewhere where there is no sun.