Saturday, November 28, 2015

Solar Skeptic Report

Marcus is a terrible cynic when it comes to the viability of Solar panels vs using electricity delivered from a mains wall socket.  Normally both in terms of cost, and the cost to the environment.

But there are times when Marcus and Agata need a mobile, self contained rechargeable power source and to this end I am testing out the 

5V 7W Foldable Solar Panel

Back to Economics
To remind you of the economics

- Let's assume the panel is not being sold at a loss
- I'm ordering it from China, direct from the manufacturer, so basically at close to cost
- This is a 5V and 7W solar panel
- Cost is 26 USD , lets say 26 CHF
- Cost of electricity in CH for 2016 is about 0.21 CHF per KWh, meaning cost of panel is 26/0.21 = 123.8 KWh = 123,800 W hours
- So assuming unlikely 7W output at all times, that is  123800/ 7 = 17687 hours = 736 days  > 2 years.
- Assuming a very generous 8 hours per day and 50% average sun that is 12 years of continuos operation for payback
- So in reality, that's never going to pay back!!

But Anyway

Let's take the case where I need a mobile power source. Does it actually work?

here is the Unit

Here is a 20,000 mAh batter pack which needs charging

0.483 Amps charging at  about 5V.  So the battery pack would take a staggering 41 hours to charge up continuously!

0.477 Amps charging

Charging the 3000mAh Smartphone battery at 0.477 amps

Charging the Hand Warmer at 0.65 Amps in Brightest Sunlight ever

The Handwarmer has a Lithium Ion batter of Capacity of 2600mAh i.e. 2.6Wh

The charger at best is producing 5V x 0.65 A =  3.25 Watts. So a full charge would take 2.6/3.25 = 50 minutes about.  Not bad.

My phone has about a 3000mAh battery so it would take again just less than an hour to charge, at least in theory.

Actually I have seen 0.65 Ampere sustained but in normal average sunlight it is about 0.45 A to 0.5 Amps.

Theoretically one is supposed to be able to get 1.2 Amps but I only ever saw upto 0.65 Amps.

Practical Considerations
If you use this whilst hiking and attempt to mount it on the back of your backpack/ rucksack bear in mind that the charge will be far from optimal.   You'd be lucky to get an average of 0.3 Amps even in strong sunlight.

In the evening when you finish trekking, you will be stationary but typically the sun will have gone down!

If we can count on 5 hours of charging at 5V and 0.2Amps average current then that is just 5,000mAh per day.   Just enough to keep the phone and say a GPS phone topped up. If you are lucky.

You will never justify these small panels on the basis of electricity payback cost.  But they can make the difference if you are away from a mains electricity source and you want to keep your phone charged so that you can use it for communications and photographs whilst away from mains power.