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I’ve been researching solar panels for some time now and really fancy having a go at putting together a system to run my computer setup off of solar power only. But I’ve decided to try walking before running (or maybe I should consider it crawling before even walking?) and just see how easy it is to power my iPhone purely from solar energy.

To power something like an iPhone from solar energy you need at least 2 things:

• A solar panel to convert light into electricity
• A battery to store that electricity until your gadget needs it to charge

The battery is important as we only get a few hours of daylight per day and that’s not necessarily when I want to go outside and charge the phone.

There are a few off the shelf products you can buy to do this, one name that seems to come up quite often is Freeloader.

This £30 gadget is a solar panel and li-ion battery all in one neat little package. The solar panel charges the internal battery, and you plug in your iPhone to charge it from said battery whenever you’re ready. According to the spec the Freeloader has a 1000mAh battery that it can charge from its 120mAh solar panel in as little as 8 hours. This is where I spot a couple of problems…

Problem 1 is that the capacity of the battery in the Freeloader is smaller than the capacity of the battery in the iPhone. The iPhone has a 1400mAh battery but the Freeloader only has a 1000mAh battery. This means that a fully charged Freeloader cannot fully charge your iPhone, simple maths tells us that it can only charge an iPhone to 70% from flat. That’s not bad though if you don’t use more than 70% of your iPhone battery in a day.
Problem 2 is the Freeloaders solar panel takes 8 hours to charge its internal battery. Now, research has shown me that this sort of rating is a best case scenario measured during what is called peak sun hours. So it takes 8 peak sun hours to charge up the Freeloader. Don’t worry about the technical details of what a peak sun hour is, but know this, in the UK, on average we only get 4 peak sun hours per day in the summer and that drops off to just 1 per day in winter. So in the summer it will typically take 2 days to charge up the Freeloader and in winter it will typically take 8 days! and remember that the Freeloader only represents a 70% iPhone charge. 8 days to get 70% worth of an iPhone charge is just not practical…

So the Freeloader is a great product, but it’s just not up to the task of powering my iPhone 365 days a year…

So I’m going to have to come up with a DIY solution…

Most solar panels on the market are 12 volts so I will buy one of those, connect it to a 12 volt battery, and charge the iPhone from the 12 volt battery using a standard iPhone car charger cable.

Sounds straightforward enough.

So how powerful a solar panel do I need and what sort of capacity will the 12 volt battery need to be?

Lets do some maths…

I need to put 1400mAh (1.4Ah) of power into a 5 volt iPhone battery every day.
Solar panels tend to be rated in Watts (which is voltage/current independent) so I need to convert these numbers to Watts.

Watts = Volts x Current

Watts = 5V x 1.4Ah = 7 WattHours

So to fully charge an iPhone from flat I need a solar panel that can generate 7 Watts per hour for 1 hour, 3.5 Watts per hour for 2 hours or 1.75 Watts per hour for 4 hours.

As I mentioned earlier, the wattage rating of solar panels is measured during peak sun hours, of which we in the UK only get 1 on average per day in winter. So according to the calculations above I need a 7 Watt solar panel if I’m to get the charge I need in winter, whereas I could make do with a 1.75 Watt panel in summer as we have 4 peak sun hours…

Solar panels seem to mostly come in 5W or 10W versions and as 5W is too small I need to be looking at a 10W panel. 10W panels seem to go for £40 or more on eBay. Calculations are one thing, but the real world is another so I need to be sure that a 10W panel is actually going to be enough. A 10W panel should generate 10 WattHours every day in winter (remember we get 1 peak sun hour per day on average) which should be more than enough but will it in the real world?

Assuming (for simplicity) that the real world performance of all solar panels is xx% of their rated performance I should be able to test my figures by buying a cheaper, less powerful solar panel and measuring the output. If it generates what is says on the box then great, if it only generates half as much then I’ll need twice as powerful a panel as my calculations said I would.

Maplins had a half price offer on a 2.4w panel, it was marked down to just £12.49 so I bought it.

I will connect it to an old 12volt battery I have lying around and measure how much charge (in WattHours) it generates every day using a special power meter. It should generate 2.4 WattHours per day on average in winter so lets see if it does over the next few days…

Filed under: Gadgets