Solar Panel arrived for testing.

Thanks to Select Solar UK I received a 15W P3 Solar panel this morning. As I write, it’s out in the garden with 660W/m2 of sun power beaming down on it! Temp in the shade is about 22 degrees.

P3 Folding Solar Panel

Its smaller and lighter than I expected too.

The first test was to measure the open circuit voltage and at about 450W/m2 sun power (I’m using this web site to give me my sun power reading – its very local to me.) it was over 20V. At 650w/m2, its open circuit voltage is about 28v which is higher than I expected.

I connected a AA battery charger with 2 AA batteries in it and it was charging straight away. With 4 batteries I had to wait until about 10:30. I also tried connecting the TabletKiosk PowerBank but it wouldn’t charge until the sun power reached about 650w/m2. I haven’t connected the Q1 yet because I’m missing a connector for a DC-DC converter I will use for protection.

Look at the graph below. Its the sun power from today and I’ve added some notes to it.

Click to enlarge.
A – 2 AA batteries. B – 4 AA Batteries. C – PowerBank

You can see by the wobbly graph that there’s a few clouds around today. Yesterday was perfect and using that part of the graph I can work out how much time there is for a given level of sun power. The sun is at or above the ‘C’ level for 6 hours a day for example. The area under the curve gives us the power too. I’m not going to get my integration maths book out right now but its fair to say that if the sun peaks at 800w/m2 (80% of Panel power) the average is something like 0.7 (RMS?) of (600+(800-600) for 6 hours. Tap tap tap. That’s 75% of 15W panel power for 6 hours….a possible 67W/hrs of power. (average 11w for 6 hours.)

67W/hrs of power is a full power bank or full Samsung Q1 extended battery which is what I think I need every day to keep me going. I might be able to get that down to 40W by being careful with the UMPC but if there are 2 days of clouds, I’ll be out of power.

This is just a preliminary test. I need to do more double checking on this. And don’t forget, its sunny today. The barometer dropped sharply this morning so tomorrow is going to be very different. It will be interesting to see if I can power anything under cloud cover.The other thing to consider is that I’ll be moving on the bike. There will be shady times! The big question is, do I take a risk and challenge and go with the 15W panel or do I take the next step up and go for a 24 or even 30W panel. Like I said, more testing needed!

I’ve put up a gallery of the P3 panel.

More testing going on today and tomorrow.

Thoughts. Should I take a simple sun meter? How much power will I lose through using a DC-DC converter? Should I buy a small multimeter to take with me?


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  • Terje

    So how many Watts of power does the TabletKiosk PowerBank require before it will begin to charge?

    I think this might be an issue for me, some powerbanks require a minimum amount of power before they will charge, and don’t allow “trickle charging”, I will have to do some more research too…

  • Chippy

    Thats a good question Terje.
    It looks like that with this panel, it needs about 2/3 sun power so about 10W ‘power’ before it kicks in.
    That reduces the amount of time for charging to about 6 hours per day. Within that timeframe you need about 5 hours good sun.

    The same is true of my AA battery charger although it kicks in at about 50% sun power.

    My other worry is floating voltages. I did plug a UMPC direct intot he panel and it started charging (would not run AND charge though.) I’m wondering how much protection there is in the typical UMPC charging circuit.