Distance since last post: 75km
Weather: Cloudy, rainy.
Forecast: Bad for the next 3-days. Looks like I’ll have to be careful!
Notes: Crashed into a lamppost while I was trying to mount my bike. No damage. Phew!

View towards Remagen (two bridge towsers can be seen at base of hill) in terrible weather.

No sun, no energy although somehow I’m managing to squeeze enough out of the clouds to charge the phone which is pretty amazing. Luckily I have enough juice on the UMPC battery and the Li-Ion battery to give me about 4 hours of computing. If I spot any sun at all over the next 3 days I’ll have to stop and sap up as much as I can. Its going to be very tight. Will I have enough left for the final report in Duesseldorf?

Right now I’m in Bonn and at home with my wife. I’m only using battery power and won’t be charging anything so there’s no change to the plan. Apart from a long bath and a good sleep tonight ready for the last two legs on Saturday and Sunday.

I know that weather is supposed to be chaos but this is just silly. The most settled weather we’ve had this year was back in April and since then its been a real mess. It doesn’t look like it wants to change much either. The whole of central Europe is stuck in a mess of clouds that does not want to move and bizarrely, Helsinki, the place I’ve just come back from in northern (and generally colder) Europe is expecting a ton of sun!

Getting everything re-organised in another country is not something I really want to do to be honest. There’s a lot of cost and time issues that would make the project too much trouble for me and my sponsor, VIA Technologies so once again, I’m going to wait. The 9-day forecast takes me up to 18th August. After that point I have about 5 more weeks left in the summer before the sun gets too weak.

I don’t really understand why I didn’t try this before. Its simple. its recommended and it works. Have I been too focused on flexibility why simplicity could be the answer?

I was speaking to Chris from Euro-Line, an importer of consumer solar products and he highlighted a document that I’d already seen. I took another look and staring me in the face was a recommended and tested solution using equipment that I already have. Its the same setup that I tested with the P3 panel. Just plug the panel into the Tekkeon MP3400 and wait for enough sun. You might remember back in the early posts that this is how I found out that Li-Ion charging solutions where not so efficient and how it set me on the path to research a more flexible solution.

With the ’12v’ 25w Sunlinq panel I have I assumed that a 12V output wouldn’t drive a 19v input and after looking at the diagram again I though ‘why are they recommending this solution? It shouldn’t work.’

Image taken from GlobalSolar.com PDF here.

Looking more closely at the specs of the panel, its clear now why it works. The 12 panel isn’t strictly 12V. The voltage varies according to the load and in fact with an open circuit the voltage is way up over 20 volts. However, with a load of around 800mA, the charging current for the power bank, the voltage sits nicely at around 20V. Tada!

With a 25W panel, 800ma at 19V is reached at around 60% sun power. On a clear summer day here, the sun is over 60% power for around 5 hours between 11 and 4pm. The charger needs 4 hours to load up 56W of energy.

Now here’s an idea. Between 12 and 2, the panel is producing 40% more energy than the Li-Ion battery is taking. Can I mop that up with a lead-acid battery?

Testing continues…

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?