Last Thursday I spent a lot of time analyzing exactly how efficient my charging solution was with a real-life test. What dropped out was a rather poor picture of how inefficient the whole solar charging setup was. From over 1.2KW hitting the area of my solar panel I managed to use about 19W. That’s a 1.5% efficiency rate and its amazing that I was able to do anything with it!

Take a look at the diagram again below. it shows the loss-points along the route from the sun to the UMPC.

More efficient UMPCs?

Of course! Any improvement in efficiency here would help. Currently a good average is around 9W and if this could be reduced to 6W average, it would be a major improvement.

Bigger battery life?

No. For my tour, the battery life or battery capacity was really not an issue. 50W/hr per day total capacity (via two battery packs; one that can be used and one that can be charged, is ideal.)

Solar Panel improvements.

From 1.2KW that hit the panel, only 660W hits the solar cells and those cells are only around 8% efficient and this is the first place we can look for improvements.

Current top-end production solar panels are 22% efficient but these are hard panels. To get the equivalent of 25W power you would need a hard panel of about 35x35cm plus frame. Lets say 40cmx40cm in total area. By using a hard panel of this size I could have actually put one on the front and one on the back of the bike to achieve a much more powerful solution. Finding a 40x40cm high efficiency panel might have been difficult though and probably less rugged. There could be a weight consideration too. Given the space restrictions on a bike, I think that a hard panel solution might have been better. In the campsite it wouldn’t have made much difference. The foldable panel was light and small and there should be no need for more than 25W of max power.

Battery tech and charging methods.

There’s a lot that needs to be improved here and the improvements can be achieved through a combination of process and of technology. What follows are the most important issues.

Lead-acid out!

The lead-acid battery proved to be a hindrance more than a help. It was heavy. It had no charge level indication and at low charge levels it couldn’t deliver enough current to drive my DC DC converter or even charge the AA batteries. In short, I didn’t use it much at all and I would drop it from my kit list if I did it again.

Li-Ion problems.

I knew that charging a battery just to have it charge another battery would be inefficient but I didn’t realize that it could be so bad. For example, the Li-Ion battery pack I have (Tekkeon/Tablet Kiosk MP3400) appears to lose about 25% energy through the input and Li-Ion charging stage. That is, you have to pump something like 20% more energy into it than it can store. But that’s not the whole story. The voltage conversion process on the output stage kills another 20% of the energy! From input to output you’re losing a shocking 40% or more energy!

But there’s another problem too and i’ve mentioned it before. The charging of Li-Ion batteries occurs at a fixed rate which means however much energy you have available and however quickly you could feed it into a Li-Ion battery, it won’t take it any quicker than its designed for. The MP3400 takes about 15W (about 0.8A at 19V) of energy to charge it and even if I attached a panel capable of delivering 50W, it would still only take 15W wasting a huge amount of available energy.

This last problem is the one that needs attention when designing a solar charging solution. I have detailed some possible solutions at the end of this article.

Direct charging UMPCs from solar.

One thing that I found annoying was that the only was I could charge my UMPC battery safely was to charge it from the Li-Ion battery. Obviously this is inefficient for the reasons mentioned above but why can’t I charge the UMPC direct from the solar panel? The main problem is that the DC input circuitry on the UMPC is an unknown factor. There’s no way to tell if there is over-voltage protection or whether it will charge a through varying input voltages and its just too much of a risk to try it out. When the DC input on the UMPC is broken, so is the UMPC! I also though about trying to charge the UMPC battery on its own but there’s no standard in connectors or charging currents and voltages so unless you want to build your own charging circuit, this isn’t possible (with the one exception of the OQO Model 02 that has an external battery charger.) I don’t really see this changing much on UMPCs in the near future though. There’s no real reason to increase the complexity of the DC circuit just because Chippy and a few others wish to use solar panels!!

How to improve the solar charging process today…

The Sunlinq 25w panel and Tekkeon MP2400 battery pack is an easy option, readily available and relatively cheap. It works, and if you use the tips above, it can be quite succesful but there are further improvements that could be made, especially if you have the time a flexibility to adjust your solution as you go. Lets assume the lead-acid battery option is too heavy and will not be used.

Ideally you will have the flexibility to add load and add solar capacity as conditions vary. This requires multiple smaller solar panels and multiple smaller Li-Ion batteries that can be set up in different situations. This is currently the only way to provide the most efficient charging solution. Buy multiple slow-charging (500mA for example) Li-Ion battery packs that can be stacked in parallel as energy availability increases.  You will need a voltage regulator on the output of the solar panel and this will need to match the input voltage of your charging solution. Preferably 12V. Fit an ammeter and voltmeter to the output of the voltage regulator so that you can monitor load and voltage. This all takes a lot of time and effort though and for most people its not worth the trouble. Ideally you would have a smart charger that does the monitoring and switches in Li-Ion packs as current availability increases. I have not seen such a solution yet and this, along with some more advanced solutions is what I’d like to see in the near future.

…and in the future.

How about a Li-Ion battery pack that has three levels of charging speed. Low, Med and High. These can be manually adjusted to match the energy available. Ultimately you would have a Li-Ion battery pack that self adjusts to the input current available. I have seen a few advanced components that claim to be able to do this but have never seen a consumer product that is able to do it. If you can get vari-charging Li-Ion batteries then there is really no need for the heavy lead-acid battery at all.

Finally, I’d like to see more UMPCs that have an external battery charger with good, efficient circuitry, over voltage protection and a wide range DC input voltage. Currently there are very few options here.

I’ll be watching this space carefully from now on and I hope that it won’t be long before I can report about new solutions to the issues of solar power and battery charging.

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.

When I did my first tests and calculations about the use of solar power to drive a PC I was quite amazed at the inefficiency of the process and today’s ‘laboratory conditions’ test proves just how much room for improvement there is. It’s thanks to devices like UMPCs that this is project is at all possible because I really doubt it would have worked with even a ‘power saving’ notebook PC.

Today I stayed at the campsite and put the Solar panel and Li-Ion battery through a 3 hours test. Its was a cloudless day with a very thin haze, 22 degrees centigrade and for reference I’m located at about 50 degrees north and 7 degrees east. The date is the 30th of August which is heading towards Autumn here in Germany. The test was done from 11:00 – 14:00 and I took the empty Li-Ion battery and charged it with the solar panel for 3 hours.

I estimate that about 1.2KW of energy hit my 7000 cm2 panel with about 660W falling on the Solar cells (3500 cm2). After conversion to electricity it created about 50w/hr of energy. Of that, about 40W was taken by the Li-Ion battery because it only uses a fixed current and voltage. It won’t adapt to the power available. Due to input voltage conversions and charging losses, this left me with an estimated 30W of energy and after taking this through yet another set of voltage conversions and charging process, left me with a rather poor 18W of power. Of course this is enough for a few hours of work but isn’t it incredible that so much power is wasted (or rather passed back as heat!)

I spent the rest of the afternoon trying to work out how this process could be improved and I’ve come up with a list of ideas that could help. I’ll talk though them in the next post but right now I need to put some more cream on the back of my legs because through all the concentration I forgot about the sun and I’ve burned the bit right behind the knee. That’s going to be really enjoyable tomorrow when I make the 70km dash to Bonn.

Here’s a diagram I created quickly on the Q1b. Hopefuly it makes things a bit clearer. How would you improve the architechture?

Distance since last post: 15km
Weather: Clouds thinning
Notes: I don’t have much faith in the lead-acid battery. The Li-Ion battery seems to be charging much more reliably.

Another day completed and I feel like I’m getting into a better rhythm. Checking emails and RSS on the mobile phone and creating rich journal updates with the Q1b. I only wish I had a  mind recorder because I’m thinking of some great ideas while I cycle but forgetting them when I get to a point where I could write them down!

The bike, which I’ve decided to call Berta (the Blue Bakers Bike) is performing fantastically well. I was a bit worried about having no gears but the fixed gear ratio is perfect for around 22km/h which, with 65KG of pack on a 25KG bike is just perfect. The thick tyres help to soak up bumps and now that I’ve pumped up the pressure a bit more, seem to roll without too much resistance. I even clocked 34kn/h on a straight today . Wohoo! Berta is Berta

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Distance since last post: 40km
Weather: Mixed, cloudy. Hazy. Warm 20-22 degrees
Notes: Feeling really good. No aches. Pushing harder today. Cant stop eating sultanas! The hills on each side of the Rhein are getting bigger!

Winter is coming…If you take notice of the geese that is. I saw a flock flying south (following the River perhaps) this morning and wondered if they knew something that I didn’t. Its was lovely and warm yesterday and its pretty much the same today. Is there some nasty weather around the corner or did they get an SMS from some Geese mates in Africa telling them to come early?

Although its been warm its been very cloudy today. Much cloudier than yesterday and yet I still managed to get some charge into the Li-Ion battery and (I think) something into the lead-acid battery. Despite that though I’m using my spare battery and thinking carefully how to use the UMPC more efficiently. Daytime use (like now!) is not the best as the backlight needs to be turned right up. That’s draining an extra 2 watts compared to evening use when I can drop the backlight to minimum.

I felt very strong this morning and powered the 85KG bike/baggage combo through to Mainz in much less time than I had planned. It was really enjoyable. While the clouds where thick I kept on cycling and ended up in Eltville where the was a lovely Rhein terrace restaurant serving Spargel Suppe (Asparagus Soup.) I stayed for an hour while the solar panel and bike rested by a tree and then layed myself down on a bench for an after-lunch nap. After buying, writing and sending a few postcards I carried on the journey. The Rhein-side path was pretty bumpy and at every chance I tried to find another route but this was really the only sensible offering, the other being a trek up to the hills! Then, after about ten minutes I heard a crash behind me and stopped as quickly as I could. I looked back to see the battery packs and cables strewn across the path along with the shattered container. Shit! I gathered it all together, repacked it and then checked everything out.I think I’ve been lucky. Everything seems to be working still so I think it was just a warning from above to tell me not to take afternoon naps!  

Only about 20km to go until the campsite and having looked closely at my plan, it appears that I’m ahead in terms of distance but behind in terms of energy capture. I need to take longer breaks. But no afternoon naps!!

Location: Oppenheim
Distance since last post: 68Km
Weather: Hot with 50% cloud cover
Forecast: Heavier cloud tomorrow. Clearing toward Thursday.
Notes: Problem with the Lead-acid battery today. It didn’t seem to charge. Will concentrate on loading the Li-Ion battery tomorrow.

Due to the cloudy weather I decided to cycle all the way through to the campsite in one stage today. I chose a route slightly away from the Rhein which had the advantage of being more direct but the disadvantage of being inland and therefore higher. Hills are not something I enjoy on the 25KG Kronan bike! The route was nice though and it took me through endless lines of grape vines (and loud, gun-like bird scarers going off every ten seconds all over the valley) that are almost ready for harvesting for wine. Every town and village seems to be advertising their Winzer (Wine) Fest!

The mobile phone I have is doing very well as my email notifier and as (filtered) emails come in I get a little beep telling me to stop and take a look. Its nice to be able to say I’m in the middle of a Vineyard’ at the end of each reply! But that’s about it for the mobile phone. Trying to do anything Web-like is slow and terribly inefficient. Firing up the Q1b UMPC every now and then keeps proving how perfect they are for Internet activities. There’s no way I would be able to write so quickly, create the maps, review and edit the images and communicate via IM through all the protocols possible without it.

I’m camped right next to a beach on the Rhein (that’s the Rhein behind me there!) and can hear the waves lapping against the shore. Every 10 or 15 minutes a huge river boat can be heard either coming down from Rotterdam or heading up from the south somewhere. Fuel, sand, containers and even the occasional passenger boat. The Rhein is a business river. I wonder how long it remains efficient compared to trains, trucks and air transport.

I haven’t planned tomorrow in detail but it won’t be as long a journey as today. The Lead-Acid battery I have (2.2KG worth of old technology) didn’t charge well and so I’ll concentrate on loading-up the Li-Ion battery. One bit of good news though is that the mobile phone charges from the solar panel even in bright daylight. If all else fails I’ll have to email the blogs via T9 but I hope that doesn’t happen. I still have a fully charged spare battery for the Q1b so I’m not in trouble yet!

Here’s a solution based on the Sunlinq 25w panel and a Xantrec 300 Plus combo lead-acid battery/inverter. Its very similar to my own solution apart from the fact that this one weighs nearly 10KG!!!

A number of blogs seemed to have picked up on this solution today and are quoting 11-12 hours charging time. This figure is a little misleading. The battery capacity is about 240w/hr and based on a reasonable 5-hour per day full-sun rate its going to take 10 hours. That’s a minimum of 36 hours duration! In middle-Europe, you’ll be waiting for 3 full days of sun!

The other point to consider is that you need to take all your AC converters with you (weight problem) and should recon on 20% energy loss by converting from 12v -> 110V and down to 12, 16, 19 or whatever voltage your device takes. Hardly efficient. Alternatively you can buy 12v car adaptors for all your equipment (can get expensive.)

My recommendation is to use a combination of a Li-ion battery with variable DC output (I’m using the TabletKiosk/Tekkeon MP3400) and a lead-acid battery (I’m using a 2.5kg 6Ah part) This gives you the best of both worlds (lead-acid flexibility and Li-Ion light weight) and cuts the total weight right down to under 4KG. At also avoids having to operate a dangerous 110v. Capacity with my solution is around 130W/hr but here’s the key. Don’t use a notebook PC, use a UMPC. They are far more efficient. With a normal UMPC you’re good for 10 hours of computing on a fully charged system (around 7 hours full-sun charge time.)

News Via GottaBeMobile.

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…