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.

The 102 (good) photos that I took on the Solar UMPC tour have now been posted in the UMPCPortal Gallery.

Found on Flickr.

...and there's my version.

We (that's me, VIA and a PR company) had tried to plan a crossing-the-line press meeting today but as it turns out, everyone is at IFA and no-one was available. It was a little disappointing but seeing as it was raining, I'm not bitter! I took the chance to jump on a train home and start the process of writing-up the project. The first think to do was unpack those smelly socks and make sure I had everything listed for anyone that might be interested in the future. The gadget bags were the most important bit unless you want to see a picture of my wash bag. No? Thought not.

It was a well-refined 10-day gadget bag I had with me on the Solar-UMPC tour so as I unpacked a few hours ago, I took the opportunity to update the pack list (Google spreadsheet available here.) and take photos of the solar setup and the computing setup I used when I was out.

First, here's the solar setup. Most of it is explained in previous posts (see this one and this how-to for example) but maybe this picture helps to simplify how I was using the devices.

The second picture shows the computing setup including the all-important gadget of the week, the USB LED lamp! The mobile phone and UMPC worked well together as a communication suite. The phone took primary role as email reader, music/radio and twitter interface with the UMPC performing the more creative roles with the map updates, blog entries, photo editing and geo-tagging.

 

The computing set-up was really good and apart from reducing cables and improving software, there isn't much i'd change in terms of components. The solar setup will defaintely need improving though and as I mentioned in this post about the inefficiencies, I have already made some notes about how I would improve it. I'll be going through my recommendations for the computing and solar setups in later posts.

Wooooooohoooooooo! Total distance covered: 450km over 10 days. UMPC, Phone, Camera, GPS and Torch all topped up from Solar energy. I made it!

Distance since last post: 65km
Weather: Dark and cloudy.
Notes: Don't drink two beers at the finish line without having something to eat first!!!

 

 

Today at about 1700 (UTC+2) I crossed the unofficial finish line on the Solar UMPC tour. The official finish happens tomorrow with my sponsors, VIA, but that will be at the same place that I enjoyed the beer shown above. For me, the tour is complete and after I've posted this and used up the last hour of battery life on the Samsung Q1b, I'll be connecting back to the electricity grid to charge up my phone and umpc for the first time in 9 days ago.

Finish line!

It has been a fun and challenging time trying to balance a 450km cycle camping trip with work and a solar powered UMPC experiment but its been fully worth it. And that includes that last three days of full cloud cover and zero solar power possibilities. I've learned a lot about how solar energy works, how it can be applied to mobile computing and how different battery technology affects the results. But it hasn't just been about solar energy. Its mainly been about energy efficient mobile computing, mobile Internet connectivity and the balance of tasks between a mobile phone and a UMPC. Although I managed to perform a lot of tasks on my simple mobile phone, none of the mapping updates, images, GPS tracks and detailed postings would have been possible without a UMPC and the VIA-based Samsung Q1b has been a reliable and efficient partner all the way through. It hasn't missed a single heartbeat.

The last 65km leg up here to Duesseldorf was a fun trip. Two friends of mine, Steve Carr and Ian Emmett, came with me and we had a good fun ride. Bessy managed to clock 38.2km/h, Steve lost a mudguard and Ian managed to get a branch stuck in his (overly complex, if you ask me!) gears. Bessy has been an absolute star too and she'll be getting a good soft rub-down when she gets home. Thanks Bessy the Blue Bakers Bike.

As we rounded the last corner of the journey and saw the Vodafone Germany HQ and a long line of riverside bars I knew it had been worth it. I feel so happy that it would be impossible to describe it within the limits of my battery life here but its been a perfect week of work. I want to start planning the next project ASAP!

Goodnight Duesseldorf. see you tomorrow on the finish line again where I'll be showing off the Solar-UMPC kit to the journalists. I hope it doesn't rain!

When i'm fully charged up (personally) again in the next few days i'll be posting all the photos, an overview of the trip and a detailed report on how things can be improved. There's a lot to be learned from the Solar-UMPC tour.

Location: Koeln
Distance since last post: 15km
Weather: Brightening. Still 100% cloud

As I was leaving Bonn this morning I passed a trio of mountain bike riders. They where looking closely at one of the bikes and I heard them say 'I think the gear has broken.' My army-pattern bike might be heavy but its as solid as a rock!

Journey today was rather short and uneventful. There was little traffic on the paths apart from the  occasional animal and a rather stupid (and probably deaf) old man that cut across me to turn into a side path. You do NOT want to be hit by my bike! Fortunately we passed each other safely and gave each other a friendly wave (sort of!)

 

I didn't get more than about 10 minutes computing power from the sun today. It was hopeless even stopping to try! Tomorrow is the last day for collecting solar energy and I am praying praying praying for just a few hours of sun to take me through to the finish line in Duesseldorf at midday on Monday.

I have updated the route map with a few more images. Hope you enjoy them.

Crossing the Rhein on a tiny Ferry (below)

Location: Sürth
Distance since last post:15km
Weather: warm but cloudy and wet.
Notes: Always wear tight underwear when cycling!

A business issue this morning cost me 25% of my battery power and with the current weather situation, cloudy and wet, that could cost me dearly. There was a brief bright period at around noon where i slammed on the breaks and stopped to put out the panel but it was short, lived. The mobile phone needs a top-up and the GPS too. It's fair to say that this has not been the best week for solar energy but despite that, it's been possible to get a few hours of umpc work done every day. The bad weather has also made me think long and hard about how the process can be improved. I have some notes that i am going to try to type up tonight but that, of course, depends on my battery!