I’ve just had a nice conversation with my energy advisors, Select Solar, about some of the issues I’ve seen with the tests I’ve done so far. The main problem being that Li-Ion batteries will not trickle charge. They require a certain level of stable voltage/current before they start to charge and this wastes the possibility of charging a battery at lower sun power. In fact, on a hazy day or with light cloud cover, the sun power might not actually go above 70% and you have no chance to charge anything. This could be major problem and I’ve decided to try and address it.
A solution to this problem, as I mentioned before, is lead-acid batteries. These are the type you will find in your car and are a tried, tested, reliable and relatively cheap solution. The problem is that they are also extremely heavy – at least 400% of the weight for like-for-like power storage. They also operate at 12v which means voltage conversions (and more electronics and power-wastage) in order to operate the UMPC.
The decision I’ve made is to buy a 70W/hr 12v lead-acid battery (2200g) and to try and use this as a charge buffer. Here’s a little sketch of the planned set-up.
The idea would be that I connect devices to the lead-acid battery as the solar power increases during the day. For example, I might add a couple of AA batteries or my mobile phone in the morning. At mid morning I might replace it with the Li-On battery and during the peak hours I could re-attach the AA battery charger with 2 or 4 batteries depending on sun power.
Two problems I can see here:
- How do you know the charge on the lead-acid battery?
- Will the lead-acid battery be able to feed up to 1.5 Amps?
There’s only one way to find out. I’ve just put an order in for a 70W/hr lead acid battery and charge controller along with some fresh AA batteries, a powerbank tip adaptor for the Samsung Q1, a 12v charger for the mobile phone and something I’ve always wanted, a flexible USB LED-lamp!!!
Later today I will probably be ordering the solar panel. I won’t be using the P3 Panel as the only advantage with that was that it could drive 19V into the PowerBank. Now that I’m going for a 12V source solution I’m going to be looking at the 25W version of this Sunlinq panel which is the same price as the 15W version of the P3 panel. There’s a risk that its going to be too big for the bike at 1m long but even if I fold 25% of it away, its still going to give more power than the 15W panel and during mid-day pause and work sessions I hope to get the full 25W out of it.
What about Lithium Polymer batteries? I saw this guy used one. Not sure…
This company seems to make a few different kinds of Li-Po batteries…
Also, I have been thinking of getting one of these for my writing projects. 25hrs on one charge… nice!
Terje
Also came across this article which hooks up a small solar panel to a NiMh battery…
Hi Terje.
That battery pack is this one (from your first comment)
http://www.xantrex.com/web/id/187/p/1/pt/10/product.asp
However, I don’t like the idea of using inverters. You take DC then store it in a battery (loss #1) and then convert it to 110v (loss #2) and then through the adaptor back to DC(loss #3) and then through the power board on the PC to the various voltages (loss #4) The inverters are also heavy, dangerous and a failure point thats just not needed.
The best method is to stick with low voltage DC I think. Most efficient would be to use the solar panel straight into the UMPC but I think thats too risky unless you can get someone to confirm that its safe. 2nd best solution would be to charge the Li-Ion battery and then use that to power the UMPC (remove the battery from the UMPC when doing this)
If sun power is low then the lead-acid battery gives you the best option. Can also give you power to charge other devices (phones, AA batts and UMPC) with a stable voltage. I hate the idea of that 2.2KG lead acid battery but I think its a neccesary evil.
A 12V UMPC would be nice. There are some around. Raon Digital Vega for example. But its too small for me.
Steve
Yeah, all that inverting and converting wouldn’t be good, but I was just wondering would a 12V Li-po or NiMh battery support charging from a solar panel unlike the Li-Ion?
They might be lighter alternatives to lead acid.
Came across the Bescor NMH54 NiMh 12V battery pack. Looks like the charger only uses .5 amps to charge the battery.
Also, the specs for this NiCD battery say it is “suitable for use as a storage battery for solar power.”
Also, just an idea, since you can charge AA batteries, why not create a 19V battery pack from a bunch of of AA batteries? 16 x 1.2v AA batteries = 19.2V
There are AA battery holders that hold 8 batteries such as this one, connect two of those together?
Charge the AA batteries using the solar panel, then connect them all together to power the UMPC.