Solar panel for touring

For discussions about bikes and equipment.
hoogerbooger
Posts: 232
Joined: 14 Jun 2009, 11:27am

Re: Solar panel for touring

Post by hoogerbooger »

Hey Scunnered

How did you get a 5W panel to charge the Cache battery ? I'm curious as I'd not thought there was a sensible hiking weight solution.

I had a 6W 12V panel and having tried all sorts of converters couldn't charge any lithium cache batteries I tried even in very bright conditions. I Could charge NiMH batteries and use them to charge one phone but not others. I now have a 21w Anker Power Port Solar panel and use it with a Portapow cache battery (700g combined), which I can also use with eWERK & Shimano dynamo hub on my rough stuff tourer. But too much stuff/weight for sensible hiking or normal cycle tours.

My main tip on panels is presume it will be gloomy and you'll need a bigger panel than you think. But perhaps there's a need to be more savvy on charging circuits and avoiding unnecessary power losses ??

All this kit is good for a back of beyond long tour. But you can end up with a lot of clobber. The cache battery and using opportunities to charge seems to have been fine for much of my current needs.
Brucey
Posts: 43113
Joined: 4 Jan 2012, 6:25pm

Re: Solar panel for touring

Post by Brucey »

6W 12V (i.e. 0.5A max current) is arguably perhaps the wrong rating for charging (USB type) cache batteries; they usually have circuitry that is happiest with 5V going in and might be wasteful if the votage is higher and the current is lower. So a panel the same size, differently configured might be capable of producing 6V 1.0A (still 6W obviously) which might work a lot better, depending on what circuits it is driving.

In terms of overall efficiency / percantage of maximum power;

a) the solar panel rating is for bright (noonday) sunshine on a clear day aimed at the panel square on.
Time of day means 10-100% potential efficiency in daylight. Say an average of 50%.
Clearness of sky means 0 to 100% efficiency, say an average of 50%
Aim of panel means (for a panel strapped flat onto a bike carrier) 30 to 80% at this latitude, say 55% average.

b) there is a converter circuit pushing the current into the battery. Even with a 5 or 6V input the converter efficiency will be between 70 and 95%, say an average of 85%

c) power in vs power out of a good battery is typically around 70% efficient.

d) the cache battery then charges the gadget battery as per b) so another 85% maybe.

e) the dischage of the gadget battery is again about 70% efficient.

So sadly you get to multiply all these things together and it is a bit of 'death by a thousand cuts' or like compound interest in reverse.

so 0.5 x0.5 x0.55 x .85 x 0.7 x 0.85 x 0.7 equals...... (drum roll)

0.048. :shock: About 5%.

In other words your nominal 6W panel is actually likely to be producing net 0.3W (in actual gadget power) on average. And even if you miraculously manage to get the panel aligned perfectly in bright sunshine on a clear day at noon, the peak net 'actual gadget power' is only two and a bit watts.

So if you want to keep a sub 3W gadget going all day (say) then the best thing (in efficency terms) would be to power it directly using a hub generator, and to have a small cache battery that takes over when you stop, for as long as it takes you to turn the gadget off.

If you want to get the best out of a solar power arrangement, it isn't a bad idea to get a panel that is (roughly) x10 or x20 more powerful than you 'need'. WIth this setup, you may run into a new problem which is that it may not be possible to use the peak current that the device may generate under favourable conditions.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Scunnered
Posts: 224
Joined: 11 Apr 2014, 11:23am

Re: Solar panel for touring

Post by Scunnered »

hoogerbooger wrote:Hey Scunnered

How did you get a 5W panel to charge the Cache battery ? I'm curious as I'd not thought there was a sensible hiking weight solution.

I had a 6W 12V panel and having tried all sorts of converters couldn't charge any lithium cache batteries I tried even in very bright conditions. I Could charge NiMH batteries and use them to charge one phone but not others. I now have a 21w Anker Power Port Solar panel and use it with a Portapow cache battery (700g combined), which I can also use with eWERK & Shimano dynamo hub on my rough stuff tourer. But too much stuff/weight for sensible hiking or normal cycle tours.

My main tip on panels is presume it will be gloomy and you'll need a bigger panel than you think. But perhaps there's a need to be more savvy on charging circuits and avoiding unnecessary power losses ??

All this kit is good for a back of beyond long tour. But you can end up with a lot of clobber. The cache battery and using opportunities to charge seems to have been fine for much of my current needs.


The solar panel is nominally 6V, 5W, but the most I have measured is 4.5W
To use it to charge a Li-ion or Li-polymer battery, you have two options:
1) Use a Li-ion charger circuit intended for this purpose. These are usually 5V input (intended for USB) and employ a linear regulator, so you can use this option if the output of the solar panel does not exceed 5.5V or so.
2) Use a DC-DC step-down regulator with the output set to 4.2V (the max. charging voltage for the Li-ion battery).
The problem with the latter is that it can "drag down" the output voltage of the solar panel, reducing the power output. To overcome this I designed a (possibly unique) max power-point circuit for the step-down regulator.
This is currently undergoing testing, but I have already decided to make an even lighter version and have ordered a 2W solar panel and a smaller battery.

Before you start any of this you need to assess your average daily power requirements and the weather conditions of your destination. If the sun is mostly obscured by clouds, you will get zilch power no matter how big your panel is, so forget it. You need direct, unobscured sunlight to generate anything useful. I would not even consider solar power here in Scotland for example, I am intending to use it in the Pyrenees.
User avatar
Embuicado
Posts: 1
Joined: 22 May 2019, 8:04am
Location: Clifton, New Jersey

Re: Solar panel for touring

Post by Embuicado »

As for charging small electronic devices, I can say the next thing.

The <SNIP> brands seem to both get great reviews.

IMHO, I would not consider purchasing one less than 20 watts. This is because your output will likely drop by 40% in the winter, plus there are some inefficiencies at work as well due to the voltage transformer. Considering that you want to have at least 6-8 watts usable, you really need a 20 watt panel to have any degree of safety.

Keep in mind that for these panels to produce anywhere near their stated wattage, they must be stationary and pointed directly at the sun with no shade whatsoever. The promo videos that show people wearing these while hiking are all baloney.

If you are going to buy one, I would strongly urge you to also have at least one, preferably two, lithium battery packs of at least 10,000 mAh each, and 20,000 would be far better. This enables you to leave one of the batteries charging next to the solar panel while you're out doing these and one to keep with you. The other issue is that plugging your phone directly into the solar panels can be problematic. If a cloud passes by and the output drops too low, the phone may 'hiccup' and need the cable to be unplugged and then plugged back in. Using the solar panels to charge a separate battery pack sidesteps this problem and gives you a means to store the excess solar energy that your phone can't.

I hope it's useful.
Last edited by Graham on 22 May 2019, 2:02pm, edited 1 time in total.
Reason: Suspected spammer ( digitalocean )
MarcusT
Posts: 349
Joined: 31 Jan 2017, 10:33am

Re: Solar panel for touring

Post by MarcusT »

I just picked this up.

https://www.amazon.co.uk/22000mAh-Porta ... pons&psc=1

I have not tried it on the road yet, but I have charged my phone and tablet with plenty charge left over.
I wish it were as easy as riding a bike
Post Reply