Portable Ebike Solar Charger - build log

[John in CR]

How's the panel holding up?

I just finished putting mine together tonight. 85v 0.3a. The panels I got were really heavy - they say 1.2kg (must be less) each for 5w. Then I bolted them to a plywood sheet which I cut out sections of. Total thing is 11lbs Yeah I may not be carrying it around too often.

I'm on the lookout for some lighter weight panels that would be more portable.

Thanks for the links AW.

Those sound like the over-stocked units that I could have picked up for $3.50/ea, but shipping was going to kill me. I just got my box of 10W modules in yesterday and they're even better than expected. I'm just waiting on quotes for the cases to quickly get production rolling. Just to give you an idea of portability a 50W solar ebike charger that will handle up to a 75-88V cutoff will fold up to fit in a case 8"x16"x.75" and weigh about 5 pounds. A 100W setup would be twice as thick and weigh double.

Let me know if you want raw modules to do your own thing, because I'm realistically at least 6 weeks out from having folding panels ready to go due to Chinese New Year Feb 10th, which is essentially a 2 week break. Unless that 31% duty they were talking about isn't in play, then yes I can beat the $3/W you paid if you want the 10W modules and come close with the 5W modules. I think these will suite your needs much better.

Regarding holding up, they're rigid, waterproof, and tough, so you almost have intentionally try to mess them up. They don't have a glass front though, so the expected live is 10 years vs the more typical 20yr+ of a quality home panel. These aren't meant for permanent installations, so not really comparable.

John

 

[John in CR]

I found a good scale and the 10W modules are 395 grams and the 5W modules weigh 205g. They're actually both a bit lighter than that includes the plastic film on the face that you peel off before using them the first time.

John

 

[veloman]

I am definitely interested in the 10watt panels at that weight and price. I also bought 10 more 5w panels, from China this time. They look like the bare panel, no edging or glass cover, much lighter, but still $15/ea shipped.

Here's mine, charging up this afternoon. At 65v, my 15ah lipo cells went from 3.850 to 3.890 in 3 hours. Had to keep moving the panel/bike to avoid the shade. My yard is pretty bad for sun, very wooded neighborhood for TX, and houses blocking the sun at this time of day.

How hot do your panels get? I put a temp sensor behind one of the panels and it reached 40 C. It was 21 degrees ambient.

 

[veloman]

I have a question about the panels voltage relating the battery voltage. If voltage at peak amps is say 85v, and I'm charging a 65v battery, does that mean I'm really only putting 65v at 0.3amps into the battery? Not 85v at 0.3amps? It's the wattage I'm wondering about. Maybe I'm only getting 20watts from my panel, when they are rated for 5 x 5w (25watts).

 

[whatever]

can you give more info on the panels? what is the backing material and what clear material is protecting the cells?
I've been experimenting with some mono cells of late. The lower their temperature the more output, I've found some 3mm aluminium for backing plate,
which keeps them much cooler, but its quite a task on how to mount them etc. I also tried foam as a backing plate, but the cell temperatures went very high.
Anyone else out there experimenting with keeping solar cells cool ?
There is a evacuated solar tube on the market that removes heat via water to hot water system, they are getting just under 50% increase in output of the cells by keeping them cool compared to same cells uncooled. So an efficient cooling system can give quite significant gains in output.

 

[Harold in CR]

There is a evacuated solar tube on the market that removes heat via water to hot water system, they are getting just under 50% increase in output of the cells by keeping them cool compared to same cells uncooled.

Any links to that info, so we can check it out further ? Thanks

 

[whatever]

yup I was searching in google: " solar cell cooling" found this link
http://phys.org/news/2012-04-naked-energy-touts-hybrid-solar.html
or can go to the companies website
http://www.nakedenergy.co.uk
they are saying a bit less than 50% increase in output

 

[Harold in CR]

Thanks for the links. 8)

 

[John in CR]

can you give more info on the panels? what is the backing material and what clear material is protecting the cells?
I've been experimenting with some mono cells of late. The lower their temperature the more output, I've found some 3mm aluminium for backing plate,
which keeps them much cooler, but its quite a task on how to mount them etc. I also tried foam as a backing plate, but the cell temperatures went very high.
Anyone else out there experimenting with keeping solar cells cool ?
There is a evacuated solar tube on the market that removes heat via water to hot water system, they are getting just under 50% increase in output of the cells by keeping them cool compared to same cells uncooled. So an efficient cooling system can give quite significant gains in output.

The modules are composite sandwich with a layer of PET as the front surface, followed by EVA, the cells themselves, and again EVA. Then to add rigidity and strength the back is a fiberglass board like a PCB. The rear has some exposed copper colored metal strips for connections, which I planned to seal with a good insulating paint.

It's generally windy here, and since these are much more open to air flow than a typical panel for permanent installations I don't see much use in extra complexity, cost, and thickness for more effort to cool them. Only while running will panel area be restricted and air flow is guaranteed then. eg The surfaces of our bikes only get hot while stopped, so it's great that we can expect greater output from a panel while riding as long as it has a good angle to the sun. While parked I'll just have more panel area to fold out rather than waste thickness with cooling efforts.

John

 

[veloman]

Ooops, almost forget the diode. The first afternoon cloud came and I had to go running out to disconnect. :lol:

That was close

I was measuring my panels current with a nearly full cloudy sky today. I still was getting between 0.05 and 0.20amps. (0.9a rating)

But of course a diode is a must. I have one on each of my panels.

 

[Cargo_Tom]

I'm keeping a keen eye on this as my cargo bike has TONS of surface for this kind of thing

 

[cycleops612]

Dunno, but intuitively...

Given its all very complex for we mere mortals and that bog standard chargers are cheap...

The circuitry in a charger, which occurs after the initial reduction from wall voltage to approximately charging voltage, should roughly suit our purposes here.

If the output from a 40v solar array were connected to a 24v chargers circuit as above e.g., it may only require some simple mods to work well. The hard part (BMS etc.) is done by a mass produced, proven and cheap item.