Solar

Apetito

Finding my (electric) wheels
Jun 5, 2010
17
0
Has any manufacturer or inventor come up with a way of charging an electric bikes 36v battery with a solar panel yet. Be nice to have one built into a rear carrier
:eek:
 

flecc

Member
Oct 25, 2006
53,152
30,567
A carrier solar panel is nowhere near big enough. A to B magazine have used two large shed-roof panels in the past to do this, but it still took ages. Realistically you need around a couple of square metres of panel at least.

A to B also found that very slow direct trickle charging that way upset some batteries, so they ended up with the panels charging lead acid batteries and then charging the bike battery from the larger lead acids at more normal charge speeds.

May be more practical when mobile in the most sunny countries with a panel kept oriented directly to the sun all the time.
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Xt512

Finding my (electric) wheels
Feb 24, 2010
8
0
As discussed there really is not enough surface area on a bike to attach a panel witch will deliver a worthwhile charge. There is a way to charge using solar wind or other renewable supply and that is to charge batteries from panels mounted on the roof of your house and use an inverter to supply the charger.

I have been doing this for years with no problems.

You will need lead acid batteries with enough capacity to take a charge and capacity to give the required charge to your batteries. I have got these in the past for free from old UPS systems.
An inverter of an adequate size, though it must be a pure sine wave design not the cheaper modified type as these tend to give transformers a hard time.
Solar panels to charge the batteries and a southern facing aspect. These come in various types, quality and prices. I like to use monocrystalline solar as these have been around a few years and have worked well for me. It is possible to get unbranded panels from Ebay for £3 per watt.
You will also have to use a solar regulator of sufficient amperage to protect your Lead Acid Batteries.
 

overlander

Esteemed Pedelecer
Apr 22, 2009
532
42
Come on guys never mind solar check this solution out :D :D

Get with the program.



 

Apetito

Finding my (electric) wheels
Jun 5, 2010
17
0
I think you are getting carried away with size needed.
My Caravan Leisure battery 120amp has needed to be mains charged once in the last 5 years. That was over a Christmas + New year rally a few years back when we never saw the sun for days and days. Normally my Solar Panel 17watt max in full sun and about 18" x 12" is size is enough to keep the battery topped up all the time. I am sure a carrier sized Panel on a bike would help a lot.
 

Grizzly Bear

Esteemed Pedelecer
Sep 14, 2007
282
0
66
Swansea
www.grizzlyfish.com
I have 116 watts of solar panels on the roof of my motorhome, and I recently took a clamp meter away with me to see what the actual output was(exciting stuff hey!:rolleyes: ).

In bright sunshine they were generating about 7 amps, in cloudy conditions it was down to 1.5 amps, this is at "12" volts of course, and with the batteries run down a bit from the previous night's usage. I then measured the power the inverter was using to run a laptop computer and found that it was taking approx. 6 amps out of the battery. So in bright sunshine 116 watts of solar panels can just about keep up with a laptop's demands. My 5 amp charger for the bikes was taking 30 amps, and from flat takes 2 hours to charge, it would therefore take about 9 hours of briight sunshine to charge one bike from flat, of course this is a very inefficient way of using the power. I am now looking at charging the bikes by using some panels in series, there by removing the losses from the inverter and the charger.

Griz
 

flecc

Member
Oct 25, 2006
53,152
30,567
I think you are getting carried away with size needed.
Not at all, a half square foot carrier size panel would do next to nothing for an e-bike in the UK most of the time, you'd struggle to see any range difference. There's a huge amount of experience with solar using direct and indirect current usage for vehicles which supports that. That's why indirect charging via lead acid is used, the outputs often too low to be of any use in direct charging of other battery types.
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jbond

Esteemed Pedelecer
Jul 29, 2010
411
2
Ware, Herts
www.voidstar.com
I wonder if we're trying too hard here. Let's take it back to basics and see if the price makes sense. Here's what I'm thinking based on 1.5 times safety factor
36v*10Ahr Li-On bicycle Battery
< 100w Li-On charger
150W invertor
12V * 45Ahr lead acid batteries
Solar BMS to 12V batteries
??? W Solar

That should give a 12v battery system capable of one complete bicycle battery charge taking them down to 30% charged or so and so not completely flat. Questions:
- How cheap can you assemble 45-50Ahr of 12v lead acid batteries?
- How much solar power cells do you need to trickle charge them so that 1-2 days of sunlight is enough for one bicycle battery charge. is one or two of these enough?
SolarPowered 12V 12W Battery Charger : Solar Battery Chargers : Maplin (12w battery trickle charger)

With a bit of 2nd hand scrounging, it might just be possible to bring this in under £100
 

tillson

Esteemed Pedelecer
May 29, 2008
5,252
3,197
I've not had time to look at the numbers, but I wonder why you would want to do this. The cost of the equipment would be a good deal more than any savings made. It is difficult to see what can be achieved.
 

flecc

Member
Oct 25, 2006
53,152
30,567
Of course solar battery charging is practical over time and some do it as shown above, but Apetito's thread was proposing a bike carrier size panel to charge while in use. That would contribute nothing useful.

This isn't untried science, we have solar powered endurance car events in very sunny Australia which have gained huge experience. They prove that very large panel areas and constant sunshine are needed for real time use. Anything less means long term charging for deferred use.
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Tim

Esteemed Pedelecer
Nov 1, 2006
770
78
London
What I'd be interested in pursuing is direct charging of a 26V Kalkhoff battery from a PV cell, without the need for a wasteful inverter stage in between. How would that work?
 

jbond

Esteemed Pedelecer
Jul 29, 2010
411
2
Ware, Herts
www.voidstar.com
I've not had time to look at the numbers, but I wonder why you would want to do this. The cost of the equipment would be a good deal more than any savings made. It is difficult to see what can be achieved.
Ah well. At current prices, there's no logical reason at all providing you have access to mains electricity. If you're trying to go off grid, or you're camping with a vehicle that can take all the kit away from a supply, then it begins to make sense. Otherwise it's probably about guilt and playing with toys as much as anything!

I'm still curious to see how cheap we can get it, if you accept a duty cycle of 1-2 days of sunlight for one bicycle battery charge.
 

stewart

Finding my (electric) wheels
Nov 24, 2009
5
0
In a world of supply disruptions, expensive mains and in a hilly place could solar or wind become practical transport fuel?

Would a (say) Rutland windcharger give good results in the UK? I had a small one years ago for a boat and it kept a couple of deep cycle lead acid batteries up, enough for 12V (black and white) TV all night, few lights, water pump. Always gave good power I never ran them down.

In a relatively exposed site could you wind charge overnight?