How to Solar Charge an Electric Bicycle

[myzter]

5 feet by 3 feet

Well if U had a slightly larger panel
63" x 38"
that would fit about 60x 6.25"x6.25" / 3.8 - 4watt solar cells
off the 'bay for around $150

The 1st question I would be asking myself how high current 8A or 16A ??

 

[REdiculous]

With 2 of these kits you'd get 75w max from a 3' x 5' setup and you'd have a spare 1' x 3' (15w) panel...for $360-ish.

 

[amberwolf]

errr.... 5 feet by 3 feet...... over the top of my trailer. I was out in the sun all day...I'm a little baked
5'x3' = 15 square feet = 1.3935456 square meters.

That's a lot more reasonable size for charging expectations.


1.3935456 x 200w = 278w
20% = 55.7w
And with the efficiency of the chargers and batteries? Yeah.... Not to hot!
That's the problem...and that 20% is probably beyond what you would actually get by quite a bit.

Are you sure about the 200w per m^2? Seems like it should be higher in the summer time....[/quote]
It's a guesstimate. 1KW per m^2 is generally what you'd get on a perfect day with the sun absolutely perpendicular overhead, both in latitude and longitude. 200W is a guess as to what you would get as an average over the whole sunrise-sunset period, since you'll get almost nothing at the start and end, and the most in the middle.

Since you're not going to have the sun right overhead at your latitude, it won't quite be 1KW; not sure exactly but at a guess 800W at noon in the summer (lots less in winter?). (there are insolation charts on the web all over at solar places that will tell you about what you get in different locations)

So if you did your charging at noon, you'd get a lot more out of them than later in the day, assuming you don't have a sun-tracker or other way to keep your panel aimed perpendicular to the sun as the spot on Earth you're occupying rotates toward and away from it. But remember: there is more scatter in the atmosphere at any time other than noon (well, at zenith), so even with a tracker it won't get as much at any other time, and it gets worse faster as it gets closer to sunset (or better the farther from dawn).


Then it also depends on which panels you get, as each has some limit to the current draw out of them, AFAIK.

Plus, you have to convert their output to wall-AC power to run your chargers (unless you are using a 12V panel and a 12V powered RC charger--this is probably a lot more efficient for your purposes, at a guess).

Oh, and I forgot about this: The extra weight of the panels is going to eat into your range on the bike, unless you also use them to recharge that (and I don't think you'd have enough spare power from them to make a dent in the power usage there, after what the lawn tools use up). Depending on how you mount the panels, they will also cause more drag, especially at higher speeds 15MPH and up, using yet more power.

 

[dogman dan]

Real world, what you get out of a solar panel is a lot less. Typically a 3x5 foot silicone panel is in the 150-200 watt range. Check your local area for average insolation. It should be 6 hrs or less. Of course it's longer in summer, but hot panels put out less power than cool ones.

Chances are, a good ballpark number would be around 100-150 watts, perhaps more if you keep moving the panel every 20 min or so. So a couple hours to fill a 300wh battery would be about your absolute max. Repointing the panel will help a lot with the average insolation, a fixed panel is pointed wrong all but about two hours of the day.

Ideally you'd have customers willing to pay a huge premium for the "green mow". If that works out, carry one panel for show, but do the bulk of your real charging at a fixed charge station at home. Keep hunting for cheap used panels, and even better, find an organization willing to support your green mow buisiness. Maybe a Texas enviromental group could help you with a fund for the panels. A grant would be cool, but even a local fund raiser like a carwash or fancy dinner, or whatever could get you a few bucks from each of the local eco minded folks. Belive it or not, you might even get $$ from the local electric company. Put out press releases about your green mow, get on TV, etc. Work it baby!

 

[auraslip]

Awwww yeahhhhh

Well, the local bike co-op has got some solar panels courtesy of a local plant that makes them. I might be able to get some after we get done building a solar lighting system for the co-op shop.

It's funny that you say I should get a panel just for show. The link I posted above probably doesn't actually charge their power tools with solar..... at least not on the go.

 

[stanz]

Just found this on instructables:

http://www.instructables.com/id/Solar-Powered-Trike/

 

[ponobill]

Depending on your situation and location a nice PV array is about the best investment around. I've installed a 6KW system at my home in Maui. Lots of sun, and very high electricity prices. While Maui is going to renewable sources quickly, the bulk of the electricity generated comes from oil. When they add a fuel surcharge to the current tariff of 23 cents a kilowatt the price gets VERY high. After tax breaks my system cost me about $20K and will pay for itself in 4 years. I don't have any other investments that are even in the ballpark of that. Been up and running about a month and a half and it's generated 1.58 MWH of power. Not bad for a backyard system.

 

[auraslip]

I want your backyard.

 

[dermot]

I've built a little switchmode charger that I'll write up if anyone is interested - bits easily sourced from ebay or the component supplier of your choice and costs around $15 in total.

You can input anywhere between 8VDC and 30VDC and it will output a CC/CV up to 60V, but power limited to around 80W, but working on improving that. Efficiency is pretty good - in the 80s to 90s.

Based on the Nat Semi "Simple Switcher" and other similar ranges of chips - still a bit 'works in progress' and I've not yet decided which chip is the best to base it on..

It is a tiny circuit, hidden in the battery box - I use it so I can charge my bike from whatever low voltage DC I have available - laptop chargers giving 16 - 19VDC work very well - as do solar cells (had to borrow one for testing). It seems to cope very well with the changing voltage as the input from the sun varies - but only done brief testing.

Last piece of the puzzle is to interface it to Gary's BMS so that the HVC opto will switch the charger to a couple hundred mA when LEDS come on.

I also found 300W/hr of unused laptop batteries - they will make a lightweight trickle-charge range extender when I get some spare time.

dermot

 

[amberwolf]

That would be interesting to see--if it does work out I could probably build it from what I have around here already, and use it with the two old 1-sq-ft cells I have for charging experiments. They're too fragile (bare cells) for portability, but it'd be interesting to see how long a stationary unit would take to charge up my pack.

Somewhere I have an old oven-timer electromechanical clock I might be able to use to make a very basic sun-tracker from.

 

[John in CR]

I've built a little switchmode charger that I'll write up if anyone is interested - bits easily sourced from ebay or the component supplier of your choice and costs around $15 in total.

You can input anywhere between 8VDC and 30VDC and it will output a CC/CV up to 60V, but power limited to around 80W, but working on improving that. Efficiency is pretty good - in the 80s to 90s.

Based on the Nat Semi "Simple Switcher" and other similar ranges of chips - still a bit 'works in progress' and I've not yet decided which chip is the best to base it on..

It is a tiny circuit, hidden in the battery box - I use it so I can charge my bike from whatever low voltage DC I have available - laptop chargers giving 16 - 19VDC work very well - as do solar cells (had to borrow one for testing). It seems to cope very well with the changing voltage as the input from the sun varies - but only done brief testing.

Last piece of the puzzle is to interface it to Gary's BMS so that the HVC opto will switch the charger to a couple hundred mA when LEDS come on.

I also found 300W/hr of unused laptop batteries - they will make a lightweight trickle-charge range extender when I get some spare time.

dermot

Dermot, my hero, yes there's absolute interest. I do need a higher output voltage though in the 80-82V range with absolutely reliability in the cutoff. If it takes a somewhat higher voltage input to achieve it, that's not a problem. What kind of input current can it handle?...my cells put out up to 8A.

 

[drewjet]

I would be very interested also, but need something in the 350 to 400 watt output.

 

[dermot]

I've not been looking at much above 60V and 1 Amp or so - higher voltage is probably not too difficult, much higher power would need a redesign from the ground up.

I've been using it so far on a 12 series LiFePO4 pack and today had a tweak on a 16series LiFePO4 one - which needs a max of 57.6V

I do have a couple of ideas from an earlier project that would stretch to an arbitrarily high voltage, but still not get much above 150W.

I can dig some notes out, but it is not a finished design.

Pulling 350W off a 12V car battery would require over 30A - a bit unrealistic for long term charging. Why do you need such high charger power while on the move?

 

[edcastrovalley]

I've built a little switchmode charger that I'll write up if anyone is interested - bits easily sourced from ebay or the component supplier of your choice and costs around $15 in total.

You can input anywhere between 8VDC and 30VDC and it will output a CC/CV up to 60V, but power limited to around 80W, but working on improving that. Efficiency is pretty good - in the 80s to 90s.

dermot

I would be interested too! I have twin 125 watt panels and 4 golf cart batteries that I charge my lipo battery pack with via an icharger 3010b but, that requires me to take my 60 volt (15s) pack apart every time I recharge. With the "switchmode charger" I may only have to disassemble the pack when I balance them, a big convenience.

 

[drewjet]

Sorry to go off topic... but I do bring it back around at the end

Pulling 350W off a 12V car battery would require over 30A - a bit unrealistic for long term charging. Why do you need such high charger power while on the move?

Let me explain what I am wanting to do and then maybe it would clear it up. I race electrathon cars. Which is basically a 3 wheeled go-cart that we have 2 ea 1 hour endurance races with in a day. We are restricted to 2 car sized batteries and 2 hours between races to charge. Many places we race have 110 volt power available, and I have 2 power supplies that can put out 25 amps each and get it recharged in the 2 hours. Some places have no power and we need to use a generator. It SUCKS bringing a generator to an electric event. I have a good supply of 12 volt deep cycle batteries, and figure I could use 2 of them in series to charge 1 of the electrathon's cars batteries if I could somehow turn the 24V of the 2 batteries into 25A/15V CC/CV.

What would be really cool is to then have solar panels to recharge the 4 deep cycles that became the charges of the car's batteries.

 

[REdiculous]

I have a good supply of 12 volt deep cycle batteries, and figure I could use 2 of them in series to charge 1 of the electrathon's cars batteries if I could somehow turn the 24V of the 2 batteries into 25A/15V CC/CV.

Why not use an inverter and your normal 110v charging setup? A 600w 24v pure sine inverter can be found for $230 or a 300w for $140.

 

[drewjet]

Why not use an inverter and your normal 110v charging setup? A 600w 24v pure sine inverter can be found for $230 or a 300w for $140.

I have thought of that, it just seams a bit of a waste to take 12 volts and bump it to 120 just to bump it back to 15 volts

 

[julesa]

Why not use an inverter and your normal 110v charging setup? A 600w 24v pure sine inverter can be found for $230 or a 300w for $140.

I have thought of that, it just seams a bit of a waste to take 12 volts and bump it to 120 just to bump it back to 15 volts

On the plus side, then you'd be able to tap into the 120v to power a sunlamp that you can place over the solar panels for when it's dark or cloudy. :lol: :lol: :lol:

 

[brisbanebikie]

I found some info relating to roll up solar pannels I talked about in my first post here..

watch this from 2:10 on.. http://www.youtube.com/watch?v=zcbgsNBm1lo&feature=player_embedded

also at this website you can buy roll up solar pannels - http://www.unisolar.com.au/

their top model stats are:
Max Power 32W
Nominal Voltage 12V
Operating Voltage 16.5V
Operating Current 1.94A
Short Circuit Voltage 23.8V
Short Circuit Current 2.4A

"typically, there are only about 2-6 hours of "peak" sun where the modules put out near maximum power (2-4 hours in the winter and 4-6 hours in the summer). To estimate daily watt-hours, multiply the number of "peak" sun hours by the rated wattage of the module"

so thats 64-128 watts of power a day.. in winter.. how much is needed to charge a bomber?

 

[REdiculous]

so thats 64-128 watts of power a day.. in winter.. how much is needed to charge a bomber?

If the panel is 32w and 32wh/mi is close to average consumption for your ebike then 2-6 hours of peak sun = 2-6 miles in the "tank". Not too bad I guess.

 

[edcastrovalley]

What would be really cool is to then have solar panels to recharge the 4 deep cycles that became the charges of the car's batteries.

Just an idea but you could try a couple of panels like these.

How many amphours are your deep cycle batteries? How deeply discharged are they after a race?

I generally see up to 9 amps in decent sunlight on each of these panels at 12 vdc. They are 60" x 23" each so they are large but still portable. You don't need the stands I got here since they work well even if you lay them on the ground. A pair of these will definitely charge up a couple of deep cycle batteries but my concern is the 2 hour charging time between races might not be enough. Especially if you are used to having a pair of 25 amp chargers around.

 

[brisbanebikie]

... 2-6 hours of peak sun = 2-6 miles in the "tank". Not too bad I guess.

you could almost go camping with your ebike and take a rollup solarpannel with you to charge it during mid day while you rest

 

[REdiculous]

... 2-6 hours of peak sun = 2-6 miles in the "tank". Not too bad I guess.

you could almost go camping with your ebike and take a rollup solarpannel with you to charge it during mid day while you rest

Who wants to wait 6 hours so they can go an extra 6 miles though? I think you'd want at least 4 times your wh/mi average so that you get 4 miles worth of charge every hour. I think for most people 4x would mean around 100-150w in panels. Going 4x would get you 8-24 miles from 2-6 hours of peak sun.

 

[mvly]

I think for this to be even feasible, you will need serious solar panels and some good sunlight throughout the day.

Here is my quick math:
My battery: 48V30Ah ~ 1440WattsHours ~ 1.5KWh battery (50 miles range all electric/no pedal)
Accounting for inefficiency on energy conversion of the charger I'll make it 2KWh requirement to fully charge the battery.
Assuming an average of 6 hours of full sunlight on all the panels per day throughout the year.
So to make 2KWh in 6 hours, I will need a panel that can spit out 333.33Watts.
Of course, I will not be able to get full power of the panels at its advertised power output, so I would say 400W or 500W panels in full good sunlight for 6 hours will be good enough to charge my battery.
Of course, then I will need 2 batteries since I would use one for riding and 1 charging.
Finally I will need a controller and inverter, etc to get started to charge my battery.

If I get it from the grid, I pay at most 20 cents per KWh. Thus, to charge my battery to full, it will cost 40 cents. Even if I inflate that to $1 for 2KWh to account for rise in energy cost in the future, it will still take a long time for me to make my money back on all the equipment assuming I use the battery once a day.

Overall, I don't think it make economical sense to get all this set up just to get free transportation.
in my opinion, if you are going solar for your house, do so. Unless you are hardcore about saving the environment, but then again I would question how much energy used and waste generated to make all the equipment that you are using to make this setup.

 

[dak664]

If I get it from the grid, I pay at most 20 cents per KWh. Thus, to charge my battery to full, it will cost 40 cents. Even if I inflate that to $1 for 2KWh to account for rise in energy cost in the future, it will still take a long time for me to make my money back on all the equipment assuming I use the battery once a day.

Well I dropped the grid to my ride endpoint since it was costing US$7.5 a month just for the connection. The 75 watt panel there recharges my bike in about 2 hours. Admittedly it is at risk for being stolen, but it has already paid for itself. The less electricity you need, the more cost-effective is PV.