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saand · 07-31-2010, 12:31 AM

Hi ragez,
I like the idea, but hopefully i can let you know about the practical issues of doing this as i have done a lot of work with solar panels in the past.

First off, if your bike is out in public your solar panels will get stolen, they are expensive and easy to carry. In australia we have some electronic road signs with solar panels that are about 4 meters up in the air above the sign. I have seen signs where people have hacksawed through a very thick pole to get the sign on the ground then they have taken off with the solar panel.
Looking at the pic of the solar panel you linked to the cost of those panels would be about 1500 or more AUD and AUD is fairly close to USD so they would be very attractive to theives.

Now for some of the electrical info.
The ability of a solar panel system to charge your batteries is dependent on
- the area of your solar panels
- the time you have to charge between trips
- how much you need to charge between trips

So for some calculations you can do
the sun puts out about 1 kW of energy for every square meter (m2), this is without any cloud cover and is when the sun is directly over head.

So to work out the energy you can expect if your bike is sitting around for a day somewhere
work out the square meters of solar panel you will have, multiply this by 1kW. This give the amount of energy the solar panels would generate at 12 midday without cloud if they were 100 % efficient.

To compensate for efficiency your panels are likey to be 15% efficient unless you spend a lot of money to get better. so multiply the previous number by 0.15. This is the energy you will get out of your panels at 12 midday with no cloud.

now to work out total energy in kwh you will get for a day. you mulitply by about 5 because you get an equivalent of about 5 hours of full light per day. This varies dependent on location and season but use 5 for a ballpark guess. This give energy out of your panels over 1 full day

Now you want to work out the energy getting to your batteries
so multiply the previous number by the efficiency of your regulator and efficiency charging your battery
so multiply by about 0.9 then 0.9 again and you will get energy going into your batteries over a full day.

example for calcs
you can get maybe 0.5 m2 of area
0.5 * 1kw = 0.5kw
0.5kw * 0.15 = 0.075 kw, (note you are looking at getting 3 by 10W units so that is 0.03kw)
0.075kw * 5h = 0.375 kwh
0.375 kwh * 0.9 * 0.9 = 0.30375 kwh

so you could get AT BEST CASE 0.30375 kwh of energy into your battery for a 0.5 m2 panel

Now compare that to how much energy you are likely to use in a day.

also bare in mind if clouds come over or you park in the shade or a bird messes up your panel (even 1 location) that decresses the overall energy you will get significantly

Either way solar panels will help but i am guessing you will still need to lug that battery around for charging. You might do better off

also to answer one of your questions, no it is not bad to use the battery while charging

for solar panels at 51v and a battery charge level of 48v your probaby a bit close. Would have to look up the specs of the panels but if you get some cloud or anything to reduce the power output the voltage will drop below 48v and you wont be able to charge your batteries.

Possibly a better thing for you would be to change to lithium batteries which are lighter then just be happy carrying them around.

good luck to you, hope i havn't diswadded you too much, still a cool idea and hopefully with this info you will be able to know what your getting into.

07-31-2010, 12:31 AM	#3 (permalink)
saand Wiki Writer Join Date: Jul 2010 Location: Melbourne, Australia Posts: 236 bugler - '91 Mazda 626 90 day: 35.89 mpg (US) Thanks: 15 Thanked 25 Times in 22 Posts	Hi ragez, I like the idea, but hopefully i can let you know about the practical issues of doing this as i have done a lot of work with solar panels in the past. First off, if your bike is out in public your solar panels will get stolen, they are expensive and easy to carry. In australia we have some electronic road signs with solar panels that are about 4 meters up in the air above the sign. I have seen signs where people have hacksawed through a very thick pole to get the sign on the ground then they have taken off with the solar panel. Looking at the pic of the solar panel you linked to the cost of those panels would be about 1500 or more AUD and AUD is fairly close to USD so they would be very attractive to theives. Now for some of the electrical info. The ability of a solar panel system to charge your batteries is dependent on - the area of your solar panels - the time you have to charge between trips - how much you need to charge between trips So for some calculations you can do the sun puts out about 1 kW of energy for every square meter (m2), this is without any cloud cover and is when the sun is directly over head. So to work out the energy you can expect if your bike is sitting around for a day somewhere work out the square meters of solar panel you will have, multiply this by 1kW. This give the amount of energy the solar panels would generate at 12 midday without cloud if they were 100 % efficient. To compensate for efficiency your panels are likey to be 15% efficient unless you spend a lot of money to get better. so multiply the previous number by 0.15. This is the energy you will get out of your panels at 12 midday with no cloud. now to work out total energy in kwh you will get for a day. you mulitply by about 5 because you get an equivalent of about 5 hours of full light per day. This varies dependent on location and season but use 5 for a ballpark guess. This give energy out of your panels over 1 full day Now you want to work out the energy getting to your batteries so multiply the previous number by the efficiency of your regulator and efficiency charging your battery so multiply by about 0.9 then 0.9 again and you will get energy going into your batteries over a full day. example for calcs you can get maybe 0.5 m2 of area 0.5 * 1kw = 0.5kw 0.5kw * 0.15 = 0.075 kw, (note you are looking at getting 3 by 10W units so that is 0.03kw) 0.075kw * 5h = 0.375 kwh 0.375 kwh * 0.9 * 0.9 = 0.30375 kwh so you could get AT BEST CASE 0.30375 kwh of energy into your battery for a 0.5 m2 panel Now compare that to how much energy you are likely to use in a day. also bare in mind if clouds come over or you park in the shade or a bird messes up your panel (even 1 location) that decresses the overall energy you will get significantly Either way solar panels will help but i am guessing you will still need to lug that battery around for charging. You might do better off also to answer one of your questions, no it is not bad to use the battery while charging for solar panels at 51v and a battery charge level of 48v your probaby a bit close. Would have to look up the specs of the panels but if you get some cloud or anything to reduce the power output the voltage will drop below 48v and you wont be able to charge your batteries. Possibly a better thing for you would be to change to lithium batteries which are lighter then just be happy carrying them around. good luck to you, hope i havn't diswadded you too much, still a cool idea and hopefully with this info you will be able to know what your getting into.