# solar panel charging question



## Technologic (Jul 20, 2008)

subevo said:


> this maybe a dumb quetion. but can you charge each battery in a string with a car 12volt charger.for example my string is 72 volts altogether made up of 6 12volt batteries.can i charge each battery without having to disconnect the cables making up the string.the reason is i already have a proper inboard charger but to save recharge costs i also have solar panels that charge up a battery bank which i convert to 240ac and connect my car battery charger.ive done this to each battery before with each one disconnected (which is time consuming).but can i do it with the cables still on.or do i need to disconnect each battery and charge it on its own.


You can charge with a solar panel as a string, you just need the voltage necessary for charging to be outputed... this can be done by a DC-DC converter or other such tool.

You can convert to AC as well like you suggested...

Edit: Blocher is correct as well about charging each in series...


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## bblocher (Jul 30, 2008)

Yes you can charge an individual 12v battery while it is still in series. You can not charge all the batteries in the string with one 12v charger.

You can buy multiple chargers (one for each battery) and charge them this way. It's less efficient but does act as a charge time balancer of the batteries.


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## subevo (Aug 23, 2008)

thanks guys.i forgot that other people have separate chargers for each battery and therefore it must be ok to attach a single charger and move to each battery in turn with all cables still connected.


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## EV59RAG (Oct 6, 2008)

subevo said:


> thanks guys.i forgot that other people have separate chargers for each battery and therefore it must be ok to attach a single charger and move to each battery in turn with all cables still connected.


If i understand this correctly then you only have one charger and manually move it if one is done. Time consuming? slow? and you have to watch it regularly to make sure to move it to the next battery..

But yes, it can be done. and you dont have to disconnect the cables of the series pack.


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## engineer_Bill (Jun 24, 2008)

Shouldn't be a problem. But there is one possible catch. Be sure you don't have any + or minus grounded. The pack shouldn't be, the charger may be,(less likely from a stand-alone solar than a wall outlet). Inverting the output from the solar to 220Ac then back to 12volts sounds kinda round-about. There are 12Volt and other DC-dc charge controllers that will go from a high voltage DC to a lower voltage directly, most solar power companies have them for common voltages I.E. 48Volts Dc to 12Volts Dc. That have charge and float settings for battery recharge.


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## JimC (Jun 13, 2009)

Subevo,

Bill has given you the only sensible option. Charging batteries to power an inverter to charge other batteries is highly inefficient. Not only that but you are increasing the running costs of the EV as you are cycling 2 batteries for every 1 battery that you are actually using and as batteries have a finite life they do need to be replaced some time.

The cable run length and cable diameter between the solar PV cells and the batteries should be considered for power loss. I cannot get my quad into my back garden which is where I can fit solar PV cells so I am looking into quick release connectors for the battery pack and I will have a pack on charge ready to swap with the depleted pack.

Further to what Bill has said I think that since the solar PV is being used to charge high capacity batteries it should be possible to do without the battery controller. Having said that I have to admit that I am no professional on these matters but it should be easy enough to research.

Best
JimC


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## Guest (Jun 14, 2009)

The argument of charging a pack of batteries to then use to charge another set of batteries my in fact be the only option available for solar use. Now if your solar panels are at your place of employment then you may just charge off the panels. Most here work during the day when PV is king. Problem is that the EV is at work and the PV panels are at home. I'd need to do the same thing. Charge a bank of batteries then run an inverter to charge another pack. Even if it is inefficient it may be the best way to use the PV. For us we don't have to worry about that because we are set up with a grid tie system. What we put in during the day is what we can extract out with out cost at night. 

So lets say he has an off grid system but wants to use solar to charge with. What would he need to do to do it as efficient as possible? 

Pete


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## engineer_Bill (Jun 24, 2008)

I would use a solar setup that is 110% to 150% higher voltage. I.e. if your car is a 96Volt use a 150Volt solar system, (you may have to use several in series). Then purchase a Dc charge controller, (again to get the correct voltage without custom electronics break up the cars pack in to sections and buy an appropriate controller for each section)


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## JimC (Jun 13, 2009)

Selecting your PV panels:
They come in 12 or 24VDC as standard. A 12VDC panel is designed to charge a 12V battery as it's actual Vout is typically 16 to 18VDC.
Output power ranges from 10W to about 200W per panel so you will need to have several panels in series to achieve the Pout required.

Selecting your charging controller.
A standard charge controller uses PWM.
A newer (and more expensive) option is MPPT ( Maximum Power Point Tracking.) A standard 12V battery requires an input V of @ 14 V when on charge. With a PWM controller excess voltage is basically ignored and lost in the charging process. An MPPT controller effectively turns over voltage into more current for charging the battery. Additionally the MPPT is intrinsically better when using solar arrays of say 24VDC or 48VDC to charge 12V batteries. At higher Voltages cable loss is reduced.

Siting your solar panel.
Everyone know that PV panels do not need direct sun to produce some power albeit at a much reduced level. What is not so well known is that if 5% of the panel is in shade and 95% in direct sunlight the panel operates as if it was 100% in shade, so your siting of the panels need not only to take into account maximum hours of direct sun light but also avoid a location where say a water tower produces a shadow which will slowly traverse the panel. There is a new type of slar panel which avoids this shadow effect but I forget its' name and I dont know if it is in the market yet.

Hope this helps.
Best JimC


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## dtbaker (Jan 5, 2008)

JimC said:


> What is not so well known is that if 5% of the panel is in shade and 95% in direct sunlight the panel operates as if it was 100% in shade,... I dont know if it is in the market yet.


almost all the 'new' panels can handle spots of shade... a good panel now kicks out 200 to 210 watts with full sun.

Just to further muddy the water... In many states you can get good tax incentives installing PV to your home, but none if you directly charge a car. If you grid-tie, then you may ALSO get some buy-back from your local utility... So financially a grid-tied system may be best.

One thing I am exploring with my wife's employer is to build a solar covered carport at work that we would basically 'own', or lease it to the company or something if it is grid-tied. Basically I am angling for a reserved parking spot so that we can offset charging the EV at work...


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## Bowser330 (Jun 15, 2008)

They have now reached 40% eff. for solar panels...cant wait for those to be sold to the public...

If 1 sqr meter of sunlight = 1kW of energy...and you had 3 square meters (on your car or at home/office) and you had 8 hours of solid sunlight during the day, you would have...

8hrs *40%*1Kw*3 sqr ft = 9.6kWH of energy..

If your EV averages 333WH/mile...10kwh = 30 miles

30 miles of charge from a day of sunlight...more or less....


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## engineer_Bill (Jun 24, 2008)

Whether or not a panel can handle shade without losing all power is dependant on whther it has bypass diodes installed that allow the power to go around the "dead" cell. Some cell manufacturers make the diode inside so it doesn't need them, others you just add diodes in parallel when you put together the panel. Most major panels have them now. Good luck getting the high efficiency panels. I have contacted several suppliers and they tell me the panels are mostly vaporware. If anyone has gotten their hands actually on a 40% panel, post it to the board! OR even a set of the 200watt'ers.


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## dtbaker (Jan 5, 2008)

engineer_Bill said:


> ....OR even a set of the 200watt'ers.


200-210 is common these days (SunPower, Sanyo, Schott) , they are about 17% efficient. http://envirokarma.org/PV/


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## Guest (Jun 20, 2009)

Ours are Kyocera 180 watt panels. We have 39 of the suckers.  Yesterday we pumped out 38 KWH and we usually get about 44 KWH per day in the summer. It was overcast and we did not get as much. 


Pete


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## dtbaker (Jan 5, 2008)

gottdi said:


> Ours are Kyocera 180 watt panels. We have 39 of the suckers.


wow, that is a HUGE system!

I have a 5kW system (24x210watt) that kicks out between 25-35kWhr per day depending on season, clouds, etc. This zeroes out my house use AND charging my EV.... and I get a check for about $100 from the utility company because they buy my gross production for their renewable energy credits. I wish I had done it sooner!


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## Guest (Jun 20, 2009)

Do you have gas appliances? We do not. We are 100% electric here and we also have to power a 5 hp well pump as well as all our electric needs. We have a 2000 sq ft home and 2 1/2 acres to water. We are almost 100% covered with our system. Sad to say but it does not cover 100% of our needs all the time. I am starting to build onto that system to make it even larger to cover all our needs including the charging requirements of our EV. Right now we are in the Black. 

Pete 

PS. Most folks that have solar also have gas and that is why they can have a much smaller system to cover the electrical needs. Most also don't have a 5 hp pump to power for full property watering.


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## dtbaker (Jan 5, 2008)

we do have gas stove and water heaters, and no well pump. I do have one room with electric heat which sucks a lot of juice in the winter, and a hot tub which is pretty good, AND a second frig in the garage that I keep trying to give up, but its too handy to store BEER.


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## engineer_Bill (Jun 24, 2008)

I stand corrected, but the solar panel supplier I called to order some said he had none in stock 6 months of backorder and no lead time for 200watt or better panels. If you know a supplier that has some on the shelf for a reasonable price post it.


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## dtbaker (Jan 5, 2008)

engineer_Bill said:


> If you know a supplier that has some on the shelf for a reasonable price post it.


I do know that they are sometimes hard to get... The guys that installed mine seem to have a pretty good distributor and usually don't have to wait long, but I dunno if they can arrange a drop-ship to anywhere else. Worth a call I guess. Try Randy or Claudia at Positive Energy (505) 424 -1112 
[email protected]


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