Solar Electric Cells

[David HK]

I have left it a bit late in life to go full blown into RE, but one thing I would like to do while time is left is to set up a 12 volt battery system for charging by solar electric cells.

I am able to source individual cells on a piece by piece basis for home assembly. The PV cell paper rating is 2 volts - 200 milliamps.

Could anyone tell me the optimum number of cells to wire in series, and likewise in parallel, so that I have around 17 volts available for battery charging. Any other advice people can give me would be very welcome indeed.

Dave HK

PS My solar hot water system is working a treat and around 3 to 4 pm on most afternoons the water temperature is around 83 degrees C.

[TomW]

Dave;

This is an easy one.

Cells in series the voltage will add for each cell you add and current will be the same as 1 cell. so 6 cells in series would be 12 volts at 200 ma.[2.4 watts]

Cells in parallel the current [amps] adds and voltage would be the voltage of one cell. So 6 cells in parallel would be 2 volts at 1200 ma [1.2 amps]. [the same 2.4 watts]

You can combine cells in multiples of series / parallel strings to get your target voltage / amperage.

12 volt lead acid batteries actually need nearer 15 volts to be fully charged and my Siemens panels open voltage is 20 or 21 volts [no load] so you need to investigate that too.

Cheers.

TomW

[veewee77]

On a side note, recheck the numbers on those cells.  Any single cell I have ever seen is .5 volts (1/2 volt).  You said those are 2 volts. . . that is probably a small panel with 4 cells on it.

Doug

[David HK]

To further expand on my first post these are my thoughts:-

String No 1   8 cells in series @ 2 volts and 200millamps per cell = 16 volts and 200 milliamps.

Add on strings 2, 3, 4 and 5 which makes up 40 cells. These are wired in series as per string one.

Then, parallel all strings to make 16 volts @ 16 watts or 1.2 amps. the table below is a further illustration:-

Volts    Milliamps    Watts    Total watts    Amps    No of cells

16    200             3.2                       8

+                   

16    200             3.2        6.4            400ma       16

+                   

16    200             3.2        9.6            600ma       24

+                   

16    200             3.2        12.8    800ma       32

+                   

16    200             3.2        16            1.2 amps   40

Are my calulations correct or am I up a creek without a paddle?

Many thanks for any comments.

David HK