1. Power Electronics
Battery
Charging System
Supplying Power to Ink

2. Choosing the Battery Battery Type has to first be chosen
“Batteries and Charge Control for Stand-Alone Photovoltaic Systems : Fundamentals and Applications” , James P. Dunlop

3. Battery Capacity
How much energy is stored in the battery measured in ampere hours
Ah will provide ‘X’ amps of current for ‘Y’ hrs
Ah = Device Wattage (W) * Time to run (hrs)/ Battery Voltage (V)
From previous calculation we assume the total amount of power that we can use is 29,000 Wh/m2 , are prototype is 3’x5’ (0.92m x 1.525m)
Therefore the total power used in a year can be about 40,600Wh
Assuming snowfall for 240hrs a year (59 days for 4hrs) the average amount of power of the device will be 170W (40,600Wh/240h)
Therefore Ah = (170W*4h)/ 12V = 56Ah
To increase battery performance and life the battery should not be consistently discharged below 60% capacity so to be safe the battery capacity should be about 90aH

4. Battery Options Trojan Deep-Cycle AGM Battery can be used
31-AGM could all be options with 5hr rate-capacity of 82Ah
Can be purchased from civicsolar for $270

5. Battery Chargers Controls incoming charge of the battery
AGM batteries are INTOLERANT to overcharge
Standard Solar Chargers or MPPT (Maximum power point tracking) charger
MPPT chargers are much more efficient
Standard chargers can lose between 20-60% of the rated solar panel wattage

6. Choosing a Battery Charger
Charger needs to be able to handle rated watt, voltage, and current rating of PV panel (charging source)
Charging source is still being determined (Full Panel or select number of cells)
For now we can base the charger chose off a SBM solar 150W panel with the following specs:

7. Possible MPPT Charge Controller
Morningstar SunSaver 15 Amp MPPT Solar Charge Controller ($225)
Power used from possible 150W:
Power= PV Panel Power * Efficiency
Power = 150W * 97.5%
Power=146.25
Charge Current = Power/Battery Voltage
Charge Current = W/12V
Charge Current =12.2A
Charging Time = Battery Ah / Charge Current
= 100Ah/ (12.2A)
Charging Time = 8.2 hrs

8. Possible Standard Charge Controller
Morningstar SS-20L 20 Amp PWM Solar Charge Controllers w/LVD ($78)
Power used from possible 150W:
Power = Voltage *Charge Current
Power = 12V *8A
Power = 96W about 66% efficient
Charging Time = Battery Ah / Charge Current
= 100Ah/ (8A)
Charging Time = hrs

9. Ink Power Supply I out Rtrace1 RTotal Rtrace2 Regulating Circuit
Battery
Rtrace3
I out
Rtrace4