How to Calculate Battery Charging Time via Solar Panel

Given:
Kia Sportage 12 Volt Car Battery 60 AH (ampere-hour) capacity
ALLPOWERS solar charger 18 volts, 7.5 watts, 0.4 amperes max
Mono-crystalline silicon panel 
* No-load voltage: 18-23VDC
* Load voltage: 18V
* Output current: 270-410 mAh (0.27A-0.4A)
* Size: 320 x 128 x 4mm / 12.6 * 5.0 * 0.12 inch
* Weight:0.323 kg / 11.4oz

Attention:
Unplug the charger at night, for it needs sunlight to charge devices


FACTORS AFFECTING BATTERY CHARGING TIME
- Battery state: the more the battery is discharged, the longer it takes to charge
- Battery rating: the more the battery AH capacity, the longer the charging time
- Charging rate: this is the Ampere rating of the charger (output current)
- Sun intensity: the clearer, brighter sky, the more voltage and more amperes from the sun
- Sun hours: amount of hours of sunlight during the day of the geographic location
- Charger efficiency: for mono-crystalline solar chargers, 85-90%
- Temperature: Colder temperatures means longer charging time


Assumptions:
Sun hours: 4 hours, average cloudy day
Location coordinates: Latitude = 48 N, Longitude = 123 W
Charging rate: average output current = (0.27A + 0.4A)/2 = 0.33 amps
Charger efficiency: 85%
Battery state of charge: 50%


12 Volt Battery State of Charge:
 Volts -- % Charged
 12.6  ---- 100 %
 12.5  ---- 90 %
 12.4  ---- 80 %
 12.3  ---- 70 %
 12.2  ---- 60 %
 12.0  ---- 50 %
 11.9  ---- 40 %
 11.8  ---- 30 %
 11.6  ---- 20 %
 11.3  ---- 10 %
 10.5  ---- 0 %



CHARGE TIME CALCULATION

Step 1: Calculate Average Daily Ampere-Hour of Charger

Ave Daily Ah =  Ave Charging rate x Sun hours x Charger efficiency

Ave Daily Ah = 0.33 Amps x ( 4 hours/day ) x 0.85

Ave Daily Ah = 1 Ah/day



Step 2: Calculate Battery Capacity Energy Top Up Amount

Battery Top Up Amount = Battery Capacity x State of Charge

Battery Top Up Amount = 60 Ah x 50%

Battery Top Up Amount = 30 Ah



Step 3: Calculate Battery Charging Time

Battery Charging Time = Battery Top Up Amount/Ave Daily Ah

Battery Charging Time = 30 Ah/1 Ah per day

Battery Charging Time = 30 days  (1 month)