Solar Panel / Battery Sizing Questions

Re: Solar Panel / Battery Sizing Questions

Ameerind,

Sizing the solar system really depends on how much power you need / loads you are planning on running.

500 watts for 1 hour, assuming 5 hours of sun "full sun" (reasonably sunny summer day), and 0.52 overall system efficiency:

• 500 watts * 1 hour * 1/5 hours of sun * 1/0.52 = 192 watts of solar panel

Same setup but running 500 watts for 10 hours a day:

• 500 watts * 10 hour * 1/5 hours of sun * 1/0.52 = 1,920 watts of solar panel

Without knowing much much and how long you will be running the power--it is impossible to give you any accurate estimate.

If you know how much power per day/month you use/need on average (watt*hours or kWHrs) and where the systems will be used (Mumbai India?)--it would be very helpful.

Just to give you an idea--Using the PV Watts Website for Mumbai India, 1 kWatt (1,000 watts) of solar panels running an off-grid system assuming 0.52 derating factor and fixed array--output by month:

"Station Identification"
"City:","Bombay"
"State:","IND"
"Lat (deg N):", 19.12
"Long (deg W):", 72.85
"Elev (m): ", 14
"Weather Data:","IWEC"

"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 19.1"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 1.8 rupee/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (rupee)"
1, 5.43, 75, 1.38
2, 6.10, 76, 1.40
3, 6.62, 91, 1.67
4, 6.84, 90, 1.66
5, 6.20, 85, 1.56
6, 4.52, 60, 1.10
7, 3.57, 49, 0.90
8, 3.71, 51, 0.94
9, 4.20, 56, 1.03
10, 5.67, 75, 1.38
11, 5.64, 74, 1.36
12, 5.22, 73, 1.34
"Year", 5.30, 855, 15.73

The third column is kWhours per Month per 1kW (1,000 Watts) of solar panels. Minimum/Maximum is 51/91 kWhrs of useful 230 VAC power per month or per day:

• 51 kWH per month * 1/30 days per month = 1.7 kWHrs per day = 1,700 Watt*Hours per day
• 91 kWH per month * 1/30 days per month = 3.0 kWHrs per day = 3,000 Watt*Hours per day

Note, the above are estimates based on the years of 1982-1999 of average available sunlight (including weather).

-Bill

Re: Solar Panel / Battery Sizing Questions

The two major types of solar charge controllers are PWM and MPPT.

PWM: much cheaper, not quite as efficient. Not a bad choice for less than 300 watts of solar panels.

MPPT: more expensive, as efficient as you are going to get. Good for cold weather (10-15% more power than PWM). Has advantage that you can use high voltage panels (Vmp~100 VDC) to send power longer distances from the solar array to the battery/controller shed (instead of trying to send 12 volt or 24 volt power/current longer distances). If you live in very hot region--solar panel Vmp (voltage maximum power) falls with high temperatures. Hot days depress battery charging voltage. Good choice for >400 watts of solar panels--but still expensive.

To read about solar charge controllers:

All About Charge Controllers
Read this page about power tracking controllers

MorningStar makes very good PWM and MPPT controllers. You can read about the various models here. Xantrex too. If you can choose a controller with a Remote Battery Temperature Sensor option--Take the option--Batteries will be charged slightly faster and too a fuller charge. If you are using sealed/AGM batteries, they are sensitive to over charging (batteries need slightly slower voltage the warmer they get).

In the end--you are probably going to be limited to products that are available (and price competitive) in your region.

-Bill