how to calculate pv solar

Re: how to calculate pv solar

First we need to figure out how much solar energy you have in your area... For Malaysia, I will use something like this for an estimate here:

Malaysia lies entirely in the equatorial region. The tropical environment has been characterized by heavy rainfall, constantly high temperature and relative humidity, The annual average daily solar irradiation for Malaysia were from 4.21 kWh/m2 to 5.56 kWh/m2. The highest solar radiation was estimated at 6.8 kWh/m2 in August and November while the lowest was 0.61 kWh/m2 in December. The Northern region and a few places in East Malaysia have the highest potential for solar energy application due to its high solar radiation throughout the year.

The average solar radiation is around 1,000 kWH/m^2 -- so we see that you have an average of 4.2-5.6 "Hours of Noontime Sun" per day in your region (try to get actual measurements for your area--local weather patterns are greatly affected by surrounding terrain and marine layer).

We generally assume a well designed/configured off-grid system with flooded cell batteries is around 0.52 efficient (yes--end to end efficiency from solar panel rating to available AC power at the outlet). And you will never be able to use 100% of the power every day--so the system should be a bit larger than you need and/or plan on using a backup generator.

And in any case--stretches of bad weather will kill solar production--so a backup generator (or just not using power) are the only options for 12 month a year operation.

Normally, we recommend 1. conservation (almost always cheaper to conserve than to generate power) and 2. know your daily power needs to avoid over/under designing your system.

So, lets say that you want 3 kWH per day worth of electricity and assume worst case average sun is 3 hours per day. The amount of solar power would be:

• 3,000 WH per day * 1/3 hours of sun per day * 1/0.52 derating = 1,923 watts of solar panels

For the battery bank, we start with planning for 3 days of no-sun and 50% maximum discharge:

• 3,000 WH per day * 3 days * 1/0.50 max discharge * 1/12v battery bank = 1,500 AH battery bank (at 20 Hour Rate)

For a 12 volt battery bank, I would suggest that 1,200 watts peak continuous loads is about the maximum... You get very high current and have very low voltage drop (11.5 volts minimum battery, inverter cutout is 10.5 volts, allows 1.0 volt drop for wiring/fuses).

• 1,200 watts * 1/0.80 inverter eff * 1/10.5 volt batt * 1.25 wiring safety factor = 179 amps

So you need very heavy/short wire to run a 1,200 watt inverter (ignoring surge current for starting loads, etc.).

Anyway--that is where I would start... Questions?

-Bill