calculation of solar system

robocop

Hi Informing for a friend

Calculate he is using about 38000 watth hour day with aircon included.

How can I calculate how many and what wattage panels to use and batteries .

Think a 10k kva split info is ok but need how to calculate  about panels and batteries.

Thanking you in advance 
Bob
 
 

BB.

Same island off Venezuela coast? (Curacao, Willemstad)

Bill

robocop

Yes Bill yes same island think 6 hours per day good sunlight  Can you give me an idea about what needed.
appreciate 
Bob

BB.

My first comment is to look at conservation... Is the home as energy efficient as practical? Lots of insulation, using energy efficient mini-split(s) (heat pump for heating and cooling if needed). It is almost always cheaper to conserve energy than to generate it.

This is just a generic set of calculations based on our rules of thumbs using Lead Acid Batteries... At this point, especially for tropical locations, it may make sense to use a slightly smaller LiFePO4 set of batteries... But that is for another post.

Sizing the battery bank. The typical design is for 2 days of "no sun" (bad weather) and 50% planned discharge (for longer battery life--And it does give a 3rd day of backup power if needed):

• 38,000 WH per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.50 max planned discharge * 1/48 volt battery bank = 3,725 AH battery bank @ 48 volts (that is not a small battery bank)

Next, the amount of solar panels. Two calculations, one based on minimum rate of charge and second based on hours of sun per day and daily loads (by season).

For an off grid power system, 5% rate of charge (based on battery bank capacity) can be used for emergency/backup power. 10% to 13% is typically the minimum suggested for full time off grid power. Can go to 20-25% rate of charge for areas that may have poor sun or poor winter sun...

• 3,725 AH battery bank * 58 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 14,029 Watt array minimum
• 3,725 AH battery bank * 58 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 28,058 Watt array nominal
• 3,725 AH battery bank * 58 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 36,476 Watt array typical cost effective maximum

And there is sizing based on the daily loads and hours of sun per day. Assuming fixed array, tilted to latitude of 12 degrees, facing south (south of equator) for Curacao, Willemstad:
https://pvwatts.nrel.gov/pvwatts.php

RESULTS

Print Results

Month	Solar Radiation ( kWh / m2 / day )	AC Energy ( kWh per month for a 28,000 Watt array )
January	5.83	2,372
February	6.08	2,223
March	6.19	2,489
April	5.89	2,288
May	5.83	2,316
June	5.84	2,269
July	5.88	2,352
August	6.26	2,508
September	6.33	2,443
October	5.78	2,311
November	5.46	2,125
December	5.48	2,200
Annual	5.90	27,896

Sizing array for 38,000 WH per day, and "worst" month of November (5.46 Hours of sun per day):

• 38,00 WH per day * 1/0.52 off grid AC system eff * 1/5.46 hours of sun per day (November break even) = 13,384 Watt array Nov Break even

And typically, for off grid solar, should plan for using 50% to 65% of daily predicted harvest (some clouds come by, more AC power needed for tools, hot weather A/C, etc.):

• 13,384 Watt array / 0.65 solar fudge factor = 20,591 Watt array suggested for minimum genset usage

Looking at somewhere around 28,058 Watt array (10% minimum rate of charge for battery bank) or even less (20,591 Watt array) because this is a very sunny region.

That is the basics... Could probably get away with a smaller Li Ion battery bank (maybe 60% of Lead Acid?) and less than 20,591 Watt array (Li Ion is more efficient and much better charge acceptance vs Lead Acid).

-Bill