Puerto Rico earth quakes

Normally, a 1,200 to 1,500 Watt AC inverter (good quality) should start the "average" refrigerator (standard compressor). If they have a modern "inverter-compressor" type fridge, it could be smaller (perhaps as low as 600-1,000 Watt inverter).

The problem with solar for emergency power systems, is you need just about as large as system to run a refrigerator for 2 weeks as you do for 9+ months. And a 12 volt system is just on the bottom edge of being able to start a standard refrigerator.

For the sake of discussion, say an 1,800 Watt AC inverter... Both a 12 volt and a 24 volt system design. Since this is for "emergency use", instead of the 2 days of storage and 50% max discharge, lets just use 1 day and 50% discharge (2x daily loads) and plan on using a genset much more when needed. And that this is for a short term (weeks, possibly a month or so, assuming that this may damage/ruin the battery bank in a few years, if not months). If this was for a long term full off grid system, I certainly would be suggesting a 4x daily use battery bank).

Looking at sizing the battery bank based on energy storage... Say 2 kW per day:

• 2,000 Watt*Hours per day * 1/0.85 AC inverter eff * 1 day storage * 1/0.50 max discharge * 1/12 volt battery = 392 AH @ 12 volt battery bank
• 2,000 Watt*Hours per day * 1/0.85 AC inverter eff * 1 day storage * 1/0.50 max discharge * 1/24 volt battery = 196 AH @ 24 volt battery bank

Note, both above would need 4x 6 volt @ 200 AH batteries (either 2 series * 2 parallel for 12 volt @ 400 AH; or 4 series * 1 parallel for 24 volts @ 200 AH). Same amount of storage energy for each...

If you assume the worst case starting surge is ~1,200 Watts, then the minimum battery bank would be:

• 1,200 Watts * 100 AH / 250 Watt surge for [12 volt] FLA battery = 480 AH @ 12 volt flooded cell lead acid battery bank minimum
• 1,200 Watts * 100 AH / 500 Watt surge for [24 volt] FLA battery = 240 AH @ 24 volt FLAA battery bank minimum
  

So... based on starting surge, a 4x 6 volt @ 200 AH battery bank is just on the minimum side of "reliably" starting a fridge compressor (i.e., 12 volts @ 400 AH or 24 volt @ 200 AH). Vs 480/240 AH banks minimum... These are very rough rules of thumbs, and they may want to try the "minimum" bank to start... Or use more batteries or larger AH rated batteries to up the bank size a bit. Remember that a full time off grid bank would probably be 4x (2x larger than above) for a more "optimum" system design.

Then there is sizing the bank based on state of charge... 5% to 13% is typical. 5% can be used for emergency/weekend system usage (with more genset runtime when needed)... 10%+ is recommended for full time, weeks at a time, rate of charge (note, panel ratings are "the same" for 480AH@12v or 240AH@24v systems--Same amount of energy storage battery banks in either one):

• 480 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 452 Watt array minimum
• 480 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 904 Watt array nominal
• 480 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,175 Watt array "typical" cost effective maximum

Then there is sizing the system based on the amount of energy usage and hours of sun per day. Since earthquakes can occur in "any weather/time of year", pick December at 4.95 hours of sun per day:

• 2,000 WH per day * 1/0.52 off grid system eff * 1/4.95 hours of sun per day = 777 Watt array "December" break even month

So--I would be suggesting a 904 Watt array minimum, and north of 1,175 Watt array would not be bad (more solar energy and less genset usage).

Anyway... Some numbers to think about.

-Bill