buying a complete system

Re: buying a complete system

Welcome to the forum Robert.

I am guessing you are out of Beirut or so...

Usually, we like to start with your loads. In general, off grid solar power is pretty expensive to buy and to maintain (new batteries every 4-8 years, new electronics every 10+ years, etc.)... So you do not want to build a system that is too large--And you do not want to build a system that is too small and not support your needs either.

Looking at your loads--That is a pretty large off grid power system. 28,000 WH per day, with 20,000 Watts being AC and 4,300 WH being the refrigerator.

The refrigerator numbers may be high... In the US, you can get a pretty large refrigerator/freezer down to near 1,200 WH per day (although, in hot weather, the power usage can double). Air conditioning weather appears to be in the May through October range.

Lets say you use 1/2 the power during the day, and 1/2 the power at night (and during bad weather, only 1/2 the power in winter).

So, lets try sizing the battery bank for 2 days of storage, 50% maximum discharge and to only carry 14,000 WH per day:

14,000 WH per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt battery bank = 1,373 AH @ 48 volt battery bank

I see you have GEL type batteries called out... In general (at least for the US market), GEL batteries are not good for solar/off grid power. We need to charge the batteries very quickly, and GEL batteries (again in the US) are only rated for 5% or 1/20 Hour charge rating--If you charge them faster, the gas and GEL develops bubbles which kills the battery.

For a full time off grid system with lots of day time loads, I would be suggesting something like a 10% to 13% or 1/8 hour rate of charge:

1,373 AH * 59 volts charging * 1/0.77 panel+charge controller derating * 0.13 rate of charge = 13,677 Watt array

And if you want to collect power in the summer months to run everything--We need to get the average sun for your location. Using a fixed array and the solarelectrichandbook:

[h=3]Beirut
Average Solar Insolation figures[/h] Measured in kWh/m²/day onto a solar panel set at a 56° angle from vertical:
(For best year-round performance)

Jan
Feb
Mar
Apr
May
Jun


3.81

4.48

5.50

6.22

6.80

7.00



Jul
Aug
Sep
Oct
Nov
Dec


6.94

6.95

6.74

5.88

4.47

3.58



So that would give us October at 5.88 hours of "minimum average" noon time equivalent sun for "summer" months:

28,000 WH * 1/0.52 off grid end to end efficiency * 1/5.88 hours = 9,158 Watt array (October is "break even" month)

So, somewhere between 9,158 to 13,677 Watt array would be "optimal" (if you really plan on using so much AC+refrigerator, then the larger array would be easier to maintain the battery bank).

I don't see any solar charge controllers listed, but if you use an 80 Amp MPPT type charge controller, then for a 13,677 Watt array, you would need:

13,677 Watt array * 0.77 derating * 1/59 volt charging = 178.5 Amps typical maximum charging current
178.5 amps / 80 amp charge controller = 2.2 charge controller ~ 3 charge controllers for that size array

Anyway, that is a start... And some guesses on my side. If you did not need the Air Conditioning (or did not need 20 kWH of AC) and had a more efficient refrigerator, the system would be dramatically smaller and less costly.

Questions/corrections to my guesses?

-Bill