off grid system for shop and home

When going off grid solar, I always suggest conservation first. Lots of insulation, double pane windows, possibly heat pump HVAC, etc...

A full off grid system, very roughly, costs around $1-$2+ per kWH for full time off grid (all the hardware costs, battery replacement every 5-7 years of so for "average" FLA batteries, etc.). One person here is probably down to $0.50 per kWH through finding good prices, self install, and carefully managing his loads (even some AC in summer)...

Anyway... I will go through the quick math for a "nominal" system design (Lead Acid batteries, our common d design rules).

Normally I would be suggesting a 100-300 kWH per month system as an aiming point. But I will use your 1,800 kWH per month. Assuming 2 days of storage (bad weather support) and 50% planned max discharge (for long battery life).

• 1,800 kWH per month / 30 days per month = 60 kWH per day = 60,000 WH per day 
• 60,000 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max planned discharge * 1/48 volt bank = 5,882 AH @ 48 volt battery bank

Next charging the bank... Two calculations. First based on AH*Voltage of battery bank. 5% minimum rate of charge... 10-13% "nominal" full time off grid charging. Second based on your daily loads and amount of sun... First:

• 5,882 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 22,153 Watt array minimum (summer/weekends)
• 5,882 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 44,306 Watt array nominal
• 5,882 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 57,598 Watt array "cost effective" maximum
  

And based on daily energy usage and hours of sun per day for fixed array for Columbia MO:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Columbia
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 51° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.36	3.67	4.49	4.91	5.03	5.28
Jul	Aug	Sep	Oct	Nov	Dec
5.48	5.34	5.17	4.48	3.35	3.11

Your energy usage varies by season (A/C, Heating, etc.)... Using December as "break even month":

• 60,000 WH per day * 1/0.52 off grid AC system eff * 1/3.11 hours of sun per day (December) = 37,101 WH array December break even

If you wanted to avoid genset usage (and fuel costs), you should plan on using only 50-65% of your predicted harvest (allow for more than a couple days of bad weather, occasional "extra loads"):

• 37,101 Watt array * 1/0.65 fudge factor = 57,059 Watt array for December w/ fudge factor

An AC inverter sized for a 5,882 AH @ 48 volt battery bank would be around 29 kWatts (nice mid-size) to 58 kWatts (max for FLA battery bank of that capacity).

Lots of room for adjustments based on what your "real" power needs (by season) and if you can do some significant energy conservation.

You can plug in your values and do some what ifs and paper designs and see what works for you.

Your thoughts?

-Bill