Off-Grid Automatic Generator Startup

Assuming this is an pure off grid system (no utility power at all)?

Your first task it to make sure your batteries are charged correctly... More or less, you want to cycle them 50% to 80% state of charge (with the genset) and ideally get to >90% state of charge at least once per week. This last charging to >90% is going to be (usually) fuel inefficient (not much charging current, but ~4+ hours of running the genset to get the batteries full). You can save fuel/money if you run the "absorb" charging at the same time as you run other loads (washer, well pumping, shop, electric cooking appliances).

And to do this, you need a good volt meter (suggest DC current clamp DMM like this inexpensive one from Sears) and a good hydrometer.

Next--What are your expectations for this off grid power system? Are you living there full time off grid, or is this a 3 season use, and shut down during the winter? Are you concerned about fuel+genset costs? Where is the system installed (nearest major city)?

In general, for an off grid solar system, we suggest 5% to 13% rate of charge to keep the battery bank happy and not need to run the genset every day (not even talking about loads yet)--And 10% or higher rate of charge for a full time off grid system. You have a pretty good size battery bank (24 volts @ 428 Amp*Hour). So--The solar array should be something like:

• 29 volts charging * 428 AH battery * 1/0.77 panel+controller deratings * 0.05 rate of charge = 806 Watt array minimum
  
• 29 volts charging * 428 AH battery * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,612 Watt array nominal
  
• 29 volts charging * 428 AH battery * 1/0.77 panel+controller deratings * 0.13 rate of charge = 2,096 Watt array "cost effective" maximum
  

And if you assume 2 days of stored energy (bad weather) and 50% maximum discharge (for longer life), your battery bank would be good for:

• 24 volts * 428 AH * 0.85 AC inverter eff * 1/2 days storage * 0.50 maximum discharge = 2,183 Watt*Hours per day
  

If you are up in the Ontario Canada region--You do not get much sun during the winter:
http://solarelectricityhandbook.com/solar-irradiance.html

Brampton
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 46° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
2.71	3.50	4.04	4.50	4.75	5.12
Jul	Aug	Sep	Oct	Nov	Dec
5.24	4.98	4.58	3.68	2.47	2.24

Toss the bottom three months (assume you must use genset, or system is not used in winter):

• 1,612 Watt array * 0.52 off grid system eff * 3.5 hours a day (avg February) = 2,934 Watt*Hour per day (typical February day)
  

Your present 400 Watt array is not much more than able to "float" the battery bank for storage.

Anyway--My first guesses/suggestions.

-Bill