Recommendations on category G2

Test procedure for category G2:

NFC58-510
See Testprocedures and ref. [3])

Selection of battery and charge controller for category G2:

• It is essential to use a charge controller that protects the battery from overcharging. The recommended end-of-charge-settings of the controller depend on the type of battery and the category of battery usage. The recommended batteries are given below, in order of preference, together with the recommended voltage settings for the charge controllers at charging.

  Recommended battery in order of preference	Controller settings (in V/cell at 25°C)	maint. months
  Flooded, Industrial, thick flat plates, large electrolyte reservoir	Charge: 2.4 V ( 2h / day) Float 2.3 V equalisation: 2.55 V (5h / 2 weeks)	3
  VRLA, Industrial, thick flat plates	Charge: 2.4 V (2 h / day) Float 2.3 V equalisation: 2.5 V (5h / 2 weeks)	12

• It is essential to use a charge controller that protects the battery from deep discharging. The control algorithm of the charge controller can be based on a SoC calculation or on voltage settings. The recommended end-of-discharge-settings of the controller are the following:
  • Low voltage Disconnect, for discharge current I10: 1.80 to 1.85 V/cell
  • Low voltage Disconnect, for discharge current 10% of I10: 1.95 to 2.0 V/cell
• If the battery will be operated outside the temperature range of 20-30 degrees it is preferable to use a charge controller that compensates for the effect of the battery temperature. It will typically adjust settings to ensure that charge and discharge cycles are modified based on temperature and voltage or state of charge. A separate battery temperature sensor should be used.
• It is preferable to use a charge controller with separate voltage sense terminals.

More specific recommendations for category G2:

The main battery issue of category G2 is the range of low charge factor (levels 1, 2 and 3). For VRLA batteries systems with charge factor levels 1 or 2 and for flooded batteries with charge factor levels 1 to 3 the main improvement is the increase of the charge factor. To achieve this the following recommendation is given:

1. Apply the recommended values for the setpoints of the charge controller in the table above.

   If this first recommendation does not improve the charge factor, consider the following recommendations:

2. Use a charge controller with a low self-consumption and with a high efficiency.
3. Reduce the load (e.g. by replacing appliances by more efficient ones)
4. Increase the electricity generation of the renewable energy sources
5. Use (or increase the use of) a back-up generator. The most efficient way is to use the back-up generator starting early in the morning and, once the threshold voltage of the battery is reached and the power output of the back-up generator is beginning to fall, continue charging the battery by means of the renewable energy source.
6. Replace the battery with a battery of lower capacity if this is possible. Due to the low charge factor, the capacity of the battery is likely to decrease quickly and therefore a battery with a lower nominal capacity but proper charge factor is likely to offer a better long-term security of supply.