Recommendations on category G3

Test procedure for category G3:

IEC61427 plus Qualibat (Combined test procedure, ageing ratio 1:0.3)
See Testprocedures and ref. [3]).
As long as no results are available for this combined test procedure, select the battery that has the best results (longest life time) for the two separate test procedures.

Selection of battery and charge controller for category G3:

• 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)	1
  Flooded, Industrial, thick flat plates, Automatic water topping	Charge: 2.4 V (2h / day) Float 2.3 V equalisation: 2.55 V (5h / 2 weeks)	6

• 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:
• 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 G3:

The main battery issue of category G3 is the high charge factor. For flooded batteries the optimum is about 120% (intensity level 4) and for VRLA batteries about 110% (intensity level 3). For flooded batteries with a charge factor intensity of 5 and VRLA batteries with a charge factor intensity of 4 or 5, measures should be taken to reduce the charge factor such as:

1. Apply the recommended values for the setpoints of the charge controller in the table above.
2. Optimise the orientation (tilt and azimuth) of the PV-module for the period of low irradiance (e.g winter).
3. Check whether the capacity of the renewable energy generator is not unnecessarily high for the required loss-of load probability. This can also lead to reduced investment costs.
4. 4. If a backup-generator is installed, consider reducing its operating time and making sure that the generator is not operated in the morning to increase the state of charge of the battery. PV production during the day will then likely lead to this considerable overcharging.