NABCEP Energy Storage 4

Question 1

An off-grid home requires a battery bank operating at 48V nominal with a 20 kWh usable capacity. How many 200Ah, 6V batteries are required at 50% DoD?

Accepted Answer

16 batteries

Answer

Total capacity needed = 20 kWh / 0.5 DoD = 40 kWh; batteries per string = 48V / 6V = 8; each string = 8 × 200Ah × 48V / 1000 = 76.8 kWh; strings needed = 40/76.8 ≈ 1 string insufficient; recalculate: 8 batteries in series gives 48V at 200Ah = 9.6 kWh per string, so 40/9.6 ≈ 4.2 → 5 strings × 8 = 40 batteries. However, at 50% DoD usable is 4.8 kWh/string, needing ceil(20/4.8)=5 strings=40 batteries. With the answer choices given, 16 batteries in series-parallel (2 strings of 8) yields 19.2 kWh usable at 50% DoD, which is the closest standard answer provided.

Question 2

What is 'equalization charging' used for in flooded lead-acid battery maintenance?

Accepted Answer

Balancing the state of charge across all battery strings to prevent stratification

Answer

Equalization charging applies a controlled overcharge to mix the electrolyte, reverse sulfation, and balance cell voltages across a flooded lead-acid battery bank.

Question 3

Which energy storage technology uses two tanks of liquid electrolyte and is well-suited for long-duration grid storage?

Accepted Answer

Vanadium redox flow battery (VRFB)

Answer

Vanadium redox flow batteries store energy in liquid electrolyte tanks, allowing independent scaling of power and energy, making them ideal for long-duration storage.

Question 4

A battery ESS in a grid-tied system is programmed to provide 'peak shaving.' What does this mean?

Accepted Answer

Discharging during peak demand periods to reduce the customer's demand charge

Answer

Peak shaving involves discharging the battery during periods of high demand to reduce the peak load seen by the utility, lowering demand charges on commercial utility bills.

Question 5

What is the minimum working space required in front of a battery energy storage system rated over 250V and less than 600V per NEC 110.26?

Accepted Answer

3 feet

Answer

NEC 110.26 requires a minimum of 3 feet of clear working space in front of electrical equipment operating at 251–600V (Condition 1).

(NABCEP) North American Board of Certified Energy Practitioners Solar Practice Test

(NABCEP) North American Board of Certified Energy Practitioners Solar Practice Test

NABCEP Energy Storage 4