ESCO Energy Storage Systems 2 — Questions and Answers
Question 1: Ice-based thermal energy storage systems are primarily used to shift what type of building load?
- Heating loads from gas-fired boilers
- Lighting loads during evening hours
- Air conditioning (cooling) loads from peak to off-peak hours (Correct answer)
- Data center server loads
Correct answer: Air conditioning (cooling) loads from peak to off-peak hours
Ice storage systems make ice at night using cheaper off-peak electricity, then melt it during the day to provide cooling, shifting the chiller load.
Question 2: What does 'state of charge' (SOC) represent in a battery energy storage system?
- The total number of charge cycles completed
- The current available energy expressed as a percentage of total capacity (Correct answer)
- The temperature of the battery cells during operation
- The voltage level at the battery terminals
Correct answer: The current available energy expressed as a percentage of total capacity
SOC indicates how much energy remains in the battery at any given moment, expressed as a percentage from 0% (empty) to 100% (full).
Question 3: A flywheel energy storage system stores energy primarily as:
- Chemical energy in electrolyte solutions
- Thermal energy in a pressurized tank
- Kinetic (rotational) energy of a spinning mass (Correct answer)
- Potential energy in elevated water
Correct answer: Kinetic (rotational) energy of a spinning mass
Flywheels store energy by spinning a rotor at high speed; the kinetic energy is converted back to electricity when the rotor decelerates.
Question 4: 'Peak shaving' in energy storage refers to:
- Selling excess stored energy back to the grid during off-peak hours
- Using stored energy to reduce a facility's highest power consumption intervals (Correct answer)
- Gradually increasing battery capacity over a project's contract term
- Trimming utility rate schedules to achieve better pricing tiers
Correct answer: Using stored energy to reduce a facility's highest power consumption intervals
Peak shaving uses stored energy to flatten the demand profile by discharging the battery during the highest-demand intervals, reducing peak charges.
Question 5: Which battery chemistry is generally recognized for the longest cycle life among commercial energy storage options?
- Lead-acid (flooded)
- Lithium nickel manganese cobalt oxide (NMC)
- Lithium iron phosphate (LFP) (Correct answer)
- Nickel-cadmium (NiCd)
Correct answer: Lithium iron phosphate (LFP)
LFP batteries are known for exceptional cycle life (often 3,000–6,000+ cycles) due to the stability of the iron phosphate cathode chemistry.
Question 6: What does 'C-rate' describe in battery energy storage systems?
- The cost per kilowatt-hour of stored energy
- The rate of charge or discharge relative to total battery capacity (Correct answer)
- The carbon intensity of the electricity used to charge the battery
- The rated capacity under cold temperature conditions
Correct answer: The rate of charge or discharge relative to total battery capacity
C-rate expresses charge/discharge speed as a multiple of capacity; a 1C rate fully charges or discharges in 1 hour, while 0.5C takes 2 hours.
Question 7: Hot water thermal storage systems are most commonly used to shift what type of load?
- HVAC cooling load during summer months
- Electric vehicle charging demand
- Water heating load from peak to off-peak electricity hours (Correct answer)
- Compressed air system demand
Correct answer: Water heating load from peak to off-peak electricity hours
Hot water storage tanks heat water using off-peak electricity or excess renewable energy, storing thermal energy for on-demand domestic hot water use.
ESCO Energy Storage Systems 2
Ice-based thermal energy storage systems are primarily used to shift what type of building load?