BESS & Microgrids · Lesson 1 of 5
Power, energy and the operating purpose of BESS
A battery energy storage system is a controlled power resource. Its power rating describes how quickly it can charge or discharge; its energy rating describes how long it can sustain a given output. A 1 MW / 2 MWh system can theoretically provide 1 MW for two hours before losses and operating limits, or 500 kW for about four hours under the same simplified assumption.
After this lesson, you should be able to:
- Distinguish kW from kWh and connect both to the use case
- Explain state of charge, usable energy and reserve
- Avoid double-counting incompatible value streams
What is physically and operationally happening?
A battery energy storage system is a controlled power resource. Its power rating describes how quickly it can charge or discharge; its energy rating describes how long it can sustain a given output. A 1 MW / 2 MWh system can theoretically provide 1 MW for two hours before losses and operating limits, or 500 kW for about four hours under the same simplified assumption.
Real operation reserves part of the battery for safety, lifecycle or resilience. Peak shaving may consume energy that an outage reserve needs later. The EMS must therefore prioritize objectives. Financial models that assume every value stream is fully available at the same moment usually overstate the result.
Define outcome
Identify resilience, peak management, renewable shifting or another measurable service.
Determine power
Find the maximum required charge or discharge rate.
Determine energy
Combine power, duration, losses, reserve and degradation.
Schedule
Set EMS priorities so services do not consume the same capacity twice.
Power, duration and usable energy
Energy is the area under a power-versus-time curve; reserve and losses reduce what can be delivered.
CHARGE →← DISCHARGE
Power, energy and value evidence profile
Illustrative discharge power over four hours. Values are educational, not Metro Power project-performance claims.
OPTIONAL ENGINEERING DEPTHUse case & value stackDefine resilience, peak, renewable or microgrid outcomes without double-counting incompatible value.+
- Separate PCS power from battery energy
- Resolve reserve versus commercial dispatch priority
- Include losses, degradation, auxiliaries and downtime
- 01Simulate the complete interval sequence and SOC
- 02Coordinate BMS, PCS, EMS, protection and transformer states
- 03Test tariff, warranty and availability sensitivities
Peak cap fails during long events
Energy depletes despite sufficient PCS power
Replay interval load and SOC
Outage reserve is unavailable
Commercial dispatch consumed reserved energy
Compare command history with EMS policy
- Interval load and generation data
- Dispatch and SOC simulation
- Approved one-line, controls and protection basis
Critical-load duration
A facility needs 500 kW of selected load for four hours during an outage.
- Load energy = 500 × 4 = 2,000 kWh
- Account for 90% path efficiency: 2,000 / 0.90 = 2,222 kWh
- Account for 80% usable window: 2,222 / 0.80 = 2,778 kWh
- Apply lifecycle allowance in the project sizing model
“A 2 MWh battery can always supply 500 kW for four hours.”
Nominal energy is reduced by usable SOC window, losses, auxiliary loads, temperature, degradation, reserve and power limits.
Check what you can explain without looking back.
Choose an answer and report your confidence. The confidence signal is stored only until you submit this page.
Which quantity describes sustained duration capability?
Why can peak shaving conflict with resilience?
What is wrong with adding every maximum revenue stream?
Continue with the controlling references.
01US Department of Energy Energy Storage HandbookSandia National Laboratories and US DOETechnology, system engineering, safety, procurement and commissioning.
Open source ↗02DOE/EPRI Electricity Storage Handbook in Collaboration with NRECASandia National LaboratoriesUtility planning and implementation context.
Open source ↗03Grid-Scale Battery Storage Frequently Asked QuestionsSandia National LaboratoriesFoundational grid-storage concepts and project questions.
Open source ↗Read the complete technical paper →