01
Fast route
Professional Check
Five boundary tests, one loss-adjusted duration calculation and a hard check on nameplate language.
- Five focused lessons
- 10 scored questions
- Answer rationales after submission
About 15 minutes
Vitreous Learning 03
Professional BESS course · Great Britain
Nameplate is the start of the question
Trace power and energy from cells to the grid boundary. Test which duration claim survives losses, reserves, degradation and operating conditions.
2 learning routes80% pass standard30 assessment questions
Choose your route
Evidence ledIECSandiaDESNZTechnical cut-off · 24 August 2026
One subject · two depths
Choose your route
This course is for professionals who already use MW and MWh and want to test whether a quoted duration is physically and contractually meaningful.
02
Full route · recommended
Detailed Course
From cell capacity and AC delivery through efficiency, auxiliaries, degradation, augmentation and market-duration evidence.
- Nine detailed modules
- Longmere worked case
- 20 scored questions
75 to 90 minutes
Scores and progress remain on this device. No account or sign-up is required.
Professional Check · About 15 minutes
Can you identify the duration that the claim actually describes?
Separate rated power, nameplate energy, usable energy and deliverable AC energy before comparing assets or services.
Lesson 1 of 5
Power, energy and duration
MW sets the instantaneous rate, MWh sets the energy quantity and duration is their ratio at a stated boundary.
A 50 MW, 100 MWh system has two hours of nameplate duration only if the numerator and denominator describe compatible ratings. Duration = energy ÷ power.
Power can be limited by the inverter, transformer, grid connection or thermal conditions. Energy can be limited by the cell inventory, operating window or contract guarantee.
PowerMW
EnergyMWh
DurationMWh ÷ MW
Hostile check
Dividing a DC energy rating by an AC grid limit mixes boundaries unless conversion treatment is declared.
Lesson 2 of 5
Name the measurement boundary
Cell, DC system, inverter output and grid meter can all report different energy for the same cycle.
Define where charging energy enters, where discharge energy leaves and whether transformers, HVAC and standby consumption sit inside the measurement. Round-trip efficiency is meaningful only across a stated pair of boundaries and a stated duty cycle.
AC-to-AC performance is often the closest operational boundary for market delivery. OEM warranties can use a different boundary.
Hostile check
Two suppliers can quote the same efficiency percentage while measuring materially different equipment.
Lesson 3 of 5
Move from nameplate to usable
The dispatchable window is the rated inventory after state-of-charge limits, reserves and control constraints.
A 100 MWh DC nameplate system operated from 5 to 95 percent state of charge exposes 90 MWh DC before discharge losses. A minimum reserve for services or warranty compliance reduces the dispatchable amount.
Usable energy should be stated at beginning of life or at a defined operating year, temperature and power.
Hostile check
A broad state-of-charge window in a brochure does not prove that the warranty permits continuous use of the entire window.
Lesson 4 of 5
Apply losses once, at the right place
Discharge-path efficiency converts usable DC energy to AC delivery. Round-trip efficiency is not the correct factor for a one-way discharge calculation.
Longmere exposes 90 MWh DC. At 94 percent DC-to-AC discharge efficiency, it can deliver 84.6 MWh AC before any separately excluded auxiliaries.
At 50 MW AC, the simplified duration is 84.6 ÷ 50 = 1.692 hours. A contractual test may specify ramping, rest, temperature and end conditions.
Usable DC90 MWh
Discharge efficiency94%
Deliverable AC84.6 MWh
Hostile check
Applying a 90 percent round-trip factor after already applying charge and discharge losses counts losses twice.
Lesson 5 of 5
Date the duration
Energy capability changes with calendar age, cycling, temperature, power rate, outages and augmentation.
State whether duration is at commissioning, guaranteed end of year, current tested condition or modelled future state. Availability addresses whether equipment can operate. Degradation addresses how much energy or power it can deliver when available.
Capacity Market treatment uses de-rated capacity under the applicable rules and auction parameters. Nameplate MW and MWh alone do not determine the accredited value.
Hostile check
A two-hour label can remain in marketing material after degradation has reduced deliverable energy below two hours at rated power.
Professional Check assessment
Answer every question before submitting. Correct answers and rationales appear only after the complete attempt.
Professional CheckQuestion 1 of 10
Detailed Course · 75 to 90 minutes
Build a complete energy and duration bridge
Define each boundary, calculate the losses and preserve the conditions under which the result is valid.
Module 1 of 9
Define the rating stack
A credible specification separates cell energy, installed DC energy, usable DC energy, inverter capability and export or import limits.
Map every rating to its physical component and measurement point. Record whether it is continuous, overload, beginning-of-life, end-of-life, nominal or guaranteed.
Use a diagram from cell terminals through DC collection, power conversion, transformer, auxiliaries and revenue meter. This prevents mixed-boundary ratios.
Hostile check
A single 100 MW headline can refer to inverter aggregate rating, connection capacity or guaranteed net export. They are not interchangeable.
Module 2 of 9
Specify the test boundary
Performance changes with duty cycle, power level, temperature, state-of-charge endpoints and rest periods.
IEC 62933 and the Sandia protocol emphasise defined parameters and repeatable test methods. Record energy measurement points, sampling, accuracy, environmental conditions and auxiliary treatment.
A factory test, site acceptance test and operational capacity test answer different questions. Keep the test objective and configuration attached to the result.
Hostile check
A test certificate for a similar equipment block does not automatically validate the installed project configuration.
Module 3 of 9
Separate one-way and round-trip efficiency
Charge efficiency, discharge efficiency and auxiliary consumption combine into round-trip performance across a chosen boundary.
If charge efficiency is 96 percent and discharge efficiency is 94 percent, the product is 90.24 percent before separately excluded auxiliaries. This simplified result assumes comparable conditions and energy bases.
Round-trip efficiency can vary with C-rate, state of charge, temperature and standby time. Use a duty cycle that represents the intended application.
Charge96%
Discharge94%
Product90.24%
Hostile check
Multiplying a measured AC-to-AC round-trip efficiency by an additional inverter efficiency double counts part of the same loss path.
Module 4 of 9
Build the usable-energy bridge
Installed energy becomes dispatchable energy only after operating windows, reserves and control limits.
Start from the warranted DC capacity. Apply the permitted state-of-charge window. Deduct any energy held for safety, service recovery or contractual obligations. Convert the result through the discharge path to the grid boundary.
Use consistent inclusion for HVAC and other auxiliaries. A gross inverter output and a net revenue-meter result answer different commercial questions.
Hostile check
Calling energy usable because the BMS can technically access it ignores warranty and operating-policy constraints.
Module 5 of 9
Model degradation and availability separately
Degradation reduces capability while availability reduces the time that capability can be used.
Calendar ageing, cycling, temperature and high state of charge can change usable capacity and resistance. Availability reflects outages, maintenance and forced derates.
A model should carry both. Ninety percent remaining energy and ninety-five percent availability do not combine into a single undefined health percentage.
Hostile check
Using an availability guarantee as a proxy for energy retention hides two different risks and remedies.
Module 6 of 9
Test power-dependent duration
The duration available at maximum export can differ from duration at a lower power because losses and control limits vary.
Run energy tests at the relevant power and temperature. Include the ramp to rated power and the point at which the system can no longer maintain the required output.
For services with minimum delivery duration, preserve recovery energy and headroom. Market eligibility can depend on a performance envelope rather than one nameplate ratio.
Hostile check
A two-hour result at 25 MW does not prove one hour at 50 MW when thermal or inverter limits intervene.
Module 7 of 9
Plan augmentation as a controlled change
Adding battery capacity can restore energy, while it changes configuration, controls, warranty interfaces and safety evidence.
Define the augmentation trigger, quantity, timing, price and responsibility. Test whether new and aged blocks can operate together within BMS and EMS limits.
Include downtime, commissioning, permits, spares and disposal. Compare planned augmentation with oversizing at initial construction using a common net-present-value boundary.
Hostile check
An augmentation line in the model does not prove compatible equipment will be available at the assumed price.
Module 8 of 9
Translate duration into market evidence
Each market or service applies its own qualifying duration, performance and de-rating treatment.
Use the current product terms or Capacity Market rules for the relevant delivery year. Record auction vintage and technical cut-off because parameters can change.
Do not substitute nameplate duration for tested service duration. Eligibility, accredited capacity and expected revenue require separate calculations.
Hostile check
A four-hour nameplate ratio does not automatically produce four-hour accredited capacity under every market rule.
Module 9 of 9
Longmere worked duration audit
A robust answer presents a bridge, a date and a sensitivity range.
Longmere has 100 MWh DC nameplate and a 5 to 95 percent operating window. Usable DC energy is 90 MWh. At 94 percent discharge efficiency, deliverable AC energy is 84.6 MWh. At 50 MW, beginning-of-life duration is 1.69 hours.
At year five, the model assumes 88 percent retained energy and 1 MWh of separately supplied auxiliary consumption during the event. Deliverable energy is 73.45 MWh and duration is 1.47 hours. The result remains conditional on temperature, test method and availability.
BOL duration1.69 h
Year 5 AC energy73.45 MWh
Year 5 duration1.47 h
Hostile check
Reporting Longmere as a two-hour battery in year five conceals the measurement boundary and the degradation assumption.
Detailed Course assessment
Answer every question before submitting. Correct answers and rationales appear only after the complete attempt.
Detailed CourseQuestion 1 of 20