📚 Engineering Terminology & Formulas

Clean Energy & Electrical Engineering Glossary

Engineering terminology, physical formulas, standards references, and modeling assumptions used across PowerLab's clean energy planning engines.

Engineering Concepts (18 Terms)

BATTERYk (dimensionless)

Peukert's Exponent

Formulated by Wilhelm Peukert in 1897, Peukert's equation models rate-capacity derating in electrochemical cells. While historically applied to lead-acid batteries (typically k ≈ 1.10–1.30 under heavy C-rates), modern lithium-ion chemistries (such as LiFePO4 and NMC) exhibit minimal rate derating (k ≈ 1.01–1.05) at standard discharge rates. Exponent values depend on cell design, chemistry, temperature, and C-rate.

t = H \cdot \left( \frac{C}{I \cdot H} \right)^k

Reference: Peukert (1897) / Electrochemical Reference LiteratureWikidata ↗

BATTERYDoD (%)

Depth of Discharge (DoD)

Depth of Discharge indicates battery capacity utilization. For lead-acid batteries, limiting routine discharge to 50% DoD is a common engineering guideline to preserve cycle life, whereas lithium iron phosphate (LiFePO4) and NMC systems typically support 80% to 95% DoD within manufacturer cycle-life specifications.

\text{DoD} = \frac{E_{\text{discharged}}}{E_{\text{nominal}}} \times 100\%

Reference: IEEE Std 485 / IEC 62619 / Industry Sizing GuidanceWikidata ↗

BATTERYC (h⁻¹)

C-Rate (Charge/Discharge Rate)

A 1C rate corresponds to charging or discharging the full nominal capacity in 1 hour (e.g., 100A for a 100Ah battery). Lower rates, such as 0.2C (a 5-hour rate), reduce internal resistance losses and cell thermal stress, which is typical for stationary solar energy storage cycling.

I = C_{\text{rate}} \times C_{\text{nominal}}

Reference: IEC 61427 / Battery Industry Testing PracticeWikidata ↗

BATTERYP_tare (Watts (W))

Inverter Tare Loss (Idle Power)

Inverters consume continuous standby power (typically ranging from 10W–25W for compact units to 25W–60W+ for residential whole-home split-phase inverters) to operate internal control logic, gate drivers, voltage sensing, and cooling fans. Over a 24-hour period, unmanaged tare loss can draw significant energy from an off-grid battery bank.

E_{\text{tare,daily}} = P_{\text{tare}} \times 24\text{ hours}

Reference: Manufacturer Specification Datasheets / UL 1741 ReferenceWikidata ↗

SOLARPSH (h/day)

Peak Sun Hours (PSH)

Peak Sun Hours integrates variable daylight solar irradiance into equivalent hours at Standard Test Condition irradiance (1 kW/m² = 1,000 W/m²). It is numerically equal to daily solar irradiation expressed in kWh/m²/day divided by 1 kW/m² (e.g., a location receiving 5.0 kWh/m²/day of cumulative insolation receives 5.0 PSH).

\text{PSH (h/day)} = \frac{\text{Daily Irradiation (kWh/m}^2/\text{day})}{1\text{ kW/m}^2}

Reference: NREL NSRDB / IEC 60904-3Wikidata ↗

SOLARβ_Voc (%/°C or V/°C)

Voc Temperature Coefficient

Silicon photovoltaic cell open-circuit voltage increases as cell operating temperature falls below the 25°C Standard Test Condition. Because manufacturer temperature coefficients are negative (e.g., -0.28%/°C), cold-weather operating conditions produce higher string voltages that must be factored into charge controller and inverter maximum input voltage limits under NEC 690.7.

V_{oc,\text{cold}} = V_{oc,\text{STC}} \cdot \left[ 1 + \beta_{Voc} \cdot (T_{\text{min}} - 25^\circ\text{C}) \right]

Reference: NFPA 70 (NEC 690.7) / IEC 61215Wikidata ↗

SOLARMPPT (dimensionless)

Maximum Power Point Tracking (MPPT)

MPPT controllers dynamically adjust the electrical operating point of the solar array using control methods such as perturb-and-observe or incremental conductance. This matches the array impedance to the battery or DC bus, achieving high DC-DC power conversion efficiency (typically 95%–98%+ under rated conditions).

P_{\text{mp}} = V_{mp} \times I_{mp}

Reference: IEC 62093 / Power Electronics PrinciplesWikidata ↗

SOLARI_poa (W/m²)

Perez Diffuse Irradiance Model

Developed by Richard Perez et al. (1990), this model transposes horizontal global (GHI) and diffuse (DHI) solar irradiance onto tilted collector surfaces. It accounts for circumsolar brightening (F1), horizon brightening (F2), and isotropic background diffuse sky radiation across varying atmospheric clearness and brightness conditions.

I_{\text{poa,diffuse}} = I_{dh} \cdot \left[ (1 - F_1) \cdot \left( \frac{1 + \cos\beta}{2} \right) + F_1 \cdot \frac{a}{b} + F_2 \cdot \sin\beta \right]

Reference: Perez et al. (Solar Energy, 1990)Wikidata ↗

HVACSEER2 (BTU/Wh)

SEER2 (Seasonal Energy Efficiency Ratio 2)

Adopted by the U.S. Department of Energy under AHRI Standard 210/240 (Appendix M1), SEER2 measures seasonal cooling performance at an increased external static duct pressure of 0.5 in. w.g. Multiplying SEER2 by 0.293071 yields an equivalent seasonal efficiency in dimensionless W/W, distinct from instantaneous operating COP which varies dynamically with outdoor and indoor temperatures.

\text{Seasonal Efficiency (W/W)} = \text{SEER2} \times 0.293071

Reference: AHRI 210/240 (Appendix M1) / DOE 10 CFR Part 430Wikidata ↗

HVACHSPF2 (BTU/Wh)

HSPF2 (Heating Seasonal Performance Factor 2)

Standardized under AHRI 210/240 (Appendix M1) and DOE efficiency regulations, HSPF2 evaluates heat pump seasonal performance across standardized climatic regions. It reflects ambient temperature degradation, defrost energy cycles, and auxiliary resistive strip heat staging. Converting by 0.293071 yields equivalent seasonal W/W efficiency.

\text{Seasonal Efficiency (W/W)} = \text{HSPF2} \times 0.293071

Reference: AHRI 210/240 (Appendix M1) / DOE 10 CFR Part 430Wikidata ↗

HVACT_design (°F / °C)

ASHRAE 99% / 1% Design Temperature

Published in the ASHRAE Handbook — Fundamentals (Chapter 14), the 99% heating design temperature is the outdoor dry-bulb temperature exceeded during 99% of hours in a typical meteorological year. HVAC engineers use this baseline to calculate peak building heat loss and determine heat pump thermal balance point sizing.

\dot{Q}_{\text{design}} = \text{UA}_{\text{building}} \cdot (T_{\text{indoor}} - T_{\text{outdoor,99\%}})

Reference: ASHRAE Handbook — Fundamentals (Ch 14)Wikidata ↗

HVACI_LRA (Amperes (A))

Locked Rotor Amps (LRA & Inrush)

Motor starting inrush current is determined by the motor's locked-rotor kVA per horsepower rating (categorized by NEMA Code Letters per NEC 430.7(B)). Inrush currents are significantly higher than nominal running load amps (RLA), requiring standby generator sizing and power electronics to accommodate transient starting kVA without excessive voltage dip.

I_{\text{LRA}} = \frac{\text{HP} \cdot (\text{kVA/HP}_{\text{code}}) \cdot 1000}{V \cdot \sqrt{\text{phases}}}

Reference: NEMA MG 1 / NFPA 70 (NEC Article 430)Wikidata ↗

EVI_breaker (Amperes (A))

NEC 125% Continuous Load Rule

Under NEC Article 625.41/625.42 and Article 210.19/210.20, electric vehicle supply equipment (EVSE) is classified as a continuous load (operating for 3 hours or more). For example, a 48A continuous charging load requires a minimum 60A overcurrent device (48A × 1.25 = 60A), subject to conductor ampacity, terminal ratings (NEC 110.14(C)), and standard OCPD ratings.

I_{\text{OCPD,min}} \ge I_{\text{continuous}} \times 1.25

Reference: NFPA 70 (NEC 625.41, 625.42, & 210.20)Wikidata ↗

EVη_charger (%)

Onboard AC-to-DC Charging Efficiency

Charging efficiency accounts for onboard charger (OBC) rectification losses, battery thermal conditioning, and baseline vehicle computer/BMS auxiliary power. Level 1 (120V AC) charging exhibits lower net efficiency (representative ~78%–83%) due to fixed parasitic loads relative to low input power, whereas Level 2 (240V AC) achieves higher representative efficiency (~88%–92%).

E_{\text{battery,net}} = E_{\text{grid,meter}} \times \eta_{\text{charger}}

Reference: SAE J1772 Reference / EV Testing LiteratureWikidata ↗

EVV2L (kW)

Vehicle-to-Load (V2L) & Bidirectional Power

Vehicle-to-Load (V2L) enables an EV to deliver standalone AC power (typically 1.8 kW to 9.6 kW depending on vehicle make and inverter design) for backup power or worksite tools. Vehicle-to-Grid (V2G) involves grid-synchronized bidirectional energy transfer. Backup runtime is modeled from usable battery capacity and user-selected driving reserves.

t_{\text{backup}} = \frac{C_{\text{usable}} \cdot (\text{SoC}_{\text{start}} - \text{SoC}_{\text{reserve}}) \cdot \eta_{\text{v2l}}}{P_{\text{load}}}

Reference: ISO 15118-20 / UL 9741Wikidata ↗

ELECTRICALVD (% / Volts)

Conductor Voltage Drop

Voltage drop is determined by Ohm's Law and conductor resistance (NEC Chapter 9, Table 8). NEC Article 210.19 Informational Note No. 4 provides an informational design recommendation (not a universal mandatory limit) to maintain voltage drop within 3% on branch circuits and 5% total for combined feeder-plus-branch circuits for reasonable electrical efficiency.

VD_{\text{volts}} = \frac{2 \cdot K \cdot I \cdot L}{A_{\text{cmil}}}

Reference: NFPA 70 (NEC 210.19 Informational Note 4) / IEEE Std 141Wikidata ↗

ELECTRICALcmil (cmil / kcmil)

Circular Mils (cmil & kcmil)

Used across the National Electrical Code (NEC Chapter 9 Table 8) to define conductor sizes, circular mils simplify resistance calculations by making area directly proportional to the square of wire diameter in mils. Standard American Wire Gauge (AWG) conductors range from 14 AWG (4,110 cmil) to 4/0 AWG (211,600 cmil = 211.6 kcmil) and up to 1,000 kcmil.

A_{\text{cmil}} = (d_{\text{mils}})^2

Reference: ASTM B258 / NEC Chapter 9 Table 8Wikidata ↗

ELECTRICALPF (dimensionless)

Power Factor (PF)

In AC electrical circuits, power factor is defined as real power divided by apparent power (PF = P / S). Under linear sinusoidal steady-state conditions, PF equals the cosine of the phase angle between voltage and current (cos θ). For nonlinear loads with harmonic currents, true power factor includes both displacement and distortion components.

\text{PF} = \frac{P_{\text{real}}}{S_{\text{apparent}}} = \cos\theta

Reference: IEEE Std 1459 / IEC 61000-3-2Wikidata ↗