Engineering Math
20 terms in the engineering math category.
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AC/DC Ratio (Inverter Loading Ratio)
AC/DC Ratio, also called Inverter Loading Ratio (ILR), is the ratio of installed DC array capacity (kW_DC) to inverter AC capacity (kW_AC). A higher ratio increases morning/evening yield but causes midday clipping. Typical ranges: 1.20–1.35 utility, 1.15–1.30 commercial, 1.10–1.25 residential.
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Availability
Availability is the percentage of time a solar plant is operational and capable of generating, accounting for inverter failures, maintenance downtime, and grid disruptions. Typical 98–99.5%; specified in O&M contracts.
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Bankability
Bankability is the qualification of a solar project for senior debt financing by lenders. Requires a robust EYA, independent engineer review, Tier 1 equipment with warranties, creditworthy off-take counter-party, and demonstrated financial returns at P90 cash flow.
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Capacity Factor
Capacity factor is the ratio of average solar plant output over a period to the plant's nameplate AC capacity. Typical values: 18–22% (fixed tilt), 25–30% (tracker desert). Compares with wind (30–45%), nuclear (90%+), coal (40–60%).
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Curtailment
Curtailment is the forced reduction of a solar plant's output by the utility operator, typically due to transmission constraints, oversupply during low demand, or grid stability requirements. Reduces plant revenue and complicates PR/availability calculations.
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Degradation Rate
Module degradation rate is the annual percentage decline in PV module power output over its operating lifetime. Typical 0.4–0.7%/year for modern modules; cumulative loss 88–90% at year 25.
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EYA (Energy Yield Assessment)
An Energy Yield Assessment (EYA) is the formal engineering report projecting a solar plant's annual energy production over its 25-year operating life, with statistical confidence bands (P50, P75, P90, P99) used by lenders and investors for project finance decisions.
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Inverter Clipping
Inverter clipping is the design-intended energy loss when DC array power exceeds inverter AC nameplate capacity. The MPPT operates intentionally off the maximum power point, capping output at AC capacity. Typically 0.5–4% annual energy loss for ILR 1.20–1.40.
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Inverter Loading Ratio
Inverter Loading Ratio (ILR) is the ratio of installed DC array capacity (kW_DC) to inverter AC capacity (kW_AC). Equivalent term to AC/DC Ratio or DC:AC ratio. Typical 1.10–1.40 depending on site and inverter.
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IRR (Internal Rate of Return)
Internal Rate of Return (IRR) is the discount rate at which a solar project's net present value equals zero — the project's effective compound annual return. Equity IRR (after debt) and project IRR (unlevered) are the two key flavors used in solar project finance.
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kWh/kWp (Specific Yield)
kWh/kWp is the unit for specific yield — annual energy production (kWh) per kW of installed DC nameplate capacity (kWp). The standard metric for comparing solar plant productivity across sites.
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LACE (Levelized Avoided Cost of Energy)
LACE (Levelized Avoided Cost of Energy) is the value of energy avoided by deploying new generation — typically the marginal cost of energy displaced from the system. LCOE < LACE means the project is economic vs. grid alternatives.
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LCOE (Levelized Cost of Energy)
Levelized Cost of Energy (LCOE) is the per-kWh lifetime cost of generating electricity from a solar plant, including CapEx, OpEx, financing, and degradation, discounted to present value and divided by lifetime energy production. The benchmark metric for comparing generation technologies.
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NPV (Net Present Value)
Net Present Value (NPV) is the sum of all future project cash flows discounted to present value, minus the initial investment. A positive NPV indicates the project creates value above the discount rate; negative NPV means it destroys value.
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P50
P50 is the 50th-percentile annual energy yield estimate for a solar project — the median value with equal probability of being exceeded or missed. It is the baseline production forecast used for revenue projections and equity returns analysis.
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P75
P75 is the 75th-percentile annual energy yield estimate for a solar project — the value the plant exceeds in 3 out of 4 years. Used as an intermediate confidence band between P50 (median) and P90 (lender-conservative).
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P90
P90 is the 90th-percentile annual energy yield estimate — the value the solar plant is forecast to exceed in 90% of years. It is the conservative production benchmark used by lenders to size debt and calculate debt service coverage ratios (DSCR).
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P99
P99 is the 99th-percentile annual energy yield estimate — exceeded in 99% of years. Used for ultra-conservative stress testing, government-backed loans, and worst-case scenario analysis.
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Payback Period
Payback period is the time required for cumulative cash savings from a solar project to equal the initial investment cost. Simple metric used in customer-facing marketing, less sophisticated than NPV or IRR for investment decisions.
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PR Calculation Methodology
PR Calculation Methodology refers to the formal procedure for computing Performance Ratio per IEC 61724-1:2021. Two main forms: standard PR (Y_f / Y_r) and temperature-corrected PR (TC-PR) that normalizes for cell temperature.
