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.
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