Glossary

Terms that appear in the application and in the report.

Energy and radiation

Albedo. Fraction of the radiation reflected by the ground or the surrounding roof (0 to 1).

DHI. Diffuse horizontal irradiance: the irradiance that comes from the sky, not directly from the Sun, on a horizontal plane (W/m²).

DNI. Direct normal irradiance: the Sun's irradiance measured on a plane perpendicular to its rays (W/m²).

GHI. Global horizontal irradiance: direct plus diffuse on a horizontal plane (W/m²).

Horizon. Elevation profile of distant hills and buildings by azimuth; when the Sun is below it, there is no direct radiation.

Irradiance / irradiation. Irradiance is power per square metre (W/m²); irradiation is the energy accumulated over a period (kWh/m²).

POA. Plane-of-array irradiance, on the plane of the modules.

Transposition. Calculation of the irradiance on the tilted plane from the horizontal one.

TMY. Typical meteorological year: a synthetic year made of the most representative months of a long series.

Module and losses

Bifacial. Module that captures light on both sides.

Bifaciality (φ). Ratio between the power of the rear side and the front side at STC.

Bypass diode. Diode that bypasses a group of shaded cells so that they do not limit the whole module.

FC / HC. Full-cell or half-cut cell module.

IAM. Incidence angle modifier: loss due to reflection on the glass when light arrives at a steep angle.

Mismatch. Loss due to differences between modules or strings connected together.

Single-diode model. Equivalent circuit of the module used to calculate its power according to irradiance and temperature.

PR (Performance Ratio). AC energy divided by (plane irradiation × peak power). It measures the overall quality of the installation.

STC. Standard test conditions: 1,000 W/m², 25 °C cell temperature, AM 1.5 spectrum.

Cell temperature. The temperature of the cells, higher than ambient because of the irradiance; it determines the power.

Electrical

Clipping. Loss when the DC power exceeds what the inverter can deliver.

Isc / Voc / Imp / Vmp. Short-circuit current, open-circuit voltage, and current and voltage at the maximum power point.

MPPT. Maximum power point tracker: inverter input that adjusts the voltage to extract maximum power.

Optimizer. Module-level DC-DC converter that makes the module work at its maximum power point.

DC/AC ratio. Peak power of the modules divided by the nominal power of the inverter.

String. Chain of modules connected in series.

Installation and energy

Roof plane. Section or plane of the roof with a given tilt and azimuth.

Self-consumption. Part of the production consumed by the client at that moment (or from the battery).

Self-sufficiency. Part of the client's consumption covered by the installation.

Azimuth. Orientation relative to north: 0° N, 90° E, 180° S, 270° W.

Surplus. Production that exceeds consumption at a given moment.

Curtailment. Surplus that is neither exported nor stored and is lost.

SoC. State of charge of the battery.

Tilt. Inclination relative to the horizontal.

Economics

CAPEX. Initial investment.

Simplified compensation. Spanish mechanism that deducts the value of the surplus from the bill (RD 244/2019), with a monthly cap.

LCOE. Levelised cost of energy: cost per kWh generated over the life of the installation.

OPEX. Annual operating costs.

P50 / P90 / P99. Production exceeded with a probability of 50 %, 90 % and 99 %.

Payback. Years to recover the investment.

PVPC. Voluntary price for small consumers (Spanish regulated 2.0TD tariff with three periods).

IRR. Internal rate of return.

NPV. Net present value of the cash flows.