ratio of output quantity to input quantity

NOTE 1 The quantity specified by the term "efficiency" is normally the power, energy, or electric charge produced by or delivered to a component.

a) ampere-hour efficiency

(Symbol: h_Ah)

ratio of the amount of electrical charge removed during discharge conditions to the amount of electrical charge added during charge conditions in an electrical energy storage device

It is calculated by:

h_Ah = I_d T_d / (I_c T_c);

where

h_Ah is ampere-hour efficiency;

I_d is discharge electric current (A);

T_d is discharge time (h);

I_c is charge electric current (A);

T_c is charge time (h)

b) array efficiency

sunlight to electricity conversion efficiency of the PV array

c) charging efficiency

generic term to express ampere-hour efficiency (or less commonly, watt-hour efficiency in an energy storage device

d) collection efficiency

ratio of the number of electrons flowing out of a PV cell to the number of incident photons in a short-circuit condition

e) PV conversion efficiency

ratio of maximum PV output to the product of PV device area and incident irradiance measured under specified test conditions, usually standard test conditions, STC

NOTE 2 See also "conditions/standard test conditions", 3.4.16e)

f) effective energy efficiency

energy efficiency during an identified period

g) inverter efficiency

ratio of the useful inverter output power to its input power, or output energy to its input energy

h) mean array efficiency

(Symbol: h_Amean)

average PV array efficiency

NOTE 3 Mean PV array efficiency is useful for comparison with the rated PV array efficiency

NOTE 4 The difference between mean and rated efficiency represents diode, wiring, mismatch and other losses during PV system operation

i) overall system efficiency

(Symbol: h_tot)

efficiency of the whole system including all the electricity sources

NOTE 5 Overall system efficiency is derived from the electricity supplied to the loads based on the solar irradiation and fuel supplies

j) partial efficiency

ratio of output power to input power, or output energy to input energy), when a component is operating below its rated output

k) partial load efficiency

ratio of the effective inverter output power to its input power, or output energy to input energy, at a specified load

l) power efficiency

ratio of active output power to active input power

m) rated efficiency

Pertaining to a PV device: efficiency of a device at specified operating conditions, usually standard test conditions, STC

NOTE 6 See also "conditions/standard test conditions", 3.4.16e)

Pertaining to an inverter: efficiency of an inverter when it is operating at its rated output

n) system efficiency

(Symbol: h_SP) (Unit: dimensionless, usually expressed as a percentage (%) over a period of time such as a month or year)

ratio of PV system output energy (W_SP) to the product of total irradiation (Q_ASP) and PV array area (A_P)

It is calculated by:

h_SP = W_SP / (Q_ASP A_P)

where

h_SP is system efficiency;

W_SP is system output energy (J);

Q_ASP is total irradiation (J ´ m^–2);

A_P is array area (m²)

o) efficiency tolerance

(Unit: dimensionless, usually expressed as a percentage, %)

permissible tolerance between the manufacturer's specified efficiency and the measured efficiency

p) watt-hour efficiency

(Symbol: h_Wh)

ratio of the amount of electrical energy removed during discharge conditions to the amount of electrical energy added during charge conditions in an electrical energy storage device

It is calculated by:

h_Wh = I_d T_d V_dav / (I_c T_c V_cav) = h_Ah V_dav / V_cav

where

h_Wh is watt-hour efficiency;

I_d is discharge electric current (A);

T_d is discharge time (h);

V_dav is average discharge voltage (V);

I_c is charge electric current (A);

T_c is charge time (h);

V_cav is average charge voltage (V)

NOTE 7 In calculating watt-hour efficiency, the ratio of average voltage to the specified final discharge voltage is often used, rather than voltages at any specified time.

q) weighted average conversion efficiency

method of estimating the effective energy efficiency

NOTE 8 Weighted average conversion efficiency is calculated as the sum of products of each power level efficiency and related weighting coefficients depend on a regional irradiance duration curve. When a PV system is a stand-alone type with a storage sub-system, the weighting coefficients depend on the load duration curve.