Photovoltaic Water Electrolysis is a technology that combines solar power generation and water decomposition through photovoltaic panels and electrolytic cells, achieving the production of renewable green hydrogen energy.
The hydrogen production efficiency of photovoltaic water electrolysis devices is primarily influenced by the following three factors:
The power generation efficiency of the photovoltaic cells themselves;
The efficiency of electrical energy transfer between photovoltaic cells and electrolytic cells;
The efficiency of the proton exchange membrane inside the electrolytic cell.
The hydrogen production efficiency of photovoltaic water electrolysis devices can be expressed by the formula^{[1]}:
η_{m} is the efficiency of the photovoltaic cells.
η_{t} is the transfer efficiency between photovoltaic cells and electrolytic cells.
η_{e} is the efficiency of the proton exchange membrane.
This article primarily explains the calculation of photovoltaic cell efficiency η_{m}. Other calculation methods in the same series will be explained in subsequent articles.
The calculation formula for photovoltaic cell efficiency η_{m} is as follows:
A_{c} is the effective area of the photovoltaic cells, determining the area of sunlight the cells can absorb, usually measured in square meters (m^{2});
G is the solar radiation intensity, indicating the energy flux density of solar energy reaching the surface of the photovoltaic cells, typically measured in watts per square meter (W/m^{2});
I_{c} and V_{c} are the current and voltage of the photovoltaic cells, respectively, with their relationship as follows^{[2]}:
I_{ph} is the photocurrent, the current generated when the photovoltaic cells absorb incident photons, measured in amperes (A);
I_{0} is the saturation dark current of the photovoltaic cells, defined as the current flowing through the P-N junction under the influence of an external voltage when there is no illumination, measured in amperes (A);
e is the elementary charge, with a magnitude of 1.6 × 10^{-19}C;
A is the ideality factor of the photovoltaic cells, typically between 1 and 2;
K_{B} is the Boltzmann constant, with a value of 1.380649 × 10^{-23}J/K;
V_{c} is the output voltage of the photovoltaic module, measured in volts;
T_{C} is the operating temperature of the cell, obtained through real-time testing, measured in degrees Celsius.
Among these related parameters, the calculation of photocurrent I_{ph} and saturation dark current I_{0} is relatively complex and requires separate explanations:
Calculation method for photocurrent I_{ph}:
G is the solar radiation intensity, measured in W/m^{2};
I_{SC} is the short-circuit current of the photovoltaic cells, defined as the maximum current that the photovoltaic cells can produce when there is no load circuit connected, measured in amperes (A);
k_{0} is the temperature coefficient at short-circuit current. Different types of photovoltaic cells and those manufactured by different companies have different temperature coefficients, measured in %/°C. Specific values can be found in relevant product documentation or by consulting technical personnel;
T_{C} is the operating temperature of the cell, obtained through real-time testing, measured in degrees Celsius;
is the reference temperature, derived from standardized testing of photovoltaic cell performance, and is 25°C.
Where T_{C} and are related by , λ is the temperature coefficient representing the relative change in voltage with temperature for photovoltaic cells under open-circuit voltage or operating voltage conditions, usually expressed as %/°C, indicating the percentage change in voltage with each degree Celsius change in temperature; G is the solar radiation intensity, measured in W/m^{2}.
Calculation method for saturation dark current I_{0}:
I_{or} is the reverse saturation current of the photovoltaic cells, representing the tiny current that flows through the cell when it is in reverse bias, meaning the positive voltage is lower than the negative voltage. This current is generated due to the natural drift of electron-hole pairs in the material and is typically minimized in practical applications as it leads to energy losses, measured in amperes (A);
T_{C} is the operating temperature of the cell, obtained through real-time testing, measured in degrees Celsius;
is the reference temperature, derived from standardized testing of photovoltaic cell performance, and is 25°C;
e is the elementary charge, with a magnitude of 1.6 × 10^{-19}C;
E_{g} is the bandgap energy, representing the minimum energy required for electron level transition in the electronic structure of semiconductor materials. Different materials have different bandgap energies, usually expressed in electron volts (eV);
K_{B} is the Boltzmann constant, with a value of 1.380649 × 10^{-23}J/K;
A is the ideality factor of the photovoltaic cells, typically between 1 and 2.
In summary, by calculating the photocurrent I_{ph} and saturation dark current I_{0}, along with testing the output voltage of the photovoltaic cell, one can deduce the efficiency of the photovoltaic cell η_{m}.