COMP-PHDec 16, 2015
On Calculating the Current-Voltage Characteristic of Multi-Diode Models for Organic Solar CellsKen Roberts, S. R. Valluri
We provide an alternative formulation of the exact calculation of the current-voltage characteristic of solar cells which have been modeled with a lumped parameters equivalent circuit with one or two diodes. Such models, for instance, are suitable for describing organic solar cells whose current-voltage characteristic curve has an inflection point, also known as an S-shaped anomaly. Our formulation avoids the risk of numerical overflow in the calculation. It is suitable for implementation in Fortran, C or on micro-controllers.
NAApr 8, 2015
A Robust Approximation to a Lambert-Type FunctionKen Roberts
The function $y = g(x) = \mathrm{log}\big(W(e^x)\big)$, where $W()$ denotes the Lambert W function, is the solution to the equation $y + e^y = x$. It appears in various problem situations, for instance the calculation of current-voltage curves for solar cells. A direct calculation of $g(x)$ may be inaccurate because of arithmetic underflow or overflow. We present a simple algorithm for calculating $g(x)$ that is robust, in that it will work for almost all $x$ values which are representable in the arithmetic of one's chosen computer language. The algorithm does not assume that the chosen computer language implements the Lambert W function.