# Posted in 2021

## T_cell_typ_avg

- 2021-06-17

This is a short note that derives the “typical average cell temperature” used in the “Weather-Corrected Performance Ratio”. The Weather-Corrected Performance Ratio 1 is defined as:

The denominator is essentially the PVWatts DC model, except the reference cell temperature is not \(T_{\mathrm{STC}}\) but rather a “typical/average” cell temperature. The report has this to say about that decision:

## Floating Point Fun

- 2021-03-09

Computers must represent real numbers with some finite precision (ignoring symbolic algebra packages), and sometimes that precision limit ends up causing problems that you might not expect. Here are a couple examples.

The function \(f(x) = \exp(x) - 1\) is kind of fun – by subtracting one from the exponential, it removes the only constant term in the Maclaurin series of \(\exp(x)\):