July 2005, Issue 180

Solar-Powered Water Pump Controller
Cypress PSoC High Integration Challenge 2004 Contest Winner

MAX POWER-POINT ALGORITHM

The maximum power-point algorithm adjusts the regulated DC bus voltage to extract the maximum amount of power from the solar array. The maximum power for a 48-V nominal array is extracted when the DC bus equals 67 V. But this is quoted with a panel temperature of 25°C. The voltage typically changes by –0.32 V/°C as the panel temperature rises.

A simple technique to monitor the maximum power-point voltage is to periodically disconnect the load and measure the DC open-circuit voltage. You can determine the maximum power-point DC voltage by multiplying the open-circuit voltage by a fixed fraction between 0.6 and 0.8. I chose a value of 0.7 for the solar pump controller and took measurements every 30 min.