Glossary: Solar Declination
**Solar Declination** is the angle between the sun's rays and the earth's equatorial plane, which varies from +23.45 degrees at the summer solstice to -23.45 degrees at the winter solstice, dictating seasonal solar panel tilt adjustments.
Seasonal Solar Positions
The declination angle changes daily as the Earth orbits the Sun. PVWatts and solar models calculate daily declination to determine optimal seasonal solar angles for off-grid power grids.