Constant power solar calculator for Sydney

Our calculator uses hourly typical meteorological year (TMY) data from NREL.

Data from TMY is for a 1 year period. The collection of this data is over many years

This calculator is for a marine application using an AGM type battery. It is important to keep the charge of the battery high to extend the life of the battery.


  • Constant power output 36W 24/7
  • Solar Panel 620W
  • Battery AGM 250Ah (3000Wh)


  • On average this system has 79.48% battery remaining at dawn.
  • 50.20% is the minimum battery charge at dawn (20 April)
  • Sydney had a few consecutive days of very bad weather. Because of this the minimum battery charge has been quite low.

Weather Predictions

  • Past weather performance is not an indicator of future weather paterns.
  • Yet, this is real historic weather data and, it is a good starting point.

Usable sunlight hours

There are three options of usable sunlight hours.

  1. When the sun is 24° above the horizion (preferred option).
  2. When the sun is 18° above the horizion.
  3. When the sun is 12° above the horizion.

When the sun is 12° above the horizon, there is not much power produced by the solar panel. This can result in misleading calculations. Yet, it is good to have to compare with actual results.


The way the calculator works.

  1. (Net day watts) = (Total watts produced by solar panel during the day) – (Total watts consumed during the day)
  2. (Sunset battery charge) = (Net day watts) + (Previous day dawn charge)
  3. (Dawn battery charge) = (Sunset battery charge) – (Total watts consumed during the night)
  4. Repeat step 1 for the next day

This calcualtor is editable.

██ coloured cells are editable