Constant power solar calculator for Hobart

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.

About this calculator

This calculator is for solar street lights using a lithium battery. It is important to keep the charge of the battery high to extend the life of the battery.

  • Location: Hobart, TAS (using solar data from Hobart (Ellerslie Road)
  • Lithium LiFePO4 battery
  • Solar panel tilted 65° and facing North


  • Constant power output 5.5W 24/7
  • Solar Panel 80W
  • Lithium LiFePO4 30Ah  (384Wh)


  • On average this system has 74.13% battery remaining at dawn.
  • 0.0% is the minimum battery charge at dawn (May – June)
  • Hobart has very short days in winter of usable sunlight. The shortest is just over 3 hours Because of this the minimum battery charge is 0.

Weather Predictions

  • Past weather performance is not an indicator of future weather patterns.
  • 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 20° above the horizon (preferred option).
  2. When the sun is 18° above the horizon.
  3. When the sun is 12° above the horizon.

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 calculator is editable.

██ coloured cells are editable