Just an addition to this thread, to point out a few perhaps un-noted factors.
1. Power in watts = volts x amps.
BUT - the rated power of a solar panel is the maximum power it will deliver under standard sunshine. Output amps from a panel increases as the voltage from the battery decreases, but the change is not linear, and the rated power is the highest figure for the two multiplied together. Unless this is the voltage of the battery when charging, the power output will be less. And typical panels give their rated power at about 18v - higher than your battery will ever be, so in standard sunlight you will never get your rated power. Worth noting that what matters as far as restoring the charge in the battery is amp-hours, not power; the difference in charging voltage versus discharging voltage is a measure of the charge/discharge efficiency of the battery.
2. The panel is rated in standard sunshine. The actual sunshine can be higher or lower, but in clear weather in much of Australia is often higher. In partial cloud cover the output can be significantly higher due to reflected light from the clouds. In snowfield conditions it can be a lot higher.
3. The panel is rated at standard temperature, usually 20C. As temperature increases, output decreases, so for much of the time in most of Australia, output will be down, but in snowfield conditions, the temperature effect can give a large increase in output.
4. The panel will only give rated output with the sun falling normally (at right angles) on the panel, as you probably realise. Up to about 20 degrees off makes little difference, but above this the loss climbs rapidly.
5. The duty cycle of the refrigerator varies with temperature. For many fridges, when used as a freezer, it is likely to approach 100% over most of Australia in summer. Anything you can do like adding an extra layer of insulation (but not restricting airflow), or keeping the fridge in the coolest possible place will help.
John
