The only source of energy for our earth is the sun. Coal, gas and oil would not exist without the sun. Even wind is only blowing because of the sun. Every day the sun’s power density of 1.32 kW/m^2 hits our earth during periods of full sunshine. Clouds reduce the power density but even on a cloudy day my solar panels produce a lot of electrical power from the reduced solar radiation reaching my roof. Cumulus clouds in fact increase the output of my panels because they reflect sunlight which would otherwise not hit the roof where the panels are. So, with the cloud reflection, I get both the direct sunlight as well as the reflected sunlight. I learned this by observation on bright sunny days with cumulus cloud patches looking like mountains of steam.

When my solar panels produce power in the order 4 kW, there is no sound except for the faint sound from the fan in the solar inverter during hot summer days. With the operating of a domestic solar system one gets aware of the sun’s power. As humans we experience the sun as light and heat. We normally don’t associate the sun with any amount measured in kW or kWh. Kilowatts (kW) denote power and power over a time period, say 4 kW coming down from the panels on the roof for 3 hours, gives 3h x 4kW = 12 kWh of energy. Energy can be expressed in different units. For example 1 kWh = 3.6 * 10^6 Joule or 1 Watt over 1 second = 1 Ws. One does not need to study physics for understanding solar power. A little knowledge of the major parameters involved in solar power is however useful when operating domestic solar.