Today, let explore another situation.

As you might aware, you are allow to install solar panel at your house's roof top to generate electricity and then sell it back to TNB under the Sustainable Energy Development Authority Malaysia (SEDA) Feed-in-Tariff (FiT) scheme. Per the scheme, the maximum power an individual can install is 12kW.

So what if you are going to use this generated power to charge your Tesla Model S electrical car that comes with 85kWh battery.
Is this sufficient?

Let’s do some calculation here. In order for the solar panel to generate electricity, it needs sun light. Few of the factors that affect the output efficiency are the angle and intensity of the sun light, which fall on your solar panel surface.

Picture above is showing the position of the sun at KL area. Sunrise starting from 07:24 morning and set at 19:27 in the evening. We can’t take full 12 hours for the calculation as the morning and evening sun aren’t as strong as the noon sun. So we take an average of 6 hour in total.

For a 12kW solar panel system, you aren’t going to get full 12kW power generated. There are losses in term of circuity and connection among the panels. Giving it a 20% drop on the overall performance is a rational number, which is 12kW x 80% = 9.6kW.

Therefore, one full day of sun light will generate:

9.6kW x 6 hour = 57.6kWh of energy

This is only 68% of the 85kWh that are required to fully charging up the Model S car battery.

In other words, you need more than a day to fully charge up your 85kWh car battery, if you purely depend on the roof solar panel generated electricity for charging.