How do solar cells work?
A photovoltaic cell or Solar PV cell is a sandwich of silicon layers, specially treated to react to light; with more electrons on top (negative charge), and less on the bottom (positive charge). When photons of light strike the top surface, these extra electrons are knocked loose and are attracted to the positively charged side, generating an electric current – like potting balls in a game of pool. Think of the white cue ball as the photon of light and coloured balls as electrons.
Each thin layer of the solar cell sandwich increases the efficiency of the cell by increasing the range of the colours of light the cell can react to, and limiting the amount of light energy wasted, not unlike like having more balls on the table and bigger pockets.
The real issue of solar power is efficiency – at an average of 11 – 15% for commercially available panels there’s a big margin for improvement. Panels of up to 40% efficiency have been proven, however I wouldn’t hold out for these just yet as they are just far too expensive for mainstream manufacture at this time.
Sunlight is free though, so that 15% is still a gift and can easily provide power to domestic appliances on the go. Camping anyone?
The limitations of renewable energy
Sporting 72 meters of wing span; greater than a Boeing 747, covered entirely in solar PV cells, Solar Impulse 2 is capable of generating enough electrical energy to carry a single pilot, essential survival equipment and instrumentation. To store enough energy to continue through the night the plane also carries 633 kg of powerful lithium ion batteries which have to be charged fully each day and will almost completely discharge over-night.
To conserve power, speed and altitude are reduced after dark, there are no environmental controls, no heaters, and no cabin pressurisation.
And the plane can only land at night when the winds are low.