Let's talk about the Solar Tree that was developed by the Council of Scientific and Industrial Research (CSIR) in New Delhi, India. Why? Because the creators are making claims that aren't supported by science. Click this link and watch the video (sorry - it won't let me embed it), and then I'll address a few points.
Solar Energy
First, a couple of definitions. Energy (measured in kiloWatt-hours, or kWh) is the ability to do work. Power (measured in kiloWatts, or kW) is the rate at which energy is produced or consumed. (Technically it's the rate at which energy is converted since energy is neither created nor destroyed.) For the purpose of this discussion, you can think of energy as power accumulated over a period time.
The solar "irradiance" - the power of sunlight reaching the Earth's surface - is about 1 kW per square meter. If you took one square meter of land and had sunlight shining upon it from directly above (perfectly perpendicular to the surface), there would be about 1 kW of power available.
Commercial solar panels are about 20% efficient, so of that 1 kW of solar power, only 20% of it, 0.2 kW, is converted into electricity.
For every square meter of space, PV panels can generate about 0.2 kW of electricity.
The CSIR spokesperson says, "It takes about four square meters of space to produce energy which otherwise, in the conventional SPV (solar photovoltaic) format, would have required 400 square meters of space." Let's do the math on that:
A solar array that covers an area of four square meters can generate 0.8 kW of power.
A solar array that covers an area of 400 square meters can generate 80 kW of power.
Why does he claim that the tree can generate more power? Because the branches are on different levels and tilted at different angles. CSIR claims that "This design facilitates placement of solar panels in a way that they are exposed more towards the sun and that way they are able to harness ten to fifteen percent more energy."
On the surface (no pun intended) that seems to make sense. It's like an apartment building - if you keep stacking more levels on top of one another, you can get much more living space with the same footprint. But it's not an apartment building. The panels near the bottom of the tree will be shaded by the ones above! Furthermore, the panels tilted at different angles means that at most, only one will be oriented perpendicular to the sunlight. So one panel is generating about 0.2 kW, while the rest are producing less.
The way to harness ten to fifteen percent more energy is to put tracking motors on the panels, so they're always pointed towards the sun throughout the day. I saw no such mechanisms in the video, and even if the panels could track the sun, you'd still have the shading issue.
If It Sounds Too Good to Be True…
… then it probably is. But don't lose your sunny disposition over this, because there is a viable Solar Tree that I examined a few years ago. I did the math on that, and it worked out. And if you want to go vertical, MIT has a solution for that too.
People often fall into the trap of thinking that if nature does something, then technology should follow suit. There are cases where that's true, but not universally. (Have you ever seen an airplane flapping its wings?) Trees have a good design, but they aren't designed for the optimal production of electricity.
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