By Editor • 3 years ago

As we discussed in a previous article, the intensity of sunlight at the Sun’s surface is about 64100 kW m-2(64.1 MW m-2) which diminish down with the distance and is about 1000 W m-2 at the Earth’s surface when the Sun is at the zenith.

Figure 01: Beam divergence of an EM (sunlight) beam with distance

This reduction in the intensity is due to the divergence of Sun’s rays as they travel a long distance from the Sun (Our Sun would look like a point source if you take a look at the long journey of Sun’s rays travelling from the Sun to Earth).

On average, the amount of energy received by a solar energy harvesting device with an area of 1 m2 at the Earth’s surface is about 1000 J  per second (Since the intensity of solar radiation is about 1000 W m-2). But….What if we can increase this figure?


It would create a flood of energy and will offer a great opportunity to harness energy from a small area leading to a more space-efficient and more cost-effective energy harvesting technology.

It is obvious that the energy yield (energy harvest) increases when the intensity of solar radiation increases. Further, high energy yield (energy harvest) obviously curtails the payback time.

The higher the intensity of solar radiation the shorter the payback time!

That means, the energy yield by a given solar energy harvesting device would,

  • Double when we double the intensity of solar radiation.
  • Triple when we triple the intensity of solar radiation.

So, it is crystal clear that the energy yield per unit area can be improved by increasing the intensity of solar radiation.

But, how can we increase the intensity?

That is the idea of concentrated solar technology.

For ease of understanding, let’s take a look at a simple analogy.

An analogy

It would take minutes to fill your cup with rainwater if you wish to collect rainwater by exposing the cup to rain. It would take, however, much less time to fill the same cup with rainwater if you are collecting rainwater from a gutter outlet.


The gutter has, of course, a small area but collects rainwater falling onto a large surface area (Roof)! So the gutter outlet would fill your cup in an instant.

Simply, you can collect a large amount of water from a small gutter outlet within a short period of time while a large surface area is needed to collect the same amount of rainwater within the same period of time if you are collecting water from rain.

This is analogous to the concentrated solar energy concept. Incoming sunlight received by reflectors (analogous to a roof) is focused onto a small area (analogous to a gutter) by using mirrors or reflectors and intensified solar radiation is then collected and converted into useful energy. Several configurations have been tested and implemented successfully to concentrate solar radiation. The payback time, initial investment, and system efficiency largely depend on the configuration used to concentrate solar radiation. Each configuration has unique and specific pros and cons. In the next article, let us discuss them one by one.