The Sun generates energy from nuclear reactions occurring in its dense, hot core. It produces a massive 382.8 trillion trillion (3,828 x 10 26) watts of electromagnetic radiation, mostly in the form of visible, infrared and ultraviolet light. As we move away from the Sun, the intensity, that is, the power per unit area, drops in proportion to the square of the distance.
How much energy do we get from the Sun to the Earth
The solar constant is the average intensity of solar radiation at a distance of 1 astronomical unit (the average distance of Earth from the Sun). Its value is 1,361 watts per square meter (W/m 2). In fact, the Sun’s output is variable and fluctuates by 0.1% around this value.
The total energy consumed by humanity in 2017 is slightly less than this figure and is 160,000 TWh. This figure includes not only the energy used to generate electricity, but also the energy used
directly for heating (e.g., by burning wood, coal, oil or gas),
For transport (mainly gasoline, diesel and jet fuel)
energy used in industrial processes.
The total amount of electricity consumed in 2017 was about 22,000 TWh.
Opportunities for solar power
There are two different ways to generate electricity from sunlight. One way is to concentrate solar energy using mirrors in a small area and use the heat generated to produce steam to spin a turbine that generates electricity. Another way is to use arrays of photovoltaic cells (better known as solar panels) to generate electricity directly from sunlight.
Most of the solar electricity is generated using solar panels. Much of this is at solar farms, such as the Topaz Solar Farm in California. It covers an area of 19 km 2 and produces about 1.25 TWh of electricity per year. As the prices of solar panels continue to fall and their efficiency increases, the amount of electricity produced in this way will continue to grow.
The growth of solar energy
One of the advantages of solar energy over other forms of green energy is that it has almost unlimited potential because of the enormous amount of energy that comes to Earth from the sun. If the problems of distribution and storage could be overcome, it would be necessary to cover only a small portion of the Earth’s surface with solar panels to meet all of humanity’s energy needs.
To calculate the size of this area, the first thing we need to consider is the amount of solar radiation that actually reaches the Earth’s surface. Although the solar constant is 1,361 W/m 2, this is the intensity of the radiation reaching the top of the Earth’s atmosphere. Even on a cloudless day, not all of this radiation reaches the earth; some is reflected back into space and some is absorbed by the atmosphere.
In fact, the Sun can only be directly overhead in the tropics. When the Sun is lower in the sky, the intensity of solar radiation decreases because its rays spread over a larger area and because they must pass through more of the atmosphere before reaching the earth. At night, when the sun is below the horizon, the solar intensity is clearly zero.
The time axis uses solar time, i.e., the Sun rises at 06:00, reaches its maximum at 12:00, and sets at 18:00. The day is assumed to be cloudless. If we average the entire 24-hour cycle, the amount of solar radiation hitting the Earth’s surface (known as solar radiation) on a clear day at the equator on the day of the equinox is approximately 340 W/m2.
At higher latitudes, the Sun is lower in the sky and therefore the amount of solar energy that can be generated is less. The amount of solar energy is reduced due to cloud cover. For example, in the cloudy northwest of Leningrad Oblast, the average annual solar radiation is only 72 W/m2 , which is about one-fifth of its value at the equator.
If we average over 12 months and over all places on the Earth’s surface, the average solar radiation will be 170 W/m 2. This means that we would need to cover 586,000 square kilometers of the Earth’s surface with solar panels to meet all of the world’s energy needs, which is about 15% more than the area of Spain.
The main problem, however, is that the countries that could generate the most solar energy (especially in Africa) actually have modest energy consumption, and many densely populated countries, especially in Northern Europe, have high energy consumption and receive relatively little sunlight.
For example, in the UK, which has a small area, receives relatively little sunlight compared to the global average and is densely populated with high energy consumption, we would need to cover about 5.2% of its surface with solar panels. (This calculation is actually an oversimplification, because it ignores the big difference between the amount of radiation in the summer and winter months.) For this to work, the excess energy generated during the solar months must be effectively stored for use during the warm winter months, which would be a huge plus!
Small scale solar power
Right now, solar power is not the largest renewable source of electricity. In 2020, 5,877 TWh were generated from renewable energy sources. Of that, the vast majority (4,023 TWh) was generated by hydropower, followed by 960 TWh from wind; solar provided 333 TWh, with the remaining 561 TWh from all other renewable energy sources combined.
One clear advantage of solar power is that it can be generated on a small scale. One four-square-meter panel attached to a rechargeable battery will be able to generate and store enough solar energy to light and cook food for a family in Africa. The solar panels have no moving parts and should last for decades once purchased. It is this ability to generate electricity on a small scale that could revolutionize the lives of some of the poorest people in the world.
For small solar installations, it is common to increase the average intensity of sunlight by tilting the panel toward the sun. For example, small solar panel arrays are often tilted to the south. Obviously, this is difficult to do for very large solar panel arrays installed on solar farms.