Month: May 2018

Evolution of Solar Energy Technologies

Solar energy was one of the pivotal elements in the formation of organisms on Earth and has been playing a crucial role throughout the evolution from the very beginning to date. Plants absorb solar energy and convert into biomass via a natural process called photosynthesis providing food, medicines, wood for furniture, and many more. Evaporation of water is predominantly governed by solar power hitting the Earth and is the driving force of hydrological cycle which is a decisive factor in determining the fate of living beings.

Nowadays, solar energy technologies have been generating braking technological and economic news bulletin. Anyway, use of solar energy is not a new concept. Even ancient civilizations had recognized the significance of solar energy and duty of the Sun. As such, many ancient civilizations had developed their own traditions to admire and praise the Sun for its precious contribution to their lives. Egyptians, Mayans, Greeks, Romans and many other ancient societies revered the Sun even as a god and worshipped. Mega structures or great temples devoted to the Sun clearly manifest how ancient people think of the Sun and its power!

Human beings have been utilizing energy from sunlight for thousands of years. Ancient Egyptians constructed their buildings so that their buildings absorb and trap heat coming from the Sun during daytime and release during night keeping the temperature at a moderate level. Ancient Romans also used sunlight to keep their homes warmer during the winter. Not only that some societies like ancient Greeks allegedly used solar energy as a weapon for mass destructions by focusing sunlight to set fire on their enemies’ ships!

Many prominent architects designed buildings so that the residents could enjoy maximum use of day lighting inside the buildings. And it is well-known that the use of sunlight was one of the most popular means used to dehydrate and preserve some foodstuff such as lemon, chilies, in ancient times. Then solar cooker was invented by Swiss physicist, Horace de Saussure in 1767 [1]. It seemed to be the very first vendible solar energy technology designed for cooking.

Image: A solar cooker [1]

Everything changed with time.

New solar energy applications and technologies were born with the growing attraction to renewable energy and concerns over climate change and pollution caused by fossil fuel burning. Different solar energy applications and different solar energy technologies are now on the market and ready to be purchased and used.

Solar energy has now become the fastest growing form of energy penetrating into the grids in many countries. Modern-day technology offers a wide range of solar energy applications and technologies which are grouped into three main classes below.

• Solar hot water systems and solar space heating/ cooling
• Concentrated solar thermal power
• Solar Photovoltaics

In addition, several other technologies have been developed but they are neither efficient nor economically feasible yet. While solar hot water systems and space heating were the first cost-effective technologies, concentrated solar power technologies and solar photovoltaics have attracted much attention and have been implemented in large-scale to generate electricity.

Each technology offers intrinsic benefits with their own technical and economic constraints. Let us discuss each of them, from next article.

You know how things get heated by sunlight even in temperate climates.

If not, just go outside and search for a boulder or stone and touch. You would feel how hot it is.

You would be thinking… How on the Earth that distant star heats the things on the Earth whilst it is far away from us.

Yes, it is really an amazing topic to think of.

As we know it, water in oceans, rivers, lakes, etc. heats up and injects a vast amount of water vapor into the atmosphere at every point in time.

So… Why do we still use electricity for water heating while the Sun is capable of heating anything exposed to its power?

Well!

Let’s discuss.

We have already discussed the amount of solar power hitting the Earth’s surface. It is nearly 1000 W/m². Any object absorbs energy from sunlight and gets heated upon exposure to sunlight.

The idea of solar thermal energy technology is neither abstruse nor new. As we discussed in the previous article, even ancient people utilized solar energy to dehydrate some foodstuffs. Anyway, the first successful solar energy device was developed in 1767 by a Swiss inventor Horace de Saussure who is credited with developing the world’s first solar collector to harness energy from sunlight [1]. It could be used for cooking or to heat water. It took more than a century to develop a vendible solar water heating system. Thereby Clarence M. Kemp patented the world’s first commercial water heater in 1891 [2]. Since then solar thermal energy has been used in various applications (water pumping, domestic water heating, swimming pool heating, etc.).

In the beginning, the solar thermal technology could not enter the market as nearby environment provided natural energy sources and sufficient amount of energy for cooking and heating. The rapid increase in global population and urbanization, however, led to shrink the potential and availability of natural energy sources hence limiting access to them. Then people started thinking of the abandoned solar water heating technology. Commercial solar water heaters were then available on the market even in European countries where average solar flux is far lower than Asian and African countries. Its popularity had been gradually growing and the demand then noticeably increased after 1960.

Israel was a trailblazer in manufacturing and installing solar hot water systems and had widely been using solar water heating systems even in the 1960s. Then the global oil crisis occurred in 1973 surprisingly, triggered a sharp increase in the number of solar hot water systems being installed. Currently, rooftop solar hot water systems provide hot water to over 50 million houses in the world [3], saving an overwhelming amount of electricity and fossil fuels thereby cutting tonnes of greenhouse emissions and alleviating the anthropogenic climate change.

Today,

Solar hot water systems are being used in all the continents except Antarctica. China, USA, Spain, Australia, Italy, Greece, and Israel enjoy the highest per capita solar energy utilization for water heating. Several solar hot water technologies have been developed and are being used. Their manufacturing cost, energy harvesting efficiency, and technical features vary with the technology. We can decide which technology fits us depending on our purchasing power, location, climate pattern and average weather conditions

In next article, let us discuss different configurations/ technologies used in solar water heating systems and the advantages of using solar hot water systems as well.

CONTINUED

In the previous article, we formulated a simple model to calculate the amount of solar power received by the Earth. Then we realized, our planet receives approximately 127, 000 TW of solar power whilst world power demand was around 17.5 TW. However, as we know it, 71% of the Earth’s surface is covered by oceans and therefore, technically/ economically not suitable for solar energy harvesting [1]. It is clear that forests, reserves, lakes, etc. would not also be available for solar energy harvesting. Further, certain regions in the world (Iceland, Alaska, Greenland, New Zealand, etc.) do not receive an economically viable amount of solar power.

In addition to aforementioned practical constraints, no technology is 100% efficient at harvesting solar energy!

So…

Is solar energy still capable of providing 100% of world’s energy requirement?

If not, to what extent would it be able to serve?

Well

First, see the gap between the demand and the total amount of solar power hitting the Earth’s surface.

Demand~ 17.5 TW

Amount of solar power hitting the Earth’s surface ~ 127000 TW

Evidently, demand is trivial!

Seizing a small percentage (0.014%) of solar energy reaching the Earth’s surface is sufficient enough. It has also been estimated that we would still have a staggering amount of solar energy being left, approximately 580 TW [2], even if we neglected the low-sunlight and technically/ economically unfeasible areas in the world.

So…

Potential of solar energy is astoundingly unbeatable and no other source of renewable energy offers a greater or at least a comparable amount of energy, to be harnessed.

Note that, 580 TW of power

• Is about 33 times the current global power demand: (580 TW / 5 TW= 33)
• Would be 9 times the global power demand by 2100 (63 TW) [3]: (580 TW / 63 TW= 9)

Just think!

Solar energy is undoubtedly capable of pumping more than enough energy to the human’s energy bucket. The exploitable amount of solar energy would keep increasing as solar energy harvesting technologies are being continually developed leading the way to sustainability. A wide range of solar energy technologies has already been developed. They offer different benefits and have different technical and economic constraints depending on the technology. Essentially, solar energy conversion efficiency also largely depends on the energy conversion technology. Among various solar energy technologies, solar hot water systems, concentrated solar power systems, and crystalline solar cells have widely been employed, all over the world.

From the beginning of this century, the cost of solar energy technologies has been dramatically falling from the sky to ground while conversion efficiency keeps improving- Paving the way for a sustainable energy market.

Today, we all see an unprecedented tendency towards the sustainability.

Never before seen…

Buildings are being roofed by solar panels.

Large brown fields or deserts are being covered by solar collectors and solar panels.

Hotels and houses are getting installed hot water systems.

Energetically…

Dramatically…

Making the 21^st century a golden era in the human history…

A carbon-neutral and sustainable era…

Winning the horrendous aftermaths imposed by the climate change!

It is now just a matter of time thanks to the falling price of solar panels and solar collectors.

In the previous article, we calculated the luminosity of the Sun and it was found to be about 3.9 10²⁶ W. Later, we realized that our Sun generates energy at a rate equivalent to 2.2×10¹³ times the global power demand (17.5 TW).

So… One can imagine…

How much energy is dissipated by one square meter on the Sun’s surface?

Let’s find out

Total power output from the Sun= 3.9 10²⁶ W

But radius of the Sun is about 695508 km [1].

So, surface area of the Sun= 4πx (695508 km)²

= 6.08x 10¹⁸ m²

Thus, intensity of solar energy at the surface of the Sun=

= 6.41x 10⁷ W m^-2

= 64.1 MW m^-2

In other words, 64, 100 kJ of energy (64, 100 kW of power) is dissipated by each square meter (per second)!

And, annual energy dissipation by one square meter=  64,100 kW x 365 x 24 h

= 5.62 x 10⁸ kWh

Note that the average electricity consumption per capita in the USA is about 7000 kWh. [2]

So, each square meter (1 m²) of the Sun’s surface dissipates a huge amount of energy equivalent to the cumulative electricity consumption of 80286 Americans.

We can see… how powerful our Sun is.

However, physics of a radiating body does not allow EM waves to travel through space without attenuating with the distance. So, Sun’s radiation starts its journey with an intensity of 6.41x 10⁷ W m^-2from the Sun’s surface and diminishes with the distance travels.

As we discussed earlier, the intensity of solar radiation weakens down to 1388 W m^-2 (intensity of sunlight on a surface perpendicular to the EM waves) when it reaches the Earth’s atmosphere. In addition to the attenuation of solar energy with distance, it further attenuates owing to the influence of Earth’s atmosphere, as we discussed earlier.

The intensity of solar radiation at a given place on our planet Earth is different from place to place and determined by dozens of factors such as latitude, longitude and weather conditions, etc.

Tropical areas receive a notably higher amount of solar energy than other areas. Obviously, the intensity of sunlight on the Earth’s surface declines with increasing latitude towards the North Pole and decreasing latitude towards the South Pole. Anyway, the intensity of sunlight hitting the Earth’s surface is approximately 1000 W m^-2 when the Sun is at the zenith.

Now let us calculate… How much solar power is received by the Earth?

First of all, following facts must be taken into consideration.

• Intensity of sunlight hitting the Earth’s surface when the Sun is at the zenith= 1000 W m^-2
• One half of the Earth’s surface is exposed to sunlight at any given point in time.
• Although the intensity of sunlight hitting the Earth’s surface differs from place to place, we can assume that the projected area of the Earth perpendicular to the Sun’s rays is always receiving 1000 W m^-2 of power.

Radius of the Earth= 6371 km [3]

Therefore, projected area of the earth perpendicular to the Sun’s rays = π (6371×10³ m)²

= 1.27×10¹⁴ m²

Image: Projected area of the Earth perpendicular to the Sun’s rays

Solar power received by the Earth = 1.27×10¹⁴ m²x1000 W m^-2

= 1.27×10¹²x10⁵ W

= 1.27×10⁵ TW

= 127000 TW

This means our planet receives 127000 TJ of energy, every second.

Note that

The global power demand= 17.5 TW

The amount of energy received by the Earth in one day is enough to fulfil the entire global energy demand for almost 7257 days

0.014% of the energy received by the Earth is equivalent to the entire global energy demand

100%= 0.014%