Introduction

Crude oil, since its discovery in the 1880s to displace coal, has been the major source of energy in our homes and industries. However, just as coal had to step down for the emergence of crude oil, many are of the opinion that it is time for an alternative source of energy to displace crude oil; putting into perspective the negative effects of crude oil on our world today – land and water pollution, acid rain and climate change are among the many issues we are having to contend with as we continue to source for energy from crude oil.

Renewable Energy Technologies (RETs) are finally beginning to give crude oil a run for its money. Solar energy has been with us for some time now; it is one of the few, out of a number of these alternative energy sources, that is managing to get a breakthrough in a society were crude oil has been ‘king’ as far as energy is concerned.

There are many reasons why crude oil is yet to be overthrown even with the devastating negative effects it is having on our lives and environment. These RETs are simply not there yet. They all have their limitations when it comes to efficiency and cost has also been a pretty big deal. I am a big fan of these technologies though and solar energy technology happens to have the biggest prospect among them.

Current Solar Power Technologies

The earth intercepts about 173,000 Terawatts of energy from the sun; that’s around ten-thousand times the amount of energy that its population (over 7 billion people) uses. The potentials of solar energy are, simply put, limitless! Solar power technology is the use of man-made technology to harness the sun’s energy for electricity production. It is a clean and renewable source of energy. The two main solar energy technologies are Concentrating Solar Power technology (CSP) and Photovoltaic technology (PV).

Concentrating Solar Power (CSP) uses an indirect method of producing electricity from solar energy. Remember when you would place a small piece of mirror under the sun rays and watch as it forms a beam that burns a piece of paper placed beneath it? That’s the kind of the concept that this technology uses. It utilizes a system of mirrors to trap sunlight and then focuses the sunlight onto a receiver where it is converted to heat. The heat is then used to generate steam to run a turbine for generating electricity in a power plant. It is more commonly applied industrially.

Photovoltaic Technology (PV) is the most common form of solar power technology as it is used in solar panels which are found on residential roofs and spaces in commercial areas; the PV cells that make up a solar panel converts solar energy into electrical energy by absorbing photons of sunlight. These PV cells are made of a semi-conductor known as silicon (the second most abundant element on earth, after oxygen). In a solar cell, silicon in its crystalline form is layered between two conductive metal strips. Each silicon atom bonds covalently with 4 neighbouring atoms. The silicon in each cell has two layers; the N-type silicon and the P-type silicon which are separated by what is known as a P/N junction. When the photons of the sun light strike the PV cell, they can knock an electron from its bond, thereby leaving a free electron which goes to the N side and a hole which moves to the P side. This electron then joins other free electrons to flow through the metallic strip to an external circuit where it gets to do electrical work. The direct current (DC) that the PV produces is converted to an alternating current (AC) with the use of an inverter and this is then used for powering our home appliances.

Why we need to take a step further

Just like most other RETS, efficiency is still a major downside to this technology. Most residential solar panels still operate with an energy efficiency of 12 to 15%, that is to say, about 12 to 15% of the solar energy it receives is eventually converted to electrical energy. This is still quite far from, say, diesel engines that have an efficiency of 30 to 41%; which is why an array of solar panels would be found on the rooftop of an average residential home to supply enough power to meet the energy demands of that home. Recently, solar panels that can have up to 46% energy efficiency values are taking the leap from theoretical existence to practical reality in laboratories but they are not yet up for residential usage.

The major issue though with the common solar power technologies is currently the fact that they rely completely on the sunlight duration to function and since the earth is constantly rotating about its axis as it revolves round the sun, we have days and nights. Nights representing the time when your portion of the earth has rotated away from the light of the sun, thereby rendering solar panels useless for that period. So even if the issue of energy efficiency is taken care of, it won’t solve the biggest challenge posed to this technology which is that of energy storage. We still have to rely on batteries to store energy during the day for use during the night and on days of cloudy weather. Batteries are good for achieving this purpose; however, they do not really come cheap because of the components used to set them up. They also do not last the life-span of a typical solar panel set up, meaning; they would have to be replaced at every point in time. When you consider the exponential rate at which energy demand is increasing, you would agree that storage may not be the long-term solution. So why not just break this barrier by going to space to tap the sun’s energy continuously and without any hindrance?

SPACE-BASED SOLAR POWER (SBSP): What is night when we can have light?

Space-based solar power is the placing of PV system-embedded satellites in the geostationary orbit (38, 500 Km above the earth) to collect solar energy directly from the sun and transmit it wirelessly to the earth to be used as electrical energy. It intercepts sunlight in outer space and wirelessly transmits the collected energy in form of electromagnetic radiation such as microwave or laser beams to a ground receiving station on the earth’s surface. The satellite is placed in a geostationary orbit so that it could have the same rotational period as the earth and therefore prevent the transmitted waves from misaligning with the ground receiver.

This concept of SBSP was first associated with an American scientist and aerospace engineer known as Dr. Peter Glaser where it was presented in his 1968 report, Power from the Sun: Its future, for which he later received a patent in 1973. Moving on, National aerospace research institutions such as NASA of the United States and JAXA of Japan have taken strong interest in this idea and have invested a lot of resources into the Research and development of this technology which could take either of two forms;

One _ Microwave Transmission; photovoltaic arrays are coupled to a microwave power transmission system and launched as a satellite into space. It is designed in such a way that the arrays are placed facing the sun while the microwave transmission disc is aimed at a ground receiving station where the transmitted wave is then converted back to electrical energy. At the receiving station, a rectifying antenna "rectenna" is used to convert the received microwaves into electricity (DC power). The microwave rectenna is normally made up of a dipole antenna and an RF diode but for the purpose of such large scale application, it would comprise of a number of short dipole antennas that are connected to each other by diodes.

Two_ Laser Power beaming; If you are having a mental picture of lasers that split materials and people into two like in your cartoons and video games? You need not worry, it doesn’t get to that extent. This method also utilizes satellite based PV arrays to convert solar power to electrical energy. The difference comes in the mode of transmission of the energy from outer space to the earth surface.

It transmits the collected energy in form of laser beams that target a PV rectenna on the ground. Since the laser beams operate in the near visible portion of the electromagnetic spectrum, at the ground receiver, special photovoltaic laser power converters which are optimized for the monochromatic wavelength of light are applied to convert the beams to electricity.

Why don’t we just launch these cool satellites right away?

The cost of setting up facilities in outer space has always been a major challenge to space-based projects. The cost of setting up a 10-25 MW SBSP prototype in low earth orbit was estimated to be around 200 million dollars. This is excluding service and maintenance cost. Paul Jaffe of the US Naval Research Laboratory estimated that $10 billion would be required to set up a demo orbital power station that would power about 150,00 homes within 10 years. 320 billion dollars has been projected to implement this technology to supply the energy demands of the whole United States till 2030. Let’s face reality here; THESE NUMBERS ARE SCARY! This is the reason why there seem to be a lack of enthusiasm and commitment on the part of governments to invest in the project. In Yasuyuki Fukumuro of JAXA’s interview, he suggested that collaboration between different nations would be needed to get a realistic chance of implementing the project as the cost would be too enormous for Japan to implement independently.

From a technical perspective, a significant fraction of transmitted energy (55–60%) is lost on its way through the Earth's atmosphere to the receiving ground station. Of the number that gets to the earth, about 10-40% is also lost due to the power conversion efficiency of the rectenna ranging from 60-90%. There are also safety issues associated with the transmission of laser beams and microwave through the earth’s atmosphere and as such, modulation of the wave’s energy would be required to prevent harm to any flying object that might wander in the beam’s path.

Looking Forward!

It’s about 50 years on since that initial idea of solar energy from space by Paul Glaser came into being and it’s still looking as though it is a near impossible task to achieve. Well, same was said about the aeroplane, the internet and many other wonderful inventions that have shaped the way we live today. As such, the possibilities of us experiencing the SBSP in this lifetime can never be ruled out, considering it has been theoretically proven and has made considerable practical progress since that 1968. From the marvels I’ve seen science and technology achieve in the little time I’ve spent with you guys on earth so far, talking from wireless communication, to microcontrollers, to nanotechnology, and to HBO's Game of Thrones… yes - Game of Thrones! I’d be damned to rule out anything anytime soon.

REFERENCES

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How do solar panels work? Retrieved on June 4th, 2018

NASA wants to collect Solar Power directly from space. Retrived on June 4th, 2018

An Introduction to Harvesting Solar Energy from Space. Retrieved on June 4th, 2018

Space island group. Retrieved on June 4th, 2018

Practical application of space-based solar power generation. Retrieved on June 4th, 2018

Future visions: Space-based solar power. Retrieved on June 4th, 2018

Space based Solar power. Retrieved on June 4th, 2018

What It Will Take to Farm Sunlight from Space? Retrieved on June 4th, 2018

Wireless Power Transfer. Retrieved on June 4th, 2018