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7.2: Harnessing Solar Power

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    85112
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    As shown in the Fig. 7.3, out of the total of 174 PW of solar power reaching the Earth, only 89 PW (51%) reach the Earth surface. Yet, we don’t need to care about the 49% “losses”, because the remaining 51% still represent a tremendous amount of power, if we compare it with the current global consumption of all forms of power, which net about 21 TW. The latter is only a tiny fraction of the 89 PW = 89 000 TW, let’s check: 21 TW/89 PW = 21/89000 = 0.00024 = 0.024%.

    This is an impressive figure – but numbers written on paper or on com- puter screens still make a much weaker impression than the same information presented in a graphic form. Such a piece of graphics, definitely worth look- ing at, was created by a German scientist, Dr. Matthias Loster – please click on this link to watch it.

    Dr. Loster's graph shows a map of Earth, with a global distribution of insolation shown using a color scale. On this map, there are six black dots. Each dot corresponds to a circular area of radius 200 km, so it’s total surface area is about 125 000 square kilometers. Suppose that each such area is totally covered by devices converting solar radiation to other forms of usable power – i.e., each dot is a giant “solar power plant”. And it turns out that the sum of output power from those six “power plants” would be 18 TW – which was the total global consumption of power in the year 2006, when Dr. Loster made the graph.

    The total area of all lands on Earth is about 150 million square kilometers. The total area of all “dots” correspond to about 750 thousand square kilometers – about 0.5% of the total land area.

    Is it feasible to use 0.5% of the land area of Earth to build solar power plants? Well, let’s take a closer look at Dr. Loster's graph, and then on a graph showing the largest desert areas on Earth.

    Loster's proposal for six systems scattered across the continents, capturing enough sunlight to produce 18 Terawatts of energy, enough to power the entire world.
    Figure \(\PageIndex{1}\): Mattias Loster's idea that six large solar arrays could power the world
    clipboard_e0ff8ac56ba868b109116d001a33dd502.png
    Figure \(\PageIndex{2}\): A map of desertification, showing the largest desert areas on Earth (source: Wikimedia Commons).

    It’s clear that Dr. Loster put his six dots in the middle of large deserts area. So, those giant solar plants won’t “steal” land from agriculture. Or occupy land that can be used for building cities – a perspective of living in an area where the temperature may reach 120F, and there is now water, is not very attractive for most people.

    In Dr. Loster’s graphics, there are then two “messages”. One is simple: See! There is “more than enough” solar radiation to satisfy all humanity’s needs for power – and it seems likely that even if the demands double or triple, there still will be enough!

    The other “message” is a bit more “hidden” because the graph does not show that the dots are all located in desert areas which are not very suitable for use for other purposes. What is more visible, however: they are arranged around the globe in such a way that some of them are always illuminated. In other words, the message is: It is possible to build a global solar power system which will provide power 24 hours a day because some of the constituent power plant will always be active. It’s clearly a great idea – yet, one must realize that the creators of such a global system would have to deal with two huge challenges: one is of technical nature, and the other of political nature.

    The technical challenge is that the power from a real global system must be available to all dwellers of the globe. So, it would be necessary not only to build the plants, but also to create a “world wide web” of transmission lines. Would it be feasible at all? Certainly, such a global system cannot be created overnight. But there are reasons for optimism. Currently, the world’s longest existing transmission line is in Brazil. It uses the High-Voltage Direct Current (HVDC) technology, is 2,375 km (1,476 miles) long, and transmits over 6 GW of power. China intends to build an even longer (3,000 km) Ultra-HVDC line, capable of transmitting 12 GW of power1. So, if a large number of such transmission lines are built, reaching to all countries, the world-wide power transmission network may become a reality. Well, perhaps in principle...

    In principle, because the other challenge is really serious. A global solar power system can work only in a politically united world. Currently, the world is divided into a number of political blocs, which compete with one another, or even wage wars with one another. If a global power system were created, then, naturally, the regions located closer to the power generating centers would have more control over the transmission lines than the regions located far away from the centers. And if a conflict emerges between two regions, one of them having more control over the system than the other – “blackouting” the adversary may be used as a powerful weapon. In today’s world, where new and new political conflicts erupt all the time, no country would be willing to risk its energy security. Therefore, the creation of a global solar power system “must wait for better times”.

    But a global system, of course, is not the only option. Almost all coun- tries in the world are now investing in solar power. The power installed by the end of 2016 is listed by country in this Wikipedia article. The world- wide cumulative power in 2016 was at least 308 GW. As far as the “new renewable power sources” are concerned, the cumulative solar power in 2016 was second only to cumulative worldwide wind power which in 2016 was 487 GW. However, the growth of installed solar power capacity in 2017 was 98 GW, almost twice as high as the growth of the installed wind power capacity in the same year (52.6 GW). Therefore, as far as the cumulative installed power is concerned, solar power may soon become the leader. Which is not surprising, considering that – as follows from the data shown in Fig. 7.1 – there is about 100 times more available solar power on Earth than wind power.

    So, solar radiation may offer us a real “El Dorado2 usable energy”. The only problem is how to convert it to electric power. Well, not exactly a problem, because there exist two mature (or almost-mature) technologies for performing such a conversion. One is the solar thermal conversion, or the concentrated solar power (CSP) method. The CPS power plants are large

    facilities, with power of tens, or even a few hundreds of MW. They can be installed only in areas of very high insolation, which is a drawback – but they can keep generating power for several hours after the sunset. The other technology is the photovoltaic (PV) conversion. There neither low nor high limit for power of PV installations – rooftop installations at single family houses are of a few kW power, while giant arrays of PV panels may deliver hundreds of MW. The PV installations are also “more tolerant” to weather caprices. We will discuss the CSP and the PV technologies in greater details in the following two Sections.

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    1. To give the Reader an idea of what 12 GW is: it’s more than the average power consumption in small industrialized European countries like Denmark or Switzerland, and about the same as the average power consumption in the Netherlands.

    2. El Dorado – a city of fabulous riches believed to exist in South America by 16th century explorers.


    7.2: Harnessing Solar Power is shared under a CC BY 1.3 license and was authored, remixed, and/or curated by Tom Giebultowicz.

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