SOLAR ENERGY

In 2018, the world’s biggest solar power plant on the outskirts of the Sahara will be ready to supply one million people with power. The technology is now so sophisticated that solar energy can compete with oil and coal. The next step will be large plants

It’s so much more than just panels on your roof. Solar energy CAN work 24/7, if it’s implemented in the right way...

SOLAR POWER

Huge solar power plants can now supply millions of people with power – even after dark.

SOLAR CELLS

Scientists are developing a new wonder material that can make solar cells much more efficient.

SOLAR POWER IN SPACE

Engineers aim to build solar power plants in space and send the energy back to Earth with microwaves.

On the Western outskirts of the Sahara, a shadow has appeared in the desert, which is usually a very hot place. In an area of 450+ hectares in the Quarzazate region of Morocco, 500,000 arched mirrors are aimed at the Sun. Instead of the heat being wasted in the sand, the mirrors capture the sunlight, converting it into power that is used in thousands of Moroccan homes.

Sunlight includes so much energy that the amount that hits us each day could provide the entire world’s energy consumption... times eight. So, engineers and scientists have long been eager to find an efficient way to take advantage of the great energy potential.

At the same time, the burning of large quantities of coal and oil has filled the atmosphere with CO , and the nations of the world have agreed to reduce greenhouse gas emissions. The climate crisis has boosted the development, and there is every indication that solar energy is heading for a major breakthrough.

MOROCCAN SOLAR ENERGY IS HOT

Today, solar energy is generated in two different ways. One method involves solar cells that take advantage of the energy of different wavelengths of light to push electrons and convert light directly into power. The other method is solar power plants. By means of mirrors, the sunlight is concentrated, and the high temperatures are used to make water evaporate, powering steam turbines and electric generators.

In many places in the northern hemisphere, the sun only shines for 1,500-1,700 hours a year. Nevertheless, solar cells can now compete with wind turbines there, because solar panels have become more efficient in recent years and crucially, much cheaper.

In sunnier countries such as Morocco, the second type of solar power plants are also well on their way to a major breakthrough, as the average number of sunshine hours is twice as high as in, say, Scandinavia.

So, the North African country is now building one of the world’s biggest solar power plants on the outskirts of the Sahara Desert, where the sun shines from a cloudless sky 3,600 hours a year in some places. The first of a total of four plants opened in February 2016. Once the entire complex has been finished, it will have a capacity of 500 MW, similar to a small nuclear reactor, and be able to supply one million people with power.

MOLTEN SALT STORES THE HEAT

The first plant in Ouarzazate consists of thousands of flexible, arched mirrors that follow the Sun across the sky. At

the centre of the arch, there is a tube filled with oil, at which the sunlight is focused to heat the oil.

Apart from generating power, the plant includes integrated energy storage. Only some of the heat is used to generate power. The rest heats large tanks of molten salt, which conserve the heat until sunset. After dark, the energy stored in the salt takes over, potentially keeping up the energy generation for three hours. In 2018, Quarzazate will be expanded by another power plant, which is built according to another principle. Instead of heating the oil of indivi-dual pipes, the mirrors of the power plant will reflect the sunlight to the top of a central solar tower. A container with oil is heated to power a power generator, and the surplus heat is stored in molten salt. With the addition of the tower, Ouarzazate can go on generating power for five hours after dark.

But that is still not enough. If solar energy is to become an alternative to fossil fuels, solar power plants must generate power for even more hours.

24/7 SOLAR POWER GENERATION

When energy is to be saved for the night, arched parabolic mirrors are the most thoroughly tested type of solar power generation. Most plants function in the same way as in Ouarzazate, where the surplus heat from the oil is transferred to large tanks of molten salt.

The method is reliable, but it is not ideal, as the transfer of heat back and forth between oil and salt causes energy loss. If the oil in the pipes could be replaced by liquid salt, the system would be much more efficient. This model is used at the Andasol pioneer plant in Spain, whose energy store is sufficient for 7.5 hours of power generation after dark.

But the method is technically demanding, as the salt hardens at a temperature of 290 degrees. So, the kmlong pipes must be kept warm at night by means of electric radiators to avoid that the system is blocked by hardened salt, and this reduces the energy advantage. Scientists from the Sandia National Laboratories in the US are trying to solve the problem with a new mixture of five salts, which remain liquid at temperatures of down to 70 degrees.

Solar power plants with a central tower are more fit for using salt for both collection and storage of heat. The advantage is that the pipe system between the container, the steam turbines, and the storage tanks is not very long, so the pipes can be kept warm around the clock with modest energy consumption.

Today, the method is used in the Spanish Gemasolar plant, which is the only solar power plant in the world that can supply power to consumers 24/7. This very quality is the crucial precondition that the solar power plants of the future can replace old-fashioned, coal-fired power stations completely.

SOLAR CELL POWER IS CHEAPER

In spite of all the sunshine hours in places such as Morocco, power from concentrated solar heat is still a little more expensive than solar cell power. Solar cell plants exist in all sizes, from small rooftop panels to the huge Californian 597 MW Solar Star plant, which is the biggest solar power plant in the world.

Solar cells have become extremely popular, particularly because the price of solar cell panels has been greatly reduced. In 1977, the panels cost $90 per watt they could supply, as compared to about 40 cents today. Solar cells now account for 1% of the world’s energy consumption. Today, 1 kWh of solar cellgenerated power costs 12-18 cents, which is only 2-3 times more expensive than power from established coal-

fired power plants. (Building a NEW coal plant makes the power more expensive than solar, due to start up costs.)

A new type of material, perovskites, can make solar cell power one of the world’s cheapest energy forms. Perovskites have the same chemical qualities as silicon, of which most solar cells are made today. Only seven years after their discovery, perovskites can convert 20% of the energy of sunlight into power, which is comparable to silicon cells that boast 40 years of development efforts.

This has made both universities and private companies try to solve the major problem of the new wonder materials: perovskites neither tolerate water nor air for more than a few seconds or minutes. So, scientists are trying to make perovskites more chemically robust and develop methods for encapsulating them into glass or plastic.

In spite of the success of solar cells, there is also the problem of storing power for the night. Often, solar cell power generation is at its lowest level, when the demand is the greatest – such as on dark, cold winter nights. However, a new type of solar cell could solve the problem by using the energy of the sunlight to split water into oxygen and hydrogen. Hydrogen can be stored from day to night and from summer to winter, and “solar hydrogen” could contribute to a breakthrough for hydrogen-powered cars with fuel cells that only emit water vapour.

MICROWAVES SEND POWER TO EARTH

If the world’s power requirement is to be met by solar cells, it is necessary to cover 1.6 % a region the size of Argentina in solar panels, which is not realistic.

But in space, there is lots of room, and the sunlight is five times more powerful above the atmosphere. So, several of the world’s energy-hungry nations plan to launch huge solar power plants into space.

They aim to place the space power plants in a geostationary orbit 36,000 km above Earth, where they hover above the same spot. The solar cell power is converted into microwaves, that can easily be sent to a receiving station on Earth’s surface, where the energy of the microwaves will be converted back into power. The technical challenges particularly involve making light and low-volume mirrors and solar cell panels, so the cost of launching them needs to fall. Moreover, the space power stations must be reliable, as repairs will be extremely difficult, subjecting astronauts to cosmic radiation. But that has not made engineers halt their efforts. Both in Russia and the US, prototypes are developed, and China and Japan plan to launch large space power plants into orbit in the 2020s and 2030s.

Morocco has not halted its solar energy efforts either. Towards 2020, the country aims to build more large solar power plants to obtain a capacity of 2,000 MW, which could supply 11 million of the country’s 34 million people with electricity. If Morocco’s largescale solar energy efforts are successful, it could serve as inspiration and contribute to a worldwide solar energy breakthrough.