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Dictionary

Global Solar Technology

Examples of manufacturing processes which can exploit solar high-temperature energy include cement and metals manufacturing and recycling heavy metal waste. These processes need heat of up to 2000°C. Concentrated solar heat can therefore potentially save huge amounts of fossil fuels.

Solar energy is intermittent - it is available during sunny days only. It can be used to generate electricity through photovoltaic cells, but a more efficient use is to concentrate the heat by focusing the sunlight with parabolic mirrors. This is useful and efficient for heating water, but can also be used in manufacturing processes, and for chemical systems generating energy storage media, such as hydrogen and methanol.

Examples of manufacturing processes which can exploit solar high-temperature energy include cement and metals manufacturing and recycling heavy metal waste. These processes need heat of up to 2000°C. Concentrated solar heat can therefore potentially save huge amounts of fossil fuels.

Solar irradiation
Map showing global distribution of solar irradiation

Current global energy consumption could be supplied by solar energy systems, at 20% conversion efficiency, covering 0.1% of the land. Solar radiation on the Earth's surface is about 1-3 kW/m2 on average. It makes sense to maximise the use of solar energy available in the range ± 30° from the equator, where solar intensity is over 3 kW/m2 for many more hours in a year. To do this, it is better to convert the energy into a chemical storage form, rather than electricity. Some of the infrastructure for such a system already exists in the petroleum industry - oil and gas, as well as coal, are after all chemical stores of solar energy from millennia ago. Oil tankers could just as easily transport fuel generated in desert regions through power-to-fuel solar thermogeneration.

Thermolysis of water

At high temperatures above 2500 K and depending on the pressure, water splits into hydrogen and oxygen.

H2O → H2 + ½O2

Um das Trennungsproblem, wobei ein Explosionsgefahr besteht mit der Trennung des Wasserstoffs vom Sauerstoff bei hohen Temperaturen, werden zweistufige Wasserspaltungs-Zyklen eingeführt, die auf sogenannten Metalloxid-Redox-Systemen basieren.

1. Solarthermal (endothermic) dissasociation of metal oxides at high temperatures (> 2300K):

MxOy → xM + (y/2)O2

2. Hydrolysis (exothermic) of metal products at moderate temperatures (< 900 K), through which molecular hydrogen and corresponding metal oxides are formed:

xM + yH2O → MxOy + yH2

With such reduction-oxidation systems, efficiencies of more than 30% can be achieved, When the solar radiation is concentrated very much and the heat generated by the cooling of the products can be recovered.

Solar collector PSI
The parabolic mirror at the Paul Scherrer Institute (PSI) follows the solar path and concentrates the sun rays 5000 times on a small circle in the Brennebene.

At current prices for fossil fuels, fuels from concentrated solar energy are not competitive. However, solar technologies will be an economically viable option if the cost of fossil fuels also includes the external costs of incineration and the reduction of fossil fuels.

In 2016, China/Taiwan produced 68% of the world's new PV modules, while Europe produced only 4% (fallen from 5% in 2015), and USA/Canada only 6%. Europe installed 33% (down from 40% in 2015) of PV installations, and China 26% (up from 21% in 2015).

Multi-crystalline Si-wafer based technology accounts for around 75% of all PV cells.

Solar Cell Efficiency

Best in lab: silicon wafer-based mono-crystalline = 26.7%, multi-crystalline = 21.9%. Thin-film: CIGS = 21.7%, CdTe = 21.0%. High-concentration multi-junction solar cells have efficiencies as high as 46%, and concentrator modules 38.9%.

CIGS: copper, indium, gallium, selenide. CIGS is made by depositing a thin layer of the four metals on a substrate, such as rigid glass or flexible plastic. The higher absorption coefficient of the material permits the cell to be thinner than conventional solar cells. EMPA (Swiss Federal Laboratories for Materials Science and Technology) and ZSW (Zentrum für Sonnenenergie und Wasserstoff Forschung, Deutschland) have both achieved efficiencies in excess of 20% for CIGS. EMPA achieved 20.4% efficiency with a polymer substrate, and ZSW 21.7% with a glass substrate.

CdTe: cadmium telluride. In multi-kilowatt systems, CdTE has lower costs than conventional crystalline silicon PV. Its shorter pay-back time is a major advantage, but the presence of the toxic metal cadmium obliges the owner to recycle the material at the end of life. Tellurium is also a rare metal, so places a limit on this technology's potential for large-scale applications. CdTe thin film technology accounts for 50% of all the thin film market, but still only 5% of world PV production, despite it being used in some of the world's largest photovoltaic power stations, such as the Topaz Solar Farm.

Crystalline silicon: more than 90% of worldwide PV production. Since being introduced around 1990, multicrystalline has gradually increased its share of the market compared to monocrystalline silicon, overtaking it around 2005. In 2014, the global market share of crystalline silicon cells was about 90%, with multi-Si making up 55% and mono-Si 35%. According to forecasts, silicon cells will continue to be the dominant photovoltaic technology in the long term and will be the "workhorse" of power generation together with wind power plants.

Commercial wafer-based silicon modules are returning around 17%, super-mono 21%, CdTe 16%. Energy payback (generated energy = manufacturing energy cost) is 1 year for multi-Si modules in high-solar regions such as Sicily.

Inverter efficiency is now 98%.

Photovoltaic Panels

Semiconductor panels (mostly silicon-based) which convert sunlight into electricity.

Types of solar panels commercially available:

Crystalline silicon

CIS

CdTe

Thin-film cells

At the end of 2016 photovoltaic plants with an output of 303 GW were installed worldwide. It is expected that the annual increase will reach 100 GW by 2020 and that the installed capacity will reach between 3,000 and 10,000 GW by 2030. In 2014, the global market share of crystalline silicon cells was about 90%. According to forecasts, silicon cells will continue to be the dominant photovoltaic technology in the long term and will be the "workhorse" of power generation together with wind power plants.