Solar energy

As solar energy or solar energy is called the energy of the solar radiation that can be used technically in the form of electricity, heat or chemical energy. Solar radiation is the electromagnetic radiation that is produced on the surface of the sun because of their temperature of approximately 5500 ° C as a black-body radiation, which ultimately on nuclear fusion processes in the solar interior back ( the hydrogen burning).

Intensity

The Earth is reaching solar radiation, since it is measured, is approximately constant; there is also no evidence of significant fluctuations in historical times. The average intensity of solar radiation is at the boundary of Earth's atmosphere approximately 1.367 kW / m²; This value is also referred to as solar constant. A portion of the incident energy is scattered and reflected by the atmosphere of solid (eg, ice crystals, dust) or liquid suspended and of the gaseous components. Another part is absorbed by the atmosphere and already converted into heat. The rest goes through the atmosphere and reaches the earth's surface. Where it is again partially reflected and partly being absorbed and converted into heat. Among other things, in photosynthesis, photo- thermal and photovoltaics it is harnessed. The percentage distribution of the radiation on reflection, absorption and transmission depends on the state of the atmosphere. This play humidity, cloud cover, and the length of the path that the rays must take through the atmosphere, a role. The incident on the earth's surface radiation is the world on a daily average (based on 24 hours), still about 165 W / m² ( with significant variations depending on the latitude, altitude and weather). The entire incident on the earth's surface energy amount is more than five thousand times greater than the energy requirements of mankind. Ultimately, the entire energy of the sun in the form of heat radiation is emitted back to space.

Use of solar energy

The quantity largest area of ​​use of solar energy is the heating of the earth, so that in the near-surface region biological existence in the known forms is possible, followed by the photosynthesis of algae and higher plants. Most organisms, including man, either directly (as herbivores ) or indirectly (as predators ) of solar energy are dependent. Fuel and building materials also come from it. Solar energy is also responsible for ensuring that there is in the atmosphere to air pressure differences that cause wind. Also, the water cycle of the earth is driven by solar energy.

In addition to these "natural" effects, there is increasing industrial use, especially in the area of ​​energy supply.

With the help of solar technology allows the solar energy use in different ways:

• Solar panels heat gain (solar thermal and photo- thermal)
• Solar cells produce direct current electric (photovoltaic )
• Solar thermal power plants generate electricity by means of heat and steam electric power
• Solar cooker or solar ovens heat food or sterilize medical supplies

Indirect solar energy is used:

• Plants and plant waste is processed to usable liquids ( eg ethanol, rapeseed oil) or gases ( eg biogas is purified from methane) occur
• Wind and hydro power plants generate electricity
• As Passive solar energy to warm homes and thus to reduce the energy demand

The solar energy is renewable energy, their use is encouraged in many countries, for example in Germany, the Renewable Energy Sources Act ( EEG).

Storage of solar energy

The solar irradiation is subject to daily and seasonal variations from zero to the maximum value of the irradiance of 1,000 W / m². In order to ensure the necessary security of energy supply, so a powered with fuel boilers are always additional measures such as energy storage, control engineering or auxiliary systems such as necessary.

In March 2011, went into the Morbach Energy Landscape, the first solar gas plant in operation in Germany. This solar energy is converted into synthetic gas and is stored in gas form.

Solar thermal systems use different types of heat storage. These range for devices for hot water usually for a few days from order - at least in the summer months - even at night and during a period of bad weather sufficient heat can be provided. Long-term storage, transfer the summer heat in the winter, are technically possible, but still relatively expensive.

In solar thermal, electric power plants is used by mirrors concentrated solar radiation to evaporate liquids and gain power a steam turbine. Heat storage ( for example, tanks of molten salt ) can also some of the heat ( low loss ) save the day to compensate for short-term fluctuations in demand or to drive the steam turbine at night.

In photovoltaic power plants generate electric power by means of semiconductor effects. The resulting direct current produced either within the framework of decentralized power generation in an island power grid used as such ( for example, by buffering accumulators) or via an inverter in an existing AC power input. Here, the storage batteries and distributed over the conversion to hydrogen and methane, and the subsequent storage in the gas system is possible. The existing gas storage facilities in Germany would be sufficient here to meet the memory requirements of a power supply which is mainly based on the generation by photovoltaic and wind turbines.

Potential of solar energy

As the largest source of energy comes from the sun per year, an amount of energy of about 1.5 x 1018 kWh to the earth's surface. This amount of energy equivalent to more than 10,000 times the world's energy needs of mankind in 2010 ( 1.4 × 1014 kWh / year).

The composition of the solar spectrum, the duration of sunshine, and the angle at which the sun's rays fall upon the surface, dependent on time of day, season and latitude. Thus, the radiated energy is different. This is for example about 1,000 kWh per square meter per year in central Europe and about 2,350 kWh per square meter per year in the Sahara. There are various scenarios, such as one of the EU renewable energy supply can be realized, including by means of energy conversion in North Africa and high-voltage direct -current transmission. For example showed satellite-based studies by the German Aerospace Center (DLR ), that with less than 0.3 percent of the available desert areas in North Africa and the Middle East by Thermal solar power plants sufficient energy and water for the growing needs of these countries and for Europe can be generated. The Trans-Mediterranean Renewable Energy Cooperation, an international network of scientists, politicians and experts in the fields of renewable energy and their development, is committed to such cooperative use of solar energy. A publication from the U.S. called Solar Grand Plan suggests a similar use of solar energy in the United States.

It was also thought about capturing solar energy via satellite and transmit to the earth. The advantage would be in a higher energy density on the ground and in the avoidance of day-night variations. Due to the large for necessary expenses, far above all previous space technology, but none of these projects has been taken concretely addressed.

Dependence of the radiation power on the incident angle

The solar radiation on the earth's surface is the main determinant of the weather and of the regional and global climate. The radiation power density (English heat flux density, irradiation ), that is, the radiation energy per unit area per unit time, depends on the angle of the sunlight. In a shallow angle less photons per unit area incident on the ground and warm it less strong than at normal incidence. This is expressed by the following formula:

Herein, the radiation efficiency, the radiation intensity at normal incidence and the angle of incidence with respect to the horizon.

The effect is enhanced by the extended distance the light must travel through the atmosphere at shallow angles.

Evaluation of the use of solar energy

Benefits

The advantages of the use of solar energy among others seen the following points:

• It is available in unlimited quantities, in contrast to fossil fuels or fissile isotopes humanly.
• Today, 60,000 people work in the German solar industry. Over 100 companies supply solar cells, modules and components, far more still are busy with planning and installation of solar systems. Approximately 10 billion euros per year are converted here, two-thirds of the value to remain in Germany. The public sector also acts as a 3 billion euro tax.
• In addition, solar power saves fuel imports - currently about 400 million euros annually.
• Solar energy is climate-friendly, it only arise in the production of greenhouse gas plant - the plant is emission-free. Solar energy lowered CO2 emissions in 2009 alone 3.6 million tons.
• There is no release of particulates, such as soot particles.

In terms of electricity generation by many small photovoltaic systems rather than large power plants following advantages are further seen:

• Cost savings due to the fact that the cost of transmission and distribution of centrally generated electricity are about as high as the cost of energy itself
• Omission of any price cartels large energy producers, which would lead to free pricing and therefore lower energy prices.
• Eliminating the need for large spare capacity. Central large-scale systems require this to avoid blackouts in case of malfunctions of individual plants. This reserve is for Germany at the moment about 40%. This capacity should no longer be kept, since a large number of small and decentralized energy producers would mitigate the risk of default of individual plants.
• Reduction of energy policy dependencies of possible trouble spots and international conflicts, such as in the Middle East region.

Disadvantages

A disadvantage following will be assessed:

• Due to the weather, daily and seasonal time-dependent solar radiation is not a constant energy supply is possible without additional memory technology. On fluctuations in consumption may also not be responding. In addition, energy is needed, particularly in cold climates or seasons when less solar energy is available ( to compensate for the increased efficiency of solar cells at low temperatures prevailing in the winter, the lower irradiation only to fractions ). For uniform availability photovoltaic generated energy effective storage capacities need to be built around based on hydrogen, which results in additional efficiency losses and infrastructure costs. In the field of thermal use certain types of power plants can be partially continue to use the heat input of the day in the night time.
• The energy through photovoltaic cells is after complete ecological balance not considered emission- free, as are required for the production of complete photovoltaic system energy, water and chemicals. The amount of energy needed to produce a modern photovoltaic system has paid for itself according to a recent study by the Energy research Centre of the Netherlands (ECN ), depending on design in Europe within approximately 1.5 to 3.5 years. Since the lifetime of the solar modules is approximately 20 to 40 years, the overall energy balance of pure however is positive. The overall environmental performance of photovoltaics is blighted addition to the aforementioned feedstocks also by the partial use of toxic materials.
• In power generation using solar energy higher costs compared to other techniques. Is electricity from wind power in Germany with 6 to 8 cents per kilowatt-hour price equal to the produced in new conventional power plants energy; the production costs for solar thermal power plants are currently in Germany, depending on location at 9 to 22 cents / kWh. Electricity from photovoltaics with 13.5 to 19.5 cents / kWh paid (as of 1 April 2012). In Germany the generality of the current consumer bears these costs, because the German Renewable Energy Act stipulates that the additional costs for solar power are distributed to all consumers. This allowance shall be - defined by law - continue to decline annually by 5 to 23 percent. The grid parity in Germany was thus achieved already in 2012. The Oil -parity, ie the ability to compete for heating oil is also considered to be achievable. The recent strong sunken prices on the world market for solar modules as well as technical innovations in other system components, such as module inverters and the possible through them reduce overall costs of photovoltaic systems ( costly DC cable can be replaced by low-cost cable for interconnection ) can move this goal within reach. Recent developments show that the cost of solar energy are still rising more than expected. Above all the EEG apportionment is apportioned to future consumers.
• The installation of solar panels on a large scale consumes significant areas that would otherwise inter alia, can also be used for agricultural production of food or have been used.