CSP developing ideas

For concentrating solar power (CSP) there are four different technology approaches – parabolic trough, power tower, linear reflector, and sterling dish .we will talk here about linear reflector technology .

That is  use a series of ground-based, flat or slightly curved mirrors placed at different angles to concentrate the sunlight onto a fixed receiver located several meters above the mirror field. 

Each line of mirrors is equipped with a single axis tracking system to concentrate the sunlight onto the fixed receiver. The receiver consists of a long, selectively-coated tube where flowing water is converted into saturated steam (DSG or Direct Steam Generation). Since the focal line in the FR plant can be distorted by astigmatism .

While the optical efficiency of the FR system is lower than that of the PT systems ,i think we can improve that by another way with increasing the fluid temperature .
What if we change the system of the receiver ?
Instead of The receiver consists of a long, selectively-coated tube ,
we wont make the tube as straight line .
the long tube will consist of a lot of small tubes .each of them will have some mirrors concentrating the sun light on it alone .
we will change a bit in the structure of the small tube .
the outer of the tube will be smaller than the inner.
the outer of the second tube will be small than the outer of the first ,so the fluid in the tube wont flow normally .
fluid flow will be slower ,so its temperature will be larger

 The use of molten salt at 550°C for either heat transfer or storage purposes is under demonstration. High temperature molten salt may increase both plant efficiency (e.g. 15%-17%) and thermal storage capacity .

The main advantage of CSP against other sources of renewable energy such as PV or wind is the capability to provide dispatchable power – by storing solar energy in thermal reservoirs and releasing it as and when it's needed i.e. during periods of peak power demand, during cloudy weather or even at night. So storage can eliminate intermittency as well as extend energy production past sun-set.
Another advantage to CSP is that it can be used as part of a hybrid energy source, in that a regular gas fired plant can be used to heat the HTF/TES materials (see below) in the event of solar down time. This configuration is much like the early hybrid cars.

Light from the sun

The sun is an average star. It has been burning for more than 4-billion years, and it will burn at least that
long into the future before erupting into a giant red star, engulfing the earth in the process.
Some stars are enormous sources of X-rays; others mostly generate radio signals. The sun, while producing
these and other energies, releases 95% of its output energy as light, some of which cannot be seen by the
human eye. The peak of its radiation is in the green portion of the visible spectrum. Most plants and the
human eye function best in green light since they have adapted to the nature of the sunlight reaching them. The sun is responsible for nearly all of the energy available on earth. The exceptions are attributable to moontides, radioactive material, and the earth's residual internal heat. Everything else is a converted form of
the sun's energy: Hydropower is made possible by evaporation-transpiration due to solar radiant heat;
the winds are caused by the sun's uneven heating of the earth's atmosphere; fossil fuels are remnants of
organic life previously nourished by the sun; and photovoltaic electricity is produced directly from sunlight
by converting the energy in sunlight into free charged particles within certain kinds of materials.

The Nature of Light Energy :

Light is energy. You need only touch a black surface exposed to the sun to realize this fact. An understanding
of the nature of light will help in comprehending how solar cells work.
The sun's light looks white because it is made up of many different colors that, combined, produce a white
light. Each of the visible and invisible radiations of the sun's spectrum has a different energy. Within the visible
part of the spectrum (red to violet), red is at the low-energy end and violet is at the high-energy end having
half again more energy as red light. Light in the infrared region (which we can't see but feel as heat)
has less energy than that in the visible region. Light in the ultraviolet region(which is invisible but causes the
skin to tan) has more than that in the the visible region.

Today, photovoltaic systems are capable of transforming one kilowatt of solar energy falling on one square
meter into about a hundred watts' of electricity. One hundred watts can power most household appliances: a
television, a stereo, an electric typewriter, or a lamp. In fact, standard solar cells covering the sun-facing roof
space of a typical home can provide about 8500-kilowatthours of electricity annually, which is about the
average household's yearly electric consumption. By comparison, a modern, 200-ton electric-arc steel furnace, demanding 50,000 kilowatts of electricity,
would require about a square kilometer of land for a PV power supply.

Photovoltaics

Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material.

A photovoltaic system  is an arrangement of components designed to supply usable electric power for a variety of purposes, using the Sun (or, less commonly, other light sources) as the power source. Solar PV total global capacity increased during 2010-2013 from 40 GW to 139 GW. In 2013 Germany had the most capacity (36 GW) .

• Off-grid without battery (array-direct)
• Off-grid with battery storage for DC-only appliances
• Off-grid with battery storage for AC and DC appliances
• Grid-tie without battery
• Grid-tie with battery storage

A small PV system is capable of providing enough AC electricity to power a single home, or even an isolated device in the form of AC or DC electric. For example, military and civilian Earth observation satellites, street lights, construction and traffic signs, electric cars, solar-powered tents, and electric aircraft may contain integrated photovoltaic systems to provide a primary or auxiliary power source in the form of AC or DC power, depending on the design and power demands.

The average family home needs a solar PV panel that provides about 3kW of electricity. This will cost between £4,000 and £6,000 and cover about 21m² of roof space.

While this may seem like a large sum you will actually make this back in about ten years because the government pays you for the electricity you produce and you save money on your energy bills.

The government payout is called the Feed-in tariff and it lasts for twenty years.

The price of a solar panel will vary depending on the quality and size .

Solar PV needs little maintenance – you'll just need to keep the panels relatively clean and make sure trees don't begin to overshadow them. In the UK panels that are tilted at 15° or more have the additional benefit of being cleaned by rainfall to ensure optimal performance. Debris is more likely to accumulate if you have ground mounted panels.If dust, debris, snow or bird droppings are a problem they should be removed with warm water (and perhaps some washing-up liquid or something similar – your installer can advise) and a brush or a high pressure hose (or telescopic cleaning pole) if the panels are difficult to reach.

Solar energy

Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermalcollectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.

The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.

Earth's land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived .

Applications of solar technology :

Solar energy refers primarily to the use of solar radiation for practical ends. However, all renewable energies, other than geothermal and tidal, derive their energy from the sun.

Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies .

• Architecture and urban planning
• Agriculture and horticulture
• Transport and reconnaissance
• Solar thermal
• Water heating
• Heating, cooling and ventilation
• Water treatment
• Process heat
• Cooking
• Electricity production
• Concentrated solar power
• Photovoltaics

CSP development

Photovoltaics (PV) is the dominant solar technology with more than 12 GW installed in 2010 alone, but PV (not to mention wind power) has inherent limitations of intermittency. This gives CSP a distinct advantage, and current advances in heat transfer and storage could increase the implementation of CSP as a significant renewable resource.

Introduction to CSP :

For concentrating solar power (CSP) there are four different technology approaches – parabolic trough, power tower, linear reflector, and sterling dish . Currently, more than 90% of installations use parabolic troughs to generate electricity.

The main advantage of CSP against other sources of renewable energy such as PV or wind is the capability to provide dispatchable power – by storing solar energy in thermal reservoirs and releasing it as and when it's needed i.e. during periods of peak power demand, during cloudy weather or even at night. So storage can eliminate intermittency as well as extend energy production past sun-set. Another advantage to CSP is that it can be used as part of a hybrid energy source, in that a regular gas fired plant can be used to heat the HTF/TES materials (see below) in the event of solar down time. This configuration is much like the early hybrid cars.

Despite these advantages however, CSP-derived electricity is expensive in comparison with other technologies. The key to CSP's commercial success remains in developing an economical and effective energy storage capability.

There are two intertwined technology paths for CSP which both need to be advanced – the solar collection technology and the heat conduction technology. In this article we will address the latter.

Developments in heat transfer and storage materials

Heat conduction technology :

Except for sterling dish technology, CSP needs a Heat Transfer Fluid (HTF), and in some cases a Thermal Energy Storage (TES) medium. The HTF and TES materials are the interface between the solar energy input and the power block.

From a commercial perspective HTF and TES are at very early development stages. Although they can function adequately, the current HTFs suffer from significant shortcomings. As far as the TES elements, this is even more challenging, with only marginal industrial activities underway.

But there is now a strong push to extend the capabilities of HTF/TES, and the results could help enable the acceleration of CSP beyond the 500 MW of current installations. Activity for both remains very much an R&D effort, especially for TES. But there is now an increased emphasis to address both the limitations of current HTF/TES, as well as to develop advanced elements. Groundbreaking research is looking at HTF and TES – for example how nanostructures can be used to tailor the fluids' thermo-physical properties?

New funding is also being directed towards a broad range of near-term improvements (as well as long-range R&D).

The key considerations for improvement of HTF/TES materials include the ability to vary the operational temperatures; the range of useful temperatures; the heat capacitance; and – very importantly – the cost. The latter is essential in the world of solar energy. The rapid implementation of PV in the last year has been accelerated by a drop in PV prices. It is essential for CSP to achieve some of the same cost reductions .

Current limitations to HTF/TES :

Up to now, CSP plants have used synthetic oils as heat transfer fluids and molten salts for thermal energy storage (molten salt can also be an HTF). .

However there are significant limitations which impact the overall cost of CSP electricity. The most proven and commonly used CSP technology is parabolic trough technology, which absorbs solar radiation and reaches temperatures of around 700°F (371°C). In the heat exchanger, water is preheated, evaporated, and superheated into steam, which runs a steam turbine. The water is cooled, condensed, and reused in the heat exchangers. Most of these plants have little or no storage and use oils which are flammable. Operating at higher temperatures enables higher power cycle efficiencies to be achieved .

The organic oil-based HTF currently tend to break down at high temperatures (around 400°C), which prevents solar thermal plants from running at maximum efficiency. Inorganic materials such as salts, on the other hand, maintain stability at high temperatures, but then solidify easily at temperatures as high as 230°C – a problem because when the sun drops in the desert, so does the temperature.

Solar Towers

 In the ST plants, a large number of computer assisted mirrors (heliostats) track the sun individually over two axes and concentrate the solar irradiation onto a single receiver mounted on top of a central tower where the solar heat drives a thermodynamic cycle and generates electricity. In principle, ST plants can achieve higher temperatures than PT and FR systems because they have higher concentration factors.

The ST plants can use water-steam (DSG), synthetic oil or molten salt as the primary heat transfer fluid. The use of high-temperature gas is also being considered. Direct steam generation (DSG) in the receiver eliminates the need for a heat exchanger between the primary heat transfer fluid (e.g. molten salt) and the steam cycle, but makes thermal storage more difficult. Depending on the primary heat transfer fluid and the receiver design, maximum operating temperatures may range from 250-300°C (using water-steam) to 390°C (using synthetic oil) and up to 565°C (using molten salt). Temperatures above 800°C can be obtained using gases. The temperature level of the primary heat transfer fluid determines the operating conditions (i.e. sub-critical, super-critical or ultra-super-critical) of the steam cycle in the conventional part of the power plant.

ST plants can be equipped with thermal storage systems whose operating temperatures also depend on the primary heat transfer fluid. Today’s best performance is obtained using molten salt at 565°C for either heat transfer or storage purposes. This enables efficient and cheap heat storage and the use of efficient super-critical steam cycles. High-temperature ST plants offer potential advantages over other CSP technologies in terms of efficiency, heat storage, performance, capacity factors and costs. In the long run, they could provide the cheapest CSP electricity, but more commercial experience is needed to confirm these expectations

Current installed capacity includes the PS10 and PS20 demonstration projects (i.e. Spain) with capacities of 11 MW and 20 MW, respectively. Both plants are equipped with a 30-60 minute steam-based thermal storage to ensure power production despite varying solar radiation .
The PS10 consists of 624 heliostats over 75,000 m2

 Its receiver converts 92% of solar energy into saturated steam at 250°C and generates 24.3 GWh a year (i.e. 25% capacity factor), with 17% efficiency. In Spain, a 19-MW molten salt-based ST plant
with a 15-hour molten salt storage system started operation in the second half of 2011. It is expected to run for almost 6,500 operation hours per year, reaching a 74% capacity actor and producing fully dispatchable electricity.
Larger ST plants are under construction (e.g. the 370-MW Ivanpah project in California with water-steam at 565°C and 29% efficiency and the 50-MW Supcon project in China) or under development (e.g. eight units with a total capacity of 1.5 GW in the southwestern United States). Large plants have expansive solar fields with a high number of heliostats and a greater distance between them and the central receiver. This results in more optical losses, atmospheric absorption and angular deviation due to mirror and sun-tracking imperfections.

Fresnel Reflectors

FR plants are similar to PT plants but use a series of ground-based, flat or slightly curved mirrors placed at different angles to concentrate the sunlight onto a fixed receiver located several meters above the mirror field.

Each line of mirrors is equipped with a single axis tracking system to concentrate the sunlight onto the fixed receiver. The receiver consists of a long, selectively-coated tube where flowing water is
converted into saturated steam (DSG or Direct Steam Generation). Since the focal line in the FR plant can be distorted by astigmatism, a secondary mirror is placed above the receiver to refocus the sun’s rays. As an alternative, multi-tube receivers can be used to capture sunlight with no secondary mirror. The main advantages of FR compared to PT systems are the lower cost of ground-based mirrors and solar collectors (including structural supports and assembly).

While the optical efficiency of the FR system is lower than that of the PT systems (i.e. higher optical losses), the relative simplicity of the plant translates into lower manufacturing and installation costs compared to PT plants.

However, it is not clear whether FR electricity is cheaper than that from PT plants. In addition, as FR systems use direct steam generation, thermal energy storage is likely to be more challenging and expensive.

FR is the most recent CSP technology with only a few plants in operation (e.g. 1.4 MW in Spain, 5 MW in Australia and a new 30-MW power plant, the Puerto Errado 2, in Spain, which started operation in September 2012). Further FR plants are currently under construction (e.g. Kogan Creek, Australia 44 MW, 2013) or consideration.