Geothermal Power – an overview, Alternative Energy Today

Geothermal Power – an overview

Geothermal Power – an overview, Alternative Energy Today

Introduction to Energy Sources

Vikas Khare, … Prashant Baredar, in Tidal Energy Systems, 2019

Environmental Impacts of Geothermal Energy

Geothermal power is a comparatively compassionate source of energy because the environmental impacts of this type of source are positive. Globally, geothermal energy generation increases year by year because it is a striking option to burning imported and domestic fossil fuels. Electrical energy production from geothermal resources creates lower greenhouse gas (GHG) emissions than conventional energy sources. According to the research of the International Atomic Energy Agency (IAEA), replacing 1 kWh of conventional energy with a kilowatt-hour of geothermal energy decreases the greenhouse gas emission impact by approximately 95%. On the other hand, geothermal growth could have negative impacts if suitable mitigation actions and monitoring plants are not in place. Any large-scale production as well as drilling operations and maintenance will generate visual impacts on the landscape, create noise pollution and waste, and affect local economies. Some developing countries have followed strict ecological regulations regarding some of the impacts related with geothermal growth, and others have not. Environment-related issues frequently addressed during the expansion of geothermal fields include wind quality, water quality, waste disposal, geologic hazards, noise, biological resources, and land use issues.

Prospects for Renewable Energy

Douglas Arent, … Alison Wise, in Energy, Sustainability and the Environment, 2011

4.5 Geothermal Technologies

Geothermal power plants are similar to coal plants in that they generate electricity by producing a high-temperature, high-pressure vapor that passes through a turbine, which spins an electric generator (Kutscher, 2009b). There are a few ideal places in the world where dry (superheated) steam exists near the surface. After drilling, that steam can simply be routed directly to a steam turbine. Direct steam plants are used in Northern California at The Geysers, the world’s largest geothermal power plant complex. More commonly, geothermal wells tap pressurized hot water. If the temperature of that water is higher than about 350°F (or about 175°C), it can be rapidly boiled in a low-pressure flash tank where a fraction of the water becomes steam. The steam is then routed to a steam turbine.

For lower temperature resources, the hot geothermal fluid is passed through heat exchangers, where it boils a secondary fluid having a lower boiling point than water, like pentane or isobutane. The resulting vapor spins a specially designed turbine.

These are called binary-cycle plants. While all geothermal power plants have very low emissions, binary-cycle plants have virtually none, because all of the geothermal fluid is returned to the ground. Binary-cycle plants also have the advantage that they do not result in any water draw-down from a geothermal reservoir, although they can decrease reservoir temperature over time.

The best geothermal resources, so-called hydrothermal resources, have three qualities: high near-surface temperatures (preferably at least 240°F, or 116°C; the higher the better), fluid content in the form of pressurized water or steam, and permeable rock. All of the existing geothermal power plants in the world are sited on hydrothermal resources.

But these resources are limited. Worse, we don’t even have a good handle on how much we have. A 2008 U.S. Geological Survey (USGS) study estimated that the United States has power production potential from identified hydrothermal resources of between 4000 MW (95% confidence level) and 13,000 MW (5% confidence level). When the USGS attempts to include potentially undiscovered resources, the range jumps to 11,000–90,000 MW (with a mean of about 40,000 MW). This is a big range, and this resource uncertainty is a key question mark for the future exploitation of geothermal resources (Kutscher, 2009b).

The resource picture gets brighter if we ease our expectations for the three qualities of good geothermal resources. If we are willing to drill down 3 to 10 kilometers, there are wide areas throughout the Western United States with adequate temperature. And although those areas tend to be dry and low in permeability, we can potentially inject water at high pressure and fracture the rock, as is often done to enhance oil and gas recovery. This is the concept referred to as EGS. When the same USGS study estimated EGS resources, the range of power production potential jumped to 350,000–720,000 MW with a mean of about 500,000 MW, which would be sufficient power to provide virtually all the annual kilowatt hours of electricity needed in the United States.

EGS has been researched in France and Australia and continues to be a topic of intense investigation, given the ubiquity and size of the global resource.

A 2006 Massachusetts Institute of Technology (MIT) report, The Future of Geothermal Energy (MIT, 2006), was quite optimistic about EGS and helped generate considerable interest. But while the EGS resource is extremely large, exploiting it in a cost-effective way is no trivial matter. For one thing, drilling costs go up exponentially with depth. And there is the challenge of properly fracturing the rock without inducing seismicity. The concept involves an injection well where high-pressure water is pumped down into the hot rock, creating permeability. The water then picks up heat as it flows to one or more nearby production wells. But fracturing the rock in a way that allows the flowing water to communicate with a large volume of hot rock without significant loss needs to be demonstrated. Water loss is not only an obvious problem for arid regions typical of EGS resources, but it also represents wasted pumping power.

The MIT study concluded that to be economical, an EGS project must obtain a continuous production well water flow rate of 80 kilograms per second at 200°C (about 390°F). Limited water availability and high drilling costs may result in shallower wells and lower temperatures, supporting binary-cycle plants. Thus far, the highest achieved flow rate at an experimental EGS site has been 25 kg per second.

A 2008 DOE study, An Evaluation of Enhanced Geothermal Systems Technology (DOE, 2008b), evaluated the MIT analysis and described the significant amount of R&D needed to create and sustain a viable EGS reservoir. The DOE has had limited funding to tackle this. That changed recently when the Obama administration announced that $80 million to support EGS R&D will be provided from the American Reinvestment and Recovery Act. Even this is a small amount compared to what will be needed. But the potential for EGS to produce large quantities of baseload power justifies the expenditure and the risk (Kutscher, 2009b).

THE CERRO PRIETO GEOTHERMAL FIELD, MEXICO

Harsh Gupta, Sukanta Roy, in Geothermal Energy, 2007

COST OF GEOTHERMAL POWER

Generation costs for geothermal power at Cerro Prieto are quite comparable to the power produced from fossil fuels (Hiriart and Andaluz, 2000). In the case of the first three power plants, CP-I, CP-II and CP-III, the cost turns out to be 3.46 U.S. cents per kWh. The cost is made up of four major components (Table 7.5):

Table 7.5. Break-up of power generation costs in U.S. cents per kWh at Cerro Prieto plants CP-I, CP-II and CP-III

Component of generating cost Cost (U.S. cents per kWh)
Power plant investment 1.63
Operation and maintenance of plant 0.36
Steam supply 1.17
Operation and maintenance of field 0.30
Total 3.46

(from Hiriart and Andaluz, 2000)

In the case of the new plant, CP-IV, commissioned in 2000, the costs are even lower. The cost of installed capacity has been projected to be USD 797 per kW, and that for power generation turns out to be as low as 2.81 U.S. cents per kWh. It must be mentioned here that the costs for generation of geothermal power vary widely for different locations. Factors influencing the cost include the pressure of steam supply, production and transmission of steam and hot water from the production site to the power plant, corrosive nature of the geothermal fluids (that affects the overall maintenance costs) and several others. The power plants are operated and maintained wholly by the CFE, a Mexican government entity, which enjoys certain cost exemptions such as geothermal royalties and development fees when compared to the private power companies. This scenario results in lowering the total cost of generating geothermal power at Cerro Prieto and other Mexican fields.

Geothermal Power Generation

Aniko Toth, Elemer Bobok, in Flow and Heat Transfer in Geothermal Systems, 2017

11.4.3 Binary Cycle Power Plants

In conventional geothermal power plants, the produced gas fluid is also the working fluid of the energy conversion process. In the binary cycle power plants the produced reservoir fluid and the secondary working fluid flows in two separated flow systems. The conventional geothermal energy conversion systems one open: the produced steam flows through the turbine, then it is rejected. The binary energy conversion system is a closed cycle: the same working fluid flows through the turbine repetitively.

A binary cycle is the closest to the classical Clausius–Rankine cycle. The working fluid receives heat from the geofluid in a heat exchanger, where it evaporates, expands flowing through the turbine, condenses, and the process repeats again.

The efficiency of the energy conversion cycle depends primarily on the steam temperature at the turbine inlet. The temperature of the wet stream decreases substantially in the flashing process. Because of this, flash technology is handily efficient and economic in the temperature region of the heat source below 170°C. For the utilization of these low temperature resources, binary cycle power plants can be applied advantageously.

A very important objective of the binary technology is to select a suitable working fluid. The suitable working fluids for binary plants have critical temperature and pressure far lower than water. These working fluids include the hydrocarbons, especially the aromatic-structure types, halogen-substituted hydrocarbons, steers, and simple-molecule materials such as ammonia, carbon dioxide, or even water.

Another important characteristic of binary cycle working fluids is the shape of the saturation curves: especially the upper boundary curve as viewed in the T–s diagram. This curve for simple molecule fluids up to four to five atoms has negative slope everywhere as it is shown in Fig. 11.18. When the number of the atoms increases the upper boundary curve becomes almost vertical for 6-10 atom molecules. For complex molecules having more than 10 atoms the slope of the saturated vapor curve is positive. In this case expansion from the saturated vapor curve happens in the superheated region, reducing blade erosion.

Geothermal Power – an overview, Alternative Energy Today

Figure 11.18. Saturation curves of different binary working fluids.

Since the critical pressure is reasonably low, it is feasible to consider supercritical cycles for these organic fluids. Considering Fig. 11.19, it can be recognized that the temperature difference between the geofluid cooling curve and the supercritical heating–boiling curve of the working fluid is not significant. Thus, the thermodynamical losses of the heat exchanger can be reduced. Some properties of organic fluids are tabulated in Table 11.2.

Geothermal Power – an overview, Alternative Energy Today

Figure 11.19. Supercritical binary cycle.

Table 11.2. Chemical and Physical Properties of Some Organic Fluids.

Name Molar Weight Tcrit (K) Pcrit (bar) Latent Heat (KJ/kg)
R125 Pentafluormethane 120 339 36.2 81.5
R218 Octafluorpropane 180 345 48.7 223
R290 Propane 44 369.8 42.5 292
R600 Butane 58 425 38.0 337
R601 Pentane 72 469.7 33.7 347
R717 Ammonia 17 405 113.3 1064
R718 Water 18 647 220.6 2392
R744 Carbon dioxide 44 304 738 167.53

It is important to assess the chemical stability of the fluid, the aggressively towards metals, and thermodynamically and transport properties of them.

A simplified schematic drawing of a binary power plant is shown in Fig. 11.20.

Geothermal Power – an overview, Alternative Energy Today

Figure 11.20. Scheme of a binary power plant (DiPippo, 2008).

The PW operates with a submersible pump (P) installed below the flash depth so as to prevent two-phase flow. The sand remover prevents erosion in the pipeline and the tubes. The heating and boiling process of the working fluid happens in two steps: first, the condensed working fluid is heated to its boiling temperature in the preheater (PH); it then turns to saturated or supercritical steam in the evaporator (E). The geofluid is always kept at a pressure above its flash point as flows through the evaporator and the preheater. An injection pump (IP) produces the necessary pressure to make the fluid flow through a fine-particle filter (FF) before finally reaching the injection well (IW).

The working fluid circulates in a secondary loop: through the preheater, the evaporator, it expands in the turbine (T) then condenses in the condenser (C). A condensate-feed pump (CP) maintains the flow in the loop.

A third, auxiliary loop is added to the system. The cooling water circulates through the condenser, and the cooling tower (CT).

The use of organic fluids with the low temperature Rankine cycle has many advantages over using water. The organic Rankine cycle efficiency is little different from that steam cycle between the same two top and bottom cycle temperature. Organic cycle deficiency is often less than water steam cycle.

The main advantage of an organic working fluid is that it can extract more heat from the primary geothermal heat source than water. This is the consequence of the organic fluid having a far lower ratio of latent heat of vaporization at lower boiling temperature v3 specific heat capacity than water.

The only definitive difference between a binary and a fossil fuel power plant is the preheater and the evaporator, where the produced hot geofluid transfers heat to the working fluid. Analyzing this phenomenon we assume that the shells of the heat exchangers are perfectly insulated, the whole heat transfer is occurred between the geofluid and the working fluid. Further assumptions are the steady flow, and the differences of kinetic and potential energy are negligible between the inlet and the outlet.

Applying the notations of Fig. 11.21, the simplified energy equation can be written as:

Geothermal Power – an overview, Alternative Energy Today

Figure 11.21. Heat transfer in the heat exchanger and pre-heater (DiPippo, 2008).

(11.39)m˙b(ia−ic)=m˙wf(i1−i4),

If the geofluid is incompressible, having very low amount of dissolved gases, the enthalpy can be written as the product of its specific heat and the temperature:

(11.40)m˙b·cb(Ta−Tc)=m˙wf(i1−i4)

The required geofluid mass flow rate for a given cycle is obtained as:

(11.41)m˙b=m˙wfi1−i4cb(Ta−Tc)

The heat transfer process can be understood easier, using the so-called T–q, or temperature–heat transfer diagram. The abscissa represents to total amount of heat, transferred from the geothermal brain to the working fluid, as it can be seen in Fig. 11.22. The transferred heat can be given either in energy units (KJ/kg) or in percent.

Geothermal Power – an overview, Alternative Energy Today

Figure 11.22. Temperature versus heat transfer diagram (DiPippo, 2008).

The flows of the geofluid and the working fluid are counter-current. The geofluid flows at first through the evaporator (section of a-b) then the preheater (b-c). The preheater provides sensible heat for the working fluid rising its temperature to the boiling point 5. The evaporation occurs between the points 5 and 1, where the temperature is constant while the evaporator provides latent heat for the phase charge of the working fluid. The place in the process, where the temperature difference is the minimum between the brine and the working fluid is the so-called pinch-point. The value of that difference is designated the pinch-point temperature difference: ΔTpp.

In the state four the working fluid is a compressed liquid, at the outlet of the feed pump. In the state five the working fluid is a saturated liquid at the boiling point, while state 1. is saturated vapor at the turbine inlet. Thus the two heat exchangers: the preheater and the evaporator can be investigated separately as:

(11.42)Q˙PH=m˙bcb(Tb−Tc)=m˙wf(i5−i1)

and

(11.43)Q˙E=m˙bcb(Ta−Tb)=m˙wf(i1−i5)

The geofluid inlet temperature Ta is always known. The pinch-point temperature difference is given from manufacturer’s data. Thus Tb can be determined knowing the turbine inlet temperature T1. In the ideal case the pinch-point occurs at the outlet had of the preheater. The evaporator heat transfer surface area between the two fluids AE can be determined from the expression:

(11.44)Q˙E=UEAEΔTlnE

where UE is the overall heat transfer coefficient, ΔTlnE is the logarithmic mean temperature difference of the evaporator

(11.45)ΔTlnE=(Ta−T1)−(Tb−T5)ln|Ta−T1Tb−T5|

The corresponding equations for the preheater are:

(11.46)Q˙PH=UPH·APH·ΔTlnPH

and

(11.47)ΔTlnPH=(Tb−T5)−(Tc−T4)ln|Tb−T5Tc−T4|

Since heat exchangers can be made in a great variety of geometrical arrangements, it must be applied different correction factors for shell and tube, pure counterflow, crossflow and plate units. These valves can be found in the handbook of Roshenow and Hartnett.

The thermal efficiency of the binary plant can be obtained as

(11.48)ηth=W˙Q˙

Since the net power of the cycle is the difference of the input and the rejected thermal power, it can be written:

(11.49)ηth=Q˙PH+Q˙E−Q˙cQ˙PH+QE

This formula is valid to the cycle, not to the whole plant. In the latter case the auxiliary power needs (pumps, cooling power fan etc.) must be subtracted from the not cycle power W. The binary power plant efficiencies depending on the heat source temperatures are plotted in.

Geothermal Energy

Ronald DiPippo, Joel L. Renner, in Future Energy (Second Edition), 2014

22.5 Worldwide Geothermal Development

The installed capacities for geothermal power generation and geothermal heat used for direct applications are reported at the World Geothermal Congress (WGC) held every 5 years. In the 2010 WGC report of geothermal electrical generation, Bertani [11] indicated that 67.3 TW·h were supplied worldwide in 24 countries. This is a tiny fraction, 0.3 %, of the estimated potential from Table 22.1. A more recent survey in 2011, DiPippo [12], put the installed power capacity at 10.7 TWe coming from 587 individual generating units (Table 22.2). Producers of electricity from geothermal energy generally report availability factors greater than 90 % (i.e. the plants are generating or ready to generate power 90 % of the time) and annual capacity factors generally above 85 % (i.e. the plants generate 85 % of the rated power on average over the year).

Table 22.2. Worldwide Status of Geothermal Power Plants, Arranged by Installed Megawatt.

Rank Country Number of Units Installed Capacity/MWe Electricity Generation/GW·h·y−1
1 United States 253 2774.43 16 603
2 Philippines 48 1840.9 10 311
3 Indonesia 23 1134 9600
4 Mexico 39 983.3 7047
5 Italy 35 882.5 5520
6 New Zealand 43 783.3 4055
7 Iceland 31 715.4 4597
8 Japan 21 535.26 3064
9 Costa Rica 8 205 1131
10 El Salvador 7 204.3 1422
11 Kenya 13 166.2 1430
12 Turkey 8 94.98 490
13 Nicaragua 5 87.5 310
14 Russia 12 79 441
15 Papua – New Guinea 6 56 450
16 Guatemala 9 44.6 289
17 Portugal – Azores 6 26 175
18 China 8 24 150
19 France – Guadeloupe 2 14.7 95
20 Ethiopia 1 8.5 10
21 Germany 4 6.75 50
22 Austria 3 1.45 3.8
23 Thailand 1 0.3 2
24 Australia 1 0.15 0.5
Totals 587 10 668.52 67 246.3
Averages per unit 18.17 114.56

Capacity in 2011 from Ref. [12] and Generation in 2010 from Ref. [11].

Since the direct use of geothermal resources for heating applications is feasible using resources at lower temperatures than those required for electrical production, more countries utilise geothermal energy for heating applications than for electrical generation. From the latest 2010 WGC report, Lund et al. [13], more than 77 countries made use of geothermal resources for heating applications. The reported installed capacity for geothermal power for direct heat use at the end of 2009 was 50 583 MWt (megawatts thermal) and the thermal energy used was 438 071 TJ·y−1 (terajoules thermal per year) or 121.7 TW·h·y−1. The average capacity factor for all direct heat applications was 27 % (Table 22.3).

Table 22.3. Worldwide Use of Geothermal Energy for Direct Heat Applications in 2010.

Application Capacity/MWt Utilisation/TJ·y−1 Capacity Factor
Geothermal heat pumps 35 236 214 782 0.19
Space heating 5391 62 984 0.37
Greenhouse heating 1544 23 264 0.48
Aquaculture pond heating 653 11 521 0.56
Agricultural drying 127 1662 0.42
Industrial uses 533 11 746 0.70
Bathing and swimming 6689 109 032 0.52
Cooling/snow melting 368 2126 0.18
Others 41 956 0.73
Total 50 583 438 071 0.27

After Ref. [13].

Lund et al. [13] reported that the heating capacity was distributed among the various applications as follows: geothermal heat pumps (70 %), bathing, swimming and balneology (13 %), district space heating (11 %), greenhouse heating (3.1 %), aquaculture pond heating (1.3 %), industrial uses (1.1 %), cooling/snow melting (0.7 %), agricultural drying (0.3 %) and 0.1 % for other uses. With regard to the thermal energy used, the largest applications were geothermal heat pumps (49 %), bathing, swimming and balneology (25 %) and district space heating (14 %).

Geologic History and Energy

C. Bauer, … S. Hirschberg, in Encyclopedia of the Anthropocene, 2018

Deep geothermal

Life-cycle GHG emissions of geothermal power generation mainly depend on the depth of the exploited heat resource, on the (drilling) technology used, on geologic conditions, and on the capacity of the plant. One can differentiate between hydrothermal and petrothermal plants, the former using naturally present hot water reservoirs and the latter creating an artificial ‘underground heat exchanger,’ also referred to as ‘enhanced geothermal systems’ (EGS), or ‘hot dry rock’ (HDR) technology. The ecoinvent database contains LCI data for EGS systems based on a case study of a specific site in Switzerland (Basel) with a drilling depth of 5000 m. The global average GHG emission for application of this technology is about 65 g CO2-equiv. kWh− 1. According to further literature, this plant type generates between 15 and 50 g CO2-equiv. kWh− 1.

Greenhouse Gas Emissions from Energy Systems, Comparison, and Overview☆

C. Bauer, … S. Hirschberg, in Reference Module in Earth Systems and Environmental Sciences, 2015

Deep geothermal

Life-cycle GHG emissions of geothermal power generation mainly depend on the depth of the exploited heat resource, on the (drilling) technology used, on geologic conditions, and on the capacity of the plant. One can differentiate between hydrothermal and petrothermal plants, the former using naturally present hot water reservoirs and the latter creating an artificial ‘underground heat exchanger,’ also referred to as ‘enhanced geothermal systems’ (EGS), or ‘hot dry rock’ (HDR) technology. The ecoinvent database contains LCI data for EGS systems based on a case study of a specific site in Switzerland (Basel) with a drilling depth of 5000 m. The global average GHG emission for application of this technology is about 65 g CO2-equiv. kWh− 1. According to further literature, this plant type generates between 15 and 50 g CO2-equiv. kWh− 1.

Energy and the Environment

G. Itskos, … P. Grammelis, in Environment and Development, 2016

6.10.5 Geothermal Energy

The developed systems that exploit the geothermal energy are called geothermal power plants. Globally, in 2013, the total installed thermal capacity was equal to ∼11,700 MW. It is estimated that geothermal energy can fulfill around 3% of global electricity demands and 5% of global heating demands by 2050 [77]. The high cost-effectiveness, the sustainability, the environmental-friendly behavior, and the reliability enhance the use of these technologies. In order to improve the system efficiency and the final electrical output, a supplementary source can be used to provide extra heat input for the working medium or extra electricity production. These additional energy sources can be biomass, solar, wind, gas, and oil.

Mainly there are four different types of power plants used to exploit the earth thermal output. The distinction among them is based on the cycle formation and its individual components. The first developed system for this form of energy was dry steam power plants, which begun to operate in 1904. The heated liquid extracted from the inner earth layers is driven through a pipeline system to a turbine, producing with the familiar, conventional way electricity. The cycle closes with the condensation of the used working medium and its return to the earth crust layers (even for further recirculation through the system). The steam power plants produce nowadays a little less than 40% of the US geothermal electricity.

However, the most common power plant type nowadays, producing 45% of the geothermal electricity in the United States, is the flash power plants. This technology is basically an evaluation of the former technology used majorly in cases where the hot mixture extracted from the inner earth surfaces has high pressure and therefore is not vaporized. The derived water gradually loses pressure as it is driven through an integrated pipeline system and as a consequence it abruptly vaporizes. The separation of the two phases is carried out in a separator. The steam is driven to the turbine, while the water can be directly used for buildings’ heating. Based on the number of the utilized steam separators, these systems can be characterized as single or double flash power plants.

The technological development in the mid-dle 1980s gave also the opportunity to the formulation of systems which are capable of exploiting the low-temperature geothermal sources, namely the springs that extract low-pressure and low-temperature mixtures (below 74°C). Approximately 15% of the installed geothermal power plants in the United States belong to this category, entitled as binary power plants. In this technology, the extracted hot mixture exchanges energy with an appropriate working medium, used to formulate a Rankine cycle. The two liquids are constantly separated and never mixed. The energy transfer takes place in a properly configured heat exchanger. The geothermal water can constantly recirculate in a closed loop, ensuring the close-to-zero emissions, the reliability of the system, and the extension of the project lifetime. A small difference to the operation of these units results in the formation of new type power plants called two-phase binary systems. Two-phase systems are similar to traditional binary cycles, except the steam flow enters the vaporizer/heat-exchanger, while the geothermal liquid is used to preheat the organic motive fluid. The steam condensate either flows into the preheater or is combined in the geothermal liquid after the preheater.

The fourth and final type of geothermal systems is called flash- binary combined cycle. This technology combines the formation and the organization of the first and third type of geothermal units. More specifically, the derived steam is driven to a high-pressure turbine for electricity production. Afterward, the low-pressure mixture is condensed in a binary system. This hybrid system combines the advantages of the two previously mentioned techniques. It presents higher efficiency as the pressure of the derived mixture is higher.

Mitigation

Lee Hannah, in Climate Change Biology, 2011

Solar Energy

Ultimately, the sun powers all major renewable energy technologies except geothermal and tidal power. The sun drives atmospheric processes that result in wind for wind power, plant growth for biofuels, and water evaporation that makes hydropower possible. Direct energy from the sun powers solar energy systems. More solar energy reaches the Earth each minute than is consumed in fossil fuels in an entire year.

Solar Thermal Technologies

Solar thermal energy uses heat to convert sunlight into useable energy. Where heat is the desired end energy use, direct conversion is possible. For instance, a south-facing window (in the Northern Hemisphere) may be used to heat a room in winter. Such direct uses of the sun’s heat are known as passive solar systems. Active solar systems concentrate or reflect the sun’s energy. Mirrors used to heat a central boiler for electricity generation or moving water through solar panels to heat it are two examples of the many types of active solar systems. Systems that use mirrors or other methods to focus the sun’s rays are known as concentrating systems, and those that do not are nonconcentrating. Many passive or nonconcentrating systems are suitable for household, decentralized use. Many concentrating, active systems are used for centralized electric generation.

Solar energy may be divided into two major categories: solar thermal and solar voltaic. Solar thermal energy relies on heating of a carrier fluid, often water. The warmed liquid may be used directly, as in hot water heating, or used to drive another process, such as electrical generation. Solar voltaic or photovoltaic systems generate energy by capturing electrons excited by photons in sunlight. Photovoltaic systems generate electricity that finds application in a number of end uses.

Photovoltaic Cells

Geothermal Power – an overview, Alternative Energy Today

Photovoltaic cells.

Source: NREL.

Photovoltaic (PV) cells use the electromagnetic properties of sunlight to generate electricity. Light falling on a PV array releases electrons, which are captured and channeled by the silicon structure of the PV cells. This stream of flowing electrons is electricity, which can be used to power any conventional electrical appliance or motor. Rooftop PV has the potential to provide as much as half of all of the world’s energy demand, if all available rooftop space were employed. A major fraction of electricity needs could be met by rooftop PV with no land use demands that might reduce wildlife habitat.

Despite massive potential, solar power currently has limited market penetration. Even in highly suitable countries such as Australia, solar provides less than 10% of energy demand. Nonetheless, worldwide, more than 140 million m2 of solar thermal collectors has been installed—more than 100 GW in energy-generating potential, which is more than total global installed wind capacity. In areas with large amounts of available land, central-receiver solar electrical generation has major potential for expansion. Solar thermal production might supply 5–20% of all energy demand worldwide by mid-century.

Photovoltaic generation has strong potential for supplying a major portion of electricity demand. Photovoltaics can be mounted on roofs in urban demand centers. Nanotechnology may soon provide photovoltaic paints that will allow electricity generation from any painted surface. It is possible that all residential electricity use could be provided by photovoltaics within the 21st century.

Mitigation

Lee Hannah, in Climate Change Biology (Second Edition), 2015

Solar Energy

Ultimately, the sun powers all major renewable energy technologies except geothermal and tidal power. The sun drives atmospheric processes that result in wind for wind power, plant growth for biofuels, and water evaporation that makes hydropower possible. Direct energy from the sun powers solar energy systems. More solar energy reaches the Earth each minute than is consumed in fossil fuels in an entire year.

Solar Thermal Technologies

Solar thermal energy uses heat to convert sunlight into useable energy. Where heat is the desired end energy use, direct conversion is possible. For instance, a south-facing window (in the Northern Hemisphere) may be used to heat a room in winter. Such direct uses of the sun’s heat are known as passive solar systems. Active solar systems concentrate or reflect the sun’s energy. Two examples of the many types of active solar systems are mirrors used to heat a central boiler for electricity generation or moving water through solar panels to heat it. Systems that use mirrors or other methods to focus the sun’s rays are known as concentrating systems, and those that do not are nonconcentrating. Many passive or nonconcentrating systems are suitable for household, decentralized use. Many concentrating, active systems are used for centralized electric generation.

Solar energy may be divided into two major categories: solar thermal and solar voltaic. Solar thermal energy relies on the heating of a carrier fluid, often water. The warmed liquid may be used directly, as in hot-water heating, or used to drive another process, such as electrical generation. Solar voltaic or photovoltaic systems generate energy by capturing electrons excited by photons in sunlight. Photovoltaic systems generate electricity that finds application in a number of end uses.

Source: NREL.

Photovoltaic Cells

Geothermal Power – an overview, Alternative Energy TodayPhotovoltaic (PV) cells use the electromagnetic properties of sunlight to generate electricity. Light falling on a PV array releases electrons, which are captured and channeled by the silicon structure of the PV cells. This stream of flowing electrons is electricity, which can be used to power any conventional electrical appliance or motor. Rooftop PV has the potential to provide as much as half of all of the world’s energy demand, if all available rooftop space were employed. A major fraction of electricity needs could be met by rooftop PV with no land use demands that might reduce wildlife habitat.

Despite massive potential, solar power currently has limited market penetration. Even in highly suitable countries such as Australia, solar power provides less than 10% of energy demand. Nonetheless, worldwide, more than 140 million m2 of solar thermal collectors have been installed—more than 100 GW in energy-generating potential—which is more than the total global-installed wind capacity. In areas with large amounts of available land, central-receiver solar electrical generation has major potential for expansion. Solar thermal production might supply 5–20% of all energy demand worldwide by 2050.

PV generation has strong potential for supplying a major portion of electricity demand. PV can be mounted on roofs in urban demand centers. Nanotechnology may soon provide PV paints that will allow electricity generation from any painted surface. It is possible that all residential electricity use could be provided by PV within the twenty-first century.

Leave a Reply



Please follow & like us :)

WP2Social Auto Publish Powered By : XYZScripts.com