Design of a Solar Power System for Portable Mesh Network
1.1 Introduction
When disaster strikes or there is a terrorist attack, the ability of first responders to save lives depends robust and reliable communication and monitoring systems to support cross-agency situational awareness and coordination of emergency response and management activities. Often in disaster situations, first responders are left without communications or power because there has been significant damage to the infrastructure. Resources can be marshaled to establish a central command and control center but it is much more difficult and time consuming to extend the reach of the command and control center into the wider community. Some of the obstacles to the rapid deployment of communications and monitoring equipment throughout the community are the lack of power when and where it is needed and having the appropriate equipment without any ‘missing pieces’. One approach to this problem is to deploy a self contained purpose designed modular equipment to meet the short term needs. It would be ideal to walk/drive to one of more locations and simply drop off one or more communication or sensor modules that could be used for form a command and control network.
Clearly battery powered equipment can enable rapid deployment of equipment but it is likely that power storage capacity of the equipment would not be sufficient to operate for days or weeks as required. While it is possible to use generators to extend the operating period they do require refueling and constant attention. A better solution is a renewable resource such a photo-voltaic solar system [1].
1.2 Research Background of Solar Power System
A legend claims that Archimedes used polished shields to concentrate sunlight on the invading Roman fleet and repel them from Syracuse [2]. Auguste Mouchout used a parabolic trough to produce steam for the first solar steam engine in 1866 [3].
A solar cell, or photovoltaic cell (PV), is a device that converts light into electric current using the photoelectric effect [4]. This is based on the discovery by Alexandre-Edmond Becquerel who noticed that some materials release electrons when hit with rays of photons from light, which produces an electrical current [5]. The first solar cell was constructed by Charles Fritts in the 1880s [6]. Although the prototype selenium cells converted less than 1% of incident light into electricity, both Ernst Werner von Siemens and James Clerk Maxwell recognized the importance of this discovery [6]. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954 [6]. These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6% [6].
Solar power has great potential, but in 2008 supplied less than 0.02% of the world’s total energy supply. There are many competing technologies, including fourteen types of photovoltaic cells, such as thin film, monocrystalline silicon, polycrystalline silicon, and amorphous cells, as well as multiple types of concentrating solar power. It is too early to know which technology will become dominant.
The earliest significant application of solar cells was as a back-up power source to the Vanguard I satellite in 1958, which allowed it to continue transmitting for over a year after its chemical battery was exhausted [6]. The successful operation of solar cells on this mission was duplicated in many other Soviet and American satellites, and by the late 1960s, PV had become the established source of power for them [6]. After the successful application of solar panels on the Vanguard satellite it still was not until the energy crisis, in the 1970s, that photovoltaic solar panels gained use outside of back up power suppliers on spacecraft [7]. Photovoltaics went on to play an essential part in the success of early commercial satellites such as Telstar, and they remain vital to the telecommunications infrastructure today [6].
The high cost of solar cells limited terrestrial uses throughout the 1960s. This changed in the early 1970s when prices reached levels that made PV generation competitive in remote areas without grid access. Early terrestrial uses included powering telecommunication stations, offshore oil rigs, navigational buoys and railroad crossings [6]. These off-grid applications accounted for over half of worldwide installed capacity until 2004 [8].
The 1973 oil crisis stimulated a rapid rise in the production of PV during the 1970s and early 1980s [9]. Economies of scale which resulted from increasing production along with improvements in system performance brought the price of PV down from 100 USD/watt in 1971 to 7 USD/watt in 1985 [6]. Steadily falling oil prices during the early 1980s led to a reduction in funding for photovoltaic R&D and a discontinuation of the tax credits associated with the Energy Tax Act of 1978. These factors moderate growth to approximately 15% per year from 1984 through 1996 [10].
Since the mid-1990s, leadership in the PV sector has shifted from the US to Japan and Europe. Between 1992 and 1994 Japan increased R&D funding, established net metering guidelines, and introduced a subsidy program to encourage the installation of residential PV systems [11]. As a result, PV installations in the country climbed from 31.2 MW in 1994 to 318 MW in 1999 [12], and worldwide production growth increased to 30% in the late 1990s [13]
Germany became the leading PV market worldwide since revising its feed-in tariffs as part of the Renewable Energy Sources Act. Installed PV capacity in Germany has risen from 100 MW in 2000 to approximately 4,150 MW at the end of 2007. After 2007 [14] [15], Spain became the largest PV market after adopting a similar feed-in tariff structure in 2004, installing almost half of the photovoltaics (45%) in the world, in 2008, while France, Italy, South Korea and the U.S. have seen rapid growth recently due to various incentive programs and local market conditions [16].
1.3 Why Portable Solar Power System?
Wireless Mesh networking would be great fit to blanket the work zones in rural areas. Generally batteries are used to power the system; there may be a need to use solar panels or some other supplementary power supply to ensure a continuous power supply for long periods of time.
In this work, we have designed theoretically Portable Solar Power System for Wireless Mesh Network. These include the theoretical analysis and calculation of Portable Solar Power System [17].
1.4 It’s feasibility in Bangladesh
More than 60% of the populations, 84 million people, do not have access to grid electricity. In the rural areas, where most of the population lives, this number increases to 80%. Other side, natural disaster is the common scene in Bangladesh. It occurs in Bangladesh almost every year.
So, our system is very effective in Bangladesh.
1.5 Thesis Organization
To understanding the fundamental of Wireless Mesh Network chapter 2 starts with a description of wireless mesh network, network architecture and Infrastructure/backbone WMNs. Further, discussion will be concentrated on the network characteristics and advantages of the network.
To insight the prospect of Solar Power System, solar power system with its advantages and the profit to use is described first in chapter 3. For theoretical analysis of solar power system its theoretical history, several applications, methods of harnessing solar energy such as the Photovoltaics (PV), concentrating solar power etc are described. Finally, how the portable solar power system can be designed are narrates in this chapter.
In chapter 4, we calculated the power which is need for our network and proposed the both design for portable solar power design and also for the mesh network.
Chapter 5 provides the conclusions that can be drawn from the work described in this thesis and provides recommendations for future research.
Wireless Mesh Networking
2.1 Introduction
Mesh networking is defined as a technique to route data between communication nodes to allow continuous network connections and reconfigurations around broken paths by locating alternatives until the destination is reached. Such a network is intended to be modular in nature, and would not require access to an Internet service provider. As originally conceived, this wireless network system allowed real-time communication in large urban areas, while provide reliable information to users through a series of wireless mesh router connections [17], in a classic wireless network, each node monitors that path between itself and an additional node. These networks are configured in a hierarchical fashion that ensures that each node uses a single connection path. The drawback to this approach is its lack of failure protection. If a node fails, the dedicated link is lost and the endpoint is unreachable until service is restored.
The establishment of multiple connection paths is a logical answer to this problem. Unfortunately, classic nodes lack the intelligent technology to select from alternate transmission paths.
Developers studied the idea of adding intelligence to each node to solve this problem. Such intelligence would track each available communication path and would logically select the best route. Added together, the multiplicity of nodes would create a mesh. This mesh would eliminate single points of failure. If one link went down, other network nodes would be alerted and could select an alternative node path. The design’s self-healing nature would ensure that the network continued to operate. User access would be maintained as would productivity levels.
Today, the concept of intelligent mesh networks is a reality. Mesh is an increasingly applied network topology as researchers improve and enhance it, and businesses deploy and utilize it. Mesh has become the technology of choice for applications as diverse as securing military perimeters to regulating product flow down factory assembly lines to facilitating the intelligent navigation of one’s morning commute [18].
2.2 Wireless Mesh Networking
As various wireless networks evolve into the next generation to provide better services, a key technology, wireless mesh networks (WMNs), has emerged recently. In WMNs, nodes are comprised of mesh routers and mesh clients. Each node operates not only as a host but also as a router, forwarding packets on behalf of other nodes that may not be within direct wireless transmission range of their destinations. A WMN is dynamically self-organized and self-con?gured, with the nodes in the network automatically establishing and maintaining mesh connectivity among themselves (creating, in e?ect, an ad hoc network). This feature brings many advantages to WMNs such as low up-front cost, easy network maintenance, robustness, and reliable service coverage. Conventional nodes (e.g., desktops, laptops, PDAs, PocketPCs, phones, etc.) equipped with wireless network interface cards (NICs) can connect directly to wireless mesh routers. Customers without wireless NICs can access WMNs by connecting to wireless mesh routers through, for example, Ethernet. Thus, WMNs will greatly help the users to be always-on-line anywhere anytime. Moreover, the gateway/bridge functionalities in mesh routers enable the integration of WMNs with various existing wireless networks such as cellular, wireless sensor, wireless-?delity (Wi-Fi), worldwide inter-operability for microwave access (WiMAX), WiMedia networks. Consequently, through an integrated WMN, the users of existing network can be provided with otherwise impossible services of these networks. WMN is a promising wireless technology for numerous applications, e.g., broadband home networking, community and neighborhood networks, enterprise networking, building automation, etc. It is gaining signi?cant attention as a possible way for cash strapped Internet service providers (ISPs), carriers, and others to roll out robust and reliable wireless broadband service access in a way that needs minimal up-front investments. With the capability of self-organization and selfcon ?guration, WMNs can be deployed incrementally, one node at a time, as needed. As more nodes are installed, the reliability and connectivity for the users increase accordingly. Deploying a WMN is not too di?cult, because all the required components are already available in the form of ad hoc network routing protocols, IEEE 802.11 MAC protocol, wired equivalent privacy (WEP) security, etc. Several companies have already realized the potential of this technology and o?er wireless mesh networking products. A few testbeds have been established in university research labs. However, to make a WMN be all it can be, considerable research e?orts are still needed. For example, the available MAC and routing protocols applied to WMNs do not have enough scalability; the throughput drops signi?- cantly as the number of nodes or hops in a WMN increases. Similar problems exist in other networking protocols. Consequently, all existing protocols from the application layer to transport, network MAC, and physical layers need to be enhanced.
Fig. 2.1: Wireless mesh networking
2.3 Network architecture
WMNs consist of two types of nodes: mesh routers and mesh clients. Other than the routing capability for gateway/repeater functions as in a conventional wireless router, a wireless mesh router contains additional routing functions to support mesh networking. To further improve the ?exibility of mesh networking, a mesh router is usually equipped with multiple wireless interfaces built on either the same or di?erent wireless access technologies. Compared with a conventional wireless router, a wireless mesh router can achieve the same coverage with much lower transmission power through multi-hop communications. Optionally, the medium access control (MAC) protocol in a mesh router is enhanced with better scalability in a multi-hop mesh environment. Mesh clients also have necessary functions for mesh networking, and thus, can also work as a router. However, gateway or bridge functions do not exist in these nodes. In addition, mesh clients usually have only one wireless interface. As a consequence, the hardware platform and the software for mesh clients can be much simpler than those for mesh routers. Mesh clients have a higher variety of devices compared to mesh routers. They can be a laptop/desktop PC, pocket PC, PDA, IP phone, RFID reader, BACnet (building automation and control networks) controller, and many other devices. The architecture of WMNs can be classi?ed into three main groups based on the functionality of the nodes:
Infrastructure/Backbone WMNs:
The architecture is shown in Fig. 2.2, where dash and solid lines indicate wireless and wired links, respectively. This type of WMNs includes mesh routers forming an infrastructure for clients that connect to them. The WMN infrastructure/ backbone can be built using various types of radio technologies, in addition to the mostly used IEEE 802.11 technologies. The mesh routers form a mesh of self-con?guring, self-healing links among themselves. With gateway functionality, mesh routers can be connected to the Internet. This approach, also referred to as infrastructure meshing, provides backbone for conventional clients and enables integration of WMNs with existing wireless networks, through gateway/bridge functionalities in mesh routers.
Fig. 2.2: Infrastructure/backbone WMNs.
Conventional clients with Ethernet interface can be connected to mesh routers via Ethernet links. For conventional clients with the same radio technologies as mesh routers, they can directly communicate with mesh routers. If different radio technologies are used, clients must communicate with the base stations that have Ethernet connections to mesh routers.
Infrastructure/Backbone WMNs are the most commonly used type. For example, community and neighborhood networks can be built using infrastructure meshing. The mesh routers are placed on the roof of houses in a neighborhood, which serve as access points for users inside the homes and along the roads. Typically, two types of radios are used in the routers, i.e., for backbone communication and for user communication, respectively. The mesh backbone communication can be established using long-range communication techniques including directional antennas.
Client WMNs.
Client meshing provides peer-topeer networks among client devices. In this type of architecture, client nodes constitute the actual network to perform routing and con?guration functionalities as well as providing enduser applications to customers. Hence, a mesh router is not required for these types of networks. The basic architecture is shown in Fig. 2.3. In Client WMNs, a packet destined to a node in the network hops through multiple nodes to reach the destination. Client WMNs are usually formed using one type of radios on devices.
Moreover, the requirements on end-user devices is increased when compared to infrastructure meshing, since, in Client WMNs, the end-users must perform additional functions such as routing and self-con?guration. (LOS) links.
Fig. 2.3: Client WMNs.
Hybrid WMNs.
This architecture is the combination of infrastructure and client meshing as shown in Fig. 2.4. Mesh clients can access the network through mesh routers as well as directly meshing with other mesh clients. While the infrastructure provides connectivity to other networks such as the Internet, Wi-Fi, WiMAX, cellular, and sensor networks; the routing capabilities of clients provide improved connectivity and coverage inside the WMN. The hybrid architecture will be the most applicable case in our opinion.
Fig. 2.4: Hybrid WMNs.
2.4 Characteristics
Multi-hop wireless network
An objective to develop WMNs is to extend the coverage range of current wireless networks without sacri?cing the channel capacity. Another objective is to provide non-line-of-sight (NLOS) connectivity among the users without direct line-of-sight (LOS) links. To meet these requirements, the mesh-style multi-hopping is indispensable, which achieves higher throughput without sacri ?cing e?ective radio range via shorter link distances, less interference between the nodes, and more e?cient frequency re-use.
Support for ad hoc networking, and capability of self-forming, self-healing, and self-organization.
WMNs enhance network performance, because of ?exible network architecture, easy deployment and con?guration, fault tolerance, and mesh connectivity, i.e., multipoint-to-multipoint communications. Due to these features, WMNs have low upfront investment requirement, and the network can grow gradually as needed.
Mobility dependence on the type of mesh nodes. Mesh routers usually have minimal mobility, while mesh clients can be stationary or mobile nodes.
Multiple types of network access:
In WMNs, both backhaul access to the Internet and peerto- peer (P2P) communications are supported. In addition, the integration of WMNs with other wireless networks and providing services to end-users of these networks can be accomplished through WMNs.
Compatibility and interoperability with existing wireless networks:
For example, WMNs built based on IEEE 802.11 technologies must be compatible with IEEE 802.11 standards in the sense of supporting both meshcapable and conventional Wi-Fi clients. Such WMNs also need to be inter-operable with other wireless networks such as WiMAX, Zig- Bee, and cellular networks [19].
2.5 Portable Mesh Network
The following design is the proposed recommendation to the install the wireless mesh networking. This design will ensure that the system will provide many years of reliable service. These recommendations can be used to evaluate pre-engineered system designs and compare system features from one supplier to another.
The Mesh router is used to model mesh network. The Mesh routers are fully featured, environmentally hardened units that provide not only the client and mesh connectivity but also backhaul points to the internet. It requires a backhaul point for internet connectivity. This may be provided via available telephony, fiber or HFC infrastructure through the use of modems.
Fig. 2.5: Portable Mesh Network
As the first step of the experiment, the point- to- point access approach is being arranged for the remote area which is shown in fig. 2.5 This system will provide a reliable service for many years and it is a portable mesh network which is easily setup any remote area. For the field test, two wireless routers are utilized to examine the point-to-point access shown in fig. 2.6 The specification of this wireless router include radios that support 802.11 a/b/g and 4.9GHz and video transmission rate of 30 fps.
Fig. 2.6: Network Setup for Experiments
The following criteria were examined in network setup for field testing:
* Maximum distance of reception.
* Minimum height requirement of the router;
* Connection compatibility (server-router or client-router) to ensure maximum access speed.
* Server-client connection rate, and
* Supplementary devices that may be included for field testing.
Initial efforts in determining the connection between the server/client and router found that the wireless connection 802.11 b/g, which is commonly used among portable notebook owners, was compatible and convenient for the server/client and router connection. This wireless selection has two advantages over the available options in the market. First, the 802.11 b/g wireless is a common component in laptop computers. Second, this connection does not require a wired connection, which is a plus as Ethernet cables may be needed if wired connections are chosen for this server/client and router connection. Clearly, for remote installations such as rural work zone locations running extensive wires to each component would be prohibitively expensive and time-consuming, both factors being disincentives for their use. Initial observation of the preliminary field experiment showed that the connection between routers can be successfully connected up to a distance of 2 miles. The preliminary results of the testing validated the troubleshooting effort, where the signal of the routers must be clear of any large obstructions. The field testing found that the mesh networking can be successfully deployed by setting the router at designated locations .Clearly; this gave an indication that in order for a mesh network to be actually used in a remote area [17].
2.6 Advantage
The advantages of this wireless network system are described as follows:
? This technology allows the system to be created locally without having to go through a service provider;
? The connection automatically searches for alternative routes as topology changes;
? Each node (or mesh router) does not need an internet gateway, instead they share fast and reliable connection;
? The technology is easy to install and manage, and backup technology can be cooperatively deployed;
? Location of the nodes can be added, removed or relocated without the effort of traditional administration;
? This network system has low power consumption and offers redundancy when nodes get disconnected; and
? Mesh network reduces interference between clients [17].
Solar Energy
3.1 Introduction
Solar energy, radiant light and heat from the Sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available renewable energy on Earth. Only a minuscule fraction of the available solar energy is used.
Solar powered electrical generation relies on heat engines and photovoltaic. Solar energy’s uses are limited only by human ingenuity. A partial list of solar applications includes space heating and cooling through solar architecture, potable water via distillation and disinfection, day lighting, solar hot water, solar cooking, and high temperature process heat for industrial purposes. To harvest the solar energy, the most common way is to use solar panels.
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 thermal collectors 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.
3.2 Solar Energy
Solar Energy is the generation of electricity from sunlight. This can be direct as with photo voltaics (PV), or indirect as with concentrating solar power (CSP), where the sun’s energy is focused to boil water which is then used to provide power. The solar power gained from photovoltaics can be used to eliminate the need for purchased electricity (usually electricity gained from burning fossil fuels) or, if energy gained from photovoltaics exceeds the home’s requirements, the extra electricity can be sold back to the home’s supplier of energy, typically for credit [20]. The largest solar power plants, like the 354 MW SEGS, are concentrating solar thermal plants, but recently multi-megawatt photovoltaic plants have been built. Completed in 2008, the 46 MW Moura photovoltaic power station in Portugal and the 40 MW Waldpolenz Solar Park in Germany are characteristic HI 8TH GRADE of the trend toward larger photovoltaic power stations. Much larger ones are proposed, such as the 550 MW Topaz Solar Farm, and the 600 MW Rancho Cielo Solar Farm. Solar power is a predictably intermittent energy source, meaning that whilst solar power is not available at all times, we can predict with a very good degree of accuracy when it will and will not be available. Some technologies, such as solar thermal concentrators have an element of thermal storage, such as molten salts. These store spare solar energy in the form of heat which is made available overnight or during periods that solar power is not available to produce electricity [21].
3.2.1 The Sun
Times at various other locations when it is 12 hours GMT. This is the time that the sun follows and is what must be used when positioning a solar collector.
The importance of comprehending the true solar time becomes apparent when one looks at the time zoning map determined politically.
The Sun is the centre of our solar system and its energy drives nearly all systems on earth. They include climate systems, ecosystems (plant & animal processes), hydrological systems, wind systems, etc.).
Solar energy is created at the core of the sun when hydrogen atoms are fused to form helium by nuclear fusion.
It is estimated that 700 million tons of hydrogen are converted into 695 million tons of helium every second.
H+ + H+ = He+++Energy
.
The remaining mass of 5 million ton is converted into electromagnetic energy that radiates from the sun’s surface out into space.
The rate at which energy is emitted from the sun’s surface is estimated at 63,000,000 W/m2. However the earth intercepts only a small fraction of this enormous energy. When travelling through outer space, which is characterized by vacuum, the solar radiation remains intact and is not modified or attenuated until it reaches the top of the earth’s atmosphere.
3.2.2 Energy from the Sun
The energy emitted from the sun and intercepted by the earth is estimated at a rate of 1.73 x 1014 kW. It is largely comprised of the following approximate ratios.
– 9% ultraviolet radiation (200 – 400 nm)
– 41% visible radiation (400 – 700 nm)
– 50% infrared radiation (700 – 3000 nm)
The amount of power received at the top of the earth’s atmosphere is relatively constant and estimated at 1.368 kW per m2. This is called the solar constant. Constituting the earth’s ALBEDO. See figure 3.1.
Fig. 3.1: Constituting the earth’s ALBEDO
The Earth receives 174 <href=”#petawatt_.281015_watts.29″ title=”Orders of magnitude (power)”>petawatts (PW) of incoming solar radiation 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 [22].
3.2.3 Solar Energy History
The Growth and Development
Solar Energy History from 400 B.C. to the present day advances.
Even when the supply of fossil fuels seemed endless, there were those who were interested in harnessing the power of the sun for energy. In 400 B.C. the Greeks were the first to implement the sun’s rays for heat. During this time they began to orient the placement of their houses to trap solar heat during winter.
Solar Energy History – 18th Century
Even though the first solar collector was built by Swiss scientist Horace de Saussure in 1767, it would be another century before French inventor Auguste Mouchout would patent a design for a motor to run on solar energy. His devices turned solar energy into steam power.
History Of Solar Energy History – 19th Century
In 1878 the first book about solar energy, A Substitute for Fuel in Tropical Countries was written by William Adams. Using mirrors Adams was able to power a 2.5 horsepower steam engine. His design known as the Power Tower Concept is still in use today.
The photovoltaic effect or the production of electricity directly from the sun was discovered by Frenchman Henry Becquerel in 1890. In 1891 American Clarence Kemp received a patent for the first solar water heater.
Solar Energy History – 20th Century
The early 1900’s brings more knowledge and improvement to the quest for solar power. In 1904 Henry Willsie built two plants in California. Willsie was the first person to use solar power at night after generating it during the day. Still he was not able to make sales and his solar company folded.
The 1950’s brings more development in the solar energy sector. The first solar water heating system was placed in a commercial building as the primary source for interior heat. The first commercial solar cells were also made available to the public.
Space programs made extensive use of solar power from the early 1960’s to present day.
By the end of the 1970’s there were over 100 solar manufacturers in the United States. With the energy crisis of the seventy’s, the realization of the importance of solar energy to replace traditional energy methods became clear. From that point until today solar energy has gradually received more and more interest and support.
Today there is a renewed focus on solar energy. More people are recognizing the need and the advantage of solar power. Solar cells are powering an array of items from household appliances to cars. Solar electric systems now power many homes and commercial businesses. The future of solar power to provide inexhaustible power supply at affordable costs is great.
3.2.4 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.
The sun’s heat and light is one of the most powerful resources to touch the planet. In the last decade, many new technologies have been adapted to help us take advantage of the massive power of the sun. The sun is always with us, so it only makes sense for us to capture its power and turn it into usable solar energy. Solar technology continues to make advances, so the future of solar energy as a mainstream power source is on the way.
How is solar energy used?
Currently there are several methods used to capture and convert the sun’s massive power of heat and light. Unobstructed access to the sun is the crucial factor for optimal use of active or passive solar energy systems. Any place that you currently use energy is a viable option for converting to solar energy use.
Solar lighting especially for outdoors is very common today. Lighting walkways and other landscape is a simple matter. Most home improvement stores now offer solar powered outdoor lighting. The use of solar power doesn’t end there. Solar powered outdoor lighting is on a small portion of capturing the sun’s power for our energy.
You can use solar energy for cooking, heating and cooling your home, water heating space heating, and even total solar energy systems to generate your own electricity. From very simple to complex grid systems solar power is available to the public.
The use of solar energy to replace traditional power sources is so important you can now get federal, state, and local incentives to use solar energy on your property. For example, installing a solar system to heat your water will result in approximately a $2000 initial cost. Depending on your location, your state/country and local government may also offer incentives. In return, you’ll save thousands on your energy bills. In addition, you’ll be using energy that doesn’t deplete natural resources and it is environ- mentally safe.
As mentioned earlier the only important factor is that you have solar access. Several communities throughout the US have developed guidelines and ordinances for solar access protection. These guidelines and ordinances prohibit structural development that could shadow solar collectors and prevent optimum performance of the solar system.
Technologies such as the Stirling engine dishes which use a Stirling cycle engine to power a generator. Photovoltaics were initially used to power small and medium-sized applications, from the calculator powered by a single solar cell to off-grid homes powered by a photovoltaic array.
Solar power plants can face high installation costs, although this has been decreasing due to the <href=”#The_experience_curve” title=”Experience curve effects”>learning curve. Developing countries have started to build solar power plants, replacing other sources of energy generation.
Since solar radiation is intermittent, solar power generation is usually combined either with storage or other energy sources to provide continuous power, although for small distributed producer/consumers, net metering makes this transparent to the consumer. On a slightly larger scale, in Germany, a combined power plant has been demonstrated, using a mix of wind, biomass, hydro-, and solar power generation, resulting in 100% renewable energy.
It is very important for the future of solar energy to encourage and carefully consider compatibility of landscaping, shading, and the placement of solar systems. Solar access should be protected in every way possible.
The future of using solar energy to replace traditional energy methods is bright. We can all look forward to using the “free” solar power in the future.
3.2.5 Passive and Active Solar Energy
Passive solar energy is being used in many ways. Passive solar energy, just as the name implies uses the heat and light from the sun without using any collectors, grids, or cells. For example, buildings are now being designed to use passive solar energy. The south side of a building always gets the most sunlight. With that in mind, buildings that are designed to use passive solar energy will have large south facing windows. Sunlit floors and walls can now be built with materials to absorb and store the sun’s solar heating.
Two other design features that help provide passive solar energy are sunspaces and trombe walls. Sunspaces (similar to a greenhouse) are constructed on the south side of a building. As sunlight passes through the glass or glazing it warms the sunspace. Ventilation allows the heat to circulate into the building.
A trombe wall is a thick, south-facing wall, painted black. Trombe walls are made of materials that naturally absorb a lot of heat. Glass or plastic glazing, installed a few inches in front of the wall, helps hold the heat. The wall heats up slowly during the day. During the night as it cools gradually the trombe wall gives off heat inside the building.
Active solar energy systems use focusing mirrors and metal plates to capture the sun’s energy. Solar radiation is absorbed by the collectors and then transfers the heat to air or water. The solar collector of an active solar system is a black absorber. This absorber absorbs solar radiation and converts it into heat. This heat is then transferred to a heat=transfer liquid and then to a heat exchanger to heat water in a tank or to be stored for later use.
Active solar systems can be used to heat water in home, swimming pools, and commercial and industrial buildings. These systems can also be used to provide space heating. Using glazed collectors much like solar water heating systems heat is transferred to a radiant floor heating system. Fans or pumps can also be used to circulate heated air.
Incorporating passive and active solar energy systems into new homes and building will save thousands on energy costs. While there may be some expense initially, adding these systems to existing structures is also well worth the investment. Consider protecting and enhancing our environment and reduce your energy costs by using solar energy [23].
3.2.6 Common methods of harnessing solar energy
Plant photosynthesis (in nature) constitutes the most dominant method of solar energy conversion when they form carbohydrates from water and carbon dioxide.
This includes land plants as well as the green chlorophyll that covers the sea surface.
Apart from the direct formation of food for animal consumption, these are also the ultimate raw materials for the formation of fossil fuels, by direct decay of dead plants and/or animals that live on the plants. In addition, animals (especially the cold blooded ones) have metabolisms that are largely dependent on the sun’s radiation. But even warm-blooded ones such as humans can absorb the sun through their skins to manufacture certain important body chemicals like vitamins.
Humans (throughout history) have also developed technologies to utilize solar energy directly. For example sun drying has for many years been used to preserve agricultural produce. In modern industry the following are the most common technologies. They are becoming increasingly more important as humankind begins to realize the impending depletion of fossil fuel stocks as well as the direct environmental cost of continued burning of fossil fuels.
Photovoltaics (PV) – are semiconductor cells, which directly convert sunlight into electricity. [Recent developments include heat conversion as well, using PV-thermal technologies]
Photovoltaics (PV) convert light directly into dc electric current. Becquerel first reported the photovoltaic effect, way back in 1839. Bell Laboratories however only produced the first practical silicon type solar cells in 1954. Initial applications were in extraterrestrial missions. The first earthly uses were in remote and inaccessible installations that required little or no maintenance, mainly in signal and telecommunications applications.
In the decade leading up to the end of the millennium the spirit of the Rio Earth summit promoted a fresh awareness of environmental sustainability. Consequently, the use of PV technology was among programs promoted by the Global Environment Fund (GEF), among others.
As mentioned, a PV cell is a dc generator. Using semi-conductor technology the cells convert sunlight directly into electricity by a quantum process. A photon from the sun’s ray strikes the material and if the energy content of the photon is at least as high as the band gap energy,of the material then an electron is elevated from its normal valence band location to the conduction band. The above action by the sun results in electron-hole charge carriers called photo-carriers. When an external electrical load is connected, a dc current (called the photo current) flows. Thus, the process is called the photovoltaic effect.
Passive Solar Heating, Cooling and Day lighting – Buildings can be designed for passive solar and day lighting by incorporating appropriate design features.
Concentrating Solar Power –
Concentrating solar power technologies use reflective materials such
as mirrors to concentrate the sun’s energy.
This concentrated energy is then (i) either converted into electricity via turbines and generators, or (ii) used directly to light interiors of buildings with the help of fibre optic guides. Additionally solar concentrators can also be used to increase the equivalent surface area of PV cells [24].
Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists; the most developed are the parabolic trough, the concentrating linear fresnel reflector, the Stirling dish and the solar power tower. Various techniques are used to track the Sun and focus light. In all of these systems a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage [25].
A parabolic trough consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector’s focal line. The receiver is a tube positioned right above the middle of the parabolic mirror and is filled with a working fluid. The reflector is made to follow the Sun during the daylight hours by tracking along a single axis. Parabolic trough systems provide the best land-use factor of any solar technology [26]. The SEGS plants in California and Acciona’s Nevada Solar One near Boulder City, Nevada are representatives of this technology [27] [28]. The Suntrof-Mulk parabolic trough, developed by Melvin Prueitt, uses a technique inspired by Archimedes’ principle to rotate the mirrors [29].
Concentrating Linear Fresnel Reflectors are CSP-plants which use many thin mirror strips instead of parabolic mirrors to concentrate sunlight onto two tubes with working fluid. This has the advantage that flat mirrors can be used which is much cheaper than parabolic mirrors, and that more reflectors can be placed in the same amount of space, allowing more of the available sunlight to be used. Concentrating linear Fresnel reflectors can be used in either large or more compact plants [30] [31].
A Stirling solar dish, or dish engine system, consists of a stand-alone parabolic reflector that concentrates light onto a receiver positioned at the reflector’s focal point. The reflector tracks the Sun along two axes. Parabolic dish systems give the highest efficiency among CSP technologies [32]. The 50 kW Big Dish in Canberra, Australia is an example of this technology [27]. The Stirling solar dish combines a parabolic concentrating dish with a Stirling heat engine which normally drives an electric generator. The advantages of Stirling solar over photovoltaic cells are higher efficiency of converting sunlight into electricity and longer lifetime. A solar power tower uses an array of tracking reflectors (heliostats) to concentrate light on a central receiver atop a tower. Power towers are more cost effective, offer higher efficiency and better energy storage capability among CSP technologies. The Solar Two in Barstow, California and the Planta Solar 10 in Sanlucar la Mayor, Spain are representatives of this technology [27]. A solar bowl is a spherical dish mirror that is fixed in place. The receiver follows the line focus created by the dish (as opposed to a point focus with tracking parabolic mirrors) [33]
Solar Water Heating, Space Heating and Cooling – Solar hot water heaters use the sun to heat water directly or indirectly via a heat heat-transfer fluid
.
3.3 Concept of seasons from an extra-terrestrial perspective
The earth’s axis is tilted at an angle of 23.5° with respect to the sun’s beam as depicted in fig. 3.2. The earth spins on this axis once every 24 hours and revolves around the sun every 365 days. The resulting periodical changes in the position of the earth’s axis relative to the sun determine the earth’s seasons.
These in turn affect the duration of daytime as well as the angle of incidence, both of which affect the amount of solar energy per unit area (or insolation) received at a particular location on earth.
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Fig. 3.2: The earth’s orbit around the sun during the year
But from earthly perspective it is more convenient to model the sun as moving around the earth. See fig. 3.3
Fig. 3.3: The sun modelled as moving around the earth
In order to be able to design the correct size of solar energy collector one needs to know (among others) the amount of energy that will be available per unit area at a given location, over a given season. Global radiation is the total amount of radiation arriving at a location. It is comprised of direct and diffuse components.
There are two variables that affect amount of INSOLATION (incident solar radiation) at an earthly location namely
· Geometric factors
· Atmospheric factors.
These can also be enumerated as geography of location (altitude, latitude), orientation, time of day, season, and climate.
Fig. 3.4 depicts changing positions of the Sun at sunrise for different seasons from the point of view of an earthly observer.
Fig. 3.4: Sunrise as seen by an earthly observer in different seasons
3.3.1 Estimating the effects of geometry on insolation
The main unit of interest and which must be maximized is Insolation, I (which is the amount of radiation per unit area over a given season). And the main reason for maximizing, I, is the minimisation of the size and therefore the cost of the solar energy collector. Low values of insolation mean that larger and therefore more expensive surfaces must be used to collect the same amount of solar energy.
Maximum radiation per surface is obtainable when the collector surface is positioned perpendicular to sun’s rays. So ideally a collector must be able to track the sun throughout the day and over the seasons to maximize energy capture. This can be achieved by mounting the panel on a sun-tracking device. In most practical situations however, this may not be possible for various reasons including economics. In such cases a panel can be positioned at a mean (or compromise) inclination in order to optimise energy capture as depicted in fig. 3.5
Fig. 3.5: Different mean positions for maximum seasonal capture of solar
Radiation from a purely geometrical point of view (with an ideally clear sky) insolation is given by
I = S cos qz
Where
S (ONE SUN) = 1000 W/m2 – is a theoretical value of solar insolation for a clear day on a su