Solar Energy Advantages – practical advice
Solar Energy Advantages are often discussed in the news, the biggest advantage may be that this is an option to achieve energy independence on an individual basis and at your own speed. You can add a solar powered attic fan or water heater or migrate a little faster with solar panels to supplement a portion of your electrical needs or get completely off the grid or somewhere in between. You have the flexibility of transitioning to solar energy as your budget allows.
Taken for Granted
Why transition to solar at all? Relying on the electric company for our electricity has been convenient. What we didn’t realize or didn’t want to know was what the energy companies needed to do in order to supply our growing needs. Maybe we would have made different choices on how we used electricity, maybe we would have wasted less if we had known what it really cost us. We took for granted that electricity would continue to be easy to acquire, relatively cheap to consume and reliable.
While it is still convenient, we know it is no longer easy to acquire or cheap to consume and in the past few years many of us have experienced rolling blackouts, power outages that lasted longer than a few days and these instances are happening multiple times and more regularly. Taking into consideration the environmental disasters of oil spills in just Alaska and in the Gulf, it’s clear that oil companies have no backup plan in the case of mishap. Now maybe the best time to really explore the advantages of solar energy and how to transition to this source of energy for our homes and businesses.
Advantages of Solar Energy, A Detailed Look
- after initial investment, all the electricity you produce is free
- incentives and rebates from governments and utility companies offset the initial investment
- new financing vehicles such as leasing and Pace offset the initial investment while preserving the incentives and rebates
- net metering gives you the opportunity of selling your excess electricity or getting a credit from the utility company
- reduce or completely eliminate your electric bill
- cost of solar panels are decreasing while efficiency is increasing
- numerous solar solutions are being developed that are less obtrusive and easier to install
- clean, renewable energy source
- no transmission costs, your energy is produced where it is consumed
- all or some of your electric needs can be supplied by solar energy, it’s up to you and your budget
- you can be totally independent of the electric company by using batteries to store your excess energy or you can remain tied to the grid and use net metering
- solar systems are long lasting systems with warranties that are 20-30 years
- virtually no maintenance and no recurring costs
- ideal for remote locations that cannot be tied to the grid
- no noise or smells, solar operates totally silent
- reduce dependence on foreign oil
- do-it-yourself options in the forms of kits are available and installation is easy
- high initial cost to purchase solar panel system
- a relatively large area is required to install a solar system
- the highest efficiency is dependent on full sun exposure
- no electricity can be produced at night, and reduced production on cloudy/rainy days
A valid question is, why entertain a solar energy system when the economy is in a slump and finances are tight? If you are concerned about the ever increasing and unpredictable energy bills, the effect of unanticipated blackouts power outages and future energy shortages, now is a great time to explore and plan your strategy to transition to solar energy. Moving to an energy solution is a multi-stepped process and will take some time and careful planning. This includes decreasing your consumption, a home energy audit, and choosing an installer
Now may be the perfect time to to begin exploring your own solar energy advantages.
1. Saves you money
- After the initial investment has been recovered, the energy from the sun is practically FREE.
- The recovery/ payback period for this investment can be very short depending on how much electricity your household uses.
- Financial incentives are available form the government that will reduce your cost.
- If your system produce more energy than you use, your utility company can buy it from you, building up a credit on your account! This is called net metering.
- It will save you money on your electricity bill if you have one at all.
- Solar energy does not require any fuel.
- It's not affected by the supply and demand of fuel and is therefore not subjected to the ever-increasing price of gasoline.
- The savings are immediate and for many years to come.
- The use of solar energy indirectly reduces health costs.
2. Environmentally friendly
- Solar Energy is clean, renewable (unlike gas, oil and coal) and sustainable, helping to protect our environment.
- It does not pollute our air by releasing carbon dioxide, nitrogen oxide, sulphur dioxide or mercury into the atmosphere like many traditional forms of electrical generations does.
- Therefore Solar Energy does not contribute to global warming, acid rain or smog.
- It actively contributes to the decrease of harmful green house gas emissions.
- It's generated where it is needed.
- By not using any fuel, Solar Energy does not contribute to the cost and problems of the recovery and transportation of fuel or the storage of radioactive waste.
3. Independent/ semi-independent
- Solar Energy can be utilized to offset utility-supplied energy consumption. It does not only reduce your electricity bill, but will also continue to supply your home/ business with electricity in the event of a power outage.
- A Solar Energy system can operate entirely independent, not requiring a connection to a power or gas grid at all. Systems can therefore be installed in remote locations (like holiday log cabins), making it more practical and cost-effective than the supply of utility electricity to a new site.
- The use of Solar Energy reduces our dependence on foreign and/or centralized sources of energy, influenced by natural disasters or international events and so contributes to a sustainable future.
- Solar Energy supports local job and wealth creation, fuelling local economies.
4. Low/ no maintenance
- Solar Energy systems are virtually maintenance free and will last for decades.
- Once installed, there are no recurring costs.
- They operate silently, have no moving parts, do not release offensive smells and do not require you to add any fuel.
- More solar panels can easily be added in the future when your family's needs grow.
You'll discover ...
- what solar energy is
- how solar energy works
- interesting facts about solar energy
- how much solar energy costs
- passive solar energy for homes, and
- how to build solar energy system
Energy from the Sun
Main articles: Insolation and Solar radiation
The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upperatmosphere.[1] 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.[2]
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.[3] Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C.[4] By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomassfrom which fossil fuels are derived.[5]
| Yearly Solar fluxes & Human Energy Consumption | |
|---|---|
| Solar | 3,850,000 EJ[6] |
| Wind | 2,250 EJ[7] |
| Biomass | 3,000 EJ[8] |
| Primary energy use (2005) | 487 EJ[9] |
| Electricity (2005) | 56.7 EJ[10] |
The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year.[6] In 2002, this was more energy in one hour than the world used in one year.[11][12] Photosynthesis captures approximately 3,000 EJ per year in biomass.[8] The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined.[13]
From the table of resources it would appear that solar, wind or biomass would be sufficient to supply all of our energy needs, however, the increased use of biomass has had a negative effect on global warming and dramatically increased food prices by diverting forests and crops into biofuel production.[14]As intermittent resources, solar and wind raise other issues.
Solar energy can be harnessed in different levels around the world. Depending on a geographical location the closer to the equator the more "potential" solar energy is available.[15]
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.[16]
Architecture and urban planning
Main articles: Passive solar building design and Urban heat island
Sunlight has influenced building design since the beginning of architectural history.[18] Advanced solar architecture and urban planning methods were first employed by the Greeks and Chinese, who oriented their buildings toward the south to provide light and warmth.[19]
The common features of passive solar architecture are orientation relative to the Sun, compact proportion (a low surface area to volume ratio), selective shading (overhangs) and thermal mass.[18] When these features are tailored to the local climate and environment they can produce well-lit spaces that stay in a comfortable temperature range. Socrates' Megaron House is a classic example of passive solar design.[18] The most recent approaches to solar design use computer modeling tying together solar lighting, heating and ventilation systems in an integratedsolar design package.[20] Active solar equipment such as pumps, fans and switchable windows can complement passive design and improve system performance.
Urban heat islands (UHI) are metropolitan areas with higher temperatures than that of the surrounding environment. The higher temperatures are a result of increased absorption of the Solar light by urban materials such as asphalt and concrete, which have lower albedos and higher heat capacities than those in the natural environment. A straightforward method of counteracting the UHI effect is to paint buildings and roads white and plant trees. Using these methods, a hypothetical "cool communities" program in Los Angeles has projected that urban temperatures could be reduced by approximately 3 °C at an estimated cost of US$1 billion, giving estimated total annual benefits of US$530 million from reduced air-conditioning costs and healthcare savings.[21]
Agriculture and horticulture
Agriculture and horticulture seek to optimize the capture of solar energy in order to optimize the productivity of plants. Techniques such as timed planting cycles, tailored row orientation, staggered heights between rows and the mixing of plant varieties can improve crop yields.[22][23]While sunlight is generally considered a plentiful resource, the exceptions highlight the importance of solar energy to agriculture. During the short growing seasons of the Little Ice Age, French andEnglish farmers employed fruit walls to maximize the collection of solar energy. These walls acted as thermal masses and accelerated ripening by keeping plants warm. Early fruit walls were built perpendicular to the ground and facing south, but over time, sloping walls were developed to make better use of sunlight. In 1699, Nicolas Fatio de Duillier even suggested using a tracking mechanism which could pivot to follow the Sun.[24]Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure.[25][26] More recently the technology has been embraced by vinters, who use the energy generated by solar panels to power grape presses.[27]
Greenhouses convert solar light to heat, enabling year-round production and the growth (in enclosed environments) of specialty crops and other plants not naturally suited to the local climate. Primitive greenhouses were first used during Roman times to produce cucumbers year-round for the Roman emperor Tiberius.[28] The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad.[29] Greenhouses remain an important part of horticulture today, and plastic transparent materials have also been used to similar effect in polytunnels and row covers.
Solar lighting
The history of lighting is dominated by the use of natural light. The Romans recognized a right to light as early as the 6th century and English law echoed these judgments with the Prescription Act of 1832.[30][31] In the 20th century artificial lighting became the main source of interior illumination but daylighting techniques and hybrid solar lighting solutions are ways to reduce energy consumption.
Daylighting systems collect and distribute sunlight to provide interior illumination. This passive technology directly offsets energy use by replacing artificial lighting, and indirectly offsets non-solar energy use by reducing the need for air-conditioning.[32] Although difficult to quantify, the use of natural lighting also offers physiological and psychological benefits compared to artificial lighting.[32] Daylighting design implies careful selection of window types, sizes and orientation; exterior shading devices may be considered as well. Individual features include sawtooth roofs,clerestory windows, light shelves, skylights and light tubes. They may be incorporated into existing structures, but are most effective when integrated into a solar design package that accounts for factors such as glare, heat flux and time-of-use. When daylighting features are properly implemented they can reduce lighting-related energy requirements by 25%.[33]
Hybrid solar lighting is an active solar method of providing interior illumination. HSL systems collect sunlight using focusing mirrors that track the Sun and use optical fibers to transmit it inside the building to supplement conventional lighting. In single-story applications these systems are able to transmit 50% of the direct sunlight received.[34]
Solar lights that charge during the day and light up at dusk are a common sight along walkways.[citation needed]
Although daylight saving time is promoted as a way to use sunlight to save energy, recent research has been limited and reports contradictory results: several studies report savings, but just as many suggest no effect or even a net loss, particularly when gasolineconsumption is taken into account. Electricity use is greatly affected by geography, climate and economics, making it hard to generalize from single studies.[35]
Solar thermal
Main article: Solar thermal energy
Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.[36]
Water heating
Main articles: Solar hot water and Solar combisystem
Solar hot water systems use sunlight to heat water. In low geographical latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar heating systems.[37] The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.[38]
As of 2007, the total installed capacity of solar hot water systems is approximately 154 GW.[39]China is the world leader in their deployment with 70 GW installed as of 2006 and a long term goal of 210 GW by 2020.[40] Israel and Cyprus are the per capita leaders in the use of solar hot water systems with over 90% of homes using them.[41] In the United States, Canada and Australia heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GW as of 2005.[16]
Heating, cooling and ventilation
In the United States, heating, ventilation and air conditioning (HVAC) systems account for 30% (4.65 EJ) of the energy used in commercial buildings and nearly 50% (10.1 EJ) of the energy used in residential buildings.[33][42] Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy.
Thermal mass is any material that can be used to store heat—heat from the Sun in the case of solar energy. Common thermal mass materials include stone, cement and water. Historically they have been used in arid climates or warm temperate regions to keep buildings cool by absorbing solar energy during the day and radiating stored heat to the cooler atmosphere at night. However they can be used in cold temperate areas to maintain warmth as well. The size and placement of thermal mass depend on several factors such as climate, daylighting and shading conditions. When properly incorporated, thermal mass maintains space temperatures in a comfortable range and reduces the need for auxiliary heating and cooling equipment.[43]
A solar chimney (or thermal chimney, in this context) is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated causing an updraft that pulls air through the building. Performance can be improved by using glazing and thermal mass materials in a way that mimics greenhouses.[citation needed]
Deciduous trees and plants have been promoted as a means of controlling solar heating and cooling. When planted on the southern side of a building, their leaves provide shade during the summer, while the bare limbs allow light to pass during the winter.[44] Since bare, leafless trees shade 1/3 to 1/2 of incident solar radiation, there is a balance between the benefits of summer shading and the corresponding loss of winter heating.[45] In climates with significant heating loads, deciduous trees should not be planted on the southern side of a building because they will interfere with winter solar availability. They can, however, be used on the east and west sides to provide a degree of summer shading without appreciably affecting winter solar gain.[46]
Water treatment
Main articles: Solar still, Solar water disinfection, Solar desalination, and Solar Powered Desalination Unit
Solar distillation can be used to make saline or brackish water potable. The first recorded instance of this was by 16th century Arab alchemists.[47] A large-scale solar distillation project was first constructed in 1872 in the Chilean mining town of Las Salinas.[48] The plant, which had solar collection area of 4,700 m², could produce up to 22,700 L per day and operated for 40 years.[48]Individual still designs include single-slope, double-slope (or greenhouse type), vertical, conical, inverted absorber, multi-wick, and multiple effect.[47] These stills can operate in passive, active, or hybrid modes. Double-slope stills are the most economical for decentralized domestic purposes, while active multiple effect units are more suitable for large-scale applications.[47]
Solar water disinfection (SODIS) involves exposing water-filled plastic polyethylene terephthalate(PET) bottles to sunlight for several hours.[49] Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions.[50] It is recommended by the World Health Organization as a viable method for household water treatment and safe storage.[51] Over two million people in developing countries use this method for their daily drinking water.[50]
Solar energy may be used in a water stabilisation pond to treat waste water without chemicals or electricity. A further environmental advantage is that algae grow in such ponds and consumecarbon dioxide in photosynthesis, although algae may produce toxic chemicals that make the water unusable.[52][53]
Cooking
Main article: Solar cooker
Solar cookers use sunlight for cooking, drying and pasteurization. They can be grouped into three broad categories: box cookers, panel cookers and reflector cookers.[54] The simplest solar cooker is the box cooker first built by Horace de Saussure in 1767.[55] A basic box cooker consists of an insulated container with a transparent lid. It can be used effectively with partially overcast skies and will typically reach temperatures of 90–150 °C.[56] Panel cookers use a reflective panel to direct sunlight onto an insulated container and reach temperatures comparable to box cookers. Reflector cookers use various concentrating geometries (dish, trough, Fresnel mirrors) to focus light on a cooking container. These cookers reach temperatures of 315 °C and above but require direct light to function properly and must be repositioned to track the Sun.[57]
The solar bowl is a concentrating technology employed by the Solar Kitchen in Auroville,Pondicherry, India, where a stationary spherical reflector focuses light along a line perpendicular to the sphere's interior surface, and a computer control system moves the receiver to intersect this line. Steam is produced in the receiver at temperatures reaching 150 °C and then used for process heat in the kitchen.[58]
A reflector developed by Wolfgang Scheffler in 1986 is used in many solar kitchens. Scheffler reflectors are flexible parabolic dishes that combine aspects of trough and power tower concentrators. Polar tracking is used to follow the Sun's daily course and the curvature of the reflector is adjusted for seasonal variations in the incident angle of sunlight. These reflectors can reach temperatures of 450–650 °C and have a fixed focal point, which simplifies cooking.[59] The world's largest Scheffler reflector system in Abu Road, Rajasthan, India is capable of cooking up to 35,000 meals a day.[60] As of 2008, over 2,000 large Scheffler cookers had been built worldwide.[61]
Process heat
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Solar concentrating technologies such as parabolic dish, trough and Scheffler reflectors can provide process heat for commercial and industrial applications. The first commercial system was the Solar Total Energy Project (STEP) in Shenandoah, Georgia, USA where a field of 114 parabolic dishes provided 50% of the process heating, air conditioning and electrical requirements for a clothing factory. This grid-connected cogeneration system provided 400 kW of electricity plus thermal energy in the form of 401 kW steam and 468 kW chilled water, and had a one hour peak load thermal storage.[62]
Evaporation ponds are shallow pools that concentrate dissolved solids through evaporation. The use of evaporation ponds to obtain salt from sea water is one of the oldest applications of solar energy. Modern uses include concentrating brine solutions used in leach mining and removing dissolved solids from waste streams.[63]
Clothes lines, clotheshorses, and clothes racks dry clothes through evaporation by wind and sunlight without consuming electricity or gas. In some states of the United States legislation protects the "right to dry" clothes.[64]
Unglazed transpired collectors (UTC) are perforated sun-facing walls used for preheating ventilation air. UTCs can raise the incoming air temperature up to 22 °C and deliver outlet temperatures of 45–60 °C.[65] The short payback period of transpired collectors (3 to 12 years) makes them a more cost-effective alternative than glazed collection systems.[65] As of 2003, over 80 systems with a combined collector area of 35,000 m² had been installed worldwide, including an 860 m² collector in Costa Rica used for drying coffee beans and a 1,300 m² collector in Coimbatore, India used for drying marigolds.[26]
Electrical generation
Main article: Solar power
Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). CSP systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. PV converts light into electric current using the photoelectric effect.
Commercial CSP plants were first developed in the 1980s, and the 354 MW SEGS CSP installation is the largest solar power plant in the world and is located in the Mojave Desert of California. Other large CSP plants include the Solnova Solar Power Station (150 MW) and theAndasol solar power station (100 MW), both in Spain. The 80 MW Sarnia Photovoltaic Power Plant in Canada, is the world’s largest photovoltaic plant.
Experimental solar power
Main articles: Solar pond and Thermogenerator
A solar pond is a pool of salt water (usually 1–2 m deep) that collects and stores solar energy. Solar ponds were first proposed by Dr. Rudolph Bloch in 1948 after he came across reports of a lake in Hungary in which the temperature increased with depth. This effect was due to salts in the lake's water, which created a "density gradient" that prevented convection currents. A prototype was constructed in 1958 on the shores of the Dead Sea near Jerusalem.[66] The pond consisted of layers of water that successively increased from a weak salt solution at the top to a high saltsolution at the bottom. This solar pond was capable of producing temperatures of 90 °C in its bottom layer and had an estimated solar-to-electric efficiency of two percent.
Thermoelectric, or "thermovoltaic" devices convert a temperature difference between dissimilar materials into an electric current. First proposed as a method to store solar energy by solar pioneer Mouchout in the 1800s,[67] thermoelectrics reemerged in the Soviet Union during the 1930s. Under the direction of Soviet scientist Abram Ioffe a concentrating system was used to thermoelectrically generate power for a 1 hpengine.[68] Thermogenerators were later used in the US space program as an energy conversion technology for powering deep space missions such as Cassini, Galileo and Viking. Research in this area is focused on raising the efficiency of these devices from 7–8% to 15–20%.[69]
Solar chemical
Main article: Solar chemical
Solar chemical processes use solar energy to drive chemical reactions. These processes offset energy that would otherwise come from an alternate source and can convert solar energy into storable and transportable fuels. Solar induced chemical reactions can be divided into thermochemical or photochemical.[70]
Hydrogen production technologies been a significant area of solar chemical research since the 1970s. Aside from electrolysis driven by photovoltaic or photochemical cells, several thermochemical processes have also been explored. One such route uses concentrators to split water into oxygen and hydrogen at high temperatures (2300-2600 °C).[71] Another approach uses the heat from solar concentrators to drive the steam reformation of natural gas thereby increasing the overall hydrogen yield compared to conventional reforming methods.[72]Thermochemical cycles characterized by the decomposition and regeneration of reactants present another avenue for hydrogen production. The Solzinc process under development at the Weizmann Institute uses a 1 MW solar furnace to decompose zinc oxide (ZnO) at temperatures above 1200 °C. This initial reaction produces pure zinc, which can subsequently be reacted with water to produce hydrogen.[73]
Sandia's Sunshine to Petrol (S2P) technology uses the high temperatures generated by concentrating sunlight along with a zirconia/ferritecatalyst to break down atmospheric carbon dioxide into oxygen and carbon monoxide (CO). The carbon monoxide can then be used to synthesize conventional fuels such as methanol, gasoline and jet fuel.[74]
A photogalvanic device is a type of battery in which the cell solution (or equivalent) forms energy-rich chemical intermediates when illuminated. These energy-rich intermediates can potentially be stored and subsequently reacted at the electrodes to produce an electric potential. The ferric-thionine chemical cell is an example of this technology.[75]
Photoelectrochemical cells or PECs consist of a semiconductor, typically titanium dioxide or related titanates, immersed in an electrolyte. When the semiconductor is illuminated an electrical potential develops. There are two types of photoelectrochemical cells: photoelectric cells that convert light into electricity and photochemical cells that use light to drive chemical reactions such as electrolysis.[76]
A combination thermal/photochemical cell has also been proposed. The Stanford PETE process uses solar thermal energy to raise the temperature of a thermionic metal to about 800C to increase the rate of production of electricity to electrolyse atmospheric CO2 down to carbon or carbon monoxide which can then be used for fuel production, and the waste heat can be used as well.[77]
Solar vehicles
Development of a solar powered car has been an engineering goal since the 1980s. The World Solar Challenge is a biannual solar-powered car race, where teams from universities and enterprises compete over 3,021 kilometres (1,877 mi) across central Australia from Darwin toAdelaide. In 1987, when it was founded, the winner's average speed was 67 kilometres per hour (42 mph) and by 2007 the winner's average speed had improved to 90.87 kilometres per hour (56.46 mph).[78] The North American Solar Challenge and the planned South African Solar Challenge are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles.[79][80]
Some vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption.[81][82]
In 1975, the first practical solar boat was constructed in England.[83] By 1995, passenger boats incorporating PV panels began appearing and are now used extensively.[84] In 1996, Kenichi Horiemade the first solar powered crossing of the Pacific Ocean, and the sun21 catamaran made the first solar powered crossing of the Atlantic Ocean in the winter of 2006–2007.[85] There are plans to circumnavigate the globe in 2010.[86]
In 1974, the unmanned AstroFlight Sunrise plane made the first solar flight. On 29 April 1979, theSolar Riser made the first flight in a solar powered, fully controlled, man carrying flying machine, reaching an altitude of 40 feet (12 m). In 1980, the Gossamer Penguin made the first piloted flights powered solely by photovoltaics. This was quickly followed by the Solar Challenger which crossed the English Channel in July 1981. In 1990 Eric Raymond in 21 hops flew from California to North Carolina using solar power.[87] Developments then turned back to unmanned aerial vehicles (UAV) with the Pathfinder (1997) and subsequent designs, culminating in the Helios which set the altitude record for a non-rocket-propelled aircraft at 29,524 metres (96,864 ft) in 2001.[88] TheZephyr, developed by BAE Systems, is the latest in a line of record-breaking solar aircraft, making a 54-hour flight in 2007, and month-long flights are envisioned by 2010.[89]
A solar balloon is a black balloon that is filled with ordinary air. As sunlight shines on the balloon, the air inside is heated and expands causing an upward buoyancy force, much like an artificially heated hot air balloon. Some solar balloons are large enough for human flight, but usage is generally limited to the toy market as the surface-area to payload-weight ratio is relatively high.[90]
Solar sails are a proposed form of spacecraft propulsion using large membrane mirrors to exploit radiation pressure from the Sun. Unlike rockets, solar sails require no fuel. Although the thrust is small compared to rockets, it continues as long as the Sun shines onto the deployed sail and in the vacuum of space significant speeds can eventually be achieved.[91]
The High-altitude airship (HAA) is an unmanned, long-duration, lighter-than-air vehicle using helium gas for lift, and thin film solar cells for power. The United States Department of Defense Missile Defense Agency has contracted Lockheed Martin to construct it to enhance theBallistic Missile Defense System (BMDS).[92] Airships have some advantages for solar-powered flight: they do not require power to remain aloft, and an airship's envelope presents a large area to the Sun.
Energy storage methods
Main articles: Thermal mass, Thermal energy storage, Phase change material, Grid energy storage, and V2G
Solar energy is not available at night, and energy storage is an important issue because modern energy systems usually assume continuous availability of energy.[93]
Thermal mass systems can store solar energy in the form of heat at domestically useful temperatures for daily or seasonal durations. Thermal storage systems generally use readily available materials with high specific heat capacities such as water, earth and stone. Well-designed systems can lower peak demand, shift time-of-use to off-peak hours and reduce overall heating and cooling requirements.[94][95]
Phase change materials such as paraffin wax and Glauber's salt are another thermal storage media. These materials are inexpensive, readily available, and can deliver domestically useful temperatures (approximately 64 °C). The "Dover House" (in Dover, Massachusetts) was the first to use a Glauber's salt heating system, in 1948.[96]
Solar energy can be stored at high temperatures using molten salts. Salts are an effective storage medium because they are low-cost, have a high specific heat capacity and can deliver heat at temperatures compatible with conventional power systems. The Solar Two used this method of energy storage, allowing it to store 1.44 TJ in its 68 m³ storage tank with an annual storage efficiency of about 99%.[97]
Off-grid PV systems have traditionally used rechargeable batteries to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission grid. Net metering programs give these systems a credit for the electricity they deliver to the grid. This credit offsets electricity provided from the grid when the system cannot meet demand, effectively using the grid as a storage mechanism.[98]
Pumped-storage hydroelectricity stores energy in the form of water pumped when energy is available from a lower elevation reservoir to a higher elevation one. The energy is recovered when demand is high by releasing the water to run through a hydroelectric power generator.[99]
Development, deployment and economics
Main article: Deployment of solar power to energy grids
Beginning with the surge in coal use which accompanied the Industrial Revolution, energy consumption has steadily transitioned from wood and biomass to fossil fuels. The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal andpetroleum.[100]
The 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies.[101][102] Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the US (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE).[103]
Commercial solar water heaters began appearing in the United States in the 1890s.[104] These systems saw increasing use until the 1920s but were gradually replaced by cheaper and more reliable heating fuels.[105] As with photovoltaics, solar water heating attracted renewed attention as a result of the oil crises in the 1970s but interest subsided in the 1980s due to falling petroleum prices. Development in the solar water heating sector progressed steadily throughout the 1990s and growth rates have averaged 20% per year since 1999.[39] Although generally underestimated, solar water heating and cooling is by far the most widely deployed solar technology with an estimated capacity of 154 GW as of 2007.[39]
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