Need of solar power
Concerns about climate change, rising pollution from fossil fuels and to meet the ever increasing demand of power supply require increasing use of renewable energy in coming years. The world needs to find new sources of clean energy. Space solar power can solve our energy and greenhouse gas emissions problems. Space Solar Power gathers energy from sunlight in space and transmits it wirelessly to Earth. Space solar power can provide large quantities of energy to each and every person
on Earth with very little environmental impact. The solar energy available in space is literally billions of times greater than we use today. The lifetime of the sun is an estimated 4-5 billion years, making space solar power a truly long-term energy solution. As Earth receives only one part in 2.3 billion of the Sun's output, space solar power is by far the largest potential energy source available, dwarfing all others combined. Solar energy is routinely used on nearly all spacecraft today. This technology on a larger scale, combined with already demonstrated wireless power transmission can supply nearly all the electrical needs of our planet. Space solar power can provide the needed clean power for any future electric transportation system. Thus, solar power collected in space and beamed to Earth could be an environmentally friendly solution to our planet's growing energy problems.
Space solar power
Proposed space solar power systems utilize well-known physical principles -- namely, the conversion of sunlight to electricity by means of photovoltaic cells. Giant structures consisting of row after row of photovoltaic (PV) arrays could be placed either in a geostationary Earth orbit or on the Moon. A complete system would collect solar energy in space, convert it to microwaves, and transmit the microwave radiation to Earth where it would be captured by a ground antenna and transformed to usable electricity. Space-based solar power (SBSP) (or historically space solar power (SSP)) is a system for the collection of solar power in space, for use on Earth. SBSP differs from the usual method of solar power collection in that the solar panels used to collect the energy would reside on a satellite in orbit, often referred to as a solar power satellite (SPS), rather than on Earth's surface. Studies looking at the feasibility of space-based solar power - orbiting satellites that would serve as high-tech space dams - suggest the concept shouldn't be readily dismissed and could generate both Earth-bound and space-based benefits. These "powersats" would catch the flood of energy flowing from the Sun and then pump it to Earth via laser or microwave beam. On earth it would be converted to electricity and fed into power grids to be tapped by terrestrial customers. In space solar power concepts, solar panel arrays would gather sunlight in orbit, and then beam it to Earth. The attraction of collecting solar power in space is the virtually uninterrupted sunshine available in geosynchronous orbit. Earth-based solar cells, by contrast, can only collect sunlight during daytime and when skies are clear. A start-up company called Solaren is designing the satellites, which it says will use radio waves to beam energy down to a receiving station on Earth. Energy beamed down from space is one step closer to reality, now that California has given the green light to a deal involving to buy 200 megawatts of power beamed down from solar-power satellites beginning in 2016.its sale. But some major challenges will have to be overcome if the technology is to be used widely.
The collection of solar energy in space for use on Earth introduces the new problem of transmitting energy from the collection point, in space, to the place where the energy would be used, on Earth's surface. Since wires extending from Earth's surface to an orbiting satellite would be impractical, many SBSP designs have proposed the use of microwave beams for wireless power transmission. The collecting satellite would convert solar energy into electrical energy, which would then be used to power a microwave emitter directed at a collector on the Earth's surface. Dynamic solar thermal power systems are also being investigated. Space-based solar power essentially consists of three parts: a means of collecting solar power in space (for example via solar cells or a heat engine), a means of transmitting power to earth (for example via microwave or laser) and a means of receiving power on earth (for example via a microwave antennas. Wireless power transmission was proposed early on as a means to transfer energy from collection to the Earth's surface. The power could be transmitted as either microwave or laser radiation at a variety of frequencies depending on system design. Whichever choice is made, the transmitting radiation would have to be non-ionizing to avoid potential disturbances either ecologically or biologically. This established an upper limit for the frequency used, as energy per photon (and consequently the ability to cause ionization) increases with frequency. Ionization of biological materials doesn't begin until ultraviolet or higher frequencies, so most radio frequencies would be feasible.
The technologies and infrastructure required to make space solar power feasible include:
· Low-cost, environmentally-friendly launch vehicles: current launch vehicles are too expensive, and at high launch rates may pose atmospheric pollution problems of their own. Cheaper, cleaner launch vehicles are needed.
· Large scale in-orbit construction and operations: to gather massive quantities of energy, solar power satellites must be large, far larger than the International Space Station (ISS), the largest spacecraft built to date. Fortunately, solar power satellites will be simpler than the ISS as they will consist of many identical parts.
· Power transmission: a relatively small effort is also necessary to assess how to best transmit power from satellites to the Earth’s surface with minimal environmental impact.
Points of concern
· One problem for the SBSP concept is the cost of space launches and the amount of material that would need to be launched. Space-based solar power must grapple with the high cost per kilogram of launching things into space before it becomes economically viable for public use. Reusable launch systems are predicted to provide lower launch costs to lower Earth orbit (LEO).
· Ways to reduce the system's weight include using inflatable mirrors to focus sunlight on solar cells, so a smaller number can collect the same amount of energy but use of mirrors introduces other challenges; including keeping the solar cells from overheating and to take care of heat dissipation because of a lot of energy is being concentrating in one place.
· Some other problems associated with terrestrial solar power collection would be such as dependence on meteorological and weather conditions, the panels being prone to corrosion cumulative radiation damage or micrometeoroid impacts.
· The space-based portion will be in a freefall, vacuum environment and will not need to support itself against gravity other than relatively weak tidal stresses. It needs no protection from terrestrial wind or weather, but will have to cope with space-based hazards such as micrometeors and solar storms.
· Power beaming from geostationary orbit by microwaves carries the difficulty that the required optical aperture sizes are very large.
· The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.
· The dangers of being close to the microwave beam would be similar to the dangers of cell phone transmissions, microwave ovens or high-power electrical transmission lines. However, lasers are also under consideration for beaming the energy from space. Using lasers would eliminate most of the problems associated with microwave.
The SBSP concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power. There is no air in space, so the collecting surfaces would receive much more intense sunlight, unaffected by weather. In geostationary orbit, an SPS would be illuminated over 99% of the time. The SPS would be in Earth's shadow on only a few days at the spring and fall equinoxes; and even then for a maximum of 75 minutes late at night when power demands are at their lowest. This characteristic of SBSP avoids the expense of storage facilities (dams, oil storage tanks, coal dumps) necessary in many Earth-based power generation systems. Additionally, SBSP would have fewer or none of the ecological (or political) consequences of fossil fuel systems. SBSP would also be applicable on a global scale because it poses no known potential threat like nuclear power. Some of the advantages associated with space solar power are mentioned here as:
· Extraterrestrial solar irradiance is 144% of the maximum terrestrial irradiance. A major interest in SBSP stems from the length of time the solar collection panels can be exposed to a consistently high amount of solar radiation. For most of the year, a satellite-based solar panel can collect power 24 hours per day, whereas a land-based station can collect for only 12 hours per day, yielding lower power collection rates around the sunrise and sunset hours.
· In space, collection of the Sun's energy is unaffected by the day/night cycle, weather, seasons, or the filtering effect of Earth's atmospheric gases.
· Does not emit greenhouse gases, does not compete for or depend upon increasingly scarce fresh water resources, does not compete for increasingly valuable farm land or depend on natural-gas-derived fertilizer.
· Space solar power will not produce hazardous waste, which needs to be stored and guarded for hundreds of years.
· Space solar power is available 24 hours a day, 7 days a week, in huge quantities. It works regardless of cloud cover, daylight, or wind speed.
· Does not provide easy targets for terrorists and does not require environmentally problematic mining operations.
· Space solar power will provide true energy independence for the nations that develop it, eliminating a major source of national competition for limited Earth-based energy resources.
· Space solar power will not require dependence on unstable or hostile foreign oil providers to meet energy needs, enabling us to expend resources in other ways.
· Space solar power can be exported to virtually any place in the world, and its energy can be converted for local needs — such as manufacture of methanol for use in places like rural India where there are no electric power grids. Space solar power can also be used for desalination of sea water.
· Space solar power can take advantage of our current and historic investment in aerospace expertise to expand employment opportunities in solving the difficult problems of energy security and climate change.
· Can provide a market large enough to develop the low-cost space transportation system that is required for its deployment. This, in turn, will also bring the resources of the solar system within economic reach.
The positive aspects of space solar power system appear to outweigh the negative ones. Space-based solar power offers energy from an unending source with no emissions and very little environmental impact. Significant breakthroughs are required to achieve the final goal of SSP cranking out cost-competitive terrestrial power. The ultimate success of the terrestrial power application of powering-beaming satellites critically depends on "dramatic reductions" in the cost of transportation from Earth to geosynchronous orbit, the group reported. Furthermore, the SSP reviewers call for ground demonstrations of point-to-point wireless power transmission. Wireless power transmission tests on Earth is progressing, specifically in Japan and Canada; Robotics, viewed as essential to SSP on-orbit assembly, has shown substantial improvements in manipulators, machine vision systems, hand-eye coordination, task planning, and reasoning; and
Advanced composites are in wider use, and digital control systems are now state of the art - both developments useful in building an SSP. All of these technologies are reasonably near-term and have multiple attractive approaches. However, a great deal of work is needed to bring them to practical fruition. In the longer term, with sufficient investments in space infrastructure, space solar power can be built from materials from space. The full environmental benefits of space solar power derive from doing most of the work outside of Earth's biosphere. With materials extraction from the Moon or near-Earth asteroids, and space-based manufacturer of components, space solar power would have essentially zero terrestrial environmental impact. Only the energy receivers need be built on Earth. Space solar power can completely solve our energy problems long term. The sooner we start and the harder we work, the shorter "long term" will be.