Space Based Solar Power
An odyssey from Concept to Reality
INTRODUCTION
Electricity is the most versatile and widely used form of energy.
The global demand for electricity is continuously
growing. Of the total generation worldwide, more than 60 percent
of energy is generated using coal-fired station resulting
in carbon dioxide emission threatening the global warming. To
mitigate the consequence of the climate change, the
generation systems need to undergo significant changes. The
installed capacity over the last century is a clear picture of
growing economy. To satisfy the increasing demand for power and
reducing CO2 emission, the future generation system
must meet the demand, reliability, efficiency and sustainability.
This has accelerated the generation using solar, wind,
tidal, and many more. The objective of such initiative is to
investigate on the feasibility, financing and development of new
plans [1]. According to the Load Generation Balance Report
2013-2014 of India, the energy requirement
registered a growth of 6.5% during the year 2012-2013 against the
projected growth of 5.1% [2]. This is due to increasing
population, advancement in living standard of the people,
discovery of new power consuming yet comfort providing
devices/appliances and improvement in the life style of the masses.
The conventional methods for generating electrical
power are insufficient for providing the increasing demand of
electrical power. Thus, there is an urgent need to
supplement the conventional sources. Solar power generation with
its associated technologies has advanced few steps
ahead in last several decades. It has been believed and investigated
since last four decades that solar energy in space free
from the weather conditions is quite different from that on the
earth. The SPS system has great potential to harness solar
power using bulk photovoltaic (PV) array in space and transmit it
to the earth using microwave. The solar energy from
sun while travelling a path to Earth is lost in the atmosphere
because of the effects of reflection and absorption.
Therefore, it would be much beneficial to absorb solar energy from
the geosynchronous orbit. A geosynchronous orbit is
any orbit which has a period equal to the earth's rotational period.
Accounting for efficiency, the PV cells produce 5 to 10
% times more power at space than at ground [3]. Thus placing
solar cells in space has a competitive advantage over solar
power plants on the Earth. A photovoltaic cell can be placed on
satellite revolving in geosynchronous orbit to absorb the
solar energy. The satellite is called as solar powered satellite. The
generated DC by the photovoltaic cell can be converted
into microwave by using magnetron, klystron or solid state
devices. The generated microwave is transferred to the earth
using antenna. The transmitted power is received by a device
called rectenna. The received power is converted into DC
power by filters and schottky diode. Power transmission using
laser beam is also possible but, the power efficiency at both
the transmitter and receiver of microwave transmission is more as
compared with laser
What is Solar Energy?
Every day, the sun radiates (sends out) an enormous amount of energy
called solar energy. It radiates more energy in one day than the world uses in
one year. This energy comes from within the sun itself. Like most stars, the
sun is a big gas ball made up mostly of hydrogen and helium gas. The sun
makes energy in its inner core in a process called nuclear fusion. It takes the
suns energy just a little over eight minutes to travel the 93 million miles to
Earth. Solar energy travels at the speed of light, or 186,000 miles per second,
or 3.0 x 108 meters per second. Only a small part of the visible radiant
energy (light) that the sun emits into space ever reaches the Earth, but that is
more than enough to supply all our energy needs. Every hour enough solar
energy reaches the Earth to supply our nations energy needs for a year!
Solar energy is considered a renewable energy source due to this fact. Today,
people use solar energy to heat buildings and water and to generate
electricity. Solar energy accounts for a very small percentage of U.S. energy
less than one percent. Solar energy is mostly used by residences and to
generate electricity.
Why Solar Energy?
While a majority of the world's current electricity supply is generated
from fossil fuels such as coal, oil and natural gas, these traditional
energy sources face a number of challenges including rising prices,
security concerns over dependence on imports from a limited number
of countries which have significant fossil fuel supplies, and growing
environmental concerns over the climate change risks associated
with power generation using fossil fuels. As a result of these and
other challenges facing traditional energy sources, governments,
businesses and consumers are increasingly supporting the
development of alternative energy sources and new technologies for
electricity generation. Renewable energy sources such as solar,
biomass, geothermal, hydroelectric and windpower generation have
emerged as potential alternatives which address some of these
concerns. As opposed to fossil fuels, which draw on finite resources
that may eventually become too expensive to retrieve, renewable
energy sources are generally unlimited in availability.
Solar power generation has emerged as one of the most rapidly
growing renewable sources of electricity. Solar power generation has
several advantages over other forms of electricity generation:
Reduced Dependence on Fossil Fuels. Solar energy production
does not require fossil fuels and is therefore less dependent on this
limited and expensive natural resource. Although there is variability in
the amount and timing of sunlight over the day, season and year, a
properly sized and configured system can be designed to be highly
reliable while providing long-term, fixed price electricity supply.
Environmental Advantages. Solar power production generates
electricity with a limited impact on the environment as compared to
other forms of electricity production.
Matching Peak Time Output with Peak Time Demand. Solar
energy can effectively supplement electricity supply from an electricity
transmission grid, such as when electricity demand peaks in the
summer
Modularity and Scalability. As the size and generating capacity of
a solar system are a function of the number of solar modules
installed, applications of solar technology are readily scalable and
versatile.
Flexible Locations. Solar power production facilities can be
installed at the customer site which reduces required investments in
production and transportation infrastructure.
Government Incentives. A growing number of countries have
established incentive programs for the development of solar and
other renewable energy sources, such as (i) net metering laws that
allow on-grid end users to sell electricity back to the grid at retail
prices, (ii) direct subsidies to end users to offset costs of photovoltaic
equipment and installation charges, (iii) low interest loans for
financing solar power systems and tax incentives; and
(iv) government standards that mandate minimum usage levels of
renewable energy sources.
Despite the cost, an advantage of photovoltaic systems is that they
can be used in remote areas. Anywhere a diesel generator is the
technology of choice, many times a photovoltaic system is a much
better life-cycle cost option.
Stand-alone photovoltaic systems produce power independently of
the utility grid. In some off-the-grid locations even one half kilometer
from power lines, stand-alone photovoltaic systems can be more
cost-effective than extending power lines. They are especially
appropriate for remote, environmentally sensitive areas, such as
national parks, cabins, and remote homes.
The solar power market has grown significantly in the past decade.
According to Solarbuzz, the global solar power market, as measured
by annual solar power system installations, increased from 427 MW
in 2002 to 1,744 MW in 2006, representing a CAGR of 42.2%, while
solar power industry revenues grew to approximately US$10.6 billion
in 2006. Despite the rapid growth, solar energy constitutes only a
small fraction of the world's energy output and therefore may have
significant growth potential. Solarbuzz projects in one of its forecasts
that annual solar power industry revenue could reach US$31.5 billion
by 2011.
Concept of Space Based Solar
Power.
The concept of SBSP was theorized over 40 years ago by renowned
scientist Dr. Peter Glaser. Since then, in response to periodic energy
crises, the idea has been re-evaluated from time to time by the U.S.
Department of Energy, NASA, major aerospace companies and
countries such as Japan and India. Their studies generally concluded
that there is no technical barrier to implementing SBSP; rather, the
principal impediment has been economics -- the ability to provide
SBSP at a cost that is competitive with other energy sources.
Solar power satellites are large arrays of photovoltaic panels
assembled in orbit, which use very low power radio waves to transmit
solar power to large receiving antennas on Earth. The resulting power
can either supplement, or be a substitute for, conventional electricity
sources. Several of the technologies required to build a working
SBSP satellite have, in principle, already been developed---and some
of the component technology is already in use across a variety of
sectors.
The advantage of placing solar collectors in geosynchronous Earth
orbit (GEO), about 36,000 kilometers above Earth, is that it uses the
constant and unobstructed output of the Sun, unaffected by the
Earth's day/night cycle.
By contrast, ground-based solar power provides a vital and valuable
addition to the Earth's energy needs, but is limited by these factors:
Weather
Variable seasons
Atmospheric blocking of sunlight
Poor direct sunlight at higher and lower latitudes
Expensive and limited storage capacity
Because none of these factors applies to SBSP, an SBSP cell can
provide an estimated 6-8 times more power than a comparable solar
cell on the Earth's surface.
A long-range wireless power transmission test was conducted in mid2008, successfully transmitting a microwave beam (similar to the kind
that would be used to transmit energy from space to Earth) between
two Hawaiian Islands across 148 kilometers---more than the distance
from the surface of the Earth to the boundary of space. This test
demonstrated the technical feasibility of transmitting SBSP to Earth.
The frequency of radio waves sent down from an SBSP satellite
would be comparable to cell phone, wireless Internet, or cordless
phone signals. Based on several studies done by NASA, this
transmission is safe to human, animal, and plant life near the
receiving antennas---large structures designed to convert the radio
waves into usable electricity.
These antennas would be placed in areas with limited access to
mainline grid power, giving rural and developing areas a muchneeded power alternative. They might also be placed close to main
power grids to provide a substantial amount of grid power.
Recently, as efficiencies of solar cells and other core systems have
increased, and the price of (and demand for) energy has risen, SBSP
has become more commercially viable. Factors that have contributed
to this development include:
Efficiency and mass of photovoltaic cells (becoming more
efficient and lighter, as well as cheaper)
Wholesale electricity cost increases
Demand for electricity (increasing rapidly)
The availability and cost of commercial space lift transportation
(becoming cheaper, faster, and more reliable, with billions of
development dollars now being invested)
The identification of additional, easily accessible revenue
streams for SBSP
With these new efficiencies and price points, the cost of a viable
SBSP solution is substantially lower than just a few years ago.
One of the major hurdles holding solar power back is the
inherent intermittency issues that come with having an
atmosphere over your head. Solar cells on the Earth's
surface can only generate electricity when the sun is in the
sky, and for many countries, especially those in the Northern
hemisphere, constant cloud cover can put a damper on a
solar economy. But what if you could bypass the atmosphere
altogether, what if you could harness solar energy directly
from the sun, in space. In 1941 science fiction writer Issac
Assimov spoke of space stations that could transport energy
gathered from the sun to various planets with the microwave
beams in his short story "Reason." Today, science fiction
could become science fact within the next quarter of a
century, at least according to Dr. Susumu Sasaki of the Japan
Aerospace Exploration Agency (JAXA). In April of 2014 JAXA
released a proposal for a series of ground and orbital
experiments that could lead to the development of a
functioning space based solar power system by the 2030s.
History of Space Based Solar
Power
The idea of collecting solar power in space is nothing new. It
did not take long after the invention of the first silicon-based
solar cells and the advent of space exploration for someone
to realize that the two technologies would make a happy
marriage. American aerospace engineer Peter Glaser penned
the first formal proposal for a space based solar power
system in 1968, just a year shy of Neil Armstrong's stroll
across the moon. He was granted patent number 3,781,647
for a satellite solar-power system (SSPS) in 1973 for a
method of transporting solar power over long distances by
beaming microwaves from an antenna in space onto a much
larger one on the ground. The ground receiver would later be
called a rectenna. Glaser, who was vice president of Arthur
D. Little, Inc. landed a contract with NASA to lead a more
comprehensive study in 1974. The initial report was enough
to make NASA fund research and development into the
project during the 70's and 80's. A change in administrations
would ultimately put a hiatus on further development of the
idea. The Office of Technology Assessment concluded that
there were too many unknowns regarding the technical and
economic aspects of a space based solar power system.
NASA would not take another serious look at Space Based
Solar Power until 1999, with its Space Solar Power
Exploratory Research and Technology (SERT) program. They
laid some of the groundwork for solar power satellite (SPS)
concept, using a geosynchronous orbit, and established
general feasibility and design requirements. Their SPS
concept entailed a gigawatt space power system with
inflatable photovoltaic gossamer structure, which utilizes
solar heat engines to generate electricity. A key lesson that
came out of this study was that launch costs for low earth
orbit would have to fall to the $100 - 200 USD per kilogram
range for the construction of an SPS to become feasible. Fast
forward to May, 2014 and JAXA is picking up where they left
off.
The Goal
Every roadmap needs a destination, and for space based
solar power, JAXA has proposed a commercially viable 1
gigawatt space based solar power system.
The system would consist of a geosynchronous orbiting
satellite outfitted with state of the art silicon based solar
cells. Orbital mirrors ensure that sunlight is always
concentrated onto the satellite's solar panels as it orbits with
the Earth's rotation, even when it resides on the side of Earth
opposite the sun. On the surface a 3 kilometer long manmade island outfitted with 5 billion miniature rectifying
antennas receives the microwaves beamed down from a
satellite 36,000 kilometers above, converting them back into
DC current. An on-island substation routes electricity through
an undersea cable directly to Tokyo's bustling electrical grid.
An ambitious project, Dr. Sasaki highlights six areas of
development: wireless power transmission, space
transportation, space construction, satellite control, power
generation and power management.
