The Promise of Solar Energy
In an increasingly carbon-constrained world, solar energy technologies represent one of the least carbon-intensive means of electricity generation. Solar power produces no emissions during generation itself, and life-cycle assessments clearly demonstrate that it has a smaller carbon footprint from cradle-to-grave than fossil fuels.
Currently, solar accounts for just a tiny fraction of the world’s electricity generation, at a mere 8 terawatt-hours (TWh) out of the more than 10,000 TWh produced by the countries of the Organization for Economic Cooperation and Development (OECD). Yet, solar technologies, including photovoltaics, concentrating solar power, and solar thermal, constitute the fastest-growing energy source in the world. With clear market signals from governments, these low-carbon technologies could provide more than 30% of the world’s energy supply in aggregate by 2040.
The Solar Photovoltaic Advantage
Photovoltaics (PV) are perhaps the most well-known and fastest-growing sector of solar technology. PV devices generate electricity directly from sunlight via an electric process that occurs naturally in certain types of material. Groups of PV cells are configured into modules and arrays, which can be used to power any number of electrical loads.
PV energy systems have very good potential as a low-carbon energy supply technology. A joint paper by scientists from Brookhaven National Laboratory, Utrecht University, and the Energy Research Center of the Netherlands demonstrates that crystalline silicon PV systems have energy payback times of 1.5 to 2.2 years for South European locations and 2.7 to 3.5 years for middle-European locations, while thin-film technologies have energy payback times in the range of 1 to 1.5 years in South Europe.
Accordingly, life-cycle carbon dioxide (CO2) emissions for PV are now in the range of 25 to 32 grams per kilowatt-hour (g/kWh). In comparison, a combined cycle gas-fired power plant emits some 400 g/kWh, while a coal-fired power plant with carbon capture and storage emits about 200 g/kWh. Even nuclear power, at 25 g/kWh on average in the United States, is outperformed by PV. Only wind power, with a mere 11 g/kWh, is better.
The global photovoltaic sector has been growing at an average of over 40% in the last eight years, manufacturing over 2,200 megawatts in 2006. PV have become competitive in all market segments, particularly grid-connected applications, as more investment in the sector has produced major advances in automation, manufacturing efficiencies, and throughput.
Several leading countries — Germany, Japan, and the United States, representing two-thirds of the global market — have provided market support programs to drive down costs. The growth of PV has driven a very classic experience curve decline in manufacturing prices, with an 18 to 20% progress ratio — for every doubling in the cumulative production of solar cells, prices come down about one-fifth.
Currently, solar modules are selling globally from $3 to $5 per watt, while installed systems are generally sold at between $6 and $10 per watt. Solar energy is the cheapest option for providing power to locations more than half a mile from existing electricity and is generally competitive without subsidies in regions with high energy prices. The PV industry is striving to reduce system costs by 50% by 2015, at which point PV will be cost-competitive with retail electricity costs in most of the United States and other developed countries.
Concentrating Solar Power: A Rapidly Scalable Solution
Concentrating solar power (CSP) plants are utility-scale generators that produce electricity by using mirrors or lenses to efficiently concentrate the sun’s energy. Two principal CSP technologies are parabolic troughs, which use rows of curved mirrors to drive conventional steam turbines, and the dish-Stirling engine systems, which are shaped much like large satellite dishes and covered with curved mirrors that heat liquid hydrogen to drive the pistons of a Stirling engine.
Life-cycle assessment of the emissions produced, together with the land surface impacts of CSP systems, show that they are ideally suited to reduce greenhouse gases (GHG) and other pollutants without creating other environmental risks or contamination. According to the European Solar Thermal Industry Association, 1 MWh of installed solar thermal power capacity results in the saving of 600 kilograms of CO2.
The energy payback time of CSP systems is approximately five months, which compares very favorably with their lifespan of 25 to 30 years. During the 1980s and early 1990s, developers built nine concentrating solar power plants in California’s Mojave Desert for a total of 330 MW. Then, for nearly two decades, no new plants were built due to the weakening of the United States federal support for renewables and plummeting energy prices.
However, CSP has experienced a renaissance in the last two years. An 11-MW plant in Spain — the first in Europe — became operational in March 2007, while a 64-MW plant in Nevada is in its final stages of construction. Currently, over 45 CSP projects worldwide are in the planning stages with a combined capacity of 5,500 MW. With more than 200 GW of resource potential in the American southwest and thousands more throughout the world, CSP offers a rapidly scalable means of low-carbon electricity generation.
A September 2005 report by the European Solar Thermal Industry Federation (ESTIF), Greenpeace, and the IEA SolarPACES found that there are no technical, economic, or resource barriers to supplying 5% of the world’s projected electricity needs from solar thermal power by 2040. The authors calculated that CSP could produce 958 TWh/year by 2025, avoiding 575 million tons of CO2 annually for a cumulative 362 million tons in the next 20 years. By 2040, they found that CSP could produce as much as 16,000 TWh per year.
Solar Thermal: Harnessing the Sun’s Warmth
Solar thermal systems provide environmentally friendly heat for household water and space heating. Simple collectors, usually placed on the roof of a house or building, absorb the sun’s energy and transfer the heat. In many climates, a solar heating system can provide a very high percentage (50 to 75%) of domestic hot water energy. Since, on average, water heating accounts for around 30% of a home’s CO2 emissions, a solar water heater can reduce its total emissions by more than 20%.
Many countries are encouraging increased use of solar hot water technology. Worldwide installations grew 14% in 2005 to an installed base of 88 GW thermal equivalent, with 46 million houses equipped with the systems. China leads the way with 62% of the installed capacity, while Israel has the highest per-capita usage with 90% of all homes taking advantage of the technology.
The IEA Heating and Cooling Program in April 2007 calculated that this global installed solar thermal capacity reduces CO2 emissions by approximately 30 million tons each year. In January, ESTIF proposed an ambitious target of installing 1 square meter of collector area by 2020 for every European — 320 TWh of installed capacity. Meanwhile, in March, the United States National Renewable Energy Laboratory calculated the current technical potential of solar water heating in the United States at 1 quad of primary energy savings per year, equivalent to an annual CO2 emission reduction of about 50 to 75 million metric tons.
The Solar Advantage for Your Home
If you’re considering home energy options, the advantages of solar energy are hard to ignore. When you add a solar energy system to your home, you can tap into the benefits of this renewable, clean, and cost-saving power source.
Solar energy is a renewable resource, meaning you’ll never run out of it. Unlike fossil fuels, which are finite, the sun will continue to shine, providing an endless supply of energy. And solar energy is clean, creating no carbon emissions or other heat-trapping greenhouse gases. It avoids the environmental damage associated with mining or drilling for fossil fuels.
By installing a solar energy system, you can reduce your reliance on the grid and potentially save on your electricity bill. Some homeowners with solar panels even have excess power that they can sell back to the utility, earning money from their investment. And according to Constellation, home buyers will likely pay more for a house with solar panels installed, as the property value can be worth up to $15,000 more than its neighbors.
Maintenance is also a breeze with solar panels, as they have no moving parts that wear out over time. Just keep them clean and in good physical condition, and your solar energy system can provide reliable power for 25 years or more.
Of course, the initial cost of a solar energy system can be a drawback, but there are ways to offset this. Some states offer solar renewable energy certificates (SRECs) that you can sell to offset the cost, and leasing options can reduce your upfront investment. And as the solar industry continues to grow and advance, costs are steadily declining, making solar an increasingly viable option for homeowners.
Powering a Sustainable Future
Solar energy is an obvious choice for a carbon-smart, reliable energy future. Greater reliance on this comparatively untapped energy resource will help mitigate climate change while stimulating economies, creating jobs, and increasing grid integrity and security.
However, without robust international and national policy support for solar and other renewable energy sources, society will continue down the path of over-reliance on highly price-volatile, insecure, and carbon-intensive energy sources. Incentives for early adopters, regulatory policies, and education initiatives must all be in place to jump-start the mass-market adoption of solar energy.
With clear market signals, the industry can build up low-carbon solar energy on a scale large enough to help solve our global energy challenges. And as the team at Solar A Systems, Inc. can attest, the future is bright for those who embrace the solar advantage.
