Introduction
Solar energy - or power produced by the sun - is a huge and inexhaustible resource. The fuel the sun produces, once converted by some system into energy, is free and isn't subject to the fluctuation of energy markets. Solar power produces no emissions, and so is a clean alternative to fossil fuels. Because solar energy is so abundant for most places on earth, it offers a unique opportunity to play a prominent role in our energy needs.
The amount of energy from the sun that falls on Earth's surface is enormous. All the energy stored in Earth's reserves of coal, oil, and natural gas is matched by the energy from just 20 days of sunshine. Outside Earth's atmosphere, the sun's energy contains about 1,300 watts per square meter. About one-third of this light is reflected back into space, and some is absorbed by the atmosphere.
By the time sunlight reaches Earth's surface, the energy has fallen to about 1,000 watts per square meter at noon on a cloudless day. Averaged over the entire surface of the planet, 24 hours per day for a year, each square meter collects the approximate energy equivalent of almost a barrel of oil each year, or 4.2 kilowatt-hours of energy every day. Northern latitudes receive less energy per amount of sunlight received due to the shape of the planet. Because the Earth is slightly oblong, northern climates are further away from sunlight than places located on the equator, and receive the light at a much greater angle. For example, Seattle, Washington in December only receives about .7 kilowatt-hours per day. It should also be noted that these figures represent the maximum available solar energy that can be captured and used, but solar collectors capture only a portion of this, depending on their efficiency. For example, a one square meter solar electric panel with an efficiency of 15 percent would produce about one kilowatt-hour of electricity per day in Arizona.
In Alaska, due to our high position of latitude, we receive much less solar energy than the rest of the United States. Some places, like Barrow, Alaska, receive no sunlight whatsoever during the winter months and 24 hours of sunlight every day during parts of the summer. Because of this unique light schedule throughout the year, solar energy development in Alaska faces unique challenges and is limited in its ability to provide cheap, clean energy.
Photo Credit: Solar Green Wind Blog
How Solar Energy Works
Solar energy provides a growing but still small fraction of energy throughout the world. To put solar energy use into perspective, the U.S. Energy Information Agency estimates that worldwide electrical generation from all energy sources for 2005 was 18 trillion kilowatt hours. According to the International Energy Agency, worldwide solar photovoltaic electrical generation was approximately 7.7 billion kilowatt hours in 2006, about 0.05% of total electrical generation. Likewise, heating energy produced by solar, while about 10 times that of solar photovoltaic electric energy production, was also a tiny fraction of total electrical generation.
As these figures would suggest, solar energy is a largely untapped resource. The development of solar energy technology has fluctuated with the price of traditional fossil fuels (i.e. oil, gas); as fuel prices are cheaper, there is less monetary incentive for people to invest in developing cheap energy capture mechanisms. However, as fossil fuels are depleted and people look for cheaper and more reliable ways to heat their homes and use electricity, interest in solar energy rises. Capturing solar energy requires a large investment on a user's part in obtaining the right technology, installing, and maintaining it to be efficient in its energy capture. However, as solar energy research progresses, cheaper and more efficient technology becomes available and easier to use, thus creating incentives for private users to make the initial investment for solar energy.
Passive vs. Active Solar Energy
Direct use of solar energy for heating or lighting is often referred to as passive solar use. The term passive is used because a building employs solar energy by virtue of its design without requiring additional equipment to actively move or store energy. In other words, passive solar systems use the energy of the sun where it falls. In this same way designers strive to employ generally conventional materials and building components to advantageously use the sun’s energy in buildings. Implementing a passive solar energy strategy involves many decisions, from the location of the building and its overall shape, to the placement of windows and skylights, to the materials to be used inside the structure.
Residential and commercial buildings account for more than one-third of U.S. energy use. If properly designed, buildings can capture the sun's heat in the winter and minimize it in the summer, while using daylight year-round. Buildings designed in such a way utilize passive solar energy—a resource that can be tapped without mechanical means to help heat, cool, or light a building. Simple design features such as properly orienting a house toward the south, putting most windows on the south side of the building, skylights, awnings, and shade trees are all techniques for exploiting passive solar energy.
Besides using design features to maximize their use of the sun, some buildings have systems that actively gather and store solar energy. Solar collectors, for example, sit on the rooftops of buildings to collect solar energy for space heating, water heating, and space cooling. Most are large, flat boxes painted black on the inside and covered with glass. In the most common design, pipes in the box carry liquids that transfer the heat from the box into the building. This heated liquid—usually a water-alcohol mixture to prevent freezing—is used to heat water in a tank or is passed through radiators that heat the air.
In addition to providing heat, solar energy can also be used for cooling systems. In desiccant evaporators, heat from a solar collector is used to pull moisture out of the air. When the air becomes drier, it also becomes cooler. The hot moist air is separated from the cooler air and vented to the outside. Another approach is an absorption chiller, such as the one used at Chena Hot Springs Resort outside of Fairbanks, AK. With an absorption chiller, solar energy is used to heat a refrigerant under pressure; when the pressure is released, it expands, cooling the air around it. This is how conventional refrigerators and air conditioners work, and it's a particularly efficient approach for home or office cooling since buildings need cooling during the hottest part of the day. These systems are currently at work in humid southeastern climates such as Florida, but are not widely used in Alaska where the air is much drier and the need for cooling in homes is limited.
Solar collectors and related technology were very popular in the early 1980s when fuel prices were high and federal tax credits were available to help develop home systems. However, in the mid-1980s, fossil fuel prices in the United States dropped, and the tax credit legislation expired. Consequently, the demand for solar energy systems plummeted. In Alaska, most solar energy systems are used in private residences or businesses. However, the study of how to utilize solar energy in Alaska's unique light climate is ongoing.
Solar Energy in Alaska
Technologies that use equipment to move or store solar energy from where it is incident to somewhere else are referred to as active solar systems.
Examples of these active system technologies are hot water systems where water is heated and the heat is stored in a reservoir, systems where high temperatures are generated to produce steam to generate electricity through conventional steam turbines, or photovoltaic systems where solar energy generates electricity directly in a semiconductor solar cell.The solar resource in Alaska is significant, but it varies dramatically with the latitude, time of year, and weather. In the northernmost portions of the state, there is abundant sunlight up to 24 hours per day in June, with no sunlight in December. In less extreme northern latitudes, the resource potential is distributed over a greater portion of the year. If solar energy is used for lighting, systems can be optimized for direct sunlight or for diffuse sunlight when skies are overcast, but the strategies differ; it is important to design for the condition that predominates.
When solar energy is used for heating or electrical generation, direct sunlight is the most effective form of solar radiation to use. In either case, building systems must be able to operate with or without the solar resource.
Current Projects
Lime Village – This 12 kW solar array was constructed to offset average electrical prices of $1.26 in the remote town of Lime Village. The combination solar-diesel generation system with 77 kW of diesel generation capacity has reduced electrical generation costs to about $0.56 per kWh.
Nome – Bering Straits Native Corporation installed a 16.8 kW solar PV array on their office building in March, 2008. The PV array produces about 16,000 kWh of electricity per year, offsetting about 1,000 gallons of diesel fuel. BSNC has also installed solar hot water heaters on two corporation-owned apartment buildings.
Challenges of Solar Energy
Major challenges to using solar energy in Alaska are its seasonal variability and its dependence on weather conditions. In general, the solar resource is most abundant in the summer, when it is least needed. However, there is a reasonable resource available for seven to eight months of the year for all but the most northern areas of the state. Direct heating and daylight with the sun require minimal technology, but they rely on good building design to prevent overloading in the summer months and to promote energy gathering during the shorter days in the winter season.
Solar Technologies
| TECHNOLOGY SNAPSHOT: SOLAR | |
|---|---|
| Installed Capacity (Worldwide) | Solar heating – 128 GigaWatts; Photovoltaic electrical – 7 GigaWatts |
| Installed Capacity (Alaska) | 100s of kW |
| Resource Distribution | Statewide, best in areas with less precipitation and with southern exposure |
| Number of communities impacted | Best use is for individual installations where there is no grid power |
| Technology Readiness | Commercial |
| Environmental Impact | Minimal, small footprints, no CO2 emissions |
| Economic Status | Payback is dependent on fuel oil prices and local resource |
| Case Studies | Solar Thermal Alternative Residential Heating Methods |
| Conclusion and References | |
For more information about solar energy technology, click on the link below.
SOLAR TECHNOLOGY
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Links and Resources
- Union of Concerned Scientists
- Current Solar Projects: A great and comprehensive resource to solar energy in Alaska, and a look at current projects.
