Introduction to Solar Energy
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.
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.
Challenges in 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 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.
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.
Energy technologies that use the sun’s radiation directly are referred to as solar energy technologies. These may be employed to heat or light living space directly, to supply energy to a heat storage system for later use, or to generate electricity.
Two major factors should be considered when employing solar energy in Alaska: the abundance of sunlight when the energy is needed and the cost of other forms of energy. Technologies other than solar must carry the load during the dark times of the year in Alaska. For this reason, the addition of a solar auxiliary system will not reduce the capital cost of a primary heating or electrical system. Primary systems must be designed to operate for months without benefit of significant solar input.
Solar Technology in Alaska
Active systems hold the most promise for Alaskan applications. These are systems that can store energy for longer periods of time or be incorporated as auxiliary energy sources into existing energy systems. Active systems also lend themselves to being controlled automatically. Because of the seasonal nature of the solar resource in Alaska, passive solar designs yield only modest benefits, since they cannot store solar energy for an extended period of time. Passive solar lighting systems use sunlight only during the daylight hours. Passive heat systems are generally effective for some hours (in some cases a few days) after collecting solar energy, and they often require active participation in the building operation.
Active solar systems most suitable for Alaska are photovoltaic systems and solar hot water systems. Except for specific niche applications, it is unlikely that photovoltaic electrical generation is suitable for reducing the cost of electricity in Alaska. Grid-connected photovoltaic systems offer the most economical means of generating electricity with sunlight. At current prices an installed, grid-connected system in Interior Alaska could produce electricity for approximately $1.50 per kilowatt hour. Connection to an electrical grid enables a photovoltaic system to avoid expensive electrical storage.
The cost of solar-generated electricity in remote areas with no electrical grid available would be significantly higher due to the cost of additional batteries and inverters. There have been only two Alaskan villages with average electrical kilowatt hour costs over $1 per kilowatt hour for the past five years. Lime Village, which has an installed photovoltaic system, has electrical costs of $1.26 per kilowatt hour. Stony River pays $1.01 per kilowatt hour.
Solar hot water systems offer more promise in Alaska than photovoltaic electrical generation does, although the present installed cost of systems is still expensive. Solar hot water systems suitable for Alaska can provide hot water for space heat or for domestic use. The low density of the Alaskan solar resource precludes the economical use of high temperature solar technologies, such as systems that generate steam to produce electricity. As an example of the difference between the cost of solar hot water and hot water from fuel oil, consider a household-sized solar hot water system with an energy cost spread over twenty years. The cost of the solar energy would be approximately $100 per million Btu. The cost of that same energy from fuel oil, if the fuel price were $6 per gallon, would be about $40. There might be some rural villages where solar could be an economical component of an energy system. On the road system, where fuel oil is less expensive, some might wish to use solar hot water for reasons other than fuel oil price alone.
Net metering is a process by which utility customers operating small generators can purchase electricity from a utility when needed and sell any excess generation back to the utility company.
In January 2010, the Regulatory Commission of Alaska formally adopted net metering for Alaska in January 2010. The new rules only apply to utilities with total retail sales of 5 million kWh or more and require that utilities interconnect with eligible customer generation systems up to a system-wide total capacity of 1.5% of their average retail demand. After reaching the 1.5% level, the utility can choose to add more power through net metering or turn down additional requests.
Homer Electric Association (HEA) and Fairbanks’ Golden Valley Electric Association (GVEA) developed the Sustainable Natural Alternative Power SNAP programs before adoption of state-mandated net metering. SNAPs allow customers who wish to support renewable energy development to do so by contributing to a fund that is held in escrow by the utility company. Individuals in the GVEA and HEA service areas who want to produce up to 25 kW of renewable electricity for the grid are paid from the escrow fund in proportion to the amount of power they produce plus the utilities avoided fuel cost. Other electric cooperatives in Alaska are also considering starting their own SNAP programs.
|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|
|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|
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.
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.
- U.S. Department of Energy Office of Energy Efficiency and Renewable Energy
- Golden Valley Electric Association
- Homer Electric Association
Solar Energy Photos
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