Spring Break 09

Solar Space Heating and Cooling

This prototype home in Tucson, Arizona, employs active and passive solar technologies, including a hidden, roof-top solar water heater, reflective window coverings, and overhangs.

Just as solar energy can heat the water for a building, it can also heat and cool the air.

Space Heating

A solar space-heating system can consist of a passive system, an active system, or a combination of both. Passive systems are typically less costly and less complex than active systems. However, when retrofitting a building, active systems might be the only option for obtaining solar energy.

Passive Solar Space Heating

Passive solar space heating takes advantage of warmth from the sun through design features, such as large south-facing windows, and materials in the floors or walls that absorb warmth during the day and release that warmth at night when it is needed most. A sunspace or greenhouse is a good example of a passive system for solar space heating.

Passive solar design systems usually have one of three designs:

• Direct gain (the simplest system) stores and slowly releases heat energy collected from the sun shining directly into the building and warming materials such as tile or concrete. Care must be taken to avoid overheating the space.

• Indirect gain (similar to direct gain) uses materials that hold, store, and release heat; the material is located between the sun and living space (typically the wall).

• Isolated gain collects solar energy remote from the location of the primary living area. For example, a sunroom attached to a house collects warmer air that flows naturally to the rest of the house.

For more information about passive solar space heating, visit the EERE Passive Solar Heating, Cooling, and Daylighting page.

Active Solar Space Heating

Active solar space-heating systems consist of collectors that collect and absorb solar radiation combined with electric fans or pumps to transfer and distribute that solar heat. Active systems also generally have an energy-storage system to provide heat when the sun is not shining. The two basic types of active solar space-heating systems use either liquid or air as the heat-transfer medium in their solar energy collectors.

Liquid-based systems heat water or an antifreeze solution in a hydronic collector. Air-based systems heat air in an air collector. Air-based solar heating systems usually employ an air-to-water heat exchanger to supply heat to the domestic hot water system, making the system useful in the summertime. Both of these systems collect and absorb solar radiation, then transfer the solar heat directly to the interior space or to a storage system, from which the heat is distributed. An auxiliary or backup system provides heat when storage is discharged. Liquid systems are more often used when storage is included.

Here is a summary of the many different types of active solar space-heating systems:

Medium-temperature solar collectors are generally used for solar space heating. Solar space heating systems operate in much the same way as indirect solar water-heating systems, but they have a larger collector area, larger storage units, and more complex control systems. They are also usually configured to provide solar water heating and typically provide 30% to 70% of the residential heating, or combined heating and hot water, requirements. Active solar space-heating systems require more sophisticated design, installation, and maintenance techniques.

• A very economical, but specialized space heating system is based upon use of transpired air collectors, mounted as an exterior cladding on a south-facing wall. These systems are used for ventilation preheating. This system heats only outdoor air. These collectors are unglazed, and a blower or fan is used to draw air through perforations in the wall to deliver ventilation air into the building. Solar ventilation air preheating systems are generally used in commercial and industrial applications that require large quantities of ventilation air, including: a) buildings that require much outdoor ventilation, such as warehouses, large manufacturing plants, and airplane maintenance hangars; b) crop drying; and c) pre-heatingof boiler combustion air.

Space Cooling

Cooling and refrigeration can be accomplished using thermally activated cooling systems (TACS) driven by solar energy. These systems can provide year-round utilization of collected solar heat, thereby significantly increasing the cost effectiveness and energy contribution of solar installations. These systems are sized to provide 30% to 60% of building cooling requirements using solar, with the remainder usually dependent on TACS fueled by natural gas. The TACS available for solar-driven cooling include absorption systems and desiccant systems. Generally, solar cooling is not used because of the high initial costs of TACS and the solar fields needed to drive them.

• Solar absorption systems use the thermal energy from a solar collector to separate a binary mixture of an absorbent and a refrigerant fluid. The refrigerant is condensed, throttled, and evaporated to yield a cooling effect, which is then re-absorbed to continue the cycle. Double-effect absorption systems (which use the heat twice in series) are about twice as efficient as single-effect systems, but require significantly higher input temperatures. Because of the high temperature requirements of absorption cooling systems, evacuated-tube or concentrating collectors are typically used.

• Solar desiccant systems use thermal energy from the solar collector to regenerate dessicants that dry ambient air; they then use that dry air in indirect and/or direct evaporative stages to provide cooled air to the load. The solar heat is used to regenerate the desiccant, driving off the absorbed water. Some systems use flat-plate collectors at intermediate temperatures.

http://www1.eere.energy.gov/solar/sh_basics_space.html

Photovoltaic Mileage

New Life-Cycle Assessment Reveals Your Photovoltaic Mileage May Vary

by Jeremy Elton Jacquot, Los Angeles on 02. 9.08

Science & Technology

Not all photovoltaic technologies are created equal; some, in fact, incur quite heavy environmental footprints - producing silicon, for example, consumes a lot of water and energy while refining zinc produces a sizeable chunk of emissions. Environmental Science & Technology's Naomi Lubick reports that Vasilis Fthenakis, a scientist at Columbia University and the Brookhaven National Laboratory, just finished a LCA of some of the leading technologies which determined that new thin-film cadmium-telluride (CdTe) materials - such as the ones we covered here - come out on top.

Benefiting from its highly efficient energy conversion, CdTe photovoltaic systems consumed less energy and produced fewer emissions; in addition, when compared to its multicrystal and ribbon silicon competitors, the CdTe technology had the lowest cost. In order to obtain these results, Fthenakis and his colleagues compared data from more than a dozen solar companies, taking into account the manufacturing process, energy conversion and various components.

Unfortunately, the assessment failed to shed light on the technologies' total environmental impact - "not telling you exactly what your impact is if you were to buy them," as Corinne Reich-Weiser, a graduate student at UC Berkeley, explaine

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d. For instance, she notes that the emissions produced during the transportation of components before production and assembly are only partly taken into consideration; moreover, the assessment is based on idealized European and U.S. grids even though most components are built in China.

Still, it provides an effective means of "easily comparing" all of the available technologies, she says, deeming it "incredibly useful." New and future solar technologies should be able to bridge that emissions gap within the coming years as companies continue innovating and expanding their operations. Fthenakis notes that the one missing element from his assessment he hopes to amend soon is the end-of-life and recycling data; he believes this should help make the technologies' emissions profiles even better.

Powershift09 Conference Brings Thousands of Activists to DC Demanding Clean Energy

I was there for the conference,too bad couldn't make to the lobby day...

by Bonnie Hulkower, New York, New York on 03. 4.0

Powershift 09 Rally on Lawn of the Capitol photo from Fritz Meyr's flickr page

Powershift 2009 was an energetic and informative conference that culminated with a march of 3,000 plus young (and young at heart) people demanding clean energy and green jobs. The inclement weather only made the march more inspiring. Other Powershift 2009 highlights included: Protestors visiting their representatives in Congress and the Senate; Four young leaders giving testimony to the House Select Committee for Energy Independence and Global Warming; and an anti-coal protest at the Capitol Power Plant.

When I arrived, I scanned the cavernous conference center for the registration area and asked a woman wearing a green t-shirt and badge that said LEADER for directions. As I walked to the table she had pointed to, the brilliance of the conference organizers dawned on me—every participant was wearing a tag that proclaimed them a LEADER!

Powershift09 conference badge photo by Bonnie H.

The event felt like the first day of school with people rushing off in small groups to various standing room only workshops and panels. Some of the content is available online on YouTube, including videos of speeches from EPA Administrator Lisa Jackson, Secretary of the Interior Ken Salazar, and Congressman Ed Markey. Beyond those speakers, many illustrious green stars that we’ve highlighted on TreeHugger.com, such as Gus Speth, Bill McKibben, and Tim De Christopher, were hanging out, mingling and chatting with the conference attendees.

Gus Speth and young leader at Powershift09 conference photo by Bonnie H.

One of the other most impressive features of the conference was the hyper articulateness of some of the youngest “leaders”, with a presentation by a 12-year old from Seeds of Green, while a program called DoRIght Leadership Corps had two high school sophomores presenting. These weren’t novelty acts; these teens and tweens eloquently delivered.

Another event highlight was the impromptu Saturday night march. My friend Antuan Cannon of Envirolution related the story to me. After the Roots concert, a spontaneous rally broke out in the convention center corridors. After being pushed by security on to the streets, the police arrived to clearing people out of the road to let cars pass. Rather than disassemble, fifty plus students began marching toward the White House.

This small group leading the way forward merged with other small groups that had the same idea. It reminded Antuan of the scene in Braveheart, when all the reinforcements appear over the horizon. As the merged group made its way to the White House, cars honked to show support, when these activists sang the National Anthem with pride. You can have high tech presentations, Van Jones speaking, the Roots rocking, but it doesn’t get anymore democratic and inspiring than that.

Saturday night Spontaneous March to White House photo via UOPowershift09's flickr page