Rising Sun

Energy uncertainty and increasing environmental awareness are driving greater exploration of solar light and power for buildings

11/01/2001


The sun, of course, lies literally at the center of our solar system. Figuratively, one could also say it lies at the center of our universe. And although the sun is approximately 93 million miles away from Earth, it bestows upon us more energy-in the form of light and heat-than we could ever possibly need. While that sounds impressive, how can that energy actually be utilized?

During the 1970s, more than a few forays were made into developing and installing solar technologies to cope with that decade's oil embargoes. But as fossil fuels became less costly, utility prices stabilized, other technologies caught up in efficiency and solar technology in the design of buildings became a fringe element in the United States. Consequently, the leadership on solar technologies slowly moved offshore to places like Germany and Japan.

But today, as utility prices destabilize and environmental consciousness develops, solar-energy systems, such as photovoltaics and daylighting, are getting a new look.

Daylighting movement

Natural light used to be an integral part of most buildings, but somewhere along the way, buildings seemingly lost touch with the world around them. It's not uncommon that these thick-walled enclosures, both tall and wide, hide a separate ecosystem that features artificial illumination powered by electrical utilities. Day after day, the sun is left waiting at the door.

The precepts of daylighting seek to change that. Many new facilities are now allowing sunlight in, especially offices and schools that experience their peak hours with the sun at its apex.

There are three major arguments for using sunlight as an illumination source: energy efficiency, life-cycle cost paybacks and occupant satisfaction and health.

Energy efficiency and life-cycle cost go hand in hand. While it is true that daylighting systems generally increase building and design costs, over time electricity savings will recoup those costs, especially if utilities offer incentives and rebates.

And while economic paybacks may justify some modern projects, the best examples in daylighting continue to occur when energy efficiency is an end in itself.

'We know most of the same things we did 50 years ago when it comes to daylighting buildings,' says Phil Gabriel, IALD, principal of Gabriel Design, Ottawa, Ontario. 'But we now have much more knowledge of fossil fuels and interest in renewable energy.'

On the other side of the equation is a growing notion that exposing people to natural light leads to a healthier environment. Not only does sunlight offer attractive arrays unavailable with electric lamps, most human beings just feel healthier in more natural, sunlit spaces. Part of this is based on the theory that a window is not just a point of entry for light, but a point of connection for people inside as well. This connection with the outdoors is a key tenet for daylighting design, and a big reason why it is growing in favor.

'Twenty years ago, daylight was seen as an intruder in a building,' says Al Borden, IALD, president of The Lighting Practice, a lighting-design firm based in Philadelphia. 'But people just work better and feel better in an environment where they are in touch with the natural cycles of things.'

While this assertion has long been accepted, studies continue to offer further proof. For example, the Lighting Research Center (LRC) of Rensselaer Polytechnic Institute in Troy, N.Y., recently completed a study of software-development workers in daylit environments vs. those in artificially illuminated spaces. Preliminary results show a 15% increase in worker productivity.

In addition, an important new facet of continuing research goes beyond quantification and is looking into the reasons behind improved productivity, health and mood in daylit buildings.

'Lighting design typically makes sure you see a certain task at a certain light level,' says Russ Leslie, associate director and professor of architecture at the LRC. 'But besides lighting for visual purposes, we are finding that lighting has an effect on a person's photobiological system.'

According to Leslie, the body can be positively affected by a natural cycle of exposure to light, with sunlight providing a much brighter and natural range of light during the day.

Design considerations

The concept of daylighting is simple: let sunlight come in rather than use superfluous electricity to provide artificial light. But the design of daylighting is a detailed practice. The design could provide some or all of the necessary light, and the considerations can encompass actions ranging from the drawing of a curtain to the use of highly sophisticated lighting controls.

Daylighting schemes certainly entail a new set of considerations compared to electric lighting design, as the designer is faced with the task of changing sunlight into usable light.

Also, manipulating the effects of natural illumination in a building involves other building designers, such as architects, interior designers and HVAC engineers. According to Gabriel, a high level of cooperation and design integration is necessary to make sure that complicated daylighting is successful both from a functional and energy-efficiency standpoint.

The lighting designer must also consider the two most insidious qualities of sunlight: glare and heat. Glare is a major problem in office buildings, especially where computer screens are present. Solar heat gain can have detrimental effects on the HVAC system and make areas difficult to control environmentally.

Also, many analyses go into dealing with a light source that, even though it occurs in a pattern, shifts on a daily and hourly basis. This involves researching information on the sun's activities and adjusting the design accordingly, which could include architectural considerations such as the site of a building, placement of apertures or the paths of light distribution.

Finally, because daylighting is affected by the position of the sun at various times of the day, the lighting scheme will need to work in conjunction with both the electrical lighting system and the interior design of the space to ensure uniform lighting and energy savings.

Manipulating sunlight may pose challenges that can be daunting to the uninitiated. On a simple level, however, daylighting design begins at the same point as any other lighting design: there are certain tasks to be performed, and a certain level and quality of light needed to perform them.

'Daylighting is not complicated because it is hard; it is complicated because it is different,' asserts Steven Ternoey, principal of Lightforms, a design consultancy based in Santa Barbara, Calif. 'These are simple concepts, they are just not taught in the schools.'

Design tools

Manipulating sunlight in a space entails a variety of considerations. Fortunately, the components and strategies at the designer's disposal have developed along with the concepts and goals.

Everything begins at the point of entry, where the direct sunlight often needs to be diffused or reflected, either to limit glare and heat or to help spread illumination throughout a space. The two primary points of entry are windows and skylights .

As a source of light, a traditional window actually does too good of a job of letting light and heat in. To combat this, many designs utilize shading above windows. Light shelves can be placed so that sunlight is reflected, thus lighting the entire room from top to bottom and helping move natural light further into a building's interior.

In addition, there has been a continuing refinement of window glazings that control the levels of light penetrating the glass. In particular, low-emmisivity, or low-'e,' glazing allows a certain level of light to pass through while resisting heat.

From an architectural perspective, spacing and placement of the windows drastically affects daylighting design. Windows higher up in a space distribute sunlight more effectively, which is why clerestory windows are often an important part of daylighting in facilities like museums and churches.

Much like clerestory windows, skylights are a fantastic way to allow light into a space and are now being developed as active components integrated with sensors and lighting elements to provide a continuous level of illumination.

Another source of daylight in a building are heliostats , which track the sun's movement during the day and funnel the light into a space by reflecting it downward. A similar device under development actually uses fiber optics to transport sunlight from the roof deep into a building (See Building Design and Construction magazine, October 2001). Both of these light sources can help to use daylighting in new fashions, allowing more natural illumination to penetrate from above.

Once inside a building, the sunlight must be smartly distributed and interact intelligently with the electric lighting system. This is where interior design can make a big difference. By using brightly colored or white walls, light is reflected around the rooms better. Keeping walls or office dividers below a certain height also gives sunlight the chance to spread through the high areas. Finally, the placement of electric light fixtures should take into account the impact of daylight.

One area of technology that continues to develop is controls, or the measures used to make sure that the electric lighting system interacts properly with daylight. Otherwise, any energy efficiency benefits can be negated and the design lighting levels will not be maintained.

The simplest and most common solution is to utilize photosensors that measure light levels in a room and adjust the intensity of the lamp accordingly. More complicated scenarios can include building-automation systems that adjust other systems throughout the building.

Daylighting barriers

Even with a growing recognition of benefits and the continuing development of tools, there are still barriers to the widespread use of daylighting. According to Borden, there are three major barriers: the first is cost, as controls are still quite expensive; the second is maintenance and operation; and last is a cultural issue, as many are not aware of daylighting options.

In general, a facility committed to daylighting has to be willing to make an extra initial investment in architectural design and control systems. Payback is obviously dependent on many factors, but according to Borden, in comparison to a conventional system, a common payback period may be six or seven years. For a forward-thinking corporate client or a hospital, this investment and resulting payback can be justified fairly easily. On the other hand, because of the different nature of their business, a retail client may not be willing to make that type of initial investment.

Also, because of highly efficient fluorescent systems, relative energy savings for daylighting are not as profound as they would have been even 10 years ago.

Maintenance and performance of daylighting systems are another major hurdle slowing down the implementation of such systems. While daylighting controls have developed to the point where they offer designers many features, there are many who question their readiness.

'The current systems are often not effective to do photosensor dimming,' says Leslie. 'Plus, these control systems are difficult to commission, and the occupants will often adjust them improperly.'

Many designers agree that maintenance is a key part of the effectiveness of daylighting design, and a possible stumbling block for building owners.

'These are relatively new and unknown systems,' says Borden. 'Facility managers have to go from replacing bulbs and ballasts to tuning sensors and replacing circuit boards.'

Finally, awareness of daylighting is hardly ubiquitous. And because large-scale daylighting must be considered early in a project, the motivation must be there from the beginning.

Education is obviously the most basic way to change this, but more dramatic steps may be required. 'The thing that would make a definite change would be a change in building codes to require certain amounts of daylighting,' says Gabriel.

Many countries in Europe, such as Germany, have such laws requiring an office building to offer some level of natural light for its occupants. This has created a much different lighting-design environment there, says Borden, as there is an accepted premise that daylight is an important, necessary part of not only the lighting in a building but also a person's environment.

In these countries, electrical lighting levels are designed at much lower intensities because they take into account daylight. Rather than special dimming systems, building developers accept that daylighting will be an important facet, and therefore, the amount of footcandles required will be lower.

Photovoltaics

Besides daylighting, the other solar energy making waves is photovoltaics (PV). Much like daylighting, the market for PV in this country is growing, with building-related applications being a large part of that. Also like daylighting, economics and paybacks lead the discussion on PV in the U.S., and it is no coincidence that government and educational facilities, which generally have longer life-cycle outlooks, are the leading adapters.

But there has definitely been a broader look at how PV can complement any building's electrical needs. Buildings can either use PV as a supplement to certain power loads, or tie the electricity back into the utility. These 'grid-connected' PV systems give the user the option of selling electricity back to the utilities, which are required by the Public Utilities Regulatory Policy Act of 1978 to buy PV energy back.

The latest round of interest has been brought about by an improvement in efficiencies and products; some utility and government incentives; and a growing number of projects that offer examples of what PV can provide.

Two types of PVs are currently available: crystalline and thin-film . The crystalline variety is the most widely used and efficient variety of PV cells at 10% to 14% efficiency. They are often used on rooftop and free-standing systems. Thin-film is generally less expensive, more flexible and less efficient-4% to 6%.

This rating relates to how well the cell converts solar energy to electricity, measured at 'standard' sun conditions. Both types have already tested at much higher efficiencies-around 30%-in the laboratory, pointing to a future where PV output will offer more significant economic paybacks.

Currently, when measured by dollars vs. each installed watt, thin-film and crystalline cells generally end up about even, economically. But it is thin-film that is leading to the most important recent development in relation to the building industry: building-integrated photovoltaics (BIPV). As the name suggests, these units consist of PV elements integrated into conventional building-skin materials, such as curtainwalls, windows, skylights, light shelves and roofing.

The ability to design and use PV as a part of a building's skin, rather than an add-on type feature, has obvious architectural benefits. In the past, many architects had trouble integrating bulky, separate PV systems into their designs.

But the most encouraging factor is the economics. BIPV cost more than traditional building exteriors, but combining PV into a necessary part of the building saves cost over separate systems and helps justify the expenditure. Also, cells incorporated into windows and skylights can offer a measure of controlled shading, which can serve a third function in daylighting applications.

According to Paul Torcellini, senior engineer and building teams leader at the National Renewable Energy Laboratory in Golden, Colo., BIPV components can actually help increase the life of building components.

'Because PV cells are looking at a 25- to 30-year payback, these building components better be durable,' he says.

Economic incentives

There is no doubt that PV technology is getting more efficient, while at the same time being sold at a lower price. This has made the lifetime cost of a PV cell more competitive with buying from the utility, although over the 25-year life of a PV cell-the most widely-used lifetime figure, although many contend a cell will outlast this estimate-the economic impact is speculative when measured against a fluctuating energy market.

'Trying to figure out payback over 25 years is very hard. It is like looking into a crystal ball,' says Torcellini. 'Payback will be evaluated [on a project], but it is a hard thing to pinpoint.'

One utility trend that is tipping the economic scale in PV's favor is peak, or time-of-use, rates. Utilities have been given the freedom to charge higher rates during high-use times, generally during the daytime hours.

'By the time everyone wants the power, that's when the power has the most cost,' says Steven Strong, president of Solar Design Associates in Harvard, Mass. 'State after state, you have very high time-of-use rates coming.'

During the day, of course, is when PV systems offer their output, and if the utilities are offering honest buyback rates, the economics become even more advantageous.

But Torcellini warns that factoring this incentive can be tricky, as peak rates are generally charged for the highest rate of use over a period of time. This means that if the PV system is not producing for a portion of time during the day, such as when a cloud passes, the facility will likely be charged the entire peak period at the highest point of use. The facility will have saved energy, but the economic incentive may have lessened considerably.

Also, many utilities have begun offering economic incentives for these types of systems, although the places that are seeing the most PV action are those that have the biggest government incentive programs . The California Energy Commission's Buy-Down Program, for example, offers rebates for 'renewable energy electric-generating' systems, including PV. This comes to $4,500 per kilowatt, or 50% of the system purchase price, whichever is less, and can substantially alter the economics.

In addition, the U.S. government started its 'Million Solar Roofs' program in 1997, aiming for one million systems installed by 2010. Included in this aggregate are PV panels as well as solar thermal systems for both space and water heating.

Through the program, the U.S. government gives some grants to organizations-companies, manufacturers, utilities-that support the development and implementation of PV systems. For the most part, the program has served as a networking and promotional tool, with a lack of significant dollars behind it.

Now, under the Bush administration, less federal government investment in PV research and development is likely. According to the National Center for Photovoltaics, a division of the U.S. Department of Energy, the new energy bill proposed by the Bush administration would cut the annual budget for PV energy systems from $75 million to $39 million. This could slow development of PV in this country but open the door for more U.S. private-sector involvement, or even a foreign invasion of services.

Foreign markets, examples

Although PV was born in the U.S., it is currently being perfected elsewhere, and multinational corporations such as Siemens, Kyocera and British Petroleum are developing the technology that Strong believes will dominate once the U.S. market matures. 'PV can help us get away from dependence on foreign oil, but what will happen is that we will get more dependent on the foreign manufacturers of PV systems. There will be a huge market, and that market will be exploited.'

According to Strong, the larger PV market overseas can be attributed to cultural and political differences. 'Americans have been obsessed with first-cost impact; Europeans not as much. They build structures to last, and the best indicator of that can be seen when you walk into a city square and see centuries-old buildings.'

In addition, Strong claims that consumers in Europe are much more aware of the practices of their companies, while their political systems have had effective 'green' politicians for a good number of years. As a result, progressive companies that make a commitment to renewable resources get larger benefits from the government and find greater favor with the public.

Either way, there is no doubt that the U.S. is beginning to see some major PV installations, and new installations overseas will continue to offer models.

One notable installation is a facility in Sodingen, Germany, where a number of buildings and structures were built inside a glass-and-PV envelope that provides all of the energy needed.

Additionally, installations in this country, such as at the Center for Environmental Sciences and Technology Management at the State University of New York at Albany give us a glimpse of what PV can accomplish. A new project at the Mary Ann Cofrin Hall at University of Wisconsin-Green Bay features the first U.S. installation of thin-film PV as an insulated glazing element. On the horizon

Economically, solar light and power are not ready to compete with traditional methods, but over time they have proven to have some level of payback. Uncertain future energy markets and a continuation of technical development, however, could brighten the economic picture even more.

The bottom line is that daylighting and PVs have goals and benefits that go beyond economics. In the big picture, solar light and power can offer buildings a renewable energy source, making the entire country less dependent on imported fossil fuels. Additionally, daylighting has proven health benefits and PVs provide reliable, continuous, maintenance-free energy.

This leads many to believe that a shift in cultural awareness is still the most significant barrier to more widespread adoption. Speaking about PVs, but certainly germane to daylighting as well, Torcellini asserts that this cultural awareness must be present in the building owner's mind from the get go.

'If the owner is not driving the process and understanding the goals, [these systems] probably will not end up in the building,' he says. 'Usually if you cost-justify things, you are really just trying to get rid of it.'



Cool Daylighting

A growing movement seeks to reverse what its practitioners contend is a false impression about the costs of daylighting systems. The concept is called 'cool daylighting,' because it aims not only to provide quality daylighting, but also to lessen the cooling-load impact of traditional daylighting design.

'We found that most new daylit buildings lose all their energy savings to higher energy costs for cooling,' says Steven Ternoey, principal of Lightforms, Santa Barbara, Calif. 'Cool daylighting seeks to reduce the energy needs for lights without putting extra strain on the HVAC system.'

To this end, some of the design strategies of cool daylighting may be counterintuitive to traditional daylighting mantras, such as the use of more windows. Cool daylighting often entails using fewer apertures than a typical building, with the thinking that fewer glass apertures lead to less solar heat gain.

Ternoey prefers to focus on high-level windows, which provide the most valuable daylighting in a space, with minimal eye-level apertures that repel heat and glare with low-emissivity glazings or manual blinds.

Cool daylighting also seeks to mitigate the cost perceptions of traditional daylighting. Most designers will tell you that part of the problem is first cost, but Ternoey contends that it doesn't have to be that way. Cool daylighting allows for a scaled back HVAC system, which Ternoey claims can offset the first cost of daylighting design. Another big part of the cost of modern daylighting systems is dimmable lighting that reacts to light levels outdoors. According to Ternoey, in a properly daylit space, dimmable lighting is not really needed.

'I like to give control back to the occupant,' he says. Rather than spending extra money on sophisticated components, Ternoey would advise that the designer spend time making sure the entire environment supports the daylighting scheme. 'Most of all, daylighting needs to be a cross-disciplinary strategy, because it affects the outside appearances, it affects the interior, it affects the HVAC. On many projects, the architects, the interior designers, the engineers all do their parts independently, which is the flaw.'

The Daylighting Collaborative, a project of the Energy Center of Wisconsin, has adopted the cause of cool daylighting and offers training on how to use daylight as a way to effectively make a significant energy difference without increasing the first cost of buildings. According to this principle, every building could, and should, be daylit.

'We don't want to just show people what you can do at $150 a square foot,' says Abby Vogen, program manager at The Daylighting Collaborative. 'We want to focus on strategies you can use on every project.'

For more information on cool daylighting, call The Daylighting Collaborative at 1-800-864-6254, or the Wisconsin Focus on Energy at 1-800-762-7077.

Solar Heat Stays Cool

The energy crisis of the 1970s begat many ideas for ways to circumvent dependence on nonrenewable fuel sources. Solar-heat applications, including panels, originated during this period, and are still used today in a variety of heating applications-mostly for residential applications.

Domestic hot water systems use solar heat as a supplement to boiler loads. Solar heating systems heat either recirculated air or intake air for a building. For intake air, a recent invention, transpired air collectors , can raise the temperature of intake air up to 40°F on a sunny day, according to the U.S. Department of Energy. Also, in certain parts of the country solar heat is used to provide a cooling load for heat pumps in buildings.

But while energy-efficiency concerns and advancing technology have lead to a greater interest in PVs and daylighting, solar heating for air and water in buildings has not received as much enthusiasm.

The reasons behind this can be traced to the single largest factor in any product's success: economics. Since the '70s, energy has become less expensive while mechanical equipment has become more efficient. While there are quality systems that have proven to function well, without an energy crisis, there is not a driving economic factor for using the sun as a major source of heating air or water in large buildings.



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