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Renewable Energy and Carbon Reduction Strategies

This article was prepared for the Sustainability Report of UNR published in 2009. It is included as Section 2.6 of this report.

By Hans-Peter Plag.

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About this article

The goal here is to discuss in which way an institution like UNR could utilize renewable energy sources to reduce the use of fossil fuels and thus the associated carbon emissions, and what steps should be taken to facilitate a transition to renewable energy sources as they become available. Whether or not certain energy sources can be integrated into the overall supply chain depends on the structure of the energy supply system as well as the form in which energy is needed by end users. Therefore, in the next section, we provide some general considerations about the main elements in the energy supply system that supports UNR. For that, we introduce the concept of direct and virtual energy, and we provide a formalism to describe and analyze the energy budget of UNR. This budget provides the basis for identifying those steps that would provide the maximum reduction in carbon emissions per dollar spent. In Sections 2 and 3 we will look at the direct and virtual energy usage with the goal to identify those elements in the energy chain that are prime candidates for reductions in usage of fossil fuels. Finally, in Section 4, we will consider different options for UNR to serve its energy needs through energy production based on renewable sources.

1 Introduction

Energy usage is by far the main contributor to carbon emissions because the main energy sources are based on fossil fuels. Reducing carbon emissions can be achieved along two main avenues: (1) reduction of energy use, in particular energy that is generated from fossil fuels, and (2) transition to renewable energy sources. These two avenues are not independent, and full utilization of renewable energy sources requires an overall concept that provides sufficient flexibility to accommodate renewable sources as they become available.

A structural analysis of the energy production and usage chain is required in order to understand how different renewable energy sources can be integrated in an optimal way into the overall energy system. The two key questions that need to be answered are: (1) What are the processes we use energy for? (2) How do we access energy? In order to answer these questions and to discuss principle characteristics of an energy concept, we take a view from the end user. This view is most appropriate for the identification of how an institution like UNR could best integrate renewable energy sources into the mix of energy sources required for energy supply to UNR.

What are the processes we use energy for? We can distinguish three main classes of usage in form of (1) lighting, (2) heating and cooling, and (3) work. While the first and second class are relatively homogeneous, the third class contains a broad range of applications, from building infrastructure and equipment, to operating different types of equipment and transportation.

The associated processes access energy in form of three principle carriers: (1) electrical current, (2) fluids/gas, and (3) solids. Today, solids contribute mainly to the generation of electricity and to heating.

The three usages listed above can take place as part of the on-campus operation (direct usage) or off-campus in order to produce products and services UNR requires for operation. For direct usage, campus has to import energy in form of electricity, fluids/gas, or solids, or produce energy in the required form directly on campus, either from imported energy in other forms or from renewable sources available on campus (for example, solar, wind, geothermal, and biomass). For the accounting of off-campus or indirect energy usage, we introduce the concept of virtual energy associated with all products and services imported by the campus. Virtual energy is the total energy used to produce and make available a material, product, or service.

A strategy for a reduction of carbon emissions resulting from energy usage will always have to address the problem of limited economic resources. Therefore, not all potential reductions are viable at any given point in time. In order to prioritize investments and make maximum use of the available economic resource, an analysis of the complete energy budget has to be carried out.

The total energy budget of the campus can written as:
(1)                   δV + δD = U + P + δS
δV = VIVE: Virtual energy, with subscripts I and E indicating import and export;
δD = DIDE: direct energy;
U: usage of energy on site;
P: production of energy on site; and
δS: change in energy storage on site.

Each term in equation (1) can be split into a part coming from or representing fossil fuels and a part coming from renewable energy. Thus, for each term we have:
(2)                   T = T(f) + T(r).
Table 6.1 gives more details on these terms and list some examples.

Considering the limited economic sources available for a slow transition of the current energy budget to one with lower carbon emissions, both reduction of energy usage and replacement of fossil energy sources through renewable sources have to be considered. For each potential measure, the reduction in carbon emission per invested dollar needs to be accounted for as well as the change in operational costs. For successful planning it is mandatory to account for the full cycle of a material, product, or service, both in terms of carbon emission and costs. The economic accounting is complicated by the fact that currently large fractions of the costs of a material, product or service are externalized (socialized) and these costs are paid for in various forms (paid directly by other individuals, other business, through governmental institutions, people in other regions or even other continents, or by future generations). There is a tendency to simplify cost-benefit analysis for actions aiming at a reduction of carbon emissions by mostly considering direct costs and gains. Partly, this is due to significant knowledge or awareness gaps. However, a land-grant university should make an effort to consider the full cost-benefit relation, including all externalized costs and virtual emissions. In some cases, understanding the full budget would require additional research, which, in an overall concept of UNR, could and should be a topic of research at UNR.

In general, a simple rule seems to suggest that energy reduction (saving) comes with a reduction of direct and externalized costs, while an increase of renewable energy production and usage normally comes with a (short-term) cost increase.

2 Direct Usage

2.1 Lighting

While centuries ago, solids and gas were key energy carrier for artificial lighting, today almost all artificial lighting is based on electricity as energy carrier. The lighting source itself, however, can be electrical filament, gas, or solid with rather different power requirements, light-emission characteristics, and environmental impacts. Likewise, some artificial lighting technologies are better suited for inside spaces while others can also be applied outside.

Table 6.1: Energy terms in the overall energy balance of an institution. Import and Export describe typical examples for an institution comparable to UNR.

VVirtual energyTotal energy used to produce and make available materials, products, or services.
Energy used to produce and supply imported materials for buildings, landscaping, and operations; equipment, food, tools, etc. M Energy used to produce or modify materials, products, and services exported from campus, including waste for recycling and dumping.
DDirect energyEnergy in form of electricity, heat, gas/oil, coal, wood, bio mass, waste for energy production.
Typically, import is in form of electricity, gas/oil, and to a limited extent, coal and wood. Other forms could be in form of heated water and bio mass. Typically, export could be in form of electricity, waste for energy production, bio mass. Could also be in form of hot water and wood.
UOn-site usage of energy Usage of energy for lighting, heating/cooling, and work; work includes all physical and chemical processes, transport. On-site energy usage includes all direct and virtual energy used for any process on campus, including dissipated energy. Careful accounting is necessary to avoid double counting.
POn-site production of energy carriers Production can be in form of electricity, heat, gas/oil, coal, wood, bio mass, waste for energy production. Production of energy refers here, for example, to on-site production of electricity, heat, or hydrogen from renewable sources (such as wind, solar, geothermal, bio-mass, wood, hydropower). In general, it would also include, for example, any oil, gas, coal or other fossil fuels available and exploited on-site, although this is not the case for the UNR campus.
SEnergy storage Energy storage can take place in form of virtual energy (in materials, products) or as direct energy. Virtual energy is stored in materials, infrastructure, buildings, etc. Not all virtual energy can be recovered. Direct energy can be stored in form of oil, gas, coal, wood, bio-mass, electricity, potential energy of water, hydrogen, heat (hot water), etc. Energy can also be stored in form of cold air available for cooling, thus reducing the energy need for cooling.

Low-energy lighting of inside spaces

In domestic households in the U.S., lighting based on incandescent lights accounts on average for 9% of the direct energy budget, and it is likely that also for UNR, lighting of insides space contributes significantly to the overall energy budget. Considering these findings, every efforts should be made to generally replace low-efficiency lighting through high-efficiency, low-energy lighting. Figure 6.1 shows a few typical lighting media and their energy requirements. Low energy lighting such as compact fluorescent lights (CFL) and light emitting diodes (LED) can greatly reduce energy consumption associated with both domestic and commercial lighting, and taking into account all costs, they can lead to significant economic savings. Compared to incandescent lamps, CFLs generally use less power for the same level of lighting: the luminous efficiency of CLF sources is typically 60 to 72 lm/W (lumens per Watt), compared to 8 to 17 lm/W for incandescent lamps. Moreover, CLFs have average life times about 8 to 15 times longer than that of incandescent lamps.

Many CFLs are designed to replace incandescent lamps and are available for most existing light fixtures. However, like all fluorescent lamps, CFLs contain mercury, which complicates disposal of used or broken lamps. It should be mentioned that in areas powered by electricity produced from coal (coal releases mercury as it is burned), CFLs actually reduce mercury emissions versus incandescent bulbs. Moreover, efforts are made to reduce mercury contents in CFLs. Nevertheless, the use of CFL requires a carefully designed concept for disposal of broken or used-up lamps.

The life time of a lamp depends on many factors, including operating voltage, defects, exposure to voltage spikes and mechanical shocks, frequency of switching on and off, lamp orientation and ambient operating temperature. For a CFL, the on-off cycle is an important factor, and the life span is significantly shorter if a CFL lamp is turned on for only a few minutes at a time.

CFLs age and over time produce less light, with the light output depreciation being exponential with the fastest losses occurring during early usage. Total loss in lighting power in the lifespan can be between 20% and 30%. However, the human eye responds logarithmically to light, and a 20-30% reduction over many thousands of hours is barely noticeable for the human eye.

Replacement of indoor incandescent lamps by CFLs also leads to a reduction of the heat produced by the lighting system. At times when both heating and lighting is required, the heating system will have to supply the additional heat previously supplied by incandescent lights. Whenever both illumination and cooling is required, the CFLs will reduce the load on the cooling system compared to what was is needed for incandescent light, thus resulting in a double saving of electrical energy.

CFLs are considered extremely cost efficient in commercial and educational buildings. Based on average U.S. commercial electricity and gas rates for 2006, Chernoff (2008) showed that replacing each 75 W incandescent lamp with a CFL resulted in yearly savings of $22 per lamp in energy usage, reduced heating/ventilation and air conditioning (HVAC) costs, and reduced labor for changing of lamps. The incremental capital investment of $2 per lamp was found to be paid back in about one month. Savings and payback period depend on electric rates and cooling requirements.

Comparing the energy budget of incandescent lights and CFLs, the higher energy demand of CFLs in manufacturing is offset by the fact that they last longer and use less energy than equivalent incandescent lamps during their lifespan. If a CFL is powered by electricity produced with fossil fuels, such a lamb may save 2,000 times its own weight in greenhouse gases.

Figure 1: The chart shows the energy usage for different types of light bulbs operating at different light outputs. Points lower on the graph correspond to lower energy use.

In the case of solid-state lighting (SSL), light is emitted from a solid object rather than from a vacuum or gas tube, as is the case in incandescent and fluorescent lamps. The solids can be light emitting diodes (LEDs), organic light-emitting diodes (OLEDs), or polymer light-emitting diodes (PLED). Compared to incandescent lights, SSL have a reduced heat generation. Available LED lamps have luminous efficacy comparable to that of CLFs, but higher levels are attainable. In laboratory studies, LEDs providing more than 150 lm/W have been demonstrated. Due to the solid-state nature, SSL have a greater resistance to shock, vibration, and wear, and typical lifespans are in the order of 50,000 hours.

Solid-state lighting is increasingly being used in niches such as traffic lights, and it is also considered an alternative for building space lighting potentially competing with CFLs. Particularly when the high luminous efficacy reached under laboratory conditions can be made available generally, these lamps will become the alternative of choice.

Daylighting for inside spaces

For lighting of inside spaces, increasingly the importance of using daylighting instead of electrical lighting is recognized. Daylighting is the practice of using natural light to illuminate building spaces. By bringing indirect natural light into the building, daylighting can provide pleasing illumination, reduce the need for electrical lighting (and thus electrical energy), and reduce costs.

In general, daylighting systems collect and distribute sunlight to provide illumination of interior spaces. Compared to artificial lighting, this passive technology directly offsets energy use for lighting, and indirectly offsets the need for air-conditioning. Moreover, extensive studies have underlined that the use of natural light also offers physiological and psychological benefits compared to rooms lit with artificial lighting.

Daylighting design implies careful selection of window types, sizes and orientation; exterior shading devices may be considered as well. Daylighting elements may be incorporated into existing structures, but are most effective when integrated into the original design of the building, taking into account factors such as glare, heat flux, and time of use. Properly implemented daylighting features then can reduce energy requirements for lighting by 25%.

However, good daylighting, requires a combination of architecture and engineering and has to be part of the design process. While there are a number of concepts to support the design processes, no fully established metrics for good daylighting are currently available. But even if they were, daylighting would still remain a mix of art and science with many environmental factors, such as climate, geographical location, building orientation, influencing the result. The apparent complexity inherent in creating appropriately lit spaces with daylighting has created a number of myths, which hamper the wider use of daylighting (see, e.g. http://www.daylighting.org/what.php). Here, we address just a few of these:

  1. Daylighting costs more: Daylighting creates less heat than electric light. Therefore, if daylighting is integrated in the design process it allows designers to downsize the air conditioning system and thus does not have to increase construction costs.
  2. Daylighting is complicated: There are now tested and tried daylighting designs available that work in most commercial and educational buildings, and these can be copied or adapted.
  3. Daylighting lets in too much heat: For daylighting the light-to-heat ratio is far better than the ratio for most efficient electrical lighting. Properly designed daylighting screens out 99% of the sun's heat.
  4. Daylighting causes glare: Glare is the result of too much light entering the building. This happens at times in all buildings with conventional lighting and this results in drawn blinds in many office buildings. Carefully designed daylighting uses window placement, shading, and low-transmittance glass to block direct sunlight and reduce or avoid glare.
  5. It's better to upgrade lighting and heating/ventilation/air conditioning efficiency: Reducing the need for electrical lighting and cooling is the most efficient way of saving energy. Since daylighting is cool, it does both. Natural light reduces the need for electrical lighting during the day and thus uses less energy for the lighting. It also reduces the heat production and thus the need for air conditioning, which further reduces the energy needed.
  6. Daylit buildings need clear glass windows: Effective lighting does not need full daylight and clear glass windows let in far too much light. Sun light is about 140 to 200 times brighter than what is needed for indoor office space. Letting in too much light creates glare and a “cave effect” where the part of the room furthest away from the window appears dark compared to the other parts. In order to reduce the contrast in the room, people often close blinds and turn on electrical lights. Therefore, well-designed daylighting reduces glare and contrasts across the room.
  7. Daylighting = skylighting: Skylighting can be an appropriate technique for daylighting, depending on the situation. For examples, hallways and very deep spaces (more than 25 feet from the window) can benefit from skylighting. However, in most cases, windows can provide the light needed. It is mainly the size and placement of windows that determine the quality of the daylighting. For example, a row of small windows near the top of the room (clerestory windows) bring in light high up in the room and create a glow of the ceiling.
  8. For daylighting to work you need sunny, clear days: Even during a completely overcast day, natural light from the sky is still 100 to 120 times brighter than needed for daylighting. In fact, at high latitudes, overcast skies can provide a better source for daylighting because it is more diffuse. At lower latitudes, daylighting is more challenging because of the intense amount of illumination, which must be reduced and controlled.
  9. There is only one correct way to daylight: There are many ways for daylighting which can be adapted to meet the needs of almost any building.
  10. Daylit buildings are all glass: All-glass buildings provide too much heat and have problems with glare. Good daylighting depends on the placement of windows and not so much on the relative amount. On average, daylit buildings have similar wall-to-window ratios as conventionally lit buildings.

Hybrid solar lighting (HSL) is an active solar method of providing interior illumination, which can be used as a complement to conventional lighting. HSL systems collect sunlight by sun-tracking focusing mirrors and transmit the light inside buildings by optical fibers. In single-story applications, HSL systems transmit up to 50% of the direct sunlight received into the building.

Considering the efficiency of daylighting in terms of reduced energy for lighting and air conditioning, UNR should thoroughly review all inside spaces in order to determine where minimal modifications would allow for efficient daylighting. HSL should also be considered as an alternative, particularly for the many spaces where direct daylight is not available.

Outside lighting

For outside lighting, in many areas, solar lights that charge during the day and are lit by light sensors at dusk are already a common sight along some walkways. Most of these lamps use SSL as light sources. Many alternatives are available but in some cases costs are still quite high. Therefore, these lights are an alternative where no connection to a power line is available and thus, solar lights offset the costs of installing a power line. For those outside lamps already connected to power lines and powered by electricity produced with fossil fuels, a more efficient solution may be to offset the fossil fuel usage through production of electricity from renewable sources elsewhere.

The use of small wind turbines for outside lighting (or other outside energy usage) is still in an experimental state. In extreme locations, such as the polar regions where sunlight may not be available for prolonged periods of months, combined wind and solar energy production in combination with large battery capacity has been developed for the powering of unmanned scientific equipment. However, such combinations are high-cost and not likely to become available for wide-spread use in the near future.

Summary lighting

In summary, lighting presents an area with a high potential for energy savings by transition from incandescent light to CFLs and, more so in the future, SSLs (in particular, LEDs). For new buildings, passive daylighting should be used as much as possible to reduce energy for lighting and air conditioning. Both in new and existing building a cost analysis should be carried out to decide whether hybrid solar lighting is feasible. The remaining electrical power needed should be as far as possible produced from renewable energy sources, either on-site (see Section 4.2) or by the supplier. In the future, a more or less general transition to LEDs as the lighting source for artificial light is likely.

2.2 Heating, Ventilation and Air Conditioning

In many cases, heating, ventilation and air conditioning (HVAC) contributes significantly to the energy budget of buildings. In the United States, HVAC systems account for over 25% and nearly 50% of the energy used in commercial and residential buildings, respectively. Therefore, HVAC has a great potential to offset a large portion of this energy through both passive reduction of energy usage and replacement of fossil through renewable sources. Similar to daylighting, maximum reduction of fossil energy use can be achieved if an overall concept for HVAC including the production of hot water is designed for new buildings. However, also modifications to existing buildings have considerable saving potentials.

In Section 4.1, we discuss details of solar thermal heat and geothermal heat as sources for heating water for different uses. Here we consider savings through reduction of energy needs. Considering that many HVAC systems in existing buildings, including many UNR buildings, are highly inefficient, combined with poorly insulated buildings and far less than optimal operational routines, the potential for reductions in energy usage are enormous. Therefore, prioritizing energy reduction over replacement of fossil source by renewable sources appears logical. The concept of passive houses provides valuable guidelines for measures that would help in increasing the efficiency of HVAC systems and reducing the energy dissipation commonly associated with HVAC systems in many residential and commercial buildings in the U.S. Although passive houses are currently on in a niche market in the U.S. (see the discussion below), the principles developed and the experience gained in Europe and other parts of the world have clarified the requirements and demonstrated the large benefit. Therefore, UNR should make an effort to promote transition to passive housing and the integration of elements of passive housing methods where possible.

Passive houses

The idea of passive houses originated in Germany in the 1970, and it is now developing into a rapidly growing market in Europe, with a few examples also available in the U.S. New European legislature requires that all new houses built in or after 2011 have to meet the passive house standards, and this will further manifest the concept in Europe. The rational for the category requirement is in the understanding that HVAC is a major contribution to the overall energy budget of a building, and passive houses reduce this fraction substantially.

Passive heating

The heating in passive houses has two main components: (1) a well insulated, air-tight house, and (2) a heat exchanger. The first component, which results from ultra thick insulation and nearly airtight doors and windows, reduces heat loss through the walls, doors and windows to a minimum. The second component ensures that used inside air can be replaced by clean air without significant loss of heat. In a fully developed passive house, these two components ensure that a passive house uses only about 5% of the energy used in a conventional house for heating. A part of the heating energy required by passive houses comes from appliances and people living or working in the house. Therefore, very little additional heat is required, which can be provided by solar energy through windows and solar collectors. If combined with solar thermal energy (see Section 6.4.1), a secondary heater can be integrated thus eliminating the need for any thermal conventional radiator.

In order to avoid problems of stagnant air and mold due to the sealed character of passive houses, which initially hampered these houses, newer passive houses include a central ventilation system to ensure sufficient exchange of inside and outside air. A central piece of the ventilation system is a heat exchanger, which ensures that the energy stored in the used but warmer inside air is transferred to the cleaner colder outside air.

Besides much lower energy requirements, passive houses exhibit also several other differences with respect to conventional houses. Importantly, temperature is homogeneous throughout the house with walls, floors and the basements having all the same temperature. Thus, thermal comfort of the inhabitants/users is greatly improved. There is no draft and air quality is also equal throughout the house. The complex windows are air-tight when closed and ensure low heat flow.

Most of the passive houses built so far globally are in German-speaking countries and in Scandinavia. There, the required parts are available off-the-shelf making building costs only 5-7% higher than for conventional houses. The additional costs are rapidly recuperated through energy savings. Therefore, many schools and other public building in Europe are now being built according to passive house standards.

These experiences show that ultimately passive house are the way to go. However, for the time being there are a number of serious obstacles that prevent the development of a broad market for passive houses in the U.S. For one, many of the required parts, including the complex windows, the low-energy-flow glassing, and heat exchangers, are currently not available off-the-shelf, thus leading to much higher building costs in the U.S. Another serious obstacle is the fact that the standard design of common U.S. homes and also commercial buildings is not compatible with passive house requirements. For example, sliding windows, the standard in many U.S. homes, are more difficult to seal than windows like the standard European window, which open like a door. In many U.S. homes, a central ventilation system is lacking. Assessing of environmental quality of housing also does not account for passive house: the LEED point system, for example, does not recognize the heat exchanger as a plus.

Passive Cooling

A potential of passive houses not explored so far is their use in warm to hot climate, where the heat exchanger could be used to keep the heat out and the cool air inside. This is a version that potentially has a large U.S. market with substantial energy savings.

Passive methods of keeping buildings cooler, often much cooler, than outside temperatures have been in use for millenniums. These “natural” methods include the funneling of cool breezes through windows, the use of evaporation from fountains to provide cooling, using building material able to absorb excess heat during the day, and avoiding heat through shading, insulation, careful choice of building orientation, and appropriate vegetation close to the building. These natural methods often take advantage of daily fluctuations in temperatures and relative humidity.

The first priority in passive cooling has to be on 'keeping cool': preventing heat from entering the building is the most efficient cooling strategy. Sunlight absorbed by roof, walls, and windows is the primary source of heat gain and needs to be combated, for example by reflective surface, effective insulation, shading (roof overhangs, vegetation, and built structures), and proper orientation of the building. Increasing roof reflectance alone can reduce the cooling costs by almost half. Since windows are the prime culprits for letting heat into the house (or out during colder days), windows should be high-performance. They need to be air-tight in order to avoid hot air from entering. Double-glazed windows with selective reflective films greatly reduce infrared energy entering the house. Proper insulation, which is relatively inexpensive, durable and works all year contributes significantly to a reduction of heat gain (or loss during colder days). Shading the house can decrease indoor temperatures by 20°F (11°C) with well-placed pants being one of the most successful shading strategies (for lower buildings) leading sometimes to up to 50% reduction in energy use for cooling. In particular, deciduous trees near the building provide shade in summer for large parts of the building surface (including also roof, walls and driveway) while they let sunlight pass in the winter. Exterior and interior shading structures also help reduce unwanted heat gain, although exterior shades are generally superior. Overhangs can be dimensioned to fully shade windows during hot periods, when the sun is high up, but to let the sun reach the windows during cooler seasons when the sun is lower in the sky. Summertime passive cooling and wintertime passive heating can be achieved through adjustable overhangs.

The shape of a building and its placing on the property also greatly impacts heat gain and thus energy needed for cooling. Depending on the prevailing climate, building material, ceiling height, size and height of windows, and compactness of floor plan are important elements to consider. Most regions in the U.S. have a climate requiring summer cooling and winter heating. In this situation, an east-west oriented axis gives maximum heat gain in winter while it reduces exposure of the building to the hot afternoon sun in summer. Moreover, in many locations, it takes best advantage of the prevailing wind directions for cooling.

Reduction of heat gain alone is not sufficient to keep buildings comfortable. A combination with passive cooling techniques, however, can be used to increase thermal comfort. Natural ventilation, usually through open windows, is an efficient means to cool interior spaces. Opening windows/ventilation during cooler nights can already contribute a lot. However, ventilation depends a lot on the choice of the window dimensions. Window design therefore has a great effect on the quantity and direction of airflow through a house. For example, sliding and double-hung windows cut airflow into half. Long, tall windows that open on the top or bottom can admit cooler air at ground level or vent hot air at the ceiling. For good ventilation, the operable window area should be 20% of the floor area with the openings equally split between windward and leeward walls. Opening windows at the lowest and highest point of the building can create a chimney effect and increase ventilation. Ventilation of the spaces that collects a lot of heat is also important. In hot, dry climates cooling by evaporation is very efficient, and fountains placed properly can be used to create cool air for ventilation into the building. Finally, coupling of thermal mass with ventilation works well in hot dry climates with large day-night temperature differences. Here, the utilization of cool nights to build a reservoir of cool air in the basement of buildings can be an efficient approach (see, for example, the WMO building in Geneva). Phase change materials can be included in the designed to extract unwanted heat during the day, and release it at night. The cooling itself can make use of passive systems, for example, with water-based systems where the water is flowing through the ground. These systems, often denoted as Earth tubes, ground-coupled heat exchanges, etc. are often a viable and economical alternative to conventional heating, cooling, or heat pumps.


HVAC (including hot water production) is an area with large potential savings both in costs and in carbon emission. Therefore, UNR should make a concerted effort to incorporate where possible elements of passive houses in form of energy reduction and implementation of passive methods. Since a number of these elements and methods are not yet standard for the U.S. market, developing sustainable skills in HVAC would benefit from a teaming up of private companies and university experts in an effort to promote this approach not just for the UNR campus but also as a basis for a more sustainable building infrastructure in the wider Reno-Sparks area. Particularly the College of Engineering could engage here and create relationships between students (internships) and companies to the benefit of both.

2.3 Work

Although many work process (transportation, operation of equipment, building processes, preparation of food, etc.) have potentials for increased energy efficiency, the main reduction of carbon emissions most likely will result from a substitution of fossil fuels through renewable sources. Where ever possible, a choice should be made for high-efficiency, low-energy processes and equipments. In support of this, UNR should maintain an inventory of high-efficiency, low-energy alternatives for equipment frequently used at UNR, so that those who have to make purchasing decision could consult this inventory.

The area of transportation deserves specific attention. On campus, for the immediate future, electric vehicles should have priority, although for a longer time perspective, hydrogen-powered vehicles appear to be a more viable avenue, particularly if these are combined with on-site hydrogen production from renewable energy sources. Electric vehicles should as far as possible be charged with solar power. In an overall balance, it is more efficient to charge the batteries at stationary solar charging station than to integrate solar panels into the car design. Therefore, using solar energy for charging of vehicles would require that these vehicles have batteries that are easy to exchange, so that “recharging” basically is reduced to the exchange of batteries at the charging station.

For long-distance off-campus use, fuel-efficient cars should have highest priority. This includes, where possible, hybrid cars.

3 Virtual Energy

Most institutions do not have direct control over the virtual energy of materials, products, and services. However, the choice between similar items should take into account the virtual energy attached to an item, not just the amount, but also the sources. Preference should always be given to products that are lower in virtual energy from fossil sources, even if this results in slight increases in direct costs. For many products, a significant fraction of the virtual energy of materials, products, and services stems from transportation. Therefore, an effort should be made to reduce virtual energy due to transport both for materials and products but also for bringing services, visitors, and staff to UNR. For materials and products frequently used on campus, it would be helpful to have inventory of these items emphasizing the virtual energy caused by long-distance travel and providing alternatives with smaller travel requirements.

It can be expected that information about the virtual energy content of an increasing number of products will be made available as part of the product specifications. For those materials, products and services frequently used at UNR, an inventory of the virtual energy associated with these items should be established and expanded as more information becomes available. Importantly, this inventory should distinguish between fossil and renewable virtual energy. Such an inventory would be an important support for those who make decision on what items to order. A frequent review of the products actually order and a comparison to those listed in the inventory would indicate to what extent UNR utilizes the potential of reducing carbon emissions through reduction of fossil virtual energy imported to campus.

4 Production

On-campus energy production will mainly be in the form of heat and electricity. In the future, production of hydrogen could also be an option. The main sources are solar and wind. The potential for on-campus production of heat and electricity using geothermal energy (except for heat pumps and passive cooling, which may be considered a special form of geothermal energy), bio-mass, and waste is limited.

4.1 Heat

Solar Thermal Energy

The term solar thermal energy (STE) denotes the technology for harnessing solar energy for thermal energy (heat). This technology uses different types of collectors to convert light into heat and to store the heat in a (fluid) thermal mass (most often, water). In many cases, STE is most effective if the heat stored in the thermal mass can be made available for several usages, for example, space heating and hot water supply.

It makes sense to distinguish three types of solar thermal collectors, depending on the temperature of the fluid medium used to store the heat: (1) low-temperature; (2) medium-temperature, and (3) high-temperature collectors. Low temperature collectors are normally flat plates, and these collectors are generally used to heat swimming pools. Medium-temperature collectors are either a set of tubes or flat plates and their main application is to provide hot water for residential and commercial uses. High temperature collectors use mirrors or lenses to concentrate sunlight, and these collectors are mainly used for electric power production. These high temperature collectors are different from photovoltaics, which converts solar energy directly into electricity.

It is interesting to note that in many countries the production of hot water for residential and commercial use is already widely based on STE, and in an increasing number of countries, STE is a mandatory element in the building code. In the U.S., however, more than 75% of the installed STE capacity is for heating of swimming pools. Therefore, a broader use of STE still has a great potential to offset carbon emissions in the U.S.

Figure 2 shows the general elements of a STE for hot water production. STE for this application is a very well developed technology. The cost-benefit ratio is very good, both in terms of direct and indirect cost-benefits. STE is easy to integrate in new buildings (and it should be a mandatory part of building codes). It is also relatively easy to add to existing buildings. STE is cost-efficient where ever sufficient amounts of hot water are required.

Systems that combine water-based heating of buildings with production of hot potable water are available. In these cases, either the thermal mass is split into two parts, one for heating and one for potable water, or a highly efficient heat exchanger is integrated, which can produce hot potable water on demand.

UNR should carefully review all systems currently in use for production of hot potable water and hot water for other uses and transition these systems to STE where ever possible. As secondary heater (see Figure 6.2), fuel cells should be considered; if not now then for future upgrades. This would allow for a combination of STE with hydrogen.

Figure 2: Typical structure of a STE system for production of hot water. A fluid (either water or another fluid) is used to transport heat from the solar collector to a solar accumulator with sufficient thermal mass. A secondary heater (gas or electricity) is available to provide heat when demand is greater than what the collector is delivering. The heat stored in the solar accumulator is used to produce hot water when needed and this water is distributed to different users, for example, washing or space heating.

Geothermal heat

Geothermal heat is an alternative where it is available nearby buildings. In this case, heat exchangers can be use to transfer heat from the geothermal fluid (often water with a number of contaminations) to water as thermal mass. Transport of either the geothermal fluid or the thermal mass is inevitably associated with heat loss and should therefore be a short as possible. This is a severe limitation for a wide use of geothermal heat. However, geothermal sources close to buildings are an element that definitely should be integrated into the system for hot water production.

Heat pumps



Before the availability of fossil fuels, biomass has been the most important source of heat for millenniums. However, combustion of biomass is associate with many pollution problems and any use of biomass for on-campus heat production would require very careful consideration of the impact of biomass combustion on the carbon cycle (see the discussion of biomass in 4.2) and pollution. If pollution can be limited, then using available biomass (which otherwise would be subject to natural degradation) instead of fossil fuels not only keeps fossil carbon out of the active carbon cycle but also reduces methane emissions effectively. Therefore, using biomass as fuel for heat production should not be generally ruled out.

4.2 Electricity

Electricity production in the U.S. is heavily based on fossil fuels (Figure 3). In 2006, a total of 70.6% of the electricity was produced from fossil fuels, 19.4% from nuclear, and only 9.5% from renewable sources. It is therefore likely that the electrical power imported to the UNR campus largely originates from fossil fuels. Consequently, any action to increase the fraction of renewable sources locally will reduce the carbon emission of UNR considerably.

In the following, we consider production of electric energy independent of its usage. The assumption is that there is a circuit that can absorb electric energy as input at any time and that is intelligent enough to ensure that the energy is stored, if not needed.

Figure 3: Sources of electricity in the U.S. in 2006 (DOE, 2006). Fossil fuels (mainly coal) were the main sources of electricity production in the U.S. Graph from http://en.wikipedia.org/wiki/File:Sources_of_electricity_in_the_USA_2006.png.

Using photovoltaic for the conversion of solar energy into electric energy is an increasingly more developed technology which has the important advantage of being easily scalable. Solar panels are scalable from small, simple panels for outside lights or the charging of small equipment to very large power plants with thousands of individual panels. Today solar panels are available as design elements of building facades, roof cover, or dedicate power generation. Therefore, on-campus production of electric energy from solar light is a fully scalable avenue to a significant offset of fossil fuels. In Northern Nevada, solar energy is very abundant and therefore an important alternative. Therefore, UNR should make every effort to steadily extend the amount of on-campus production of electricity from solar energy. Like in the case of wind energy, solar energy is a supply-driven energy, with large seasonal and diurnal variations. Intermittency is a challenge, but since in the near future solar energy will not develop into the main energy source, the electric grid will be able to accommodate variations in supply.

At UNR, where possible, solar energy should be used to charge batteries for on-site use of equipment, thus avoiding any exchange with the electrical grid. Extending this form of usage requires careful planning of a campus-wide system of equipment using the same batteries so that batteries charged in central locations can be used for a wide range of equipments. Currently, a lack of standardization and common batteries for a large set of equipments hampers the planning of such concepts, but it can be expected that such standardization will happen in the future.

A future form of storage of solar energy will be hydrogen. In this case, fuel cells (see Section 6.4.4) appear to be the means for conversion of hydrogen into electric energy. For a research institution, the still pending technical development in order to make this route fully economical is not so much to be considered a challenge but an opportunity.

Most commonly, wind energy is today converted into electric energy which is then supplied to the grid. This energy source is highly intermittent and in most locations exhibits intraseasonal and often very large subdaily variations in availability. Wind energy depends mainly on velocity and mass of the air, with the latter depending exponentially on elevation. Most wind energy is associated with infrequent high wind speeds. At any location, the potential can be expressed as wind power density.

Without considerable means of storage, wind energy is a fuel and not a capacity saver. If electricity based on wind is fed directly into the grid, intermittency and limited short-term predictability pose considerable problems for the grid operators. Different forms of storage are in use, for example, storage of the energy in hydro-power. In the future, on-site production of hydrogen may be an alternative. The first wind farm producing on-site hydrogen was opened recently in Europe, thus turning this energy into a demand-driven one. However, this development is at an initial state.

For classical wind farms, the average wind power density has to exceed a certain threshold. It is uncertain that this threshold is reached in many locations in the Reno-Sparks area. Considering the current limitations of conversion of wind energy into electrical energy and of the options for storage, as well as the associated investments, wind energy is not considered a promising candidate for on-campus energy production. However, increasingly highly efficient small wind-generators are developed, which could be an interesting addition to the mix of energy sources exploited on campus. Particularly in wind-prone places around buildings, these new turbines could be installed and thus help to offset the use of fossil fuels for UNR energy supply.

In most locations with high geothermal energy potential, this energy source has limited intermittency and is therefore an interesting addition to a energy system. In particular, geothermal energy is well suited for heating (including the production of hot water, see Section 6.4.1). However, production of electricity from geothermal energy requires considerable investments in infrastructure and operation. Therefore, on-campus conversion of geothermal energy into electric energy does not appear to be a reasonable alternative for UNR.

In principle, biomass (see Section 4.3 for a definition) can be used for generation of electric energy. In its generation, biomass extracts CO2 from the atmosphere. During processes of biodegration, the carbon is returned as a mixture of mainly CO2 and CH4 . Most energy production from biomass not only replaces the same amount of fossil fuels but also shifts the composition of the carbon emission to almost exclusively CO2. Thus, utilizing available biomass for energy production has two major advantages compared to the use of fossil fuels and biodegradation of available the biomass: it keeps fossil carbon out of the active carbon cycle and it reduces the emission of methane. Biodegradation through rotting can result in an emitted carbon mix with up to 50% methane, while open burning still produces 5% to 10% methane, while controlled combustion in a power plant results in a nearly complete conversion of the carbon stored in the biomass to carbon dioxide. However, productivity of the gathering ground around a power plant limits the size of power plants using biomass as fuels, and long-distance transports of biomass to larger power plants is not economical. Even smaller sized biomass power plants, that are increasingly common in Europe are not considered of any relevance for on-campus production of electrical.

On longer terms, fuel cells are expected to develop into a versatile source for electric energy on demand. However, fuel cells offset fossil fuels only if powered by hydrogen (see 6.4.4). Since the generation of electric energy with fuel cells also produces heat, fuel cells are used most efficiently if both the generated electricity and heat are utilized.

4.3 Bio fuels

Biofuels are solid liquid or gaseous fuels obtained from biosmass. Here biomass is defined as living or recently dead biological material that can be used directly as fuel, converted into fuels, or used for industrial production. In the context of the renewable energy discussion, biomass includes, for example, plants grown for energy or other production (e.g., wood, sugar cane, oil palms), trash such as dead trees and branches, wood chips, etc. It also includes plant or animal matter utilized for production of fibers, chemicals or heat. Biodegradable waste that can be burnt as fuel or converted into other energy carriers (e.g., gas) is also considered biomass. The term biomass excludes organic material which has been transformed over time by geological processes into substances such as oil, natural gas, and coal.

Biomass as defined above is part of the carbon cycle and thus can have an detrimental impact on overall carbon emission, if biomass production disturbs the carbon cycle, for example, through land use change (such as deforestation). Therefore, any use of biomass for energy generation needs careful considerations of the overall effect on the carbon cycle. Agrofuels, which are biofuels produced from specific crops rather than waste materials or processes, can compete with food production and thus cause serious co-lateral societal problems. In fact, a number of studies have shown that the overall impact of agrofuels is to increase carbon emission, if carbon emissions associated with land-use changes are accounted for. This and the impact on food production has let the European Commission to dramatically increase limitations on import of biofuels. In the U.S., the discussion is still on-going and a clear trend is not emerging.

On average, biofuels are most commonly used to power vehicles, heat homes, and for cooking. Two main strategies are commonly used for the production of liquid and gaseous agrofuels leading to either ethyl alcohol (from yeast fermentation of plants high in sugar) or oil (from plants high in oil content). New developments also indicate that algae high in oil content can used to convert biomass into oil. UNR is engaged in cutting-edge research in this field.

Opportunities for on-campus production of biofuels through these processes appears limited due to space requirements, except for algae, which can be exploited with much lower space requirements. UNR should continue research in this area and potentially support this through actually employing the emerging technology in pilot test site, maybe in partnership with commercial partners.

Considering the potential negative effects of biofuel production, particularly for agrofuels, on land use and food supply, importing biofuels for on-campus production of heat and/or electric energy or for use in UNR vehicles requires careful attention with respect to the origin of these biofuels and an assessment of the overall cycle. Biofuels produced out of waste biomass appears to be associated with less potentially negative impacts and should therefore be given preference.

4.4 Hydrogen and fuel cells

The combination of hydrogen as energy carrier and fuel cells for the extraction of energy from hydrogen is increasingly considered the most sustainable avenue to a clean-energy economy. Electrochemical extraction of energy from hydrogen via fuel cells is an especially clean method of meeting power requirements, particularly if hydrogen was produced with renewable energy sources. It is important to note that hydrogen is an energy carrier, not an energy source. Hydrogen must be produced by adding energy from other energy sources. Although in this process fossil fuels could be used as energy source, and hydrogen could be (and currently is) produced from (subsurface) reservoirs of methane, natural gas, coals, oil shale, a truly sustainable approach would solely use renewable energy sources to extract hydrogen from water. Combustion of hydrogen in internal combustion engines, which is similar to petroleum combustion, results in nitrogen oxides as by-products and should therefore be avoided. Hydrogen fuel cells emit only water during use.

However, hydrogen is only as clean as the energy sources are that were used to produce it. Since in the U.S. most currently available hydrogen is produced with fossil fuels, the overall energy budget of available hydrogen is heavily biased towards fossil fuels. This will be the case unless the hydrogen is produced using electricity generated by hydroelectric, geothermal, solar, wind or other clean power sources.

A comprehensive assessment of the renewable energy-hydrogen chain has to take into consideration the impacts of an extended solar-hydrogen economy, including the production, use and disposal of infrastructure and energy converters. Although there are currently a number of pending technical issues, increasingly solutions for these issues appear and promising avenues are emerging. These lead for example countries in Europe, energy producers in Germany, car builders in Japan, and airplane builders in the U.S. to invest in technology development and the building up of infrastructure for a hydrogen-based economy.

5 Summary and Recommendations

In most cases, reducing fossil fuels through reducing energy usage, both direct and virtual, will be the most cost-effective approach. Energy production based on renewable sources is currently still associated with considerable investments and should only be consider in conjunction with reduction of usage.

Currently, the most viable production of energy from renewable sources is likely solar heat, followed by solar electricity. The technology for the former is developed to a high level and advanced off-the-shelve solutions are available. Solar heat can easily be stored using water as thermal mass. Moreover, using water as thermal mass, solar heat can be combined with other energy sources (gas, oil, electricity, biomass) in order to bridge gaps with insufficient solar heating. However, full utilization requires building infrastructure that preferably uses water-based heating. Integration of the hot-water provision and heating systems increases the overall efficiency of the solar heating, since the heat stored in the thermal mass can be extracted for both uses when needed.

Currently, solar electricity would use the electrical grid for storage and bridging of temporal variations in energy availability. For specific applications, such as suitable outside lighting, portable equipment, cars and other vehicles, etc., solar energy could also be stored locally in suitable batteries.

Future alternatives include storage of supply-based renewable energy in hydrogen and the use of fuel cells for the production of electricity and heat when needed. Many studies of long-term sustainable energy concepts agree that only a combination of solar energy as the source and hydrogen as the main storage and carrier provide a viable long-term route. Therefore, UNR should focus research on this technology, and UNR should support research through a combination of research activities and pilot operational facilities.


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