Interest in Net Zero Energy (ZNE) buildings is growing around the country—this fall Santa Monica voted to approve the world’s first ZNE building requirement for new single family homes and Boise unveiled Idaho’s first commercial ZNE building. But while ZNE buildings are an energizing concept that is broadly accepted, there is little information on what is required to actually meet these goals.
In Design Professional’s Guide to Zero Net Energy Buildings, Charles Eley presents a practical, accessible guide to developing ZNE buildings. Based on Eley’s 40 years of experience as an architect and mechanical engineer, as well as interviews with other industry experts and data from select ZNE buildings, the book:
- Describes how building energy use can be minimized through smart design and energy efficiency technology, and presents practical information on how to incorporate renewable energy technologies to meet lowered energy needs;
- Identifies the building types and climates where achieving ZNE will be a challenge, and offers solutions for these special cases, and;
- Discusses how ZNE can move beyond premium buildings to work for shopping center developers, school districts strapped for funds, and other mainstream buildings.
A preview chapter is available below:
Design Professional’s Guide to Zero Net Energy Buildings by Charles Eley © Island Press In the Design Professional’s Guide to Zero Net Energy Buildings, Charles Eley draws from over 40 years of his own experience, and interviews with other industry experts, to lay out the principles for achieving zero net energy (ZNE) buildings, which produce as much energy as they use over the course of a year. The book shows the reader through examples and explanations that these solutions are viable and cost effective. You can order the book at the Island Press website as well as Amazon, Barnes and Noble, and your local independent bookseller.
CHAPTER 3 Here Comes the Sun
The Future of Renewable-Energy Systems. It is not possible to completely eliminate energy demand in our buildings. Energy utilization indices (EUIs) will never go to zero through smart building design alone. We need to heat our buildings when it is cold and cool them when it is hot. We need to power our computers and other equipment. Lighting can be minimized through daylighting, but not eliminated altogether. We do need energy—just not as much as we are currently using. This chapter shows how we can produce what we need without using fossil fuels and without adding carbon dioxide (CO2) to the atmosphere.
The Potential of Renewable Energy The energy we receive from the sun is vast. In a little less than twenty-six minutes, the earth receives enough energy to power the global economy for a year.1 An area about fifty miles by fifty miles square (roughly 2 per-cent of the state of Colorado) receives enough sun to continuously and cleanly power the United States economy at our current rate of energy use.2 And this is before we do all we can to reduce our energy consumption. These are theoretical numbers and assume that the process of turning solar energy into electricity is 100 percent efficient. NREL has made a more realistic estimate that takes our current technology into account.3 NREL estimates that to produce all the energy to power its economy, the United States would need to take about 0.6 percent of the total United States land area, or about 2 percent of the land area now used for crop production. To look at it another way, we would need about 1,000 square feet of collector area for each person.
The annual sunlight that arrives at a building site is greater near the equator and less in northern (and southern) latitudes, but of course it is also affected by sky conditions. Figure 3-1 shows the variation in annual insolation (exposure to sunshine) in the United States. The southwestern portions of the country have the greatest solar potential, especially the desert areas of southern California, Nevada, Arizona, and New Mexico. These are areas where large, utility-scale solar power plants are now being constructed. The areas with the least annual insolation are the northern states around the Great Lakes and western Washington around Puget Sound. Alaska has the least insolation because it is so far north. Hawaii, of course, is bathed in sunlight. The data in figure 3-1 is expressed in average daily kilowatt-hour of energy per square meter of collector surface area facing south and tilted at an angle equal to the latitude of the location.
Figure 3-1: Annual Average Daily Insolation in the United States (W/m2) This map displays the average daily solar exposure (insolation) on a surface facing south and tilted at an angle equal to the latitude of the location. (Source: National Renewable Energy Laboratory.)
Direct energy from the sun is the purest form of renewable energy. It is extremely reliable and non-depletable, but variable. For any given spot on the planet, we have sun during the day but not at night. We receive more sun in the summer and less in the winter. We receive more energy on sunny days and less on cloudy days. Dealing with the variability of sun-light is a challenge, but it is not insurmountable. As we transition toward an economy powered by solar energy, our utility grids will be able to buy the excess energy we produce during the day and power our lights at night when the sun is down. In the short term, serving this energy storage function will actually benefit most utilities, since the times when insolation is most abundant align with times when the utility is experiencing its peak loads. In the long term, we will incorporate batteries and perhaps other forms of energy storage in our buildings.
Some buildings are already doing this. The RMI Innovation Center (see appendix) has a set of batteries with a capacity of 45 kWh (about half of the battery capacity of a Tesla automobile). Banks of these batteries can be used to even out the daily demand for power in small buildings. In the future, some of this storage function may be performed by our electric cars when they are plugged into the grid.4
Other forms of non-depletable renewable energy include wind energy, geothermal energy, and ocean tides and waves, but the sun is the driving force behind these forms of energy as well. Wind energy is a significant contributor to the energy grid here and in many other countries. In the United States, wind represents 5.7 percent of the installed electricity generating capacity at the national level, and in Iowa and South Dakota more than 25 percent of electricity generation is from wind.5 Modern wind tur-bines are quite large and very different from the windmills used to pump water on your grandfather’s farm. Each requires 15–20 acres of land. A typical wind turbine has blades over 100 feet long and a total height of over 300 feet—and the next generation could be even bigger. Each is rated to produce 1.5–2.0 megawatts (MW) of peak power.6
Wind is also variable, but in a different way from solar. The sun does not heat our planet evenly because of the Earth’s rotation and shape. This results in different atmospheric conditions. When there is a difference in air pressure between one area and the next, this causes the air to move from the high pressure area to the low pressure area. We call this moving air the wind. While it is driven by the sun, wind does not start at dawn and stop at dusk. In coastal areas, the wind blows from sea to land throughout the day, especially in the afternoons. At night, the direction often reverses, but wind turbines work no matter the direction of the wind. There are many other complexities as well that affect the speed and direction of the wind.
1. The Earth receives about 8.2 million quads of energy a year, or 936 quads per hour. The energy of the world economy is on the order of 400 quads per year. This means that in about 26 minutes (calculated as (400/936)Í60), we receive all the energy we need.
2. The sun produces about 12.2 trillion watt-hours per year per square mile. This works out to be 0.042 quads of energy per year per square mile (12.2Í1012 Wh Í (3.412 Btu/Wh) / 1015 Btu/quad). Sunlight arriving over an area of 2,400 square miles is about equal to current United States energy consumption. This is an area about 50 miles square, or about 2 percent of the state of Colorado. For the source of the data on 12.2 trillion Wh per year, see: http: //www.ecoworld.com/energy-fuels/how-much-solar-energy-hits-earth.html.
3. Denholm and Margolis, “Land-Use Requirements and the Per-Capita Solar Footprint for PV Generation in the United States,” Energy Policy 36 no. 9 (August 2008): 3531–43.
4. Electric vehicles (EVs) are currently designed to take power from the grid, but to date, none have the capability to provide power to the grid. Providing power in both directions would require a redesign of the current generation of EV chargers.
5. The Wind Energy Foundation publishes data from time to time on the industry. See: http: //www.windenergyfoundation.org/interesting-wind-energy-facts.
6. The widely used GE 1.5-MW model, for example, consists of 116-foot blades atop a 212-foot tower for a total height of 328 feet.