In recent years there has been a large amount of research into sustainability and ways in which to “go green”, due to increased awareness and concern for the environment in which we live and the effects that we are having on it. This increased attention to environmentalism has lead to people asking the question “what can I do to help”. There are many avenues that are open to people, from hybrid cars to recycling. Two options that are slowly gaining prominence are sustainable power generation and green home. This has been for a variety of reasons, but one of the main reasons is the initial cost investment for sustainability. This site is meant to shed light on the different options available to those who wish become more environmentally friendly, and to also provide some economic information on these options.
We begin our discussion by providing options to reduce the usage of the amount of energy from fossil fuels, namely the energy provided from the local electricity grid. Three quarters of the world’s energy consumption is from fossil fuels, meaning that most of your energy is likely to come from fossil fuels . While there are many options for individual energy generation, three options immediately come to mind for feasibility, wind power, solar power, and combined heat and power generation. A final way to help the envionment is to have your home LEED certified. These options will be explored and then analyzed for the ones that are economiclly feasible.
Solar Power for Home Use
When one thinks of an environmentally friendly, economically sustainable green home, one of the first ideas that comes to mind is the use of solar energy as a source of power. Imagine the classic stereotype of this home power source – endless fields of solar panels providing power to an unusually shaped home in a remote location somewhere, most likely inhabited by some environmental extremist. Sadly, this is what many people imagine when they consider solar energy as an energy source capable of powering a house. Certainly this misconception is far from typical.
It is true, though, that one of the most obvious ways to use solar energy at home is to incorporate a network of solar cells, also known as photovoltaic cells. The function of solar cells is to convert energy from the sun into electric current. Solar cells are made of semiconductor materials, most commonly silicon. When sunlight strikes the solar cells, the solar energy excites electrons in the semiconductor. The direction of the electron motion is controlled through the use of electrodes. This flow of charge creates an electric current that can be used as a power source. The highest efficiency available today is about 40%, while typical systems have an efficiency closer to 20%. This is the basic principle of operation for a photovoltaic cell.
Of course, the electricity provided by the cell is in the form of direct current. As is, direct current is unusable in nearly all typical household appliances. To alleviate this issue, an inverter is generally used to convert direct current to alternating current. Additionally, tracking systems are sometimes utilized in an effort to keep the photovoltaic cells oriented toward the sun. The result is that more energy can be collected from the sun (approximately a 30% average increase in output), but including a tracking system increases system startup costs.
Furthermore, it is possible for such a system to produce more power than is needed by the house on which it is installed. In this case, equipment is installed that allows the excess energy to be transferred to the local power grid. If and when this happens, the homeowner is financially compensated for the energy provided to the power company.
Another issue to work around is the obvious fact that the sun does not always illuminate the photovoltaic cells, such as at night, or in the case of heavy cloud cover. In these circumstances, it is necessary to provide energy to the house through other means. Typically, a battery system is one of the subsystems associated with a photovoltaic power system. Some of the energy collected by the solar panels is stored in batteries for later use when direct sunlight is unavailable.
The diagram below illustrates the basic components of a household solar energy system and how the system works to provide power for the house.
Image courtesy of HowStuffWorks (http://science.howstuffworks.com/solar-cell6.htm)
For a typical single-family house, a total conversion to solar power is estimated to cost between $100,000 and $200,000, including parts, labor, etc. Another perspective is that it costs between $8 and $10 per watt to install a photovoltaic system. A low estimate to purchase a 15 kW system is approximately $73,000, although this does not include labor. One additional method to realize the price of solar energy is to consider levelized cost. This distributes the cost out over the system’s lifespan, and by this method, solar power costs about $0.30 per kilowatt-hour. Unfortunately, government regulations prohibit homeowners from performing self-installations of solar energy systems. Looking on the bright side (no pun intended), however, a photovoltaic energy system for a house will normally last in excess of 20 years with minimal maintenance required. The amount of time required for the system to “pay for itself,” so to say, varies widely, and is a function of the photovoltaic conversion efficiency, amount of illumination the system receives, and the overall system size.
Of course, there are advantages and disadvantages to a photovoltaic energy system. Such systems require very low maintenance. Additionally, they operate silently and have no emissions, so there is no noise or chemical pollution. It is easy to modify existing systems, allowing for expansion as needed. Furthermore, the government offers financial incentives to homeowners who choose to utilize solar power in their homes.
The main disadvantage of photovoltaic systems is the high startup cost associated with purchasing the equipment and paying for the installation. A large area of photovoltaic panels is required to provide a sufficient amount of power. Efficiency is limited by the amount of sunlight available in the given region, and also due to losses in converting to alternating current. Energy storage is also an issue, as sunlight is not always available.
For homeowners who do not want to make such a large investment in solar energy, it is still possible to use solar power on a smaller scale, in conjunction with conventional power from the utility company. One such option is a solar water heater. This device operates very similarly to a conventional electric water heater, but some or all of the electricity is provided by photovoltaic cells. A solar water heater will generally “pay for itself” within 4 to 8 years.
There is yet another method by which to utilize the sun’s energy – and it doesn’t even involve photovoltaic equipment! It is known as passive solar energy. By using green building techniques, such as designing a home to have many southern-facing windows, the sun can be used for lighting, thus saving energy to some degree. Also, lots of thermal mass of dark color should be placed on the southern face of the house. This will absorb heat from the sun, thereby reducing heating costs.
While solar energy is an environmentally friendly, sustainable power source, it is not necessarily practical in all circumstances. The greatest hindrances to photovoltaic energy are the high initial costs and the fact that it is difficult to produce enough power to exclusively power a home. However, the best bet for homeowners who want to incorporate solar energy into their homes is to use solar water heaters and also passive solar techniques. Solar power can be economically feasible to some degree, and future prospects look promising.
Wind Energy for Home Use
Energy harvested from the earth’s winds is another environmentally sustainable, economically feasible source of power for home use. Wind power is virtually unlimited, as wind can never be depleted. One method of harvesting wind energy is the use of large-scale wind farms. However, it is becoming continually easier for the average homeowner to make use of this source of power through the use of home wind turbines.
A diagram of a typical wind turbine is shown below.
Image courtesy of the US Dept. of Energy (http://www1.eere.energy.gov/windandhydro/wind_how.html)
Extracting electrical energy from the wind is a relatively simple concept. When the wind blows normal to the blades, the blades are forced to spin due to “lift”, much like blowing on a pinwheel. This turns a rotor, causing a low-speed (about 30-60 rpm) shaft to turn. This shaft is geared to turn another shaft at a higher speed (about 1000-1800 rpm). It is this high-speed shaft that runs a generator, creating electricity via induction. To provide AC power, the current produced in the generator may have to pass through an inverter. The electricity produced is typically 60 Hz, so that it can be used the same way as electricity from a wall outlet. In higher end wind turbines, a feedback control system exists, such that a wind vane and anemometer sense the wind’s direction and speed, respectively. The controller drives a yaw motor to point the rotor into the wind to maximize efficiency, and it also regulates the speed. Typical minimum operating wind speeds range between 8-16 mph, with maximum speeds at 55 mph. If the wind speed exceeds the maximum limit, a disc brake is applied to reduce the shaft speed, so that the generator is not damaged.
Wind energy is one of the least expensive sources of renewable energy, with an average cost around $0.04 to $0.06 per kilowatt-hour. Furthermore, homeowners who decide to utilize a wind turbine may be eligible for tax credits or other government incentives. The relatively high initial cost of purchasing and installing a wind turbine may seem rather high at a range between $6000 and $22,000 for a small turbine, but utilizing such a system can reduce a typical power bill by 50-90%. It usually takes between 6 and 15 years to recover the initial investment by savings on the power bill. Another monetary factor to consider involves the height of the tower. Because winds are usually stronger at higher altitudes, it is desirable to have as high a tower as possible. The downside is that a higher tower means a higher cost to the homeowner. However, it has been observed that relatively small investments in increased tower height lead to a substantially larger increase in power generation. An additional incentive to using wind energy to power a home is that excess energy (that is harvested by a wind turbine but not required for use in the home) can be sold back to the power utility company.
Wind turbines are not only beneficial from a financial perspective, but also they can be of great significance to helping the environment. Over a service lifetime of approximately 20 years, one small residential wind turbine could eliminate the creation of as much as 1.2 tons of pollutants and 200 tons of greenhouse gases that would otherwise be created by traditional power generation techniques. Because wind turbines have no harmful emissions, there are no pollutants to contaminate the surrounding air and water. Furthermore, the production of wind energy does not require the use of water as is common in the harvesting of traditional power sources such as coal and nuclear energy.
While there are numerous benefits to harvesting wind energy on an individual scale, doing so is not for everybody. One factor is the amount of property the home lies within. The minimum recommended lot size for the installation of a wind turbine is one acre. Because of the size of the turbine (typically having blades 20 feet in diameter and a tower 80 feet high), relatively large amounts of open space are necessary to ensure that there is an unimpeded flow of air to the blades.
Another disadvantage of wind turbines is that, as with most clean renewable energy sources, there is a significantly higher startup cost than with conventional systems. Also, turbines produce some amount of noise, and homeowners may not want a hideous piece of industrial-looking machinery in their yards. From a more practical standpoint though, wind patterns do not always correspond to peak electricity demand times. As a result, batteries must be used to store energy for periods of time when the wind cannot suffice to produce the required energy levels. Additionally, prime locations where there are sufficient winds tend to lie far from cities, where the power is needed.
Homeowners interested in installing a wind turbine system should take at least one year’s worth of wind data. This must be analyzed in order to predict the effectiveness of such a system, and also to assist with sizing. The following figure indicates the average annual wind power estimates for the United States.
Image courtesy of the US Dept. of Energy (http://www1.eere.energy.gov/windandhydro/wind_potential.html)
Wind turbines are a versatile power system. They can be used either in conjunction with the existing power grid, or they can be configured as a stand-alone, grid-independent system. In fact, wind turbines can be used for other purposes than producing electricity. In addition to electricity generation, wind energy can also be used to produce mechanical work, for example, to pump water from the ground or from a lake.
Wind energy for residential use definitely holds promise for the future. It is relatively cheap and also environmentally friendly, but the high startup costs undoubtedly negate this option for some homeowners. With continuing research, wind turbines can be made more efficient and priced lower, making them more affordable. Even still, they are not appropriate in all locations. The best thing a homeowner who is considering wind power can do is to take wind measurements and speak with a financial advisor, in order to determine if a wind harvesting system is technically and economically feasible for the circumstances.
Combined Heat Power
While residential fuel cells are not currently available, Combined Heat and Power systems are available. Combined Heat and Power systems typically use a fuel such as natural gas to produce the heat and electricity. Remarkably, only about 10% of the fuel is lost to the exhaust, which is as good as a high efficiency furnace. The overall efficiency can come very close to 90%, which is far better than the 30 to 40 percent produced from a central power station. These units range in power production from 1 kW to 6 kW, and the cost is about $10,000-$20,000 according to toolbase.org.
The EPA describes the CHP systems as follows: “Gas turbine or reciprocating engine CHP systems generate electricity by burning fuel to generate electricity and then use a heat recovery unit to capture heat from the combustion system's exhaust stream. This heat is converted into useful thermal energy, usually in the form of steam or hot water. Gas turbines/engines are ideally suited for large industrial or commercial CHP applications requiring ample amounts of electricity and heat.” A current CHP system is produced by Elliot Energy Systems and has equipment and process as in the following diagrams :
This system is actually a higher yield industry device and produces about 100 kW of electricity.
The CHP technology is mostly made for industries or large commercial buildings, but there is a push to have these adapted to home use, and this push has yielded some promising results. Honda announced the commencement of its retail sale of its micro-CHP system for residential homes on 04/03/2007, the freewatt™ . This unit produces 3.26 kW of heat and 1.2kW of electricity, and claims to save home owners approximately 30% of their current heating cost (assuming an 80% percent standard efficiency system). The Honda freewatt™ costs around $13,000 including installation . At that price it would take the average home owner in a northern climate about 13 to 26 years to fully pay off the cost of investment, not including inflation. The benefits of this system are its low emissions and positive impact on the environment, but the high cost is a major deterrent.
There are many ways in which to sustainably generate power for a home, but sustainability can also be addressed with other methods. The standard way to address sustainability is through “Green Buildings”, which aim to lessen the impact of humans on our environment. Green homes are validated by certification through the Leadership in Energy and Environmental Design rating system (LEED). This system has traditionally been for commercial buildings, but in January of this year the Green Building Council, which runs LEED, produced a rating system for residential homes. This rating system is based on a number of factors which total 136 credits .
•Innovation & Design Process- This is a measure of your own innovation in finding new ways to help the environment, worth up to 11 credits.
•Location & Linkages- The placement of the home in a socially and environmentally responsible way, worth up to 10 credits.
•Sustainable Sites- The use of the entire property, in order to minimize the impact of the site, worth up to 22 credits.
•Water Efficiency- Indoor and outdoor water efficient practices, worth up to 15 credits.
•Energy & Atmosphere- Energy efficiency, especially the heating and cooling aspects, worth up to 38 credits.
•Materials & Resources- Efficient utilization of materials, selecting environmentally friendly ones, and minimizing construction waste, worth up to 16 credits.
•Indoor Environmental Quality- Improved indoor air quality, and low exposure to pollutants, worth up to 21 credits.
•Awareness & Education- Knowledge of the home owner about the maintenance and operation of a green home, worth up to 3 credits.
Each of these groups can be broken up into different subgroups, with a different amount of credits given to each subgroup. The ratings of these individual subgroups are summed, to give you your total credit number, which is then used to rate your home:
There are a number of options available to address each of the categories listed above, and a good site to learn more about what you can do is . These categories are analyzed in more depth in the following sections.
Innovation & Design Process
This site is meant to give some understanding of the current state of green homes, so this section will not be covered. There are plenty of opportunities for innovation, if you are interested in this field.
Location & Linkages
Location & Linkages
This requirement can only be attained with a decent amount of research into the area that you wish to +++place your home. The site should be close to previously developed homes, water lines, bike trails or roads (to reduce dependence on auto mobiles), and have open spaces for encouraging group activities. This may be feasible if you don’t already have a home and are trying to decide where to build one, but is impractical if you have a set location in mind or if you are updating your home.
Sustainable sites can also be thought of as sustainable landscapes, and how the land can be used to improve the environment. The idea of the sustainable sites can be broken up into 8 major goals :
1. Lower Greenhouse gas emissions
2. Lower the “Urban Heat Island Effect”
3. Promote biodiversity
4. Lower the amount of water waste (due to lawn irrigation)
5. Reduce water pollution (less pesticides on other plants than what is used on grass)
6. Reduce yard waste
7. Increase the public health (plants calm people and make them feel safer, cleans the air)
8. Reduce energy consumption (use local plants to cut down on energy for transportation)
These goals can be accomplished through the careful selection of a variety of plants. Picking the correct types of plants can save you money due to lower irrigation costs as well. The fulfillment of the sustainable site goal will be different depending on where you live. This is an economically feasible idea, because the plants should be of local varieties, so they have a low transportation cost and should not be expensive.
To increase water efficiency there are a number of options available. One of the options is to use a greywater system. Greywater is water that is used in the house and captured for further uses later on, excepting toilets. Home water use percentages can be seen in the next figure, which shows the possibilities for reclaiming the non-black water.
The benefits of this system are as follows :
• Lower fresh water use
• Less strain on septic tank or treatment plant
• Greywater treatment in topsoil is highly effective
• Less energy and chemical use
• Groundwater recharge
• Plant growth
• Reclamation of otherwise wasted nutrients
The best (and typically safest) use of greywater is for irrigation of plants and a garden, which allows you to make your own vegetables, in an environmentally friendly manner. These systems can save $5-$20 a month, but they cost over $1,500 . This is clearly not an economically feasible system in the short run, and should be avoided if you have a tight budget.
There are a number of smaller scale water saving techniques. Most showers can be outfit with water conserving heads, which limit the amount of water that flows through the opening . These shower heads cost about $15 dollars, which clearly makes them an economically feasible solution for those on a tight budget.
You can also save water by planting drought resistant plants, so that they do not need to be watered as much. These plants cost about as much as other plants, but are cheaper to keep irrigated and so they save you money.
Energy & Atmosphere
There are many ways to save energy and reduce emissions, but the primary energy generation techniques have already been covered. Saving energy once it has been generated is also important, hence the idea of the improving the house shell. The idea is to keep the heat or cool air inside the house and to prevent their loss to the environment. One of the methods for accomplishing this is through the use of Polyurethane Foam as a roofing agent. This creates a continuous layer of insulation that prevents the thermal bridging from traditional roofing materials. It is also coated in a white reflective material that prevents even more energy absorption . The same idea is present in the use of spray polyurethane foam insulation, which can save up to 20%-40% of energy use. Plastics can also be used as windows, which have a lower thermal conductivity than traditional building materials . Some doors with a core of foam plastic can be used to insulate the house . Most of these energy saving techniques are not economically feasible if you already have a home, but they are certainly feasible options for new home construction, and prices vary from contractor to contractor.
A cheap but effective way of reducing heating costs is to increase the insulation on your pipes. Adding a half-inch layer of foam insulation to your pipes can save you about $25 dollars per year. Another way to save energy is to replace your light bulbs with fluorescent lights. For example, you can save about $60 per year if you replace your five most used light fixtures . These options reduce the amount of emissions from a natural gas heater, or the emissions from producing the electricity for an electric heater or lighting . Clearly, this is economically feasible step down the green path.
Materials & Resources
Your home construction can have a very large impact on the environment, or a small one, depending on the materials that you choose. Steel and aluminum can be recycled and used again for construction purposes. Recycled steel saves 50-70 percent of the pollution from creating new steel, while aluminum saves almost 85 percent. Steel has long been the most recycled material in America, so lots of steel products contain recycled steel. A recent trend has been the use of steel framing for buildings. A 2,000 square foot house uses between 40 and 50 trees, which is quite a bit of forest .
Timber can also be recycled for reuse in a home. There are two types of timber recycling. The first is to reuse old pieces of wood for new purposes, like old doors cut down to make fence posts . The other way is to actually use timber that is recycled. Recycled timber is not nearly as popular as recycled steel, but there is a market for it, and reused hardwoods have a beautiful and antiquated look. The old timber typically comes from wharves or bridges, and is then re-milled for the desired purpose.
An overarching theme of construction material selection should be to use local materials, so that their transportation pollution is minimized. If you are going to build a new home, choosing the correct construction materials can go a long way to making it environmentally friendly, at an initial cost that is not much more than normal construction methods.
Indoor Environmental Quality
A popular choice for controlling the indoor air quality is through the use of indoor vinyl wall coverings. Oil based paints can have up to nine times the Volatile Organic Compounds that a vinyl wall covering would . These may sound like they would look terrible, but they can actually be produced very tactfully. These can cost anywhere between $2.00 and $30.00 per yard, which can be affordable for any price range.
Awareness & Education
This requirement is put in place to ensure that all the above requirements will be maintained. The tenant or owner must know enough about the system they are running to ensure that it is kept up to standards, through maintenance and repairs. This also includes public awareness, which means advertising that you have a sustainable home or publishing a website with information about your home. This is important to help promote LEED initiatives and environmentalism.
The three energy generation options that were discussed are more efficient than producing the electricity by current means and transmitting it to the house. One of the main reasons is because the losses due to power transmission over the electric grid to your house can be upwards of 30% . These power generation systems can pay for themselves in a number of years, but they all have a large start-up cost, for a reasonably sized system. If you have the money, and you truly care about the environment, then these would be good options for you. If you don’t wish to generate your own power but you wish to help the environment, your own home can be certified as a Green Home if meets the criteria of the checklist at the U.S. Green Building Council’s website . The truth is that you can spend almost as much money as you want on creating a green home, but there are a number of things that you can do with a reasonable budget, below about $1000:
• Use vinyl wall covers instead of oil based paints - $2 per square yard of cover
• Plant low water consuming plants – Price depends on area, but you can use local plants
• Insulate hot water pipes – less than $0.25 per foot
• Switching light bulbs – about $7 per bulb (varies by wattage)
• Water limiting shower heads – about $15 per shower head
• Education – knowledge will help you as much as all the above ideas and the best part is that it is free!
Sources and Suggested Readings on Solar Energy
Sources and Suggested Readings on Wind Energy