Wind and sun energy are underutilized in most homes. Wind power can be used to ventilate your home or generate electricity. Sunlight may be used to light your rooms, heat your hot water, warm your home, and generate electricity.
The practicality of renewable energy varies widely by climate zone. New England produces lots of wind, but only a few sites are good for windmills. Kansas is an excellent place for windmills and wind is scarce. Florida is great for sun, but poor for wind.
The average USA household uses 11,000 kWh of electricity per year. In Florida, with high demands for air conditioning and water heating a household may use 20,000 kWh.
Solar generated hot water is mainly used to heat swimming pools and household water. In cool climates it is sometimes used for home heating. Typically solar hot water systems are paired with a gas or electricity backup.
Many have first experienced solar hot water while running their garden hose. Sunlight striking the hose surface is transformed into heat. The heat travels through the hose wall and heats the water inside.
In a similar way, solar hot water collectors transmit the sun’s energy to tubes, pipes or tanks of water. Some hot water collectors are made of plastic; others are metal. Some are open to the air; others are enclosed in insulated boxes or evacuated glass tubes. All collector surfaces are dark to absorb maximum solar heat.
“Passive” systems require no pumps. “Active” systems pump water or anti-freeze heat exchange fluid back and forth between a solar collector and a storage tank. Active systems use thermostatic controls to operate pumps and valves. The Florida Solar Energy center website has a good description of the types of household solar heaters http://www.fsec.ucf.edu/en/consumer/solar_hot_water/homes/system_types.htm
Solar pool blankets are basically big sheets of bubble wrap, only more durable and resistant to the UV rays of the sun. They can raise a pool temperature 10o to 15o F over a comparable non-heated pool. Some people use solar blankets, instead of mechanical pool heating, to extend their swimming season.
The Florida Solar Energy Center (FSEC) recommends that if you heat a pool, use a pool blanket: “Not to do so is much like heating a house without a roof – the heat just goes right out the top. Use of a cover retains more than two-thirds of the collected heat needed to maintain a comfortable swimming temperature” http://www.fsec.ucf.edu/en/consumer/solar_hot_water/pools/sizing.htm).
If natural gas is used to heat a 15 by 30 foot pool, a solar pool blanket could save thousands of dollars in annual heating costs. If solar heating is used a pool blanket would reduce the required collector size by 50%.
Solar pool blankets have other benefits as well: They reduce pool maintenance costs by slowing evaporation of both water and chlorine. They also lower the amount of pool debris.
For safety, pool blankets should be completely removed before swimming. Manual and powered rollers are available for removing and replacing the cover.
The average USA household uses 11,000 kWh of electricity per year. In Florida, with high demands for air conditioning and water heating a household may use 20,000 kWh.
Photovoltaic (PV) systems which produce electricity from sunlight, are used to meet some or all of this demand. A system rated at 2 kilowatt peak capacity can produce 3,600 kWh annually; a 5 kilowatt system 9,000 kWh.
The heart of a photovoltaic system is the 1- to 4-inch silicon cells which convert sunlight into electricity. They produce 1 or 2 peak watts of power each. These cells are wired together and grouped into panels which are supported by mounting hardware.
A stand-alone PV system has a charge controller and batteries to store electricity. A grid-connected system has an inverter which converts the direct current, generated by the panels to regular household alternating current (ac). It also has a meter which allows a homeowner to sell back excess current to the utility.
A PV solar cell is a semi-conductor. It consists of a sandwich or two types of treated (doped) silicon. The “N” negative side of the silicon sandwich is an election donor. The “P” positive side is an electron acceptor. The “N” and “P” sides have electric contacts and are connected together to form an electrical circuit.
A current is generated when solar photons dislodge electrons in the sun-facing “N” side, which subsequently gravitate to the lower “P” side. This electron movement creates a current which is captured by the electric contacts on negative and positive sides of the cell.
In a LED light, also a semi-conductor this principle works in reverse. An electrical current goes in and light comes out, when electrons moving from the “N” side reach the “P” side.
Currently, commercial PV systems convert 10 to15% of sunlight into ac electricity. Systems with 30% efficiency are being developed. A 15%-efficient one kilowatt system would have with 67 square feet of panels, producing up to 1,800 kWh annually.
The basis for the PV efficiency rating is the comparison of solar power density with ac electricity output. The brightest noon-time summer sun illuminates one square foot of collector with 100 watts of light; the day/night annual average (e.g., in Florida) is 20 watts of sunlight per square foot. At 15% efficiency, one square foot of PV panel (in Florida) produces 15 watts of ac peak power in blazing sun; its annual average output is 3 watts (26 kWh/year).
PV systems produce the most power on hot summer days, which is a good thing. This is exactly when home air conditioner usage and grid peak demand is highest.
PV systems have a bright future, and will be seen on buildings everywhere. PV solar panels are becoming more efficient and more widely mass produced. Electric rates are rising, while the cost of PV power is falling. The time will come when home PV power will be cheaper than grid-supplied power.
For self-reliant Americans, wind turbines are a powerful symbol of energy independence. Wind turbines installed in rural and semi-rural yards are typically sized to deliver 30% or more of an annual home’s energy use of 11,000 kWh.
Wind is created because the sun heats the Earth unevenly, due to the seasons and cloud cover. This uneven heating, in addition to the Earth’s rotation, causes warmer air to move toward cooler air. This movement of air is wind.
Wind turbine use in the U.S.A. has a grand tradition stretching back 150 years. In the American Midwest between 1850 and 1900, a large number of small windmills, perhaps six million, were installed on farms to operate irrigation pumps.
Starting in 1927, 30,000 Jacobs windmills were installed in rural areas which had no central electrical grid. With propeller diameter of 15 feet, the Jacobs windmills generated 5,000 to 6,000 kWh/year in windy western states. The electricity generated was stored in batteries.
This lucrative market for farm wind generators deteriorated when the rural electrification project started in 1936. Grid power distribution provided a farm with more dependable usable energy for a given amount of capital investment.
In the 1970’s, small wind started coming back. “Living off the grid” was the mantra the 1970s back-to-the-land movement. In the 21st century, increasing energy prices and global warming are again heating up the home wind market. Today’s wind pioneers install their home and farm generators for oil independence, carbon neutrality, and green jobs. The small wind turbine market has blossomed since the implementation of President Barack Obama’s federal stimulus plan, which gives homeowners a 30% tax break (with no cap!) for installing a wind turbine before December 31, 2016.
We are in another golden age of small wind innovation. A web search will reveal the most fascinating efforts to make small wind turbine more efficient, affordable, and quieter. For fun, check out the innovative vertical axis turbine designs is at http://peswiki.com/index.php /Directory:Vertical_Axis_Wind_Turbines. The United States sold almost half of the small wind turbines installed worldwide last year, netting $77 million of the $156 million made globally.
Where is Wind Power Practical? The small-turbine industry market is farms, shops and homes in rural and semi-rural areas. A wind-turbine is most practical in breezy open areas. Space is needed to allow unobstructed wind flow, site a tower, and to prevent noise and vibration impacts. A wind turbine operating at low rpm will generate less noise and may be safer.
Installing a home wind turbine is not a simple undertaking. You need to carefully assess its feasibility and design for your site and budget. Wind systems are big capital investment. According to the American Wind Energy Association turbines cost between $6,000 and $22,000 installed. The typical annual return on investment ranges from 5 to 15% depending on your average wind speed and system design
Windmills do most of their work at 10 to 20 miles-per-hour (mph) wind speeds. Table 1 shows that average winds in excess of 10 miles-per-hour are necessary to make the most of your investment. Also, that a turbine of at least 12- foot diameter is necessary to make a big dent in home electrical use.
Conclusion: No doubt about it. Picking out a wind turbine is not like picking out an Energy Star refrigerator. There is no sticker on the label which will tell you how much power it will produce and at what life-cycle cost. It is very challenging to predict turbine performance in your particular backyard.
The small wind industry is not mature. Wind turbines are expensive and independent testing for performance is not keeping up with innovation. So it is a challenging for a consumer to pick the best engineered turbine for their site and budget.
Technical Factors for Calculating a Wind Turbines Performance: The following is intended to introduce the key technical factors which will influence the performance of a wind turbine.
Wind Speed and Tower Height: Potential wind power is surprisingly sensitive to wind speed. Table 1 shows that a 15-foot wind turbine might generate 1,172 kWh/year in an 8 mph wind, and 9,376 kWh/year at 16 mph. For each 50% increase in wind speed, the potential wind power increases over three-fold! For each doubling of wind velocity the power increases eight-fold.
Dark Blue = More annual wind to White = less
Wind turbines are often mounted on 50 to 100-foot towers because more wind is available high up than on the ground. Doubling the height of the tower increases the wind speed by 10% and the expected power yield by 34%.
Assessing a site’s wind power potential can be tricky and expensive. Published wind maps are a starting place for wind prospecting. However, there is no substitute for local field data with anemometers in place for a year or more. Measurement of wind speed at different tower heights will assist in the choice of optimal tower height for cost-effective performance.
Swept Area: The area: which catches the wind is called the “swept area. For example, the circle of 15 foot diameter windmill defines a swept area of 176 square feet.
Air Density and Altitude: Air is not so thin. Its density approximates 2 pounds per cubic yard or 1 kilogram per cubic meter. This is why it can turn huge wind turbines. In high altitude areas of Colorado air density and turbine performance is reduced by 20%.
Wind-Turbine Efficiency: Let the buyer beware. Based on independent tests, some windmill manufacturers overstate the annual kWh production of their wind turbines. Very small turbines might convert as little as 10% of the wind’s energy into plug power. Home-size turbines capable of generating 2,000 kWh/year or more might have a 20-25% conversion efficiency. Large commercial wind turbines might have a 30% conversion efficiency, and be capable of producing 4 million kWh/year– enough to power 350 homes! The highest theoretical efficiency of any wind turbine is only 59% according to Betz’s Law. Conclusion: Read independent testing reports and pick the brains of knowledgeable experts.
Electrical System Design: A home wind system can produce standard AC current directly, and be tied into the grid. Alternatively, it may store the electricity in a battery bank prior to its conversion (via an inverter) to standard AC form. Grid systems have a higher overall efficiency.
To view the DOE’s EERE wind site: CLICK HERE
Hydro-electric power is wonderful gift of the sun god. Each year the sun’s huge power evaporates the equivalent of a 3-feet layer of water covering the earth. When this water comes back down again as rain, snow, etc. gravity pulls it down mountains, hills and valleys and finally to the sea. This is the basis of hydro-power: the energy of water moving from a high place to a low place. This is known as potential energy.
Let’s take this idea down to earth. Suppose you constructed a large cistern, the 90,000 cubic-feet volume of your home, on a 50-foot hill above your home. The water would contain a potential energy of 18 kWh. Suppose that you: 1) drained the cistern in 24 hours at a rate of 1 gallon per second, and 2) directed the water through a micro-hydro-electric water turbine located in your home. The gallon-per minute flow would carry a mechanical energy of around 600 watts; of this amount 300 watts (50%) would be converted to electricity. Over the course of a day, your turbine would generate 9 kWh of electricity, about 30 percent of an average home’s energy use.
Micro-hydro Systems for Homes: A parallel example, will illustrate the requirements for home hydro power. Suppose you diverted stream water into a water pipe which runs down a horizontal distance of 200 feet, and a vertical distance (or head) of 50 feet. If you connected the lower end of the pipe to a hydro-electric water turbine you could generate 300 watts of electric power at a flow rate of 1 gallon per second.
You could double your harvest to 600 watts by doubling the head to 100 foot. If, at the same time, you also doubled the pipe’s water flow to 2 gallons per second you could harvest 1,200 watts. Over the course of a year you would generate 10,500 kWh/year– enough electricity to run the average U.S.A. home.
The most commonly used “impulse” style hydro-electric turbine uses a nozzle at the end of the pipeline that converts the pressurized pipe water into a fast moving jet. This jet is then directed at the turbine wheel, the shaft of which is connected to an electric generator. The water passing through the turbine is re-directed back into the stream.
A home micro-hydro system can produce standard AC current directly, and be tied into the grid. Alternatively, it may store the electricity in a battery bank prior to its conversion (via an inverter) to standard AC form.
The net result: You just borrowed the energy from the water. Hopefully you designed your system so that it will not harm the fish and other life in the stream while you borrowed that energy.
Planning for Micro-hydro: Micro-hydro is not a simple plug and play device. You need to carefully assess its feasibility. Is it legal in my jurisdiction, and under what conditions? Is there enough stream flow to make it worthwhile? Can I harvest the energy without harming stream ecology. What is the best configuration of the system for my site? Will it pay its way? The annual return on the investment typically ranges from 5 to 20% depending on your location and system design.
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