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Enota Solar Design Project
Proposal
Submitted by:
Department of Electrical & Computer Engineering Tennessee Technological University Cookeville, TN 38505
To:
Dr. Suan Freed Enota Mountain Retreat Hiawassee, GA 30546
Faculty in Charge:
Ali T. Alouani, Professor of ECE
October 2008
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1. Abstract In an era of high energy prices, many decision makers are looking to use alternative sources of energy and to educate the public to do the same. Such is the case of Enota Mountain Retreat. This study’s objective was to implement the optimal solar power system for Enota and create an informational display to educate their visitors. There are hundreds of off the self solar systems but they are not optimized for individual applications. In this proposal we offer several specific solutions, with varying prices, for Enota to choose from. In the conclusion we suggest our optimal solution.
2. Introduction Enota Mountain Retreat is located in Hiawassee, Georgia. “Enota is a non-profit conservation facility committed to preserving our beautiful land with a limited number of accommodations including cabins, full hook-up RV sites, pop-up & tent sites and a Retreat Center for conferences, groups, events and seminars. Enota is rated to be in the top 100 camping destinations in the country. [1]” Enota approached Tennessee Technological University with two alternative energy projects. These projects were for the design of a hydro power plant and for the design of a solar system. The solar system was to be implemented into one of the log cabins that are available for rent to Enota visitors. This project benefits Enota in two ways. First, this system will lower the total energy usage from the grid which also leads to a smaller carbon footprint. Second, this system will have an educational display to teach visitors about solar energy. The display will show visitors how solar energy is harvested and used, the many different applications of solar energy and how cost effective the system can be. A solar panel absorbs the energy of sunlight in the form of electrons. These electrons are directed in one direction across the panel which creates a direct current, DC. Solar cells were first produced in 1883 by Charles Fritts [2]. Scientists at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have set a world record in solar cell efficiency with a photovoltaic device that converts 40.8 percent of the light that hits it into electricity. This is the highest confirmed efficiency of any photovoltaic device to date [3]. There are three common types of solar systems. An off-grid system uses a bank of batteries to store excess energy for use when needed. A grid-tied system is used to sell excess energy back to the electric grid for credit and a hybrid system is grid-tied with battery backup. The hybrid system is meant to be self sustaining but if needed, can draw extra power from the electric grid or sell power back. The basic components that make up a hybrid solar system are; the solar panels, batteries, inverters and charge controllers. The solar panels charge the batteries while in sunlight. The charge controller determines how much power the batteries need to reach full 2
charge. The inverter converts the direct current from the batteries to an alternating current for use in the residence and also determines when to switch from battery to grid power. Energy has become one of the highest commodities in today’s market. Numerous people rely on energy and that number increases every day. The race is on to produce as much energy as possible. However, until recently energy has been heavily derived from nonrenewable fossil fuels. Many believe the only solution to our growing energy needs is to build an energy infrastructure of renewable energies. The most common renewable energies are solar, wind and water. The current downside to these renewable sources of energy is that the systems have to be quite large to produce a significant amount of energy. However, these systems can be scaled down and used in applications such as small energy efficient housing or rural areas where power distribution is not available.
3. Literature Survey In designing a solar power system for the cabin at Enota, we are using the newest most cost-efficient technology. However, to understand new more efficient methods we researched past projects. By doing so, we can learn from others mistakes and hardships. By understanding the difficulties we will face, we can be better prepared for them. The following are two examples and tips from other solar projects. Rockriver [4] Looking through some do-it-yourself documents we found the detailed experience of Shane from Rockriver. Shane wanted to become more self sufficient and decided to start with a solar system consisting of 4, 190 watt solar panels. He documents his experience very thoroughly on this website and has a few tips we can take from it. Shane says he lowered his average monthly electric bill by half in just two steps. His first step was to change the incandescent light bulbs to compact florescent and second was installing timed power strips on the electronic devices with phantom loads. “A phantom load is when a device is plugged into the wall and is turned off but still uses power when turned off [4].” The rest of the installation is mostly straight forward and standard but he offers one other tip about panel positioning. “It is recommended to tilt your panels to equal your latitude and then for winter months add 15 degrees to the tilt and in Summer Subtract 15 degrees from the tilt [4].” Bob’s Solar Project [6] Bob Goodsell undertook a project similar to ours, installing a PV system with battery backup [5]. One of the major disadvantages to Bob’s design was that he did not incorporate net metering, or selling power back to the grid [6]. During sunny days when the batteries were completely charged, the rest of his power was just wasted. Our system is designed to have the capability to net meter, thus selling excess power back to the power company. Another issue Bob ran into is the overheating of his solar panels. The conversion of sunlight to electricity is dependent on the temperature of the panels. If the panels get too hot, the output will go down. He used the solar shingles directly mounted on his roof, with no air gap behind them and no aluminum frame to dissipate heat. Because of this, his output in May was higher than in July. Our system utilizes panels with aluminum frames to help dissipate heat. Also, both mounting options have a sufficient air gap under the panels, keeping them at a 3
normal temperature. Also, Bob used flooded non-sealed batteries. Thus he has to maintain the water level of these batteries to prevent damage or battery failure, as well as vent dangerous fumes out of his house. Our system uses sealed batteries, so there is never any off gassing or need to check any fluid levels.
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4. Conceptual Design
For the conceptual design, there are a few major components that are needed. First, a load calculation is needed to determine how much power is needed. Then one can determine the types of panels and the layout of the panels. Also, one needs to determine the type of inverter, safety disconnect, batteries, and battery charger. For the data output, a computer and display will be used, and a brochure will be given for educational purposes.
Cabin Layout before Solar System
Typically for a load calculation you look at old power bills to estimate usage. However, this location has no old power bills as it shares a power meter with another building. Thus, we made a list of all appliances in the cabin and their power ratings. Then we estimated how long per day each appliance would be used. This gave us the power use of each appliance per day. We then separated the appliances into groups. Our appliance groups were small, medium, and large. The small appliances are thing such as lights, electronics, microwaves, etc. The medium appliances are things like the air conditioner. The large appliance group has the oven and the water heater. We used these appliance groups to develop three different systems that will all meet the requirements. The first system, referred to as the large system, is running the entire cabin (all appliance groups) exactly as is. This requires a system with an average daily output of 13.4 kW per day. About half of this energy is going to the large appliances, which are the hot 5
water heater and the stove. These appliances also require a special 240 volt, two phase inverter. Next, the medium option is the most cost effective solution: to convert the large appliances (stove and hot water heater) to natural gas, and then run the rest of the cabin (all the other groups) off of a 7.4kW solar system. Since natural gas costs about $9.00/1000 ft^3 and contains 1,030 BTU/ft^3, [7] natural gas costs $0.00000874 per BTU. Electricity costs about $0.12 per kW, and since one kW = 3414 BTU [8], electricity will run about $0.0000351 per BTU. Thus natural gas appliances will cost about one forth as much to run for an equivalent amount of use. Tankless hot water heaters can reduce expenses even more, by only heating water as it is being used, eliminating standby losses. The final system, referred to as the small system, is not designed to run the complete cabin load, but to reduce the amount spent on electricity. This system produces 4.1kW of solar energy, and would leave the larger appliances connected to grid power and the solar system would only power the smaller loads. This option will not yield a zero net energy building, which is a building that produces enough excess energy each summer (when peak production is) to offset any energy bought to get through the winter (when there is less sun). The small option would not be able to sell as much power back to the grid due to the smaller size of the system. By compiling a list of panels based on output power, price, and size we were quickly able to narrow down the field of panels to only the best options. The least expensive panel per watt was based on amorphous silicon solar cells [9] and would require many low rated low efficiency panels. Only slightly more expensive were some panels based on highly efficient multi-crystalline cells [10] that would use just a few large rating panels. However, once the costs of wiring, mounting, and other parts of the system are considered, a system based on the high efficiency panels will be less expensive. Also, these panels are covered in tempered glass and have been tested to withstand hail, thermal cycles, thermal shocks, and other relevant tests. These panels will provide a hassle and maintenance free system for a minimal additional cost when compared to the low efficiency panels.
Kyocera Solar Panel [11] 6
For the Enota solar system, there are two different ways to approach the layout of the panels and equipment. For the layout of the panels, they can either be pole mounted [12] where a pair of panels is mounted on a galvanized pole using a metal bracket, or they can be flush mounted [13] on a small shed roof. For the rest of the equipment, it will be mounted on a plywood box with a plexiglass front, allowing the equipment to all be located near the panels and to allow the components to be easily seen. For the roof mounting system, this box will be located under the roof to protect if from the weather. For the pole mounting system a roof will be put over the box which will be mounted near the poles. A clear CAD model showing both layouts is shown below. Either of these layouts will let the panels face due south and allow the rest of the equipment to be easily seen but still protected from the weather.
Pole Mounted Layout
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Pole Mounted Layout
Shed Mounted Layout
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Shed Mounted Layout
A solar inverter converts direct current (DC) electricity to alternating current (AC) to allow one to use household appliances or to connect to a utility grid [14]. There are three different load categories that were evaluated to determine which inverter would work best for that given system. The small load (1000W) and the medium load (1800W) use the same type of inverter. The large load (5000W) uses a more expensive inverter. The capabilities that are needed for the system (data output capabilities and connecting to the grid) are not available in the lower power inverters, so we need to get an inverter that has higher power than what is really needed for the system. This also allows for one to upgrade the system if interested without having to replace the inverter. Some of the larger load inverters also have the ability for battery backup and charging the batteries. This capability is not required, but it is a nice addition for the large system. The large load also requires 240V to power the large appliances, whereas the small and medium loads require 120V.
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Xantrex GT 2.8 Grid Inverter [15] It is very important to use a safety disconnect for the solar system installation. A disconnect is a switch that disconnects the solar array from the inverter [16]. Some inverters include a safety disconnect, while others require an additional component installed.
Midnite Solar Mini Disconnect [17] Lead-acid batteries are the most common in solar energy systems because their initial cost is lower and because they are readily available nearly everywhere in the world [18]. There are many different kinds of lead-acid batteries, but the most important characteristic is whether they are deep cycle batteries or shallow cycle batteries. Sealed deep-cycle lead-acid batteries are essentially maintenance free. They never need to have water added. A newer type of sealed battery uses "Absorbed Glass Mats", or AGM between the plates. Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage [19]. An excellent choice of a sealed, deep-cycle battery is the Concorde Sun-Xtender. SunXtenders have a wide range of operating temperatures from -40F (-40C) to 160F (72C) as well as a low self-discharge of approximately 1% per month at 77F (25C) [20].
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Sun Xtender Sealed PVX890T Battery [21] A charge controller is a regulator that is placed between the solar panels and the batteries. Regulators for solar systems are designed to keep the batteries charged at peak without overcharging [22]. Since the load requires the use of high voltage solar panels, the only way to get full power out of these panels is to use an MPPT controller [23]. A MPPT, or maximum power point tracker is an electronic DC to DC converter that optimizes the match between the solar array and the battery bank. They convert a higher voltage DC output from solar panels down to the lower voltage needed to charge batteries [24].
Maximum Power Point Tracker Controller [24] Initially we had planned a folded brochure that explained the solar powered cabin. However, after speaking to Swan, it was clear that a single one sided 8"x10" paper would be more adequate for Enota. This would fit into their welcome and introduction package that each visitor receives. The information located on this page is meant to intrigue the reader. Ideally after reading the information the visitors will walk over to the cabin and gain more
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knowledge of solar energy. Below are examples of a possible slide show display and an example of the brochure. How it works
Solar Power Output Over Time Power Output
10000
1. Sunshine is energy in the form of electrons.
9000 8000
2. These electrons are gathered by the solar panels.
1 kW/hour 4kW/day 1.46MW/year
Price ($)
7000 6000 5000 Initial Cost
4000
Output ($)
3000 2000 1000 0 17 34 51 68 85 102 119 136 153 170 187 204 221 238 255 272 289 306 323 340 357
0
Time (Days)
4. The house runs off the energy stored in the batteries.
3. The power generated by the solar panels is either stored in batteries or sold back to the power grid.
Enota Solar Power Plant Enota is a non‐profit conservation facility committed to preserving our beautiful land with a limited number of accommodations including cabins, full hook‐up RV sites, pop‐up & tent sites and a Retreat Center for conferences, groups, events and seminars. Enota has abundant solar power which is renewable and free to use. Enota spends an average of $3000 a month on the electric bill. The objective of this solar project is to take advantage of the available solar power to generate electric power which can be used by a log cabin. The 10 solar panels, placed outside the cabin, can produce as much as 1kW of energy per day and is estimated to save Enota $350 per year. At that rate the system will pay for itself within 7 years. This system is designed to store excess energy during the day to a bank of batteries which can be used during the night. However, it is also possible to sell the excess energy back to the power grid.
We chose a small computer such as the EEE PC [25] because it has the proper hardware to run our display at an economic price. The EEE PC that is recommended consumes 22W [26]. A 17" monitor was selected because it should be suitable size for viewers up to 7' away. Also in comparison to a smaller screen such as a 15" model, this 17" [27] is actually cheaper and uses minimal power at 32W.
ASUS Eee PC 2G Surf Notebook [25]
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I-inc 17” Widescreen LCD Monitor [27]
Enota is responsible for completing the on site tasks necessary for the installation of the solar system. These include acquiring any needed permits for this work, working with the power company on grid sellback and getting a net metering power meter installed at the solar site, replacing the current wiring from the shower house to cabin with wiring that runs from the grid to the designated solar site and then to the cabin, building the mounting system following the detailed blueprints that will be provided by the design team.
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5. Project Management The following timeline shows tasks to be completed in order, and are due at the end of the week that they are filed under.
02/16/08
Fall Semester Decision by the industrial client on which system to choose(small, medium, or large solar system) industry client. Wiring diagram completed submit the parts order form. Spring Semester Any blueprints needed by Enota for on site construction will be completed. Enota's system will be assembled at TTU and tested. Testing and display interface starts
03/02/08
Testing completed at TTU
04/13/08
System installation at Enota site
11/20/08 11/30/08
01/26/08 02/02/09
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6. Parts and Cost Estimation Enota Solar Project Cost Estimation
Materials Cost Panels
Small 4.1 W $4,550.00
Medium 7.4 W $7,280.00
Large 13.4 W $12,740.00
Charge Controller
$200.00
$200.00
$200.00
Batteries
$470.00
$870.00
$1,410.00
Inverter
$1,800.00
$1,800.00
$3,300.00
Safety Disconnect
$0.00
$0.00
$760.00
Computer and Display
$300.00
$300.00
$300.00
Wiring
$200.00
$300.00
$400.00
Total for materials
$7,520.00
$10,750.00
$19,110.00
Pole Layout Mounts Poles Concrete Building
$500.00 $90.00 $28.00 $80.00
$800.00 $120.00 $32.00 $80.00
$1,400.00 $210.00 $44.00 $80.00
Estimated total system cost for pole layout
$8,218.00
$11,782.00
$20,844.00
Shed Layout Building Concrete Bolts
200 32 20
350 32 32
600 32 56
Estimated total system cost for shed layout
$7,772.00
$11,164.00
$19,798.00
Currently these estimations do not include shipping or taxes.
Since this solar system will be generating power back over time, it will pay back dividends in the form of reduced power bills. To estimate exactly how much money it is saving, we found the value of the electricity the system will produce, applying the increasing cost of the kW over time. We can then find out information such as how long until the system will pay for itself. After the
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system cost has been recouped, any savings on energy cost become profit. The medium system calculation includes the effect of switching the stove and water heater to natural gas.
Small Medium Large
Total Cost
kW / day
Years to recoup cost
$7,772.00 $11,164.00 $19,798.00
4.1 7.4 13.4
16.4 10.5 14.0
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Profit for system lifetime $7,941.25 $34,442.75 $31,557.50
7. Conclusions Based on our calculations we recommend the medium system. We chose the medium system because it meets the power requirements needed to power everything in the cabin so long as the oven and water heater are replaced. This is the most cost effective solution. However, if the capital is not available for new appliances the small system would be sufficient for powering the small appliances and lighting as well as give an educational model. Also, the small system could be upgraded to a larger system at some point in the future.
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8. References [1] Enota. “Enota Mountain Retreat, Cabins, Stream-side RV site, Camping, Retreat Center.” 21 October 2008. [2] Wikipedia. “Solar Cell.” 21 October 2008. [3] National Renewable Energy Laboratory. “NREAL: NREL Solar Cell Sets World Efficiency Record at 40.8 Percent.” 2008. 21 October 2008. [4] Rockriver.us. “Do-it yourself wind turbine solar panel installation.” 22 9 October 2008. [5] Bob Goodsell. “Bob’s Solar Project.” 10/7/2006. Bgoodsel Solar Blog. 10/9/2008. [6] Wikipedia. “Net Metering.” 10/9/2008. [7] Wikipedia. "Natural Gas." 19 October 2008. Natural Gas. 19 Oct. 2008. [8] The Solar Guide. "Amperes, Volts, Watts, Horsepower, BTUs." All About Energy. 19 Oct. 2008. [9] Wholesale Solar. "Thin-film Silicon PV Module." 2007. Kaneka. 26 Sept. 2008. [10] Kyocera Solar. "KD205GX-LP." Kyocera. 26 Sept. 2008. [11] Wholesale Solar. “Kyocera Solar KD205GX-LP 205.” 2007. 26 Sept 2008. [12] Northern Arizona Wind & Sun, Inc. "Mounts for Solar Electric Panels." 19 April 2005. Solar Panel Mounts 4 Oct. 2008 [13] SPI Renewable Solutions. "Types of Solar Panel Mounts." Solar Panel Info. 9 Oct. 2008. [14] Wikipedia. "Solar Inverter." 17 October 2008.
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[15] Wholesale Solar. “Xantrex GT 2.8 Grid Inverter.” 2007. 17 October 2008. [16] SolTrex. "How Solar Energy Works" 2003-2008. 17 October 2008. [17] Wholesale Solar. “MNDC125, MNDC175, MNDC250 Disconnect Power Centers.” 2007. 17 October 2008. [18] Solar 4 Power. “Solar Power Battery Information.” 18 October 2008. [19] Northern Arizona Wind and Sun. “Deep Cycle Battery FAQ.” 1998-2007. 18 October 2008. [20] Solar 4 Power. “Deep Cycle Batteries – Concorde.” 18 October 2008. [21] Atlanta Solar. “Sun Xtender Sealed PVX890T 12V.” 2004. 18 October 2008. [22] Northern Arizona Wind and Sun. “Deep Cycle Batteries FAQ” 1998-2007. 18 October 2008. [23] Northern Arizona Wind and Sun. “Charge Controllers for Solar Electric Systems.” 19982007. 18 October 2008. [24] Northern Arizona Wind and Sun. “Maximum Power Point Tracking Charge Controller.” 1998-2007. 18 October 2008. [25] Amazon. “ASUS Eee PC 2G Surf.” 1996-2008. 15 October 2008. [26] B & H. “ASUS | Eee PC 2G Surf Notebook Computer.” 2000-2008. 15 October 2008.
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[27] TigerDirect. “I-inc IF171ABB 17” Widescreen LCD Monitor.” 2007-2008. 15 October 2008.
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