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La Yuca small scale renewable energy 2011

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Figure 1: Small scale renewable energy hybrid system

Objective Statement

The objective of this Appropriate Technology project was to construct a small scale renewable energy system. This system was designed to serve as an educational tool, reduce fossil fuel use, along with having an acceptable pay-back time.

Background

In the Summer of 2011 the Humboldt State University Dominicana Program worked in collaboration with Universidad Iberoamericana (UNIBE), REVart, and the community of La Yuca, Santo Domingo. Together, they worked on exploring solutions to the energy demands of La Yuca. It was chosen that a prototype solution would be designed and constructed. The finished product, as seen in Figure 1, consists of two components. These components are a small scale vertical axis wind turbine and a 10 watt solar panel.

Location

La Yuca del Naco, Santo Domingo, Dominican Republic
Locationofturbine.png

Criteria


Table 1: Criteria

Criteria Weight Description
Safety    10 Safety is the ability of the design to prevent injury of any kind. The small scale renewable energy system must not be unsafe.
Effectiveness    10 The effectiveness of the small scale renewable energy system is the extent to which the system transfers energy, can be used as an educational tool, and the system's ability to be marketed locally.
Durability    10 Durability is the ability of the system to sustain a functioning state.
Aesthetics    5 Aesthetics is the system's level of visual appeal.
Payback Time    8 The small scale renewable energy system must have a payback time of one year or less while having an initial cost of USD $200.
Maintainability    8 Maintainability of the system is defined as the total cost required to sustain the functionality of the system. The maintenance cost is measured in money and in time.
Reproducibility    8 Reproducibility of the design is defined as the ability to which the design is able to be reproduced and marketed.

The Design

During six weeks of intensive study and work, the group decided to utilize a solar-wind hybrid system. The reason for this decision is due to climate of La Yuca. It was noticed that the area did not receive a large amount of usable wind speeds. However, there was a large quantity of sunlight in the region. Moreover, the wind appeared to be the strongest when there was little to no sun. By combining the two systems we felt that we could better utilize the available natural resources.

The group decided to use our system to light the room that the appropriate building group built for the Escuela Basica Nurys Zarzuela in La Yuca.

Turbine

Due to the variation in wind speeds as well as direction, a VAWT was determined to be the best suited turbine design. The diagrams in Figure 3 bellow give a more detailed look into the design of the turbine and the turbine frame.

Design and Construction Process

Figure 4: Testing a VAWT prototype

Design

  • Decided upon a solution by:
    • Determining and weighing project criteria
    • Discussing alternative solutions
  • Built several prototypes for testing, one can be seen in Fig. 4
  • Used a scalable vector graphics program (SVG) to design the turbine's blades

Construction

  • Built blade frames
  • Fastened aluminum sheeting to the blade frames, aluminum donated by the local newspaper company
  • Built the main frame that would house the blades, Figure 5b
  • Attached the blades to the frame using bearings
  • Mounted the permanent magnet and sprockets
  • Connected the bike chain to between the motor and the shaft sprocket, Figure 5d
  • Welded feet to the legs of the frame which were used to bolt the turbine to the cement roof
  • Welded a flat metal piece to the top of the frame which would hold the solar panel


Materials used:

  • Angle Iron
  • Sheet metal
  • Bicycle gears
  • Bicycle chains
  • Bearings
  • Rebar
  • Solid metal pipe


Electronics

Electrical energy is transferred from both a 10W solar panel and a wind turbine capable of achieving 30W at full capacity. By using a hybrid solar-wind power system, the battery bank is able to charge during the day by solar power and charged by wind power when there is ample wind. When storms approach, the wind generator will be able to produce power since insolation is minimal during full cloud cover. This hybrid system is meant to increase the overall time in which the batteries are charging.

Electricity is sent from the tandem power sources across a 14 gauge electrical wire to a charging station. This wire should be a short distance in order to reduce electrical loss from the transmission of electrons over long distances. If there is a need to transmit power over a large distance (<100ft) a transformer may be necessary to raise the voltage level to an appropriate level as to not incur as much voltage loss (110-220V). This electrical power is sent to a 24V relay which is able to divert the electricity away from the batteries in the case of a voltage spike from high wind gusts. This diversion of power is sent to a shunt resistor. The shunt resistor is a coil of wire which will convert electrical energy into thermal energy, producing a greater load on the wind turbine. This slows the turbine down until it reaches a lower speed and will not overcharge the system.

If the system is not overcharging, the electrical energy it transmitted from the relay to a solar charging controller. This controller has multiple functions and will take on the job of regulating battery charging voltage, switching on/off a 12/24V circuit through a timer or if system voltage is too low, and will display the status of the charging system, batteries and 12/24V circuit. The model used in this system was a pulse width modulated EPRC-5. The charge controller has three pairs of terminals for electrical connections: solar panel-wind generator, batteries and lighting. Attached to the controller is a display for functions such as: automatic lighting control, timers, test mode and controller mode. In the current system, the controller was programmed to “Mode-6” which ran the controller without any automatic lighting control or timers.

The battery bank was connected directly to the EPRC-5 charge controller with the sole addition of an inline fuse rated at 8amps. The charge controller is able to regulate battery voltage and maintain a full charge when there is ample power to supply. The lighting used was a series of 12V LEDs, and thus were also directly connected to the lighting terminals of the charge controller adjoined to a 4amp fuse and switch. The LEDs where wire to the ceiling of a room and were turned on and off with the flip of the nearby switch.

The charging station was constructed into a box mounted to the wall and easily accessible with a hinged cover and pad lock. The box was inside of the room in order to prevent water and weather from harming the system electronics.

If there are any questions about the construction or troubleshooting of the system, please contact Alex Bancroft at his university e-mail: ab290@humboldt.edu

Components

Device Specifications Description Picture
The Solar Panel 10 watt This panel was used in parallel with the turbine to transfer solar radiation into electrical energy.
LaYucaSolar.jpg
Shunt GH-120W 50Ω A shunt is a device that acts as a bypass, which allows current to pass through another point in the circuit. For this project, the shunt was used to dissipate excess energy in the form of heat.
DRshunt.jpg
Solar Charge Controller 12/24V

5A

The solar charge controller regulates the voltage that goes from the solar panels to the battery. Most solar charge controllers monitor the battery charge and will open the circuit when the battery is full, thereby stopping the charging process.
DRsolarcharge.jpg
LED 27 LEDs

33.75W (for the entire light series)

Light Emitting Diodes that were used for our project due to their high light output at low wattage.
DRled.jpg
Car Battery 12V

40Ahr

The charge on the battery will be used to light the LEDs in the system.
DRbattery.jpg
Permanent Magnet Motor 90V DC, 1.4A, 1745rmp (max)

0.10hp

The permanent magnet motor is used to convert the mechanical energy of the turbine movement to electrical energy.
DRmotor.jpg
Relay 24V The relay is used to divert unwanted, or excess, current to the shunt.
Relaypic.jpg




Cost

Budget

Materials Unit Price (DOP) Quantity Cost (DOP) Cost (USD) Our Actual Cost (DOP) Our Actual Cost (USD)
10 watt Solar Panel 2,850 (1,710 donated) 1 2,812 75 (45 donated) 1,125 30
Gears 410 1 410 10.93 410 10.93
Permanent Magnet Motor and Shunt 1,500 1 1,500 40.00 1,500 40.00
Battery and Terminals 1,870 1 1,870 49.86 1,870 49.86
Diodes, Switches, and Zeners 50 1 50 1.33 50 1.33
Inverter 1,400 1 1,400 37.33 1,400 37.33
Solar Charge Controller 1,300 1 1,300 34.67 1,300 34.67
LED lights 55.50 (donated) 27 LEDs 1,498.50 39.96 free free
Electrical wire $5/ft 300ft 1,500 40 1,500 40
Turbine (construction labor) $20,000 (donated) 1 20,000 533.33 free free
Black Metal Pipe 635 1 635 16.93 635 16.93
Angular Iron 2,435.47 1 2,435.47 64.95 2,435.47 64.95
Total = $35,411.47 $944.31 $12,225.47 $326.01



Timeline

Figure 6: Project Timeline

















Results

Payback Time

Figure 7: Wind Turbine Payback Period
Figure 8: Solar Panel Payback Period
Figure 9: Average monthly savings and full sun hours

The payback time of the system has been divided into two parts. The payback time has been calculated separately for the wind turbine and the solar panel. These calculations were made assuming that the user uses all of the energy that the system is able to output. Maintenance costs and change in energy prices are not factored into these calculations.

Wind Turbine

The payback time for the wind turbine was calculated using an estimated energy output or energy savings of [math]1 kWh/10 days[/math] or [math]0.1 kWh/day[/math]. Also, the payback period was calculated excluding any labor costs as these services were donated. The cost of energy used to calculate the payback period was [math]$0.136/kWh[/math][1].


As seen in Figure 7, the payback period of the wind turbine is approximately 59.63 years. The equations used to calculate the wind turbine payback period are shown here:

[math]Asv = Esv*c[/math]
[math]Asv = AnnualSavings[/math]
[math]Esv = Energy Savings/year[/math]
[math]c = EnergyCost/unit[/math]
[math]P = I/Asv[/math]
[math]P = Payback Period (yrs)[/math]
[math]I = System Initial Cost [/math]
[math]Asv = Annual Energy Savings[/math]

Solar Panel

As seen in Figure 8, the payback period of the solar panel was calculated to be 14.9 years. A 22 year average of 5.07 hours of full sun per day was used in the calculations[2]. This data was also used to show the relationship between monthly hours of full sun and monthly money saved, which may be seen in Figure 9. Also, the cost of energy used to calculate the panel's payback period was [math]$0.136/kWh[/math] and the initial cost used was $30 USD. The equations used to calculate the solar panel payback period are shown here:


[math]Esv=Ppv*S*n*365days/yr[/math]
[math]Esv = Energy Savings/year[/math]
[math]Ppv = Rated Power Of Panel[/math]
[math]S = FullSunHours/day[/math]
[math]n = Efficiency[/math]
[math]Asv = Esv*c[/math]
[math]Asv = AnnualSavings[/math]
[math]Esv = Energy Savings/year[/math]
[math]c = EnergyCost/unit[/math]
[math]P = I/Asv[/math]
[math]P = Payback Period (yrs)[/math]
[math]I = System Initial Cost [/math]
[math]Asv = Annual Energy Savings[/math]

Wind Turbine Efficiency

The wind turbine's efficiency was calculated using an estimated output of [math]0.10kWh/day[/math], an air density of [math]1.225 kg/m^3[/math], a yearly average wind velocity of [math]6.27m/s[/math][3], and the wind turbine's wind swept area of [math]1.115m^2[/math]. It is important to note that this efficiency calculation produces an instantaneous efficiency. In this case the instantaneous efficiency was calculated using an average wind velocity. The calculated efficiency of the wind turbine will vary depending upon the instantaneous conditions of the system such as velocity and air density. The instantaneous efficiency was calculated to be 4.53%.

The mathematical equations used to calculate this efficiency are shown below:

[math] P = p*A*V^3[/math][4]
[math]P = PowerPontential[/math]
[math]p = air density[/math]
[math]A = WindSweptArea[/math]
[math]V = velocity of wind[/math]
[math] P[/math]1[math]*n=P[/math]2
[math] P [/math]1[math] = PowerPotential[/math]
[math] P[/math]2[math] = PowerOutput[/math]
[math]n = efficiency[/math]

Next Steps

The next step is to utilize the knowledge gained through this design process by applying it to future projects. By applying this gained experience to future projects, it is hoped that more effective systems may produced. In this case, the system's effectiveness was measured using payback time. Many parts of the design can be improved upon in order to reduce the payback time of 59.63 years.

Reducing the initial construction costs of the turbine, given the same surrounding conditions, will lower the payback time significantly. Reducing these costs can be done in various ways. For example, the turbine's frame could have been constructed using mostly rebar instead of angle iron. Furthermore, the solar charge controller could have been homemade instead of store bought, which could save about $24.

Another area of significant improvement could be the systems gearing. Special care should be put into the configuring and placement of the gears so that they may operate as smoothly as possible. The more smooth the operation of the gears, the more work that is being done that is used to generate electricity. Also, selecting a sufficient gear ratio is crucial in optimizing energy output. Both of these improvements could greatly improve the efficiency of the wind turbine system.

Video

Authors and Team Members

Taylor Edwards
Rosa Anali Guzman Molina
Dane Noland
Alex Bancroft
Julio Lorenzo

LaYucaSyst.JPG

Helpful Files

File:Layucavawt.pdf Power Point Presentation on PDF

References

  1. "Electricity Prices for Households." Energy Information Administration, 10 June 2010. Web. 9 Sept. 2011. <http://www.eia.gov/emeu/international/elecprih.html>.
  2. "Parameters for Sizing and Pointing of Solar Panels and for Solar Thermal Applications - Pivot Data - Santo Domingo, Dominican Republic." Метеостатистика для Доминиканской Республики. Meteostatistics for the Dominican Republic. Web. 9 Sept. 2011. <http://dominican-meteo.ru/en/santo-domingo/pivot/solar-panels>.
  3. "Meteorology (Wind) - Pivot Data - Santo Domingo, Dominican Republic." Метеостатистика для Доминиканской Республики. Web. 16 Oct. 2011. <http://dominican-meteo.ru/en/santo-domingo/pivot/wind>.
  4. Grafman, Lonny, and Henk Daalder. "Energy from the Wind." Appropedia: The Sustainability Wiki. 6 July 2011. Web. 10 Oct. 2011. <http://www.appropedia.org/Energy_from_the_wind>.