Hybrid Wind and Solar Powered Outdoor Lighting
Team:
MET-421-001
Senior Design Project I
Winter 2014
Abstract 1
Project Description 2
Photovoltaic Cells 3
Wind Turbine 4
Integrated Controls Unit 6
Battery 7
LED Lighting 8
Patent /Market Review 9
Economic Analysis 9
Conclusion 13
References 14
Appendix 15
Abstract
The United States Department of Energy has laid out a vision in 2011, which includes to have the U.S. secure a leading role in clean energy technologies. With current global considerations to conserve natural energy resources and convert to more sustainable methods of power generation, applied efforts need to be developed in order to integrate known methods of energy creation, and still be able to provide reliable results. In areas where considerable seasonal changes occur, the changes in weather throughout the year does not provide a consistent energy source with respect to solar or wind energy sources. The team is proposing to develop a Solar/Wind hybrid power system specifically to retrofit current street lighting and supplement the current electrical service. The system will be comprised of a Savonious Wind Turbine and a Photovoltaic panel controlled by an Integrated Controls Unit. The system will be capable of providing sustainable power throughout the year, where solar energy is ideal during summer months and wind power being ideal during fall, winter and spring. Unit will be capable of being incorporated into current street lighting structures across North America (with a specific focus to the structures existing in the Greater Philadelphia area) and be able to provide a significant reduction in consumption of natural resources and energy cost.
Project Description
With the increased focus on global carbon emissions as well as the rising prices for electricity it is becoming desirable to find new and innovative ways to utilize as much renewable energy sources as possible. Many cities like Philadelphia and the surrounding areas are undertaking projects to convert streetlights from high-pressure sodium (HPS) bulbs to more efficient Light-Emitting Diode (LED). LED technology is approximately 50% more efficient than the HPS luminaire. For our basis the Cree XPS1 IP66 type II was chosen. This is a 52-W 5400-lumen output fixture. By using 12 hours as the average length of time a light will be operating per night and requiring 120 VAC this means that the minimum output requirements of our system is 0.624 kWh and 5.15 Ah. For our system we will be utilizing an 80-W output PV and assuming 5 hours of sunlight per day we will generate .4 kWh leaving the turbine to compensate for the remaining .24 kWh. The Integrated Controls Unit will take the electrical DC outputs from the PV and the turbine and will be filtered through a DC-DC rectifier and then supplied to the battery. There will be a feedback sensor that will monitor the amount of charge of the battery to maintain a voltage range between 12.7 and 12.2 volts. When fully charged the excess will be feed into the power grid and when fully discharged, as defined by the designers, the grid will be the sole energy provider until the battery is recharged to a determined level. We will be utilizing an 80-W output PV and assuming 5 hours of sunlight per day we will generate .4 kWh leaving the turbine to compensate for the remaining .24 kWh. Based on weather observations the consolidation of Solar and Wind energy provides an opportunity to maintain consistent energy production throughout the entire year. Wind power being an effective source for generating electricity, but with a drawback of being inconsistent since it relies on natural wind. And solar energy being ideal in summer months, with the integration of both sources, we are able to improve reliability.
Figure 1- Philadelphia 2013 weather data (Wunderground.com).
Photovoltaic Panels
Photovoltaic (PV) panels, or more commonly referred to as “solar panels”, are devices that convert solar radiation energy into electrical energy. The concept is based in the photoelectric effect observed in plants; natural photosynthesis of all plants in the land and oceans can produce 8x the current combined energy requirements of humanity . Most commonly, they are a panel of solid-state semiconductors made from crystalline silicone, and can either be in monocrystalline or polycrystalline layout . Photovoltaic panels are a well-researched alternative energy, and the reliability of these panels has been increasing to since their inception. Today’s PV solar panels can produce anywhere from 10 microwatts to 300 watts , and because of their silence, reliability, low maintenance, and no negative environmental by-products, we have decided to use these as a backup power generation source to the wind turbine.
PV panel efficiency can be affected by many different factors. The first factor is the design and construction of the PV panel. As said above, PV panels can be either monocrystalline or polycrystalline. Monocrystalline PV panels can achieve up to 25% efficiency in ideal test conditions, and usually achieve in the 15-20% range . In addition, monocrystalline PV panels usually take up less space than polycrystalline. However, they are much more susceptible to reduced efficiency due to partial shading or snowfall, or even complete failure, as they are constructed of one single silicone crystal. Polycrystalline PV panels, on the other hand, have a rated efficiency between 13.5-17% . They are less costly to produce, and less susceptible to shading efficiency reductions and failure. However, they are also more sensitive to high temperature, and in hot weather, their efficiency can actually be reduced. (In fairness, all PV cells reduce in power output as the temperature increases, but it is a more substantial side-effect in polycrystalline PV cells .)
There are many other types of PV cell construction, such as organic PV cells and thin film cadmium telluride (CdTe) PV cells, but these are more specific to a certain application, and much more costly. Because of this, we will mainly consider traditional mono- or polycrystalline PV cells. Our solar panel choice on this matter will be determined mainly by cost per watt output, followed by durability.
The second design factor that can affect PV panel efficiency is the fill factor, or the space between solid-state conductors in a panel. The fill factor can be estimated by Equation 1 below .
Fill Factor=PmaxVoc*Isc=Umpp*ImppVoc*Isc
Equation 1 - Fill Factor Estimation
The higher the fill factor, the more efficient the solar panel should be, and most PV cells should have a fill factor greater than 07 .
As stated, a third factor affecting the efficiency of a PV panel is the temperature. PV panels are all tested under ideal Standard Test Conditions (STC) at 25 degrees Celsius. However, real-life conditions are much more variant, and as such, we need to correct the efficiency by the temperature derating factor (ηt). The equation for the temperature derating factor is shown below, in Equation 2,
ηt=1-γ*T-Tstc
Equation 2 - Temperature Derating Factor
where gamma (γ) is the power temperature coefficient, which will vary depending on the solar panel we choose. We will be considering the temperature changes when we calculate our overall efficiency by using current and historical data from both the National Weather Service and local weather agencies in and around the Philadelphia area. However, because the temperature derating factor is small and will nominally affect our calculations, for our initial calculations of power needs, we are using simplified equations.
In our setup, we have aimed to keep our photovoltaic grid to one single panel capable of charging the battery to 75%. We have chosen this for multiple reasons. First, multiple PV panels would be unappealing, aesthetically. (If possible, we would like to have no photovoltaic panel at all and power the entire system from the wind turbine, but due to low wind turbine efficiencies, we have chosen to include a photovoltaic as a backup power source, for the reasons above.) Second, size and spacing constraints would limit how many panels we would be able to put on the top of a light pole, and still be able to achieve a cost-effective efficiency (panel overlap would reduce each panel’s efficiency). Finally, because so much research has been conducted on photovoltaic efficiency, and photovoltaic efficiency has improved so much in the last 20 years, we believe that we can provide 75% of the power input to the battery from the photovoltaic panel with ease.
In our calculations, we have set a standard in our calculations that the PV cell will provide 75% of the necessary power to fully charge the battery. As stated in the Battery section, we will need to fully charge a 12 V, 39 A*h battery with a 50% DoD, (and assuming that the battery can never be fully charged, we set the upper limit of charging to 98%) meaning that from the PV panel, we need to produce 225 W*h, as shown below in {}.
Power Needs=12 V*39 A*h*0.5=225 W*h
Equation 3 - Calculation of Power Output Needs
We average a daily charging time of 12 hours for our photovoltaic panel to work. This means we would need to produce an output equal to 14.04 watts, as shown below in Equation 3.
Power Needs from PV Panel=225 W*h12 h=14.04 W
Equation 4 - Power Needs of PV Panel
The average solar panel output efficiency is 20% . With this in mind, we have determined we need at least a 70 W solar panel to achieve our goal outlined above.
Wind Power
Wind energy is a great sustainable energy source providing power generation with little to no carbon emissions and the ability to be used nearly everywhere. Wind turbines are gaining a lot of lead way as a viable method of generating electrical power. According to the American Wind Energy Association, over the last 5 years, wind power generating capacity increased 31%. In 2013 alone, new wind capacity installed in the U.S. topped 1,087 MW. Wind power is also one of the largest sources of power generation amongst renewable resources. In 2013, wind generated power accounted for 32% of total power generated by any renewable source only behind hydroelectric power (Eia.gov). This clean efficient power source also makes for a good source of home and commercial use. As of 2012, the commercial use of wind power totaled 30MW and its MW usage increased by close to 3000% since 2009 (only 1 MW generated) (Eia.gov). This insurgence in wind power is a primary reason as to why incorporating a wind turbine would have positive feedback.
The main parts of a wind turbine; the blades, the rotor, and the generator. The system works by using natural wind to rotate the blades. As the wind crosses over the blades of the turbine, a pressure differential is created across the blades. Using the surface geometry of the blade, the low pressure field that is generated behind the blade, causes the blade to rotate. The rotation generated however is typically too slow to generate power. To accomplish this, gears are introduced into the body of the wind turbine. By attaching a large gear to the rotor of the turbine to a series of gears to perform a gear reduction, the amount of RPM’s turning on the shaft of the generator is approximately 1800 RPM’s as opposed to the input of 60 RPM’s (Energy.gov). This gear reduction is essential in the generation of power through wind. Typical wind speeds for the Mid-Atlantic area range between 5 to 6 mph which is average at best. Once a high amount of RPM’s are reached, the generator then begins to generate power to be used for industrial or commercial use.
Vertical Wind Turbine
The wind turbine design that will be used for the purposes of a compact turbine is the savonius style turbine. The main reason for choosing the savonius style turbine is due to its compact size and small rotational angle area. Most large scale wind turbines have a rotational diameter of 10 meters and must directly face the oncoming wind. The blades must also adjust their pitch to fully capture most of the winds energy. Unlike the horizontal turbines used in large scale energy production, the savonius style turbine captures the wind from any direction due to its blade orientation, as seen figure 1 below. This reduces the complexity of the turbine and the controls needed to operate the design. It also allows for a small fitting area on top of light poles and even traffic light.
Figure 2: Savonius Wind turbine; the blades of a savonius turbine are vertical as opposed to the horizontal blades of a large scale turbine. It allows for the use of wind from any direction without the need to rotate the directions of blades.
In order to calculate the amount of RPM’s our turbine can generate need to now the historical wind speed of the given area. We were able to gather wind information from the Philadelphia Airport to calculate an average amount of RPM’s. To calculate the number of RPM’s we will use the equation as follows:
N=(60* γ*V)/(π*D) (Franquesa pg. 3)
Where N is the number of RPM’s generated by the turbine blades, γ is the tip-speed ratio, V is the wind velocity, and D is the diameter of the path the blades make. Given rotor design consisting of a diameter of 0.305 meters and the average wind velocity of 3 meters per second in the area, we find the generated RPM’s to be approximately 190 RPM without loses due to the resistance of the motor.
Turbine Generator
For our turbine blades to be able to produce electricity, the rotor needs to be connected to a device that generates the needed electricity. To accomplish this, we will use a geared DC motor. Typically, current is feed through the motor turning electrical potential into mechanical energy. If we were to reverse the process and rotate the shaft of the motor, we can transfer the mechanical energy of the rotor into electricity. The main concern with using a motor for usage of a wind turbine is the amount of RPM’s that can be generated by the turbine. Most common 12VDC motors operate at approximately 1800 RPM’s. With large scale turbines only rotating at around 60 RPM and our turbine only rotating around 20 to 30 RPM’s, we need to find a way to increase the RPM’s to the generator. We propose to use a specialized motor called a gear motor. The gear motor has a set of gears that are attached to the shaft of the motor that will increase the rotation of the turbine by the gear ratio of the motor.
Charge time=amp hoursfull load amps=39Ah3.8A=10.26 hours (operatingtech.com pg. 5)
This gives use sufficient amount of time for the generator to charge the battery if the conditions for the photovoltaic cell are poor and providing little power. Based on a linear power curve for a DC motor, if the input RPM is low, say about 15 RPM we can determine the amperage output to be approximately 2.0 amps which gives us a charge time of roughly 20 hours.
Integrated Controls Unit
Our original idea for an integrated control unit was to use a series of operational amplifiers (“op-amps”) connected to sensors to monitor the voltage levels in the battery, the current levels through the circuit, and the power and current outputs of both the photovoltaic panel and the wind turbine. However, our light will be a 40 W LED lamp, which is beyond the power capabilities of most op-amps. Because of this, we will most likely need to connect all the monitoring and sensing equipment to a microprocessor. We will determine which microprocessor to use when we are more confident of our power output averages and upper limits.
Battery:
When deciding on what type of battery to power this light with the three main types were considered. Lead acid, absorbed glass matt (AGM), and gel. Almost immediately traditional lead acid was discarded due to the inherent environmental risks as well as the increased maintenance required with the need to renew the water levels. Gel batteries were taken out of consideration due to the lower power capacity in like sized batteries. This left us with the AGM, which in many configurations is combined with a Sealed Lead Acid (SLA) style. The benefits of using the AGM are that they can be mounted in any position without concern for leakage. AGM’s have excellent life capacity as long as, on average, the depth of discharge (DoD) does not exceed 50%. Because of these characteristics a 12V, 35 Ah deep cycle battery is being considered for our application. It was necessary to provide adequate power while keeping size and weight to a minimum.
LED Lighting
LEDs have many advantages over HPS luminaires. They are directional which provides much more even lighting than other light sources. This means that less light needs to be produced in order to light the same amount of area as other lights. Less light dramatically reduces light pollution by placing the light where it is desired. LED technology is environmentally friendly as well. According to a comparison done by GE in 2011, 95 Watt LED’s were compared to 100-Watt induction lamps [7]. The comparison showed that LED’s provided 16% more lumens per Watt (LPW) than induction lamps on average, as well as providing a slower rate of decline over the life of the luminaire. Also comparing the life span of an LED is approximately 4 times that of the HPS. LED’s are unaffected by vibrations, which make them idea for areas of high vibration such as bridges, overpasses and high traffic roads.
Economic Analysis
Proposing we completely remove our poles from drawing power from the grid we would be able to reduce the demand by 115W. The demand reduction, DR, also includes the watts saved by the installation of the new ballast. If the lamps run for an average of 12 hours per night, from 6 pm to 6 am, for 365 days a year, we calculate the annual amount of usage to be 4380 hours. As stated by the Philadelphia Electric Company in their November 2014 tariff, the cost of power for street lighting is $0.07 per kWh with a distribution cost of approximately $205 per light pole per year. Using this information we can find our cost saving (CS) to be:
CS=DR*Hours*Energy cost+(Number of Poles*Distribution cost)
CS=(.115kW * 4380hrs/yr * $0.07/kWh) + (1 pole * $205/pole-yr) = $240.26
Using our cost saving per light we are then able to calculate our simple payback period, SPP. Using the SPP we can determine roughly how many years it would take for our cost savings to cover the cost of the kit.
SPP=ICCS
In this equation, we account for the implementation cost, IC, of our kit. This is the cost in which we are offering to our customers, installed. We plan to present our kit to the market at a maximum of $1000. As we begin to build and design our kit, we may come across a lower price due to ordering materials in bulk, removing un-needed parts, and cutting down labor time. Our suggested SPP we be:
SPP=$1000$240.26/yr ≈4.2yrs
In about 4 years, the kit would have save enough money for the township or city to pay of the implementation of the kit on the poles. After the 4.2 years, each pole fitted with the kit will start to save $240 per year. If our kits can run for a minimum of 10 years without replacement and little maintenance, each kit will save a minimum of $1392 over its lifetime.
Another consideration to take into account is the environmental impacts the kit will also produce. We will assume the current power being generated to the street lights in use now is coal. Our kits will be saving 503.7 kWh per pole. As stated in “Guide to Energy Management,” there is 3412 Btu per 1 kWh. There is also 25,000,000 Btu per 1 ton of coal. With this, we can find that:
503.7kWhyr*3412BtukWh*1 ton ofcoal25,000,000 Btu ≈ 0.069 tons of coal
Our kits can save approximately 0.069 tons of coal per light post. If an area has roughly 100,000 light poles, we can save 6,900 tons of coal a year, further improving our environment.
Patent Review:
The proposed project has a lot of prior information which deals with the main components of this project, wind turbines and solar panels are used in many different forms to generate power. Noted below are some patents that closely relate to our project, but our project distinctions are essentially using the wind turbine and solar panel as a hybrid power source to specifically provide energy to a street light.
The Malcolm Patent (US8288884 B1) involves the integration of a wind turbine and a solar panel as a power source. The design focuses on the tower supporting a wind turbine and a solar panel that is mounted in a way that allows to swivel along the base in order to allow it to follow the sun. This patent is mainly directed as an integration of the two sources as a viable method of creating electrical power.
The Mann Patent (U.S. Pat. No. 7,321,173) involves specific support structure that uses cups as a wind capturing device and photovoltaic cells to power the roadway lights.
The Doan Patent (U.S. Pat. No. 4,200,904) incorporates a solar powered and photovoltaic panel to power a streetlight augmented by a wind turbine. Which is described as being totally independent from external power sources.
Our particular design will incorporate an improved design wind turbine at the high point of already existing street light structures. It will require the retrofit of current lighting systems, and improved to be more energy efficient. Photovoltaic panel will be used as a main power source integrated with a wind turbine to provide an improved capability of providing consistent sustainable energy throughout the year, with the main objective of supporting the external already existing power system.
Conclusion:
Based on the proposed testing locations of Delaware county Pa, Philadelphia Pa, and Chester County, PA where reasonable solar energy exist during summer months, and a considerable wind speed exists in the non-summer months. The team proposes to develop a hybrid Solar/Wind powered Streetlight assembly with using theoretical analysis to determine appropriate solar panels and design a wind turbine with expectations or system to provide a 50% cost savings or grid energy reduction.
References:
- Energy.gov,. 'Secretary Chu Unveils The 2011 Strategic Plan'. N.p., 2014. Web. 20 Nov. 2014.
- Eia.gov,. 'U.S. Energy Information Administration (EIA)'. N.p., 2014. Web. 20 Nov. 2014."Energy.gov."
- Energy.gov,. 'How Do Wind Turbines Work?'. N.p., 2014. Web. 20 Nov. 2014.
- Nrel.gov,. 'NREL: Dynamic Maps, GIS Data, And Analysis Tools - Wind Maps'. N.p., 2014. Web. 20 Nov. 2014.http://www.ajdesigner.com/phpwindpower/wind_generator_power.php
- Ajdesigner.com,. 'Wind Turbine Power Generator Equation Formulas Design Calculator'. N.p., 2014. Web. 20 Nov. 2014.
- McFadyen, Steven. 'Photovoltaic (PV) - Electrical Calculations'. Myelectrical.com. N.p., 2014. Web. 20 Nov. 2014.
- Usa.com,. 'Delaware County, PA Weather - USA.Com™'. N.p., 2014. Web. 20 Nov. 2014.
- Induction Street Lighting Compared To Other Source Technology’S.. 1st ed. Review of HPS, Induction and LED Street Lights, 2011. Web. 20 Nov. 2014. Work cited: https://ewh.ieee.org/r2/delaware_bay/0311/Street%20Lighting%20Comparrison%20IND%20HPS%20LED%202152011%20%5BCompatibility%20Mode%5D.pdf
- Franquesa, Manuel. KleineWindräder: Berechnung Und Konstruktion. Wiesbaden: PfriemerImBauverl., 1989. 2008. Web. 14 Nov. 2014.
- "A Guide to Battery Charging." (n.d.): 1-7. Operatingtech.com. Operating Technical Electronics, Inc. Web. 14 Nov. 2014.
- Capehart, Barney, Wayne C. Turner, and William J. Kennedy. Guide To Energy Management. 5th ed. Lilburn, GA: The Fairmont Press, 2008. Web. 20 Nov. 2014.
- Nrel.gov,. 'NREL: Dynamic Maps, GIS Data, And Analysis Tools - Solar Maps'. N.p., 2013. Web. 20 Nov. 2014.
- HID To LED Wattage Cross Reference. 1st ed. Howard Lightning. Web. 20 Nov. 2014.
- "Energy.gov." How Do Wind Turbines Work? Accessed November 4, 2014.http://energy.gov/eere/wind/how-do-wind-turbines-work
- "Wind Maps." NREL: Dynamic Maps, GIS Data, and Analysis Tools -. September 10, 2014. Accessed November 4, 2014.http://www.nrel.gov/gis/wind.html
- http://www.ajdesigner.com/phpwindpower/wind_generator_power.php
- http://myelectrical.com/notes/entryid/225/photovoltaic-pv-electrical-calculations
Appendix A:
Map of Pennsylvania showing the amount of kWh produced per square meters per day produced by a photovoltaic cell. In the Philadelphia area, the average amount of kWh/m2 –day is about 4.5 to 5.0. (Nrel.gov)
Map of Pennsylvania showing the velocity of wind in meters per second. In the Philadelphia area, the average wind velocity ranges from 3.0 to 5.0 m/s (Nrel.gov)
Figure 1 – Philadelphia 2013 wind speed information (Usa.com)
Figure 2 – Philadelphia 2013 Temperature information (Usa.com)
Figure 3 - Philadelphia 2013 Weather Data (Wunderground.com)
Figure 4 - Theoretical Wind Turbine power output based on 2013 wind speed.
