Photovoltaic Design and Installation Bucknell University Solar Scholars Program Presenters: Colin Davies ‘08 Eric Fournier ‘08
Outline • Why Renewable Energy? • The Science of Photovoltaics • System Configurations • Principle Design Elements • The Solar Scholars program at Bucknell (walking tour)
What’s wrong with this picture? • Pollution from burning fossil fuels leads to an increase in greenhouse gases, acid rain, and the degradation of public health. • In 2005, the U.S. emitted 2,513,609 metric tons of carbon dioxide, 10,340 metric tons of sulfur dioxide, and 3,961 metric tons of nitrogen oxides from its power plants.
40% 85% of our energy consumption is from fossil fuels!
Why Sustainable Energy Matters • The world’s current energy system is built around fossil fuels • Problems: • Fossil fuel reserves are ultimately finite • Two-thirds of the world' s proven oil reserves are locating in the Middle-East and North Africa (which can lead to political and economic instability)
Why Sustainable Energy Matters • Detrimental environmental impacts • Extraction (mining operations) • Combustion • Global warming? (could lead to significant changes in the world' s climate system, leading to a rise in sea level and disruption of agriculture and ecosystems)
A Sustainable Energy Future • Develop and deploy renewable energy sources on a much wider scale • Bring down cost of renewable energy • Make improvements in the efficiency of energy conversion, distribution, and use Three Methods: - Incentives - Economy of scale - Regulation
Making the Change to Renewable Energy • Solar • Geothermal • Wind • Hydroelectric
Today’s Solar Picture • Germany leads solar production (over 4.5 times more then US production) – Japan is 2nd (nearly 3 times more then US production) – this is mainly due to incentives • Financial Incentives • Investment subsidies: cost of installation of a system is subsidized • Net metering: the electricity utility buys PV electricity from the producer under a multiyear contract at a guaranteed rate • Renewable Energy Certificates ("RECs")
Solar in Pennsylvania • Pennsylvania is in fact a leader in renewable energy • Incentives • Local & state grant and loan programs • Tax deductions • REC’s (in 2006: varied from $5 to $90 per MWh, median about $20)
Harnessing the Sun • Commonly known as solar cells, photovoltaic (PV) devices convert light energy into electrical energy • PV cells are constructed with semiconductor materials, usually silicon-based • The photovoltaic effect is the basic physical process by which a PV cell converts sunlight into electricity • When light shines on a PV cell, it may be reflected, absorbed, or pass right through. But only the absorbed light generates electricity.
Part 2: Learning Objectives • Compare AC and DC electrical current and understand their important differences • Explain the relationship between volts, amps, amp-hours, watts, watt-hours, and kilowatt-hours • Learn about using electrical meters
Electricity Terminology • Electricity = Flowing electrons • Differences in electrical potential create electron flow • Loads harness the kinetic energy of these flowing electrons to do work • Flowing water is a good conceptual tool for understanding
Electricity Terminology • Voltage (E or V) • Unit of electromotive force • Can be thought of as electrical pressure • Amps (I or A) • Rate of electron flow • Electrical current • 1 Amp = 1 coulomb/second = 6.3 x 1018 electrons/second
Electricity Terminology • Resistance (R or Ω) • The opposition of a material to the flow of an electrical current • Depends on • Material • Cross sectional area • Length • Temperature
Electricity Terminology • Watt (W) are a measure of Power • Unit rate of electrical energy • Amps x Volts = Watts • 1 Kilowatt (kW) = 1000 watts
Electricity Terminology • Watt-hour (Wh) is a measure of energy • Unit quantity of electrical energy (consumption and production) • Watts x hours = Watt-hours • 1 Kilowatt-hour (kWh) = 1000 Wh
Power and Energy Calculation • Draw a PV array composed of four 75 watt modules. • What size is the system in watts ?
Electricity Terminology • Amp-hour (Ah) • Quantity of electron flow • Used for battery sizing • Amps x hours = Amp-hours • Amp-hours x Volts = Watt-hours • A 200 Ah Battery delivering 1A will last _____ hours • 200 Ah Battery delivering10 A will last _____ hours • 100 Ah Battery x 12 V = _____ Wh
Types of Electrical Current • DC = Direct Current • PV panels produce DC • Batteries store DC • AC = Alternating Current • Utility power • Most consumer appliances use AC
Meters and Testing Clamp on meter Digital multimeter • Never test battery current using a multimeter!
Part 1: Learning Objectives • Understand the functions of PV components • Identify different system types
Photovoltaic (PV) Terminology • Cell < Module < Panel < Array • Battery – stores DC energy • Controller – senses battery voltage and regulates charging • Inverter – converts direct current (DC ) energy to alternating current (AC) energy • Loads – anything that consumes energy
DC System Options • Battery backup vs. discontinuous use • LVD option in charge controller • Load controllers
AC System Options • Combined AC and DC loads • Hybrid system with back up generator • Grid tied utility interactive system without batteries • Grid tied interactive with battery backup (why might you need this?)
Complexity Low: Easy to install (less components) Grid Interaction Grid can supplement power No power when grid goes down Grid-Tied System(Without Batteries)
Complexity High: Due to the addition of batteries Grid Interaction Grid still supplements power When grid goes down batteries supply power to loads (aka battery backup) Grid-Tied System(With Batteries)
Part 3: Learning Objectives • Learn how a PV cell produces electricity from sunlight • Discuss the 3 basic types of PV cell technologies • Understand the effects of cell temperature and solar insolation on PV performance • Gain understanding of module specification • Identify the various parts of a module
Solar Cells and the PV Effect • Usually produced with Semi-conductor grade silicon • Doping agents create positive and negative regions • P/N junction results in 0.5 volts per cell • Sunlight knocks available electrons loose • Wire grid provides a path to direct current
Available Cell Technologies • Single-crystal or Mono-crystalline Silicon • Polycrystalline or Multi-crystalline Silicon • Thin film • Ex. Amorphous silicon or Cadmium Telluride
Monocrystalline Silicon Modules • Most efficient commercially available module (11% - 14%) • Most expensive to produce • Circular (square-round) cell creates wasted space on module
Polycrystalline Silicon Modules • Less expensive to make than single crystalline modules • Cells slightly less efficient than a single crystalline (10% - 12%) • Square shape cells fit into module efficiently using the entire space
Amorphous Thin Film • Most inexpensive technology to produce • Metal grid replaced with transparent oxides • Efficiency = 6 – 8 % • Can be deposited on flexible substrates • Less susceptible to shading problems • Better performance in low light conditions that with crystalline modules
Selecting the Correct Module • Practical Criteria • Size • Voltage • Availability • Warranty • Mounting Characteristics • Cost (per watt)
Voltage Terminology • Nominal Voltage • Ex. A PV panel that is sized to charge a 12 V battery, but reads higher than 12 V) • Maximum Power Voltage (Vmax / Vmp) • Ex. A PV panel with a 12 V nominal voltage will read 17V-18V under MPPT conditions) • Open Circuit Voltage (Voc ) • This is seen in the early morning, late evening, and while testing the module) • Standard Test Conditions (STC) • 25 º C (77 º) cell temperature and 1000 W/m2 insolation
Effects of Temperature • As the PV cell temperature increases above 25º C, the module Vmp decreases by approximately 0.5% per degree C
Effects of Shading/Low Insolation • As insolation decreases amperage decreases while voltage remains roughly constant
Other Issues • Surface temperature can be measured using laser thermometers • Insolation can be measured with a digital pyranometer • Attaching a battery bank to a solar array will decrease power production capacity
Part 4: Learning Objectives • List the characteristics of series circuits and parallel circuits • Understand wiring of modules and batteries • Describe 12V, 24V, and 48V designs
Series Connections • Loads/sources wired in series • VOLTAGES ARE ADDITIVE • CURRENT IS EQUAL • One interconnection wire is used between two components (negative connects with positive) • Combined modules make series string • Leave the series string from a terminal not used in the series connection
Parallel Connections • Loads/sources wired in parallel: • VOLTAGE REMAINS CONSTANT • CURRENTS ARE ADDITIVE • Two interconnection wires are used between two components (positive to positive and negative to negative) • Leave off of either terminal • Modules exiting to next component can happen at any parallel terminal
Quiz Time • If you have 4 12V / 3A panels in an array what would the power output be if that array were wired in series? • What if it were wired in parallel? • Is it possible to have a configuration that would produce 24 V / 6 A? Why?