Solar Photovoltaics

Main Types of Solar Energy• Passive Solar Space Heating (Building Design)

- Building Orientation & Landscaping- Window location, glazing type, eaves, insulation & air sealing- Thermal mass collector (wall/floor) & distributor

• Solar Thermal - Solar Water & Space Heating (SWH)- Solar Pool Heating (SPH)- Concentrating Solar Power (CSP) (electricity producing)

• Solar Photovoltaic (PV) (electricity producing)

2011 Global Cumulative PV Capacity67.4 GW = 80 billion kWh = 20 million households

Europe – orangeRest of World – yellowSource: EPIA Market Report 2011

Source: EPIA Market Report 2011

Growth of Solar PV in the US3.1 GW cumulative grid-connected PV - 3rd quarter 2011

(2010 ended with 2.6 GW cumulative - 2011 4th quarter statistics not out yet)

U.S. Solar Market Insight: 2010 Year in Review Executive SummarySolar Energy Industries Association & GTM Research

U.S. Solar Market Insight: 2010 Year in Review Executive SummarySolar Energy Industries Association & GTM Research

Insolation Across the US

Insolation - Incident solar radiation (Irradiance); a means of measuring the amount of solar radiation available at a specific place over a period of time.

PA Solar Share Requirement

0.02 0.17 0.73 4.30 19.4648.70 77.57

129.70

225.72

397.82

473.81

557.60

649.33

749.30

858.02

0

100

200

300

400

500

600

700

800

900

1,000

2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021

MW

Cap

acity

Equal to Offsetting Electric Consumption for about 91,000 Average Homes in Pennsylvania per Year

Photovoltaic (Solar Electric) Technologies

Monocrystalline(Single Crystalline) Thin Film

(Amorphous Silicon)

Polycrystalline(Multi-crystalline)

Prevalence of Technologies

Source: http://solarcellcentral.com/markets_page.html

Monocrystalline Silicon

- cells saw-cut from a single cylindrical crystal of silicon- manufacturing process is complicated, resulting in slightly higher costs than other technologies- most efficient of the photovoltaic technologies - around 15%

Polycrystalline Silicon

- cells cut from an ingot of melted and recrystallised silicon (molten silicon is cast into ingots of polycrystalline silicon, these ingots are saw-cut into very thin wafers and assembled into complete cells creating a granular texture look)- cheaper to produce than monocrystalline type, due to the simpler manufacturing process- slightly less efficient, with average efficiencies of around 12%

Typical Crystalline Cell Module

Solar Cell

Solar Panel or Module

Solar Array

Monocrystalline vs MulticrystallineSharp NT175U1Monocrystalline

Sharp NE-Q5E2UMulticrystalline

Cell Effic. = 16.20%Module Effic. = 13.45%

Cell Effic. = 14.55%Module Effic. = 12.68%

PhotovoltaicApplications

Car Port

Street Lighting

Commercial Building

Amorphous Silicon- cells are composed of silicon atoms in a thin homogenous layer rather than a crystal structure- absorbs light more effectively than crystalline silicon, so the cells can be thinner - known as "thin film" PV technology- easier and therefore cheaper to produce - can be deposited on a wide range of substrates, both rigid and flexible, used on curved surfaces and "fold-away" modules - less efficient than crystalline based cells, with typical efficiencies of around 6%- ideally suited for applications where high efficiency is not required and low cost is important

Range of PV Module Efficienciesand Power Densities

Efficiency Watts/SqFt

Monocrystalline ~ 13% to 18.7% 11 to 17.4

Polycrystalline > 10% to 14.7% < 10 to 13.6

Amorphous – Si 6% to 6.3% 5.8 to 5.9

Electrical ConductivityNucleus & Inner Shells of

Orbiting Electrons

Valence Shell (Outer Shell of Orbiting

Electrons)

Conductors - Elements whose outer electrons (one or two) are easily disengaged from orbit around their nuclei, thus contributing to the flow of electricity (e.g. metal wire)

(Tsunami Effect)

Insulators - Elements whose electrons (six or seven) are closely integrated into their atoms and are not easily jarred loose, thus making them strongly resistant to electric flow (e.g. rubber insulated coating around metal wire)

Semiconductor - Any of a number of elements, including silicon, whose electrical properties lie between those of conductors and insulators, making them only marginally conductive of electricity; (these have three to five electrons in the valence shell)

Electrons knocked free of their atoms occupy what is called the conduction band, which is where the flow of electricity occurs.

Silicon

Musical Chairs: When Sunlight (e.g. Photons) Shines on Pure Silicon

Electrons are bombarded by photons, transferring enough energy to liberate them from their atomic orbit and become free electrons.

The free electrons eventually lose this energy and fall back into a vacant hole of a neighboring atom.

This analogy of musical chairs is such that there are equal amount of free electrons and vacant holes for their return. Uncontrolled flow of electrons or current, without voltage potential does not provide a means for us to capture this energy.

If we remove some of the chairs, we can essentially tap some of this energy from the surplus of electrons that can’t find vacant holes to fill.

Doping Silicon

We can create a means of getting some control of the musical chairs game and tap some of the solar energy striking the silicon material. By doping the silicon with a tiny bit of Boron (making it slightly positive or adding more chairs), and doping other silicon with a tiny bit of Phosphorous (making it slightly negative or adding more electrons), and making a sandwich of these two layers, we would essentially be introducing a surplus of free electrons.

PV Cell Stagnant – Open Circuit Voltage

When making this semi-conductor, or sandwich of positively and negatively charged silicon layers, an atom thin layer called the cell barrier is inherently created – which has a static electrical charge that lasts the life of the solar cell.

The n-silicon layer is on top facing the sun with the p-silicon layer underneath. The photons pass through both layers, liberating electrons in both of them. But since there is an abundance of electrons in the top layer, they are too sluggish to pass through the cell barrier; whereas, the more energized free electrons in the lower p-silicon layer can breach the cell barrier into the upper layer. This quickly results in the solar cell being very top heavy with free electrons – thus, creating a voltage potential across the layers.

PV Working – Nothing Less Than Elegant

By connecting a load across the layers allows the surplus of free electrons - with no chairs to sit in or holes to fill - a path to exit the top layer down into the bottom layer. In doing so, some of the electrical energy is tapped from these electrons, by passing through the grid-like metal contacts on the solar cell supplying electricity to an induced load.

Photovoltaic - Key Components

PV Modules - Produces direct current (DC)

Inverter - Inverts DC to alternating current (AC); may produce square wave, modified sine wave, or pure sine wave output; synchronous inverters match up to the utility's sine wave in grid-tied applications.

*Controller - Regulates voltage from the PV panel to the batteries; controls the voltage to the load; disconnects the batteries from the load before batteries completely drain.

*Batteries - Should be deep cycle, typically lead acid type; should be sized for 3 to 7 days storage for remote applications.

Other Components - Several disconnects (i.e., circuit breakers) between the major components, ground fault protection system, lightning arrestors, battery charger, proper grounding wiring, and monitoring equipment.

*Only used for solar PV systems with battery backup

Solar Energy Benefits

• Renewable• Clean• Silent• Safe• Decentralized or Centralized• Battery back-up for Grid-outage• Modular• Low Maintenance• Continually Improving Technology• Domestic Energy• Job Creation• Economic Incentives• Long-term Cost-Effective• Offsets Electric Bill Payments > 25 yrs

Challenges

• Fairly Expensive Up-front but Costs Decreasing

• Incentives change• May not be Applicable in all Places –

Requires a Large Amount of Surface Space with Ample Sun Exposure

• Public Perception• Toxic When Producing PV Modules,

but Insignificant Over its Long Lifetime

Let’s Go Solar !!!