Photovoltaic Systems Engineering Review of Energy and Power SEC598 (SEC501) Photovoltaic Systems Engineering (SEC501 Solar Engineering and Commercialization, I) Session 02 Review of Energy and Power August 22, 2017

A Quick Review of Energy and Power Energy is a measurement of capacity to do work. It is expressed in units of joules (J) Power is the rate at which energy is employed. It is expressed in units of watts (W). One watt equals one joule per second

A Quick Review of Energy and Power Energy is a measurement of capacity to do work Work is defined as an amount of force applied to an object it to move it a certain distance: The work done to move an object of mass m against the force of gravity to a height h is:

A Quick Review of Energy and Power A few words about energy and power: Energy is a measurement of capacity to do work. It is expressed in units of Joules (J) Energy is expressed in two different forms: Kinetic Energy – energy in motion Potential Energy – energy in position Consider the pendulum

A Quick Review of Energy and Power PE = mgh h PE = 0

A Quick Review of Energy and Power Lets suppose a ball is moved to the top of the ramp, and it gains potential energy of If the ball is moved to the top of the ramp in 100 seconds, the power required to do this is If the ball is moved to the top of the ramp in 1 second, the power required to do this is

A Quick Review of Energy and Power The original units for energy and power came from thermal science One calorie (1 cal) is the energy required to raise one gram of water by one degree Celsius (1oC) One kilocalorie (1kcal) is the energy required to raise one kilogram of water by one degree Celsius (1oC) – this is 1 food calorie One British Thermal Unit (1 BTU) is the energy required to raise one pound of water by one degree Fahrenheit (1oF) The proper unit for energy (work) in the scientific community is the Joule (J) 1 cal = 4.18 J 1 BTU = 1055 J

A Quick Review of Energy and Power The most common unit for energy in energy policy and engineering circles is the kilowatt-hour (kWh) 1 kWh = 1000W . 1hour = 1000W . 3600 sec = 3,600,000 W.sec = 3,600,000 J = 3.6MJ But the energy content of fuels (like coal, oil) is usually quoted in BTUs 1 kWh = 3.6MJ .0.00095 J/BTU = 3412 BTU The BIG unit of energy measurement is the Quad: 1 Q = 1015 BTU = 2.93 x 1011 kWh = 293 TWh

A Quick Review of Energy and Power So what is the size of 1 kWh, in common, everyday values? Suppose Prof. Pasqualetti decides to read a book before retiring for the night, so he switches on a reading light with a 100W bulb. He reads for 10 hours, then switches off the light. Prof. Pasqualetti’s light bulb has consumed an electrical energy value of: 100W * 10hours = 1000Wh = 1kWh

A Quick Review of Energy and Power Another example of 1 kWh Now suppose Prof. Pasqualetti decides to go to Argentina and climb Mt. Aconcagua. How much potential energy does he gain during the climb?

A Quick Review of Energy and Power Energy is “conserved” – it is neither created nor destroyed. But it can be converted from one form to another Energy is also expressed in several different formats: Optical Energy Chemical Energy Mechanical Energy Thermal Energy Electrical Energy

A Quick Review of Energy and Power Optical Energy is the energy contained in light; Optical Power is the rate at which optical energy is delivered. Chemical Energy is energy stored in atomic bonds, and in the motion or separation of ionic charges. The lead acid battery, or the AA dry cell, stores chemical energy. Mechanical Energy is the energy in moving or displaced objects at both microscopic and macroscopic scales. A spinning flywheel has kinetic mechanical energy; water stored behind a dam has potential mechanical energy. Thermal Energy refers to the energy associated with heat and its transfer

A Quick Review of Energy and Power Electrical Energy is the energy contained in electrons and other charged particles; Electrical Power is the rate at which electrical energy is delivered to an “electrical load” Electrical Power is calculated by multiplying the Electrical Current and the Electrical Voltage in the electrical device Current is a measure of the flow of electrons (amperes) Voltage is a measure of the potential energy (volts)

A Quick Review of Energy and Power Electrical power can be “delivered” from an electrical source (a battery, a generator, a solar cell) and is consumed or dissipated by an electrical load (a motor, an electrical stove, a computer) An examination of the power equation shows that the power is zero when the current is zero (open circuit) or the voltage is zero (short circuit)

A Quick Review of Energy and Power Energy is “conserved” It is neither created nor destroyed. The expression, “The solar module created 100 joules of energy” is technically incorrect But it can be converted from one form to another The expression, “The solar module converted 100 joules of optical energy into 20 joules of electrical energy and 80 joules of thermal energy (heat)” is technically correct.

A Quick Review of Energy and Power A few words about units, cont. The SI format is Number Modifier Unit 750,000 W is expressed as 750kW 7,500,000 W should not be expressed as 7500kW, but rather 7.5MW 1 - 999 k, M, etc

A Quick Review of Energy and Power A few words about units The organization, SI, has established these “attachments” to simplify Scientific Notation Order of magnitude SI name 109 Giga (G) 1012 Tera (T) 1015 Peta (P) 1018 Exa (E) 1021 Zetta (Z) 1024 Yotta (Y)

(3% of US electricity demand) The Solar Enterprise Both nationally and globally, the solar business has grown by leaps and bounds in the last two decades Current US Solar Power 44.7 GW (3% of US electricity demand)

US Photovoltaic (PV) System Installations SEIA

US Photovoltaic (PV) System Installations SEIA

The Solar Enterprise SEIA

Advantages to solar power Inexhaustible input power The sun’s lifetime is billions of years Direct conversion to electrical power Optical energy -> Electrical energy Zero emissions during operation No carbon footprint Earth-abundant raw material supply (for cells) Silicon is the most abundant element in the earth’s crust Reliable and durable technology

Disadvantages to solar power 1. It is an intermittent energy resource Night and day 2. It adds instability to the electrical grid Clouds, shadowing produce output with fluctuations 3. It has low power density 80% of incident sunlight is unused 4. Its power curve does not match the system demand profile With higher penetration, its marginal value shrinks to zero 5. It is a disruptive technology It produces “load defection”, possibly followed by “grid defection”

The Solar Resource – as observed in Phoenix

What has fueled this growth? Technological Factors Silicon solar cells and modules Inexhaustible input power at zero cost Societal Factors Concerns about fossil fuel and nuclear power plants An increasing awareness of sustainability issues Economic Factors Steady reduction in cost of PV systems Favorable government policies and business climate

What might impede this growth? PV system components Dependence on materials that are not earth-abundant High labor costs New PV system components Problems with smart components Certain economic and business factors Hostile interactions with utilities, utility regulating bodies Net metering issues Power demand charges Expansion of low cost natural gas supply and use in utility scale electricity generation Recent analysis showing that solar energy suffers from a “merit order effect” which will shrink its value with increasing penetration into the energy market