Estimating solar energy requirements to meet U.S. energy needs:

an outreach event

Daniel Esposito,1 Vernon Alt2

1Columbia University2Northrup Grumman Corporation

20 mW

60 W

1.2 kW

1 GW

An Introduction to Energy and Power• Energy is the capacity to do work and has the unit of Joules (J)• Power is the rate of energy consumption or generation and has

the unit of Watts (W), equal to one Joule/second.

3,500,000,000,000 W

= 3.5 TW= 3.5x1012 TW

Primary Power Use in the U.S.

Today’s Question: How Many Solar Panels are Needed to Power the U.S.?

B.) Virginia102,000 km2

A.) Connecticut13,000 km2

D.) Alaska1,507,000 km2

C.) Texas684,000 km2

(40,000 mi2)

(5,000 mi2)

(267,000 mi2)

(588,000 mi2)

Photovoltaic Energy Conversion

ElectricityLight

Load

U.S. Energy consumption= 3.5 TW

Solar Panel

Area?

Why Solar Energy?1. Solar is abundant

130,000 TW

Why Solar Energy?1. Solar is abundant2. Solar is widely available across the globe

Why Solar Energy?1. Solar is abundant2. Solar is widely available across the globe3. Solar is a renewable resource

Why Solar Energy?1. Solar is abundant2. Solar is widely available across the globe3. Solar is a renewable resource4. Solar is environmentally friendly. It does

not emit green house gases or other pollutants while operating

Description of a Solar Cell 4 main components of a solar cell:

Sun light

3. back contact2. front contact1. Semiconductor

4. wires(+)(-)

Electricity

Leads

Measuring electrical power produced by aa solar cell

1. Voltage (units: Volts)2. Current (units: Amps)3. Area (units: cm2)

Multimeter

Quantities to be measured

Power = (Voltage) x (Current) [=] Watts

Calculating Required Area of Solar Panels:

1. Find electrical power from a single solar panel (Ps ) :

(unit: Watt)

2. Find number of Solar Panels required to get 3.5 TW:

Number of Panels = 3,500,000,000 ,000 Watts

(Power from 1 panel)x(6/24)

3. Find total area occupied by solar panels

Total Area = (Number of panels) x (Area of 1 Panel)

Ps = (Voltage) x (Current)

Virginia102,000 km2

Connecticut13,000 km2

Alaska1,507,000 km2

Texas684,000 km2

(40,000 mi2)

(5,000 mi2)

(267,000 mi2)

(588,000 mi2)

How did you do???

Why Isn’t Solar Energy More Prevalent?

1.$$$$$$$$$$2.Solar Intermittency

Why Isn’t Solar Energy More Prevalent?

Price trends in U.S., 1976-2009^

^ J. Newman, J. Electrochem. Soc., 2012.

3. Efficiency

Final Questions?

Extra Slides

What is Electricity, and how do we quantify the energy/power in electricity?

•Electricity is the flow of negatively charged electrons •Three major metrics to describe electricity:

1. Voltage (V) 2. Current (I) 3. Power (P)

electron(-)

(+)

V

Power= Current x Voltage

Unit: WattUnit: Volt Unit: Amp

(-)

(+)

𝑷=𝑰𝒙𝑽 ❑

•Light is made of photons•The more photons being emitted by a light source, the brighter the light source appears, and the more power being released by the light source

Power Power

low

high

What is Light?

How do we measure the power contained by Light?

1. Brightness (B)

Flux meter

2. Power, also known as Irradiance (PL )

unit: lux

unit: mW / cm2

Detector

PL = B/1,000

=60 billion light bulbs

=3 billion toasters

=4 thousand nuclear plants

3,500,000,000,000 W

Primary Energy Use in the U.S.

Technology (Math & Science)

Policy Business•Politicians•Psychologists•Sociologists•Urban planners

•Economists•Bankers•Marketing

•Engineers (Chemical Electrical, Mechanical, Civil)•Scientists (Chemists, Physicists, Biologists)•Technicians & skilled workers

How do we make Solar Panels more common

Sustainable Energy Future

Where does Energy Come From?

(Oil)

2 MAJOR Problems with fossil fuels

1. Fossil fuels are non-renewable

2 MAJOR Problems with fossil fuels

2. Global Warming / Pollution

Fossil Fuels(Coal, oil, natural gas)

Energy

2 MAJOR Problems with fossil fuels

Fossil Fuels(Coal, oil, natural gas)

Energy

2. Global Warming / Pollution

Some outgoing light is trapped by the earth’s atmosphere and warms turns it into heat

Some light is radiated back into space by earth

Much of the sun’s radiation is absorbed by the Earth

Greenhouse Gas Effect

One More Important Metric: Efficiency

ElectricityLight

PL PPV

One More Important Metric: Efficiency

Power produced by the solar panel

Power from the sun or light

Conversion efficiency=

ElectricityLight

PL PPV

PPV

PL

=

Electrical Loads

2 Amps

20 mAsmall lights

Refrigerator

80 mARadio