History of Solar Energy

Solar energy has been used by humans for thousands of years.  For example, ancient cultures used energy from the sun to keep warm by starting fires with it.  They also kept their homes warm through passive solar energy designs.  Buildings were designed so that walls and floors collected solar heat during the day that was released at night to keep them warm.  If you have ever stood in the sun to get warm then you too have utilized solar thermal energy.

The discovery of photovoltaics happened in 1839 when the French physicist Edmond Becquerel first showed photovoltaic activity.  Edmond had found that electrical current in certain materials could be increased when exposed to light.  66 years later, in 1905, we gained an understanding of Edmonds' work when the famous physicist Albert Einstein clearly described the photoelectric effect, the principle on which photovoltaics are based.  In 1921 Einstein received the Nobel Prize for his theories on the photoelectric effect.
Solar cells of practical use have been available since the mid 1950’s when AT&T Labs first developed 6% efficient silicon solar cells.  By 1960 Hoffman Electronics increased commercial solar cell efficiencies to as much as 14% and today researchers have developed cells with more than 20% efficiencies.  20% efficient means that out of the total energy that hits the surface of a solar cell, about 20% is converted into usable electricity.
The first long-term practical application of PV cells was in satellite systems.  In 1958 the Vanguard I, was launched into space.  It was the first orbiting vehicle to be powered by solar energy.  Photovoltaic silicon solar cells provided the electrical power to the satellite until 1964 when the system was shut down.  The solar power system was so successful that PV’s have been a part of world-wide satellite space programs ever since.  The sun provides endless nonpolluting energy to the satellite power systems and demand for solar cells has risen as a result of the telecommunications revolution and need for satellites.
The energy crisis and oil embargos of the 1970’s made many nations aware of their dependency on controlled non-renewable energy sources and this fueled exploration of alternative energy sources.  This included further research into renewable sources such as solar power, wind power and geothermal power.
An economic breakthrough occurred in the 1970's when Dr. Elliot Berman was able to design a less expensive solar cell bringing the price down from $100 per watt to $20 per watt.  This huge cost savings opened up a large number of applications that were not considered before because of high costs.  These applications included railroads, lighthouses, off-shore oil rigs, buoys, and remote homes.  For some countries and many applications, solar energy is now considered a primary energy source, not an alternative.

What is Solar Energy?

The Law of Conservation of Energy:

• Energy can only change from one form to another.
• Energy can not be created or destroyed.

Solar Energy is the energy from the Sun.  The Sun is a big ball of heat and light resulting from nuclear fusion at its core.  The nuclear reaction releases energy that travels outward to the surface of the Sun.  Along the way to the surface the energy transforms so that by the time it is released it is primarily light energy.  Sunlight.  The two major types of solar energy that make it to Earth are heat and light.
Solar energy is often called "alternative energy" to fossil fuel energy sources such as oil and coal.

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One example of our use of solar heat energy is for water heating systems.  A solar panel is used to collect heat.  The heat is transferred to pipes inside the solar panel and water is heated as it passes through the pipes.  The hot water, heated by the Sun, can then be used for showers, cleaning, or heating your home.
We also use solar thermal energy through passive solar designs.  Windows or skylights in your home can be designed to face the Sun so that they let heat into the house, keeping you warmer in the winter.
The light energy from the Sun can be transformed into electrical energy and used immediately or stored in batteries. Photovoltaic (PV) panels are the devices that convert light energy into electrical energy.

Energy changes from one Form to Another.

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Let's look at a solar powered vehicle that runs on electricity directly from solar energy as a simple example in the transformation of energy from one form to another.

• Sunlight hits the PV panel and the panel transforms the light energy into electrical energy.
• The electrical energy (electricity) passes through the wire circuit to the motor.
• The motor transforms the electrical energy into mechanical energy to turn the drive shaft which turns the wheels.
• The wheels rotate on the ground to move the vehicle transforming mechanical energy into vehicle motion (kinetic energy).

Solar Vehicle Ideal Energy Chain:  
Light Energy >> Electrical Energy >> Mechanical Energy >> Kinetic Energy

Energy transformation is not perfect.....

The above case is ideal because not all systems are perfect and in reality there will be losses of energy from our system.
In a simplified view of this case some losses will be from:

• friction of electrons passing through the wires;  this is released as heat energy.
  
• friction of the drive shaft or wheels on the ground;  this is released as either heat or sound energy.
  

Even with these losses the law of conservation of energy still holds.  The amount of energy into a system will always equal the amount of energy out of a system.

What is Solar Power?

The word solar stems from the Roman word for the god of the sun, Sol.  Therefore, the word solar refers to the Sun and “solar power” is power from the Sun.

When we say something is solar powered, we mean that the energy it uses for power came directly from solar energy or sunlight energy.  The sun provides Earth with 2 major forms of energy, heat and light.  Some solar powered systems utilize the heat energy for heating while others transform the light energy into electrical energy (electricity).
There are many practical applications for solar power that are in use today.  Passive solar home designs utilize heat energy.  By slanting windows in a house and facing them to the south you can control the heat energy that enters the house.  During the winter when the Sun is low in the sky it shines into the window to warm and illuminate the house.  During the summer when the Sun is high in the sky the slant of the windows keeps the sunshine out so that the house stays cooler.
There are vehicles that run on solar power.  Some have PV panels as a direct power source that convert light energy into electricity to power their motors.  Since those cars will not run when the sun is not available it is more practical to have a car powered by batteries that can be recharged with solar energy.
In countries and locations where traditional power sources are not available it is more economical to power a house with solar energy.  To these people, solar is not an alternative energy; it is their primary energy source.

The Sun & Energy

The sun is a star.  It is the largest object in our solar system and one of the larger stars in our galaxy.  The source of energy in the Sun is at its core where hydrogen is converted to helium in a thermonuclear reaction.  This energy travels from the core to the surface of the Sun and is released into space primarily as light.  The energy that comes to the Earth is in 2 main forms, heat and light.

Every hour, enough sunlight energy reaches the Earth to meet the world’s energy demand for a whole year.

--- U.S. Department of Energy ---

The amount of energy from the Sun that reaches the Earth annually is 4 x 10¹⁸ Joules.***

4 x 10¹⁸ Joules/ Year ÷ 365 Days/ Year = 1 x 10¹⁶ Joules/ Day
1 x 10¹⁶ Joules/ Day ÷ 24 Hours/ Day = 4 x 10¹⁴ Joules/ Hour
The amount of energy consumed annually by the world's population is about 3 x 10¹⁴ Joules.

Speed of Light Energy from the Sun to Earth.

The earth is the third planet from the sun at a distance of about 93,000,000 (93 million) miles.  If you could pitch a fast baseball to the sun at 100 miles per hour (mph) it would take the ball over 100 years to get there.  On the other hand, it only takes light energy 8½ minutes to reach the earth from the surface of the sun, traveling at the speed of light of course.

Pitching a Baseball at 100 mph to the Sun***

93,000,000 miles ÷ 100 miles/ hour
= 930,000 hours to reach the Sun.;
930,000 hours ÷ 24 hours/ day
= 38,750 days to reach the Sun;
38,750 days ÷ 365 days per year
= 106.16 years to reach the Sun.

Light Energy traveling to Earth***

The speed of light is equal to about 11,000,000 (11 million) miles/ minute. 
93,000,000 miles ÷ 11,000,000 miles/ minute
= 8.45 minutes for light  to travel from the Sun to Earth.
***Calculations are rounded for simplicity.

What are Solar Panels?

Solar panels collect heat energy from the sun. We call this heat solar thermal energy. A simple example of a solar panel is a closed box with a top made of a transparent material such as glass or plastic.

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The sun shines through the glass and heats up the inside of the box. This is the same type of heating that happens to the inside of a car when it sits in the sun. In some cases the inside of the box is painted black so that it absorbs more heat. The heat that is collected inside the box can then be used for several purposes. The most common uses for solar panels is to heat air or water.

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A system that uses solar thermal energy to heat air is not complex. A transparent top is attached to a box. The box has an inlet pipe for cool air. The cool air can be pushed into the box using a fan. The cool air moves through the inlet pipe into the box. Inside the box the air is warmed by the heat energy from the sun rays. As more cool air is pushed into the box the warm air is forced out the other end of the box through the outlet pipe. The warm air can now be used to heat something like your home. Some very large systems use a solar panel on the roof of a house to heat a whole room.  The warm air in that room is then blown through vents to heat the whole house.
Solar panels that are designed to heat water work almost the same way as ones designed to heat air. In a simple example there is a pipe that runs through the inside of the box.

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The sun rays heat the air inside the box. The heat in the air is transferred to the pipes then the heat in the pipes is transferred to the water. As cool water is pumped into the inlet pipe the warm water is forced out of the outlet pipe. We can now use this warm water for something like a bath or shower.
These pictures are only a simple representation of the basic concepts.  In practice, solar water and air heaters can be more complex.
The terms "Solar Panel" and "Photovoltaic Panel" describe two different devices.  We use the terms as follows:
A Solar Panel collects and utilizes heat energy from the sun.
A Photovoltaic Panel transforms light energy into electrical energy.

What are Photovoltaic (PV) Panels?

Photovoltaic Panels are are used to transform sunlight energy into electrical energy.  ”PV panel” is the common name for a photovoltaic panel.  Literally translated photovoltaic means "light-electricity".

Photovoltaic means "light-electricity".  It is formed from photo- which means light and -voltaic which means electrical current or electricity.
PV panels are made up of smaller sections called solar cells.  Solar cells, like batteries, each have a rated value of voltage (V or volts) and amperage (A or amps).  The total power in wattage (W or watts) delivered is the voltage times the amperage.
Volts x Amps = Watts or
V x A = W
Batteries can be arranged in parallel or in series depending on the requirements of the device we want to power.

Batteries in Parallel (large image)

In parallel the amperage is additive and the voltage is constant.  If we have batteries that are 1.5 V each and 1.8 A each then:
A_total = A₁ + A₂
A_total = 1.8 A + 1.8 A = 3.6 A and
Power = 1.5 V x 3.6 A = 5.4 Watts

Batteries in Series(large image)

In series the voltage is additive and the amperage is constant.
V_total = V₁ + V₂
V_total = 1.5 V + 1.5 V = 3.00 V and
Power = 2.25 V x 1.8 A = 4.05 Watts
How many of these batteries will you need and how will you have to arrange them if you want to power a 6 volt radio?

Solar Cells or Panels in Parallel (large image)

In parallel the amperage is additive and the voltage is constant.  If we have cells that are 0.5 V each and 0.1 A each then:
A_total = A₁ + A₂
A_total = 0.1 A + 0.1 A = 0.2 A and
Power = 0.5 V x 0.2 A = 0.1 Watts

Solar Cells or Panels in Series (large image)

In series the voltage is additive and the amperage is constant.
V_total = V₁ + V₂
V_total = 0.5 V + 0.5 V = 1.0 V and
Power = 1.0 V x 0.1 A = 0.1 Watts
Solar cells are connected and arranged into a single panel.  Some standard panel sizes are 12 volt and 24 volt.
How many of these cells will you need and how will you have to connect them to make a 12 volt solar panel?
If you have 2 panels that are rated at 12 volts each how many of them will you need and how will you have to connect them if you want a 24 volt system?
The terms "Solar Panel" and "Photovoltaic Panel" describe two different devices.  We use the terms as follows:
A Solar Panel collects and utilizes heat energy from the sun.
A Photovoltaic Panel transforms light energy into electrical energy.

What are Solar Cells?

Solar cells are devices which convert solar light energy directly into electricity and function by the photovoltaic effect.  Photo- means light and -voltaic means electrical current or electricity  (light-electricity).  A solar cell provides direct current (DC) electricity that can be used to power DC motors and light bulbs among other things.  Solar cells can even be used to charge rechargeable batteries so that electricity can be stored for later use when the sun is not available. The fully charged batteries are portable energy that can be used whenever and wherever they are needed.

Solar cells provide DC electricity similar to batteries however, batteries differ because they operate through a process known as an electrochemical reaction.  This process will provide an electrical current (electro-) from a chemical reaction (-chemical) that occurs inside the battery.  When you hook up a motor to the battery, also known as a load, the reaction begins and electrons flow as shown in the picture: "Battery Circuit".  Direct current (DC electricity) is different from the alternating current (AC electricity) that is used to power the TV, refrigerator, and other appliances in your home however, DC can be converted to AC when needed.

Battery Circuit (large image)

Solar cells produce DC electricity from light.  Sunlight contains packets of energy called photons that can be converted directly into electrical energy.  You can’t see the photons but they hit the cell and produce free electrons that move through the wires and cause an electrical current as shown in the picture: "Solar Cell Circuit".  The electrical current is the electricity that powers the motor.  Although you can't see the photons you can see the light and you can assume that the amount of photons hitting your solar cell is related to the amount of light hitting your solar cell.  A greater amount of light available means a greater amount of photons are hitting your solar cell and the more power you get from it.

Solar Cell Circuit (large image)