Solar Energy Explained - EnergizedPAK

This article will give you a basic understanding of solar energy, its history and applications. 

What is Solar Energy?

Solar energy is the energy emitted from the sun (a natural nuclear reactor). Our planet captures more than billions of photons (tiny packets of energy) from the sun every day. These photons determine the climate and support life on earth. 

Two interesting facts about Solar energy,

1. “Our sun emits more energy in one second than the combined consumption of every person who either has lived or is living on earth!”

2. “Did you know that less than two hours of sunlight striking our planet can fulfill our electricity needs for an entire year.”

History of Solar Energy

From the very beginning, people have been harnessing solar energy by using it to cook food, stay warm or find the way in the darkness. People used simple magnifying glasses to concentrate sunlight into beams so hot they would cause wood to catch fire. In France, over a century ago, a scientist used heat from a solar collector to make steam to drive a steam engine.

Almost 100 years ago, people scientists and engineers began researching ways to use solar energy in earnest. In 1936, Charles Greely Abbot, an American astrophysicist invented a solar boiler. 

In the mid-1950s, Bell Telephone discovered that an element found in the sand called silicon (Si) creates an electric charge when exposed to sunlight. This led to the discovery of solar cells that capture the sun’s energy and convert into electricity.

Among other renewable energies, solar energy has been adopted more quickly. In the U.S alone, there are several state and federal incentives and policies contributing to driving down the cost of solar panels far enough to become more widely consumed. According to the market insights for the year 2019 provided by Solar Energy Industries Association (SEIA), The installed solar photovoltaics capacity in the U.S  can power 13.1 million American homes and this number is expected to double over the next five years. 

Solar Energy Applications

Applications of solar energy can be classified into three main categories.

  • Residential (Homes, Farms, etc.)
  • Commercial (Buildings, Industries, etc.)
  • Utility (Power Plants etc.)

As you’re aware, solar energy is spread out over a large area and is not constant at any specific area or place at one time. How much solar energy an area receives depends on several conditions which include the time of day, the season of the year, the latitude of the area, and the clearness or cloudiness of the sky. 

A solar collector is like a parked car on a sunny day. As sunlight passes through the car’s glass windows, it is absorbed by the dashboard, seat covers, walls, and floor of the car. The light that is absorbed changes into heat. The car’s closed glass windows let the light in, but don’t let all the heat out. If the car windows are open the heat will more quickly dissipate, but that’s another matter.

From the example above, a solar collector is an object which does three things:

  • it allows sunlight inside the glass (or plastic);
  • it absorbs the sunlight and changes it into heat;
  • it traps most of the heat inside.

Note that all solar technologies used today work on the principle of sunlight collection.

We have classified the applications of solar energy into 2 categories.

  1. Solar Space Heating (Thermal Applications)
  2. Solar Electricity (Power Applications)

Solar Space Heating

Space heating means heating the space inside any structure with roof and walls. It could be a house, a shop or a factory, etc. 

There are three types of solar space heating systems. 

  1. Passive
  2. Active
  3. Hybrid (A combination of both passive and active)

Passive Solar Space Heating

In a passive solar building, the whole structure operates as a solar collector (heat absorber) and does not use mechanical or electrical devices. The main design requirements of a passive solar space heating structure are:

  • Latitude, sun path, and insolation (sunshine)
  • Seasonal variations 

Passive Solar System


To help you understand better, let us take an example of a passive solar house. It would not have any special mechanical equipment such as pipes, ducts, fans, or pumps to transfer the heat Instead, the house is designed in such as way that it relies on properly positioned windows. Since the sun shines from the south in North America, passive solar structures are built so that most of the windows face south. 

A passive solar house would convert solar energy into heat just as a parked car would. Sunlight passes through a building’s windows and is absorbed in the walls and floors.

To control the amount of heat in a passive solar house, the doors and windows are either closed to let the heated air in or opened to let the air out. 

Usually, at night, passive solar homeowners use heavy curtains or shades by pulling them over their windows to keep the day’s heat inside. 

While in summers, awnings or roof coverings are used to help keep the house cool by shading the windows from the blazing sun.

Most passive homes are located in a quiet and peaceful place. A home heated naturally by warming the walls or floors is more economically beneficial than using mechanical and electrical devices to heat the air inside a house. 

It’s always convenient to use solar energy equipment to make electricity for your house. That way you are both warm and lit up!!!!

After the installation of solar energy equipment, your passive home solar system would now be labeled as a hybrid solar system.  

Active Solar Space Heating

An active solar building operates on both mechanical equipment and the solar collection (heat absorption) principle. Active solar structures are commonly used at places where solar energy is not sufficient.  

For active systems, special solar collectors that look like boxes covered with glass are used. Dark-colored metal plates inside the boxes absorb the sunlight and change it into heat. You may ask have one observation, why use only dark colors? Well, dark colors especially black absorbs more sunlight than any other light color. 

Depending on the usage, air or a liquid flows through collectors and is warmed by this heat. The warm or heated air or liquid is then distributed to the rest of the house just as it would be with an ordinary furnace system.

Solar collectors are usually placed high on roofs where they can collect the most sunlight. They are also put on the south side of the roof where no tall trees or tall buildings will shade them.

To read more about active solar space heating, click here.

Storing Solar Heat

Why do you store anything? The answer would be to use it later. The same logic applies here. You need to use an efficient heat storage system to keep yourself warm during nights or on rainy days. Otherwise whats the point of investing money on the solar energy system.

Storing heat is a challenge confronting any solar heating system; whether passive, active, or hybrid. 

In passive solar homes, heat is stored by using dense interior materials (masonry, adobe, concrete, stone, or water) that retain heat well. These materials are good absorbers and retain surplus heat and radiate it back into the house when its dark and cool. Some passive homes may have walls up to one foot thick.

In an active solar home, heat can be stored in two ways

  • A large tank to store hot liquid, or
  • Rock bins beneath a house to store hot air.

Houses with active or passive solar heating systems may also have a backup system that can be a furnace, wood-burning stove, or another heat source to provide heat in case there is a long period of cold or cloudy weather. 

Solar Hot Water Heating

Conventional water heating is expensive and is the second leading home energy expense, costing an average family between $350-$800, a year. 

We can always use solar energy to heat our water. Based on your location, family size and water usage habits, a well-maintained and efficient solar water heater (geyser) lasts 15-20 years longer than a conventional water heater and can pay for itself in five or less. 

Note that most solar water heater manufacturers provide excellent warranties and financing plans. 

A solar water heater works on the same principle as solar space heating. A solar collector is mounted on the roof, or in an open area with direct sunlight. It collects sunlight and converts it to heat. When the collector becomes hot enough, a thermostat starts a pump. The pump circulates a fluid, called a heat transfer fluid, through the collector for heating. The heated fluid then goes to a storage tank where it heats water. The hot water may then be piped to a faucet or showerhead. Most solar water heaters that operate in winter use a heat transfer fluid, similar to antifreeze, that will not freeze when the weather turns cold.

Taking advantage of the latest advancements in solar technology, residential and commercial property owners based on their location can either install solar water heating systems (geysers) or design their buildings with solar heating.

Today over 1.5 million homes in the U.S. use solar heaters to heat water for their homes or swimming pools.

Solar Electricity

Solar energy can be utilized and produced in several ways, the most common of which is with photovoltaic panels (also known as solar or Photovoltaic or PV panels) that convert sunlight into electricity. 

There are two main solar electricity systems:

  • Photovoltaic Electricity
  • Solar Thermal Electricity

Photovoltaic Electricity

In the mid-1950s, Bell Telephone discovered that an element found in the sand called silicon (Si) creates an electric charge when exposed to sunlight. This led to the discovery of solar cells that capture the sun’s energy and convert into electricity.

Simply put, a solar cell is a semiconductor device made up of wafers of pure silicon (Si) doped with special impurities, which convert sunlight either visible light, ultraviolet (UV) radiation or infrared (IR) radiation into direct current (DC) by using photovoltaic action of the cell without the use of any moving parts.

Solar cells or PV cells operate according to the photovoltaic effect. Here, “Photo” means light and “Voltaic” means electricity. They are constructed with a positive and negative layer which together creates an electric field.

Solar Energy Power Plant

Solar panels directly convert sunlight (photons) to electricity (voltage). When sunlight (photons) hits a solar cell, electrons are knocked out of their respective atoms and if conductors are attached to the positive and negative sides of a cell, it forms an electrical circuit. When these electrons flow through an electrical circuit they generate electricity.

Solar or PV solar panels generate direct current (DC) electricity. With DC electricity, electrons are unidirectional and flow in one direction around a circuit. 

Solar Thermal Electricity

Solar thermal systems use the sun’s heat to make electricity. We’ve discussed a lot about solar thermal heating above, the principle is the same. Solar thermal electricity systems use solar collectors with mirrored surfaces to concentrate sunlight onto a receiver to super-heat a liquid. 

This super-heated liquid makes steam that drives a steam turbine to produce electricity like most conventional power plants.

Solar thermal systems are of three main types: 

Central Receiver System

A central receiver system uses large mirrors on top of a high tower to reflect sunlight onto a receiver. This system is also known as a Solar Power Tower.

Dish-Shaped System

This system uses a dish-shaped solar collector to collect the sun’s energy. This system resembles a TV satellite dish.

Trough System

This system is most promising and uses mirrored troughs to collect sun’s energy.