Solar energy or solar power is energy from the sun that is converted to thermal or electrical energy.
When you say renewable energy, the first thing that comes to mind is solar power. It is known to be the most abundant and cleanest renewable energy source.
Besides that, among all renewable energy sources, solar panels are relatively easy to install compared to turbines and such.
This energy is not only confined to providing electricity or power.
Modern technology allows this energy source to be harnessed for lighting (solar tubular light) and for heating (solar water heater, solar cooker).
There are four main ways to harness solar energy. Each will be briefly discussed in this article:
1. Photovoltaics (Solar Electric)
This is what we commonly see as solar panels. They crown rooftops, road signs and even streetlights.
A solar panel works by allowing photons to break electrons free of their atomic bonds. These subatomic movements consequently generate a flow of electricity.
Firstly, this article will introduce you to photons. Photons are also known as particles of light.
They are the particles travelling from the sun to the photovoltaic cells on the solar panel.
A photovoltaic cell is what solar panels are comprised of. They are the smaller units we see on a solar panel’s surface that ‘catches’ the photons.
Photovoltaic simply means they convert sunlight into electricity.
Each photovoltaic cell is basically a sandwich made up of two slices of semi-conducting material, usually silicon — the same stuff used in microelectronics.
An electric field is needed for each cell to work.
To get this done, manufacturers “dope” silicon with other materials, giving each slice of the sandwich a positive or negative electrical charge.
Electric fields occur when opposite charges are separated. Manufacturers seed phosphorous on the top layer of silicon which adds extra electrons making a negatively charged top layer.
A positive charged layer is produced by giving a dose of boron to the bottom layer which results in fewer electrons.
Some other components of the cell turn the electrons into usable power.
Metal conductive plates on the sides of the cell collect these electrons and transfer them to wires. At that point, the electrons can flow like any other source of electricity.
The electricity produced will then travel from the solar panels to other equipment that helps regulate, store, and distribute power to your household/building or devices.
Some examples of these equipment are charge controller, the battery and inverter.
The inverter is responsible for distributing the power to different circuits of the building. For storage, you can rely on the batteries you install for the system.
Solar panels depend on sunlight, which means night time, bad weather, or obstructions from the sunlight may keep the solar panels from providing electricity.
But worry not, for having the batteries charged during the day could provide electricity during these times where the sun is out.
Sixteen sets of 2kW batteries can last a typical household 3 to 5 days when the weather is bad and the sun isn’t giving enough light.
2. Solar Heating
An example of this is a water heater which can replace the use of electricity and natural gas in heating the water in your shower.
Solar heating technologies collect the thermal energy from the sun and use this heat to provide hot water, space heating, and pool heating for residential, commercial, or industrial applications.
Solar water heater installation is comprised of three main elements: the solar collector which is somewhat the equivalent of the PV cells on solar panels, insulated piping, and a hot water storage tank.
The solar collector is responsible for transferring the thermal heat from the sun to the water.
This heated water will then flow to the storage tank where it will be stored until use.
Auxiliary heating can remain connected to the hot water tank for back‐up if necessary.
A single water heater with a tank capacity of 200 liters can supply hot water for up to six rooms.
Besides that electricity is not consumed, solar water heaters also require low maintenance.
Another example of solar heating is solar air heating.This is a solar thermal technology used for commercial and industrial buildings in which the energy from the sun is captured and used to heat air.
It is mostly used in heating the inside of houses or buildings. It can also be used in agricultural drying.
Most solar air heating systems are wall-mounted, which allow them to capture a maximum amount of solar radiation in the winter.
Specially perforated solar collector panels are installed several inches from a south facing wall, creating an air cavity.
The air is heated around 30-100°F above ambient on a sunny day.
The solar heated air is then ducted into the building via a connection to the HVAC intake.
3. Concentrating Solar Power
This way of harnessing is typically built at utility scale or for large-scale purposes.
Concentrating solar power (CSP) plants use mirrors to reflect sunlight into one particular point, concentrating the energy from the sun to a single or common solar energy- absorbing tool.
This heats water stored in the system turning it into steam to drive traditional steam turbines or engines that goes through generators to create electricity.
The thermal energy concentrated in a CSP plant can be stored and used to produce electricity when it is needed, day or night.
This technique uses curved mirrors which focus the sun’s energy onto a receiver tube that runs down the center of a trough and a high-temperature heat transfer fluid, such as synthetic oil that absorbs the thermal heat to make steam and consequently generate electricity thru turbines.
The oil reaches temperatures of 750°F or even higher.
A typical solar collector field contains hundreds of parallel rows of troughs connected as a series of loops, which are placed on a north-south axis so the troughs can track the sun from east to west.
Compact Linear Fresnel Reflector
It uses the principles of curved-mirror trough systems.
But it uses long parallel rows of lower-cost flat mirrors instead of curved ones.
These modular reflectors focus the sun’s energy onto elevated receivers, which consist of a system of tubes through which water flows.
The concentrated sunlight makes steam by boiling the water in these tubes, generating high-pressure steam for direct use in power generation and industrial steam applications.
These systems use a central receiver system, which allows for higher operating temperatures and thus greater efficiency.
Computer-controlled flat mirrors (called heliostats) track the sun along two axes and focus solar energy on a receiver at the top of a high tower which makes it look like a lit beacon.
The focused energy is used to heat a transfer fluid (over 1,000° F) to produce steam and run a central power generator.
In using molten salt as a transfer fluid and as thermal energy storage medium, energy storage can be efficiently incorporated, allowing 24 hour power generation.
With this technique, mirrors are distributed over a parabolic dish surface to concentrate sunlight on a receiver fixed at the focal point.
In contrast to other CSP technologies that employ steam to create electricity via a turbine, a dish-engine system uses a working fluid such as hydrogen that is heated up to 1,200° F in the receiver to drive an engine such as the Stirling engine.
4. Passive Solar
Solar technology can be distinguished into active and passive. Photovoltaics and concentrating solar power are examples of active solar technology.
Passive technology includes designing, constructing and orienting rooms or buildings to optimize the use of sunlight and orienting space to favorably use sunlight for the comfort of people without the use of moving parts or electronics.
Passive solar heating is the least expensive way to heat your home.
This design aims to keep buildings heated and ensure that the building’s overall thermal performance retains that heat in winter; but allows the heat to escape in summer.
Examples of passive solar design is the application of northerly orientation of daytime living areas, selection of appropriate glazing, thermal mass for storing heat, insulation and draught sealing, and floor plan design to address heating needs including zoning.
Solar energy is a flexible power source. It can be used for household and commercial buildings. It can also be used in a utility- scale solar power plant.
Although it’s not as simple as adding wind turbines in wind energy, solar energy is flexible enough when it comes to expansion.
Individual or sets of solar panels or mirrors can be added to the existing capacity of your home or a power plant.
But for CSP, it depends on many variables such as land availability, limited cloud cover, access to water sources and such.
Solar energy is clean energy; and most importantly, it has many uses and applications. It is not only concentrated to providing electricity but also heating and lighting.