What are solar panels?

Solar panels, also known as solar panels, are devices designed to capture and transform solar energy into useful energy. Solar panels fall into two main categories, each with a different function and purpose.

Photovoltaic (PV) solar panels

Solar photovoltaic panels are designed to convert solar energy directly into electricity. The photovoltaic effect is the process by which semiconductor materials (such as silicon) exposed to sunlight produce electric current. The main components are:

Photovoltaic cells: Individual units that convert light into electricity.

Photovoltaic module: An assembly of photovoltaic cells connected and encapsulated to form a panel.

PV system: One or more PV modules, inverters (which convert the produced direct current into alternating current) and other components, such as mounting and wiring systems, are included in the package.

Subtypes of photovoltaic panels:

• Monocrystalline: High efficiency and long life. They are more expensive to manufacture.

• Polycrystalline: Less efficient than monocrystalline but less expensive.

• Thin Film: Lower efficiency, but can be more flexible and lighter.

Solar thermal panels

Solar thermal panels are constructed to capture thermal energy from the sun and transfer it to a medium (such as air or water) for use in heating, water heating or steam production. They generate heat rather than electricity from sunlight.

Types of solar thermal panels:

Flat plate solar collectors: These are mainly used to heat water for domestic use. They consist of a flat box with a black absorber that absorbs heat and transmits it to the circulating fluid.

Evacuated tube collectors: These are more efficient in cold climates and have a higher thermal efficiency. They use glass tubes containing a heat transfer fluid and an absorber.

Concentrating solar systems: Use mirrors or lenses to concentrate sunlight onto a small area that reaches extremely high temperatures. They are suitable for industrial applications and for large solar power plants producing electricity.

Main differences between photovoltaics and thermals

Photovoltaic panels generate electricity, while thermal panels produce heat. Photovoltaic panels are used in electrical energy systems, from small devices to large solar installations. Thermal panels are used to heat water, air or produce steam for heating or industrial processes.

Photovoltaics rely on the photovoltaic effect, while thermals use heat absorption and heat transfer. Both types of solar panels represent key technologies in the transition to more sustainable and renewable energy sources.

How photovoltaic solar panels work

Photovoltaic solar panels convert sunlight into electricity by means of the photovoltaic effect, which is a process that occurs in semiconductor materials.

Here is a step-by-step description of how they work:

Collecting sunlight: Sunlight is made up of photons, which are particles of energy. When photons strike the surface of a photovoltaic cell, they are absorbed by the semiconductor material (usually silicon).

Electron-hole pair generation: Photon energy excites electrons in the semiconductor material, raising them to a higher energy level. This process creates electron-hole pairs: a free electron (negatively charged) and a hole (positively charged).

Charge separation: Photovoltaic cells are designed with a junction of two layers of semiconductor materials, one n-type (electron-rich) and one p-type (hole-rich). The junction between these two layers creates an internal electric field that pushes electrons into the n-layer and holes into the p-layer, separating the charges.

Generation of electric current: The separation of charges establishes a voltage between the two layers. When an external circuit is connected between the n- and p-layer, electrons flow through the external circuit from the n-layer (negative) to the p-layer (positive), generating an electric current.

Energy conversion and use: The direct current (DC) generated by the PV cell can be used directly in DC applications or converted to alternating current (AC) via an inverter for use in the conventional power grid. PV systems can include batteries to store energy and provide electricity when there is no sunlight.

Operation of solar thermal panels

Solar thermal panels are designed to capture thermal energy from the sun and use it to heat a fluid, which can be water, air or a heat transfer fluid. Here is a step-by-step explanation of how solar thermal panels work:

Collecting solar radiation: Solar energy collectors absorb solar radiation. Flat plate collectors consist of a flat box with a transparent cover (glass or plastic) and a dark absorber plate that absorbs the radiation. The solar radiation heats an absorber inside an evacuated (airless) tube in evacuated tube collectors, which reduces heat losses by convection and conduction.

Heat transfer fluid heating: The solar collector absorbs solar energy in a heat transfer fluid that circulates through tubes in contact with the absorber plate or inside the evacuated tubes.

Circulation of the heated fluid: The heated fluid, driven by a pump or by natural circulation (thermosyphon), circulates through the pipe system. A pump regulates the fluid flow in active systems. Due to the differences in density between the hot and cold fluid, the fluid circulates naturally in passive (thermosyphon) systems.

Heat transfer to the water in use: The hot fluid passes through a heat exchanger before being transferred to the water in the storage tank. The heat exchanger can be inside the storage tank, known as an internal heat exchanger, or it can be a separate component, known as an external heat exchanger.

Hot water storage: The heated water is stored in the storage tank and can be used for domestic or industrial purposes. In general, the tank is well insulated to reduce heat losses.

Control and regulation of the system: A control system monitors the temperature of the water and the transfer fluid in the storage tank. The pump is activated to circulate the hot fluid when the temperature of the fluid in the collector is higher than that of the water in the tank. To ensure safe and efficient operation of the system, additional valves and sensors may be present.

Residential solar panel applications

Solar home systems

• Installation of solar panels on roofs or gardens to generate electricity.
• Reduction of electricity bills by producing part or all of the electricity needed.
• Possibility to sell surplus energy to the grid in some countries.

Domestic water heating systems

Use of solar thermal collectors to heat water for showers, toilets and other domestic uses.

Storage of hot water in tanks for all-day use.

Swimming pool heating systems

Use of solar thermal collectors to maintain swimming pool water temperature.

Extending the swimming pool season by maintaining a comfortable water temperature.

Solar heating systems

Use of solar thermal energy for indoor heating via radiators or underfloor heating systems.

Integration with conventional heating systems to reduce fossil fuel consumption.

Solar lamps for gardens and outdoors

Use of small photovoltaic solar panels to power outdoor lamps and security lights.

Greater security and savings in electricity consumption by using solar energy.

Commercial applications of solar panels

Commercial Solar Power Plants

• Installation of large arrays of solar panels on the grounds or roofs of commercial buildings.

• Electricity production for offices, factories and other commercial buildings.

• Reducing long-term operating costs and improving business sustainability.

Water heating systems for hotels and hospitals

• Use of solar thermal collectors to heat large volumes of water used in laundries, kitchens and bathrooms.

• Significant reduction in energy costs associated with water heating.

Solar air conditioning systems

• Integration of solar thermal systems for heating and cooling of commercial buildings.

• Use of absorption technology for solar air conditioning in large buildings.

Applications in industrial processes

• Use of solar thermal energy for processes requiring heat, such as drying, pasteurisation and heating of fluids in factories and industrial plants.
• Reduction of fossil fuel use and carbon emissions.

Solar lighting for commercial areas and car parks.

• Implementation of solar-powered outdoor lighting systems in car parks, walkways and common areas.
• Improved energy efficiency and reduced operating costs.

Combination of solar energy with other energy systems.

• Integration of solar panels with wind generators, energy storage systems and back-up generators.

• Ensuring a constant energy supply and reducing dependence on the grid.

Materials used in the manufacture of solar photovoltaic systems

1. Semiconductor Materials

Monocrystalline silicon:

• Characteristics: High purity, single crystal silicon cells.

• Efficiency: High (15-20%).

• Durability: High, lifetime of 25-30 years.

• Impact: Higher efficiency due to purity and uniform crystal structure, but more expensive to manufacture.

Silicio Policristalino: 

• Characteristics: Composed of multiple silicon crystals.
• Efficiency: Moderate (13-16%).
• Durability: High, useful life of 20-25 years.
• Impact: Less efficient than monocrystalline silicon, but cheaper and easier to manufacture.

Amorphous Silicon (Thin Film):

• Characteristics: non-crystalline silicon, very thin layers.

• Efficiency: Low (6-10%).

• Durability: Moderate, lifetime 10-20 years.

• Impact: Lower efficiency, but flexible and lightweight, ideal for specific applications such as portable devices or curved surfaces.

2. Protective glass

High resistance to impact and weather conditions. Protects the photovoltaic cells, ensuring durability and minimising efficiency losses due to physical damage or adverse environmental conditions.

3. Encapsulants – Ethyl-Vinyl-Acetate (EVA)

Plastic material that encapsulates the cells. Provides protection against moisture and vibration, contributing to the durability of the panel.

4. Backing Materials – Tedlar-Polyester-Tedlar (TPT)

Protective layer on the back of the panel. Provides additional protection against moisture and mechanical damage, improving the durability of the panel.

5. Aluminium frame

Lightweight, corrosion resistant. Provides structural support and ease of installation, maintaining the integrity of the panel over time.

Materials used in the manufacture of solar thermal panels

1. Absorbent Materials

Copper: High thermal conductivity. High heat transfer efficiency, high durability, but more expensive.

Aluminium: Good thermal conductivity, lightweight. Good efficiency and lower cost compared to copper, but lower durability in some corrosive environments.

2. Absorbent coatings

High absorption of solar radiation, low thermal emissivity. Improves efficiency by maximising solar energy absorption and minimising heat loss.

3. Tube Materials (copper or aluminium)

High thermal conductivity. High heat transfer efficiency, with increased durability in vacuum tube systems due to reduced thermal losses.

4. Insulation (rock wool or polyurethane)

High thermal insulation capacity. Minimises heat losses, improving system efficiency and heat retention in the collector.

5. Coated glass (tempered glass or low-emissivity glass)

High light transmission, impact resistant. Protects the absorber material and tubes, improving durability and efficiency by allowing more sunlight to be captured.

Impact of solar panel materials

Materials that have high purity and conductivity, such as monocrystalline silicon and copper, often have better power conversion efficiency.

Selective coatings and high transmission glasses also improve system efficiency.

The use of materials such as aluminium and tempered glass that are resistant to corrosion and wear can extend the lifetime of the panels.

The cells and internal components are protected against adverse environmental conditions by encapsulants and additional protective layers.

Common benefits of solar panels

• Reduced electricity and heating bills.
• Possibility of tax incentives and subsidies in some countries.
• Reduction of carbon footprint and contribution to the fight against climate change.
• Use of a clean, renewable energy source.
• Reduced dependence on energy suppliers and fluctuations in energy prices.
• Increased property value by having renewable energy systems installed.

The installation of a solar system in brief

1. Find out if the roof structure or its location can support the weight of the panels and the sunlight.
2. Calculate the required capacity and choose the necessary components (panels, inverters, supports, batteries).
3. Install and fix the support structure for the solar panels.
4. Convert direct current to alternating current by wiring and connecting the inverter.
5. Connect to a storage system or to the grid.
6. Configure the inverter and verify that the system is working.
7. Inspection and approval by local authorities if necessary.

Solar system maintenance at a glance

Check for damage or dirt on the panels and mounting system.

Panels should be cleaned frequently to maintain their efficiency.

Using monitoring systems to assess energy production and identify problems.

Check wiring and connections, and maintain batteries in storage systems.

As recommended by the manufacturer, update software and replace worn components.

Conclusion: the benefits of regular maintenance

Panels are kept in good condition to ensure maximum efficiency. Regular inspections can extend the life of a system. Reduces the risk of structural damage or electrical failure.

A solar system will operate efficiently and safely over the long term, providing economic and environmental benefits. This is achieved with proper installation and regular maintenance.

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