Collecting Energy from the Sun

Not all solar energy collection relies on direct electricity generation. A large share of the sun’s energy arrives as heat, which can be captured, transferred, and converted into useful services with very high efficiency.

Thermal conversion focuses on absorbing solar radiation and raising the temperature of a working medium (liquid, air, or solid). This heat can then be used directly or converted into other forms of energy.

Direct Use of Solar Heat

• Domestic hot water: Heating water for sanitary and household use.
• Space heating: Supplying low-temperature heating systems such as floor heating.
• Industrial process heat: Pre-heating fluids or air for industrial applications.

Heat-to-Mechanical and Heat-to-Electric Conversion

At higher temperatures, solar heat can be converted into mechanical or electrical energy using thermodynamic cycles.

• Concentrated Solar Power (CSP): Mirrors or lenses concentrate sunlight to generate high temperatures.
• Steam or gas turbines: Heat drives a turbine connected to an electrical generator.
• Organic Rankine Cycles (ORC): Suitable for lower-temperature heat sources.

While these systems are less common at household scale, they illustrate that solar heat can be transformed into electricity through pathways different from photovoltaics.

Thermal-to-Thermal Synergies

Heat collection often pairs naturally with thermal storage. Capturing heat when the sun is available and releasing it later improves overall system efficiency and resilience.

Solar thermal systems collect solar energy as heat rather than electricity. They are widely used for domestic hot water, space heating, and sometimes cooling (via absorption chillers).

• Flat-plate collectors: Simple design, robust, moderate temperatures.
• Evacuated tube collectors: Higher efficiency, especially in cold climates.

Thermal collection often achieves higher overall efficiency than PV when the end use is heat, but it lacks the flexibility of electrical energy.

Wind energy is an indirect consequence of solar radiation. Uneven heating of the Earth’s surface creates temperature and pressure differences in the atmosphere, which in turn generate air movements we perceive as wind.

From an energy perspective, wind can be seen as solar energy that has been converted first into thermal gradients and then into kinetic energy.

From Wind to Electricity

Wind turbines capture the kinetic energy of moving air using aerodynamic blades. The rotational motion is transmitted to a generator, producing electricity.

• Rotor and blades: Convert wind speed into rotational motion.
• Generator: Converts mechanical energy into electrical energy.
• Power electronics: Condition and adapt the electricity for grid or local use.

At small scale, wind turbines can complement solar installations by producing energy at night or during overcast and windy conditions.

Some systems aim to harvest multiple forms of energy from the same surface area. Examples include photovoltaic-thermal (PVT) panels, which produce both electricity and heat, and experimental approaches inspired by natural processes such as photosynthesis.

These hybrid concepts highlight the idea that solar collection is not limited to a single pathway, but can combine electrical, thermal, and chemical energy production.

Once energy is collected, it must be transported with minimal losses and then transformed or stored for later use. These aspects are covered in the next sections:

• Transporting Energy: cabling, AC vs DC, losses and efficiency.
• Transforming & Storing Energy: batteries, heat storage, and household uses.