Short Definition
Solar thermal energy uses solar radiation to generate heat. Solar collectors absorb the radiation and transfer it to a heat transfer fluid. In contrast, PV converts solar energy into electrical power.
Solar Thermal Energy at a Glance
Solar thermal energy provides heat for domestic hot water, space heating, suitable industrial processes, or district heating networks.
A heat transfer fluid carries the heat generated in the collector through a heat exchanger to a hot water or buffer storage tank.
A differential temperature controller operates the circulation pump based on the collector and storage tank temperatures.
The usable thermal yield is limited by factors such as solar radiation, heat losses, and the available storage capacity.
How Does a Solar Thermal System Work?
Solar collectors absorb incoming solar radiation and heat a heat transfer fluid. This is often a mixture of water and antifreeze that circulates in a closed solar circuit. A circulation pump transports the heated fluid to a heat exchanger. The heat exchanger transfers the heat to a hot water or buffer storage tank without mixing the two fluids.
A solar controller continuously compares the collector temperature with the temperature inside the storage tank. It activates the circulation pump when the collector temperature is sufficiently higher than the storage temperature, allowing useful heat transfer. If the temperature difference falls below a defined threshold, the controller stops the pump to prevent heat from being transported back from the storage tank to the collectors.
The collector, supply, return, and storage temperatures, as well as the volume flow rate, are measured directly. The current thermal power is calculated from the volume flow rate and the temperature difference between the supply and return lines. Integrating this power over time determines the generated amount of heat. The calculation must account for the temperature- and medium-dependent properties of the heat transfer fluid. In simplified form:
Thermal power = volume flow rate × volumetric heat capacity × temperature difference
For water-glycol mixtures, the relevant fluid properties depend on factors such as the composition and temperature of the medium. Pump operating states, pressures, and additional storage or system temperatures can also be monitored.
Where Is Solar Thermal Energy Used?
Solar thermal systems are primarily used for the following purposes:
Domestic hot water: The system heats water for showers, washbasins, and other hot water consumers.
Space heating support: Solar-generated heat is temporarily stored in a buffer tank and used to support space heating.
Industrial process heat: Solar thermal energy is particularly suitable for processes with a continuous heat demand at an appropriate low or medium temperature level.
Whether an application is technically suitable depends on the required temperature level and the collector type used.
Solar district heating: Large collector fields can feed heat into local or district heating networks.
Benefits, Limitations, and Technical Requirements
Solar thermal energy can reduce the amount of fuel or electricity required for heat generation. It is particularly suitable where continuous heat demand exists during periods of high solar irradiation. Thermal storage makes it possible to partially separate heat generation from consumption over time.
However, heat generation varies according to the time of day, weather, and season. Heating demand is often high during winter, while the available solar yield is lower. Heat losses, the required temperature level, and storage capacity also limit the usable thermal yield.
If there is insufficient heat demand during periods of high solar irradiation, the system may enter stagnation. In this state, the heat transfer fluid reaches very high temperatures and may partially evaporate. Stagnation does not automatically indicate a fault; it can be an anticipated but thermally demanding operating condition. The expansion vessel, safety components, heat transfer fluid, and hydraulic design must therefore be suitable for this condition.
Reliable operation requires correctly sized collectors, pipework, pumps, heat exchangers, and storage tanks. A suitable solar controller and temperature sensors, as well as volume flow sensors where required, are also necessary. Proper hydraulic design is essential for transferring and storing the generated heat efficiently.
How Does EcoPhi Support Solar Thermal Monitoring?
EcoPhi can primarily integrate solar thermal energy into the monitoring of a combined energy system. Provided that suitable sensors, heat meters, and communication interfaces are available, thermal measurements can be recorded and displayed together with PV generation, electricity consumption, and other energy data.
This allows operators to centrally evaluate temperatures, calculated thermal power, heat quantities, and operating states. The specific integration depends on the available interfaces of the measuring devices and system controllers. Control of the solar circuit itself normally remains the responsibility of a dedicated heating or solar thermal controller.
Short Summary
Solar thermal energy generates heat from solar radiation and can support domestic hot water production, space heating, industrial process heat, or heating networks. Its value depends primarily on suitable heat demand, correct system design, and sufficient storage capacity. In combined energy systems, thermal and electrical measurements can be monitored together.
Frequently Asked Questions About Solar Thermal Energy
What Is the Difference Between Solar Thermal Energy and PV?
Solar thermal energy generates heat, while PV produces electrical power. Both technologies can operate in parallel within a combined energy system.
Can Solar Thermal Energy Fully Heat a Building?
A complete supply is technically possible but generally requires a specially designed system, very low heat demand, and often a large or seasonal thermal storage system. The building’s energy performance, collector area, and heating system are also decisive factors. In conventional installations, solar thermal energy therefore usually supplements another heat generator.
How Is the Yield of a Solar Thermal System Determined?
Temperatures and volume flow rate are measured using suitable sensors. These measurements and the medium- and temperature-dependent properties of the heat transfer fluid are used to calculate the thermal power and generated amount of heat.
Can EcoPhi Control a Solar Thermal System?
A dedicated system controller normally controls the solar thermal system itself. EcoPhi can integrate available thermal measurements into higher-level monitoring, provided that suitable sensors, meters, and interfaces are available.