Impact Partner Content: Absa | by Justin Schmidt, Head of New Sectors, Absa
In article two of a four-part series, Justin Schmidt, Head of New Sectors at Absa, unpacks solar thermal with upcoming articles on wind as a technology as well as concluding the series with a view on the technologies which are changing the future state of the industry. With some houses using a much as 30% to 40% of their energy consumption on water heating, solar thermal is a popular means for many households of reducing their energy bills.
Solar Thermal, an introduction
Solar Thermal (ST) technologies, also known as Solar Water Heating (SWH) systems, extract heat energy from the solar radiation. ST technologies operate through active heating, meaning it relies on the sun’s solar irradiation for heating a working fluid. This operates by absorbing solar irradiation from the sun and uses it to heat water flowing through a collector. This heated water is typically transferred to a storage tank and consumed throughout the day. The storage tank acts as a buffer, allowing hot water to be available throughout the day when needed. The most common solar thermal technologies are evacuated tube and flat-plate collectors, which is used in low-temperature applications (< 100 °C).
In most large-scale applications, a backup heat source is implemented to generate hot water when the solar resource is low (consecutive days of cloudy weather). For residential systems, the tank is typically equipped with an electrical resistive element. In large-scale systems, electrical elements, heat pumps or boilers that use conventional fuels, such as coal, gas and paraffin provide the heat. For industrial processes with higher temperature needs (steam), ST systems are typically installed for preheating. Preheating allows for the ST system to heat the cold-water supply and feeds this hot water to a storage tank, before being fed into a boiler for steam production, allowing for significant reduction in the use of conventional fuels by boilers, which in turn leads to associated financial savings.
Our leading class renewable energy resource, the sun
ST systems use solar radiation to generate hot water. More specifically, it is the radiation component, referred to as the Global Horizontal Irradiance (GHI). South Africa has an abundance of solar resources – even the cloudier regions are more suitable than the best regions in some of the European countries leading in SWH installations, such as Germany and Austria.
Source: Solargis
The map above indicates the available solar resources in South Africa for one year. It is important to note that the areas with lower levels do not have lower radiation, it is merely less available throughout the year due to weather conditions such as cloud cover.
Financial considerations for your business and household when investing in Solar PV
The cost of ST systems has declined steadily over past years, although the cost of large-scale systems can vary significantly depending on the size and the design requirements. For example, large-scale systems may require special components (tanks, controls, etc.) to be effectively integrated into existing industrial processes, which may significantly increase overall costs. The cost of large-scale ST projects is usually presented on a specific cost (ZAR/m2) basis. The specific cost represents the total cost of the project per square meter of collector area installed.
Large-scale ST systems can be expected to have high upfront capital costs when compared to other non-renewable energy sources, such as heat pumps. Studies have also shown that ST systems can generate heat at a lower cost than most conventional fuels used in boilers for process heat, including Heavy Fuel Oil (HFO), paraffin, electricity, diesel, petrol and Liquid Petroleum Gas (LGP). This substantiates its financial viability as an attractive investment for offsetting the use of conventional fuels, reducing the carbon footprint and generating savings.
Lifespan and costs of Solar PV
Typically, ST collectors are expected to have a functional lifespan of between 20 and 25 years, depending on the specific technology and manufacturer. There are existing systems that have been in operation for longer periods. This could be attributed to regular and proper maintenance. However, other smaller components of ST systems, such as the pumps, controllers and valves, might need more frequent replacement due to shorter service life and unexpected failure. Typically, well-established ST collector manufacturers provide warranties of up to 10 years on their products. Other smaller components (pumps, valves, etc.) of ST systems can be expected to have shorter warranty periods.
Suitable implementation
ST systems are commonly used in households to generate hot water for daily domestic needs but is also frequently installed on a larger scale for generating hot water for commercial and industrial activities. Commercial activities with a good potential for the implementation of ST technologies can be identified as businesses/buildings where large volumes of hot water at low temperatures (< 100 °C) are consumed daily, such as hospitals, hotels, apartment blocks and laundromats, among others. The application of ST technologies could be a practical solution for many industrial activities with a high demand for process heat, for example, the food and beverage, manufacturing, agriculture and textile industry, among others.
Solar heat for industrial processes has proven feasible and has been implemented in many cases around the world. For industrial processes where steam is required (> 100 °C), large-scale ST systems could be used for preheating. The ST system is used to raise the temperature of the cold- water supply before being fed into a boiler to generate steam. This allows significant reduction in the use of conventional fuels and carbon emission, and at the same time generates financial savings.
Conclusion
When thinking about your company or household’s water heating requirements, Solar Thermal may be a viable option for you. Given the reducing costs of technology, increasing energy costs, our abundant sunlight and the long lifespan of the technology the business case is often sees one of the shortest pay back periods across all renewable energy technologies. ST is therefore a key enabler to achieving the UN Sustainable Development Goals by reducing households and businesses carbon footprints as well as their energy bills.
