BTE Solar: A Comparative analysis of PVT Systems with Traditional Photovoltaic and Solar Thermal Systems

Against the backdrop of the current global energy transition, solar energy, as the cleanest and most renewable form of energy, is rapidly integrating into the production and life of human society. The main ways of solar energy utilization include photovoltaic power generation (PV) and solar thermal utilization (ST). The former directly converts solar radiation into electrical energy through the photoelectric effect, while the latter absorbs solar radiation through collectors and converts it into thermal energy. It is often used for domestic hot water, heating or industrial heating. In recent years, a new technology that combines the advantages of both - photovoltaic and solar thermal integration (PVT) - has gradually come into people's view and demonstrated unique value in research and commercial application. This article will compare the PVT system with traditional photovoltaic and solar thermal systems from multiple perspectives, and explore their advantages and disadvantages.

I. Comparison of System Composition and Working Principle

Photovoltaic System (PV)

The core of a photovoltaic system is the solar cell module, with common materials being crystalline silicon or thin-film cells. When sunlight shines on the surface of the battery, photons excite electrons in the semiconductor material to form an electric current, which is then converted into alternating current through an inverter to supply power to households or the power grid. The structure of the PV system is relatively simple, and its main function is to generate electricity.

2. Solar Thermal System (ST)

The solar thermal system mainly consists of flat plate collectors or vacuum tube collectors. After being exposed to sunlight, the absorbing plate converts the energy into heat, which is transferred to the hot water storage tank through the working medium (water or antifreeze) for hot water supply or heating. The power generation capacity of the ST system is almost zero, but its thermal efficiency can usually reach 40% to 70%.

3. Photovoltaic and Solar Thermal Integrated System (PVT)

The PVT system combines photovoltaic modules with collectors, collecting heat energy from the residual heat on the back of the photovoltaic panels while generating electricity. This not only avoids the efficiency decline of photovoltaic cells caused by high temperatures, but also improves the comprehensive energy efficiency per unit area. Its core concept is "one board generating both electricity and heat simultaneously".

Ii. Energy Efficiency and Performance Comparison

1. Photoelectric efficiency

For a simple photovoltaic system, the photoelectric conversion efficiency of common components is between 18% and 22%. An increase in temperature will lead to a decrease in efficiency. For every 1℃ rise in temperature, the average output power of photovoltaic panels drops by 0.3% to 0.5%. Therefore, in hot regions, the heat dissipation problem on the back of photovoltaic panels is more prominent.

The PVT system maintains a more stable power generation efficiency by cooling the photovoltaic modules to lower their operating temperature. Research shows that under the same environmental conditions, the power generation of PVT can be increased by 5% to 15% compared with traditional PV systems.

2. Thermal energy efficiency

The advantage of the solar thermal system lies in its high thermal efficiency. The efficiency of flat-plate collectors is approximately 50% to 70% at medium and low temperatures (30 to 70℃), while vacuum tube collectors perform better in winter or in high-latitude regions. In contrast, the thermal efficiency of PVT is slightly lower, generally ranging from 40% to 60%, but considering that it generates electricity simultaneously, its overall energy efficiency is higher.

3. Comprehensive efficiency

The greatest advantage of PVT lies in its overall efficiency. The efficiency of pure photovoltaic or solar thermal systems ranges from 20% to 70%, while the overall efficiency of PVT systems can reach 70% to 80%, and some advanced products even exceed 85%. This means that for roofs of the same area, PVT can generate more usable energy.

Iii. Economic Comparison

1. Initial investment

As mature technologies, PV and ST have relatively low installation costs when installed separately. Due to its complex design and high production process requirements, the PVT system is generally more expensive than a single system. However, if the need for simultaneous power generation and heating on the same roof is taken into account, the "combined installation" of PVT may instead reduce the costs of brackets, pipelines and space.

2. Operation and maintenance

The operation and maintenance of photovoltaic systems are simple, mainly involving regular cleaning of components and inspection of electrical equipment. The solar thermal system requires maintenance work such as anti-freezing, anti-scaling, and regular replacement of working fluid. PVT combines the two, making operation and maintenance slightly more complex. However, due to its high structural integration, the overall stability is not bad.

3. Payback period of investment

In regions with high electricity and heat prices (such as Europe and Japan), the payback period of a PVT system may be shorter than that of a single system. Especially under the support of distributed energy policies, the combined benefits of power grid connection subsidies and thermal energy substitution make the economic efficiency of PVT more prominent. However, in regions where energy prices are low or policy support is insufficient, the promotion of PVT still faces resistance.

Iv. Comparison of Application Scenarios

1. Resident families

Household users usually need electricity and hot water. If the roof area is limited, installing a PVT system can achieve dual energy output in a confined space, which is particularly suitable for urban residences and villas.

2. Commercial and public buildings

Buildings such as schools, hospitals and hotels not only have a large demand for electricity but also require a stable supply of hot water. PVT can provide an integrated solution to reduce equipment footprint and maintenance costs.

3. Industrial field

Some industrial productions (such as food processing, textile, and chemical industries) have a large demand for low-temperature thermal energy. Traditional solar thermal power can meet some of the demands, but the electricity demand is also very high. PVT has the potential to replace some fossil energy in these fields.

4. Agriculture and Greenhouses

In agricultural greenhouses, both photovoltaic power supply to drive equipment and thermal energy to maintain temperature are needed. PVT can simultaneously meet two demands and enhance the energy self-sufficiency rate.

V. Comparison of Environmental and Social Benefits

PV and ST play a significant role in reducing carbon emissions. PVT can not only replace thermal power to reduce carbon dioxide emissions, but also reduce the use of gas or coal-fired boilers. Under the major trend of carbon neutrality, the value of PVT becomes more prominent. At the same time, it also alleviates the problem of insufficient roof space and avoids the embarrassment of having to choose between two options within a limited area.

Vi. Existing Problems and Challenges

High cost: Currently, the price of PVT is still higher than that of individual systems, which limits its popularization.

Lack of technical standards: The international standards for the testing, certification and installation of PVT are still not unified.

Insufficient market awareness: Many consumers and engineering contractors have limited knowledge of PVT, which makes market promotion difficult.

Operation and maintenance complexity: Although the overall integration is high, it involves two systems, namely power and heat, which impose higher professional requirements on installers and maintenance personnel.

Vii. Future Development Directions

New material applications, such as selective absorption coatings and thermal conductive composite materials, help to enhance thermal efficiency.

Modular design: Makes PVT as easy to install and replace as ordinary photovoltaic modules.

Combined with energy storage: The dual energy storage system of electric energy storage and thermal energy storage will enhance the energy utilization flexibility of PVT.

Policy promotion: Government subsidies, carbon reduction rewards, green building certifications, etc., may all facilitate the application of PVT.

Viii. Summary

As an emerging way of solar energy utilization, PVT is not merely the superposition of photovoltaic and solar thermal energy, but achieves higher comprehensive energy efficiency through system integration. Compared with traditional photovoltaic power, it solves the problem of efficiency decline caused by temperature rise. Compared with traditional solar thermal energy, it offers the added value of electrical energy output. In terms of economy, space utilization, carbon reduction and other aspects, PVT has demonstrated obvious advantages. Of course, its promotion still faces challenges in terms of cost, standards and awareness. With technological advancements and policy promotion, PVT is expected to become an important component of distributed clean energy in the future.