The historical development of Photovoltaic Thermal (PVT) technology: From concept to Commercialization

Introduction

The global energy structure has undergone tremendous changes over the past half century. Photovoltaic and solar thermal (PVT) integrated systems have gradually emerged as an innovative solution capable of simultaneously meeting the two basic energy demands of electricity and thermal energy. The PVT system integrates photovoltaic cells and solar collectors in a single flat plate, not only maximizing the utilization of solar radiation but also significantly enhancing the overall energy conversion efficiency.

Although PVT Solar Panel is generally regarded as a relatively new technical concept, its history can actually be traced back to around the 1950s. From the experimental prototype in the early 1970s to the gradually mature commercial application today, the development process of PVT reflects a broader path for the development of renewable energy - including the coordinated evolution of technological breakthroughs, policy support and market cultivation. This article aims to sort out the historical context of PVT technology and explore how it has gradually evolved from a theoretical concept to a commercially viable comprehensive energy solution.

Origin: 1970s - the nascent stage of the concept

The initial stage of PVT technology was in the 1970s. During this period, due to the energy security warnings brought about by the two oil crises in 1973 and 1979, the global emphasis on renewable energy rose sharply. Researchers are actively seeking alternatives to fossil fuels. Solar energy is regarded as one of the most promising directions due to its universality and sustainability.

The traditional utilization of solar energy is divided into two major categories: photovoltaic and solar thermal. However, engineers have noticed that during the operation of photovoltaic power generation, the increase in temperature will lead to a decline in power generation efficiency. This phenomenon has given rise to a key idea: Can the waste heat be recovered while cooling the photovoltaic panels and achieve effective utilization of thermal energy 

The PVT concept in the early 1970s was mainly based on air systems, aiming to be combined with building heating and ventilation systems. The basic structure consists of a photovoltaic panel, behind which there is an air flow channel to capture and circulate hot air. Although the improvement in efficiency is not significant, this lays the conceptual foundation for PVT as a dual-function system.

Expansion and technological progress: The 1980s - 1990s 

The 1980s and 1990s were periods when photovoltaic technology made continuous progress and academic interest grew increasingly intense. With the popularization of crystalline silicon photovoltaic panels and the improvement of cost-effectiveness, researchers have begun to study liquid cooling as a more effective cooling method than air circulation.

The air-based photovoltaic (PVT) system was improved by enhancing the pipeline design and integrating with the space heating system.

This has promoted the development of liquid photovoltaic (PVT) systems, which use water or antifreeze as the heat transfer medium to absorb heat more effectively. This method can effectively cool photovoltaic panels and achieve a higher level of heat output, making it suitable for household hot water or industrial applications.

During this period, a large number of laboratory studies and experimental installations were carried out in universities in Europe, North America and Asia. Technical models have been developed to analyze energy flow, predict performance and optimize design. Although commercial benefits remain limited, the academic foundation of modern photovoltaic technology has been firmly established.

The early 21st century was a crucial turning point for the development of global renewable energy. During this period, Europe and Japan took the lead in conducting large-scale research and application demonstrations of solar energy technology. The building-integrated photovoltaic and solar thermal (BIPVT) system emerged against this backdrop. BIPVT not only integrates photovoltaic collectors as part of the building's exterior envelope, such as exterior walls, skylights or roof components, but also realizes the integrated integration of power generation, heating, architectural aesthetics and insulation performance, significantly enhancing the building's comprehensive energy efficiency and visual appeal.

Europe is actively exploring the integration path of photovoltaic power generation in urban energy systems through demonstration projects in the EU Renewable Energy Plan. Japan has incorporated its photovoltaic research into its national strategy to enhance its energy self-sufficiency rate and reduce its reliance on imported fuels. Meanwhile, photovoltaic power has begun to attempt to couple with various technologies such as heat pumps, seasonal heat storage and district heating networks to form a hybrid energy system. Although it was still a niche application at that time, its potential for cross-domain integration had initially attracted the attention of policymakers and the industry.

Entering the 2010s, with the significant decline in photovoltaic costs, the increasing urgency of climate issues and the strengthening of policy incentives, the global deployment of renewable energy has entered an accelerated channel. PVT technology is also gradually moving out of the laboratory and towards the initial stage of commercialization. Many enterprises from Europe, Israel and Asia have successively launched various PVT products, covering flat plate collectors, glazed/non-glazed types and concentrating systems. The important factors driving commercialization at this stage include:

• Advancements in material technology, such as high-efficiency heat exchangers, selective absorption coatings, and long-lasting packaging processes;

• The overall energy efficiency of the system has been enhanced, with the comprehensive benefits generally exceeding 70%, which is particularly advantageous in scenarios with limited space.

•  The demand for distributed energy solutions in the residential, commercial and industrial sectors continues to grow.

• Actual cases have also confirmed the multiple benefits of the PVT system, including reducing energy costs, increasing the self-consumption rate of solar energy, and improving the return on investment in the context of combined utilization of electricity and heat.

Since 2020, driven by the goal of "carbon neutrality" and increasingly strict climate policies, the global energy transition has entered a new stage. Many countries have set net-zero emission targets for the mid-century, bringing broad prospects for photovoltaic and solar thermal integrated technology. Integrated solar technologies such as PVT are now enjoying unprecedented development opportunities

The COVID-19 pandemic has further highlighted the importance of energy resilience and localized clean energy production. Therefore, PVT has been increasingly applied in the following fields: 

• Residences and families seek efficient systems to meet their demands for electricity and hot water.

• Commercial buildings, benefiting from the integration of BIPVT, have reduced their operating energy costs. 

• In industrial processes, especially in the food processing, textile and chemical industries, medium and low-temperature heat is of vital importance. 

Meanwhile, technological innovation is constantly expanding possibilities: 

• The combination of PVT and heat pumps has achieved efficient heating and cooling throughout the season. 

• Integrated with thermal energy storage, it has achieved better load management. 

• The intelligent control system has improved demand matching and grid interaction.

Nowadays, PVT is no longer regarded as an experimental technology but has become a strong competitor in the renewable energy market, supported by dozens of commercial suppliers and increasingly popular worldwide.

The advantages of promoting popularization

There are several reasons why PVT is recognized as a highly valuable solar energy solution:

• High comprehensive efficiency: The comprehensive efficiency of photovoltaic and solar thermal (PVT) integrated systems can reach over 70%, while the efficiency of independent photovoltaic systems is approximately 20%. The utilization efficiency of solar thermal energy is generally between 40% and 60%.

• Superior photovoltaic performance and durability: The PVT system can reduce the thermal stress of photovoltaic modules through effective heat dissipation, extend their service life, and enhance the stability of power generation. 

• Efficient space utilization: The PVT system can simultaneously output electrical and thermal energy over the same area, which is particularly important in urban or space-constrained application scenarios. 

• Wide application fields: It can be widely used in various scenarios such as residential, commercial, industrial and agricultural ones. 

• In line with the sustainable development goals: PVT technology helps reduce carbon emissions, promotes the integration of renewable energy into the grid, and supports the implementation of distributed energy strategies

Challenges and challenges 

Although photovoltaic power generation (PVT) has made progress, it also faces many challenges:

• Compared with independent photovoltaic or solar thermal power generation, the initial cost is higher. 

• The requirements for system design and maintenance are complex. 

• Compared with traditional solar photovoltaic power generation, the current market's understanding of photovoltaic thermal integration (PVT) technology is still relatively limited. 

• The current policy support system often fails to fully take into account the characteristics of such hybrid technologies, resulting in numerous restrictions for them when applying for incentive measures. 

• Breaking through these bottlenecks is of crucial significance for promoting the large-scale application of photovoltaic and solar thermal systems and fully unleashing their energy potential.

Conclusion 

Looking back on the development of PVT technology, from the concept proposal in the 1970s to its gradual commercialization today, this technology has gone through nearly five decades of evolution. It not only marks the shift of solar energy utilization methods from "single power generation" or "single heat production" to an integrated model of "combined heat and electricity supply", but also reflects the overall trend of the renewable energy industry moving from experimental exploration to market application. 

Against the backdrop of the world's joint efforts towards carbon neutrality, PVT technology, with its highly efficient compound energy conversion, stable cogeneration of heat and power, and excellent system adaptability, demonstrates a unique application prospect. It is not only applicable to various energy consumption scenarios, but also better meets the multiple requirements of the future energy system for cleanliness, low carbon, flexibility and high efficiency. 

The development history of PVT is not only a maturation process of a technology, but also a vivid example of the joint effect of innovative mechanisms, policy support and market demand to drive energy transformation. Looking ahead, PVT is expected to play a more significant role in building a new energy system dominated by renewable energy.