A Combination of Photovoltaic & Solar Thermal Technologies Works Better

Generally, solar power generation technology includes photovoltaic power generation technology and solar thermal power generation technology. The former is based on the principle of photovoltaic effect and uses solar cells to convert light into electricity; while the latter makes use of large-scale arrays of solar mirrors to collect heat, produces steam through heat exchangers and then the steam comes up will drive turbines to generate electricity. Because both belong to solar power generation technology, the two are often put together to make some comparisons. But whether photovoltaic power will have a brighter prospect or solar thermal power will quickly come from behind, there’re hot debates across the industry.

So in the next several decades, what kind of development will appear in the solar technology field? Which technology route is the most economical? And can the combined power generation model provide greater opportunities for solar power generation? At present, the German Aerospace Center (DLR) Follow @DLR_en is carrying out in-depth research on theses issues, aiming to analyze the trends in the development of photovoltaic and solar thermal power generation technologies by 2030.

Competition between photovoltaic and solar thermal is inevitable

This research, called THERMVOLT, focuses on how different solar power generation technologies generate economical, reliable and high-quality electrical energy in the absence of sufficient sunlight. Specifically, this research is conducted through comparing several aspects like the system principles, technical requirements, and economic and environmental benefits of the two solar power generation technologies.

In regard to solar thermal technology, the electrical energy generated can either supply for daily use or be stored in the form of heat. Its application areas are not limited to power generation, can also be used for hydrogen production or industrial heat utilization and other fields.

In fact, the biggest advantage of solar thermal generation is the use of thermal storage can weaken the instability of solar radiation on the quality of its power generation; while solar thermal power generation can better fit conventional power generation and the existing power grids. On the other hand, the back-end system in the generation process is equipped with steam generators, steam turbines and other equipment – it’s possible to implement combined power generation through the supplementary combustion of fossil fuel. Also in the future, solar thermal power generation can integrate with biomass power generation. In this way, solar thermal generation is able to support the basic load of power grids, having the possibility that can replace the large-scale traditional power plants in the power system.

India One Solar Thermal Power Plant
India One Solar Thermal Power Plant by flickr@brahmakumaris

For photovoltaic power generation technology, it converts light directly into electrical energy. Hence, when compared with solar thermal technology, it has a better advantage in required areas, costs and technical difficulties. But the photovoltaic technology itself does not have the ability to store energy – the electricity can only be stored into batteries separately. So in this regard, photovoltaic technology does not seem to have obvious advantages in costs, technical requirements and environmental benefits. However, as the cost of photovoltaic generation has been continually cut down in recent years and the cost of storage batteries is expected to decline significantly in the next few years, this situation will be better improved.

From a commercial point of view, there’s similarity in the resource requirements for the two power generation technologies – both rely on the energy from the sun – and this results in inevitable comparisons and competition between them in the short term.

It is also worth noting that the current global proportion of renewable power generation is approaching the ceiling on the acceptable capacity of the power grids. If the problem of energy storage hasn’t been well solved, the consumption of renewable power is certain to be an increasingly tough issue.

Determine the optimal capacity ratio between photovoltaic and solar thermal technologies by simulating power plant models

During the previous research, the researchers from the German Aerospace Center simulated the costs of various photovoltaic and solar thermal generation modes. Efforts were also put on determining the optimum capacity ratio between the two types of generation technologies in a combined mode – to achieve the lowest carbon emissions and the lowest cost of power generation, under a fixed total scale.

In these simulation models, the virtual solar thermal power plants were equipped with energy storage systems and fossil fuel supplementary combustion systems, while the photovoltaic combined cycle power plants were equipped with battery storage systems that could be operated cooperatively.

These models chose sunny areas like Morocco and Saudi Arabia as testing locations to “build” the power plants, with a designed total capacity of 100 MWs. And these models included the years 2015, 2020 and 2030.

In a “complete year”, this type of analysis was implemented in detail on an hourly basis, with the size of solar arrays and the capacity of energy storage determinate. Researchers would construct an efficiency model and take into account some influence factors (such as wear) and different cost estimations – to calculate the optimal cost of electricity after optimizing the system.

The combination of photovoltaic and solar thermal technologies shows better results

Solar Magazine: Solar Industry News and Insights

The results of previous research show that under the existing conditions, the combination of photovoltaic and solar thermal is the most promising solar power generation technology route.

Photovoltaic power plants can send electricity into power grids; while in the peak period, such as night, the energy storage systems in solar thermal power plants can generate electricity to satisfy the power demand. Though there may be needs to add fossil fuel supplementary combustion, it’s relatively easy to work and the cost will not be too high.

It is said that the German Federal Ministry of Economics and Technology has provided a funding of around €500,000 for the research. The Institute of Solar Research and the Institute of Engineering Thermodynamics at the German Aerospace Center, Lappeenranta University of Technology (LUT) and industry partners like Fichtner GmbH and M+W Group also participate in the research.

The research report will be finalized and submitted by the end of 2016. comment↓


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