Molecular solar thermal energy storage system

Characteristics of molecular solar thermal energy storage system

Researchers at Chalmers University of Technology in Sweden have proposed an efficient hybrid solar thermal energy storage system that combines energy storage from chemical bonds in the molecular solar thermal energy storage system with thermal energy storage in hot water.
 
Table of Contents
youtube play button

The system is designed to store solar energy in liquid form, and by connecting it to an ultrathin chip thermoelectric generator, the team has now demonstrated that it can generate electricity, a development they believe lays the foundation for self-charging electronics that use solar energy on demand.

Efficient solar energy conversion and solar energy storage solutions are critical to the development of a sustainable society. Technologies for converting solar energy into heat and electricity are being widely used. The most common concepts of solar energy conversion are solar-to-electrical energy conversion (photovoltaic power) and solar-to-thermal energy conversion (solar water heating system).

The most common photovoltaic technology is based on monocrystalline silicon solar cells. The maximum efficiency of monocrystalline solar photovoltaic cells is estimated to be 32% due to spectral losses, while typical efficiencies of current modules are as high as over 20%. In contrast, solar water heating systems (SWH) typically have an efficiency (solar heating) of 20-80%. Learn more about monocrystalline photovoltaics from polycrystalline vs monocrystalline article.

Efficient solar energy conversion and solar energy storage solutions are critical to the development of a sustainable society

Recently, a team of researchers from Sweden and China has developed an energy system that is said to be able to store solar energy as chemical energy for up to 18 years and make the combined solar water heating system and solar energy storage efficient up to 80%. More importantly, this energy storage system can also be integrated into electronic products such as headphones, smart watches and phones through an ultra-thin chip as a generator. The team of scientists from Chalmers University of Technology in Sweden has been working on the direct storage of solar energy in the chemical bonds of organic chemicals and has developed the molecular solar thermal energy storage system.

Demonstrated in concept as early as 2013, the system stores solar energy as potential chemical energy in photoisomerization in chemical bonds, enabling solar energy storage in a liquid medium that can not only release energy from the sun on demand, but also And also transportable. Scientists at Chalmers University of Technology in Sweden have recently teamed up with researchers at Shanghai Jiao Tong University to take this solar energy storage system a step further, combining it with a compact thermoelectric generator to convert solar energy into electricity. Experiments have shown that it can generate electricity on demand.

Hybrid solar system composed of molecular solar thermal energy storage

What is a molecular solar thermal energy storage system

Molecular solar thermal energy storage systems store solar energy as latent chemical energy in photoisomerization in chemical bonds with specially designed molecules of carbon, hydrogen and nitrogen at its core. When it comes into contact with sunlight, the atoms within the molecule rearrange to change its shape and convert it into energy-rich isomers that can be stored in liquid form.

Schematic diagram of norbornadiene-tetracycloalkane molecular solar heat storage system

Schematic diagram of norbornadiene-tetracycloalkane molecular solar heat storage system

In a molecular solar thermal energy storage system, the parent molecule is exposed to solar photons and thereby converted to high-energy photoisomers, which are kinetically stable; At the same time it can be isomerized back to the parent molecule by thermal activation or using a catalyst and release heat.

For example, the molecular solar thermal energy storage system based on norbornadiene-tetracycloalkane, scientists expose a hydrocarbon called norbornadiene to light, which changes its chemical bonds, turning it into a tetracycloalkane, solar energy is stored in chemical bonds as latent chemical energy in the process.

Changing the temperature of the tetracycloalkane or exposing it to a catalyst has a reversal effect, releasing energy in the form of heat. The system shows an energy storage density of up to 966 kJ kg-1  and a storage time of over several months.

Molecular solar thermal energy storage system can store solar energy in liquid form

Molecular solar thermal energy storage system can store solar energy in liquid form

After research, the requirements for an efficient molecular solar thermal energy storage system can be summarized as:
(1) The parent compound must absorb most of the solar spectrum;
(2) Photoisomers shall not compete to absorb sunlight;
(3) The quantum yield of the photoreaction should be 100%;
(4) The stored energy density should exceed 300 kJ kg -1;
(5) Photoisomers must remain stable for a long time
(6) All reactions must be performed quantitatively, for example to allow for multiple solar energy storage-release cycles.

Hybrid solar system

On the basis of the molecular solar thermal energy storage system, researchers from Chalmers University of Technology have proposed a hybrid solar system consisting of a molecular solar thermal energy storage system (MOST) and a solar water heating system (SWH), making it possible to exploit sub-bandgap photons that cannot be exploited by molecular solar thermal energy storage systems.

This hybrid solar system can efficiently utilize the low-energy photons of a solar water heating system (SWH) and store high-energy photons in the form of chemical energy in a molecular solar thermal energy storage system (MOST). By storing part of the solar energy using a norbornadiene-tetracycloalkane (NBD-QC) system, long-term energy storage and on-demand energy delivery can be added to existing low- or mid-temperature solar water heating systems (SWH).

Schematic diagram of the hybrid solar energy conversion device.

The upper collector is used for conversion of molecular solar thermal (MOST); the lower collector is used for solar water heating system (SWH) system.

To demonstrate the effect of incorporating molecular solar thermal-based energy storage into the SWH, the researchers designed a microfluidic hybrid device. The hybrid installation consists of two layers, SWH on the bottom layer (dark grey) and molecular solar thermal on the top layer (light grey).

The upper molecular solar thermal section consists of a fused silica microfluidic chip; it allows high-energy photons from the solar spectrum to photochemically convert norbornadiene (NBD) to tetracycloalkane (QC).

As shown, photons with energies below the norbornadiene (NBD) absorption initiation point efficiently pass through the upper layers of the device, and used to heat the water in the lower collector, which consists of a 3D-printed flow cell covered with a quartz glass sheet.

The frontal dimensions of the device are ≈ 2 by 2 cm.

The spectral overlap of the solutions used for NBD 1 and 2 and the solar spectrum in the visible range

(a) The spectral overlap of the solutions used for NBD 1 and 2 and the solar spectrum in the visible range (1.5 AM);The red line represents the transmittance of molecular solar thermal, (dotted line corresponds to 1, solid line corresponds to 2). (b) Chemical structures of compounds 1 and 2.

Meanwhile, to further evaluate the performance of norbornadiene, the most promising compound ( 2 ) was subjected to cyclic testing (photoisomerization and subsequent thermal inversion) in solution at 60 °C.

Compound (2) underwent 127 cycles with negligible degradation, showing excellent robustness. In addition, cycling tests were performed under ambient conditions (no outgassing), resulting in 0.2% degradation per conversion cycle, suggesting that an oxygen-free environment is required for negligible degradation.

details of normalized absorption (au) for cycles 81 to 86.

In the cycle test, thermal reaction was performed at 60 °C after photoconversion, for a total of 127 cycles. The normalized absorption (au) of the solution of 2 after each half-cycle of thermal inversion and photoisomerization is shown on the way. Inset shows details of normalized absorption (au) for cycles 81 to 86.

“This technology means we can store solar energy in chemical bonds and release the energy as heat when needed,” said the team leader. “Hybrid solar systems combine chemical energy storage with water-heated solar panels that can convert more than 80 percent of incoming sunlight.”

Characteristics and challenges of molecular solar thermal energy storage system

Since a portion of the energy in a molecular solar thermal energy storage system is stored in chemical bonds, there is the potential for very stable long-term storage, which is limited by the size of the storage capacity. This energy can be transported and delivered in very precise quantities and with a high degree of reliability.

Meanwhile, the technical performance demonstrated by the experimental system is 397 kJ kg-1 = 110 W h kg-1 (current compound: norbornadiene), Slightly lower than the 140 W h kg-1 of the lithium iron phosphate blade battery by BYD, one of the top 10 lithium ion battery manufacturers; the potential is 966 kJ kg-1 = 268 W h kg-1 (unsubstituted norbornadiene),

It is very competitive with the energy density of modern lithium-ion battery chemistries, suggesting that it may be a viable technology in any application that uses battery energy for resistive heating. It also exceeds the melting enthalpy of most common phase change materials (eg, 200-270 kJ kg-1 for paraffin).

Therefore, the molecular solar thermal energy storage system is also competitive from a heavyweight energy density point of view. In addition, the molecular solar thermal energy storage system exhibits strong recyclability, as previously described, in the cycling test (photoisomerization and subsequent thermal inversion), compound (2) underwent 127 cycles with negligible degradation, showing excellent robustness.

Any future larger-scale application of molecular solar thermal technology faces two main challenges, which together form a long-term R&D roadmap. The first challenge to be overcome in the further development of this thermochemical storage technology may be the toxicity of the solvent. Reducing toxicity or eliminating solvents would open up more potential applications, such as portable cooking appliances that can be charged by the sun and cooked when the sun goes down.

Secondly, like any new technology, molecular solar thermal technology also faces the challenge of high cost. Before such a system can compete with other solar renewable technologies in bulk energy applications, cost reductions need to be achieved through the large-scale production of the constituent chemicals.

Future applications and development

The molecular solar thermal energy storage system works by absorbing photons and storing energy in a metastable photoisomerization state, its captured energy can be stored in this liquid state for up to 18 years, before a specially designed catalyst restores the molecule to its original shape and releases the energy as heat.

The Chalmers University of Technology team is now collaborating with scientists from Shanghai Jiaotong University in China, who use a compact thermoelectric generator to convert heat into electricity.

The Chalmers University of Technology researcher said, “A generator is an ultra-thin chip that can be integrated into electronics such as headphones, smart watches and phones. We’ve only produced a small amount of electricity so far, but the new results show that the concept does work, and it looks very promising. Concept illustration of molecular solar thermal energy storage system for charging mobile devices

The proof-of-concept current output is up to 0.1 nW (power output per unit volume is up to 1.3 W m-3), which may be very small, but the scientists see great potential in their molecular solar thermal energy storage system, which can be stored by a single Solve the intermittent problem of solar energy for months or years and utilize it on demand.

Concept illustration of molecular solar thermal energy storage system for charging mobile devices

Professor of Chemistry and Chemical Engineering at Chalmers and head of the study, said, “This is a whole new way of generating electricity from the sun. It means we can use the sun to generate electricity regardless of weather, time, season or geographic location. It It’s a closed system that can operate without CO2 emissions.”

Having demonstrated that the system can be used to generate electricity, the team is focusing on improving its performance while working on an affordable commercial solution for charging gadgets and heating homes. In addition, the system can also be used in satellite thermal control systems.

Breaking the barriers to commercialization in the competitive solar space will be a significant and difficult challenge, but given the innovative nature of solar technology and the current worldwide trend towards phasing out fossil fuels, breakthroughs are likely to be happening.

Related post

Leave a Comment

Your email address will not be published. Required fields are marked *

tycorun logo

TYCORUN ENERGY

We offer lithium ion battery products, solutions, and services across the entire energy value chain. We support our customers on their way to a more sustainable future.

Products

Recent Posts

Hot Posts

Contact Form Demo (#3)
Scroll to Top

Request A Quote

Email:info@takomabattery.com