The sun has been referred to as a primary inexhaustible energy source capable of meeting energy demands on a global scale. Electricity can be generated from solar energy either directly using photovoltaic (PV) cells or indirectly using concentrated solar power (CSP) technology. The advantage of PV systems is that they can be installed quickly and easily. CSP technology, however, is promising because of its high capacity, efficiency, and energy-storage capability.
Progress has been made to improve solar energy efficiency in both options. However, the biggest challenge to fully integrating solar energy into the energy mix is a lack of solar energy storage. The global power grid is not suited for intermittent energy. So, any viable renewable energy source must be consistent and reliable, as well as cost-competitive.
Read part 2 of our white paper- 2021 Power Generation and Renewable Energy Trends, to explore renewable energy technology trends, both established and newer technologies including solar, wind, marine, and hydroelectric.
A lot is changing in solar energy, specifically regarding:
innovations into efficient energy storage technologies,
identification of lower cost,
more abundant materials for PV solar cells, and
upgrades to tracking systems to make solar panels more efficient in capturing the sun’s energy.
One of the more exciting possibilities for solar energy is a satellite power station that could transmit electrical energy from solar panels in space to Earth via microwave beams.
Battery storage is required for solar energy because of cloudy days and nightfall, both of which limit sun exposure. However, there are challenges to overcome. Currently, lithium-ion batteries still dominate the market. There are growing concerns; however, about their toxic effects, limited duration, and safety risks relative to overheating. In addition, lithium is a finite resource and environmentally taxing to mine.
Tremendous research has been done to identify cheaper and more abundant elements that could be used instead of lithium. Elements receiving the greatest interest include silicon, sodium, aluminum, and potassium. However, the electrochemical potential of some of these elements is lower than lithium, which means the energy density of the battery may be reduced. Such limitations have opened the door to using a combination of alternative materials.
Sodium-sulfur batteries, for example, are promising for large-scale energy storage because they are long-lasting and highly efficient at producing electricity. Sodium-sulfur battery electrodes contain molten sodium and molten sulfur, and the electrolyte is solid, A remaining challenge, however, is that these batteries currently need to operate at very high temperatures. Researchers at the Massachusetts Institute of Technology, cited in a September 2019 article in Cleantech Concepts, are investigating the possibility of sodium-sulfur options that can operate at room temperature.
Flow batteries are another attractive option gaining greater interest. They consist of two tanks of liquids that feed into electrochemical cells. Their advantage is that they store the electricity in the liquid rather than in the electrodes. This makes them more stable than lithium-ion batteries and gives them a longer lifespan. In addition, the liquids are less flammable, and the design of the flow battery means it can easily be scaled up simply by building bigger tanks for the liquids.
One type of flow battery, known as the vanadium flow battery or vanadium redox battery, is already available commercially. It is a type of rechargeable flow battery that employs vanadium ions in different oxidation states to store chemical potential energy. The attraction of the vanadium redox battery is that you can charge and discharge it at the same time, something that can’t be done with a lithium battery. China had anticipated completing construction on the world’s largest vanadium flow battery in 2020, according to a May 2020 article on the VanadiumCorp website, COVID-related lockdowns in the country put the project behind schedule.
Like any alternative design, there are downsides to vanadium flow batteries, namely that the liquids can be costly, and they aren’t quite as efficient as lithium-ion batteries.
Beyond flow batteries, there are plenty of other developments creating excitement in battery research and development. For example, researchers at RMIT University in Melbourne are developing a proton battery that works by turning water into oxygen and hydrogen and then using hydrogen to power a fuel cell. Other research teams are exploring 100% lithium-free ion batteries using materials such as graphite and potassium for the electrode and aluminum salt liquids to carry the charged ions.
In addition, researchers in China are looking at improving the existing technology of nickel-zinc batteries, which are cost-effective, safe, non-toxic, and environmentally friendly. Like the vanadium flow batteries, however, they don’t last as long as current lithium-ion batteries. Work is also underway on saltwater-based batteries, with one design already being used for residential solar storage.
While battery innovations are helping to store more energy, work also continues to find solutions designed to capture more energy from the sun.
The concept of using tracking systems to position solar panels in such a way that they capture more sunlight is not new. Various studies have suggested that by following (tracking) the movement of the sun, output from solar panels can be boosted roughly 20%-30%. Traditional tracking systems are built on a single axis, but newer dual-axis systems can capture more energy. The greater energy, however, comes at a steep cost, making dual-axis tracking systems cost-prohibitive for many applications.
New designs and technologies are reducing those costs. Not only are efforts underway to make dual-axis tracking systems less expensive, but new solar panel materials are also being identified. Some solar farms, for example, are hoping to switch from silicon to perovskite, a crystal-like structure that consists of calcium titanium oxide. Preliminary studies suggest that perovskite could increase electricity generation by a third. However, no perovskite solar panels are yet commercially available as engineers are still working to overcome stability problems with the material.
Regardless of the material used, a key concern relative to the reliable use of tracking systems continues to revolve around condition monitoring and maintenance. The trackers are subject to tremendous load variances, especially when working in dusty, windy environments. Since many solar farms in operation today are in remote areas, visual inspection of the tracking systems and solar panels is time-consuming and expensive.
That’s why Parker launched its Voice of the Machine Cloud Software and SensoNODE™ Gold Sensors, which provide a wireless, remote monitoring solution.
By monitoring the pressure levels of the solar panel tracking system’s hydraulic loads, end users can easily calculate how much extra pressure is being put on the panels. A change in the supported load can sometimes indicate structural damage that needs to be addressed before the scheduled visit from field technicians.
Enhanced energy storage solutions in the form of alternative battery designs and higher-efficiency, lower-cost solar panel tracking systems represent a part, but not all, of the necessary solutions to make solar energy more reliable. The power is there, but more work must be done to help solar energy reach its full potential.
To learn more about trends in the solar industry, read our Power Generation and Renewable Energy Trends White Paper – Part 2.
This article was contributed by the Fluid Gas Handling Team.
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