Top Trends Driving Green Energy Systems

Innovation and Top Trends Driving Green Energy Systems

Adam Kimmel for Mouser Electronics

Introduction

The 2015 COP 21 meetings in Paris were a significant step toward globally targeting climate change. The conference captured the countries' commitments in the Paris Agreement, in which nations promised to limit global temperature rise to below 2°C (target 1.5°C) by 2100. Participants will achieve this by targeting a climate-neutral world by 2050.

The good news for global economies is that green (or renewable) energy aggressively addresses climate change while carrying a market opportunity expected to reach $2 trillion by 2030. This article will outline the current state and recent technical developments for green energy sectors.

Renewable sources already comprise a significant proportion of global energy generation. Hydropower is the high majority, but wind and solar are quickly catching up. Figure 1 shows the global energy generation in 2021, illustrating how wind and solar have gained on hydropower in recent years.

Figure 1: Modern renewable energy generation by source, World 2021. (Source Hannah Ritchie, Max Roser and Pablo Rosado (2022) - "Energy". Published online at OurWorldInData.org. Retrieved from: 'https://ourworldindata.org/energy')

Solar Energy

There has been significant innovation in the field of solar and photovoltaic (PV) energy, though barriers to implementation include the following:
•    The land required to house the power infrastructure
•    Equipment and installation costs
•    Inverters and power conversion equipment
•    Technology to integrate with the power grid
•    Aesthetic of installing a large area of solar panels on consumers' rooftops or agricultural land

Given the importance of increasing the proportion of solar energy and the timing to meet Paris commitments, governments are beginning to mandate solar panel installation to remove the choice from consumers. For example, Tokyo is mandating solar panels on new houses built after 2025.

Solar Cells and Integrated PVs
Two primary drawbacks of solar energy are that it is intermittent and inefficient. Logically, power sourced from nature is less efficient and reliable than highly processed energy. For example, commercial solar panels are only between 15–20% efficient with a theoretical ceiling of ~30% for a single material. These limits are dictated primarily by energy conversion losses and solar dispersion before hitting the panel face.

Engineers are integrating PVs wherever practical to increase the overall power output of an inefficient process. With the highest solar efficiencies coming from southern-facing, unshaded surfaces, system designers can optimize the number of panels for maximum value. In addition, the large footprint of solar panel arrays can create secondary benefits like shading parking lots with solar structures or leveraging tall buildings whose flat rooflines are not visible to people below.

Ocean Solar
Since space is a vital consideration for solar, another emerging trend is putting solar energy systems out to sea. The large amount of open water on earth provides natural benefits for offshore floating PVs (also known as floatovoltaics), such as liquid-cooled integration with the seawater and added source energy via water reflecting solar rays onto the panels. In addition, liquid cooling carries a much higher heat transfer efficiency than air-cooled systems, which can reduce component sizes for a comparable amount of energy production.

Solar for Agriculture
Like floatovoltaics, agrovoltaic (or agrophotovoltaic) energy takes advantage of a large area to place PVs—in this case, installing solar panels on farmland to integrate with crop-growing operations. This practice also provides remote, resilient energy in locations that may not have ready access to the electrical grid or that can augment grid power allocated to agriculture. Adding power generation to land that is already profitable for farming increases its value, and the panels can reduce soil temperatures and evaporation, increasing the yield of the farmland.

Concentrated Solar Power
Another way to mitigate the natural inefficiency of solar energy is to collect the renewable power onto a small area using concentrated solar power (CSP) mirrors or lenses and then convert it to thermal energy for on-demand use. This thermal-to-electrical conversion is similar to how Stirling engines and steam turbines operate. Additionally, enabling factors for CSP include access to high-voltage transmission lines, sufficient land acreage, and high-quality sunlight (like in the U.S. Southwest).

Innovation in PV Materials
Commercial, single-material PV operates at a very low conversion efficiency, around 20%. However, there are significant material advancements that address that limit. For example, simply reducing the PV cells' material thickness increases the materials' physical flexibility, reduces costs, and improves the sustainability profile with less material. In addition, thinner PVs reduce conduction losses across the material thickness (heating up of thicker material), increasing energy conversion efficiency.

Another advancement in PV materials is implementing bismuth (Bi)-based materials and coatings to push past the ~30% theoretical limit. The leading coating material is perovskite, which raises the theoretical efficiency limit to 43% through expanded wavelength absorption on the solar spectrum, which in turn increases the quantity of available source energy. Perovskite durability remains an open question, however, which could limit the duration of the increased efficiency over the solar cells' lifetimes. Other films and coatings have demonstrated 5–10% efficiency gains by capturing and redirecting light beams, similar to CSP.

Wind Energy and Hydropower

Renewable power has become more affordable due to technology advancements and increased market adoption. But while construction of new wind and solar plants is currently more economical than that of coal or gas plants, fossil fuels still dominate global consumption compared to renewables.

However, as the demand for green energy skyrockets due to global sustainability commitments, the costs per unit (kWh) of wind and solar power generation capacity are also falling—occasionally lower than cost per kWh of fossil fuels. As a result, renewable energy's lower capital and per-unit cost when compared to fossil-derived power create a compelling business case when met with unconstrained global demand.

Hydropower, which comprises the highest proportion of renewable energy production, takes advantage of water's prevalence. This method harnesses the kinetic energy of flowing water, which spins a turbine to drive a coupled generator, producing electricity. In addition, many of the wind innovations leverage integration with ocean sources.

Local Turbine Assembly and Construction
The massive size of wind turbines complicates the transportation of complete units and creates headaches for logistics leaders. As a result, engineers are designing turbines for construction on-site and transporting them in pieces. This approach simplifies turbine transport while reducing the number of unique parts. This in turn allows an increase in production quantities of the remaining parts, improving turbine economics through economy of scale.

Blade Aerodynamics and Numerical Modeling
To improve the efficiency of wind power production, engineers are focusing on blade design. For example, engineers use 3D numerical modeling or a computer-aided engineering approach called computational fluid dynamics (CFD), which analyzes static and dynamic conditions to predict the optimal design.

Digital Twins
Digital twinning, which replicates a physical part with a digital match. The digital twin incorporates performance data from the physical part for model calibration. Then, design updates can happen rapidly in the digital realm before manufacturers begin a new physical prototype, saving massive amounts of time and costs.

Energy Harvesting
Energy harvesting takes advantage of the fact that any differential in properties creates the opportunity for power generation. For example, many residential water storage tanks are elevated to provide consistent delivery pressure. Engineers have devised ways to harness naturally occurring differentials in thermal energy, salinity, and tidal pressures in the ocean for hydropower.

Ocean Thermal Energy Conversion and Gradient Energy Capture
Temperatures can vary significantly from surface water to water hundreds of meters deep. Ocean thermal energy conversion (OETC) devices use hot and cold seawater to vaporize and condense a working fluid in a vapor-compression refrigeration cycle. The larger the temperature difference, the higher the energy efficiency and output. Similarly, osmotic and tidal wave pressure differentials can produce energy as the initial state seeks equilibrium with the lower-energy state.

Energy Storage and Grid Integration

A significant source of green energy innovation is occurring in energy storage. Renewable energy is inconsistent, so storing the power allows the user or utility to dictate how to smooth out the intermittency.

Battery Chemistry
With the rise of electrification, battery chemistry is constantly evolving. Technologies like lithium iron phosphate (LFP), sodium ion, and solid-state are poised to improve the power density, charge/discharge speed, and safety profile.

The improvement of battery chemistry is essential for the longevity of electrification solutions. However, as engineers develop and apply battery products to an expanding array of applications, ensuring their safety is equally important. This objective is especially true for Li-ion batteries susceptible to thermal runaway.

Product Spotlight: Analog Devices LTC6811 Multi-Cell Battery Monitor
Analog Devices has developed a robust system that solves battery monitoring for ISO 26262-compliant systems: The LTC6811 12-channel multi-cell battery monitor (Figure 2) can measure up to twelve cells connected in series at a maximum measurement error of 1.2 millivolts. With a cell measurement range of 0V to 5V, the LTC6811 offers a measurement error of 1% or less and takes just 290µs to measure all the system's cells. Moreover, the LTC6811 employs an isoSPI™ interface for high-speed, long-distance communication with the host processor that is not susceptible to RF interference.

 
Figure 2: Analog Devices LTC6811 12-channel multi-cell battery monitor. (Source: Mouser Electronics)

The monitor includes passive balancing and PWM duty cycle control for power regulation and extended lifetime within each cell. It can draw power from the battery itself or an external power source, and it also employs a 16-bit delta-sigma analog-to-digital converter (ADC) with a programmable third-order noise filter. This feature is significant as noise is one of the critical metrics in electric systems.

The robustness and broad applicability of the LTC6811 to multiple battery chemistries and systems make it ideal for battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs), grid energy storage, battery backup systems, and high-power portable equipment, among other use cases. In addition, when a solution uses a battery of the specified loading, the LTC6811 monitor can gauge its performance and indicate when performance metrics fall off to help predict an impending failure.

Distributed Energy Storage and Microgrids
As the trends and innovation in wind and solar evolve, integrating that energy with the electrical grid will be the next critical hurdle to driving the energy transition. Like gallium nitride and silicon carbide semiconductors, grid electronics allow various energy forms to communicate through power integration. In addition, this technology provides distributed energy storage in alternative power forms.

Grid electronics also enable microgrids—local collections of power sources that can operate independently, like a generator, or integrate with the grid. These arrangements provide an additive effect of all renewable energy sources to augment primary grid power or strengthen resiliency during outages, improving power utilization efficiency. As a result, battery monitors like the LTC6811 are critical to ensure performance when a remote microgrid does not have access to the primary power grid.

Microcontrollers
Microcontrollers give operators control over how they distribute renewable energy. Integrating these controllers with AI-driven smart systems can automate the power balance for optimal efficiency, adapting to changes in demand or during peak periods. The controllers can also adapt to fluctuations in voltage through power intermittency and correct them in-application.

Vehicle to Grid (V2G)
One of the most significant shifts from the electrification movement is how engineers think of energy, treating it increasingly like a fluid that can travel back and forth where needed. However, access to green energy—or the lack thereof—is a significant challenge to widespread adoption, even after costs reach parity.

With this in mind, the proliferation of electric vehicles may solve the access problem, as they can act as mobile batteries or create a bi-directional path between the vehicle and the grid. This is especially beneficial for remote areas that are not connected to the grid, enabling these areas to create power resiliency should they have excess stored energy. This application can also improve the business case for Class VIII (on-road, heavy-duty) trucks while reducing power demand and intermittency of the existing grid. As a result, V2G will be a significant green energy enabler.

Conclusion

With all the movement and trends around green energy, the primary challenges to adoption are still intermittency and inefficiency. To address these hurdles, new developments leverage the benefits of decentralization to add an intermediate storage mechanism and shift power deployment to the final stage. To complement, engineers are leveraging the existing features of natural energy to further increase their effectiveness.

How these inventions integrate with the existing grid will determine the speed and effectiveness at which green energy becomes widespread.