Carbon Footprint Reduction in Energy Sector with Higher Penetration of Renewable Energy Resources

Abstract

Energy sector is a big source of carbon emissions. Traditionally, it is built, almost entirely, on fossil fuels with the exception of hydro and nuclear power plants. In line with the global mobilization toward tackling global warming by reducing carbon emissions, energy sector is trying to transition its generation portfolio to clean and sustainable energy sources. Renewable energy sources such as solar, wind, and wave provide energy without carbon emissions and provide a good alternative to traditional fossil fuels such as coal or natural gas. Another opportunity lies at the intersection of energy with transportation sector, another big contributor to carbon emissions. When electrified with renewables, transportation sector can both reduce its carbon emissions and provide support to electrical grid via novel solutions such as smart charging. However, these benefits come at a price. Non-dispatchable nature of renewable energy sources and their low inertia create operational and planning issues that make it hard to ensure demand is always met and the system operates in a healthy way. This chapter covers how renewable penetration can be increased while mitigating these issues with novel solutions. These include novel optimization ideas based on nature and new devices such as smart inverters.

1. Introduction

Industrial Revolution has surely transformed the humanity and its life on this planet. One of the biggest impacts of industrialization and burning more fossil fuels is the amount of carbon emissions and the resulting global warming [1]. The effects of this phenomenon can be observed in constant increase in temperature, melting icecaps, rising sea levels, and extreme weather events. Acknowledging the fact that greenhouse effects of carbon gases in the atmosphere cannot be ignored anymore, nations around the world started carbon-reduction initiative such as Kyoto Protocol, EU 2020 vision, and so on [2].

Energy sector is one of the most prominent sources of carbon emissions as shown in Figure 1 [3]. Traditional source of energy for electrical systems has been fossil fuels such as oil, natural gas, and coal. They have been a reliable bulk source of energy for large-scale power plants. On the other hand, their constant use made energy sector, and electrical systems, a big contributor to the global warming. For this reason, transformation of electrical system’s generation portfolio has been at the center of carbon reduction and global warming mitigation efforts [4].

Figure 1.

Sector-based greenhouse gas emissions, CC BY [3].

In principle, the idea is to deploy more renewable energy sources (RES) in the energy grid. The intended use might be direct electricity generation or an alternative approach such as direct heat capture. Some uses envision integration of RES at bulk generation stage, while some others are intended for much smaller applications at the distribution network level [5]. In addition to generation efforts, some attention has been diverted to increased use of storage devices and their alternative implementations such as electric vehicles being used as mobile storage devices. There are innovative solutions that use small-scale renewable energy resources to energize isolated communities that would, otherwise, be left without electricity [6]. These solutions focus on harvesting the available energy locally with minimal investment and provide energy to these marginalized communities at a low cost [7].

At every stage of such transformation, the power engineers face difficulties. This is due to the fact that traditional design of power networks was sketched thinking that energy flow will always be unilateral from bulk generation sites to bulk consumption sites that are clearly separated [8]. Although transmission lines have some flexibility to accept novel devices such as flexible AC transmission systems (FACTS), especially distribution networks are very vulnerable to such new deployments. They are not very stable; voltage and frequency values tend to experience big swings, and distribution network hardware such as the cables or transformers are bound by their lower electrical and thermal ratings [9].

In order to address these issues, researchers have been working on a myriad of ideas. The overarching question is how to increase renewable energy penetration, and thereby decrease the fossil fuel share in power generation, while keeping the disturbances caused in system operation to a minimum? Such solutions may be developed in the form of a novel device such as a smart inverter or virtual synchronous generator. Alternatively, a novel control approach can be developed that allows for more renewable energy and compensates for their negative impacts by being faster, more effective, and efficient. It is also possible to develop a holistic energy management system that combines novel hardware and software solutions in an integrated manner.

Rest of this chapter discusses the share of electrical power generation in global carbon emissions and the efforts toward increasing renewable energy share to reduce the overall carbon footprint of energy sector. It presents examples of novel solutions developed for various issues encountered in this process. Furthermore, it also discusses the side effects of these novel solutions, how they impact the overall system operation, and how they can be mitigated, again with examples from the literature. Finally, it draws the conclusions and provides perspectives for future research directions for interested individuals from the academia.

2. Energy-related global carbon emissions

Carbon emissions due to energy generation in all of its forms has been the leader in sectors related to greenhouse gas emissions. While the historical trend has been a steady increase in carbon release into the atmosphere since the early 1900s, a significant change in the rate of increase has been observed around 1950s. This trend has not changed ever since. It is true that the annual average rate of carbon emissions worldwide has been relatively lower in 2023, still with a 410 million tons of emission increase, and the overall emissions in 2023 reached 37.4 billion tons, a new record in history [10]. It is worthy to note that the increase in carbon emissions between 2019 and 2023 would have been much higher (around three times as much) had it not been for the positive impact of five key technologies for clean energy: electric vehicles, solar energy, nuclear energy, wind energy, and heat pump.

Figure 2 shows amounts and annual rate of change of carbon emission-related to energy sector in gigatons between 1900 and 2023.

Figure 2.

Global carbon emissions related to energy, 1900–2023, IEA CC-BY [10].

For an optimist, there is good news in these numbers. They show that the clean energy initiatives around the world can and do make a difference. The carbon emissions growth in the past four years is kept to one-third of what it would have otherwise been. In this fashion, global economic growth and prosperity can be sustained with a very small change in the carbon emission growth. With the right amount of interventions and a bit of luck, that can even be kept to zero; that is, there will not be any more carbon emissions growth from year to year; instead, it will be kept constant.

On the other hand, a more cynical person, or a more realistic person as they like to call themselves more often than not, can interpret these results as all doom and gloom. Despite every country and sector doing their best to cut down carbon emissions, we could not prevent its growth. What is more worrying is that extreme weather events related to greenhouse effect, such as droughts, have had a strong impact on power generated from hydroelectric power plants and reduced the overall output from this, arguably only dispatchable, renewable source. Instead, fossil fuels had to be used that caused 170 million tons of emissions, more than 40% of the overall carbon emissions growth last year. It is possible that the negative impact of global warming will trigger more extreme events that could reflect on these values more significantly.

A more neutral approach may help us understand that we are somewhere in between. We are nowhere near reaching goals set in Paris Agreement, far from it. However, we cannot overlook the fact that carbon emissions in advanced economies were reduced by around 4.5%, while GDP in these economies increased by 1.7%. Thanks to the transformations undertaken by the countries with advanced economies, their carbon emissions are back where they were roughly fifty years ago. The coal demand of these countries is the same as what it was in the 1900s. One of the reasons for this change is, unfortunately, due to the migration of industrial endeavors to other countries such as China where the annual emission growth was a whopping 565 million tons. Considering the global overall carbon emission growth was roughly 150 million tons less, 2023 would have been a year with negative carbon emission growth had it not been for China’s carbon-intensive growth model. Carbon emissions per capita is 15% higher in China than in advanced economy countries. Global drought mentioned above caused roughly 33% of its emissions growth last year. India is another country that has been effected by the change in rainfall, where the weak monsoon season caused electricity production to move away from hydro. This resulted in a 25% increase in its emissions growth for the year 2023.

Figure 3 shows the total and per capita carbon emissions by different regions. It can be observed that European Union, Japan, and US have a downward trend in both the absolute amount and the per capita. China and India have both experienced significant carbon emissions, although India’s annual growth is smaller.

Figure 3.

Absolute amount and per capita carbon emissions [10].

To understand these trends, it is important to investigate the drivers behind these changes. As shown in Figure 4, the biggest change in the European Union was renewable electricity deployment. The second largest driver for this reduction in carbon emissions was lower industry-related emissions. Hydro and nuclear recovery, due to better precipitation and reactors that are put into service after much-needed maintenance, respectively, were significant factors as well. The biggest driver that caused an increase in carbon emissions was the GDP growth (Figure 5).

Figure 4.

Carbon emission change between 2022 and 2023 in EU [10].

Figure 5.

Carbon emission change between 2022 and 2023 in the US [10].

Lessons learned from the changes in carbon emissions of the US were significantly different. The biggest driver that caused the carbon emissions to fall despite a positive GDP change was the switch from coal to gas. Renewable energy deployments can be cited as the second biggest factor. However, that requires mentioning that half of this positive impact has been negated by the poor wind conditions and shortfall of the hydroelectric power generation. In other words, renewables had a positive impact, but their impact has been limited due to extreme weather conditions. This shows that a holistic approach is needed to reduce the carbon footprint of energy sector. Sometimes, switching from one fossil fuel to another may turn out to be the biggest positive impact.

A final look at Figure 6 shows us that the biggest impact on the global carbon emissions is still due to the energy sector. Therefore, the potential for the biggest positive impact or improvement lies therein. The second most influential sector is the transport sector. Clean energy use in transport is almost always associated with linking it with the electricity sector [12]. Electrification of transport sector, including ships, trains, and land vehicles, can be a game changer [13]. This requires proper planning and charging coordination with the electrical grid [14].

Figure 6.

Carbon emissions change by region and sector for 2023 [11].

In all emerging market and developing countries (EMDE), the carbon emissions have risen for all sectors, that is, energy, transport, industry, and building sectors. For advanced economies (AE), all of these sectors have experienced a reduction. The world, in general, has experienced carbon gas emission reduction only in buildings sector. Considering their relative amounts, energy sector is the most influential and promises the biggest change.

3. Issues related to increasing renewable energy penetration in future grids

The previous section discussed what a big role energy sector in general, and electricity generation in particular, plays in global carbon emissions. Observing this fact, researchers have focused their efforts on transitioning from traditional fossil fuels to cleaner alternatives. Although it looks like a pretty straightforward decision, there are different barriers that hinder a mass migration to these alternative fuel sources.

First of all, these resources are intermittent, which means, unlike fossil fuels, they cannot be dispatched at will. This creates a massive issue for power system operation and planning [15]. From power system planning point of view, the golden rule is to always keep the demand and supply equal. This is not negotiable, and not doing so will have detrimental effects on the stability of the system that, in worst cases, may lead to blackouts [16].

In traditional power systems with fossil fuel fired power stations, it is relatively easy to manage this. Firstly, it is easier to estimate the consumption amount as the loads and consumer profiles are not as flexible and more predictable. Secondly, thanks to the storable nature of fossil fuels such as coal, oil, or gas, it is possible to have a large amount of power readily available and can be dispatched by increasing or decreasing the fuel input, thereby ensuring that power generation is equivalent to the consumption. Also, in the past, power networks used to have more operation margins that allow for changes. For instance, transmission lines were operating much lower than their thermal and electrical capacities. The only issue was finding the required energy and transmitting it.

Figure 7 shows a sample daily solar radiation in Sultanpur, India [17]. The profile is not smooth and has steep transients and constant variations. Furthermore, the solar radiation estimation calculations yield only the daily average solar radiation, not how it may fluctuate in time. Nor do they take into account sudden changes such as cloud coverage. Therefore, solar energy cannot be the primary source of energy in these systems. There should always be some additional measures, such as storage or dispatchable generation source, that can step in to meet the demand if solar energy fluctuates or diminishes. It is also important to note that most of the renewable energy sources are affected by the weather and seasons. Their energy output varies, and their seasonal variability needs to be compensated by other means. As shown in Figure 8, different seasons such as a dry season or a tropical one have significantly different energy outputs. For instance, PV output is very limited in a continental warm summer setting, while it can meet half of the demand in a tropical setting. It goes without saying that successful integration of renewables requires effective mitigation of both short-term and long-term variability in their nature [11].

Figure 7.

Variations and fast transients in a typical daily solar radiation profile [17].

Figure 8.

Seasonal variations in the energy yield of renewable energy resources [11].

As mentioned earlier, another major issue related to integration of renewable energy resources is in power system operation. This manifests itself in the stability and health of two key operational parameters, voltage and frequency. For example, Figure 9 shows the voltage profile of a 100 V distribution network. On the bottom left, a network with no PV penetration is shown. Voltage gradually drops as one gets further away from the local transformer [18].

Figure 9.

Voltage issues related to local renewable energy generation.

Bottom middle shows when PV panels are installed on these households, and they start injecting power into the grid. Since this is not what the distribution networks were initially designed for, a significant voltage rise appears. In some cases, this voltage rise goes beyond the higher limit. In order to avoid this, and although it means rejecting free and clean energy, the PV generation is limited, that is, curtailment. This shows that due to physical restrictions, it is not possible to harvest all the available renewable energy at a particular location. Even if, feasibility studies show a much higher harvestable potential. In theory, if all the transmission and distribution networks are fully refurbished, they can accommodate more renewable penetration. However, it is not realistic to expect this due to high costs, regulatory limitations, and public disapproval.

Issues related to the stability of the frequency are caused by the inverter topologies that are used to interface most of the renewable energy resources and storage devices to the existing grid [19]. These topologies are built by solid-state electronics that switch at a very high frequency to mimic AC systems. Traditionally, the power grid’s frequency is set by rotational motion that takes place inside the synchronous generators. Due to their physical structure and rotor rotating inside an electromagnetic field, these systems have an inertia that resists sudden changes in the interconnected system. This is an excellent security mechanism as it inherently gives frequency stability to the system. As shown in Figure 10, inverters have several legs of solid-state inverters, some filters, and advanced measurement and control loops [20]. They lack any rotating parts that would give an inertia to their operation. This is not a big issue if the penetration of renewable energy, and the number of inverters that are used to interface them to the grid, is not high. It becomes an issue when they are used in very high penetrations, in isolated areas or weak grid situations, for instance, places that are very far away from the grid to benefit from its stability.

Figure 10.

A typical inverter topology with advanced control [20].

Finally, it is possible to cite lack of necessary market and economic tools as a barrier as well. Researchers have focused on mitigating technical and physical limitations that hinder deep penetration of renewables. Recently, it has been acknowledged that even if technical barriers are entirely removed, there are regulatory and financial barriers in place [21]. This includes centralized bidding structures where small-scale or individual power producers cannot participate, regulatory limits about how to sell energy and which channels to use, bureaucracy around obtaining necessary licenses as a producer, consumer, or prosumer etc. Assuming that almost every household or electric vehicle owner can participate in the market, the number of participants and the information technology infrastructure required to deal with an energy market with that many stakeholders make it very challenging. Traditional energy markets with centralized market operators and only a handful of participants cannot meet the needs of a power grid with very dynamic and active market.

4. Solutions toward mitigating issues related to higher penetration of renewables

Researchers have investigated different approaches to mitigate various issues mentioned in the previous section. When it comes to managing non-dispatchable behavior of renewables, the solutions focus on creating a generation mix, which may or may not include storage systems, to address intermittent and unpredictable nature of renewable energy resources. The very basic approach towards this is ensuring that the capacity of the storage systems or dispatchable generators is equal to the critical loads in a system. In other words, even in a contingency case where the renewable energy resource is completely lost, due to cloud coverage for PVs or storm conditions for wind turbines, the system can still sustain itself. An example microgrid that is designed in a fail-safe manner is shown in Figure 11 [22].

Figure 11.

Microgrid with renewable energy sources and storage system [22].

It is also possible to use grid-connection as a fallback mechanism, in case the renewable energy sources fail to generate the estimated energy as shown in Figure 12. Such systems can be designed to harvest as much clean energy as possible, when available. In other cases, grid connection can always be utilized to make up for the demand-supply mismatch.

Figure 12.

Harvesting renewable energy sources with grid connection [23].

In both cases presented above, the main objective is to build the most optimal system so that the available renewable energy is harvested as much as possible. Some researchers have attempted to combine different storage technologies to come up with a better cost-performance ratio and a longer life cycle. One such attempt is shown in Figure 13 where battery and supercapacitor pair is utilized to make use of different characteristics of these technologies [24]. Batteries need longer times to charge, have a limited discharge power, and are affected by charge-discharge cycles which reduces their lifetimes. However, they can come in large capacities and are relatively cheaper. Supercapacitors, on the other hand, can charge and discharge very quickly, are expensive, and have better charging performance.

Figure 13.

Battery-Supercapacitor pair for enhanced solar energy capture [24].

The benefit of such solutions is that if the intermittency of renewable energy, in this case solar, is managed more effectively, it is possible to rely on it more and increase its share in the generation portfolio. In case of any issues, the balancing system will compensate and ensure reliable operation of the system. In the long run, more renewable energy is capture and fed into the system. Especially for setups where fossil-fuel fired generators are used as fail-safe solutions, as an example see Figure 14, this reduces carbon emissions due to the power system generation [25].

Figure 14.

A microgrid where diesel generator is used as a fallback solution when solar energy is not available [25].

A more integrated way of doing this involves communication with all system components, for instance, generators, loads and storage devices and, in some cases, weather stations for renewable generation prediction. These are called energy management systems (EMS) and are designed to monitor the condition of the power system and make decisions in real time. As shown in Figure 15, EMS controller maintains communication with all components and ensures safe and reliable operation of the power system while maximizing renewable energy capture such as from wind turbine (WTG) or central receiver solar thermal system (CRSTS) [26].

Figure 15.

EMS design to maximize renewable energy capture [26].

These decisions can be done with a simple flowchart, if-else mechanism, or lookup table. However, system based on such deterministic solutions fall short in maximizing renewable energy capture. Therefore, more advanced EMS approaches incorporate machine learning approaches such as artificial neural networks [27] or fuzzy logic [28] to search the most optimal operating point in the solution space. As shown in Figure 16 [29], such systems may utilize more than one artificial intelligence approach [30, 31, 32, 33]. The ultimate objective stays the same: maximizing the renewable energy utilization rate while managing intermittency to ensure power system operation stability.

Figure 16.

Use of artificial intelligence in energy management systems [29].

One important aspect of these solutions is that they require extensive communication between all components present in a power system [34]. Designing a system where a macro player such as a power producer and a micro player such as an electric vehicle in a residential household can exchange mutually legible messages is a tall task [19]. This is especially so in power systems where extensive communication or message exchanging has not been traditionally implemented [35]. This requires a standard communication approach to be developed in power systems. While this topic is very broad and cannot be fully discussed in this chapter, interested readers are encouraged to refer to these works for further details [36, 37]. An unwanted result of such standardization is cybersecurity vulnerabilities that created unprecedented issues in power systems [35, 36, 37, 38, 39, 40, 41, 42, 43]. This is also a very recent and fertile research field that cannot be properly discussed here and needs its own discussion avenue. Interested readers can refer to these works as a start [44, 45, 46, 47, 48, 49, 50].

The above solutions focus only on making sure that the demand and supply are equal in a simplistic manner. They do not take operation of power systems and system dynamics into account. This is important because when a generation source is lost, this has negative impacts on the voltage and frequency of the system. On the other hand, too much generation or active power injection causes these parameters to increase and reach their limits [37]. Both of these cases need to be carefully avoided. Figure 17 shows how an increase in the load disturbs the system frequency and how its magnitude as well as its duration are dependent on the controller topology that is employed [51]. This shows that using more sophisticated controllers such as (IPD-(1 + I)) is advantageous. Some researchers focused on using cascaded controllers so that the system can be more robust and effected less by the disturbances. As shown in Figure 18 [52], such topologies can prove to be much more stable and ride through disturbances with less impact and in shorter time.

Figure 17.

Traditional controllers and their reaction to load increase in a system observed as a frequency disturbance [51].

Figure 18.

Comparison of different controller topologies, cascaded controllers are more stable with less overshoots [52].

Figure 19 shows how a 1% increase in the system load disturbs the system frequency and how long different controllers need to stabilize it [53]. Here, two different optimization algorithms have been utilized to enhance the response time and operation of the controllers: African vulture optimization algorithm (AVOA) and a version of AVOA that is enhanced by sine cosine approach, that is, Sine Cosine-Adopted African Vulture Optimization Algorithm (SCaAVOA).

Figure 19.

Frequency disturbance caused by 1% increase in system load and its reduction with different control approaches [53].

It is a very dynamic and active research field where such different optimization algorithms are implemented and benchmarked against each other under different power system conditions [54]. There are different inspirations for such optimization techniques. A recent development has showed that imitating behaviors observed in the nature may prove to be very useful in such situations [55]. Figure 20 [56] shows how a power system can become more robust and stable when different nature-inspired optimization algorithms are employed. Expectedly, the more robust a system is, the more renewable energy deployments it can accommodate as it can effectively mitigate the intermittent nature of these resources. It is very exciting to see that carbon footprint of power systems can be reduced with solutions received from the nature. In a strange way, nature helps lift off burden of carbon emissions from the nature itself.

Figure 20.

Benchmarking of different optimization techniques to stabilize speed, differential evolution (DE), genetic algorithm (GA), whale optimization algorithm (WOA), and grasshopper optimization algorithm (GOA) [56].

In addition to controller and optimization approaches discussed above, there are full-fledged novel technologies or devices that are developed to support this transition. The two leading concepts are smart inverters and inverters with virtual inertia. Smart inverters, also known as inverters with advanced capabilities, are devices that can provide additional grid support such as reactive power injection [57]. Figure 21 shows how smart inverters provide positive or negative reactive power into the system to provide stability, depending on the system voltage [58]. When this figure is contrasted with the case depicted in Figure 9, the distinction between conventional inverters and smart inverters becomes clearer. Due to their benefits, smart inverters are required by several grid operators for renewable energy deployment [59]. Similar implementation can be done to provide frequency support via frequency-watt control in smart inverters [60].

Figure 21.

Volt-Var functionality implemented in smart inverters [58].

In a similar fashion, virtual inertia is an effort to mitigate the negative impacts of inverter-interfaced renewable energy resources on the system. Control mechanisms in inverters is revised to include resistance to voltage and frequency changes as a real electric machine with rotating parts would [61]. With this much needed change, the inverters are being converted from being grid-following into grid-forming inverters. When frequency-watt capability is combined with df/dt capability in smart inverters, virtual inertia can be successfully implemented. Figure 22 shows control hardware in the loop testing for a smart inverter controller that has fully functioning virtual inertia capability [62]. Disturbances in the system such as load or generation change triggers a frequency disturbance. In order to recover frequency to its nominal value, that is, keep the system stable, smart inverter with virtual inertia capability exchanges reactive and active power to ensure that frequency change is limited and returned to its value.

Figure 22.

Virtual inertia implemented in smart inverters [62].

The solutions and technologies discussed above focus on one thing and one thing only: to reduce negative impacts of renewable energy sources on the power system operation with an aim to maximize their penetration. This is the gateway towards reducing the share of fossil-fuels in energy sector and reducing the carbon footprint in a significant way. The final piece of the puzzle lies with the energy markets. Traditional markets were designed for bulk energy trading, which addresses mostly fossil-fueled power stations, with the exception of hydroelectric and nuclear power plants [63]. Successful integration of renewable energy resources requires these paradigms to change [64, 65]. Generation at much smaller scale should be possible; non-dispatchable generation should be accepted, and auxiliary services to stabilize the system should also be incentivized and monetized [66, 67]. Distributed nature of renewable energy resources and the fact that peer-to-peer energy trading is much more convenient lends itself to novel trading ideas such as Blockchain as shown in Figure 23, [68]. This will unlock the potential of independent, distributed, and deregulated energy markets [69].

Figure 23.

Renewable energy trading with Blockchain technology [68].

5. Conclusions

Replacing fossil fuels with clean renewable energy resources is not an option anymore. Changing weather conditions, more frequent extreme weather events, and their apparent impacts on life make it clear that a transition must be made. As one of the biggest sources of carbon emissions, power sector’s transformation will have large impact. Furthermore, when integrated with the transportation sector, another big carbon emission source, an interdisciplinary solution can be developed.

The solution lies in harvesting clean and mostly nondepletable renewable energy resources and replacing fossil fuels with them. There is more than enough potential in alternative energy sources such as solar, wind, wave, and geothermal. However, their non-dispatchable and non-predictable nature creates issues for power engineers. It is not possible to fully rely on these resources without compromising the health and stability of the entire power system. Researchers have been working towards developing novel approaches, solutions, and devices that will mitigate these negative impacts. These solutions have been covered in this chapter in detail, what part of the problem they address, and how they do it.

This research field is very promising, and there are exciting opportunities for future work. Development of an inverter with a comprehensive virtual inertia functionality is an important step towards reducing carbon footprint of the energy sector. Integration of all power system systems and devices with a common language for better monitoring and control is an active research field. Due to competing interests, different stakeholders lock horns and make it very difficult to come up with an ultimate solution. Integration of household items and smart meters with larger systems creates opportunities for solutions such as demand side management and energy dispatch at the consumer end. However, these systems create cybersecurity and privacy issues that need to be tackled before such systems can be implemented at large scale.

Conflict of interest

The authors declare no conflict of interest.