Second-Life Electric Vehicle Batteries for Home Photovoltaic Systems: Transforming Energy Storage and Sustainability

Abstract

Solar-based home PV systems are the most amazing eco-friendly energy innovations in the world, which are not only climate-friendly but also cost-effective solutions. The tropical environment of Malaysia makes it difficult to adopt photovoltaic (PV) systems because of the protracted rainy monsoon season, which makes PV systems useless without backup batteries. Large quantities of lithium-ion battery (LIB) trash are being produced by the electric vehicle (EV) sector. A total of 75% of the highest capacity levels have been discarded. By 2035, it is predicted that the wasted LIBs held as a result of expensive recycling and difficult material separation would carry up to 1200 GWh. An economical and sustainable option is offered by our study, which prototypes a replicated LIB pack that is incorporated into a PV home system. This study investigates the transformational power of second-life electric vehicle batteries (SLEVBs) when incorporated into home photovoltaic (PV) systems. The concept entails reusing existing electric vehicle batteries for stationary applications, offering a unique approach to extending the life of these batteries while meeting the growing need for sustainable domestic energy storage. The study looks at the technological feasibility, economic viability, and environmental effect of introducing SLEVBs into household PV systems, giving vital insight into their role in revolutionizing energy storage techniques and promoting sustainability. In comparison to the Lead–Acid Battery (LAB) system, the SLEVB system has a cheaper total cost of ownership, with savings of 12.62% compared with new LABs. A CO₂ emission reduction of at least 20% is achieved by using the SLEVB system compared with LABs. Electricity can be provided in houses in rural areas where there is no electricity. As a result, the security and superiority of the life of rural residents will improve. It is anticipated that the suggested strategy will lower EV pricing, enabling EV adoption for M40 and B40 groups. Consequently, the Malaysian and worldwide EV business will remain viable.

1. Introduction

Electric vehicles (EVs) and home photovoltaic (PV) systems have spurred a new wave of inventive solutions in today’s globe. Due to the increasing global popularity of electric cars, there will soon be a surge in the availability of old batteries that are no longer adequate for vehicles requiring dependable acceleration and range. This confluence has become a center of innovation as people’s awareness of the value of renewable energy sources and the uptake of electric vehicles grow. There has been a significant rise in global apprehensions over the decarbonization of energy systems in recent years. PV panels are highly promising distributed energy generation systems that primarily contribute to the building service industry [1]. Concerns about the effects on the environment are growing, and many countries have made using carbon dioxide-free, eco-friendly energy sources a priority. Global demand for sustainable energy solutions has fueled technological advancements that bridge the gap between electric mobility and household energy independence [2]. Combining second-life EV batteries with household PV systems provides a cost-effective and sustainable energy storage option. Reusing EV batteries with a high capacity reduces PV system costs and extends battery life, supporting sustainability goals. This integration stores extra solar energy generated during the day for use during high demand or when solar power is unavailable, improving system efficiency and reliability. Stored energy can be used during peak demand or power outages, giving homeowners more control over their energy consumption and minimizing grid dependence. Renewable energy sources, such as solar energy and wind energy, are unstable and intermittent during generation and greatly rely on climate conditions, and thus, these valuable electric energies are difficult to apply continuously and stably. Moreover, the efficacy of renewable energy is contingent on geographical location, which restricts its widespread implementation in specific areas. To tackle this issue, the employment of energy storage systems may greatly improve the utilization rate and stability of renewable energy [3]. The energy storage system (ESS), when combined with renewable energy systems that use photovoltaic (PV) panels, is commonly employed in stand-alone (off-grid) systems. Its primary function is to engage in peak shaving and power shifting, specifically during peak load hours, predominantly at night. The cutting-edge idea of second-life electric vehicle batteries (SLEVBs) is setting the standard for home photovoltaic (PV) systems. The idea of converting discarded electric car batteries into stationary energy storage devices is investigated in this study. It explores the complex effects of this integration on energy storage efficiency and environmental sustainability.

In spite of their good contributions to energy management solutions, energy storage devices have significant environmental implications. The primary focus of this phenomenon pertains to the retrieval of primary resources, namely cobalt, nickel, and lithium, as well as the energy-intensive procedures involved in the production of lithium-ion batteries. However, this impact could be mitigated by extending the lifespan of the batteries that are no longer needed in electric vehicles and instead used in less demanding applications, like residential structures [4]. In such applications, the initial state of health (SOH) of second-life batteries typically ranges from 75% to 80% of their nominal capacity [5]. The implementation of second-life applications is anticipated to yield financial advantages, hence enhancing the affordability and desirability of renewable energy for end users. Over repeated charge and discharge cycles, lithium ions in the battery’s electrolyte might become stuck in the anode or cathode components, reducing active material and capacity. The micro-health parameters stand for the performance of active material and electrolytes inside the battery, and the changes in the micro-health parameters can present the battery’s internal health state. The identification of the micro-health parameter method under the same charging condition can improve the test efficiency and add the classification basis for retired batteries [6]. In the continuously changing energy environment, where resource preservation and climate change mitigation are pressing goals, the integration of SLEVB with household solar systems seems to be a new method.

The International Energy Agency (IEA) estimates that 11.2 million new electric vehicles (EVs) will be sold worldwide in 2025, making about 6% of all vehicle sales. Europe, North America, and China were the main EV markets. According to the Stated Policies Scenario (SPS), the number of global EVs (apart from two- and three-wheelers) will increase from around 11 million in 2020 to 145 million in 2030 or by 7% for all vehicles worldwide. By that year, the BEV proportion of EVs will have reached 67%. According to the SDS, there will be 230 million EVs on the road worldwide by 2030, making up around 12% of all cars. According to the IEA, the European Automobile Manufacturers Association (ACEA) 2021 reported the estimated number of retired LIBs will be 18.1 million in 2040. The forecasts for the quantities of lithium-ion batteries reaching their end of life from the EV sector until 2040 are shown in

Table 1. Lithium-ion battery retirement forecasts from the EV sector till 2040.

Year	Number of Electric Vehicles Sold (Millions)	Estimated Number of Retired Lithium-Ion Batteries (Millions)
2020	3.1	0.55
2025	11.2	2.0
2030	31.1	5.5
2035	59.8	10.7
2040	100.4	18.1

. These forecasts show the increasing number of LIBs that will reach the end of their lifespan in the electric car industry. Battery degradation is essential not only for maintaining vehicle performance and range but also for maximizing the value proposition of electric vehicles. The degradation of EV batteries over time is shown in

Table 2. The degradation of EV batteries over time.

Time Period (Years)	Average Battery Degradation Rate (%)
1	2.5
2	5.0
3	7.5
4	10.0
5	12.5
6	15.0
7	17.5
8	20.0
9	22.5
10	25.0

.

This highlights the need for efficient recycling and repurposing techniques to reduce environmental consequences and prevent resource depletion. These batteries contain important but toxic elements, and their incorrect disposal or recycling can pollute soil, water, and air. EV battery raw material extraction and processing also degrade the environment. Improved recycling, collection, and secondary-use applications are needed to reduce EV battery waste. Reusing discarded EV batteries for stationary energy storage could improve battery life and encourage a circular economy. To realize the environmental benefits of electrified mobility and sustainable energy systems, EV battery trash must be managed well.

By 2030, the BEV proportion of EVs will be 71%. By 2030, it is expected to accumulate a total of over 1000 GWh of SLB equivalent storage in the world [7]. In 2023, 14.2 million new PHEV and BEV were delivered, indicating a +35% growth. Ten million BEVs were fully electric, while 4.2 million were hybrid plug-ins and range extenders. Figure 1 and Figure 2 show the electric vehicle sales in the global accumulated sales of EV and SLB, respectively.

Recently, the European Union declared that new petrol and diesel vehicles will not be allowed to be sold after 2035 [8]. Furthermore, within the next 10 to 30 years, more than 20 countries have pledged to phase out the sale of automobiles using internal combustion engines. As a result, the demand for EV batteries will rise significantly over the next ten years, with estimates of 1.6 TWh in the SPS and 3.2 TWh in the SDS compared with a worldwide output of 0.16 TWh in 2020 [9]. By 2026, the worldwide market for automotive batteries is projected to have grown from its 2020 valuation of USD 43 billion to USD 59 billion. In Malaysia, sales of electric cars (EVs) remained low when compared to sales of conventional automobiles [10]. Nonetheless, a number of reasons, including government incentives, rising environmental consciousness, and developments in EV technology, contributed to the growing interest in EVs. Alongside the rises in EVs in the majority of nations, the global light car market had a robust comeback, rising by +10.5%. The ups and downs of the car industry do not correspond to the adoption of EVs. Stronger influences include environmentalism, financial incentives, a better charging infrastructure, and successful EV debuts. Strong car market recoveries tend to slow down EV share growth, but slowing overall vehicle sales usually accelerates EV share rises. In Malaysia, EV sales jumped by 286% to 10,159 units in 2023 compared with 2022; hybrid sales saw a 40% increase as well. Figure 3 depicts the electric vehicle sales in Malaysia.

SLEVB has enormous transformational potential, providing not only a sustainable afterlife for used EV batteries but also a strategic answer to the issues posed by intermittency and storage constraints in renewable energy systems [11]. This study aims to give a thorough knowledge of how incorporating SLEVBs into house PV systems might spark a paradigm change toward more resilient, environmentally friendly, and self-sufficient energy infrastructures. This study seeks to provide useful insights to the discussion on sustainable energy practices and the growth of decentralized power generation by delving into technological details, economic considerations, and environmental implications. As we engage in this investigation, we want to discover SLEVB’s transformational potential as a cornerstone in the ongoing story of energy storage and sustainability.

A multitude of studies have been conducted to examine the use of second-life batteries for energy storage systems (ESSs) in residential structures. Hart et al. [12] conducted a study on the utilization of second-life batteries in a microgrid. They employed an equivalent circuit model (ECM) and subsequently verified the accuracy of the model by comparing it to experimental data. In addition, an evaluation was conducted to examine the performance of the microgrid using various architectural configurations. The findings indicated that the integration of second-life batteries into grid-connected or -islanded microgrid applications was effective, as it did not disrupt the regular functioning of the system. The integration of a 3 MW second-life battery energy storage system (ESS) with the grid for peak shaving in China was introduced by Sun et al. [13]. A mathematical model was built for the system, along with a cost-effective model for the BSS. Evidence has shown that utilizing second-life batteries in the power grid for peak shaving in China is economically advantageous, particularly for grid operators. Mathews et al. [14] conducted an investigation into the effects of second-life battery packs with a varying state of health (SoH) on the system’s performance. The study employed a semi-empirical deterioration model to illustrate the comparative profitability of second-life batteries in photovoltaic (PV) systems as compared to first-life batteries. The mathematical model for the size and optimization of a stand-alone photovoltaic (PV) system for a net zero energy residential building was created by Cusenza et al. [15]. In order to optimize load matching in residential structures, the researchers conducted a second-life battery sizing analysis. The findings of this study indicated that the optimal ratio of battery size to total power generated by photovoltaics (PVs) is crucial for achieving the best load match. The rest of the paper is organized as follows: Section 2 discusses the electric vehicle (EV) battery life cycle. Second-life EV batteries for home PV systems are described in Section 3. Enhancing sustainability with second-life EV batteries is shown in Section 4. In conclusion, final observations and recommendations for future work are given in Section 5.

2. Electric Vehicle (EV) Battery Life Cycle

The cycle life of LIBs varies from 1000 to 10,000 years, and their lifetime spans 5 to 15 years. It is anticipated that the number of retired EVBs will rise dramatically due to the growing use of EVs as an environmentally friendly mode of transportation [5]. Chen and colleagues predict that by 2030, one million EVB packs will be decommissioned, and by 2040, 1.9 million [9]. The worldwide supply of second-life batteries is likely to reach 15 GWh by 2025 and 112–227 GWh by 2030, according to McKinsey, while the IEA predicted that 100–120 GWh of EVBs will be retired by 2030, an amount approximately equivalent to the current annual battery output [7]. For retired EVBs, several circular economy strategies, such as recycling and second-life uses, are being investigated. Electric car batteries are routinely changed when they reach 70 to 80 percent capacity, mostly because the range they give at that point begins to decline. Almost all of the key elements included within them, including lithium, nickel, and cobalt, are reusable. Repurposing retired EVBs for usage at the pack or module level in different domains is known as “second life” [7]. After a battery has been used once or twice, recycling entails separating and purifying the battery’s constituent parts for use in fresh batteries. Recycling has gained more attention as a result of the sharp increase in demand for lithium and cobalt brought about by the expanding manufacturing of electric vehicles.

Numerous scholarly investigations have focused on the benefits associated with the recycling of retired batteries from the transportation industry. Based on the study’s results, decommissioned EVBs can be utilized in scenarios where electric vehicles (EVs) do not require a significant amount of energy storage. Retired EVBs have the potential to decrease the costs associated with the implementation of energy storage systems (ESSs) [9]. The utilization of intermittent renewable energy sources can ultimately derive advantages from the retirement of EVBs [7].

If the State of Health (SOH) of a battery is greater than 80% during the remanufacturing process, it is reconditioned and used again in electric vehicles. However, if the SOH is between 40% and 80% during the repurposing process, the battery is repacked and utilised in energy storage systems that are connected to alternate energy sources or Uninterruptible Power Supplies (UPS) (Scheme 1). The power-type batteries utilised in this study are suitable for repurposing. Batteries with State of Health (SOH) levels below 40% will be sent for recycling in order to reclaim valuable materials. The main recycling techniques for LiBs are pyrometallurgical and hydrometallurgical processes. Malaysia is deficient in recycling technologies and lacks the necessary infrastructure. In order to efficiently manage battery waste in Malaysia, it is crucial to prioritise the implementation of reuse technologies, as the current processes for collection, separation, and sorting are insufficient.

3. Second-Life EV Battery for Home PV Systems

A convincing example of innovation at a time when there is a critical need for eco-friendly energy alternatives is the combination of household solar (PV) systems with electric vehicle (EV) technology [16]. Using second-life electric vehicle batteries (SLEVBs) for residential energy storage has become a viable and possibly ground-breaking option in the context of global efforts to cut carbon emissions and transition to renewable energy sources [17]. Combining home solar panels with electric vehicle batteries is one possible technology convergence that might aid in the electrification of mobility and the decentralization of energy generation. By recycling abandoned EV batteries for stationary uses in residential settings, SLEVB provides an affordable and environmentally responsible response to the erratic and intermittent nature of renewable energy sources [7]. Second-life EV batteries must be characterized to determine their capacity, voltage, internal resistance, and degradation patterns. Characterization sometimes involves advanced testing equipment and methods. The characterization procedure can be standardized to compare battery packs and verify compatibility with household PV systems. Standard battery testing and reporting procedures would simplify integration and improve interoperability. Second-life EV batteries have unique properties and operating conditions; therefore, sophisticated battery management systems (BMSs) are needed [18]. These BMSs should use advanced state estimation, balancing, and heat management algorithms. Integrating adaptive control systems that dynamically modify battery operations based on environmental, energy, and grid circumstances can improve system performance and battery lifespan. Using predictive maintenance algorithms to detect battery failures or degradation trends can reduce downtime and optimize maintenance schedules. Integrating systems must be safe, especially given second-life EV batteries’ thermal runaway and cell deterioration threats. Safety practices, including temperature monitoring, current limitations, and rapid shutdown, can reduce these dangers and protect property and persons [19]. Smart grid and demand–response solutions can improve integrated PV and battery system flexibility and efficiency. Integrating smart meters, grid controllers, and energy management systems with communication protocols and standards allows for real-time energy flow monitoring and control [19]. Focusing on grid services like frequency management, peak shaving, and voltage support can boost integrated system profitability and grid stability. Comprehensive lifetime assessments are needed to analyze the environmental impact of using second-life EV batteries in household PV systems. Considering energy usage, greenhouse gas emissions, and resource depletion throughout the system’s life cycle can help determine its sustainability and environmental benefits. Recycling and reusing end-of-life batteries can reduce the environmental impact and promote a circular economy. The health and capacity of second-life EV batteries must be accurately assessed before using them in household PV systems [20]. Traditional voltage and impedance measurements may not reveal these batteries’ true health. The battery’s state of health (SOH) can be better assessed using electrochemical impedance spectroscopy (EIS) and model-based estimate algorithms [20]. Internal parameters like electrode degradation and electrolyte aging can be evaluated. Real-time monitoring devices that track battery performance indicators can help measure SOH and anticipate lifespan. Battery data analysis using machine learning and AI algorithms improves predictive maintenance and SOH estimation [21]. These algorithms can detect tiny battery performance changes and anticipate decline better. Innovative hardware and software integration is needed to make second-life EV batteries compatible with home PV systems. Voltage converter technologies and adaptive energy management algorithms can reduce voltage and capacity differences between EVs and stationary storage batteries. Integration and interoperability are achieved by standardizing BMS–PV system inverter communication standards. Different battery chemistries, voltages, and capacities can be accommodated by modular and scalable integration methods [22]. Integration technologies improve energy flow, system efficiency, and safety. Bidirectional inverters that control PV generation and battery storage enable dynamic energy management and grid interaction. Advanced energy management algorithms optimize charge and discharge cycles based on user demand, weather, and battery conditions [23]. Modular integration platforms with plug-and-play configurations simplify PV and battery system installation and maintenance. Inverters with grid-forming characteristics can island, improving system resilience and reliability during grid interruptions. There are several difficulties with integrating second-life EV batteries into residential PV systems;

Table 3. Challenges for integrating second-life EV batteries into home PV systems.

Challenge	Description	Solution
Battery Health and Compatibility	Second-life EV batteries may not match PV system specs [24].	Thorough testing before integration ensures compatibility.
Safety Concerns	Risks like thermal runaway or fire hazards associated with batteries [25].	Implement safety protocols and proper battery enclosure.
Battery Management System	Lack of a robust BMS for monitoring and optimizing battery performance.	Install reliable BMS to regulate charging and discharging.
System Integration	Difficulty integrating batteries with existing PV systems and household grids [26].	Seek professional help for seamless integration.
Grid Interconnection	Meeting regulations and utility requirements for safe grid connection.	Ensure compliance with local regulations and utility standards.
Warranty Coverage	Limited or unclear warranty coverage for second-life EV batteries.	Negotiate extended warranties or seek warranties from reputable suppliers.
Integration Complexity	Complexity in integrating second-life EV batteries with PV systems [26].	Seek professional assistance and thorough planning for seamless integration.
Regulatory Compliance	Ensuring compliance with local regulations and standards [26].	Stay updated on regulatory requirements and work closely with authorities and utility companies to meet compliance standards.
Voltage and Capacity Matching	Ensuring second-life EV batteries match the voltage and capacity of PV systems [25].	Conduct thorough testing and evaluation to verify compatibility before integration.
Performance and Reliability	Ensuring consistent performance under varying weather conditions [24].	Regular maintenance and monitoring for optimal performance.
Environmental Sustainability	Managing environmental impact and promoting sustainable practices [2].	Ensure responsible disposal and promote eco-friendly practices.

lists these difficulties.

The issues and worries raised above highlight the many aspects and potential obstacles related to using used EV batteries for residential solar systems. Thorough evaluation, planning, and implementation are required.

3.1. Home PV System Battery Sizing and Packaging

The proper battery size and packing must be selected throughout the battery system design process for a home photovoltaic (PV) system in order to maximize performance, reliability, and economics. The summary of the variables to be considered when sizing and packing batteries for a home solar system is shown in

Table 4. Variables for sizing and packing batteries for a home solar system.

Variable	Description	Considerations
Energy Storage Requirements	Assess energy needs for sizing battery capacity.	Account for seasonal variations and household consumption patterns.
Battery Capacity	Determine required capacity based on energy storage needs.	Consider depth of discharge, cycle life, and backup autonomy.
Battery Chemistry	Select suitable chemistry balancing performance and cost.	Consider energy density, cycle life, and environmental impact.
Physical Size and Weight	Evaluate dimensions and weight for compatibility.	Ensure fit within available space and ease of handling during installation.
Packaging and Enclosure	Choose protective packaging ensuring safety and longevity.	Include ventilation, thermal management, and protection against damage and elements.
Modular Design	Option for scalability and flexibility in design.	Plan for future expansion or upgrades with easy addition or replacement of battery modules.
Integration with PV System	Ensure seamless integration for efficient energy management.	Coordinate with PV components like inverters and charge controllers for optimized operation.
Safety and Compliance	Implement safety features and comply with regulations.	Include overcharge protection and adherence to electrical codes and standards.

.

That second-life batteries will perform uniformly or that their degradation can be easily predicted is optimistic. The SOH of second-life batteries can vary significantly based on their first-life history, charging habits (rapid charging, depth of discharge), temperature exposure (extremes of heat or cold), and usage intensity (driving patterns, load demands) might affect battery degeneration and health [27]. Poor operating conditions or numerous high-stress charging cycles may accelerate battery degradation and limit capacity. Electric vehicle usage habits and climatic circumstances vary; therefore, SLEVB deterioration might differ even between battery packs of the same make and model [28]. Variable degradation rates can affect SLEVBs’ residual capacity, internal resistance, and cycle life, making performance prediction difficult. SLEVB SOH fluctuation makes determining the economic viability of incorporating these batteries into home energy storage systems difficult. Some SLEVBs may still be suitable for household usage, but others may have degenerated to the point where replacement or maintenance expenses outweigh their economic benefits. For educated residential system deployment decisions, lifespan cost calculations must account for SLEVB performance and degradation rates. Residential system energy storage and delivery efficiency can also be affected by SLEVB SOH variability. Lower SOH batteries may have larger internal losses, lower energy retention, and lower cycle life, lowering system efficiency and performance. Optimizing SLEVB utilization in residential energy storage systems requires adaptive control methodologies and energy management algorithms that cater for their unique properties. Intelligent battery management systems (BMSs) can optimize SLB charging and discharge, reducing battery stress. Charging during excess solar power and discharging during peak demand hours can avoid deep discharge cycles [29]. This variability can affect both the economic viability and the energy storage efficiency of using SLEVBs in residential systems. Batteries having an average state of health (SOH) of 50% might be employed in low-demand uses, such as energy storage systems (ESSs), for various uses where a large discharge current is not necessary. A battery’s state of charge (SOC) and state of health (SOH) indicate different aspects of its state and performance [29]. SOC represents the current charge level of the battery, whereas SOH indicates the long-term decline in the battery’s capacity. Although the SOC of a battery can change dynamically with charge and discharge cycles, the SOH generally diminishes gradually as the battery ages and endures degradation. Monitoring both SOC and SOH is crucial for efficient battery management, guaranteeing peak performance and maximizing the battery’s useable lifespan. Figure 4 shows the step for the state of SOH measurement. They are related because both metrics help manage and analyze batteries.

The state of charge (SOC) is calculated from the following.

$$State of Charge \left(SOC\right)=\frac{Current Charge stored in the battery \left(C_c\right)}{Maximum Charge capacity of the battery \left(C_m\right)}\times 100\%$$

(1)

The state of health (SOH) is calculated from the following.

$$State of health \left(SOH\right)=\frac{Battery Capacity at time \left(C_t\right)}{Nominal Capacity \left(C_{Nom}\right)}\times 100\%$$

(2)

Figure 5 depicts the state of health (SOH) trend for a fleet of 48 second-life electric vehicle (SLEV) 2012 Nissan Leaf Generation 1 (ZE0) batteries over time. The general information of 2012 Nissan Leaf Generation 1 (ZE0) batteries is shown in [30]. According to Figure 5, the average capacity of the batteries is 32.5 Ah. The amount of capacity left in the battery that may be used for a second-life application must be checked. In accordance with the manufacturer’s instructions, the battery is charged at room temperature with a 0.2 °C rate until it is fully charged [30]. Following charging, it is allowed to rest for one to two hours at room temperature and full charge. Subsequently, the battery is emptied at a rate of 0.2 °C until it is completely empty. At the conclusion of this discharge, the capacity must be noted. Utilizing recorded current and time data, the discharge battery’s capacity is computed.

PowerLab, Arbin Battery Tester, Chromag Battery Tester, and several other measurement instruments frequently compute this automatically [30]. When conducting tests for battery open-circuit voltage (OCV), insulation, capacity, charge/discharge cycle, internal resistance, and self-discharge, no anomalies were found. However, when the capacity test and internal resistance were run, different results were seen. As a result, the internal resistance and remaining capacity of these batteries are categorized based on commonalities. In calculating a battery’s state of health (SOH), the number of cycles provides crucial insight into its usage history and degeneration over time.

The capacity loss is calculated from the following:

$$Capacity Loss \left(C_L\right)=Degradation Rate per cycle \left(D_R\right)\times {Number of Cycle (N}_{cycle })$$

(3)

$$Battery Capacity at time \left(C_t\right)=Nominal Capacity \left(C_{Nom}\right)-Capacity Loss at time \left(C_L\right)$$

(4)

The average capacity is calculated from below formulation:

$$Average Capacity \left(C_A\right)=\frac{\sum Battery Capacity at time \left(C_t\right)}{Number of Battery \left(N_b\right)}$$

(5)

$$Average State of health \left(SOH\right)=\frac{Average Capacity at time \left(A{C}_t\right)}{Nominal Capacity \left(C_{Nom}\right)}\times 100\%$$

(6)

From Equation (6), the following is calculated:

$$\begin{gathered} Average State of health \left(SOH\right)=\frac{32.5 Ah}{65 Ah}\times 100\% \\ =50.01\% \end{gathered}$$

A home PV system with ESS is an example of such an application. Consequently, this application was selected to conduct the experiment and track the system’s degradation over time.

To size storage systems properly, household energy usage trends must be understood. The amount of energy saved and used depends on daily, weekly, and annual consumptions. A home with higher nighttime energy usage needs a larger storage capacity to save daytime energy for later use. The analysis of previous energy usage data or load profiling studies can help optimize storage system sizing by revealing consumption patterns. Effective storage system sizing requires peak demand identification. Peak demand occurs when energy usage is highest. Storage systems lower grid pressure and peak demand charges by storing energy during off-peak periods and discharging it during peak demand times [31]. Properly sizing storage systems for peak demand maximizes energy use and homeowner savings. Storage system sizes must account for seasonal PV energy production variations owing to solar irradiation and daylight hours [32]. Sunnier months boost energy output, while winter decreases it. Size storage systems changes to meet seasonal energy production changes, maintaining dependable energy supply year-round and reducing grid reliance during low solar generation. The system is made up of a 1000 W solar panel, a controller, maximum power point tracking (MPPT), a 500 W load, and batteries that are meant to store energy for 2 days in full load in order to account for weather variations and the possibility of some days with no sunshine. Figure 6 portrays the home PV system battery sizing and packaging.

3.2. Overall Cost Analysis for the Home PV System

An overview of the different parts needed to establish a home photovoltaic system employing second-life electric vehicle (SLEV) batteries is given in this cost study. The precise expenses could differ based on variables, including the size of the system, its location, the installer’s fees, and any applicable incentives. SLEVB prices depend on supply and demand. SLEVBs may be less cost-effective than alternatives due to more demand than supply [33]. Low demand or oversupply can cut prices, making second-life storage systems more cost-effective. Changes in market conditions, technology, and regulations can affect prices. SLEVBs may need additional testing, paperwork, and engineering changes to meet safety standards. This can raise the upfront cost of installing these batteries in household energy storage systems. Getting quotations from reliable installers and suppliers is crucial if you want precise costing for your particular project.

Table 5. The equipment for a home photovoltaic system.

Cost Component	Description	Estimated Cost
Solar Panels	Cost of purchasing and installing photovoltaic panels for energy generation.	USD 2.4–USD 3.6 per watt
Inverters [34]	Cost of inverters required to convert DC electricity from solar panels into AC electricity.	USD 100–USD 350 up to 4000 watts
Battery Storage (SLEV) [30]	Cost of acquiring and installing second-life electric vehicle batteries for energy storage.	USD 71.4–USD 80.4 per kWh
Balance of System (BOS)	Cost of additional components such as charge controllers, wiring, mounting hardware, and monitoring systems.	40% of overall project cost
Installation Labor	Cost of professional installation services, including labor, associated fees, and any necessary electrical work.	7% of overall project cost
Permitting and Inspection	Cost of obtaining permits and inspections required for legal compliance and system approval.	8% of overall project cost
Maintenance and Repairs	Estimated cost of ongoing maintenance, repairs, and replacements over the system’s lifespan.	10% of overall project cost
Financing Costs	Interest expenses associated with financing options such as loans or leases for system acquisition.	5% interest expenses
Tax Credits and Incentives [35]	Potential savings from tax credits, rebates, and incentives offered for renewable energy installations.	Tax incentives (34% initial, 14% annual)

shows the equipment needed to install a home photovoltaic system.

The full range of the economic factors influencing the cost-effectiveness of second-life-based storage systems is shown in

Table 6. Economic factors for cost-effectiveness of second-life-based storage systems.

Economic Factors	Description
Fluctuating Electricity Prices	Consideration of variations in electricity prices over time, including time-of-use pricing, peak demand charges, and dynamic pricing structures [36].
Changes in Incentives or Subsidies	Evaluation of government incentives, rebates, or subsidies for renewable energy storage systems, including the potential impact of policy changes [37].
Potential Future Advancements in Battery Technology	Anticipation of advancements in battery technology that could lead to cost reductions, improvements in energy density, and longer cycle life [38].

.

When compared to lead–acid batteries (LABs), Li-ion batteries (LIBs) usually have a longer lifespan. Depending on usage and climatic conditions, a well-maintained LIB can live anywhere from ten to fifteen years or longer [39]. The process of charging and discharging a battery, or “cycling”, can shorten the life of LIBs. Faster degradation can generally be caused by deeper discharges and larger charge/discharge rates. LABs are frequently utilized in stationary applications, as well as in automobile applications. When compared to LIBs, their lifespan is usually lower. Under typical circumstances, an LAB can last three to seven years [39]. On the other hand, poor maintenance, such as charging too little or too much, can drastically shorten their life. LAB degradation can also be sped up by deep discharges and hot weather. Technology innovations, economies of scale, and improved production capacity have all contributed to the steady decline in the cost of LIBs over time. Figure 7 shows the general information on LABs and LIBs.

As of 2022, LIB prices for large-scale stationary storage systems varied from around USD 100 to USD 200 per kWh. Price increases for automotive-grade LIBs may be related to greater safety and performance criteria. LABs are often less expensive per kWh than LIBs. For large-scale stationary applications, Lead–Acid Battery costs varied from around USD 80 to USD 150 per kWh [40]. Although the cost of lead–acid car batteries varies, in general, they are less expensive than LIBs. This cost investigation will compare the LAB and second-life Li-ion battery (SLB) total cost of ownership (TCO) for a household photovoltaic (PV) system over a ten-year period. In order to shed light on each battery technology’s long-term financial feasibility, this research will take into account the initial costs of installation, ongoing maintenance, and operating expenditures.

Table 7. Cost analysis assumptions for the 10-year period.

Assumption	Description
System Capacity	Both systems have a capacity of 5 kW.
Battery Capacity	Equivalent storage capacity for both SLB and LAB systems.
Initial Installation Costs	Includes PV panels, inverters, battery storage, installation labor, and miscellaneous equipment.
Maintenance Costs (per year)	Regular maintenance expenses for both battery types.
Operational Costs (per year)	Includes electricity tariffs, battery replacement costs, and any additional expenses.
Battery Replacement Costs	Replacement of batteries after 5 years.

provides a clear overview of the key assumptions used in the analysis.

Table 8. Overall cost analysis for the period of 10 Years.

Cost Category	SLB System (USD )	LAB System (USD )	Description
Initial Installation	USD 15,000	USD 10,000	Cost of installing the home PV system, including PV panels, inverters, and batteries.
Maintenance (10 years)	USD 2000	USD 4000	Total maintenance expenses over 10 years, covering routine checks and upkeep.
Operational (10 years)	USD 3600	USD 9200	Operational costs such as electricity tariffs, battery replacements, and additional expenses.
Total Cost (10 years)	USD 20,600	USD 23,200	Overall total cost of ownership for the home PV system over the 10-year period.

shows the overall cost analysis for a period of 10 Years.

The expenses of the Lead–Acid Battery (LAB) and the home PV system using a Second-Life Li-ion Battery (SLB) are broken down in this table over a ten-year period. The table’s bottom summary of each system’s total cost demonstrates that, in comparison to the LAB system, the SLB system has a cheaper total cost of ownership, with a 12.62% saving compared with the LAB system. The overall cost analysis for the period of 10 years is shown in Table 8.

3.3. Practical Implementation of Second-Life EV Battery for Home PV Systems

Reusing used EV batteries for a residential PV system is a feasible approach that is being implemented at the Multimedia University. Through this project, we hope to encourage the use of renewable energy sources and sustainability by showcasing how practical it is to use EV batteries as energy storage devices in homes.

The Multimedia University has installed a 30 kW three-phase (each phase 10 kW) on-grid home PV energy storage system (ESS) utilizing SLEVB. The Multimedia University Café is equipped with solar panels that convert sunshine into electricity due to its exceptional efficiency. Solar energy is captured and transformed into electrical power by the installation of solar photovoltaic (PV) panels [41,42]. The PV array’s DC electricity is converted by an inverter into AC electricity that may be utilized to power electronics [43,44]. Used electric vehicle (EV) batteries are used as energy storage devices. When there is abundant sunshine or low sunlight or when there is great demand, these batteries release the extra energy produced by the PV array. Figure 8 shows the system algorithm for the on-grid home PV energy storage system (ESS) utilizing SLEVB. In order to ensure the ideal cycles of charging and discharging and prevent overcharging or over-discharging, a battery management system BMS is connected to the EV batteries to monitor and regulate their performance [7]. The state of charge (SOC), state of health (SOH), and temperature of the SLEVs may all be observed by users [30]. Users may maximize energy management and savings by modifying system parameters using the control functions interface, including energy priority, charging or discharging schedules, and grid interaction modes. Proactive management and troubleshooting are made possible by the alerts and messages users receive about system conditions, battery maintenance, and possible problems. Bidirectional power flow is made possible by the energy storage system’s connection to the grid [41]. It is possible to export excess energy produced by the PV array to the grid and import energy from it when required. The energy storage system is connected to the electrical loads of the Multimedia University, which uses the grid, EV batteries, and PV array to obtain electricity as needed.

The voltage, current, and power needs of the system determine whether batteries should be arranged in series or in parallel [30]. A 55 V battery system was chosen for this arrangement. Three packs of batteries, each with seven modules linked in series, make up the battery arrangement. Every module has a separate micro BMS. Consequently, a series connection of seven units generates nearly 55 V. An average SOH of 50.01% is equivalent to 32.5 Ah. Figure 9 depicts the system architecture and configuration of a 30 kW on-grid ESS that was installed in the Multimedia University Café utilizing SLEVB. To improve efficiency and sustainability, the system makes use of energy storage technologies and renewable energy sources. Figure 10 depicts the picture of the practical implementation of on-grid 30 kW capacity ESS utilizing SLEVB at the Multimedia University Café. Once the batteries were installed in the Multimedia University Café, they were evaluated again after 180 days of use. It was found that the degradation rate of batteries can vary, and it is not always the case that batteries with higher remaining capacity will degrade slower or faster than those with lower remaining capacity. After 180 days, the average state of health (SOH) in terms of remaining capacity was determined to be 45.06%, showing a decrease of 4.95%.

Figure 11 provides an overview of the system monitoring setup (SMS) utilized by Multimedia University Café’s on-grid energy storage system. The EMS and monitoring systems are crucial parts for optimizing energy consumption, ensuring system efficiency, and providing real-time insights into system performance.

EMS for DC voltage and current is essential in renewable energy, electric car, and battery storage systems. This system monitors, controls, and optimizes the DC power network energy flow. The EMS employs sensors or meters to constantly monitor the voltage and current levels at different locations within the DC power network. Real-time measurement data are collected to offer precise insights into the system’s operation and state. The EMS overview for DC voltage and current is shown in Figure 12.

Residential, commercial, and industrial applications require an energy management system (EMS) for AC input power. This system monitors, controls, and optimizes grid or renewable AC power use. The EMS continually analyzes grid or renewable AC input power voltage, current, frequency, and power factor. Smart meters and power quality analyzers collect real-time energy consumption and quality data. EMS prioritizes energy usage based on demand, efficiency, and user preferences while distributing AC power to system loads. To reduce peak demand and energy consumption, load shedding, demand response, and load scheduling are used. Figure 13 and Figure 14 show the EMS overview for AC input power and total energy utilized by Multimedia University Café’s on-grid energy storage system, respectively.

Carbon emissions and reliance on fossil fuels are reduced by energy storage technology, which makes it simpler to integrate renewable energy sources like solar power into the grid [41,45]. By installing a home PV ESS utilizing SLEVB, The Multimedia University has reduced carbon emissions by approximately 21.09 tons, and standard coal saved 17.76 tons in 1.7 years, which is shown in Figure 15. By storing extra solar energy during times of low demand and releasing it during times of peak demand, the technology reduces electricity expenditure. This lessens the grid’s peak electricity use. Energy storage technologies lessen supply and demand volatility by providing ancillary services like voltage support and frequency regulation [46]. In the event of blackouts or grid outages, the energy storage system may serve as a backup power source, ensuring that Multimedia University’s critical loads always have access to electricity.

4. Enhancing Sustainability with Second-Life EV Batteries

Reusing batteries obtained from electric vehicles (EVs) presents a substantial opportunity to advance sustainability in multiple spheres; as a result, it generates advantages for the environment, society, economy, and society at large [47]. In order to foster a circular economy and increase sustainability, it is possible to prolong the operational life of electric vehicle (EV) batteries through recycling, which can also be utilized for stationary energy storage [48]. The integration of recycled electric vehicle (EV) batteries into the energy infrastructure of the nation contributes to the advancement of energy security, resilience, and grid stability [49]. Figure 16 illustrates the way in which second-life EV batteries contribute to sustainability.

The implementation of these batteries contributes significantly to the achievement of domestic sustainability objectives and the reduction of greenhouse gas emissions by facilitating the integration of renewable energy sources and decreasing reliance on fossil fuels [50]. The availability and affordability of energy are improved by the implementation of economical energy storage solutions that recycle electric vehicle batteries [51], specifically in economically disadvantaged regions.

This initiative promotes social justice and enables both businesses and individuals to actively engage in the shift toward sustainable energy alternatives. The utilization of used electric vehicle (EV) batteries in academic settings may present benefits for disciplines including sustainability studies, engineering, and environmental science. The examination of battery longevity analysis, performance enhancement, and battery reuse contributes to the expansion of knowledge and inspires novel ideas [51].

By utilizing reused electric vehicle (EV) batteries, the sector promotes the growth of the renewable energy market and advances energy storage technology. By repurposing EV batteries for business and industrial applications, industries may boost their competitiveness, reduce operating costs, and enhance energy efficiency [47]. Reusing EV batteries helps the environment by reducing the negative effects of battery manufacture and disposal [52,53,54]. Our efforts to prolong the life of these batteries and optimize their application in energy storage systems help to save natural resources, reduce pollution, and lessen our environmental impact. CO₂ emission is reduced by at least 20% when using SLB compared with lead–acid [55]. According to projections based on business as usual, global CO₂ emissions will increase from 35.3 billion metric tonnes in 2018 to about 43.08 billion metric tonnes in 2050 [41]. Based on estimates from the US Environmental Protection Agency (EPA), the Inflation Reduction Act (IRA) is predicted to reduce US economy-wide CO₂ emissions by 35% to 43% by 2030, including power generation and usage [41]. Energy efficiency and renewable energy must rise if greenhouse gas emissions are to be reduced by at least 55% by 2030 [56]. Figure 17 shows the projected global CO₂ emissions from 2030 to 2050.

In conclusion, utilizing used EV batteries to increase sustainability is a complete approach that, when addressing energy and environmental challenges, will benefit the nation, society, business, academia, and the environment equally. We can make full use of second-life EV batteries to create a more stable and sustainable future for all if we band together and welcome innovation.

5. Conclusions

Using second-life electric vehicle (EV) batteries can greatly enhance the energy storage capabilities of home solar (PV) systems, offering a promising strategy for maximizing their potential. Homeowners can improve the longevity of electric vehicle (EV) batteries and promote sustainable energy practices by utilizing solar power through the recycling process. Integrating second-life EV batteries into household photovoltaic (PV) systems provides numerous advantages. First and foremost, used electric vehicle (EV) batteries offer a more affordable option for energy storage thanks to their lower price compared with brand-new batteries. This allows a broader group of homeowners to benefit from domestic solar energy storage, thereby encouraging the use of renewable energy technologies.

In addition, incorporating electric vehicle (EV) batteries into residential photovoltaic (PV) systems helps promote sustainability by minimizing waste and maximizing resource efficiency. Using batteries for stationary applications instead of discarding them after their automotive lifespan helps reduce the environmental impact of battery disposal and production. Furthermore, second-life electric vehicle (EV) batteries offer a high level of scalability and versatility, enabling homeowners to customize their energy storage capacity according to their individual requirements. The system’s flexibility enables the efficient utilization of excess solar energy produced during peak production, which can be stored for later use during periods of low sunlight or higher energy demands.

Exploring future research opportunities in the field of integrating second-life batteries into residential photovoltaic (PV) systems offers promising prospects for overcoming current constraints and maximizing their capabilities. Advancements in battery technology are crucial for improving the energy density, cycle life, and safety features of second-life batteries. Research should prioritize the development of innovative battery chemistries, materials, and manufacturing techniques to enhance performance and durability. Furthermore, it is important to investigate advanced battery management systems (BMSs) specifically designed for repurposed batteries. Advanced BMS algorithms and control strategies have the ability to enhance performance, extend lifespan, and guarantee safe operation. Moreover, it is essential to examine integration methodologies in order to achieve a smooth and seamless integration into household photovoltaic (PV) systems. This involves investigating modular designs, hybrid storage arrangements, and grid-interactive capabilities in order to optimize flexibility and efficiency. Furthermore, it is necessary to conduct thorough lifecycle studies in order to determine the environmental consequences of reusing batteries. Research should prioritize investigating recycling and reusing solutions to reduce waste and advance sustainability. Finally, it is crucial to tackle regulatory obstacles and promote legislative frameworks that are conducive to wider adoption. In order to fully utilize second-life batteries in integrated residential PV systems, future research should focus on prioritizing technological breakthroughs, integration techniques, environmental considerations, and regulatory reforms.