Nearly 840 million people still lack access to electricity, while over a billion more have an unreliable electricity connection. In this article, the three different electrification pathways-grid extension, centralized microgrids, and standalone solar-based solutions, such as pico-solar and solar home systems (SHS)-are critically examined while understanding their relative merits and demerits. Grid extension can provide broad scale access at low levelized costs but requires a certain electricity demand threshold and population density to justify investments. To a lesser extent, centralized (off-grid) microgrids also require a minimum demand threshold and knowledge of the electricity demand. Solar-based solutions are the main focus in terms of off-grid electrification in this article, given the equatorial/tropical latitudes of the un(der-)electrified regions. In recent times, decentralized solar-based off-grid solutions, such as pico-solar and SHS, have shown the highest adoption rates and promising impetus with respect to basic lighting and electricity for powering small appliances. However, the burning question is-from lighting a million to empowering a billion-can solar home systems get us there?The two main roadblocks for SHS are discussed, and the requirements from the ideal electrification pathway are introduced. A bottom-up, interconnected SHS-based electrification pathway is proposed as the missing link among the present electrification pathways.

Photovoltaic (PV) solar energy is variable and not completely predictable; therefore, different energy storage devices have been researched. Among the variety of options, electrochemical cells (commonly called batteries) are technically feasible because of their maturity and stability. However, PV-battery systems face multiple challenges such as high cost and complexity of installation. Cost is the main concern when trying to enable new solutions for the solar market, especially when competing with other renewable technologies, but most importantly, with fossil fuels to reduce the effects of climate change. As a consequence, a new concept that integrates all the components of a PVbattery system in a single device is introduced. By integrating a power electronics unit and a battery pack at the back of a PV panel, referred as PV-battery Integrated Module (PBIM), the cost of the total system can decrease and become a viable alternative for the solar market. Because the concept is relatively new and not all the challenges have been previously addressed, this dissertation strives to prove the feasibility of the concept and to fill the gaps that have been identified in the literature review. Firstly, an off-grid PV-battery system was selected, and a sizing methodology was proposed to investigate the limitations and boundaries of the integrated device. Having sized the system, the thesis explored the implementation of an energy management system in order to control smartly the direction and magnitude of the power delivery. Then, a thermal model was developed to characterize the thermal response of the PBIM and to recommend a thermal management system to decrease the temperature of operation of the battery pack and power electronics. Finally, by testing a PBIM prototype and developing an integrated model that reproduces the temperature and power flows expected, a battery testing methodology was developed for finding a suitable battery technology that can comply with the requirements set by the expected operating conditions of the device. Therefore, the research carried out in this dissertation proves that the integration of PV-battery system in one device is technically feasible.

With almost 1.1 billion people lacking access to electricity, solar-based off-grid products like Solar Home Systems (SHS) have become a promising solution to provide basic electricity needs in un(der)-electrified regions. Therefore, optimal system sizing is a vital task as both oversizing and undersizing a system can be detrimental to system cost and power availability, respectively. This paper presents an optimal SHS sizing methodology that minimizes the loss of load probability (LLP), excess energy dump, and battery size while maximizing the battery lifetime. A genetic algorithm-based multi-objective optimization approach is utilized to evaluate the optimal SHS sizes. The potential for SHS to cater to every tier of the Multi-tier framework (MTF) for measuring household electricity access is examined. The optimal system sizes for standalone SHS are found for different LLP thresholds. Results show that beyond tier 2, the present day SHS sizing needs to be expanded significantly to meet the load demand. Additionally, it is deemed untenable to meet the electricity needs of the higher tiers of MTF purely through standalone SHS without compromising one or more of the system metrics. A way forward is proposed to take the SHS concept all the way up the energy ladder such that load demand can also be satisfied at tier 4 and 5 levels.

The use of batteries is indispensable in stand-alone photovoltaic (PV) systems, and the physical integration of a battery pack and a PV panel in one device enables this concept while easing the installation and system scaling. However, the influence of high temperatures is one of the main challenges of placing a solar panel close to a battery pack. Therefore, this paper aims to select a suitable battery technology considering the temperature of operation and the expected current profiles. The methodology for battery selection is composed of a literature review, an integrated model, the design of an application-based testing, and the execution of the aging test. The integrated model was employed to choose among the battery technologies, and to design a testing procedure that simulated the operational conditions of the PV-battery Integrated Module (PBIM). Two Li-ion pouch cells were tested at two representative temperatures while applying various charging/discharging profiles. After the testing, the LiFePO4 (LFP) cells showed better performance when compared to LiCoO2 batteries (LCO), where for instance, the LCO cells capacity tested at 45∘C, faded 2,45% more than the LFP cells at the same testing conditions. Therefore, LFP cells are selected as a suitable option to be part of the PBIM.

Off-grid solar home systems (SHSs) currently constitute a major source of providing basic electricity needs in un(der)-electrified regions of the world, with around 73 million households having benefited from off-grid solar solutions by 2017. However, in and of itself, state-of-the-art SHSs can only provide electricity access with adequate power supply availability up to tier 2, and to some extent, tier 3 levels of the Multi-tier Framework (MTF) for measuring household electricity access. When considering system metrics of loss of load probability (LLP) and battery size, meeting the electricity needs of tiers 4 and 5 is untenable through SHSs alone. Alternatively, a bottom-up microgrid composed of interconnected SHSs is proposed. Such an approach can enable the so-called climb up the rural electrification ladder. The impact of the microgrid size on the system metrics like LLP and energy deficit is evaluated. Finally, it is found that the interconnected SHS-based microgrid can provide more than 40% and 30% gains in battery sizing for the same LLP level as compared to the standalone SHSs sizes for tiers 4 and 5 of the MTF, respectively, thus quantifying the definite gains of an SHS-based microgrid over standalone SHSs. This study paves the way for visualizing SHS-based rural DC microgrids that can not only enable electricity access to the higher tiers of the MTF with lower battery storage needs but also make use of existing SHS infrastructure, thus enabling a technologically easy climb up the rural electrification ladder.

Given the complementary nature of photovoltaic (PV) generation and energy storage, the combination of a solar panel and a battery pack in one single device is proposed. To realize this concept, the PV Battery-Integrated Module (PBIM), it is fundamental to analyze the system architecture and energy management. This paper focuses on selecting a suitable architecture among the different options, while also indicating the control strategy that the converters must follow to ensure appropriate performance. Also, several modes of operation for the complete system are introduced to implement energy management. For the selected DC architecture, two case studies, viz. off-grid and peak-shaving for a grid-tied system, were employed to characterize the response of the model demonstrating its utility to perform maximum power-point tracking, excess solar power curtailment, and battery charging and discharging. The proposed control and system architecture prove to be feasible for a PV battery-integrated device such as PBIM.

The fluctuating nature of solar power generation makes the coupling of energy storage and solar energy inevitable. This paper explores the integration of all the typical components of a PV-battery system in one single module, introducing a prototype of the so-called PV-Battery Integrated Module (PBIM).
The electrical and thermal performance of the prototype were studied in order to analyse its behaviour under severe testing conditions. The prototype exhibited an appropriate charging efficiency of 95.7% on average, while the battery pack operated safely (at less than 45◦C). When compared to a conventional system (battery and charge controller in a separated manner), the mean solar panel temperature of the prototype was 9.34% higher. However, in terms of power, the thermal losses in the PBIM resulted in an average increase of just 1.3 W (4.6%) in comparison to a conventional system. The testing validated the applicability of the integrated concept in harsh conditions, providing valuable information for future design improvements.

Solar Home Systems (SHS) have recently gained prominence as the most promising solution for increasing energy access in remote, off-grid communities. However, the higher than standard testing conditions (STC) temperatures have a significant impact on the SHS components like PhotoVoltaic (PV) module and battery. A modeling methodology is described in this study for quantifying the temperature impact on SHS. For a particular location with high irradiation and temperatures and a given load profile, an SHS model was simulated, and the temperature-impact was analyzed on the performance and lifetime of the SHS components. Different PV module temperature estimation models were applied, and the corresponding dynamic PV outputs were compared. The nominal operating cell temperature (NOCT) model was found inadequate for estimating PV module temperatures under high irradiance conditions. The PV yield was found to be affected by almost 10% due to thermally induced losses. When different levels of temperature variations were considered, the battery lifetime was seen to be up to 33% less than that at 25 ° C. The modeling methodology presented in this paper can be used to include the thermal losses in SHS for rural electrification, which can further help accordingly in system sizing.

The past few years have seen strong growth of solar-based off-grid energy solutions such as Solar Home Systems (SHS) as a means to ameliorate the grave problem of energy poverty. Battery storage is an essential component of SHS. An accurate battery model can play a vital role in SHS design. Knowing the dynamic behaviour of the battery is important for the battery sizing and estimating the battery behaviour for the chosen application at the system design stage. In this paper, an accurate cell level dynamic battery model based on the electrical equivalent circuit is constructed for two battery technologies: the valve regulated lead-acid (VRLA) battery and the LiFePO₄ (LFP) battery. Series of experiments were performed to obtain the relevant model parameters. This model is built for low C-rate applications (lower than 0.5 C-rate) as expected in SHS. The model considers the non-linear relation between the state of charge (SOC) and open circuit voltage (V_OC) for both technologies. Additionally, the equivalent electrical circuit model for the VRLA battery was improved by including a 2nd order RC pair. The simulated model differs from the experimentally obtained result by less than 2%. This cell level battery model can be potentially scaled to battery pack level with flexible capacity, making the dynamic battery model a useful tool in SHS design.

The rapid increase in the adoption of Solar Home Systems (SHS) in recent times hopes to ameliorate the global problem of energy poverty. The battery is a vital but usually the most expensive part of an SHS; owing to the least lifetime among other SHS components, it is also the first to fail. Estimating battery lifetime is a critical task for SHS design. However, it is also a complex task due to the reliance on experimental data or modelling cell level electrochemical phenomena for specific battery technologies and application use-case. Another challenge is that the existing electrochemical models are not application-specific to Solar Home Systems. This paper presents a practical, non-empirical battery lifetime estimation methodology specific to the application and the available candidate battery choices. An application-specific SHS simulation is carried out, and the battery activity is analyzed. A practical dynamic battery lifetime estimation method is introduced, which captures the fading capacity of the battery dynamically through every micro-cycle. This method was compared with an overall non-empirical battery lifetime estimation method, and the dynamic lifetime estimation method was found to be more conservative but practical. Cyclic ageing of the battery was thus quantified and the relative lifetimes of 4 battery technologies are compared, viz. Lead-acid gel, Flooded lead-acid, Nickel-Cadmium (NiCd), and Lithium Iron Phosphate (LiFePO₄) battery. For the same SHS use-case, State-of-Health (SOH) estimations from an empirical model for LiFePO₄ is compared with those obtained from the described methodology, and the results are found to be within 2.8%. The relevance of this work in an SHS application is demonstrated through a delicate balance between battery sizing and lifetime. Based on the intended application and battery manufacturer's data, the practical methodology described in this paper can potentially help SHS designers in estimating battery lifetimes and therefore making optimal SHS design choices.

The coupling of solar panels and energy storage is inevitable and especially pertinent in places with no access to the electricity grid. This combination must be modular, providing the opportunity to scale up the system if energy demand increases, but also easy to install and user-friendly. These requirements validate the PV-Battery Integrated Module (PBIM) as a potential solution for stand-Alone applications. In this paper, we assess the performance of directly integrating a battery system at the back of a PV panel in comparison to a typical solar home system (SHS) with all the components in a separated manner. The study is carried out using data from a community in the countryside of Stung Treng (Cambodia). First, the optimum battery size and PV panel rating were determined using the loss of load probability metric. Second, the extra PV power losses in the case of (PBIM) were calculated, finding that it is 2.16% less efficient than a normal SHS due to the poorer heat dissipation induced by integrating the converter and batteries at the back of the PV panel. Third, the battery capacity faded by 1% after a year of simulation. Although when compared to a typical SHS PBIM results in slightly higher system losses, the losses are moderated and their impact is minimum when considering the expected benefits derived from using PBIM in SHS. Therefore in this paper, we validate the feasibility of PBIM as a solution for standalone systems in developing countries.

Due to the variable nature of the photovoltaic generation, energy storage is imperative, and the combination of both in one device is appealing for more efficient and easy‐to‐use devices. Among the myriads of proposed approaches, there are multiple challenges to overcome to make these solutions realistic alternatives to current systems. This paper classifies and identifies previous efforts to achieve integrated photovoltaic storage devices. Moreover, the gaps and future perspectives are analysed to give an overview of the field, paying attention to low‐power devices (<10 W) as well as high‐power devices (>10 W). We focus on devices that combine solar cells with supercapacitors or batteries, providing information about the structure, materials used, and performance. On the one hand, small power devices must concentrate on including power electronics to increase the efficiency of the system as well as ensuring a safe operation; likewise, more attention should be drawn to validate the feasibility of novel concepts by carrying out more realistic and standardised tests, including long‐term testing. On the other hand, high‐power devices must be researched thoroughly to evaluate the impact of high temperatures on energy storage and solar module ageing; furthermore, optimum system sizing is a relevant topic that deserves attention and its relation to modular solutions. This critical literature review serves as a guide to understand the characteristics of the approaches followed to integrate photovoltaic devices and storage in one device, shedding light on the improvements required to develop more robust products for a sustainable future.

The proliferation of Solar Home Systems (SHS) in recent times hopes to provide an alleviating solution to the global problem of energy poverty. Battery is usually the most expensive but important part of an SHS; it is also normally the first part to fail. Estimating the battery lifetime can help make informed system design choices, and it is therefore an important exercise for an SHS designer. Battery lifetime modelling is often a complex task requiring empirical data or reliance on modelling cell level electrochemical phenomena. This paper presents a simple battery lifetime estimation method specific to the application and candidate battery choices at hand. An SHS application specific simulation is carried out for a year and the effect of microcycles on the battery activity is analyzed. The concept of active Depth-of-Discharge (DOD) is introduced. Cyclic ageing of the battery is thus quantified and relative cycle lives of 2 battery technologies are compared. A delicate trade-off is demonstrated between battery sizing and lifetime. The described methodology is also compared with an empirical model and the lifetime results are found to be within 3.85%. The methodology described in this paper can potentially help SHS designers in making quick, reasonable estimations of battery lifetimes based on the intended application and battery manufacturer's data.

Solar-battery systems are still expensive, bulky, and space consuming. To tackle these issues, we propose a novel device that combines all the components of a solar-battery system in one device. This device might help reduce installation cost compared to the current solar-battery systems as well as provide a plug-and-play solution. However, this physical integration means higher temperatures for the components. Therefore, this paper presents a thermal analysis of the physical integration concept to evaluate its feasibility, focusing on the batteries, the most delicate components. The thermal analysis was conducted using a Finite Element Method model and validated with experimental results on a prototype. According to the model, the temperature of the components (battery and converters) reduced drastically by adding an air gap of 5–7 cm between the solar panel and the components. Even under severe conditions, maximum battery temperature never surpassed the highest temperature of operation defined by the manufacturer. Moreover, the maximum battery temperature decreases even further by applying a phase change material as a passive cooling method, reducing it by 5 °C. As a result, the battery pack operates in a safe range when combined with a 265 Wp solar panel, demonstrating the potential of this concept for future solar-battery applications.

The paper provides a comparison of four PV-battery architectures with dc and ac backbones, in terms of autarky, energy efficiency, battery size and reduction of annual electricity cost. The comparison is conducted based on the residential load and irradiation data from the Netherlands. The effect of different PV generation is also analyzed by comparing the results with irradiation data from Costa Rica. The results show that the ac coupled architecture gives the best performance.

We present a novel approach to physically integrate a PV module, dc/dc converter, dc/ac microinverter and a battery pack. The main advantages and challenges to realize this integration are presented. Since the thermal management is one main challenge to tackle, a 1D thermal model is developed, and the respective simulation results are obtained.

This paper focuses on the most common PV-storage architectures that are designed for residential applications and that incorporate storage devices like batteries, hydrogen systems, supercapacitors, and flywheels. The main motivations and a comparison of the advantages and disadvantages of the architectures are presented. Moreover, some common approaches to performing intelligent power management are introduced.