The urgent need to address global warming and transition to sustainable energy solutions has driven the development of innovative heating systems. Among those solutions, several district heating alternatives have been proposed to combine heat pumps and thermal energy storage tanks. This paper addresses the integration of photovoltaic thermal systems (PVT) with aquifer thermal energy storage (ATES) within a fifth-generation district heating network as an innovative combination to minimise electrical power consumption from the grid, thereby reducing grid dependency and CO2 emissions. The proposed configuration is tested for the Werfgebied district in Hilversum, the Netherlands A Python model of the multi-energy carrier system is developed to investigate the effects of configuration, storage distribution, and component sizing within the district heating network, embedding the thermal and electrical behaviour of the components and their interaction. The results show that an optimal configuration for the ATES and PVT combination involves a single ATES well rather than distributed thermal energy storage. The results indicate that the aquifer's size significantly affects the overall operating temperature and its fluctuations. A larger ATES maintains a stable but relatively colder temperature. If constrained by a maximum allowed ATES temperature of 20 °C, the optimal ATES size is 175 000 m3; however, when considering the overall benefit and excluding that constraint, the optimal system size comprises an ATES of 380 000 m3 and an 800 module PVT system, reducing the overall emissions by 856 tonnes of CO2 equivalent compared to the case without the district heating. ... Read more

Thermal comfort accounts for significant residential energy consumption in high latitudes; however, quantitative information about insulation improvements is not widely available. First, we performed a study to quantify the effects of improving the insulation in walls, roofs, and windows of typical dwellings in the Netherlands (a studio, an apartment, and a stand-alone house). Our results indicate that improving from single- to double-glazing is the most significant change, reducing gas consumption up to 50%, whereas the difference between double- and triple-glazing is less than 7%. Improving the roof insulation, filling cavity walls with insulation, or adding external wall insulation did not show attractive business cases, as the payback time was too high. Second, we evaluated upgrading the dwelling energy label by improving the insulation or adding a PV system and a heat pump. The results showed that, for energy labels C or above, the insulation reached a saturation point where it is not attractive to improve it before its end-of-life proactively. Instead, investing in the energy system by adding a PV system and a heat pump has better payback times. Our results allow policymakers and project developers to focus on the most relevant changes to accelerate the energy transition. ... Read more

High shares of photovoltaic energy in low-voltage distribution systems lead to voltage limit violations. Deploying energy storage systems in the network can compensate for the mismatch between the generation and the consumption; nevertheless, the mismatch is unevenly distributed throughout the network, suggesting aggregated control strategies as a solution. This paper proposes two coordination control strategies of batteries to address network overvoltage conditions caused by high penetration of photovoltaic systems. The leader–follower coordination strategy determines a battery’s utilization factor by using the node closest to a voltage violation as a reference. The leaderless control uses a shared utilization factor to avoid excessive usage of a particular agent in the network. We tested both approaches in the 18-node CIGRE network for scenarios when not all agents were available and when they had different starting states-of-charge. Our results demonstrate that both strategies are capable of voltage control; however, the leader–follower control leads to uneven storage usage, ultimately leading to short-time failure to comply with the voltage limits under extreme conditions where neighbouring agents must compensate for the unavailable one. Conversely, the leaderless approach presents more balanced use of the agents thanks to the distributed utilization factor, resulting in a more robust control strategy. ... Read more

The inclusion of PV and heat pumps in residential low-voltage distribution systems is a fundamental component of the energy transition. Nevertheless, adoptions below 40% can already cause voltage conditions incompliant with the standard EN50160 during winter. Aggregated storage systems have been proposed as a solution; however, the literature generally assumes full observability and controllability of the assets, which is unrealistic in many cases. This paper evaluates the potential of aggregated single- and multi-carrier storage systems to maintain voltage stability in low voltage networks, considering separated controllers for the prosumer and the aggregator. We used a real 301-node residential distribution network in the Netherlands as case study. Our results demonstrate that aggregated multi-carrier energy storage can ensure the voltage conditions established in the standard EN50160 for energy transition adoptions up to 80%, while aggregated single-carrier storage can reach 60% and centralized storage only 40%. We concluded that aggregation of storage assets increases the utilization of the existing grid infrastructure, reducing reinforcement costs for the DSOs. However, the energy storage assets’ high investment costs lead to unattractive conditions for single- and multi-carrier storage, compared to a case with only PV and heat pumps. Considering the current market conditions, using storage for voltage support would require economic compensations. These findings provide DSOs valuable insight on alternative solutions to grid reinforcement and centralized storage to address the challenges of the energy transition. ... Read more

The energy transition encourages using heat pumps at the residential level, which results in a multi-carrier energy system when combined with PV and battery storage. Optimally controlling such systems has proven challenging. The numerous constraints required, different response times per energy carrier, and the need for forecasting methods also increase the complexity and computational cost. We propose an adaptable energy management system strategy for any system architecture with a reduced number of constraints using genetic algorithms with a discrete-continuous approach for the power setpoints. Using random forest regression, we also created short-term estimation models for the PV generation and electric and thermal demand, with error distributions centred near 0 %. Our results demonstrate that the strategy can solve the power allocation problem in the order of 1 s, including forecasting 60 minutes, minimizing electric costs, and ensuring thermal comfort. ... Read more

The magnitude and effect of residential E-cooling demand on the Dutch energy market have not been studied in the literature. However, due to rising temperatures and the increase in the adoption of heat pumps, the effects of residential e-cooling demand are expected to rise sharply in the upcoming decades. First, a thermodynamic model of different Dutch residential buildings described the magnitude and patterns of residential E-cooling. Second, the effects of E-cooling on the distribution network were tested using the IEEE 906-bus European LV network. Third, a country-wide simulation of the effect of residential E-cooling on the energy market was done in Plexos from 2025 to 2050. The results showed a doubling of the cooling demand between 2025 and 2030 and a maximum annual cooling demand of approximately 0.4 TWh. In addition, it was shown how the demand for residential cooling could decrease local power quality when more than 40 % of households actively cool their houses simultaneously, increasing network costs. Finally, it was also proven how power prices could increase due to higher demand and how revenue for specific generation components could double or decrease by 2% during heat waves when accounting for residential E-cooling demand. ... Read more

The integration of renewable energy sources and heating electrification strategies in households is an unavoidable component of the energy transition. Unfortunately, the pace at which such integration occurs has proven challenging for the distribution system operators. On the one hand, system operators design low-voltage networks for low, unidirectional power flows at the connection points with the consumers, with expected lifetimes of several decades. On the other, the decreasing prices, together with the economic and environmental incentives to install (mainly) rooftop PV systems and heat pumps, create highly stochastic, bidirectional and potentially high-power power flows at the connection points of the former consumers, transforming them into prosumers. This thesis studies the misalignment between the interests of system operators and prosumers, proposing realistic alternatives that are achievable in the short term. This thesis hypothesizes that the aggregation of residential multi-carrier energy storage systems would be capable of bridging the interests between prosumers and distribution system operators. To validate the hypothesis, this thesis is comprised of five research topics.

Distribution system operators commonly address the grid congestion through infrastructure reinforcements, which is slow and expensive. Chapter 2 studies how energy storage systems with different carriers can provide a collaborative solution involving prosumers as ancillary services providers at the distribution level. Specifically for the European urban context, this chapter analyzed renewable energy sources, batteries, supercapacitors, hydrogen fuel cells, thermal energy storage, and electric vehicles through a thorough review of successful implementations. The correlations found between individual energy storage technologies and ancillary services provided insight into the flexibility opportunities each technology can provide to the grid. It was concluded that multi-carrier systems would provide the most robust yet flexible solution.

Based on the previous premise, Chapter 3 evaluated four multi-carrier energy system configurations for a Dutch household. The chapter also provides analytical models for every component (including the thermal losses from the thermal storage to the ground) and the space heating and electrical demands. The results suggest that using a heat pump combined with a photovoltaic system and a battery provides the best trade-off for the prosumer. The photovoltaic-thermal system alone could not supply the thermal demand required for comfortable space heating nor reach temperatures high enough to charge the thermal storage. Combining the thermal storage with the heat pump allows a certain degree of flexibility for the heat pump activation at the cost of COPs between 0.8 and 1.38 when used to charge the thermal storage, thus increasing energy consumption and equivalent emissions considerably.

Chapter 4 then elaborates on different energy management strategies to control the multi-carrier systems as proposed above. Two adaptable energy management system strategies were proposed for any system architecture with a reduced number of constraints. The first strategy uses genetic algorithms with a discrete-continuous approach for the power setpoints, maximizing thermal comfort and minimizing energy cost and CO2equivalent emissions. The EMS employs random forests for short-term predictions of the PV generation and electric and thermal demand. The results demonstrate that the strategy can solve the power allocation problem in the order of 1 s, including forecasting 60 minutes. This strategy, however, is too computationally demanding for complex distribution systems with multiple houses. Therefore, the second strategy uses a policy-based heuristic method to control the multi-carrier system, minimizing energy costs and maximizing thermal comfort. Also, this strategy allows the EMS to follow, or not, an external power setpoint from an aggregator, resulting in control decisions in the order of 30 ms. In addition, an ageing-aware EMS was briefly introduced, demonstrating the importance of ageing the BESS during operation.

Chapter 5 investigates, from a cost perspective, what conditions can make it attractive for individual prosumers to participate in a low-voltage ancillary service market, specifically power curtailment and peak shaving. For the former, it was shown that there are conditions where curtailing power does not significantly reduce the system's revenue but greatly reduces the peak power injected into the grid. However, it was also shown that curtailing might affect the power electronic components of the solar converter, potentially reducing its expected lifetime compared to a normal operation without curtailment. Similarly, an estimation of the degradation of the batteries for the cases with and without providing peak shaving was done using a semi-empirical ageing model, concluding that doing peak shaving to ensure a fixed power exchange with the grid will drastically reduce the life of the battery. Therefore, following an external setpoint to reduce occasional peaks would extend the battery's life. The results suggest that power curtailment and peak shaving can be attractive for prosumers, thus creating opportunities for ancillary services business models at the residential scale.

Chapter 6 incorporated households with single- and multi-carrier energy storage in a low-voltage distribution network to quantify the benefit of aggregation for the prosumers and system operators. The aggregator is generally assumed to have full observability and controllability of the assets, which is unrealistic in many cases. For this reason, this chapter considered separate controllers for the prosumers and the aggregator. Using a real 301-node low-voltage residential distribution network in the Netherlands, it was demonstrated that aggregated multi-carrier energy storage can ensure the voltage conditions established in EN50160 for penetrations of PV systems coupled with heat pumps up to 80 %. In contrast, aggregated single-carrier storage can reach 60 % and centralized storage only 40 %. Despite generating an economic benefit while supporting the grid, the high investment costs for both single- and multi-carrier storage result in unattractive conditions for prosumers compared to a case with only PV and heat pumps, requiring compensations for around half of the energy purchase costs for the single-carrier storage and higher than the total energy costs for the multi-carrier.

In summary, it was proved that, from a technical perspective, aggregated residential multi-carrier energy systems are a robust yet flexible solution for the voltage problems caused by the energy transition in residential low-voltage distribution networks. However, the current state of thermal storage makes the technology too expensive to be economically attractive. ... Read more

The urge to reduce the dependence on natural gas for heating at the residential level has led to the deployment of different fossil fuel-free alternatives. In the Netherlands, two technologies are leading the transition: heat pumps, due to their high COP, and photovoltaic–thermal systems, due to their dual electric-thermal output. However, both represent a challenge for users and grid operators, aside from their stochastic behavior. Heat pumps alone can surpass a typical Dutch house's total energy and power consumption. Photovoltaic–thermal systems, as their only electric homologs, usually have a mismatch between generation and demand, causing energy injections to the grid. From the electric perspective, storage systems are a proven solution to reduce the energy exchange with the distribution network. This paper proposes four multi-carrier energy system configurations for a Dutch household, comprising different combinations of a photovoltaic–thermal system, a battery energy storage, a heat pump, and an underground water tank thermal energy system, providing analytical models for every component (including the thermal losses from the thermal storage to the ground), and the space heating and electrical demands. We determined the components’ compatibility and evaluated the combinations considering their thermal performance, electrical performance, and equivalent CO₂ emissions. The results suggest that using a heat pump combined with a photovoltaic system and a battery provides the best trade-off. The photovoltaic–thermal system alone could not supply the thermal demand required for comfortable space heating nor reach temperatures high enough to charge the thermal storage. Combining the thermal storage with the heat pump allows a certain degree of flexibility for the heat pump activation at the cost of COPs between 0.8 and 1.38 when used to charge the thermal storage, thus increasing energy consumption and equivalent emissions considerably. ... Read more

The massive deployment of PV systems in residential buildings is causing voltage challenges in low-voltage distribution networks. Worldwide, DSOs started requesting users to curtail power when this is injected back into the grid. Although many commercially available inverters can perform curtailment, the degradation effects of curtailment still have to be investigated. This paper estimated how power curtailment affects the reliability of a boost converter working below MPPT voltages. Using the mission profile method, we determined the conduction and switching losses on the converter switch as the critical component, based on its temperature and current profiles. The results suggest that curtailing the power requires the operation point to move towards lower PV voltages, leading to deeper thermal cycles, therefore reducing the expected lifetime of the converter by up to 80 % for power injection into the grid below 1.5 kW. From the operational perspective, this might require premature replacements compared to operating under MPP conditions, affecting the revenue forecast before the enforcement of curtailment. For power injection above 1.5 kW, the LCoE does not change compared to the case without considering the degradation. However, near zero-injection conditions, the difference in LCoE between considering and not considering replacements increases exponentially up to 135 %. ... Read more

In low-voltage distribution networks, the high penetration of renewable energy generators in residential buildings has proven challenging for system operators. In response, the grid operators can reinforce the grid infrastructure or deploy battery energy storage systems throughout the network to compensate for the voltage fluctuations. Alternatively, new energy markets for ancillary services have been proposed to involve the prosumers; however, most are at medium and high voltage levels. This paper investigates, from a cost perspective, what conditions can make it attractive for individual prosumers to participate in a low-voltage ancillary service market, specifically power curtailment and peak shaving. We considered a prosumer with a 2 kWp PV system for both ancillary services, adding a 10 kWh battery for the peak shaving case. Curtailing power to comply with the maximum power exchange with the grid does not create any significant change in the LCoE of the PV system, keeping it near 0.072 €/kWh for permitted return grid powers above 1.25 kW. Scenarios closer to zero-injection increase exponentially the LCoE to 0.222 €/kWh. Using a semi-empirical ageing model, we estimated the degradation of the batteries for the cases with and without providing peak shaving, concluding that doing peak-shaving to avoid demanding more than 1 kW from the grid extends the battery life by up to 320 % while increasing its LCoS only 9.5 % when compared to a zero-consumption scenario due to the reduced depth-of-discharge and number of cycles. The results suggest that power curtailment and peak shaving can be attractive for prosumers, thus creating opportunities for ancillary services business models at the residential scale. ... Read more

Industry plays a significant role in the energy transition due to its share of energy consumption. More complex energy systems are proposed to accelerate the energy transition, including coupling renewable energy sources and energy storage to supply part of the industrial loads locally. In this work, we used a multi-objective genetic algorithm to optimally size an industrial hybrid power system comprising a PV system, a battery energy storage system, and a diesel generator to minimise energy costs and overall equivalent CO2 emissions. The results suggest that the system does not require high power and capacity components to minimise the energy cost and equivalent CO2 emissions, highlighting the importance of the EMS strategy. In our case scenario, the optimal HPS reduced the emission cost by 46.7 % and the energy cost by 8.7 %. For the EMS, we proposed a rolling horizon average approach, which defines a setpoint for the power exchanged with the grid to minimise its change rate in time. The EMS dispatched the power to minimise the sudden changes in the demand from the network, with a power allocation priority order of PV, BESS, and generator. We also evaluated the effect of adding the optimally sized hybrid power system into a CIGRE medium-voltage distribution network, using a real industrial load profile for each node. The hybrid power system improved the voltage sag on the hybrid power energy system node and its neighbouring nodes. ... Read more

The uncontrolled inclusion of renewable energy sources in the distribution network causes severe overvoltages. Simultaneously, electrification strategies, such as heat pumps and electric vehicles, increase the peak demand, causing undervoltages. The combination of both phenomena has proven challenging for distributed system operators who are accountable for power quality and accessibility. System operators address those voltage issues with network reinforcements, but such projects are costly and time-consuming. We identified that the cost and qualified workforce availability are the main challenges of premature grid reinforcement. This paper evaluated peak-shaving and power curtailment at the low voltage distribution level as market-based alternatives to provide flexibility using the business model canvas. We identified the main actors that would benefit from peak-shaving and power curtailment at the residential level, their relationships, and the value proposition's challenges. We proposed a business model where residential prosumers receive compensation for supporting the network to prevent the distribution system from surpassing the projected power flows. Both alternatives offer system operators more control over the power flow to ensure power quality while decreasing costs, as fewer or no premature grid reinforcements might be needed. The business opportunity resources are categorized as technical and regulatory, highlighting the latter as the main challenge for the business model. We discussed two residential prosumer case scenarios for the Dutch context, one with a PV system and one with a PV and a heat pump. Our analysis suggests that the business models are technically possible for peak-shaving and power curtailment with existing technologies for the selected target. However, the former requires more complex activities and is limited to a narrower segment, as it requires prosumers with PV, storage and high-load devices, such as heat pumps. ... Read more

Batteries are one of the main tools to provide the flexibility distribution and transmission systems need due to their increasing dependence on weather conditions. However, environmental and economic factors pose a significant problem. New types of batteries that do not rely on rare earth metals and organic solvents but instead use water and more common ions could be a cost-effective and environmentally safe way to provide energy storage in the future. We studied the performance of sea-salt cells designed as a low-cost, environmentally friendly method to store electricity. We used a constant current charge/discharge test with different currents, from 50 mA to 300 mA, to identify the maximum efficiencies of the cell. Then, we introduced a new strategy to determine the cut-off voltage to discharge the battery, inspired by the maximum power point found in photovoltaics. We used a constant voltage charge to determine the cell’s energy density. However, evidence of side reactions urged us to use constant current charge/discharge tests to identify the battery’s capacity based on the efficiencies drop. Results showed a maximum energy efficiency of 74.6% at 200 mA and a maximum Coulombic efficiency of 88.7% at 300 mA. The cut-off voltage of the cell during discharge should be between 1.4 V and 1.6 V. The energy densities range from 10.1 Wh/kg(6.53 WhL) with an efficiency of 57.5% and 4.18 Wh/kg(2.7 WhL) with an efficiency of 69.8%. ... Read more

In the context of building electrification the operation of distributed energy resources integrating multiple energy carriers poses a significant challenge. Such an operation calls for an energy management system that decides the set-points of the primary control layer in the best way possible. This is done by fulfilling user requirements, minimizing costs, and balancing local generation with energy storage. This last component is what enables building flexibility. This paper presents a novel aging-aware strategy for operating grid-connected buildings that combine multiple energy carriers (heat and electricity), storage devices (electric vehicles, batteries, and thermal storage), and power sources (solar photovoltaics, solar collectors). The novel energy management algorithm presented considers the aging of the batteries to enhance the operational differences between storage technologies, thus making explicit the trade-off between the services provided by the hybrid energy storage system and its degradation. This unlocks grid cost reductions between 20–45 % depending on the season when compared to state-of-the-art solutions. ... Read more

The number of electric vehicles in Costa Rica has increased steadily in recent years. If purchasing power is considered, the owners of electric vehicles likely live in horizontal or vertical residential condominiums, which have a single connection point to the electricity distribution network. For this reason, an uncontrolled increase of electric vehicles in a horizontal or vertical condominium can jeopardize the capacity of the circuit, especially the transformer and the protection. This article studies the impact that the installation of chargers for electric vehicles in a condominium can have. In addition, different strategies for minimizing the technical and user impact were compared. The results show that using renewable energies is not recommended given the probability distributions of charging time of electric vehicles. Instead, the use of energy management strategies is the most attractive alternative ... Read more

Along with the widespread adoption of solar energy, it is fundamental to develop methods and tools that help practitioners during the design phase of photovoltaic (PV) systems. Currently, multiple commercial software can quantify a particular location's annual energy yield while including the horizon's shading effect (e.g., mountains, buildings, and trees). To do so, precise information about the PV system's surroundings is necessary. This information is gathered by specialized equipment or by having access to satellite imagery. Therefore, to offer a more practical approach, we propose a method that requires only a cellphone camera, a fixed point for taking a panoramic photograph, and a compass. Once the panoramic image is taken, the obstacles’ width, height, and altitude are calculated, and the skyline is built. With this information, the method correlates the position of the sun with meteorological data to include the effect of shading on direct irradiation. The method was tested using one–year meteorological data to determine the best orientation of a PV system. The image processing method and the general method were validated by getting PV power generation data and aerial images and comparing them to the method's predictions. Therefore, we introduce a method that, with low computational complexity, facilitates the study of shading on the performance of PV systems. ... Read more

Energy storage is vital for a future where energy generation transitions from a fossil fuels-based one to an energy system that relies heavily on clean energy sources such as photovoltaic (PV) solar energy. To foster this transition, engineers and practitioners must have open-access models of PV systems coupled with battery storage systems (BESS). These models are fundamental to quantifying their economic and technical merits during the design phase. This paper contributes in this direction by carefully describing a model that accurately represents the power directions and energy dealings between the PV modules, the battery pack, and the loads. Moreover, the general model can be implemented using two different PV generation methods, the Gaussian model and the meteorological data-based model (MDB). We found that the MDB model is more appropriate for short-term analysis compared to the Gaussian model, while for long-term studies, the Gaussian model is closer to measured data. Moreover, the proposed model can reproduce two different energy management strategies: peak-shaving and maximizing self-consumption, allowing them to be used during PV–BESS sizing stages. Furthermore, the results obtained by the simulation are closed when compared to a real grid-tied PV–BESS, demonstrating the model’s validity. ... Read more

The energy transition requires electrical alternatives for domestic heating. Heat pumps are the most common alternatives to gas boilers. However, heat pumps consume a significant amount of electrical power. We simulated an 18-node low voltage network with five buildings with six apartments each to evaluate the effect of deploying heat pumps as part of multi-carrier energy systems at the residential level. We also combined heat pumps with solar collectors and thermal energy storage to quantity whether a more complex system benefits the low-voltage network. Replacing the gas boilers for heat pumps in the majority of the buildings resulted in voltage drops below the limit of the standard EN50160. The voltage drops were significantly improved when we included solar collectors and thermal energy storage in the domestic heating system. ... Read more

Fifth-generation energy networks are combined networks of heat and electricity, that have the ability to generate, distribute, store and share energy between consumers. Knowledge on the dynamic behaviour of the physical phenomena related to energy generation, distribution and storage provides insight into the performance of the system as a whole. A mixed-integer linear algorithm is proposed, implementing a partitioned clustering program for subsequent classification of typical demand, grouping specific days with similar demand profiles together. From this arrangement, the optimal network configuration can be determined using an objective function, minimizing the economic and environmental impact. To validate the optimization results, a simulation of the network was built, which mimics its physical dynamic behaviour, and through which the distribution and storage capabilities of the network can be assessed. Advanced advice on fifth-generation energy networks is presented that can be applied to early-stage network design, reducing costs and emissions, along with data on the implementation of renewable energy technologies and their performance. Additionally, this research provides the foundation for numerical modelling of such energy networks which contributes to future research. ... Read more