• Energy Research

This paper presents theoretical and experimental work that is being carried out in a grid-connected residential building demonstrator available at the Instituto de Energía Solar (IES) of the Universidad Politécnica de Madrid (UPM) in Madrid, Spain. The house is provided with a building-integrated photovoltaic (PV) system coupled to a battery energy storage system (BESS), and a heating, ventilation, and air-conditioning system (HVAC) based on two air-to-air direct expansion reversible heat pumps. Thermal loads, HVAC consumption, and PV generation are simulated using different dynamic models, and they are validated with actual data derived from monitoring the experimental campaign. A model of intelligent control of BESS is proposed, which aims to supply the selected application (HVAC load) with two control strategies: increasing PV self-consumption and grid-peak shaving. This model has been validated with experimental data (error < 10%). Furthermore, the study includes ageing and degradation effects on the batteries to make allowance for realistic lifetime assessment. The results of the case study show that in a building without a BESS, the self-consumption rate is about 30%; however, with the implementation of the proposed control, it could achieve approximately 50%, depending on the BESS capacity and the PV generator nominal power. Likewise, by using a combination of both strategies, it is possible to reduce both contracted power and energy consumption (77% and 49% respectively for case study).

Abstract The proposition of Net Plus-energy Buildings (NPEB) leads to the need to carry out studies of load matching in contrast with the grid impacts of distributed generation (DG). This paper performs simulations with the EnergyPlus software tool concerning a NPEB operating in four Brazilian metropolitan areas. The analyses include photovoltaic (PV) performance parameters and Load Matching and Grid Interaction indicators (LMGI). New grid impact indicators are defined in order to study the impacts of DG in the power grid. In the second stage, the work investigates economic aspects under net metering supporting. Results show the annual amount of electrical demand covered by PV varies from 29 to 51% with more potential in situations with higher PV production and higher cooling load, and the annual PV electricity that supplies the loads varies from 24 to 36% according to the seasonal variations of PV-load correlation. The levels of exported electricity into the grid are high in Brazil with annual mean power peaks surrounding 0.7 but can surpass 0.8 in the sunniest periods. The economy demonstrates the building achieves grid parity from 6 to 18% discount rates and the payback time is given for different scenarios of investment costs, discount rates and electricity tariffs.

In this paper, we use the correlation between the average wind speed and the elevation above sea level to present a regression model for calculating the average wind speed and evaluating the wind potential in the southern region of Ecuador. After obtaining the regression model, an adjustment factor based on the topographic slope has been included, mainly since the wind speed could vary largely as it blows across the lower slope regions or intermediate hills of mountains. Once the wind speed was obtained, both at 10 m and 100 m, the wind power density was calculated, which includes the impact of wind speed and air density. Finally, the model accuracy was obtained by comparing other free access data sources including actual data from meteorological stations, using statistical parameters to quantify the error. According to the results obtained, we find that wind speed has a good correlation with the terrain elevation of the southern region of Ecuador. The simulated wind speed compared to the actual data has errors between 7.75% and 16.89%, which indicates that the model can predict with > 83% accuracy. In addition, both the root means square error and the standard deviations have around 1 m/s of error.

The transition to cleaner and more sustainable energy sources involves the use of solar photovoltaic energy. This energy source has the potential to reduce greenhouse gas emissions and dependence on fossil fuels. The research project focused on the development of a web-based tool for sizing photovoltaic systems in Ecuador. This tool considers several factors, including technical, theoretical, economic and environmental aspects. The tool allows sizing based on electricity consumption and power requirements. Furthermore, the tool provides technical information, CO2 reduction data and economic perspectives based on the operation of the electricity system in Ecuador. The comparative validation with installed systems and similar web tools demonstrated the reliability and robustness of the developed tool.

Heating, ventilation, and air conditioning (HVAC) systems provide the people working/living inside buildings with ‘conditioned air’ so that they will have a comfortable and safe environment. Thermal comfort is considered as an aspect of a sustainable building in almost all sustainable building evaluation methods and tools. In fact, in the building sector, HVAC systems represent between 40 and 60% of energy consumption. In this paper, two thermal comfort methods have been experimentally analysed (Predicted Mean Vote or the so-called Fanger’s method, and the Adaptive Comfort Method). The measurement campaign was divided into two stages. In an initial stage, HVAC electrical consumption, indoor temperature, carbon dioxide concentration, relative humidity, global horizontal irradiance, and outdoor temperature were measured through controlled conditions, performing a considerable number of tests in 112 days, covering all seasons. Later, in a second phase, with the experimental data, the two thermal comfort methods were calculated analytically. In both cases, the main conclusion is that – when the HVAC system was working with minimum energy consumption – more than 80% of the possible occupants would be satisfied with the indoor temperature, by more than 90% of the time.

Demand charges are widely used for commercial and industrial consumers. These costs are often not well known, let alone the effects that PV can have on them. This work proposes a methodology to assess the effect of PV on reducing these charges and to optimise the power to be contracted, using techniques taken from exploratory data analysis. This methodology is applied to five case studies of industrial consumers from different sectors in Spain, finding savings between 5 % and 11 % of demand charges in industries with continuous operation and up to 28 % in cases of discontinuous operation. These savings can be even greater if the maximum power that can be contracted is lower than the optimum. The demand charges in Spain consist of a fixed part proportional to the contracted power and a variable part depending on the power peaks exceeding it. Since for the variable part the coincident and non-coincident models coexist, a comparison is made between the two models, finding that in the general case PV users can achieve higher savings with the coincident model.

On-site photovoltaic (PV) and battery systems intend to improve buildings energy performance, however battery costs and monetary incentives are a major drawback for the introduction of these technologies into the electricity grids. This paper proposes an energy refurbishment of an office building based on multi-objective simulations. An innovative demand-side management approach is analyzed through the PV and battery control with the purpose of reducing grid power peaks and grid imported energy, as well as improving the project economy. Optimization results of load matching and grid interaction parameters, complemented with an economic analysis, are investigated in different scenarios. By means of battery use, the equivalent use of the grid connection is reduced by 12%, enhancing the grid interaction potential, and 10% of load matching rates can be increased. Project improvements indicate the grid connection capacity can be reduced by 13% and significant savings of up to 48% are achieved on yearly bills. The economy demonstrates the grid parity is only achieved for battery costs below 100 €/kWh and the payback period is large: 28 years. In the case with only PV system, the grid parity achieves better outcomes and the payback time is reduced by a half, making this a more attractive option.

Abstract Due to its zero-marginal-cost, the high penetration of renewable energy sources in the electricity markets threatens incumbents’ business models who are gradually shifting towards fixed power charges instead of the traditional energy charges. The purpose of this study is to assess the impacts of these fixed power charges on the economics of PV systems under self-consumption schemes. Using real demand and generation data, simulations include detailed computation of annual billing savings, payback-time, self-consumption and self-sufficiency of a dwelling coupled with PV-battery system. A range of PV array and battery sizes are explored for different storage control strategies. Billing scenarios include a) only energy charges, b) Portuguese case (high energy charges and low fixed charges), c) Spanish case (low energy charges and high fixed charges), and d) only fixed charges. Results show that fixed charges require adding storage to residential PV systems. In spite of battery relative high costs, results also show that photovoltaics can be profitable with payback times below 10 years in all scenarios, as long as appropriately sized and with the suitable storage control strategy.