Developing a Sustainable Solar-Residence Architecture Like a Home Unit without Energy Consumption from the Power Grid

Abstract

The objective of this work is to identify the premises and strategies for the design of a zero-energy solar house and propose the systematization of its process. The focus of the application is on the single-family residential typology. The method consists of analyzing the whole process from the initial phase of the architecture project to the use of automation systems, aiming at the best use of solar energy in terms of sustainable development and high energy efficiency. Each phase of the process has significant importance in the performance of the residential unit, however, the influence that one phase has over another plays a fundamental role in the final result. The process of systematization encompasses all these phases, starting from the demands for energy in a solar house and introducing strategies to meet these demands. The prototype of the zero-energy solar house is used as an example of the application of this process for the development of a parametric solar house. The results show a strong positive correlation of linear dependence between the assumptions and strategies used in the architecture of the house and the solar system, allowing a conclusion of the dependence relation on sustainability, thermal comfort, visual and energy efficiency.

1. Introduction

Methods of using and harnessing the sun’s energy have been applied for a long time, providing several benefits to mankind. Growing global demand for energy and recent concern about the scarcity of natural resources have increased the demand for renewable energy, in particular, solar energy. However, the use of renewable energy is not the only way to achieve sustainable development. Increasing the efficiency of energy systems is also an effective way to reduce greenhouse gas (GHG) emissions and provide more energy for consumption.

In Brazil, hydroelectric power comprises 64.9% of the National Interconnected System (SIN), making the Brazilian electrical matrix comparable to those of developed countries. Nevertheless, the share of renewable energies can be further increased by the incorporation of solar systems in the residential sector, which would also impact national energy consumption. Studies show the huge potential for the exploitation of solar energy in the country, due to favorable levels of solar radiation throughout the year and because photovoltaic systems (PVSs) for distributed generation are approaching economic feasibility [1]. In addition, the residential sector accounts for 26% of total electricity consumption in the country, and it is expected that this participation will remain at the same level for the next 10 years, with an estimated increase of 48.3% by 2021 [2]. Such facts indicate the great impact that the incorporation of solar systems in the residential sector can cause on the national consumption of energy.

The objective of this study is to analyze and consolidate premises and guidelines for the design of a solar house. This project will focus on the development of a single family residential typology in terms of a zero-energy building (ZEB) aiming at sustainable development while maintaining environmental comfort and energy efficiency.

1.1 Current contribution on zero-energy solar house, with premises and strategies

The solar combisystem presents a high potential to contribute to the net-zero energy status of a building [3]. However, the energy requirement in a building is affected by parameters such as the envelope characteristics [4] and the weather [5]. The influence of these parameters on the energy demand can impact significantly energy management. Thereby, Raza et al. [6] proposed a demand forecast study of integrated photovoltaic intelligent buildings to improve their accuracy.

Another way to reduce energy consumption by the residential sector and increase the energy efficiency of solar systems is through the application of passive techniques to residential architecture. The incorporation of architectural features into residential buildings aiming at the full use of solar energy helps to maintain environmental comfort and reduce energy consumption. Studies on the bioclimatic architecture of buildings that use solar energy, either actively or passively, can be found in [7, 8, 9, 10]. In this work, a housing unit that uses solar energy in architecture and energy generation, regardless of achieving a zero balance is defined as a ‘solar house’ [11].

According to Torcellini et al. [12], a ZEB is a building that produces, through local renewable sources, enough energy to equal or exceed its annual energy consumption. The ZEB can be connected to the public grid and integrates a system of distributed generation of electricity. In this study, the focus will be on the generation and use of solar energy by single family homes based on the development of a ZEB, regardless of reaching a zero-energy balance.

Initiatives to prospect, enable and analyze the quality of efficient solar energy projects were carried out in the USA, with competitions between universities to participate in the American Solar Decathlon Solar Energy (composed by Architecture, Engineering & Construction, Energy Efficiency, Communication & Social Awareness, Neighborhood Integration & Impact, Innovation & Viability, Circularity & Sustainability, Comfort Conditions, House Functioning and Energy Balance) in the years 2002, 2005, 2007, 2009, 2011, 2013, 2015, 2017, 2019 and then by the US and Spanish governments, which signed a memorandum of understanding in 2007 to create the first European edition complementary to the US Solar Energy Decathlon to encourage the use of solar energy and created the Solar Decathlon Europe. Spain hosted the first two competitions in 2010 and 2012 [13], the others were in France (2014), Hungary (2019) and the next in 2021/2022, in Germany [14].

Other regions were awarded the event, such as Solar Decathlon Latin America and Caribbean, in Colombia, which was held in 2015 and 2019, Solar Decathlon Africa, in Morocco (2016), Solar Decathlon China (2011, 2013, 2018, 2021), and Solar Decathlon India (2010/2021) [14]. Initiatives like these develop new sustainable technologies and transform society and the energy market.

Sustainable projects need to make several predictions, among others, of the air temperature in the almost zero energy building cooling system, with natural ventilation to reduce the dependence on mechanical systems and the use of models that can accurately predict the air temperature, therefore, in the naturally ventilated mode, they are fundamental to understand the current or future natural ventilation potential [15]. In southern European countries, summer temperatures can contribute to increased energy consumption, due to the cooling system of family units with less economic resources and may suffer from a lack of fuel to use air conditioning systems and one of the solutions to reduce the discomfort of thermal sensation is the optimization of natural ventilation to reduce energy consumption, improve cooling and serve social housing in coastal areas [16]. The European Union introduced the concept of construction of near-zero energy buildings in the system reformulation, using integrated solar technologies with dynamic occupancy in Finland and other northern European countries [17, 18]. Hybrid systems of integrated renewable energy, with a storage system, are important and efficient systems in the use of sustainable energy to serve localities [19].

In the study carried out by Zinzi and Mattoni [20], in the Italian cities of Rome and Turin, they described that it is important to guarantee energy efficiency, thermal comfort and indoor environmental quality, keeping construction and operation costs low. For the development of the project, three types of analysis were used: thermal comfort, energy performance and financial calculation. In both projects, the results were satisfactory.

The use of solar energy in buildings can mitigate the major challenges of energy shortages and global warming [21], and the management and integrated planning of energy resources are necessary to attract new investments, with the construction of sustainable environments, in projects that provide favorable conditions to the consumer market, with a reduction in the cost of electricity, with the application of innovative technologies in shared electricity generation, transmission and distribution and integrated [22].

To validate the study developed in this work, a solar house prototype used as a case study is taken as a study target. This prototype is a model of a zero-energy solar house (ZESH) and is analyzed qualitatively, considering general strategies for the passive use of solar energy. Furthermore, the ZESH concept is adapted to the Brazilian scenario where artificial lighting technologies, a domestic hot water system (DHW) and photovoltaic generations are considered for quantitative analysis.

Several works describe about zero energy solar house [12, 13, 15, 17, 19, 20, 21, 23, 24], but rare bibliography to the strategies used in zero energy solar house and this study seeks to complement the gap that exists on the subject, systematically contributing with new knowledge for decision making in the application of projects, using new premises and strategies, complementing the known strategies of innovation, sustainability and PVSs used in the design of a solar house (summarized in Table 1), as well as the basic principles for a zero energy solar house (ZESH). Fundamentally coming as a method for systematizing assumptions and strategies for the design of the mentioned zero-energy solar house, like several methods can influence the design results of a zero-energy solar house, among which are the solar geometry, the strategies used for thermal and/or visual comfort, as well as the solar house strategy, to consumption and installations.

Strategy	Description
Solar geometry	It consists of the study of solar orientation, envelope volumetry, design and orientation of openings and sun protection elements. All these elements can be applied in the architectural design of buildings for optimizing comfort conditions and minimizing the use of energy consumption.
Thermal/visual comfort	The design of a bioclimatic architecture embraces aspects such as control of passive solar gains, natural ventilation and use of natural lighting. A. Controlling of passive solar gain can be achieved by selecting the building materials, the arrangement of the protection elements and the orientation of the building and openings. B. Natural ventilation and evaporative cooling are important to air renewal in the indoor environment, also this can be a strategic means of removing heat from the air. C. The combination of natural lighting and artificial lighting is an essential strategy used to meet the required demand for illumination in the internal environment of a building. The location and size of the openings and use of reflexive surfaces are important elements to maximize the use of natural lighting, ensuring visual comfort and minimizing energy consumption. For artificial lighting, the use of sensors, independent electric circuits and new technologies are some of the strategies used to control and enhance its efficiency.
Solar systems	It can be applied in the design of a building to maximize the use of solar radiation for water heating and electricity generation.
Residential automation systems	It can be applied for integration and monitoring the different systems operating in a solar house. Also, the information collected by these systems can be used to inform the occupants about the generation and consumption of energy to increase the energy efficiency consumption and comfort, ensure the safety of the occupants and maximize the operation of the systems.

Table 1.

Strategies for a solar house design.

2. Solar geometry

The position and angle of incidence of solar radiation on the facades of a building—throughout the day and year, for a particular site of implantation, considering the apparent movement of the sun—are determined by the study of solar geometry. This study can be used either for the use of solar radiation in a building, for example for natural lighting of the environment, or the protection of its surfaces from the direct incidence of the sun.

Buildings located in the tropics receive, in the summer, the less solar incidence in the north-facing facades (for the southern hemisphere) than east–west facing facades. However, in winter, the solar incidence of north-facing facades is higher than for those facing east–west. This indicates that geometries involving the use of more elongated facades orientated towards north and south obtain better use of the sun throughout the year.

Solar charts can contribute to the study of solar geometry. These charts graphically represent the apparent trajectory of the sun projected on a horizontal surface, for specific latitudes [25, 26, 27]. Their use allows to determine the hours of sunshine on horizontal and vertical surfaces for a given orientation [13]. In addition, it is also possible to determine, for a given day and time, the azimuth and solar elevation that can be used in the geometric study of the shading for the application of protection elements in facades [26].

The study of solar geometry and its application on architectural projects can also be carried out using physical and electronic models, assisting in the study of the effect of solar radiation and shadows on buildings. In this way, it is possible to adequately predict and design buildings in terms of solar orientation, envelope volumetry, design and orientation of openings and sun protection elements.

An accurate study considering all these aspects in architectural design can substantially influence the comfort conditions and the energy consumption for the environmental conditioning of a building.

3. Sustainable solar-house architecture

The air combines three parameters that influence the thermal comfort of an environment: temperature, humidity and speed (or movement). When climate conditions are analyzed based on temperature and humidity, it is possible to define four types of climates: hot and dry, hot and humid, cold and temperate [27, 28].

The architecture that seeks to adapt to the climatic conditions through its own design solutions and its own elements, favorably using these conditions and seeking to satisfy the thermal comfort needs of the occupants is a so-called bioclimatic architecture [27, 29, 30].

The study of the strategies to be adopted for each climate can be carried out using a bioclimatic (or psychrometric) chart. In these charts, through the relationship between temperature and relative air humidity, regions are defined in which it is possible to identify the most adequate strategies to reach the thermal comfort of the environment for a given location throughout the year.

The following items present the concepts related to the passive strategies oriented to the thermal comfort of the residential buildings and related to the control of the passive solar gains, natural ventilation and evaporative cooling.

3.1 Control of passive solar gain

Solar radiation can penetrate directly into the building through the openings or be absorbed by wall and roof surfaces. By focusing on the surfaces, solar radiation results in heat gain. This gain, and the consequent storage of heat in the environment, depends on the intensity of solar radiation and the thermal properties of both closing and internal materials to the building [25]. Direct gains occur when solar radiation strikes directly into the building, through lateral or zenithal openings. The use of transparent elements allows direct gains and can contribute to generate the greenhouse effect when there is a need for heating of the interior environment [30, 31]. Indirect gains occur when elements of high thermal inertia are exposed to direct solar radiation. These elements accumulate heat and emit it to the environment using radiation and convection, when the temperature of the internal environment decreases [25, 31]. Figure 1 illustrates examples of passive forms of solar utilization that can be applied to the architecture of a solar house. Diagram (A) demonstrates direct or semi-indirect heat gain through a glasshouse. Diagrams (B), (C) and (D) show indirect passive gain forms where walls of high thermal mass accumulate the heat that will later be released to the environment to be heated.

Figure 1.

Passive solar systems [21, 31].

However, it may be necessary to avoid solar gain in some climates or seasons of the year. Protection elements such as eaves, grilles, brises-soleil, marquises, external and internal blinds and vegetation can be applied together to the opening areas. The effect of solar protection of these elements on transparent surfaces depends on factors such as the ability of the material to reflect solar radiation, the location of this protection and its relative effect on solar radiation and heat convection, and their distribution about transparent surfaces [27].

Using selecting the building materials, the arrangement of the elements and the orientation of the building, these gains can be enhanced in the winter and inhibited in the summer. These solutions should be taken into consideration as these gains impact occupant comfort and energy efficiency to maintain environmental comfort.

The subsequent items 4-A1, 4-A2 and 4-A3 present features such as thermal inertia, thermal insulation and solar factor, respectively, which interfere in the transfer of heat, depending on the conditions of radiation incidence, opacity or transparency to radiation, surface conditions, mass, thickness and other materials properties and construction elements.

3.1.1 Thermal inertia

The thermal inertia is related to two important phenomena of the thermal behavior of buildings, the damping and the delay of the heat wave caused by the heating or cooling of materials. The greater the thermal inertia of the building, the greater the damping and the delay [25]. High thermal inertia materials can be used to control heat gains and losses in a building in the heat or cold [26].

The amplitude variation between the inner and outer temperature and the absorption of temperature peaks can be controlled by thermal inertia. Hot and dry climates are favorable to the application of this technique, due to the great thermal amplitude that they present between day and night. The thermal mass exposed to solar radiation absorbs heat during the day and returns it to the indoor environment at night when the temperature decreases. At night, the thermal mass cools and thus contributes to reducing the temperature of the internal environment during the day, since it absorbs heat again.

In cold climates, it is possible to use thermal mass in internal elements of the building, and thermal insulation in the external walls and openings, so that the heat retained in the material exposed to the solar radiation during the day is irradiated to the internal environment [31]. The insulation helps to preserve the heat in the interior environment, as well as the heat coming from appliances and the occupants’ activities. Examples of high thermal mass materials are stones, massive bricks, adobe walls, concrete, water and green roofing.

The improper application of elements of high thermal inertia can act unfavorably to the internal environmental conditioning. Examples of this are the high thermal inertia buildings with mostly diurnal occupation or established in places where winter solar gains are insignificant. In these situations, the high thermal inertia may contribute to delay the reestablishment of the comfort conditions using air conditioning systems, increasing the energy consumption [32].

On the other hand, for low inertia buildings, Phase Change Materials (PCM) have been used to increase thermal mass [33]. Such materials absorb or release energy during their phase change, in temperature in the range of environmental comfort. Such a feature gives the material the ability to absorb temperature peaks. Examples of applications are the incorporation of PCM microcapsules into gypsum panels, into mortars or storage of material in tanks or compartments that are in contact with indoor air.

3.1.2 Thermal insulation

Thermal insulation is an indicated strategy for situations where thermal losses and gains are to be avoided. In cold climates, insulation is important for maintaining the heat inside the environment generated by passive solar gain strategies, or even active heating systems. In climates where temperature and humidity are high and artificial cooling systems are used, thermal insulation contributes to the use of these mechanical systems more efficiently.

The thermal insulation of a material can be determined by its coefficient of Thermal Conductivity (λ). The higher the value of λ, the lower the performance of the material as thermal insulation [30].

The choice of insulation depends on the need for insulation; performance in terms of durability, resistance and fire behavior; rainfall and technical issues regarding its installation in buildings.

3.1.3 Solar factor (SF)

The glass properties are an important factor in the energy fluxes through the openings, which can allow or inhibit thermal gains by solar radiation and heat losses of the interior environment [26, 30]. A characteristic commonly associated with glazed surfaces is the solar factor that is determined by the properties of absorptivity, emissivity and transmissivity. This factor represents the “relationship between the amount of energy flowing through a window and that strikes on it” [30].

An example of its use is in glasses with properties of low emissivity (or low-E). They reduce heat transmission by reducing the solar thermal gain, but allow the passage of visible light. It is, therefore, an alternative to allow natural lighting to contribute the control of heat exchanges.

3.2 Natural ventilation and evaporative cooling

Natural ventilation is essential to buildings because, in addition to promoting air renewal in the indoor environment, which is important for health, it contributes to thermal comfort in hot and humid climate regions and in hot periods, being one of the strategies indicated in the bioclimatic chart.

Natural ventilation can be described as the “displacement of air through the building, through openings, some functioning as an entrance and others as an outlet” [25]. Differences in air pressure between the internal and external environments influence this displacement, as well as the sizing and positioning of the openings. According to Frota & Schiffer [25], natural ventilation can be obtained in two different ways. The first form occurs through the action of wind and is caused by the movement of air through the environment due to the force of the winds. The second form is obtained by the chimney effect, resulting from the difference in air density.

A strategy that can be adopted in conjunction with ventilation is evaporative cooling, which consists of removing heat from the air through the evaporation of water or evapotranspiration of plants. It is indicated for hot regions or periods with low relative humidity [30]. This strategy can be applied with the use of fountains, water mirrors and masses of vegetation in the vicinity of buildings. Water spray systems can also be adopted.

4. Strategies for visual comfort

Natural lighting influences the health and well-being of the occupants, for example by regulating the circadian system and mood, as well as contributing to the health of the environment, since sun exposure can eliminate viruses and bacteria.

Light affects the appearance of the indoor environment through general lighting and the performance of visual tasks that require specific levels of illumination. To meet the demand for lighting in the internal environment, natural and artificial lighting must be combined, aiming at the visual comfort of the occupants and the efficiency in the consumption of electric energy.

4.1 Natural lighting

In buildings, natural light can be obtained basically from three sources. The sun provides light through direct radiation, the sky provides diffused light, and the surfaces can provide reflected or indirect light [18]. The light of the sun and the light of the sky are both important, but they differ considerably in their characteristics. While sunlight results in high levels of illuminance, resulting in sharp contrast, diffuse light from the sky can result in more homogeneous illumination, with no excessive contrast between different points in the same environment, or between the interior and exterior of a building [34].

The Daylight Factor (DF) or Daylight Contribution (DC), is the ratio between the level of indoor and outdoor lighting [29, 30, 35]. This ratio is expressed as a percentage value. This percentage of lighting that will be available in the interior varies according to the size and location of the openings, the obstructions of the sky, the properties of the transparent closures to the light, and also according to the reflections of the interior surfaces [26].

According to ABNT [35] and Corbella [29], the luminous flux of the exterior can reach a point inside a building in three different ways. Using the light that reaches a point of the internal environment coming directly from the sky, defined as Sky Component (SC); by the light that reaches the interior after being reflected by external surfaces, defined as Externally Reflected Component (ERC) or by the light that is reflected by the surfaces of the internal environment itself, being determined by the shape, arrangement and colors of these surfaces, and defined as Internally Reflected Component (IRC).

Geometry also has an important influence on access to natural lighting inside buildings. Considering only the presence of openings in facades, distances of up to 5 meters can be illuminated naturally, and deeper distances are only partially illuminated [30]. Thus, for the same total constructed area, different geometries may allow greater or lesser access to natural light.

The illuminance in an environment increases with the size of the apertures. The Window-to-Wall Ratio (WWR) expresses the percentage value of the net area of an opening divided by the area of the wall containing it. Hastings, Wall [36] demonstrate in a study that, for WWR up to 50%, the increase of the illumination in the interior varies proportionally with the increase of the area of the opening. However, from a 50% WWR, the gains in terms of natural light are no longer so significant.

The use of windows on opposite facades of the same environment is a strategy that contributes to a more uniform distribution of natural light within buildings, reducing contrast and obfuscation. The orientation also influences the quality of natural lighting, as already mentioned in the Solar Geometry section. The graphs in Figure 2 demonstrate the interior lighting curves for unilateral openings, and the illumination variation in the different orientations (the analysis in Phoenix is for reference only, to show the differences between Northern and Southern hemispheres).

Figure 2.

Variation of natural lighting according to the depth of the environment and orientation of the openings [21].

For the use of natural lighting, different solutions can be adopted. The light shelves are horizontal devices that can be coupled to the windows, contributing to shade part of the opening, and allow greater penetration of the natural light inside the building, using the reflection of the light that in them penetrates to the ceiling of the internal environment, which favors the use of IRC [26, 29]. These elements can also avoid situations of discomfort and visual fatigue by contrast and dazzle [26].

Zenith lighting is a strategy that provides a more uniform distribution of lighting in the internal environment when compared to lateral lighting. Mansards, domes, sheds are examples of this type of application taking advantage of SC. Also, light tubes are elements capable of conducting natural light through a pipe into the building.

Sunlight can and should be used, however, strategies to take advantage of this feature must be appropriately integrated with other strategies to provide environmental comfort. Corbella [29] points out the importance of avoiding an excessive incidence of direct solar radiation in lighting projects in buildings located in tropical areas.

The sensitive use of natural light along with adequate elements to control the direct incidence of the sun and the levels of illumination in the interior should be considered an integral part of a passive solar project [34]. The single-family residential typology presents great flexibility to integrate different strategies and systems for the use of natural lighting, qualifying the internal environment and promoting visual comfort and efficiency in energy consumption.

4.2 Artificial lighting

A good artificial lighting project should be developed in a way complementary to the use of natural lighting available in each environment. The artificial lighting project comprises different steps, which include identifying the required lighting levels; the perception of the characteristics of the place to be illuminated, such as colors, types of surfaces and their dimensions; the choice of luminaires and lamps and their technical properties; to perform the calculation and determine the number of light points [29].

Among the strategies used in the control and efficiency of artificial lighting are the use of automatic systems such as photoelectric sensors, dimmers, presence sensors and time programmers and the adoption of independent electric circuits. An example of such circuits is the task lighting that is used to complement natural lighting and facilitate user autonomy by meeting their demand without having to provide higher illuminance throughout the environment.

The use of different artificial lighting technologies also has a great impact on energy consumption, the heat dissipated to the internal environment, the quality of the lighting and the need for system maintenance. Light Emitting Diodes (LED) systems have achieved market penetration and offer several advantages over incandescent and CFL lamps [37]. Table 2 compares characteristics of LED, LFC and incandescent lamps.

Lamp Type	Watts	Lumens	Lifetime (hours)	Energy use (MJ/20 million lumen-hours)
Incandescent	60	900	1 k	15.1 k
CFL	15	900	8.5 k	3.78 k
LED	12.5–5.8	800	25–45 k	3.5–1.6 k

Table 2.

Differences between artificial lighting systems.

CFL: Compact fluorescent lamp; LED: light emitting diode; and MJ: Mili Joule.

Appropriate design strategies, adequate use of natural lighting and efficient technologies can contribute to the reduction of energy consumption by artificial lighting systems. In this way, it is possible to meet the demands of the occupants, satisfying the visual comfort parameters with energy efficiency.

5. Solar systems

The study of solar geometry is not limited to the use of the sun in passive strategies for environmental conditioning. It extends to the feasibility study of the use of solar systems, such as water heating and electricity generation. The analysis of the solar radiation in the different surfaces of the envelope of a building allows to take advantage of these systems. In new buildings, attentive to variation of solar radiation on surfaces allows to generate the shape of the envelope in order to obtain the best guidelines for the use of solar radiation in these systems, optimizing its yield.

5.1 Solar heating system (SHS)

Solar collectors are systems that convert sunlight, shortwave radiation that penetrates through the glass, into heat, and enable the use of solar radiation for heating water.

The SHS consists basically of three parts, the solar collectors, the thermal reservoir, and the water circulation system, which can be of natural circulation (thermosyphon) or forced circulation (pumped). In addition, they may also contain equipment such as a hydraulic pump and differential temperature controller.

The water heated by this system is stored in the thermal reservoir and will serve for consumption, supplying showers, sinks, kitchen sinks, appliances, and can also be used for heating the environment through, for example, water radiators.

The broadest SHS for residential use can be divided into three technologies, evacuated tube and glazed collectors, and unglazed collectors, the latter being the least efficient technology and whose application is mainly intended for pool heating [28]. Figure 3 illustrates the difference in the performance of solar collectors.

Figure 3.

Comparison between different technologies of solar collectors and their efficiency [38].

The integration of SHS into buildings requires a study that considers the availability of envelope sites where these systems can be installed, the incidence of seasonal radiation on these surfaces, the design of the system based on hot water demand, and the space required for storage of heated water [38]. More efficient systems and better solar orientation result in a smaller area occupied by collectors for the same amount of heated water. The architectural design can also favor the efficiency of these systems by approaching points of collectors, storage and consumption, reducing losses with the transport of heated water.

From the economic point of view, Raimo [39] shows that the time of the return of the investment in SHS varies according to the solar coverage rate (SCR) and the efficiency of the system Thus, this period can be of a few months, for an efficient system and a high SCR, or reach about 8 years when the system presents low efficiency and the SCR is less favorable. The lifespan of these systems is about 20 years [31].

Another advantage of SHS is that the installation does not depend on specific legislation since these systems are not interconnected to public networks or infrastructures, such as the photovoltaic systems. On the other hand, the design of the system must be in accordance with the demand and also with the space available to store the volume of heated water. “Super or under-dimensioning of a solar heating system can turn out to be a worthless, unprofitable and even costly investment” [40].

Considering the sizing of the SHS, it is important to address the concept of Solar Fraction (SF), which is defined by the percentage of the total demand for hot water that is supplied by the solar system [26, 31]. From the environmental point of view, the use of these systems has advantages in reducing GHG emissions when compared, for example, to electrical or gas systems. Avoided emissions can be measured based on the solar fraction that will have an SHS, comparing the energy that is no longer consumed from non-renewable sources, such as LPG, or even the electricity available in the network.

5.2 Photovoltaic system

Photovoltaic cells are independent power plants capable of converting solar energy directly into electrical energy. Several cells are interconnected to generate a photovoltaic module, which can be associated in series or parallel by configuring a larger power unit, and this association can be integrated with the buildings.

PVSs can be installed alone or connected to the distribution network. In Brazil, through a compensation system, a building connected to the grid can generate energy through a PVS. The surplus energy generated is injected into the grid and, when necessary, the building uses power supplied by the grid. PVSs connected to the grid do not require the use of batteries because they export surplus energy to the grid, which serves as a virtual storage system [38]. Figure 4 shows schematically the components and operation of a photovoltaic system connected to the grid.

Figure 4.

Photovoltaic system connected to the grid [21].

The integration of photovoltaic modules into the architecture can take different forms. Research focused on Building Integrated Photovoltaics (BIPV) have been contributing to the evolution and diversification of the photovoltaic modules available in the market, to facilitate this integration, in new and existing buildings. Examples of such applications are in windows and skylights, parapets and elements of roof or facade.

In addition, the integration of PVSs into building components contributes to the reduction of the final cost of these systems, since they are integrated with these components, instead of overlapping them, reducing costs with the module structure to photovoltaic cells [38]. Figure 5 illustrates some of these possibilities.

Figure 5.

Integration of PV modules to building components [21, 41].

From the environmental point of view, the PVS is a clean and renewable source of energy, not emitting gases like CO2, NOx and SO2 to generate electricity, and silicon modules are not toxic products, even at the manufacturing stage [31]. The lifespan of PVS consolidated technologies is 30 years, which the nominal power rating of the module is approximately 80% after 25 years of use, and inverters have a useful life of about 15 years [42]. A study carried out based on PVSs available in the market indicates that the time of return is less than 2 years for the main commercialized technologies [43].

Ruther [44] and Roaf et al. [31] point out some advantages of distributed photovoltaic generation in urban buildings, e.g. the reduction of losses in the transmission and distribution stages; the possibility of using the surfaces of the envelope for generation, without needing to occupy additional areas for the PVS; possibility of offering a high capacity factor to network feeders with daytime peak consumption; and modularity and ease of installation, providing quickly generation capacity to the distribution network. The absence of noise, reliability, low maintenance and the possibility of moving or transferring the system from one building to another, if necessary, are other positive aspects attributed to photovoltaic modules [31].

6. Energy consumption in a solar house

The electrical energy consumed in buildings is associated with the use of appliances and equipment, and these are generally the focus when it comes to reducing energy consumption. However, the consumption of these equipment depends not only on its efficiency, but also on the interaction with the envelope of the buildings and with the occupants [45]. Among the equipment used in a residence, those that have their demand and, therefore, their consumption more associated with the physical characteristics of the building are those used for the environmental conditioning, that is, artificial lighting systems and air conditioning.

To better understand residential energy consumption, let us take as an example the Brazilian case. Procel [46], on research into equipment checkout and use habits, rates the specific energy consumption of appliances and equipment in the Brazilian residential sector, as shown in Figure 6.

Figure 6.

Share of appliances consumption in Brazilian dwellings [46].

Bioclimatic strategies and the use of natural lighting can contribute to building performance, providing environmental comfort to the occupants and reducing the consumption of electricity with artificial lighting and air conditioning systems.

Decoupling of generation and consumption steps in the energy use cycle contributes to energy inefficiency. The ZEBs can reestablish this connection as they promote greater awareness of the occupants of energy generation and consumption. In this sense, residential automation systems are an important tool to integrate and monitor the different systems operating in a solar house, and inform the occupants about the generation and consumption of energy. The storage of the data of operation and performance of a house allows mapping tendencies that can be analyzed to look for solutions to increase the efficiency in the energy consumption for the maintenance of the environmental comfort [47].

Residential automation has been gaining market space as a way to increase not only the efficiency of the operation of the buildings, but also the comfort, convenience and safety of the occupants. The automation system integrates several components structured into a control skeleton that provides refined measurement data from sensors that detect equipment consumption, home appliances, electronics, lighting systems, power generation systems, temperature conditions, humidity, brightness, meteorological data, presence of people, among others. These, in turn, are registered and can be managed, or controlled, by users through interactive interfaces such as computers, mobile phones and the like.

Studies have shown the possibilities of avoiding waste of energy in energy consumption, or other natural resources such as water, through residential automation systems, which can be programmed to turn on or off equipment based on the presence of people, in the definition of temperature and lighting levels, helping to avoid wasted energy [47, 48].

Bartram and Woodbury [48] point out that the challenge of the automation project is to balance the responsibility of requesting actions on the part of the user and also to assist in the accomplishment of these actions. The possibility of viewing historical expenditure data in monthly or annual periods tends to exert a great influence and impact on the user, which can also positively influence the seek for greater conservation of energy [44]. These systems and their interfaces present great potential to extend the design possibilities in homes that aim at energy efficiency and can instigate people to use natural resources more rationally.

6.1 Solar house model

The use of solar energy, directly or indirectly, in urban or rural buildings has great energy potential [38] and makes it possible to contemplate the energy demands to be used in a solar house. Examples of these uses are: allowing internal heating, which results from the generation of direct solar gains and also by the solar water heating system; effective use of natural lighting and use of shading elements to prevent internal overheating.

A solar house prototype is used as an example to show the application of different sun-use strategies in architecture and is the result of a study carried out in Madrid, Spain, located in the Northern Hemisphere, with geographic position 40.4168° N and 3.7038° W, where the implanted solar geometry was considered. The study allowed us to observe that the south orientation was considered the most favorable, as it benefits from the sun throughout the year. As a result, the geometry is more elongated on the east–west axis, while the largest area of openings is located on the south side of the prototype. However, the roof, which is the surface that receives the highest incidence of solar radiation throughout the year, was chosen for the installation of solar systems. The diagram in Figure 7 illustrates these strategies [24].

Figure 7.

Solar house prototype [24, 49].

The control of the incidence of solar radiation throughout the year is performed by shading devices, aiding in thermal comfort and the availability of natural light. In the southern facade, a system of automated external blinds was installed. The east and west facades are protected by verandas with bamboo frames. In the interior are applied translucent blinds. Components of high levels of thermal insulation are applied to the floor, walls and roof and the openings are sealed and double-glazed with a low-e coating. The application of these passive solutions for the maintenance of internal thermal comfort gave a daylight autonomy of 60%, contributing to the energy saving. The artificial lighting is designed to complement the use of natural light and uses LED technology, which ensures greater efficiency than other technologies.

The application of a DHW solar system with evacuated pipe technology, with a solar fraction of about 90%, provides hot water, which can be used to feed radiators for space heating. The PV system consists of 48 modules with an efficiency level of 18.5%, accounting for an installed capacity of 11.04 kWp.

The efficiency of the operation is improved through the use of a home automation system integrated with the equipment and the general prototype process. The system provides to the occupant’s information about power generation and consumption, allowing more efficient control of the use of appliances such as for lighting and thermal comfort. This equipment can be programmed to be activated or to work only under certain conditions pre-established by the occupants. The combination of solar systems and strategies for sun use guarantees the prototype a positive energy balance throughout the year, as shown in the graph of Figure 8.

Figure 8.

Solar house annual energy balance considering the prototype located in Madrid [24, 49].

The estimation of the annual energy balance of the House prototype was carried out considering its implementation in Madrid. According to the rules and regulations of the SDE, an occupancy schedule was defined and energy consumption of household appliances was estimated considering a couple’s daily routine and interior comfort conditions for certain temperature and lighting ranges. Energy consumption and generation calculations, conducted using Energy Plus software by Team Brazil members, also took into account the climate data from Madrid. For the calculation of energy generation, was adopted the same PV panel used in the prototype, which is a monocrystalline technology SunPower 230 Solar Panel with a 15.8% efficiency, and the solar collectors were vacuum system SOLTER PU 200/5 [21].

The prototype Solar House adopts as premise the harnessing of sun. It exemplifies a model of the solar house, designed in the light of an adequate study of solar geometry and solar orientation. In addition, it shows that the combined use of strategies and systems can improve the performance and efficiency of the housing unit.

7. Systematization of premises and strategies for a solar house

Distinct is the premises and strategies for using the sun in the architecture of a solar house, be they design solutions or systems that may be incorporated into the building. As described throughout this study, and demonstrated through the Solar House prototype, these strategies relate to one another, interfering with each other, as well as with the outcome of the edification as a whole. Therefore, the earlier the architectural use of the sun is taken into account in the design process, as a guideline in the choices of premises and the strategies to adopt, the greater the benefits arising from the use of this resource in the architecture.

In addition, many factors may limit the application of these assumptions and strategies, e.g., economic, cultural, technical, technological, or other. It is important to see in a systemic way the possible strategies to be adopted and the interfaces between them, to obtain greater energy efficiency and environmental quality as a result, within the limitations of each project. The diagram shown in Figure 9 starts from the use of solar energy as a fundamental premise in the design of a Solar House. Then the energy demands of a solar house are incorporated and, sequentially, the strategies that can be applied to the use of the sun in the architecture are added to the diagram, increasing the use of technologies and the consequent complexity of the project.

Figure 9.

Demands, premises and design strategies for a solar house.

In this work, the premises and strategies considered the most relevant within the scope of this research were listed. There is a multitude of other strategies, or even derivations of the demands and strategies presented. In this way, it would be possible to incorporate to this diagram structure new elements, increasing its complexity and refinement regarding the adoption of design solutions for a solar house.

Thus, starting from the use of the sun as a premise, a housing unit can be considered the most elementary version of a solar house when conceived considering an adequate study of geometry and solar orientation. Other strategies and systems can be incorporated, through different arrangements and combinations of these solutions, improving the performance and efficiency of this unit. In addition, preparing the building so that strategies can be incorporated into future steps, for example, leaving waits for SHS and PVS when they cannot be adopted at first, is also essential considering the lifespan of a solar house.

Table 1 presents the summaries of the assumptions and strategies of solar geometry, thermal and visual comfort, solar systems and home automation.

8. Outcomes analyses and final considerations

The use of the premises and strategies of the solar house project allowed satisfactory results in the use of architectural techniques and technologies to keep the climate control and the visual lighting system comfortable [23], as well as resulted in the generation of electricity, with gains physical and economic resources applied to the project.

The Solar House project was dimensioned with balconies and designs to control heat exchanges, for thermal comfort and with large openings to amplify the use of natural light, to aid visual comfort. The automation system, with controllers designed to reduce energy consumption as a function of demand [50, 51] allows the interaction between the resources of the solar system, such as thermal heating, lighting and energy generation by photovoltaic cells [52] and equipment for general use, controlling electricity consumption.

In addition to individual and/or collective projects in the implementation of solar systems, with highly satisfactory results, some countries, such as Denmark, China, Germany and Austria, have made extensive investments in the energy market, with technological solutions in large-scale solar thermal systems [53]. Several contributions from solar resources have motivated the implementation of these models of thermal and electrical energy generation, as they are non-polluting and provide a clean form of energy. In Figure 10, the diagram systematically presents the results found.

Figure 10.

Diagram of solar energy for a solar house.

In Section 6, Figure 8, the excess energy available for the electricity grid is presented, at the approximate average value of 1030 kWh/month, equivalent to 58.79% of the total andTable 3 [21] reinforces the positive results in implantation of solar systems, including the simulated average values of energy generation and consumption in one year.

Month	Generated energy (KWh)	Energy consumed (KWh)	Energy exceeded (KWh)	Percentage (%)
Jan	1253	747	506	40.38
Feb	1387	721	666	48.02
Mar	1852	679	1173	63.34
Apr	1918	634	1284	66.94
May	2204	676	1528	69.33
Jun	2405	743	1662	69.11
Jul	2451	801	1650	67.32
Aug	2012	785	1227	60.98
Sep	1599	710	889	55.60
Oct	1496	688	808	54.01
Nov	1268	728	540	42.59
Dec	1182	754	428	36.21
Average	1752.25	722.17	1030.08	58.79

Table 3.

Generated energy capacity (KWh).

KWh: KiloWatt-hour.

The data allow showing the Pearson correlation, with r = 0.995, demonstrating a strong positive relationship between generated energy and surplus energy (energy produced minus consumed), which returns to the electricity grid. The percentage of energy exceeded, 58.79%, demonstrates the efficiency level of the solar house’s energy system.

The experience in the solar house allowed us to verify some advantages and disadvantages in its implementation in relation to the materials, techniques and equipment of the solar system:

1. Advantages—allows you to model hourly variations in occupancy, simulate bioclimatic strategies, decrease the cost of electricity, due to the improvement in thermal comfort (design of windows, doors, side openings, thermal plates, natural ventilation network, artificial conditioning, thermal control, etc.) and visual (natural and artificial lighting system).

2. Disadvantages—high initial cost for installing the solar house, due to materials, equipment, as well as the limited energy generation during the day.

The parameters and variables allow achieving thermal, visual, acoustic, air quality, etc. comfort, depending on the architecture, solar geometry, air temperature, radiant temperature, relative humidity, air velocity, physical activity, clothing, thermal exchanges: conduction, convection, irradiation (thermal gain), etc. They are important to the process of analyzing the premises and strategies of a solar house.

The solar intensity, as well as the temperatures and relative humidity of the air, are important variables for the design of the solar house and, in this sense, the averages, maximum and minimum values of the cities of Madrid and Sao Paulo are presented.

Average temperatures (°C) and relative humidity (%):

1. Madrid—Average temperature range: from 0–33°C (Min −9°C and Max. 40°C), with average annual temperature: 14°C. Relative air humidity: 10 to 80%, with average annual humidity: 55.4% [54].

2. Sao Paulo—Average temperature range: from 12–28°C (Min 2°C and Max. 40.4°C), with average annual temperature: 26.1°C. Relative air humidity: 12 to 88%, with average annual humidity: 79.56% [55].

Table 4 supports the proposal of the efficiency of the solar house, given the growth of the solar energy matrix in Brazil. The Brazilian installed power grew approximately 130% from 2018 to 2019, 70% from 2019 to 2020 and in the first four months of 2021, it had more than 15% [56]. These data provide the potential of the Brazilian electrical matrix about the generation of solar energy, which has a large installation capacity in the country, due to the climate, the reduction of implementation costs and, mainly, for the sustainability and improvement of climate comfort, visual and environmental.

Year	Solar energy Brazil		Electric generation capacity
	Installed capacity (GW)	Growth (%)	Overall capacity (GW)	Ratio (solar energy)/(general energy) (%)
2016	0.024	14.29	150.338	0.016
2017	0.935	3795.83	157.112	0.595
2018	1.798	92.30	162.840	1.104
2019	2.473	37.54	170.118	1.454
2020	3.287	32.92	174.412	1.885

Table 4.

Solar energy capacity in Brazil [56].

GW: Giga Watt.

The installed solar power in Brazil, in 2018, was 1.8 GW and corresponded to 1.1%, in 2019 it increased to 2.47 GW and, in 2020, to 3.29 GW, representing 1.88% of the matrix Brazilian energy, therefore, shows a significant growth of solar energy in the country.

Table 5 presents the statistical data, demonstrating a strong relationship between the growth of the capacity of the solar system and the Brazilian energy system, as well as the significance and importance of this modal for the Brazilian energy system.

	Solar power	General power
Average (GW)	1.703	162.964
Variance (GW)	1.630	93.978
Standard deviation (GW)	1.277	9.694
Comments	5	5
Correlation (r)	0.963
Mean difference hypothesis	0
gl	4
Stat t	−36.87782931
P(T<=t) one-tail	1.61411E-06
one-tailed critical t	2.131846786
P(T<=t) two-tailed	3.22823E-06
two-tailed critical t	2.776445105

Table 5.

Correlation of statistical data on Brazilian solar and energy capacity.

GW: Giga Watt; r: Pearson correlation; gl: degree of freedom; Stat t: t statistic; P: Probability.

Strategies and premises are important for the solar house process and statistical data prove this, with r = 0.963 and P-value <5% (0.00000161).

9. Conclusions

In this work, several solutions were presented through which the architecture can benefit from the sun to provide environmental comfort to the occupants and efficiency in the consumption of electricity. The single-family housing typology, due to its characteristics, presents an ease to incorporate many of the premises and strategies presented, from those involving only the study of solar geometry and orientation in relation to the sun, to the incorporation of sophisticated systems and technologies.

The theoretical approach and the practical examples of bioclimatic concepts, material properties, design strategies, solar systems, equipment and technologies for energy conservation, allow us to intuitively understand that all these solutions, if well used, contribute to an architecture of quality, for the benefit of the occupants and the environment. The prototype Solar House was used to demonstrate the practical application of these premises and strategies, as well as the interfaces between them.

The results demonstrate the importance of the solar system for the Brazilian energy matrix and how solar houses contribute to this process of energy reduction, through the sustainable solutions presented in this study.

Finally, it is pointed out the contribution of this type of housing unit towards sustainable development, leading to a reduction in greenhouse gas emissions [24, 49].

Acknowledgments

To Daniela Miwa Uemura (Msc) for the translation from Portuguese to English of this work in the first version, with the content and form, and to Prof. André Luiz Lorenção for general review.