بررسی عرضه و تقاضای انرژی در همسایگی خورشیدی

The paper presents a study of solar electricity generation and energy demand for heating and cooling of housing units’ assemblages. Two-story single family housing units, located in northern mid-latitude climate are considered in the study. Parameters studied include geometric shapes of individual units, their density in a neighborhood, and the site layout. The plan shapes of the housing units included in this study are rectangles and several variants of L shape. Site layouts studied are characterized by a straight road, a south-facing or a north-facing semi-circular road. Rectangular units and a site layout with straight road serve as reference for evaluating the effect of shape and site parameters. Results indicate that a significant increase in total electricity generation (up to 33%) can be achieved by the building integrated photovoltaic (BIPV) systems of housing units of certain shape-site configurations, as compared to the reference. The energy load of a building is affected by its orientation and shape. Increased heating demand by L variants (by up to 8%) is more than offset by annual electricity production of their BIPV systems (by up to 35%). Heating and cooling loads depend significantly on unit density in a site; Attached units require up to 30% less cooling and 50% less heating than detached configurations of the same site. Variation of surface orientation, particularly in curved site layouts, enables the spread of peak electricity generation over up to 6 h. This effect may be beneficial to grid supply efficiency. Energy balance assessment indicates that some unit shapes generate up to 96% of their total energy use. Neighborhood configurations studied generate between 65% and 85% of their total energy demand.

The design of net zero energy solar buildings involves a two-fold approach of enhancing energy efficiency while optimizing active solar energy production using photovoltaics and thermal collectors. A net zero energy house (NZEH) generates as much energy as its overall energy consumption, over a typical year [1]. The net zero energy balance can be estimated based on on-site energy consumption or source energy consumption [2]. A successful methodology that may lead to net zero energy status depends upon selecting suitable technical strategies that respond to defined objectives in a specific context [3]. This paper considers the on-site energy consumption. Coupling energy efficiency measures with active energy production techniques, such as photovoltaic and solar thermal collectors, enables the transformation of buildings into zero-energy systems or even net energy generating systems. Reduction of energy consumption can be achieved through several measures, such as airtight, well insulated building envelope, implementation of HVAC efficiency measures, including the use of heat pumps, combined with geothermal energy or solar collectors, and finally the use of energy efficient appliances. Window properties and size, especially on the equatorial facade, can maximize passive heating. Solar heat gains can reduce significantly purchased heating energy. A well designed passive-solar building may provide 45–100% of daily heating requirements [4]. Near-equatorial facing roof surfaces are considered optimal for capture of solar energy for electricity and heat generation, and therefore for the integration of photovoltaic/thermal systems. In Canada, building integrated photovoltaic (BIPV) technology is estimated to be potentially capable of providing up to 46% of total energy demand of the residential need [5]. This figure is determined based on a conservative methodology which estimates the available area of roofs and facades for integration of grid connected PV systems, while accounting for architectural and solar constraints [6]. The performance of a PV system depends mainly on the tilt angle and azimuth of the collectors, local climatic conditions, the collector efficiency, and the operating temperature of the cells. During the winter months, the insolation can be maximized by using a surface tilt angle that exceeds the latitude of the location by 10–15°. In summer an inclination of 10–15° less than the site latitude maximizes the insolation [7]. The PV system is commonly mounted at an angle equal to the latitude of the location, to reach a balance between winter and summer production [8], [9] and [10]. Building shape plays an important role in governing energy consumption in buildings, as well as having a significant effect on thermal performance and capture of solar energy [11] and [12]. Rectangular shape is generally considered as optimal for passive solar design and for energy efficiency [13]. However, under certain design conditions in urban context, this shape may not be optimal [12]. For instance, rectangular house plan does not allow uniform penetration of daylight, especially to the north part of the house, where minimum windows are suggested for northern climates. Furthermore, it should be born in mind that shape design is governed by many constraints other than energy efficiency, such as functional demands and quality of life of occupants. For these reasons it is important to explore the penalties, as well as the benefits associated with plan layouts other than rectangular, and with different roof geometries. Design of solar neighborhoods for exploitation of solar radiation for passive heating, for improved daylight, and for electricity generation, involves consideration of key parameters, including, in addition to building shapes, their density within a site, and the site layout. Spatial characteristics of neighborhoods and land use regulations can significantly affect solar potential and energy demand of buildings. Land-use patterns influence local temperature distributions [14]. High density development reduces cost and energy use, on one hand while reducing solar accessibility, on the other [15]. Site shape and layout of streets within this site can determine orientation of buildings and thus influence their accessibility to solar radiation [16]. Several studies have focused on investigating the distribution of solar radiation on different surfaces in a built environment, as well as on the availability of solar energy and its optimization, at the urban scale [17], [18] and [19]. Compagnon [20] proposed a methodology for estimating the amount of solar energy available to a building of any shape, taking into account obstructions due to the surrounding landscape and associated reflections. Kampf et al. [21] have developed a methodology, employing a multi objective evolutionary algorithm, to minimize energy demand of buildings in an urban area and to maximize incident solar irradiation whilst accounting for thermal losses. Notwithstanding the interest in the effect of urban development on solar energy, and the various investigations conducted to optimize solar energy, several aspects are not sufficiently addressed. The study presented in this paper forms part of an ongoing research into the effects of certain design parameters of residential neighborhoods on their solar potential and energy performance [11], [12] and [22]. The current study presents an investigation of the electricity generation potential by building-integrated photovoltaic system, and of the energy demand of two-storey single family housing unit assemblages. Climatic data of Montreal, Canada (45°N), serve as input for the analysis. The main objective is the evaluation of alternative patterns of neighborhood to achieve potential net zero energy communities. The main parameters employed in neighborhood design included in this investigation are the shape and orientation of individual units, the density of units in a site, and the site layout.

This study evaluates housing neighborhoods characterized by the shape of housing units and their density and by the layouts of the sites in which these neighborhoods are located. The potential of these neighborhoods to generate electricity is compared with energy demand. The study assumes design strategies for solar energy houses and energy demand data as proposed in the literature for mid-latitude locations (Montreal, Canada). Housing units considered in this study are two-storied with a total floor area of 120 m2. Housing units’ shapes include, in addition to rectangle, which serves as a reference, L shapes with varying values of the angle enclosed by the wings. The three site layouts considered are straight road, south-facing semi-circular road and north-facing semi-circular road. Housing density is considered trough detached configurations as lower density and attached configurations as higher density. Effect of rows of housing units is also considered for the straight road site. EnergyPlus building simulation program is used for estimating energy generation and demand. The main results of this study are discussed in the following. 4.1. Energy generation • BIPV electricity production of roofs with a given tilt angle is affected primarily by the area of near-south facing roof surfaces, shade and orientation. Active roof area is largely affected by the shape of the housing units. Some shapes, such as in L variations, allow optimizing roof area for a given floor area. For instance total annual energy generation can be increased by up to 50% relative to the rectangular shape. This can be even more beneficial on a neighborhood scale, where the total electricity generation by the neighborhood can be significantly increased. • The density effect is analyzed by studying attached units versus detached units, and analyzing the effect of row configurations. Attaching the units in multiplex configurations has the effect of increasing total active roof surface in some configurations. On the other hand it may produce some mutual shading by some configurations of L. The row effect does not have significant effect on electricity generation for a row distance larger than 5 m, in this study due to the uniform height of all units. A maximum reduction of 7% is observed for a 5 m row distance. • The effect of site layout on electricity generation is mainly due to its interaction with the housing shape design. A favorable combination of shapes and layout can result in significant increase of energy production. For instance, L variant configurations, employed around a curved road, can yield up to 33% more electricity generation than the rectangular configuration, used in the same layout • Another effect, resulting from variation in orientation of units in a curved layout is a shift in peak generation time by roof surfaces of differing orientations. A difference as large as 6 h of peak generation of different units can be achieved in a specific site layout. Shift of peak production can be beneficial for matching grid requirements. 4.2. Energy consumption for heating and cooling • Deviation of shape from the rectangle, which is considered the optimal shape for energy demand, generally involves increase in heating load. A typical value of increased heating load is in the range of 2–8%. The increase of heating load of non-rectangular shapes is associated with decrease of the solar gain in winter due to mutual shading by wings, and their rotation relative to south, as well as with the increased area of the building envelope for a given floor area. Cooling load is also affected by increase of solar radiation on the rotated wings and by the large envelope area. • Heating and cooling loads depend strongly on unit density in a site. Attaching units in multiplexes reduces heating loads by up to 30% and cooling load by up to 50% compared to the detached configurations of the same site. Heating and cooling loads of detached units are not highly sensitive to the spacing of the units. • Arranging the units in south-facing rows affects significantly the obstructed row, due to shading. The heating load is inversely related to the distance between rows, while the cooling load of both exposed and obstructed rows is significantly lower than for the single row configuration. For instance with a distance of 10 m between rows, the heating load of the obstructed row can increase by up to 25% for the rectangular units. At 20 m distance the effect is negligible. • Units in curved layouts have generally larger heating and cooling loads than in a straight road configuration. For instance, the increase in heating load of some L variants is up to 25% in some configurations of north-facing curve and 18% for south-facing curve. For the rectangular configuration the increase of heating load is some 8% for attached units and 11% for detached units, in both curved layouts. One reason of the increase of loads in curved roads is the mutual shade of the units, as for instance in north-facing curve, where L variants shade significantly each other. This shade can be reduced by more careful design of the relative ratio of self-shading surfaces. Cooling load is increased since the units are originally designed to be south-facing, implying large window size on the south facades. In the curved layouts, some of these units are oriented towards west or east, resulting in increasing transmitted radiation in the mornings and evenings, when the sun is at low altitude during the summer period. 4.3. Balance between electricity generation and electricity use • In attempting to achieve a balance between energy demand and energy production it should be noted that heating and cooling demand constitute no more than 10–15% of total energy demand, when energy efficient heat pump is used. The rest of energy consumption is attributed to appliances, water heating and other items that are not affected by parameters considered in this study. The main objective, therefore, is to maximize electricity production, even at the expense of some increase in heating and cooling load. • The general comparison between energy consumption, assuming energy efficient measures, and the energy production, show that several unit shapes included in this study are very close to achieve net zero energy status. For instance the units of L variants can produce up to 96% of their energy use, while the rectangular shape with hip roof (reference case) produce some 65% of the energy use. The rectangle with a gable roof (optimal roof), on the other hand, produces about 2% more than its energy use. Manipulation of roof design can help in improving production/consumption ratio. Multi-faceted roofs such L and its variants, in addition to increasing production associated with increased surface area, produce several peaks of generated electricity, due to the different orientations of surfaces. • Some of the studied neighborhood configurations constitute near net zero energy communities. For instance the detached L variants and attached obtuse-angle of the north-facing curved site produce 85% of their energy consumption. The attached rectangular (trapezoid) configuration of the same site produces 70% of its total energy consumption. Additional measures can be taken to lower energy use for domestic hot water and space heating by implementing technologies such as hybrid thermal/photovoltaic systems.