The new model is being tested on a small area of the municipality of Miraflores de la Sierra. The LIDAR data allows an accurate description of the urban environments through the creation of a digital surface model.
The Model
Then a map is created with the orientations and slope of each point of the roofs. This flexibility in positioning the panels significantly changes the amount of electricity produced.
Data
Area of study
Land register
Monuments and landmark buildings
Lidar
An INS (Inertial Navigation System) is also required to determine the aircraft's orientation and pitch. Using the position of the laser sensor and its measurements, a georeferenced elevation point cloud is obtained with high accuracy.
Solar radiation
Geostationary satellites provide information of the Earth's atmosphere and clouds with high spatial and temporal resolution. This provides us with a range of the global hourly solar radiation on a horizontal surface and of the direct normal radiation.
Digital surface model
- Classification and processing of the LIDARS’s data
For this reason, a reclassification of the LIDAR data is necessary to determine as precisely as possible the determination of the various elements. First, the software makes an automatic classification of the data using three categories: vegetation, buildings and land.
Determination of the utilizable surface
- Monuments and landmark buildings
- Accessibility to the roofs
Although Miraflores de la Sierra is a municipality where the presence of these buildings is not very large, some of them must be taken into account. Thus, in the end, we get a surface where it is in principle possible to place a PV system. It should be known throughout the year and for every point of the roof.
One way to proceed is to start with the irradiance on a horizontal, unshaded surface and then estimate the actual irradiance at each point on the roof, taking into account the specific slope and orientation and the presence of shadows. It uses the date of global solar radiation on a horizontal surface, obtained with a statistical approach by satellite images [27]. The basic idea is that it is possible to split the total irradiation G into its three fundamental components: the direct irradiation B, the diffuse D and the reflected R.
These components are functions of the horizontal surface irradiance and the angle between the Sun and our arbitrary surface.
Position of the Sum
It takes the earth 24 hours to make one revolution, so one hour is equal to one angle of 15 degrees. Zenith and azimuth define a single vector pointing towards the sun at any instant [Figure (4.4)].
Components of the global irradiation
In this case it is necessary to assume that the reflection of the environment is uniform. The behavior of the environment is described by the reflection coefficient ρ which is 0 for a completely black and non-reflective object and 1 for a perfect mirror. It is possible to neglect this effect because the reflected component is smaller than the diffuse component and therefore this correction is of second order and does not strongly affect the result.
Solar systems on a roof can be placed with a simple structure parallel to the roof or depending on the slope and orientation of the roof, it may be opportune to mount the solar panels on a static structure that makes it possible to arrange the panels on a certain slope and orientation to maximize energy production [ see fig.(5.1)]. We develop an approach capable of: (1) distinguishing between these two cases and (2) calculating photovoltaic potential for panels with a different disposition than that of the roof. Therefore, the real presence of the panels is not included in DSM (as for example done with other simulation tools like PVsyst).
Under panels mounted with a slope and orientation different from that of the roof itself (from www.mounts4solar.com).
Optimal disposition
This essentially depends on whether to maximize: the output relative to the panel area or the output relative to the roof area. Until recently, since panels were expensive, it was standard to maximize production relative to the surface area of the panels. Recently, panel prices have decreased significantly, therefore, in some cases, it may be more convenient to arrange the panels in such a way that the production per panel area is less, but it is possible to assemble more panels under the same roof. in order to maximize the production of the single roof.
Choosing the best solution in each particular case is beyond the scope of our work, so the roof is divided into two general categories. In this case, these types of roofs are simply called "flat" and the panels are inclined and oriented to the maximum. In any other case, for "sloped" ones, it is not appropriate to mount additional structures, then the orientation and slope of the roof and panels will be the same.
And for the roof of the first category, the optimum coincides with the maximum production in relation to the surface of the PV panels.
Effective surface
Optimal distance between lines
Shadow
By knowing the placement of the panels and the position of the sun during the year with some geometry, it is possible to calculate whether at any given time a panel line will cast a shadow on the next line. It is possible to reduce to this result any case where the roof has a different orientation (−180 ≤ αtejado ≤ 180) and slope (0 ≤ βtejado ≤ 90) by a rotation of αtejado around the z−axis and one of βtejado around the x− axis. Therefore, in a general case the shadow factor is given, where in Eq. (5.8) the position of the sun in the new coordinate (Eq. (5.11)) is replaced.
This equation is not valid if ys′′ < 0 when the sun illuminates the back of the photovoltaic panels and therefore the shadow factor can be considered equal to 1. This correction factor is smaller than 1 (LSN−cosβ =dF >0), so not taking it into account overestimates the effect of the shadow and underestimates the radiation received by the panels and namely the energy produced. Over the year, this correction is secondary because it is non-zero only in the early hours of the day and during sunset, especially in winter when the PV panels produce only a small fraction of the total electricity.
Conclusion
The result is a slope and orientation map of the panels different from the slope and orientation map of the roof. Finally, this map and the shadow map will be used as input to the radiation equations [Eq. To reduce the calculation time in this step, the range of tilt and orientation is divided into fields of 5 degrees.
This makes it possible to combine many points of the roof grid and significantly reduce the time for calculating the radiation map. In this case, there is an object on the roof (circled in red) that casts its shadow on part of the roof early in the morning and therefore the radiation is lower in this area. During the central hour of the day, the roofs are almost completely illuminated by the sun [see Ap. (A)].
The shadows affect the roofs only in the hours when the sun is low and therefore only a small fraction of the total annual radiation is missed.
Irradiation threshold
At the beginning, the entire surface of the city is considered after several criteria eliminate the areas that are not usable. Now with the map of the solar potential it is important to choose the part of the roofs where it is really convenient to install PV panels, it depends on the amount of solar radiation that a PV panel can receive in a particular location .
Area threshold
The dotted lines are obtained using Eq. (7.2) and the continuous lines with our direct approximation. It is clear that the empirical expression is only valid for orientation close to the optimal and otherwise leads to an overestimation of the losses and therefore to the wrongful neglect of a large part of the roofs. Determination of the suitable surface. An algorithm distinguishes these areas and eliminates them from the usable surface.
Figure 7.5 shows the part of the roofs that can be used. Taking into account the occupancy factor Cd [Eq.(5.5)], it is possible to calculate the surface area of the PV panels AP V. Almost all panels on the market are fundamentally composed of two technologies: crystalline silicon or thin films.
Efficiency
Low efficiency modules, such as thin films, will require more roof than higher efficiency modules to achieve the same performance.
Installed power
Performance ratio
- Shadow’s effect
- Temperature’s effects
- Losses
The actual effect of partial shades on the electricity production of the photovoltaic field is non-linear and depends on the interconnections between the modules. In a PV array, the current of each cell array is limited by the current of the worst cell in the array. An important factor in the operation of PV panels is also temperature, which can lead to corresponding losses.
This expression neglects the effect of the wind, which usually helps cool the PV panels. The two different typologies can reach a temperature difference of about 10o−20oC thanks to wind cooling. In addition, there are the losses due to the spread of the parameters in the PV generator.
Normally, the actual parameters of the PV modules have an uncertainty specified by the manufacturer.
Results
This is used to create a map of the shadow and to identify the areas suitable for placing a solar system. To do this, it is necessary to identify the surface of the roof using the "catastrophe". For the first typology, the radiation incident on the roof is calculated using the map of the shadow and the map of the slope and orientation of the roofs.
Once it is, the amount of radiation that can be used to generate current is known to be effective. The use of a more accurate method leads to a more optimistic result with respect to the one of the preceding work [13]. As well as the possibility to optimize the location of the panels on flat roof, leads to an increase in the annual production.
The image (A)-(A.2) shows the evolution of the shadow during two typical days of the year. Fig. (D.1) shows the variation during a typical day of spring without determining the energy production. A high-resolution assessment of the technical potential for residential roof-mounted photovoltaic systems in Germany.
