Photovoltaics and Flat Extensively Greened Roof – Integration of Two Complementary Technologies

The author described in the diploma thesis the system of green flat roofs, rooftop solar power plants and their integration into one complementary system. He examined three hypotheses which he tested throughout the entire assignment. Thus, in summer months, temperatures of green surfaces up to 30 °C cooler can be achieved compared to the nearby surroundings. The hypothesis is confirmed on the basis of these results. In the second hypothesis, he examined the positive effect of shading by PV panels on the vegetation of the green flat roof.

Problem

The author described in the diploma thesis the system of green flat roofs, rooftop solar power plants and their integration into one complementary system. He examined three hypotheses which he tested throughout the entire assignment. First, he examined the positive effect of the microclimate of green flat roofs on the operation of PV panels.

He found that the green roof, through evapotranspiration (transition of water into gaseous state through the surface of the earth and plant leaves) of retained rainwater and reduced heat accumulation on the roof surface, creates a cooler microclimate in its own surroundings.

Solution and Method

Thus, in summer months, temperatures of green surfaces up to 30 °C cooler can be achieved compared to the nearby surroundings. PV panels have reduced electrical energy production when they heat up above their optimal operating temperature of 25 °C. Thus, it is established that PV panels have on average 6% greater electrical energy production compared to PV panels on a classic flat bitumen-gravel flat roof.

Results

The hypothesis is confirmed on the basis of these results. In the second hypothesis, he examined the positive effect of shading by PV panels on the vegetation of the green flat roof. In a multi-year comparative study, it was established that green roofs on which PV panels were installed had, due to reduced direct solar radiation, a lower surface temperature by 2.5 °C and reduced evaporation rate, which mitigated the impact of summer drought periods.

The result of these two factors was greater vegetation biomass and a greater number of different plant species. The hypothesis is confirmed on the basis of these findings. In the final hypothesis, he examined the complementarity of these two systems and whether they meet the criteria for ecologically sustainable construction and living.

It was established that the systems have no negative effects on each other, although one might initially assume that both systems compete with each other for space. When the systems are combined, it is established that they improve the already existing positive properties of the other system. The green climate creates a cooler microclimate, which improves the efficiency of PV panels, whilst the solar cells, through shading, reduce the impact of drought periods and increase the biodiversity of vegetation. Throughout the entire diploma thesis, he examined the assertion about ecologically sustainable or sustainable construction of the integrated system. ** To confirm this hypothesis, he verified three criteria:** ** energy-related,** ** ecological,** ** environmental.** The system meets energy criteria in reduced energy use and consequently reduced production of greenhouse gas emissions, as a green roof, when properly constructed, has exceptionally good thermal insulation properties, which reduces heating costs in winter and cooling costs in summer.

PV panels, with the help of a rooftop solar power plant, can meet most of the energy needs of a building. With careful use of the roof, a building can in certain cases also generate surplus energy. The system also meets ecological-environmental criteria very well.

With the help of a green roof, we return lost green surfaces to nature and offer living space to various animal and plant species. By retaining and slowly releasing rainwater, we relieve the water supply infrastructure, which can be of exceptional importance in heavier rainfall for urban centres, as due to the loss of green surfaces they have no possibility of retaining precipitation. Green roofs, due to evapotranspiration of moisture in the soil, cool the roof structure and the surroundings of the building, which in urban settlements reduces the impact of the urban heat island (UHI).

Due to this, the need for cooling the building is lower, the consequence of which is fewer greenhouse gas emissions, which can be further reduced by using a rooftop solar power plant in combination with a green roof. An important ecological aspect of green roofs is the return of lost surfaces due to construction and expansion of urban settlements. Thus, with the help of such a roof, we gain new living spaces, both for people in the case of extensive greening with arranged rooftop gardens and walking paths, and for various animal species in the case where the roof has only extensive greening with the single purpose of protecting the waterproofing of the roof covering.

This waterproofing, due to the technical and thermal characteristics of green roofs, also has a greatly extended lifespan (60–90 years) compared to classic bitumen roofs (15 years), as it is protected from UV radiation and mechanical damage by the vegetation and soil layer. The constant temperature of the roof structure reduces shrinkage and expansion of the waterproofing, which also extends the lifespan. For the purposes of confirming the hypothesis, he examined two academic studies.

The most widespread was Köhler's research, conducted between 2001–2006. This examined individual interactions between PV panels and green roof vegetation and to a large extent strengthened and justified the thinking about positive interaction of the systems. The second academic study (Mohammed Alshayeb and Jae D.

Chang), which was conducted on a smaller scale (only one month), also confirmed the initial results. The basic hypothesis, which was set at the beginning of the diploma thesis, that the green flat roof system and the photovoltaic panel system are complementary and offer an ecologically sustainable method of construction and living, was confirmed on the basis of these findings in all points.