The demonstrator site in Ljubljana will be set up at the Faculty of Electrical Engineering (FE), which is a member of the University of Ljubljana (UL). The members of the University of Ljubljana are spread out in many buildings across the city of Ljubljana. The Faculty of Electrical Engineering is situated at Tržaška cesta in Ljubljana and consists of four interconnected buildings with enough roof space for about 200 kW photovoltaic power plant.
There is enough space on the Faculty of Electrical Engineering’s horizontal roof for a PVPP with a capacity of around 200 kW depending on the exact PV module power. Parts of the roof are already covered with different kinds of photovoltaic panels, which are being used for research purposes. The physical location of the PVPP is on the roof of four different faculty buildings.
This is an excellent location for a PVPP due to the ample amount of sunlight that shines on the site. There is also plenty of space for additional panels on facades if needed in the future. Installing a PVPP at this location will help to reduce the University of Ljubljana’s carbon footprint and contribute to awareness of all stakeholders of the faculty on the production of electricity from renewable energy sources.
The Faculty of Electrical Engineering is the perfect place to install a PVPP due to its prominent location and its importance in educating students on renewable energy sources. Most important of all – students can see the power plant in action and learn from it directly.
In the beginning of the AURORA project, we started screening both the social readiness as well as the legal limitations. Obstacles were encountered in both fields. Discussions with students and poll results showed that students are not keen on financial investment, but their interest is rather on gathering knowledge about renewable energies. However, faculty and university employees possess greater financial resources. Nevertheless, if students were to contribute only symbolically, it would disproportionately increase management costs and create a financially imbalanced community, potentially discouraging employee participation. Additionally, such symbolic contributions would result in minimal financial gains, which may also discourage students.
We also investigated different legal possibilities of establishing an energy community. During a meeting between AURORA project managers, the Faculty of Electrical Engineering management, and a lawyer specializing in corporate law and renewable energy, it was discovered that Article 10 of the Higher Education Act, which addresses the legal capacity of the university and its members, is currently deemed unconstitutional. This article is presently the subject of a legal dispute and prohibits the formation of new legal entities by its members. Furthermore, as public institutions, the Faculty of Electrical Engineering and the University of Ljubljana require explicit approval from the Government of Slovenia to establish or co-establish any new legal entity. Consequently, neither the Faculty of Electrical Engineering nor the University of Ljubljana can currently establish new legal entities
To address and circumvent these obstacles, we have decided to create a virtual energy community specifically for students, called the Student Energy Club (ŠEK). This will allow us to address the legal and social challenges while promoting energy awareness and encouraging investment in photovoltaic power plants to achieve energy independence. The purpose of these communities is not primarily to raise funds for investments but rather to raise awareness about renewable energy sources among students and faculty members.
At the same time, to fulfil the AURORA objective to set up a PV power plant and to have a power plant for demonstration purposes for students and employees and to get real-life data of electricity production to virtually offset an individual’s carbon footprint in the AURORA app, we started the procedure to install the first stage of the Solar PV Power Plant using our internal funds. The PV power plant will offset an important amount of faculty’s electricity consumption and offset its CO2 footprint as well as reduce the virtual citizen CO2 footprint for all participants in ŠEK.
Faculty’s PV potential
We have relied on a study of all available faculty surfaces that can eventually be covered by PV panels. In the study, we included all the roofs, south-facing facades and canopies over parking places. The study included detailed shading analysis for all surfaces and was based on a 380 W PV module with dimensions of 1755 · 1004 mm2. The study on the other hand did not go into detail from a civil engineering point of view and did not include static and fire safety assessments. In total, it is possible to install 432 kW of PV panels that would produce 392 MWh of electricity annually.
PV Power Plant plan
For the purpose of the AURORA energy community, the PV power plant will be primarily installed on the rooftops of the buildings of the Faculty of Electrical Engineering within the University of Ljubljana, at the address: Trzaska cesta 25, SI-1000 Ljubljana, Slovenia. The coordinates are:
- Latitude: 46.04° N
- Longitude: 14.49° E
We focused on the surfaces where PV installation is the most feasible. For the canopies above parking places, a building permit would be required. As such an endeavour requires detailed elaboration and a lengthy legal procedure (up to 2 years) that would be certainly out of AURORA’s time scope. There are even stricter requirements for the facades, where vertical fire safety and the danger of snow falling off the modules must be considered.
Considering this, we focused on the roofs, where a PV plant is legally considered as a building appliance and does not require a building permit. However, static and fire safety assessments must still be made. The total predicted power is 190 kW, which is in the range of the AURORA project objectives for each demonstration site.
The power plant was designed in 3 stages:
Each stage is predicted to have its own connection to the faculty’s electricity grid. Due to existing infrastructure, such an approach is more cost-effective than laying new cables towards a unified connection point. It is important, that all the stages are connected to the internal grid, as this allows direct self-consumption of the produced electricity.
Stage 1
In stage 1 the PVPP was anticipated to be installed onto the roof of building B. This roof has several different orientations: flat, 7° towards south-southeast, and 7° towards north-northwest (labelled in Figure 14Figure 13). Due to low roof angles, and to better align with the overall daily electricity demand (see Figure 16Figure 15) we predicted installation in a 10°east-west orientation. This increases the number of module orientations to seven. In addition, some modules in the west section of Stage 1 may experience some shading. To fully exploit the potential of all installed modules, we predicted the use of power optimizers. We also predicted to use modules of different technologies in the middle section of Stage 1. This section has four equally oriented parts, which will be used to install the modules with the cells of the following technologies:
- Passivated Emitter Rear Contact (PERC)
- Interdigitated Back Contact (IBC)
- Silicon HeteroJunction (SHJ)
- Tunnel Oxide Passivated Contact (TOPCon)
Special attention will be paid to find the most similar modules, i.e. to have the same laminate structure (e.g. glass-glass or glass-backsheet), the same colour of backsheet and frame, and similar cell size. This will emphasize the difference between cells of different technologies, rather than differences in the module’s bill of material (BOM).
We have communicated the detailed conceptual plan with QPV to prepare for monitoring and inclusion of the Ljubljana Demonstrator to the AURORA monitoring platform.
Stage 2
In Stage 2a the three roofs of the building D, and in Stage 2b the remaining roof of the building A are to be used for installation. The south (the lowest) roof of building D is oriented 25° towards S-SE with the inclination of 5°. PVPP will be laid parallel to the roof and fastened onto the standing seam of the copper cladding. The north two roofs are horizontal, covered with a bitumen layer. Since the structure of the roof is a strong concrete slab, PV modules will be installed in E-W orientation on 15° inclined triangles loaded with ballast. The remaining free roof of building A is similar to roof B with the exception that the structure of the roof is made of wood. Here the modules are again planned to be installed in 15° E-W orientation on triangles anchored into the roof structure.
Stage 3
In stage 3 the final roof of building C will be covered with PV panels. This roof has two sides with 14°incilnation, one facing e-NE (-115° from S) and the other facing W-SE (+65°from S). Due to sufficient inclination, the PV modules will be installed parallel to the roof and since the roof is covered with copper cladding, standing seam clamps will be used.
Production and self-consumption
As already elaborated in Deliverable 3.1, the electricity demand of the faculty is usually low during weekends and holidays and over the nights because most people are at home. During working daytime hours there is an increased need for university-related operations. The base consumption of 4 MWh per day is present throughout the year, with variable increases of 1.5 to 3 MWh, depending on the circumstances. 7 days periodicity is due to the working week, and the increase in June and the first half of July is due to air conditioning. The decrease in the second half of July and August is due to the summer holidays, and the increase from October until the last week of December is due to intense study semesters and shorter days. In total, in 2021 1.9 GWh was consumed, out of which about 10% can be offset by a planned 200 kW PVPP.
A typical working hour increase corresponds very well to the predicted generation of the power plant with modules installed in a 10°east-west orientation. Detailed circumstances around May 1 are shown in Figure 16. The chart shows that with a proposed 200 kW solar system, all the generated electricity will be used on-site. In the case of an unlikely surplus, electricity will be exported to the grid and will be sold to the electricity provider at an annual power purchase agreement negotiated by the market price.
