Boosting Winter Electricity with Alpine Roofs

^{Created by LT, ZHAW, on 19.12.2024}

This article is an adaptation of a confrence contribution at the EUPVSEC 2024 in Vienna.
Created by the Photovoltaics Research Group at ZHAW, Winterthur.

At higher latitudes, one half of the year delivers a significantly lower energy yield due to the seasons. As a result, expensive seasonal storage systems are built up to close this energy gap. In Switzerland and other alpine countries, open-space alpine plants are currently being planned to supply electricity specifically in winter. In the current work, it is shown that the proportion of winter electricity can also be increased with PV roof systems in the Alps by means of design changes, so that electricity can be produced much more cheaply and closer to the consumer in winter. For this purpose, bifacial modules are proposed vertically with ground cover ratios in the range of 0.5 to 1 and, depending on the conditions, mounted either on flat roofs in east/west orientation or on pitched roofs oriented as far as possible to the south. We show that the winter electricity can be increased by about 30% compared to the reference, but at the expense of a reduction in the total annual yield.

The monthly energy yield was simulated using PVsyst V7.4, allowing the calculation of specific energy yield in kWh/kWp as well as energy yields per unit of roof area. To account for snow coverage during winter on modules with low tilt angles, the Townsend monthly snow loss model was applied. The simulations were conducted for Arosa, Switzerland, at an elevation of 1’775 meters.

In the simulation, an albedo value of 0.8 was applied from November to March, while a value of 0.2 was used for the remainder of the year. The winter electricity share was calculated by summing the energy yields for the months of October to March.

The Ground Cover Ratio (GCR) of the simulated flat roof installations ranged between 50% and 100%.

• Irradiation Advantages in Alpine Regions: Higher irradiation levels in the Alps compared to the central plateau result from reduced fog and enhanced albedo effects, enabling significant electricity yields even during winter.
• Winter Performance Benefits: Vertical module installations avoid snow coverage, and bifacial modules capitalize on reflected light from snow surfaces, increasing the proportion of winter electricity generation.
• Winter Yield Enhancement Trade-off: Increasing winter electricity generation by approximately 30% compared to the reference is achievable but results in a reduction in the total annual energy yield.
• Tilt Angle Trade-offs: Steeper module tilts reduce annual energy yields due to dependency on snow conditions but can remain economically viable in areas with prolonged snow cover, especially when winter electricity has a higher value.
• Roof Pitch and Azimuth Effects: For pitched roof systems, changes in roof pitch and azimuth angles influence energy yields similarly to alpine ground-mounted systems, as detailed in the article Energy yield / Winter yield.
• Limited Orientation Scope in Simulations: The study focused solely on east/west and south-oriented systems; other orientations require project-specific analyses. Nevertheless, bifacial vertical modules were observed to yield comparable results across various orientations.
• Time-Dependent Yield Considerations: Electricity yield variations based on the time of day were not examined. Future studies should incorporate time-based generation profiles to align with dynamic electricity tariffs or specific consumption patterns.