A Study on the Development of Roof Solar Photovoltaic (PV) System Combined with Greenhouses

CHOU,LI-YU（China Productivity Center Agricultural Innovation Department II ）

I. Exacerbation of Climate Change and Urgency of Green Energy Policies: Current Status of Roof Solar PV System in Taiwan

In response to global climate change, the world is striving to reduce greenhouse gas emissions and formulate the governance and transformation strategy for sustainability and circularity. To achieve its energy transition goals, Taiwan has been focusing on four key directions since 2016: reduction of coal-fired power generation, increase of natural gas in the energy mix, phase-out of nuclear power, and development of green energy. A comprehensive roadmap and strategy have been laid out toward the target of installing 29 GW of renewable energy capacity by 2025.

The goal for solar photovoltaics (PV), which accounts for the largest share of renewable energy, is 20 GW in installed capacity by 2025. Current projections allocate 12 GW for ground-mounted solar PV systems and 8 GW for roof solar PV installations. As of October 2023, the installed capacity is 4.33 GW for ground-mounted solar PV and 7.33 GW for roof solar PV - still a long way to go to meet the 2025 target.

In recent years, solar PV has been a topic of ongoing controversy, particularly regarding its impact on agriculture and the concerns over ground-mount projects as "fake farming, real solar".

To align with national energy policies and address these concerns, the Ministry of Agriculture has adopted the principle of "agriculture as the foundation with green energy as added value". Green energy infrastructure is governed by the Regulations for Examining the Application of Structuring Farming Facilities on Agricultural Land (hereinafter referred to as “the Regulations on Structuring Farming Facilities"). Nationwide initiatives promote the combination of agriculture and green energy, including the installation of roof integrated solar PV panels on agricultural production, storage and distribution facilities (such as greenhouses, material storage rooms, collection and distribution centers, and processing plants) and the development of ground-based aquavoltaics.

Legislative amendments over the years have adjusted the hurdle for ground-mount solar installation applications and incorporated crop yield assessments into the review of roof solar PV panel installation applications. These measures aim to improve regulatory oversight and review rigor, thereby fostering win-win outcomes for agriculture and power generation while ensuring adherence to established principles.

II. Relationship Between Greenhouses and Roof Solar Photovoltaic (PV) System

In promoting the agricultural production, storage and distribution infrastructure, greenhouses share similarities with roof solar photovoltaics in the context of agriculture and energy. The integration of both has become one of the most popular facilities as it enhances land-use efficiency on top of existing operations, opens up the possibility of long-term sustainable development, and generate additional incomes.

Below are some examples on how greenhouses and roof solar photovoltaics can be integrated.

Sharing of Land Resources

Both greenhouses and roof solar PV panels require dedicated space but serve different purposes. Greenhouses create an optimal environment for crop growth, while roof solar PV panels generate renewable energy. The combination of these two achieves land-use efficiency and enhances space utilization.

Moderate Shading

Since greenhouses are designed to create the optimal growing conditions (e.g., light exposure) for crop production, the Regulations on Structuring Farming Facilities stipulate that solar PV panels cannot occupy more than 40% of the total roof area of greenhouses and cultivation facilities in a controlled environment. Additionally, non-transparent roofs of auxiliary structures should be prioritized for the installation of solar PV panels. Only after meeting these requirements can the remaining panels be evenly distributed over the roofs of crop cultivation areas, to ensure adequate sunlight penetration without adverse effects on plant growth.

Without completely blanketing the roofs, roof solar PV panels provide a certain degree of shading effect, mitigate water evaporation from plant leaves and provide more stable conditions for crop growth.

For example, the Association for Preservation of Nature, Culture and History of Linbian Township in Pingtung County has been collaborating with Agricultural Research and Extension Stations under the Ministry of Agriculture in Taoyuan and Kaohsiung since 2019 to conduct trials on growing vanilla orchids (Vanilla planifolia) under solar PV panels. Vanilla orchids are a high value crop, requiring relatively low light and thrive in humid and semi-shaded conditions. Excessive direct sunlight can damage the plant. Hence, the installation of solar PV panels on top of the greenhouse reduces the risks of damage, costs and financial losses.

Energy Complementarity

To maintain stable conditions for crop growth, greenhouses usually consume substantial energy for environmental control systems and timed sprinklers. As the production area is inherently limited, the installation of roof solar PV panels can provide renewable energy and reduce the high temperature caused by heat absorption of facilities. This helps owners save on energy cost, generate additional incomes and boost the overall efficiency.

However, combining greenhouses with roof solar PV system also presents several challenges, including:

Construction and Maintenance Costs

The cost of constructing and maintaining roof solar PV panels and greenhouse structures is relatively high. There are structural requirements for greenhouses to support the weight of solar panels. The deployment of solar PV panels and relevant electrical facilities may increase the overall agricultural investment costs.

Environmental Impact

The production and handling of solar PV panels can have environmental implications. In particular, recycling is one of the most common concerns we have received since 2020 when we started to assist the Agriculture and Food Agency in the assessment of interest in installation of roof solar PV panels on agricultural production, storage and distribution facilities. All the environment effects should be considered holistically to ensure environmental sustainability and not to compromise the governance and goals for sustainability and circularity.

Constraint on Choice of Crops

Whilst non-transparent roofs of auxiliary structures should be prioritized for the installation of solar PV panels, roof solar PV panels still provide a certain degree of shading effects. This, however, limits the choice for crops that can be grown within the greenhouse. It is necessary to take extra heed of whether the crops are suitable for indoor growth, so as not to undermine the greenhouse’s function to create a stable environment for crop growth or cause any increase of cultivation costs.

As previously mentioned, the greenhouse with roof solar PV panels provides vanilla orchids with a stable growth environment. However, the domestic market for vanilla orchids is approaching saturation. In addition, factors such as its long growth period, the need for hand pollination, and a high fruit drop rate result in a slow return on investment. Therefore, it is advisable to carefully consider various aspects and thoroughly assess the suitability of crop conditions.

III. Conclusion

How to resolve the current issues surrounding photovoltaics, overcome the challenge associated with the integration of agriculture and power generation, and promote energy transition are all key considerations moving forward. The combination of greenhouses with roof solar PV panels presents an innovative approach with the potential to achieve synergy between agriculture and energy. This method can meet today’s energy demands and enhances agricultural productivity. However, it also introduces certain challenges and issues that need to be resolved.

To navigate these difficulties, it is necessary to integrate expertise and technology from different domains and call for collective and ongoing efforts from multiple parties. Continued innovation and advancements in technology help to achieve sustainable development of agriculture. This collaborative endeavor in energy transition will contribute to the balance between sustainability and effectiveness.