Executive Summary To further accelerate and increase the productivity and profitability of future agrivoltaic (AV) projects, the Hawaii Agriculture Research Center (HARC), Clearway Energy Group, and Longroad Energy initiated an AV Research and Demonstration project at Clearway’s existing Mililani solar array in 2021. The project successfully demonstrated the ability to grow numerous crops within the rows of an operational solar project with minimal impact on Clearway’s existing operations. Highlights include:
- Construction of four commercial-scale hydroponic lettuce troughs and eight full cycles of commercial lettuce production for yield analysis. - Development of eight, 180-foot vegetable beds and multiple cycles of 14 different vegetable crops. - Collection of environmental data to understand how panels impact growing conditions across row transects. - Presentation of the project at the Hawaii Agriculture Conference and numerous site visits with farmers, regulators, Hawaii legislators, and other stakeholders.
Environmental Data Collection and Analysis The Mililani site has had continuous weather monitoring with four Spectrum Technologies WatchDog 3000 weather stations since 2021. Two were located directly under the solar panels and two were placed in the center of the alleys between panels. These stations take data every 15 minutes of various environmental data including temperature, UV, photosynthetically active radiation (PAR), relative humidity, rainfall, and evapotranspiration. Construction of the Hydronic Troughs Ground was leveled using a scope and bulldozer. Each trough is approximately 100-ft long, 8-ft wide and was constructed with approximately common building materials (dimensional lumber, plywood, metal stakes etc.). Styrofoam sheets to hold the lettuce were custom-made on island.
Preparation of the In-ground Crops Site prep for the vegetable crops directly under the panels was installed in June 2022. We treated the area for weeds with herbicide, wetting the soil with low-ground sprinklers to wet the soil for ripping, followed by disking with compost. We finished with the dripline installation of four lines per bed. We sampled the soil and submitted a soil test. The report indicated a good soil pH and minimal additional nutrients (some calcium and sulfur) were needed. Compost was disked in to compensate for some minor nutrients and increase soil porosity.
Hydroponic Lettuce Production and Economic Analysis The hydroponic lettuce trials focused on five lettuce varieties, each sourced from Johnny's Selected Seeds. They provide a range of types that are popular in local commercial markets. As of December 2022, eight cycles (full troughs) have been harvested and yield data collected for each cycle. Preliminary results indicate hydroponic lettuce to be a good fit for AV, but longer- term study is needed. Economic and detailed yield analysis will be made publicly available as part of a graduate school thesis at the University of Hawaii in April 2023.
Directly Under Panel In-Ground Vegetable Crop Screening Our initial plantings served as a screening of crops that could do well in AV systems and have high potential value in the local market. We met with several local experts on which vegetables to target and based on these discussions, we decided to plant the following varieties and crops for our initial screening process: - Radish and Daikon - Melons and Kabocha Squash - Broccoli and Cauliflower - Bush Beans - Eggplant - Poha Berries - Bunching Onion - Lavender - Strawberries - Dryland Taro and Sweet Potato Most of these crops were successful but a much larger scale and repeated plantings are needed for conclusive yield analysis in these systems. This screening allowed us to pinpoint which crops we would like to test at scale and what agronomic hurdles to expect.
Project Outreach, Tours, and Media The project, even in its early stages, has generated a tremendous amount of interest and attention from various stakeholders in the industry. Numerous site visits and tours have been conducted since June 2022. Visitors to the site have included State Senators and Representatives, the Department of Education representatives, Department of Energy representatives, Land Use Commission, Department of Agriculture representatives, HECO Representatives, Kamehameha Schools, Ulu Pono, and GoFarm Alumni. We hope to build on this momentum by continuing to host tours to facilitate nuanced conversations around the research being done as well as the challenges and benefits of AV systems in Hawai’i for all stakeholders. We hope to also introduce video media as well as more printed materials to share with a boarder audience and visitors alike.