Novel seasonal application of low-level solar concentration to contribute to net-zero buildings

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Khattra, Gurneet Kaur
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Due to excessive fossil fuels consumption, the concentration of carbon dioxide is predicted to be approximately 500 ppm by 2050, impacting global biodiversity for generations. Increasing the percentage of recent solar energy use—sun, wind, hydro, and biomass—to address our global energy needs is of fundamental importance. With buildings representing nearly 38% of global emissions, solar energy can contribute to reduce impact: increasing the productive use of solar insolation from building grounds using reflective tracking mirrors, referred to as Sunflower, is a critical component. To this effect, a Sunflower model is developed from first principles to evaluate the productive use of low-level solar magnification from building grounds and rooftops. This model predicts the solar insolation incident onto a user chosen target with many Sunflowers to contribute to net-zero buildings. The model inputs are flexible, for example, change in number of Sunflower mirrors and their target specifications, including seasonal relocation to optimally reduce energy demand in a building, are part of user inputs. The model utilizes a single ray-tracing method to evaluate the solar irradiation redirected onto the building using low-cost solar tracking mirrors. This model developed in Python is based on solar angles and weather data to calculate the redirected hourly solar flux onto a chosen target. Using NREL’s Solartrace program based on the Monti-Carlo method, model results are validated within an error of 2.35%. The Sunflower model is then applied to predict the displaced energy in an outdoor pool heating application. The pool heating approach using Sunflower bypasses second law inefficiencies as the pool is heated by the irradiations directly from sun without the use of an intermediate thermal fluid. Multiple case scenarios are established to evaluate the optimal mirror angles to increase the solar intensity for a given seasonal configuration. The Sunflower model predictions for applications in Winnipeg, Manitoba (Latitude 49.9o) using 10 Sunflowers shows that seasonal pool heating load can be reduced by 67%, with a yearly GHG savings of 5.1 tons of CO2eq. For this case, the average yearly solar intensity ratio for a single Sunflower with a horizontal target is 1.81, and averages 1.50 during summer months when solar insolation is higher. For a similar application in the remote community of Arviat, Nunavut (Latitude 61.1o), currently depending on diesel fuel, pool water heating requirements can be reduced by 40% using 15 Sunflowers.
Renewable energy, Heliostat, Low-level magnification, Sunflower, Pool heating