Computational Imaging for Long-Term Prediction of Solar Irradiance

TL;DR

This paper introduces a novel imaging system and algorithm for long-term solar irradiance prediction by accurately detecting horizon clouds and estimating their velocities, significantly improving forecast horizon over previous methods.

Contribution

The paper presents a new wide-angle imaging system and a spatio-temporal analysis algorithm for long-term solar irradiance prediction, addressing resolution issues near the horizon.

Findings

Predicts solar occlusion and irradiance for tens of minutes ahead

Achieves an order of magnitude longer prediction horizon than prior work

Demonstrates system effectiveness through simulations and outdoor tests

Abstract

The occlusion of the sun by clouds is one of the primary sources of uncertainties in solar power generation, and is a factor that affects the wide-spread use of solar power as a primary energy source. Real-time forecasting of cloud movement and, as a result, solar irradiance is necessary to schedule and allocate energy across grid-connected photovoltaic systems. Previous works monitored cloud movement using wide-angle field of view imagery of the sky. However, such images have poor resolution for clouds that appear near the horizon, which reduces their effectiveness for long term prediction of solar occlusion. Specifically, to be able to predict occlusion of the sun over long time periods, clouds that are near the horizon need to be detected, and their velocities estimated precisely. To enable such a system, we design and deploy a catadioptric system that delivers wide-angle imagery with uniform spatial resolution of the sky over its field of view. To enable prediction over a longer time horizon, we design an algorithm that uses carefully selected spatio-temporal slices of the imagery using estimated wind direction and velocity as inputs. Using ray-tracing simulations as well as a real testbed deployed outdoors, we show that the system is capable of predicting solar occlusion as well as irradiance for tens of minutes in the future, which is an order of magnitude improvement over prior work.