Background

Power output from photovoltaics (PV) is directly related to the amount of sunlight, or irradiance, striking the panel. Irradiance is modulated by the solar position and the level of atmospheric attenuation, which is the absorption and scattering of sunlight due to water and ice particles in clouds, fog and haze, as well as other particulates such as dust, ash, and smog. Complex, nonlinear, and dynamic atmospheric processes affect these particles, and create large uncertainty and variability in solar power generation. At high PV penetration levels, the range of variability and uncertainty in power production complicates electric grid operations and can lead to inefficiencies. Solar forecasting systems (SFS) provide information to reduce the uncertainty in solar power generation and enable grid operators and management systems to address the variability, improving operational reliability and economic efficiency.

In the short-term, transient clouds are the primary driver of PV power fluctuations. As a cloud passes between the sun and panel, PV power output can drop by 60-80% within seconds. High resolution (time and space) cloud monitoring is required to predict these large, quickly occurring fluctuations (ramps). Currently, total sky imager (TSI) systems are the best option for high-resolution sky monitoring, however, they typically cost over $20K per instrument. Additionally, to be used as a SFS, the TSI requires additional instrumentation to determine cloud position and attenuation. This limits the TSI as a cost effective option for solar forecasting, particularly for distributed PV, which requires widespread deployment.

Technology Overview

Researchers at the University of Hawaii’s Hawaii Natural Energy Institute have developed a novel ground-based irradiance mapping and prediction instrument for short-term proactive management of solar energy generation. The Affordable High-Resolution Irradiance Prediction System (AHRIPS) monitors sky conditions with an omnidirectional camera and thermopile-based pyranometer and uses stereographic pattern tracking techniques, solar geometry and clear-sky irradiance models, and a cloud advection/diffusion algorithm to forecast future cloud and irradiance conditions.

Features

Low production cost

Off-the-shelf components
Open-source hardware

Flexible deployment

Fully wireless operation
Self-powered
Compact weather-proof housing

Autonomous operations in an edge-computing framework

Standard operational deployment is a cluster 3-5 AHRIPS instruments
Onboard high-performance, single-board computer processes imagery and generates forecasts at the instrument
Generates 3D cloud maps and 4D cloud surface trajectories using stereographic tracking methods
Requires no additional instruments to generate irradiance and power forecasts
Contains additional environmental sensors necessary for accurate PV power modeling
AHRIPS instruments directly exchange information: upwind conditions to increase forecasting horizons, irradiance observations for improved estimation of cloud attenuation, and operational communication and status metrics

Self monitoring and calibrating

A single-board microcontroller monitors the state of the instrument and onboard computer
Irradiance observations (and PV power output in self-powered version) allow for realtime calibration and validation of forecasts
External calibration coe.

Benefits

Higher penetration of PV systems
Reduced PV generation uncertainty
Tighter operation reserve management
Gain insight into windflow in the urban environment
Improved management of building thermal loads
Improved management of grid-tied battery storage

Affordable High-Resolution Irradiance Prediction System

IP Status

Seeking