Renewable Energy Forecasting

From Models to Applications

Georges Kariniotakis

• Publisher: Woodhead Publishing
• Year: 2017
• Print ISBN: 9780081005040
• eBook ISBN: 9780081005057
• Topic: Technology & Engineering
• Subtopic: Renewable Power Resources
• Index: Technology & Engineering

Renewable Energy Forecasting: From Models to Applications provides an overview of the state-of-the-art of renewable energy forecasting technology and its applications. After an introduction to the principles of meteorology and renewable energy generation, groups of chapters address forecasting models, very short-term forecasting, forecasting of extremes, and longer term forecasting. The final part of the book focuses on important applications of forecasting for power system management and in energy markets.Due to shrinking fossil fuel reserves and concerns about climate change, renewable energy holds an increasing share of the energy mix. Solar, wind, wave, and hydro energy are dependent on highly variable weather conditions, so their increased penetration will lead to strong fluctuations in the power injected into the electricity grid, which needs to be managed. Reliable, high quality forecasts of renewable power generation are therefore essential for the smooth integration of large amounts of solar, wind, wave, and hydropower into the grid as well as for the profitability and effectiveness of such renewable energy projects.- Offers comprehensive coverage of wind, solar, wave, and hydropower forecasting in one convenient volume- Addresses a topic that is growing in importance, given the increasing penetration of renewable energy in many countries- Reviews state-of-the-science techniques for renewable energy forecasting- Contains chapters on operational applications

Part One

Introduction to meteorology and measurement technologies

Outline

1. Principles of meteorology and numerical weather prediction

2. Measurement methodologies for wind energy based on ground-level remote sensing

1

Principles of meteorology and numerical weather prediction

Sue Ellen Haupt, Pedro A. Jiménez, Jared A. Lee, and Branko Kosović Research Applications Laboratory, National Center for Atmospheric Research, Boulder, Colorado, United States

Abstract

Numerical weather prediction (NWP) models are important tools in the process of generating forecasts of wind and solar power output from a farm. Before running an NWP model or being able to interpret its output, however, modelers and forecasters ought to develop an understanding of several foundational principles that undergird a successful NWP forecast. These foundational principles include atmospheric motion, observation sources and quality, data assimilation, the need for postprocessing model output, the value of probabilistic predictions, and how to perform validation and verification of the forecast. Additionally, knowledge about how the NWP model is discretized in space and time, the conditions under which the physical parameterizations have been tested and work well, and the quality of the initial and boundary conditions are all essential to producing a useful forecast. All of these principles are discussed, as is an example of tailoring an NWP model (WRF-Solar) specifically for solar power forecasting.

Keywords

Numerical weather prediction; General circulation; Scales of motion; Chaos; Predictability; Data assimilation; WRF-Solar; Postprocessing; Probabilistic forecasting; Verification and validation; Big data

1.1. Introduction to meteorology for renewable energy forecasting

Renewable resources are fast becoming the predominant energy source of the future, but to harvest them requires an understanding of the causes of their variability and the ability to predict numerous atmospheric processes over a range of scales. This understanding of the atmosphere is the key to harvesting renewable energy, specifically wind and solar power, in at least three ways. First, one must be able to characterize the resource availability to appropriately site plants and elements (such as wind turbines) within those plants. Second, it is imperative to forecast the resource on time periods of minutes to seasons to properly plan how to blend the renewable resources into the grid while continuing to meet the load obligation. Third, forecasts of expected energy generation and variability, including forecasts of extreme weather or sudden changes in the weather that may affect energy generation, are helpful in planning operation and maintenance of the sites. Thus, understanding the atmospheric physics and dynamics that ultimately cause the wind and solar resource to vary is key to modeling and forecasting for renewable energy. In this section, we briefly review the causes of atmospheric motion and the basics of forecasting before getting into more detail in subsequent sections.

1.1.1. Atmospheric motion

The atmospheric circulation arises because the Earth is spherical and the Sun's rays impact the Earth more directly near the equator than at the poles. The warmer tropical atmosphere is less dense than the polar atmosphere, forcing the predominant motion from the polar regions toward the tropics at the surface. Thus, the tropical air converges and rises at the Inter-Tropical Convergence Zone near the thermal equator, while the movement of surface air out of the polar regions causes a polar subsidence. This resulting circulation includes a return flow aloft from the tropics toward the polar region as the primary solar-forced circulation, known as the Hadley circulation (Anthes et al., 1981). Because the Earth rotates on its axis, it is actually a bit more complicated than that. This rotation creates an apparent Coriolis force that turns the flow toward the right in the northern hemisphere and toward the left in the southern hemisphere. In addition, this Coriolis force, due to the conservation of angular momentum, causes there to be not a single hemispheric-spanning Hadley cell, but rather three primary cells in each hemisphere (Fig. 1.1). The thermally indirect Ferrel cell encompasses the mid-latitudes and acts to mix the air through large-scale eddies and vertical instabilities. These instabilities generate waves that form the low- and high-pressure waves that continually pass over the mid-latitudes, transporting warm air poleward and cool air equatorward at the surface, with prevailing westerly winds at mid-latitudes and tropical easterlies in the regions near the equator. Finally, the polar cell is a thermally direct circulation, exhibiting high pressure from subsiding air at the poles.

The Earth's 23.5°-tilted axis generates the seasonality of the flow, the diurnal heating patterns cause the rise and fall of the atmospheric boundary layer (the lowest kilometer or so of well-mixed air), differential ocean and land heating rates cause further instabilities, and mountain ranges impede atmospheric flow, frequently leading to the generation of new low-pressure systems in the lee of the mountains. All these forcings work together to form the variability of the atmospheric flow (Fig. 1.1). Introductory meteorology texts (e.g., Holton, 2004; Wallace and Hobbs, 2006) provide more details of this general circulation theory and demonstrate how it can be codified into a series of partial differential equations of conservation of mass, momentum, and energy to model the flow, known as the Navier–Stokes equations. These equations codify the changes in the wind, temperature, and other atmospheric properties due to the forcings and are the basis of numerical weather prediction (NWP) models (Section 1.3).

Figure 1.1 Depiction of the general circulation of the atmosphere.

Although the solar radiation that hits the earth is the source of atmospheric motion, it is modified by atmospheric constituents including aerosols and water vapor, which are important to both the details of the circulation and to forecasting solar power. The large amount of water vapor in the atmosphere both impacts the flow and the cloudiness of the atmosphere. Because water vapor is less dense than air, moist air rises, generating adiabatic cooling, which can lead to condensation into clouds. Various processes cause this lifting of moist air and cloud formation. The most basic one is daily surface heating, which warms the moist air near the surface, causing it to become less dense and rise. Thus are formed the “popcorn” cumulus clouds that often grow, merge, and become more solid clouds at the top of the boundary layer. Another process that forces rising motion involves the weather fronts associated with the atmospheric waves, particularly the warm fronts leading the low-pressure cells and their attendant cold fronts. Although the processes that form clouds ar...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• List of contributors
• Part One. Introduction to meteorology and measurement technologies
• Part Two. Methods for renewable energy forecasting
• Part Three. Applications of forecasting to power system management and markets
• Index