Solar energy and weather

Countries are transitioning to a net-zero emissions focus for future electricity supply. The majority of the technologies used to achieve this are dependent on the weather, such as wind and solar farms. Consequently the weather will play a substantial role in the energy produced from these technologies. One type of solar technology involves generating electricity from solar photovoltaic (PV) panels. The Sun emits energy in the form of solar radiation, approximately 1361Wm−2 annually at the top of the atmosphere, normal to the incoming rays. About 30% of this is reflected back to space with about 70% reaching the Earth's surface. This can be captured and turned into electricity, using PV panels. These convert sunlight into electricity through the process of a solar cell absorbing solar radiation to excite electrons into higher energy states. PV output is generated by shining light on a substance and creating a voltage. Power generation fluctuates with the variation of in-plane irradiance. PV panels are situated with optimised inclination angles to achieve maximum power generation over the year. The intensity of solar radiation depends on a number of factors including geographic location, season and time of day. Solar radiation input arrives in the form of both direct beam and diffuse radiation (Figure 1). Passing clouds are the main cause of blocking light from reaching the panels. The concentration of aerosols, water vapour and ozone in the atmosphere determine how much solar radiation is absorbed, scattered or reflected before reaching the ground. This is called diffuse radiation. When the Sun is lower in the sky, rays travel through a greater path length of the atmosphere and they become more scattered and diffuse, resulting in a greater component of diffuse radiation. Seasons control the amount of sunlight on any particular day, with up to 18h in summer and as little as 8h in winter around Ireland and the United Kingdom. During winter, the Sun is also lower in the sky. The diurnal cycle of sunlight means the greatest amount of solar energy is generated around solar noon and of course, none is generated during night time. The quantity of energy produced depends on the type of PV module (i.e. the semi-conductor material used in the modules), the system set-up (module orientation and tilt angle), along with the prevailing meteorological conditions. PV module efficiency is primarily influenced by the amount of solar radiation that arrives at the PV modules and the temperature of the PV modules. Module temperature in turn depends on the ambient air temperature, the intensity of the solar radiation and on the cooling effect due to local wind speed and direction. Power output decreases with an increase in module temperature and increases as a non-linear function of solar radiation. The weather can affect PV output in other, less direct ways. PV panel efficiency decreases with the presence of dust and dirt (which can be washed away by rain or with regular cleaning), or by frost and snow on the solar panels. Beyond the panel itself, weather conditions such as temperature and humidity can change the efficiency of other components, including the inverter, transformer and the transmission process. The ideal weather for solar energy generation is cold, sunny and windy. The Sun provides the energy for the panel and the cold air surrounding the panels keep it cool along with the cooling effect of the wind on the panels, removing any excess heat generated by the instrument itself. Ireland and the UK have a mild ambient temperature meaning the PV modules operate at lower temperatures and are therefore more efficient. Even though these locations are not known for their sunny climate, long daylight hours during summer can still generate large amounts of solar energy. Local weather conditions influence solar radiation as it passes through the atmosphere leading to variability in the amount of solar energy available. Forecasting solar energy generation is very important, as the presence of a single cloud can result in a sudden ramp downwards in generation, potentially shifting from very high (~100%) to almost no power and vice versa within seconds. Forecasting therefore ranges from time scales of just minutes in advance, to days ahead (when energy system operators need to schedule storage or source an alternative supply of energy), to long-term planning of solar farm construction. There are many useful resources available to assist with this decision making process, including the Photovoltaic Geographical Information System (PVGIS) 1 1 https://ec.europa.eu/jrc/en/pvgis (Huld et al., 2011). The global effort to become more sustainable is continuously driving advances in renewable energy, particularly in solar energy technology and forecasting techniques. These advances will help the transition away from fossil fuels, and allow more of the energy needs of our modern society to be provided by renewable energy sources. This publication has emanated from research supported (in part) by Science Foundation Ireland (SFI) under the SFI Strategic Partnership Programme Grant Number SFI/15/SPP/E3125. The opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Science Foundation Ireland.

Перевод пока недоступен