torsdag 27. november 2014

The new combination of solar cells and supercapacitors

By PhD students attending the
Norwegian Research School in Renewable Energy 2014, NORREN


The world’s climate is subject to change through the emission of greenhouse gases such as CO2, which has increased rapidly over the past decades. The share of renewable energy sources in the world’s power supply need to increase in order to reduce CO2-emissions and global warming. Many of the renewable energy sources are intermittent sources – meaning that it is not possible to predict when they will produce electricity. For instance the power production of a solar cell depends on the weather conditions. If it is completely cloudy there is not much production, but if the day is a partly clouded one the production rate can vary a lot. This is illustrated by Figure 1 (a), showing the power production of a solar cell on a partly cloudy day. An energy storage system is needed to store energy during excess production, and to deliver energy in times of energy deficit. While lithium-ion and nickel metal hybrid batteries can store large amounts of energy (up to 180 Wh/kg), they fall short during rapid changes in production and load. Supercapacitors can complement the battery in a hybridized energy storage system for solar cells, such as to supply the necessary high power when needed and hence increase the battery lifetime (Glavin et al., 2008), or they can smooth the power output from solar cells such as to reduce the voltage peaks and stabilize the voltage to the grid (Figure 1 (b)). Simulations done by Björn Veit and Thomas Hempel in our group work also proves that supercapacitors works very well in responding to the solar cell power output as shown in Figure 1 (c)).

Figure 1. (a) Power production from a solar cell on a partly cloudy day, (b) power smoothing (red curve) by using supercapacitors, and (c) the simulation scheme using supercapacitors integrated with solar cell module.