Efforts to expand solar capacity face several challenges. One of the most significant impediments to solar power, like wind power, involves the availability of its source. Solar radiation is rarely constant and varies with changing atmospheric conditions (clouds and dust), and the changing position of the Earth relative to the sun (day and night). Solar energy is also relatively weak because it must first pass through the atmosphere, which protects the Earth from the sun’s intensity. As such, the intermittent and variable manner in which solar energy arrives on the Earth’s surface means it creates reliability problems. This necessitates some form of back-up energy system to be installed for when the sun is not shining or the weather is adverse.