Several practical benefits result from energy storage technologies. By bridging the gaps during peak demand or renewable energy intermittency, they keep the power supply reliable. Going without power even for a short period can upset daily life substantially; in severe circumstances, it may even lead to the outbreak of social unrest so avoiding such breakdowns certainly lowers human suffering. Furthermore, customers buying energy storage directly save on their electricity costs: they can use stored electricity during high-tariff periods. Storage extends the benefits of renewable energy systems. It can use up surplus energy when that energy's otherwise at risk of being wasted, or mixed with lower-quality sources provided by the grid. Plus a place to store electricity without environmental penalty even makes possible shorter, higher-load periods than would be feasible otherwise--because you can stockpile what's gained during those low-load times and use it later in times or places enriched with planned increases of demand. Lastly, energy storage can recoup excess energy by feeding it back into the grid when prices are favorable thus providing an additional revenue stream.