When it comes to renewables, the main obstacle they present stems from their intermittency and variability. Creating energy from the sun, wind, ocean or even agricultural waste means coming to terms with irregular or even unpredictable performance. Another problem is that the most useful form of energy that we have is, of course, electricity. We use it to get around, generate light and heat, cook and run all of the devices that surround us. Electricity, however, isn’t readily available in nature. We have to produce it using other forms of energy.
Additionally, once we’ve generated it, if we can’t find a way to use it immediately, we lose it. Forever. Given that we can’t sit around in the dark, we have to find a way to obtain energy exactly when we need it. To achieve this, all of the renewable energy plants in existence today are connected to a storage system or grid. When the sun is shining or the wind is blowing, isolated plants store the energy that goes unused at that time and maintain it for when it is needed. Plants connected to grids, instead, simply transfer the excess energy to the grid, from which it can be retrieved when needed. Grid operators do the same with their grids, which are often as large as countries or continents.
Usually, excess electricity is stored as hydraulic energy; leftover energy is used to obtain water from the sea or low-elevation lakes and pump it to high-elevation lakes. When energy is needed, the water is then released through a penstock, and the force of the water moves a turbine, which generates new electricity. If there is an uptick in the demand for energy and the grid doesn’t contain enough, it can be purchased from abroad, or, in the worst case, thermal power stations can be brought into operation.