A DC energy storage system may include first and second DC terminals for connection to a DC link, a DC energy storage converter including a number of modules connected in series between the first and second DC terminals, each module including at least one switching element and at least one battery, the or each switching element and the or each battery in each module being combinable to selectively provide a voltage source, and at least one fire-resistant protective barrier arranged to separate the modules into converter sections, each converter section including at least one module of the number of modules.