Seite - 128 - in Clean Water Using Solar and Wind - Outside the Power Grid

128 Clean Water Using Solar and Wind: Outside the Power Grid robust and have a longer lifespan. They are more expensive; but the price of lithium batteries has dropped by nearly 20% per year since 2010. Lithium represents the key limiting resource for most batteries. The largest reserves of lithium by far are found in Chile, ahead of China, Argentina and Australia. Lithium batteries are lighter, more robust and more compact compared to lead-acid batteries. They can be discharged more and have a longer lifespan, but are more expensive. The two main types of lithium batteries used in solar applications are lithium cobalt oxide and lithium iron phosphate. Today the cheapest lithium battery is the Tesla Powerwall, with a cost of around 500 USD/kWh. Kittner et  al. (2017) explain that R&D investments in energy storage projects have been remarkably effective in bringing the cost per kWh of a lithium- battery down from 10,000 USD/kWh in the early 1990s to a trajectory that could reach 100 USD/kWh in 2019. This means that storage prices are falling faster than solar PV or wind technologies. 10.3.3 Saltwater batteries There are interesting new types of batteries still in a development phase. Saltwater or sodium-ion batteries have attractive properties. They do not contain heavy metals but instead use saltwater electrolytes, consisting of sodium sulphate in an aqueous solution. This means that a saltwater battery can be easily recycled, in contrast to a lead-acid or a lithium battery. Today there are battery stacks available for 48 V or 24 V with a current rating of 82 Ah (see below) and above 2 kWh energy capacity. An interesting feature is that these battery stacks can be connected in parallel even if the discharges and voltages of the individual battery stacks are not the same. This cannot be done with lead-acid batteries. Saltwater batteries are interesting not only from a performance point of view but also due to their price. This kind of battery is maintenance- free; even discharging deeply does not have a large impact on its performance. The price is of the order 400–500 USD/kWh. A saltwater battery can have up to 3,500 cycles with a 90% discharge. This corresponds to an operational life of almost ten years. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user