Page - 73 - in Clean Water Using Solar and Wind - Outside the Power Grid

Water treatment 73 Sometimes it is possible to collect the brine in an evaporation pond. In a hot climate the water in the brine evaporates and the salt can be collected and used for other purposes. 5.3.5 Renewable energy for desalination The energy required for desalination has three functions: to perform the pre-treatment, supply the high-pressure pump for the RO and overcome the membrane’s resistance to the flow of the water. The energy is electrical and can come from a wide range of sources. Desalination based on the use of renewable energy sources can provide a sustainable way to produce fresh water. Currently an estimated 1% of desalinated water comes from energy from renewable sources, mainly in small-scale facilities. But larger plants are starting to add renewables to their energy portfolio. Typically, the energy requirement for RO of seawater is 3–5 kWh/m3 (IEA-ETSAP & IRENA, 2013) for the whole process. Some sources say that 1.5–2 kWh/m3 is achievable to desalinate seawater. The theoretical limit for RO is around 1 kWh/m3, while the practical limit seems to be around 1.5. For brackish water the energy required is in the range 0.5–2.5 kWh/m3. Solar PV and wind power can provide necessary energy, but electric energy storage is an important challenge, considering the intermittent nature of the production (Chapter 10). An important aspect is that excess energy can be stored as produced desalinated water, which can be a cost-effective storage solution when generation exceeds demand. Thermal desalination requires both electricity and thermal energy, and – in total – more energy than the membrane process. Seawater desalination via MSF consumes typically 80 kWh/m3 of heat energy (or 290 mJ/m3) plus 2.5–3.5 kWhe/m3 of electricity (IEA-ETSAP & IRENA, 2013). Bearing in mind the remarkable cost reduction of renewable technologies, desalination via renewables can already compete with Excess energy can be stored as produced desalinated water. This can be a cost-effective storage when generation exceeds demand. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user