Solar water distillation

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Description

Solar water distillation is the process of using the energy from sunlight to separate freshwater from salts or other contaminants. The untreated water is placed into a still basin which absorbs heat, eventually reaching high temperatures, causing the water to evaporate, cool and condense into vapour, leaving the contaminants in the underlying basin. The vapour forms as drops on an overlying cover (usually glass) that are channelled and collected in a separate basin as freshwater. Solar water distillers are simple and relatively cheap technologies that provide alternative sources of freshwater in water stressed areas. Saltwater or soft water (surface water with few ions) can be used to produce safe drinking water, while more heavily polluted water such as waste water should only be used for non-drinking purposes such as industrial water reuse, unless additionally treated. Small and simple solar water distillers are usually built for single households, though larger systems can also be set up for shared use.

Implementation

Solar water distillers are typically used in remote areas where there is limited access to freshwater and centralized distribution systems. Technical experts may be required to introduce the system and train direct users in use and maintenance. The systems require siting on flat and open areas with access to water and sunlight. The “roof” of the system is installed with a transparent cover (often glass), placed at an angle to receive maximum sunlight. The sun penetrates through the cover and into the underlying still basin. The untreated water is collected in the still basin and heated up by the sun, eventually evaporating and separating from the contaminants. It is important that the material used for the still basin can absorb heat, for example a leather sheet, silicon, reinforced plastic, or steel plate. The slanted cover funnels the thin layer of condensed water from its underside into a channel (pipe, tube), which leads to a separate water storage container so it can be used for domestic purposes or drinking water. The remaining contaminants in the still basin should be appropriately disposed.

Environmental Benefits

  • Diversifies the sources of freshwater and therefore reduces stress on local freshwater reservoirs.
  • Uses a renewable and free source of energy.

Socioeconomic Benefits

  • Bears no associated operational energy costs and installation is relatively cheap.
  • Provides safe drinking water from saltwater or soft water (grey water and waste water should be treated prior to distillation), alleviating water stress and health risks from contaminated drinking water.

Opportunities and Barriers

Opportunities:

  • Relatively cheap and low-maintenance system, particularly for remote communities 
  • Solar water distillers can be used at the household level, as well as scaled up through programmatic approaches
  • Climate change adaptation and mitigation benefits (renewable energy source)

Barriers:

  • Rate of distillation is usually very slow (6 litres of distilled water per sunny day/m2 ), so not suitable for larger consumptive needs
  • Materials required for the distiller (e.g. glass or high quality plastic) may be difficult to obtain in some areas
  • If not correctly disposed of, the distillation process waste stream can be a potential source of environmental pollution for due to its high concentrations of salts and/or pollutants

Implementation considerations*

Technological maturity: 4-5

Initial investment: 1-3 (depending on size and complexity of distiller)

Operational costs: 1-2

Implementation timeframe: 1-2

* This adaptation technology brief includes a general assessment of four dimensions relating to implementation of the technology. It represents an indicative assessment scale of 1-5 as follows:

Technological maturity: 1 - in early stages of research and development, to 5 – fully mature and widely used

Initial investment: 1 – very low cost, to 5 – very high cost investment needed to implement technology

Operational costs: 1 – very low/no cost, to 5 – very high costs of operation and maintenance

Implementation timeframe: 1 – very quick to implement and reach desired capacity, to 5 – significant time investments needed to establish and/or reach full capacity

This assessment is to be used as an indication only and is to be seen as relative to the other technologies included in this guide. More specific costs and timelines are to be identified as relevant for the specific technology and geography.

Sources and further information