Project Title: Atmospheric Water Generator
Problem Statement: Many homes in Pakistan experience severe shortage of water. In fact, areas of high relative humidity such as Karachi have 40g of air per cubic meter (at 38C and 85% relative humidity). Condensing this moisture using a solar power dehumidifier can provide water for household use. Depending on air quality, filtration or UV light sanitization may also be required. Off the shelf dehumidifier should be modified to run on solar (DC power), but for the first prototype we would use an inverter to convert DC to AC, and run the dehumidifier on AC power. A rechargeable battery will be required to provide a relatively uniform power input to the dehumidifier.
System Price target: Rs 50000 (including humidifier, solar panel, charge controller, rechargable battery, inverter and solar panel stand). Lower when we can later modify the wiring on the dehumidifier to run directly on DC power.
Target Performance: 5 liters of water per day in summer and 4 liters per day in winter using a 300W solar panel
Dehumidifier: Off the shelf unit modified to run off battery supplying through a DC to AC invertor. Later, we want to modify the wiring and look to run directly using DC power output from solar panel. We would use a dehumidifier with Energy Factor > 2 liters/kWh of energy under stated test conditions related to humidity and temperature. And target humidifiers that can produce 15 to 30 liter per day of water, if run for 24 hours using line power, so with off grid power from solar panel, and with input power in the 250W to 600W range, we can run it for few hours every day to get about 5 liters of water. Ideally, it should be based on variable speed technology, so as the batter drains, or solar power falls off, the dehumidifier will run at partial speed/performance, rather than stopping completely. The run cycle of dehumidifier, the charging cycle of the battery should be streamlined to get the maximum performance over a 24 hour cycle.
Rechargeable Battery: Select a battery that can provide about 1.5kWh of energy to the dehumidifier every 24 hours, at the rated power of the dehumidifier. Since we cant drain the battery 100%, we would have to choose a unit that will still retain enough charge after draining 1.5kWh of energy, so it will still work for a couple of years without losing performance significantly. It may have to be placed in a shade and rechargeable batteries are temperature sensitive. The lead acid version my last a few hundred cycles, while Li ion should give a couple of thousands cycles of life, given that we would charge and discharge it once every 24 hours.
Solar Panel stand: A simple adjustable stand that can help us change the angle of elevation of the solar panel and support it across the entire perimeter so the solar panel doesnt slide out and get damaged. The homeowner should be able to place a pencil of stick on the solar panel, and adjcut the angle of elevation of the panel to make sure the shadow length is minimal at midday, and sunlight is incident at 90 degrees onto the solar panel. Changing the panel to face slightly eastwards in the morning and westward in afternoon is desirable but not necessary. For summer winter seasonal cycle, we may leave the panel at +30 degrees angle of elevation facing the south in summer, and essentially flat in the winter when the mid-day sun in Karachi is almost directly overhead.
Charge Controller: Allows output from solar panel to charge a deep cycle battery, and pushes the excess to the dehumidifier, if the latter will run at partial power.
Inverter: This will take the output from the battery (and/or solar panel) and convert it into 220V 60Hz to run the dehumidifier.
Associated wiring, selected to minimize losses and plug and play capability
One complete unit assembled and functional, solar powered atmospheric water generator. We should plan on testing two or three different dehumidifiers during the prototype phase. Also, detailed Bill of Material, list of suppliers and pricing, as well as detailed assembly and wiring instructions with images uploaded on sawayra.org as all projects are open-source to maximize deployment. The prototype unit will be tested and data on performance – liter per day, as a function of daytime temperature and relative humidity will be summarized. After the prototype phase, we will assemble some units for the pilot phase and deploy in a secure fashion to various parts of Karachi. A zakat based or qarz-e-hasna model will be used at this stage, since Sawayra is a non-profit charity and our effort is fi sabeel illah (humanitarian).
Do market survey of available dehumidifiers and solar panels to properly size the system. In doing so, price, water extraction efficiency and power consumption must be considered. Finalize detailed design by July 2016 … parts and equipment, source of supply etc. Procurement completed by August 2016. Assemble and test at NED/University of Houston and collect data for a week. Functional units with documentation available by Sept 2016, and we do six to nine months of testing. Pilot phase of deploying 5-10 units will be done in Summer 2017, and then we will raise more funds to scale up in Summer 2018, insha Allah.
Sawayra Mentors: Samad Aziz Mian (firstname.lastname@example.org) and Omar Aquib Hasan (email@example.com)
Appendix 1 – Additional Information:
Current pricing of bottled water in Pakistan is Rs 30 per liter, so a Rs 50000 humidifier with ability to provide even an average of 4.5 liters of clean water daily over the course of the year, will provide Rs 200 of water per day or Rs 50000 of water per year. In other words, we are targeting one to two year payback time for the person purchasing the unit. Sawayra’s plan is to provide these units under declining balance option to poor households e.g., the home-owner pay Rs 5000 upfront, and then pays the balance as Rs 1000 per month until the entire amount is paid off, so we can then seed the purchase for another household. There will be no riba involved in the transaction under any circumstances.
After the initial prototyping we will deploy some units securely across Karachi in the pilot phase. The intent is to assess the performance and prove-out the approach over summer 2017 in Pakistan, after which we can look at expanding in various directions including moving from portable dehumidifier to larger industrial dehumidifiers using more solar panels, and intended for school, hospital and other similar places.
Appendix 2 – Technical and Weather Data
Figure 1. Year round relative humidity and dew point in Karachi, Pakistan
Figure 2. Year-round Karachi temperature range
By cooling the air below the dewpoint will cause its water vapor to condense. Additionally, the further below the dew point we go, and longer the period of contact with a surface on which the condensate can form, the greater the degree of moisture extraction. The table below shows the dew-point at which condensation will start, as a function of ambient air temperature and relative humidity.
Figure 3. Dewpoint table as a function of temperature (F) and relative humidity (%)
Water content in air as a function of temperature and relative humidity can be calculated by using online resources such as https://www.ready.noaa.gov/READYmoistcal.php . It shows that at 35C (95F) and 85% R.H., there is 30grams of water in each cubic meter of air. Our design should target pumping two to four cubic meter of air past the cooling coils per minute – i.e. minimum 120 cubic meters per hour. So around 60% moisture extraction, we can get 1.0-1.2 liters per hour. Since the solar panel will run during daylight hours, but at peak capacity for only 3-4 hours around noon time, the expectation is to get about 4-8 liters per day depending on temperature, humidity etc. Condensation efficiency may be increased by adding surface area in the form of loose copper sponge or additional ducting. We will also need to do water quality analysis to assess if filtration or UV lamp is required.
Appendix 3 – Other Information
Figure 4. Design of an atmospheric water generator – filtration and UV light can help purify the water. Our design will run on solar power.