Solar Water Pasteuriser 1: INTRODUCTION. Make free clean drinking water using the sun.
Channel: solaryes
Date: 2013-03-26

A Very Simple, Virally deployed Flow-Through, Solar Thermal Water Pasteurizer Could Save Lives In The Tropics. Introduction. (See the other more detailed videos, as well.)

How do I build my solar water pasteurizer?
 You can convert a large sheet of corrugated iron or a sunny part of your actual metal roof into a solar thermal water pasteuriser.
 (a) First, insulate underneath it with straw or foam. This stops heat from escaping downwards. 
(b) See the video diagram, tape on top a double, side-by-side zigzag of food grade flexible silicone pipe.  This pipe is often used in dairies.
(c) Inside the top loop, now fit the thermostatic valve. This only lets clean water flow when it has been pasteurized over 80C.  
(d) Put a second sheet of black roofing metal on top of it all. Black catches the sun's rays. 
(e) To stop heat from escaping upwards, over the top of it all, now add some simple glazing, glass or polycarbonate. It must not touch what is below.
(f) Block all the gaps around the edges to stop heat loss.
(g) Finally, add two empty water tanks: the lower one is for clean pasteurised water. Each should hold enough water for a week.

How does this simple solar water pasteurizer actually work?

Fill the top tank with river water or pond water, which may contain disease-causing pathogens. The sun heats the solar pasteuriser whenever it shines.  If the water inside was not allowed to flow, it would actually boil! But instead of boiling, when the water inside becomes heated to 80C the thermostatic valve opens, and this lets safe, heated (pasteurised) water flow through. The valve needs no external power and automatically shuts again when the water is below 75C, to stop living pathogens from passing through.  The top of the panel is much hotter than the bottom, because it contains a "counterflow heat exchanger" of parallel pipes, which recover heat from the outgoing water.  Using this design pasteurises much more water each day.  The system needs no pump: when the valve opens, gravity makes the water flow from the top contaminated tank to the lower clean tank, always going via the top hot zone, which kills all pathogens. Whenever the sun is too dull to operate the pasteuriser, it usually tends to rain. Rain water, being clean, may be used in preference to pasteurising pond or river water.

Short term initial deployments intend to reliably deliver drinking water for three small communites totaling around 100 people, depending on the installations' final size and performance.  Longer term, many sensitive assumptions associated with the mathematics of exponential growth come in. If viralised, and assuming the most optimistic a doubling rate of three months, then:

Year 0: 100 people will have clean water at the end of the third deployment and if it viralises...
Year 1: 1,600 people
Year 2: 25,000 people
Year 3: 400,000 people
Year 4: 6.5 million people
Year 5: 100 million people

This extrapolation is, of course extremely ambitions, but it might just be possible: market penetration of mobile phones in the tropics happened far faster and has risen far higher. Convenient, safe water is also very important. If viralisation does not happen, then growth be minimal, beyond the initial hundred or so people, or it may slowly extend to a perhaps few thousand people. But if viralization does happen, suitable global press and PR coverage could even radically shorten the above timescale.

Beyond the leading issue of access to safe drinking water, many other potentially calculable wider outcomes are also expected to scale up, roughly in proportion both in the short and long term. While, no estimate will be offered here to quantify these benefits, as discussed before, it is expected that these benefits will include: improved air quality, preservation of local scrub or forest biomass, strengthened community confidence, local recycling and micro-enterprise, wealth and resilience, and, of course, the relief of suffering from waterborne diseases, asthma and scalds, and, finally, top of the list, the saving of lives.