Distillation

The basics

Distillation is nature’s own way of cleaning water: The solid water evaporates, becomes a gas and reunites into a solid in the form of rain. This life-giving “trick” is that whatever is in the water, besides water, will not evaporate into a gas and will simply be left behind. WaterStillar® produces clean H2O with a natural content of O2 and CO2. There is no difference in water quality whether a small or large amount is produced – there is no correlation between capacity and quality.

Purified or “still” water may also be water that is cleaned through reverse osmosis or deionization. But distilled water should be the process of evaporation and condensation in order not to confuse the terms and technologies.

Designing a distillation apparatus, such as the WaterStillar systems, we have considered and balanced out cost, power consumption, rigidity, migration issues, life span, simplicity, maintenance, and performance. Then, we put it into a Danish design.

Ice cubes from distilled water are crystal clear.

Evaporation without boiling gives the cleanest water quality
No physical contact between drink water and feedwater
High temperatures keep bacteria growth at an absolute minimum
WaterStillar® systems are opaque and therefore prevents algae growth
Steam is aggressive and will bind unwanted metal ions. Therefore a special glass/ceramic material or food grade stainless steel is used. No plastic.
Taste is neutral, minerals/gas/flavors can be added for desired water taste and health reasons
Organic solvents (e.g. petrol, oil, pesticides, chlorine) will evaporate just like water. But these substances are removed by an activated carbon pre- or post-treatment filter.

Unlimited use

Distilled water may be used for any purpose:

Better tasting tea and coffee. Eliminates scale build-up on pots and tea kettles
Crystal clear ice cubes
Use it for all cooking and baking
Excellent for mixing powdered milk, juice mixes and dehydrated soups
Use it for all infant care
Excellent for low sodium diets or sensitive stomachs
Pure drinking water for your pets
Watering your plants – flowers keep fresh for longer time
Spraying house plants – no spots on leaves
Brushing your teeth
Contact lenses
Steam irons, humidifiers, vaporizers and car batteries
Water for injection (prep with salt/medicine) in remote places
Process water in food industry
and much more. There are no restrictions.

Distillation and energy

The amount of energy required to vaporize a liquid is called the heat of vaporization. For water, this amounts to 2,256 kilojoules per kilogram at 100°C (970 Btu per pound at 212°F). The same amount of heat must be removed from the vapor to condense it back to liquid at the boiling point.

Distillation is today by far not the most effective way of cleaning water due to the huge energy demand. Therefore some “tricks” are seen to improve the effectiveness. The heat generated from vapor condensation is transferred to feed water to cause its vaporization and thus improve the thermal efficiency – this is what WaterStillar Works does by reusing this condensation energy in 5 to effects. This increases production in a given area and makes it possible to run the system on electrical supplement power during nighttime.

Another “trick” is to lower the pressure and boil water at a lower temperature. In this way, the production rate goes up but introduces other problems with higher complexity and biofouling.

There are a few, new and big solutions (eg. California, Spain) that make cubic meters of purified water through distillation. But most water distillation systems today are making liters for drinking purposes or where extremely clean water is needed (dental, pharma, medic, process water).

The power of the sun allows a certain volume of water to be evaporated and the efficiency of solar stills is often measured by GOR (gained output ratio) – a ratio telling how much distilled water is made by how much power . The solar power of a certain day, on a certain location is easily measured. The amount of energy needed to evaporate water at a certain pressure is well known. These 2 factors will give a certain efficiency of the solar still – an oversimplified example: The daily irradiance in hot and sunny place is 6 kWh per m2 and is takes app 650 watts to evaporate 1 liter of water – then a daily output of (6/0,65) 9 liters from 1 m2 would mean 100% efficiency or a GOR value of 1.

Solar stills - old news

Earliest recorded solar stills are from mid 18 century – miners in Las Salinas, Chile got their drinking water from solar stills in 1870. See picture above. Today solar stills still are a niche product, since filters and deep groundwater wells provide fresh water in most places.

Distillation of water is quite simple. A black box with a sloping glass cover and a collection gutter – that is a traditional basin solar still. The performance from simple solar stills is always less than 100%. Typical production is in the range of 1-4 liters/m2/day. There are some challenges in these systems – When the glass gets milky, the efficiency simply goes down and heat energy loss are another issue.

Improving this small amount can be done in many ways. Reflectors, sloping design, fans, flow through wicks, thermal solar collectors, insulation, active cooling, multi-effect design, heat storage and the list goes on. (REF: P. Vishwanath Kumas et al. 2015). Adding this to the basin still improved performance – but also cost and complexity is added to the equation.

Most energy efficient are the multi-effect solar stills (like WaterStillar Works). WaterStillar Family is a improved basin still. Both using high performance thermal solar collectors, eliminating some of the design issues with a classic basin type still.

WaterStillar's first principles thinking

Simplicity in our design give products that will actually work.

Water really wants to evaporate and condense again (=distillation).

Close to waters boiling point, nothing much can survive. (=sterile)

Water is a great solvant, so to keep water clean it shouldn't be in touch with materials that will allow contaminants to migrate back into the water.

Distillation is quite energy demanding, so either we use free solar energy and/or reuse energy.

One important answer to sustainability is to design long lasting things that is both repairable and reusable.

If customers and employees are not treated well, no company will survive.

If we do not innovate and make mistakes, we will not see improvements.

Types of small solar stills

The world has seen a number of attempts to make solar stills for decentralized water production. From the survival plastic bag and a hole in the ground to multiple effect systems with industrial type controls and sensors etc.

It seems that these systems can be categorized in 5 groups and combinations hereof. It also seems that the higher yield, the higher the complexity in the system is.

The quest for all of us working in this field is to find the sweet spot where price, yield, rigidity, lifespan, design, water quality and ease of maintenance is balanced out and gives the world a useful device or system.

Small solar distillation systems is still way less than 1% of the water purification market. A shame, since the power is free and dustillation gives the cleanest water possible.