Background/Tutorial/FAQ

Background

The practice of this project involves the capturing of sunlight with a concentrator (an object that concentrates light, in this case a parabolic mirror). The concentrator will have a focal point, the point where all of the light will be pointed towards, and that will heat up the object it is aimed at.
We intend for our purificator to work in Nigeria, a country which is very close to the equator and so, has generally constant amounts of sunlight. This means that we do not have to worry about changing the tilt angle of the parabolic mirror as the day progresses. If however, we were to modify it to work in a place like Philadelphia, that would be the first thing on our list to change.
Solar energy works as follows:
The Sun creates beams of sunlight which carry energy. This energy comes in the form of thermal energy and can be harnessed as such or solar panels can be utilized to change the solar energy into electrical energy. This thermal energy can be utilized to heat objects very well, particularly if a concentrator is used. A concentrator, such as a mirror, is an object that directs sunlight towards a small area, making the collective force larger.

Definitions:

Concentrator - an object that captures sunlight (or light in general) and redirects it, making it focus on a smaller area
Thermal Energy - energy due to heat, in the case of this project this thermal energy comes from the sun and is redirected by the concentrator
Distillation - the process of separating the component substances within a liquid through the process of boiling and condensation, in this project, the boiling will be accomplished through thermal energy from the sun redirected by the parabolic mirror towards a conductive metallic pot.

Tutorials

How to:

Collect/concentrate sunlight:

     To collect or concentrate sunlight, a reflective surface is required, preferably one that is curved in a parabolic way such that it can collect the sunlight and concentrate it on a single point, called the focal point. With a parabolic mirror, this is easily accomplished, as the mirror will concentrate the light on its own. We decided to buy one, not make one, because it would make the process much easier since none of us had any experience with working with glass. It was relatively easy to buy it : we got it off ebay.com.

Distill water:

      Distillation is a simple process, involving boiling and condensation. It works on the principle that different liquids have different boiling points and we can use these differences in boiling point to separate them.
      In order to boil the water, supply heat to a container, in this case an aluminum pot with heat applied from sunlight being redirected by the concentrator. Condensation is a little bit trickier. A tube must be attached for the boiled water to flow through, leading to another cooler, container, where the water vapor can condense and return to liquid form. A filter will be placed right before the cooler container to further remove impurities. We have hopes of using a charcoal filter with a sieve length of 0.5micrometers or less, but that all depends on the cost we accrue for other, very important parts. If we cannot, we will improvise with normal filters.

FAQs

Why did you decide to use a concentrator rather than electric solar panels?

         The choice to use a concentrator to redirect the light rather than electrical solar panels to boil the water was a simple one that came down to efficiency and price.
First of all, using electrical solar panels to conduct electricity didn't make very much sense, because doing that would be converting heat energy to electrical energy just to convert it back to heat energy in a heating coil. Because the solar panels would be ineffective at efficiently converting the energy, a lot of heat energy would be lost during the conversion process. This would require us to use multiple solar panels, which was not just feasible for our design( we want to be used by a family of six).
           Also, price factors weighed heavily on the decision. We did our research on the price of solar panels and the amount of energy we would need, and our calculations said that we would need many solar panels to supply enough energy to sufficiently heat up a heating coil. Each solar panel was going to be at least thirty dollars, which would have been financially impossible to accomplish for the group. The price for getting the panels was estimated to be about 2000 dollars.
On the other hand, using a parabolic mirror removed any problems with funding and also our calculations showed that it should supply ample energy to adequately boil the water.


What difficulties do you expect with executing this project?
   Having an up and running solar water purificatory system should not prove to be too much of a problem. But,we do expect challenges on the way.These challenges could include finding the most cost-effective way to solve the problems we might be presented with by this project. This might mean a lot of improvisation.
    How do you know the mirror system will work adequately?

We did the following calculations to find a general (almost certainly low-range) estimate of the amount of energy created and the amount of water boiled by that amount of energy.


Are you going to know if the water produced is actually pure? You can't just have someone taste it, right?

We intend to purchase a water purity testing kit from Amazon.com to test the water at the end. This kit will give us reliable readings on the pH levels, any metallic impurities in the water, and bacterial problems with the water as well. If the test comes back positive for impurities, we will add some improvements like better filters for instance.

Calculating amount of output for our proposed system:
milliJoules created by our system = solar constant*Adish*Time(seconds)
solar constant = 1.361 kW/m^2 = 136 mW/cm^2
Adish = pi*r^2, (we did this to simplify calculations as the surface area of a concave dish is tough to calculate and estimating it as a circle rather than a dish gives us less surface area, meaning our estimate is on the lower range)  
Time will be 3600 s, an hour
We decided on a dish with radius, r = 16.51 cm

mJ = 136*16.51^2*pi*3600 = 422180 J

Finding amount of water boiled with this amount of energy:
Q = 422180 J
422180 = m(4.18)*(60)
m = 1683 g/hr = 1.683 L/hr

How much does this project look like it is going to cost?
For now, we have put the cost of this project at $30 per group member( $150 in total). Due to improvisation though, this cost could go up slightly over the course of the following weeks.

How long do you hope this project will take?
We hope to have built and tested our project by week 9. We will then use the extra week to prepare for our presentation.

Where can I get more information on these kinds of projects?
Well, you can watch this video which gave us the idea of using parabolic mirrors, instead of solar panels here. Ignore the title, he doesn't technically have the power of 5000 suns.
Also, look at this article on CSP technology( Concentrating Solar Power) here