Why are you using abrasive particles?
I am using silicon carbonate particles because, after some searching, it was the only small black particle I could find that was available presorted into the approximate size that I needed and available in a quantity that I needed. There are MANY types of particles out there, and I have no doubt that my choice of silicon carbonate is not the best choice. Its just used what I could find off-the-shelf. If a particle could be found that was soft or round, it would be a much better choice because it would help to solve the crazing problem. If you have an idea about a particle, just drop me an email or post a comment.
Why are you trapping the particles in the panel and not just using black fluid?
When I started this, black fluid is the first thing I came up with. I research it a bit and found that people had tried this idea out in the 70's and found a few problems, including the staining of the inside of the panels and the difficulty in maintaining a suspension. However, for me there is one big issue that I have with the idea: its messy! What we are talking about here is filling the tank with INK.
To really understand why I don't like this solution you have to understand what I intend to use the panels for: cheap solar space heaters. The idea is a stand-alone water tank/pump/controller that sits in the corner of a room. An insulated hose goes onto the roof and captures heat from the panels. The unit simply radiates the heat into the room and stores heat in its tank for the night. Since space heating is the most significant source of energy consumed in a home in north America, and since the majority of house-hold heat comes from the burning of fossilize fuels, I think this is THE application for solar panels. They would pay for themselves in two years and could be easily installed in almost any home. Think of it as a "solar fire place". The unit would tell the user exactly how much heat has been captured and how much it has saved the owner in heating costs and also pounds of CO2.
Now, suppose that this device was filled with black fluid. If a leak sprang, or really anything happened that let loose this liquid into the room...oh boy! The ideal fluid here is water. I am going to work really hard to insure that water is all that is ever needed. When the owner installs the unit they can fill it from their sink. When they want to move it, they can empty the water into their garden or down the drain. If a leak springs or the unit spills, they have water to mop up not ink or chemicals. Water is also much cheaper and has a huge heat capacity. Its perfect really, except for its freezing point.
Have you tested the efficiency?
Yes, but...the problem is that my first prototype leaked a little bit and I did not insulate it because of this. Efficiency measurements without the insulation is pointless. My measurements showed me two things. First the panel was as efficient as I could want given the condition I measured it in (>800w per M^2). But again, without insulation, these numbers are pointless. Second, the variability in my set up was huge. I was measuring the input and output water temperatures and the flow rate. What I need to do is use a circulation pump on a close system and measure the increase of temperature over time. When I have another prototype panel that in insulated i will do this. However, the physics of the design and the functionality of the first prototype lead me to think it will be just as efficient, or more efficient, then traditional panels.
Why don't you just use black plastic as the absorber?
The whole reason for this blog is to solve the overheating problem. This occurs when you have a well-insulated panel build from plastic. The key here is "well insulated". If its not well insulated it will not work in the winter, but it will also not overheat. If you insulate the panels, they will work in the winter but they will overheat (and melt) if you do not remove the heat. The particle panels turn off, thus allowing me to build well insulated panels out of plastic. The result is heat in the winter.
