The transition to a fully-renewable global energetic system has to be done in small but sure steps. New inventions pave the way towards sustainable technologies, and their experimentation on small and medium scale improves their survival chances and lowers their implementation price.
One such invention is being developed in Australia, by a company named “Sunengy“. Their proposal is of a water-borne solar capturing system. Instead of putting the cells on the ground, occupying a lot of usable space, losing energy to cool them down, Sunengy’s LSA (Liquid Solar Array) technology combines a solar concentrator and a photovoltaic cell, with Sun-tracking and storm protection mechanisms.
Water is used to cool down the cells (resulting in longer life and better efficiency). The equivalent land-based 1 square meter concentrator must be provided with 1 square meter of convection cooled aluminum fin area to dissipate the 700 W of radiation absorbed by the PV cells and not converted into electricity just to achieve 80 °C cell temperature.
The whole LSA system can bear winds of over 100mph, protecting itself by sinking the lens into water. With time, sand and other impurities deposit on the lens, especially because of repeated sinking into water. A strategy was determined to wipe the dust from the surface with a thin rubber vane while the lens cover is underwater. This was tested and found to keep the lens cover dry and salt-free for over 500 immersion cycles. Hence it is expected that similar wipers will be required on production models.
Laboratory experiments showed that the system can output about 80W/m². The measured 5.3 amp steady output from the concentrator corresponds to 3.2 W (at 0.6 V out) or 80W/m2. The lens area is 16 by 25 cm or 0.04 square metres. The plot is scaled up to watts per square meter. The solar input is assumed to be 770 W/m2 of direct insolation in calculating the efficiency (clear sky in midwinter at 34 degrees latitude). The lens intercepts 31 W of direct sunlight (roughly 400*770W/10000).
Hence the direct sun overall efficiency is about 10% (from 3*100/31 %) with all optical and electrical losses. This represents the minimum that can be achieved with a poor grade of PV cell (the one used is about 14% efficient). Any production system is likely to do at least 35% better overall, simply by using a better grade of PV cell (19% is available cheaply).
The costs that such a system could save are tremendous, Sunengy saying they will be able to go lower than 60 cents/watt in the long run, with normal usage costs of $1.30/W, from $3 – the minimum nowadays.
If you want to see their system rendered in action you can click here and here (WMV video). Below is their system presented at Clean Tech Forum 2009:
Ah, offshore. That is a different story. I wonder how they cope with waves though, and the lenses are bound to act like sails, and also salt spray drys as a white crust on things like windows (I used to live in the islands) which would certainly not be good for the lens efficiency.
I don’t mean to sound overly skeptical, it just seems like the ocean is a very erratic environment compared to land, and the challenges are many.
The big problem that I can see it that you are limited to areas with lots of Sun, open space, and plenty of clean water (since there will be lots of evaporation), and not too much wind and dust as that would turn the water dirty and stick to the wet lens. I don’t think that is too common.
The other problem is that the system can’t be used on the top of buildings because the great weight of the water would require a very expensive roof.
I think they would have done better to cool the cells with water, but rather than keep it in a pool, use it for a hot water heater, which would increase the amount of useful energy it produces by over 75%. I figure since 10% is being turned into electricity, the majority of the rest must be turned into heat.
The idea was not to put these things on buildings’ tops, but rather deploy them offshore, where water is not a problem, and cooling them either.