The system can work with other species of plants and algae, nevertheless moss was chosen because of its eligible properties. As mosses are commonly found in cities: in cracks between paving, on roofs, on walls and trees, the system can be well adapted into the urban environment. Advantages of mosses over higher plants include reduced weight loads, increased water absorption, no fertilizer requirements, high drought tolerance and low maintenance.
Compared with silicon-based photovoltaic cells, a solar cell that uses biological material to capture light energy would be cheaper to produce, self-repairing, self-replicating, biodegradable and much more sustainable. The manufacturing process is harmless to the environment. Furthermore BPV panels can exist in the places where solar panels are not efficient – northern countries with the lack of direct sunlight.
Biophotovoltaic cell represents an organization of units combined in series or parallel circuits. Unit is a full operating bio-electrical system. It consists of the anodic biological material (moss), the anode, the cathode, the cathodic catalyst, the “salt bridge” that permit to the positive charge (generally protons) to travel from the anodic biological material to the cathode. The anode represents the mixture of hydrogel and carbon fibers that help to attract the electrons. Hydrogel is a polymer that can absorb water up to 400 times to its weight, it keeps complementary humidity for the moss and it is pH neutral. The materials are not damaging any metabolism. Thus first tests to check how fibers coexist with moss and polyacrylate were made. One unit 100×100 mm: for the anode were mixed carbon fibers and hydrogel in cubes (sliced for thinner small sheets) + a layer of carbon fabric, the mixture was covered with moss. The cell showed 0,35 volts. Meanwhile “moss plantation” was set up wherefrom anode would be taken for embedding it to the structure. For this fibers with polyacrylate were mixed and moss was placed atop and pressed down + moss was divided in small pieces and distributed over the same mixture. After 1 months moss grew through the mixture of carbon fibers and hydrogel.
Design of a system. Bricks represent sort of a container that can create special microclimate that helps to keep moss alive. The bottom part inside that brick is glazed to be waterproof, the rest is a porous clay without a coating. This clay absorbs water, so the system could be passive receiving water from rain, where hydrogel retains liquid for a long period.
The first elements were made to see if the method of slip clay casting works. Slipcasting is a technique for the mass-production of pottery and ceramics. A liquid clay body slip is poured into plaster moulds and allowed to form a layer, the cast, on the inside cavity of the mould. For a hollow cast mould, once the plaster has absorbed most of the liquid from the outside layer of clay the remaining slip is poured off for later use. Generally there are few steps in making a plaster mold: a) forming a shape made of clay; b) formwork around the matter + several divisions for pieces of the mold; c)pouring liquid plaster. In this project those items have been overstepped, the plaster mold was done with the milling CNC machine. So the shape was created digitally that means accuracy and precision.
Receiving data. There was made a device that can read Lux, Humidity, Temperature and Volts every 5 seconds with sensors and save it directly to .csv file. Here is a graph with 4 days, where you can see the relation of voltage and humidity.
The initial idea is to go for the facade, so the scale of the first prototype was quiet small considering it as a ventilated facade brick. As far as the customization technic and the electrical components are functioning the shape transfers to a new design. It is predicted by the system of assembling, by the forces that are distributed through the whole volume, and by the specific conditions linked with the fabrication process (the size of bits for milling, the quantity of pieces for the mold, the way clay is casted). Elements are gathered by the relief on their side faces without adding any cement mixture. Electrical connections are passing through those system joints. Moss is not exposed to the direct sunlight, blocks provide the required shading.
One Unit is giving 0,4 – 0,5 Volts. Six bricks are connected in the series circuit to increase the voltage- 3 different modules, two of each ones. Two and more groups that were connected in series are combined in the parallel circuit to increase the current.