Moss Voltaics is a green façade system that aims to explore how moss might be used as a source of renewable energy and how it can be implemented to the urban scale.

Mentioned emerging technology is called bio-photovoltaics (BPV) which uses the natural process of photosynthesis to generate electrical energy. In this process, plants using light energy consume carbon dioxide and water from the environment to convert it into organic compounds. Those compounds are required for the vital processes of a plant.

“When the moss photosynthesises, it releases some of these organic compounds into the soil which contains symbiotic bacteria. The bacteria break down the compounds, which they need to survive, liberating by-products that include electrons.”

By providing an electrode for the micro-organisms to donate their electrons to, the electrons can be harvested as electricity.

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 to 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 for example.

A biophotovoltaic cell represents an organisation of units combined in series or parallel circuits. A unit is a fully operating bio-electrical system. It consists of the anodic biological material (moss), the anode, the cathode, the cathodic catalyst, the “salt bridge” that permit the positive charge (generally protons) to travel from the anodic biological material to the cathode. The anode represents the mixture of hydrogel and carbon fibres that help to attract the electrons. A 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 the first tests to check how the fibres coexist with moss and polyacrylate were made. One unit 100x100mm for the anode was mixed carbon fibres and hydrogel in cubes (sliced for thinner, smaller sheets) and 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 into the structure. For this, fibres with polyacrylate were mixed and moss was placed atop and pressed down plus, the moss was divided into small pieces and distributed over the same mixture. After 1 month, moss grew through the mixture of carbon fibre and hydrogel.

Design of the system:

Bricks represent a sort of container that can create a special microclimate which helps to keep moss alive. Inside the brick, the bottom part is glazed to make it waterproof and the rest is a porous clay without a coating. This clay absorbs water so that the system could be passive receiving water from rain where hydrogel retains liquid for a long period of time.

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 the clay, the remaining slip is poured off for later use.

Generally, there are few steps in making a plaster mould.

1. Forming a shape made of clay
2. Formwork around the matter plus several divisions for pieces of the mould
3. Pouring liquid plaster.

In this project, those items have been overstepped, the plaster mould was done with the milling CNC machine. So the shape was created digitally which means more 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 a .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 façade, so the scale of the first prototype was quite small considering it was a ventilated façade brick. As far as the customisation technique 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 number of pieces for the mould, the way the clay is cast). 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 one.

Two and more groups that were connected in series are combined in the parallel circuit to increase the current.