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Last edited 23 Sep 2022
Bio-solar is a relatively recent term which combines a biologically derived element with a solar element or function. It is used in relation to a variety of products from buildings, to systems, products and processes.
Bio-solar is sometimes used to describe a building that is based on passive solar design and also constructed using primarily bio-based or natural materials. It is also more specifically used (particularly in Germany) to describe a building design with two structural layers or a building within a building.
These buildings are based on the principles of a trombe wall or a winter garden, as a high proportion of the second structural envelope is often transparent, so the air between it and the internal building remains warm. This means the internal building is not exposed to the temperature differences of the outside or to the elements, so can be built with lower levels of insulation, air tightness and weather protection.
The term bio-solar roof describes a roofing solution that combines energy generation through the installation of photovoltaic panels, with an intensive or extensive green roof. Apart from the known benefits of green roofs, such as reducing the urban heat island effect, water retention and biodiversity, bio-solar roofs can be beneficial to the efficiency of photovoltaic panels because many run most efficiently when the ambient temperature is around 25 degrees. A biosolar roof can help keep ambient temperatures lower than with a standard black or white roof construction, with some studies estimating a increase of around 1% in the electricity generating potential.
The Queen Elizabeth Olympic Park, in London, UK, and the New Garden Quarter, Chobham Farm installed a number of bio-solar roofs as part of a green infrastructure programme, which was then developed in to a Green Infrastructure Guide which was published as a freely available industry tool for designers that can be downloaded here.
The term 'bio-solar panel' might be informally used to describe biological photovoltaics (BPV), or biophotovoltaics, as well as living solar panels because they involve microbial processes. These are are a new breed of energy generating solar photovoltaic panels, similar to a fuel cell, which primarily comprise a biological photosynthetic material to capture solar energy and directly produce electrical power. As a relatively new field of research, biosolar panels may vary considerably in their design approaches as well as the materials used. In principle they are defined by the type of light harvesting material used and the biological material used for electron transfer to the anode.
The Department of Biochemistry at the University of Cambridge describes Biological Photovoltaics (BPV) as; "..biological electrochemical systems, similar to microbial fuel cells. In a BPV system, photosynthetic material is employed in the anodic half-cell where it oxidises water using light energy. Some of the electrons generated by water photolysis are transferred to an electrode (anode). At the cathode, a reaction with a relatively high potential consumes electrons and creates a potential difference between the two electrodes, driving electrical current through an external circuit."
It states: "BPV systems can employ whole algal or cyanobacterial cells as the light harvesting material, or purified photosynthetic sub-cellular fractions such as thylakoid membranes or isolated photosystems. Sub-cellular photosynthetic material is able to transfer electrons to the anode more effectively, but cannot repair itself. In contrast, we have demonstrated that BPV systems using whole organisms can generate power for months at a time. This ability to self-repair and self-assemble will hopefully make BPV systems a cost-effective alternative to conventional solar panels."
Bio-solar electrolysis or solar assisted microbial electrolysis is a complex area of research but essentially uses a variety of techniques related biological photovoltaics to directly split water into its component parts of hydrogen and oxygen.
The most common types of electrolysis today are alkaline electrolysis, which is a well established technique and the newer method of proton exchange membrane (PEM) electrolysis. An electrolyzer has two metal electrodes sitting in a container of salted water (electrolytic solution), when an electrical charge is applied, hydrogen and oxygen separate to the electrodes. The latter, although with some issues, is seen as having great potential in the field of hydrogen production because of its ability to benefit from renewable energy which reduces the carbon footprint of producing hydrogen fuel.
Hydrogen is seen by many as having great potential as a zero carbon fuel because it contains approximately 3 times the energy of natural gas or gasoline and is abundant on earth. Currently 95% of hydrogen production involves steam reforming of natural gas (grey hydrogen) or coal gasification (brown hydrogen). Using solar assisted microbial electrolysis or bio-solar has the potential to produce what some call green hydrogen.
Microbial electrolysis cell (MEC) systems for hydrogen generation are composed of a microbial fuel cell (MFC) and a bio-photoelectrochemical cell (BPEC) but the field is in continual development and variations are tested regularly.
 Bio-solar purification (BSP).
The EU funded project BioSolWaRe-LIFE researched phytoplankton photosynthesis and photo-oxidation (oxidation caused by light) in closed systems to remove dissolved compounds and hazardous bacteria from wastewater. Whilst this project did not complete its objectives, a variety of other approaches have had greater success using solar radiation to destroy bacteria and clean wastewater. One such Bio-Solar Purification system patented by Helio put technologies is use in the Middle-East to recycle water for uses such as plant watering.
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