Solar glass is used to replace conventional construction materials such as glazing or cladding, whilst also generating electricity on site.
In multi-storey buildings where roof space is often limited, façades and windows usually offer the most potential for electricity generation, thus the development of solar glazing is set to play an important role in the growth of ‘urban micro-generation’.
As well as being aesthetically pleasing and visually innovative, solar glass can improve the return on investment from the building, the more so if the product used is MCS certified and thus able to qualify for the Feed-in Tariff.
Transparency varies from 0% (fully opaque) to 50%, with a choice of colours / aesthetics on offer.
Solar glazing can be used in many ‘BIPV’ (Building Integrated PhotoVoltaic) applications:
|Polysolar PS-A opaque series panels (4.6 kWp), Future Business Centre, Cambridge|
The design of any building integrated (BIPV) solar system needs to optimise solar energy generation whilst complying with Building Regulations, meeting the desired aesthetic, meeting economic constraints and allowing for future maintenance.
Solar glazing can achieve the following functionalities:
As with standard roof-mounted solar panels, there are two types of solar glass available, performing in line with their non-building integrated counterparts:
Crystalline technologies generally provide the highest ‘STC’ (standard test conditions) efficiency values, between 12% and 17% for multicrystalline modules and up to 20% for monocrystalline modules.
The STC efficiency of thin film technologies typically ranges from 6% - 8% for amorphous silicon and up to 13% for CIS modules. However ‘standard test conditions’ – radiation of 1000W per square metre at a temperature of 25°C – rarely apply in reality, and the STC efficiency does not necessarily reflect the yield, or energy output that can be derived from these modules over a year in a given location or position.
Thin film technologies tend to operate optimally at 700 to 800 W/m2 radiance and continue working down to very low radiance levels: ~10% sunlight. Unlike crystalline modules which require direct sunlight, thin film works in ambient and reflected light, on the dullest days. Thin film exhibits less degradation than crystalline cells do at high temperatures.
The performance differentiation in different light levels should be considered with reference to the geographic location of the project, the local climate, the orientation of the panels on the building and the application. PV panels on a vertical façade will receive lower light levels than those optimally angled on a roof. Equally those facing North will receive less direct light than those facing South.
As well as different aesthetics (see below) thin film solar glazing has various advantages which need to be considered with reference to each specific project. These are set out on our dedicated 'thin film' page (under 'Why thin film?').
Left: Polysolar PS-CT-64/48 units (2.8 kWp), Solar Bus Shelter, Canary Wharf
Right: Polysolar PS-MC-SE monocrystalline glass panels
The effect of transparency is commonly achieved in the PV module by the combination of transparent unoccupied areas and a pattern of opaque solar cells. The arrangement and distribution of the solar cells within the module thus controls the degree of transparency. This makes it possible to create interesting and innovative light effects. If the module is required to have less transparency, the intermediate areas not filled with cells can also be coloured.
Solar windows have an opacity varying between 50% transparent and fully opaque.
Achievement of ‘semi-transparency’ depends on the underlying technology. With crystalline cells, light transmission is adjusted by altering the spacing between the cells. With thin film, the active layer is partially removed to allow the light to pass through, or an ultra thin film deposition of the active solar materials is combined with two layers of transparent conductive coatings.
Conventional solar cells are generally black or blue in the case of crystalline silicon and brown or black with thin film.
To achieve colour effects that differ from the cell colour, coloured laminates, coatings or films can be used. This makes it possible to create interesting effects such as logos on PV modules or colours that match the existing building. A compromise between design and output must always be found when designing coloured solar modules.
The Romag PowerGlaz product is manufactured in the UK. Each pane is custom made, ensuring a high quality finish.
The glass can be ordered with a tinted finish to meet specific project requirements. It can be single-glazed or double-glazed as required.
Dimensions are specified on a case-by-case basis but the maximum sizes are 4m x 2.2m for single-glazed units and 3.6m x 2.1m for double-glazed units.
The PowerGlaz solar glass comes with the usual solar PV warranty package:
Performance is guaranteed to be at 90% of original output after 10 years and at 80% after 25 years.
The product is guaranteed against visual defects for 5 years.
Colourless / Black Opaque Thin-Film PV Glazing (cadmium telluride)
|Polysolar PS-CT-64 20% transparent panels (7.68 kWp), Donnington Park Farmhouse Hotel|
Partially Transparent / Opaque Amber Thin-Film PV Glazing (amorphous silicon)
|Polysolar PS-C901 transparent panels (15.7 kWp), Sainsbury's Petrol Station, Bishop's Waltham|
This glazing is made using amorphous silicon technology, utilising the equivalent of powdered silicon in very small quantities. This is vacuum deposited along with transparent, conductive oxides on both glass surfaces with the active PV material between as a semiconductor. The glass is then laminated together as a sandwich to create a uniquely translucent module.
Partially Transparent / Opaque Black Thin-Film PV Glazing (amorphous silicon tandem)
Incorporates micromorph technology to achieve high efficiency and sleek aesthetics. Ideal for BIPV curtain walling and facades.
Glass/glass monocrystalline and polycrystalline (PS-PC-SE) PV panels
Similar in appearance to standard solar panels, glass / glass monocrystalline and polycrystalline panels achieve the highest power densities available from solar glass. The panels are available in a range of colours and transparencies.
Key features are as follows: