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Tue 12 Jan 2010 04:00 AM

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The sun shines on BIPV

The integration of photovoltaics into building structures means that facilities managers are increasingly having to look at energy modelling and resource utilisation issues. fmME takes a closer look at this latest trend.

The sun shines on BIPV
A worker at the 10 MW Masdar solar plant in Abu Dhabi.
The sun shines on BIPV
Masdar City has the first grid-connected solar power plant in the UAE.
The sun shines on BIPV
An example of PV integrated into a building envelope.

The integration of photovoltaics into building structures means that facilities managers are increasingly having to look at energy modelling and resource utilisation issues. fmME takes a closer look at this latest trend.

Energy modelling is a critical component of building design at the concept stage. MEP engineers are playing an increasingly vital role in determining the energy efficiency of new building projects, which is necessary to ensure their compliance with the soon-to-be-regulated ‘green’ building ethos, as well as promoting their long-term sustainability. Apart from the regulatory perspective, many think such an approach also encompasses an ethical or moral responsibility, meaning the ‘feel good’ factor of renewable energy.

PV installations throughput the world reached a record high of 5,95 GW in 2008, representing a staggering growth of 110% over the previous year, according to market research from Solarbuzz of the US. A total of 81 countries contributed to this total market, lead by Europe, Spain, Germany and Korea. On the supply side, world solar cell production achieved a consolidated figure of 6,85 GW in 2008, up significantly from 3,44 GW a year earlier. Overall capacity utilisation rose to 67% in 2008, while thin-film production (the latest efficiency advance in PV panel technology) rose a phenomenal 123% increase in 2008.

When it comes to solar power in the region, many think of vast solar energy ‘farms’ spread across the deserts of the UAE, taking advantage of both the region’s high insolation factor and its availability of large tracts of open space. This is quite removed from the normal electro-mechanical and plumbing ambit of a typical MEP contractor. But there is an aspect of PV technology dovetailing with the construction industry that offers huge scope for the MEP sector.

Facing the change

Known as Building-Integrated Photovoltaics (BIPV), pundits claim this is poised to change the face of construction, energy and urban planning in the coming decade. The Department of Energy in the US, for example, has estimated that BIPV technology has the potential to generate half of its electricity needs.

This goal seems increasingly achievable, as solar energy is expected to attain ‘grid parity’ by 2015, meaning it will be able to supply electricity as cost-effectively, or even more cheaply, than electricity produced by conventional means such as coal-fired power stations. What better way then to capitalise on the utility potential of solar energy by applying it to the building industry, which is struggling to reduce its own carbon footprint in order to save precious natural resources?

Kyocera Solar, one of the world’s largest vertically-integrated producers and suppliers of solar energy products, comments that BIPV represents the combination of proven renewable power-generating technology and the building exterior or façade, using tried-and-tested construction methodology. (Kyocera solar modules are distributed in the UAE by Green Energy LLC). The main implication is that solar panels are taken into account with the structure itself being built. This immediately offers a plethora of benefits:

• Financial appeal – costs are combined for a building material and power generation;

• Distributed power generation – greater independence and less reliance on centralised fossil fuel power sources;

• Economies of scale – leverages a large inventory of constructed surface area for renewable power production;

• Improved real estate values – capitalise on short- and long-term property investment;

• Easy integration to standard construction practice – can be retrofitted to existing construction or installed new;

• No independent support structures – minimise system cost;

• Hassle-free operation – low to no maintenance, with no moving parts; and

• Improved aesthetics – avoids the look of being an afterthought or add-on.“Interest in BIPV, where the PV panels actually become an integral part of the building, has been growing worldwide in the energy and construction industry. Solar panels can be integrated into many types of exterior materials, including roofs, walls, shadings, or windows. BIPV not only creates environmentally-friendly solar power, but enhances co-existence with nature and visual harmony,” argues Kyocera. Put simply, BIPV allows the construction industry to ‘harness the sun’.

Global leader

Scheuten is a global leader in solar power systems, with a module manufacturing facility in Germany. Scheuten Middle East MD Reza Shaybani commented that incorporating PV technology into the building envelope itself is not nearly as esoteric as it sounds. Instead it represents a natural convergence of various trends. These are the large unused surfaces of a typical high-rise building (especially in a place like Dubai), combined with the unlimited power of the sun and the current ‘green’ trend.

“Let us use this potential!” is Shaybani’s simple, yet forceful, message. “Why integrate PV in façades and roofs? It reduces the dependency on grid-supplied power, especially during peak hours, while simultaneously functioning as a façade material. Thus not only does it look modern and innovative, but it produces power as well,” said Shaybani.

Seamless integration

The company’s Multisol modules can be integrated seamlessly into the architecture of any building, or even retrofitted without any major problems. They are available in three different sizes and various performance classes, meaning optimal flexibility for customised requirements. Features include a sturdy aluminium frame for straightforward installation, together with a patented pluggable connection system. The frame has a wide glass insertion depth to be able to withstand winds, while the plug system at the edges ensures solid interconnection of all frame components. The modules boast such attention to detail as an internal groove providing rapid drainage for any condensation.

The International Energy Agency (IEA) comments that, “in order to assess the potential of BIPV, an analysis of the building stock with respect to suitability of the building skin for PV deployment is required. Some building surfaces will have technical limitations; others will have limited capabilities to generate PV power due to inadequate orientation, inclination or shading effects.” The IEA defines such suitability in two main categories:

• Architectural suitability includes corrections for limitation due to construction (HVAC installations, elevators, terraces, etc.), historical considerations, shading effects and use of the available surfaces for other purposes; while

• Solar suitability takes into account the relative amount of irradiation for the surfaces, depending on their orientation, inclination and location, as well as the potential performance of the PV system integrated into the building.

The IEA concludes that, with a good solar yield assumed to be 80%, the achievable level of solar-power production by PV roofs and façades varies from 15% to 60% (the ratio used is BIPV solar-power production potential over current electricity consumption). The achievable level depends ultimately on the building area available, as well as on solar radiation levels and electricity consumption. All these factors imply that BIPV could have a massive potential in the UAE, where major players like Scheuten are positioning themselves carefully to take advantage of the ‘desert renewables boom’.

Future potential

So let us look a bit closer at what BIPV entails, as well as its future potential. The National Renewable Energy Laboratory (NREL) notes that “the integration of PV panels into buildings during construction is one of the fastest-growing segments of the solar industry.” Steven Strong from Solar Design Associates, described as North America’s oldest and most respected renewable-energy design firm, says there is burgeoning international interest in using PV elements as an ‘exterior weather skin.’ He says that PV specialists and innovative designers in Europe, Japan and the US are now exploring ‘creative’ ways of incorporating solar power into their work. “A whole new vernacular of solar energy architecture is beginning to emerge,” comments Strong. This is good news for the MEP sector, because where there are architects, there is a need for MEP contractors and consultants …

A complete BIPV system comprises the following elements:

• PV modules (thin-film or crystalline, transparent, semi-transparent or opaque);

• A charge controller to regulate the power into and out of the battery storage bank (in standalone systems);

• A power-storage system;

• Power-conversion equipment (including an inverter to convert the DC output from the PV modules into compatible AC current);

• Back-up power supplies (such as diesel gensets); and

•Appropriate support and mounting hardware (wiring and safety disconnects).Below are some important design considerations associated with BIPV systems.

Shift the peak:If the peak building loads do not match the power output of the PV array, batteries can be incorporated to offset the most costly load periods. This system can also serve a dual function as an UPS;

Ensure adequate ventilation:High operating temperatures have a detrimental effect on PV conversion efficiencies. This means allowing appropriate ventilation behind modules in order to dissipate the heat;

Integrated daylighting and PV collection:By using semi-transparent thin-film modules, or crystalline modules with custom-spaced cells between two layers of glass, designers can use PV to create unique daylighting features in façade, roofing or skylight PV systems. The BIPV can also mitigate the additional cooling load and glare associated with large expanses of architectural glazing;

Shading devices:Conceiving PV arrays as awnings over viewing-glass areas of a building can provide the necessary passive solar shading. When sunshades are taken into account as part of an integrated design approach, chiller capacity can be reduced, while perimeter cooling distribution may even be totally obviated.

Relatively new

Finally, the Research Institute for Sustainable Energy (RISE) cautions that the use of BIPV is still relatively new.

“Ensure that the design, installation and maintenance professionals involved with the project are properly trained, licensed, certified and experienced in PV systems work,” it urges contractors.

While there are numerous companies in the UAE supplying solar-energy products and systems, the relative newness of the technology means there is a potential dearth of installation and maintenance experience. This is one arena where the MEP sector can stand the construction industry in good stead by filling this gap.

Examples of integrating PV into a building envelope

• Solar cells can be incorporated into the façade of a building, complementing or replacing traditional view or spandrel glass. These installations are often vertical, reducing access to available solar resources, but the large surface area of buildings can help compensate for the reduced power;

• PV can be incorporated into awnings and saw-tooth designs on a building façade. These increase access to direct sunlight, while providing additional architectural benefits such as passive shading;

• The use of PV in roofing systems can provide a direct replacement for batten and seam metal roofing and traditional three-tab asphalt shingles; and

• Using PV for skylight systems can be both economical and an exciting design feature.

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