Construction World March 2015

ENVIRONMENTAL ENGINEERING

Design for SOLAR ENERGY By John Hope-Bailie, a director of power provisioning specialist, Powermode.

Globally, the move towards the construction of green or sustainable buildings is gaining momentum. The terms refers to an environmentally responsible structure that is resource efficient. The concept encompasses all stages of the building’s life-cycle, from siting to design, construction, operation, maintenance, renovation and demolition.

Background This requires close co-operation between the design team, the architects, engineers, and the client at all project stages. One of the objectives demanded by many supporters of modern, sustainable buildings is carbon neutrality. Carbon neutral buildings are engineered to release no greenhouse gases at all or to balance the emissions they produce using trade-offs. These emissions usually come from elec- tricity consumption, the burning of fossil fuels, on-site waste water treatment and a range of other processes that might be performed in the building. Key to reducing emissions is the use of renewable energy resources, of which one of the most popular and prolific is solar power. Solar power is a clean sustainable energy technology drawing on the planet’s most plentiful and widely distributed renewable energy source – the sun. Emerging green building design prac- tices accept solar power as an ideal comple- ment to the classical building design goals of economy, utility, durability and comfort. Embracing solar power Today, designers and architects are looking beyond the now traditional solar-powered hot water geysers – which remain important elements in solar-powered buildings – to embrace the full extent of solar photovoltaic (PV) power generation. Solar PV installations convert solar radiation into direct electricity current using semiconductors that exhibit a photo- voltaic effect. Solar PV panels or modules are composed of a number of solar cells which transform sunlight into electricity

without the need for moving parts or envi- ronmental emissions. How solar PV system works In a solar PV system the PV modules are connected to create an array, either in series or in parallel configurations depending on specific voltage and current requirements. Combiner boxes are used to combine the inputs from multiple strings of modules into one output circuit. An important component of any array is the inverter which converts the DC current from the PV modules into an alternating current (AC) that can connect seamlessly to a building’s conventional electricity wiring circuits. In a grid-tied installation (where the solar circuitry is linked to the utility company’s grid, for example) the inverter is also tasked with sensing the utility power frequency and must synchronise the PV-produced power to this frequency. When utility power fails (due to a power outage) the inverter will automatically stop producing AC power to prevent ‘islanding’ or putting power back into the national grid when workers might assume the system is de-energised. This safety feature is built into all grid-tied inverters. Optimising electrical infrastructure One of the benefits of designing a green building from the outset is the optimisations that can be made in the electrical infrastruc- ture. Essential and non-essential circuitry (from a solar perspective) can be designed

and then installed at the construction phase in a simplified process, compared to a retro-fit. No ‘chopping and hacking’ required. For example, burglar alarms, outside lighting and key main lights inside the building can be treated as essential and given priority, while swimming pool pumps, air conditioning and similar systems can be treated as non-essential. This becomes a key exercise, especially if battery backup and storage is to be included in the design. In the domestic area, for example, the solar PV-based house will have a number of special design features, including non-elec- trically-powered ovens and hobs, solar powered swimming pool pumps (set up to run during the day to minimise storage demands), LED lights and a lack of under- floor heating – the planning and simplifica- tion of which ahead of construction will mini- mise costs. Energy efficient guidelines Despite any official encouragement or support for solar installations in South Africa, many architects are beginning to design buildings following energy efficiency guidelines. These include creating structures that readily integrate solar PV panels and systems, rather than fitting them ‘as an after- thought’ to existing structures. The efficiency and reliability of solar installations including PV modules, inverters and batteries can be substantially improved in residential, commercial and industrial buildings by their architects’ early ‘buy-in’ to solar technology. Before setting out to design a ‘solar- friendly’ building, it is important for archi-

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CONSTRUCTION WORLD MARCH 2015