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Solar quest: how to harness nature to power homes

Options for lowering your carbon footprint may be limited at home, but solar and green energy developments are opening up a range of new possibilities

PUBLISHED : Monday, 26 June, 2017, 9:21am
UPDATED : Monday, 26 June, 2017, 9:21am

If you’ve ever taken a dip in one of our city’s public swimming pools, its waters were likely warmed by solar power.

You’ve probably been in a building powered by solar lamps and photovoltaic (PV) installations – Hong Kong Museum of Art, for example, or Kowloon Hospital – or strolled after sundown by the glow of LED solar lamps installed in various parks around the city.

But at home, it’s a different story. Unless yours is one of the few private developments to incorporate renewables among their energy sources, or you live in public rental estates where partial use of PV systems is now encouraged, the chances to harness nature to lower your carbon footprint are limited.

This is despite the fact that Hong Kong is blessed with abundant sunshine, a government pushing green energy to meet its carbon-reduction targets, and,  experts say,  countless numbers of urban rooftops which are eminently suitable for solar systems.

The question is, though, who owns those rooftops?

According to local legislation, says architect Kevin Chu of COC Design, solar panels added to a building, which has multiple owners, may be deemed an illegal structure.

In the case of his own Discovery Bay mid-rise apartment, this has prevented Chu from installing the solar set-up he would like. He’s had to settle for outdoor lamps, creating a cosy rooftop space with solar-powered LED lamps purchased online (from suppliers on sites like www.alibaba.com/ and https://iprice.hk/solar/ ), also available from outdoor living retailers such as Maori Furniture.

“On average, a rooftop of around 1,200 sq ft [my size] you will use about 10 area lights,” Chu says. Since most lights are LED bulbs, this means a power usage of about 22W each, he reasons – or about 220W for lighting the space –  “which would cost about HK$100 per month for the lighting bill”.

“With solar lighting, the cost is zero – although one has to remember that during cloudy days the lights need two to three days to fully charge,” Chu says.

However, the installation – where permissible – of 6kW of solar panels (costing around HK$40,000), plus a 2kW wind turbine (costing around HK$7,000), could generate 8kW of power in ideal conditions within a day, Chu says. On the basis that the average, Hong Kong household’s summer usage is 20kW per day, such a set-up would nearly halve the home’s monthly electricity bill.

“So by spending HK$47,000 on such a system [not counting labour costs] you would gain a return in about six years,” Chu says. If the household converts all electric lighting to LEDs, the average daily usage drops to 15kW per day as old style halogen or filament bulbs use more than five times as much energy, he adds.

Householders seeking greener energy can replace their window glass with energy-harvesting solar glass, if they are renovating their home. Window replacements are usually permissible under Hong Kong building regulations, Chu says. Energy-harvesting solar glass is readily available now, he adds; much of it is produced in China.

Some of the main buildings at Hong Kong Science Park, whose Phase 3 is one of the largest projects in Asia that puts sustainable building practice into action, have solar cells built into its windows, demonstrating how such systems (called Building Integrated PhotoVoltaics, or BIPV) can be incorporated into a house or building in a discreet way. The solar glass generates electricity, while still being aesthetically pleasing, and replaces the need for reflective glass and/or window shades to shield the occupants.

Another option is to install a piezoelectricity flooring system, such as that used in the Zero Carbon Building show flat, in Kowloon Bay, which harvests electrical energy from the mechanical stresses caused by the motion of walking across the floor.

The future holds more promise for greater domestic application of green energy systems. For instance, Tesla, the electric car maker, has developed an architectural roofing system for homes which turns sunlight into electricity.

It is comprised of two types of tiles—solar and non-solar. Customers can select how many solar tiles they need based on their home’s electricity consumption.

When viewed from street level, Tesla’s Solar Roof looks like ordinary roofing tiles. With an integrated with Powerwall home battery system, energy collected during the day can be generated, stored and used day and night, providing uninterrupted power even if the grid goes down.

The company claims that the roof will pay for itself over time – a period which would vary depending on various factors, such as roof size, the price of local electricity, and annual sunlight hours.

The Tesla Solar Roof is being launched in the US this summer, with roll-out to overseas companies slated for 2018. No announcement has been made about plans to supply the Hong Kong market.

Scientists around the world are also working to develop paint which can absorb solar energy – you simply apply it to a building’s façade.

Meanwhile, Chu is part of a team attempting to develop solar-absorbing blinds, with photovoltaic cells embedded in the fabric, which may be fitted either inside or outside any window.

Finally, energy provider CLP has a solar energy assessment service which can help householders to identify opportunities to generate greener power for their homes. You can register for the service at www.clp.com.hk.