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The Debate: Green Roofs vs. Solar Panels (Part 2 of 2)

Some say paint them white, some say create public space but two of the greenest uses for a roof top are still competing for space.


Holly Wu, Director of Marketing
for Asia Pacific, Middle East,
and Africa, Suntech Power
Holdings Co., Ltd.

Why Solar? It’s Time to Look Up

Think about it. Almost all of the energy that humans consume is really just some form or byproduct of solar energy from plants, to animals, to fossil fuels. The sun ultimately powers everything we do and everything we make. Everyday, houses and buildings around the world are bathed in nature’s original source of energy and life. In just one hour, the sun provides earth with enough energy to meet our annual electricity demands.

Today, anyone can look up and directly harness the sun’s energy. We no longer need to hazardously dig miles under the ocean to extract and combust fossilized remains of solar energy. With advanced photovoltaic technology, you can elegantly turn abundant solar energy directly into electricity without noise or emissions that will power you home, your business, or your community.

Healthy Returns on Investment

A solar installation is a one-time investment. Solar panels can be guaranteed for at least 25 years, and will probably last for several decades longer. So once you make the initial investment, a solar installation will continue to produce clean electricity as sure as the sun shines. The levelised cost of electricity (measured in $/kWh) produced over the lifetime of the solar system will likely become cheaper than the price of retail electricity from the grid. This milestone is called grid parity, which we have already achieved in several markets with high electricity prices and lots of sunlight, such as Hawaii and Italy. Solar panels will keep your electric bill low for decades despite the rising costs of fossil fuels. In some places, it is not uncommon for individuals to recoup their initial investment after eight or ten years, after which they benefit from decades of free and clean electricity. At the same time, a rooftop solar installation will typically absorb between 15 percent and 20 percent of the sun’s energy, which otherwise would become heat, thereby reducing a building’s air conditioning demands.

From 50W to 5,000,000W

Solar technology represents the world’s most scalable method of electricity generation. In other words, anyone can directly harness the sun’s energy; from 50Wp installations for basic lighting, to 500,000Wp rooftop installations for factories or theatres, to 5,000,000Wp installations for powering entire communities. Some Building Integrated Photovoltaic (BIPV) products replace traditional construction materials (such as a shingled roof or a concrete wall) with structural materials that generate electricity. Rooftops can become a solar array, with no additional or exterior mounting materials required and windows can become electricitygenerating by applying a thin film coating on the glass surface. If you have the rights to just a bit of land or rooftop space, then you can use solar panels to directly harness nature’s original source of energy and life.

It’s Your Future

The environmental and social costs of carbon-based energy production are staggering. Solar power not only reduces heat and energy consumption but replaces the source of energy to one that emits nothing. Additionally it provides energy security where carbon resources alone cannot provide this.

In conclusion. The world needs more individuals and communities to show leadership, take responsibility, and demand a better way of energy production. Where better to start than your own rooftop? It is not a question of if we can. It is a question of if we will. The sun shines on us all, rich and poor alike but we must decide how we will use that energy.


Bruce Rowse, in CarbonetiX, Australia

From an energy consuming perspective having solar panels on one’s roof is always an excellent approach as it is possible to generate at least the electricity on site and perhaps even put some of it back into the grid. It also looks great as it promotes one’s environmental credentials, which is why lots of government organisations and businesses prefer them to energy reduction strategies. They are more high visibility. Very importantly PV panels are much more affordable and easier to retrofit than transforming a hitherto normal roof into a green roof despite the high cost of the panels and inverters.

Realistically though for larger energy consumers the solar panels will make little more impact aside from their visibility. A small PV system in most cases covers only 2-5% of a site’s electricity usage, There are few sites that have either the budget or the roof space to fit a large enough system to substantially reduce power usage.

A better strategy for financial and/or environmental gains is to make a building as energy efficient as possible through means involving changes to the HVAC and lighting systems as well as improvements to the building envelope. Insulation, draft stopping and shading are some of these other improvements. So does ‘green roofing’ qualify as one of these measures? Yes, absolutely! If it can be done; the benefits are numerous. Green roofs provide extra protection against summer heat and winter cold as they act as insulators and even help in reducing noise. Green roofs conserve energy required for heating and cooling therefore reducing the dependency on energy hungry air conditioning systems.

Previously unused ‘waste of space’ can be turned into useful space as green roofs are usually designed to be enjoyed by building occupants. A roof garden can provide a relaxing environment to employees, who potentially could grow flowers or even fruit and vegies to eat. In addition it could provide a habitat for animals. Some people even use them for beekeeping.

Obviously a green roof reduces greenhouse emissions by absorbing CO2. So from a pro-environmental viewpoint green roofs offer many advantages over PV systems.

However, constructing a green roof can be quite costly and the long-term energy and maintenance savings should be considered. As always it is much more affordable to design and construct a new building than converting one.

What are the economic benefits?

According to computer generated building information models, a building with a green roof could expect to reduce its summer cooling energy by 25 percent and reduced heat losses in winter could show a similar saving on heating costs. Therefore, the potential for such a building to reduce its HVAC equipment rating is considerable. As can be seen above, solar panels alone wouldn’t offer similar savings, unless they are super-sized to match the buildings electricity consumption meanwhile other benefits of a green roof would not be attained.

In conclusion more environmental benefits are presented from green roof as compared to solar panels, however obviously ease of installation and cost are a major factor. It could be argued that the best benefits are provided by solar panels combined with a green roof as these can greatly improve their efficiency – but that’s another story….A building with a green roof could expect to reduce its summer cooling energy by 25 percent.

RFP Eco-Build magazine is Asia’s first title dedicated to promoting sustainability and an environmentally friendly approach to our built environment. An essential publication for investors, developers, government officials, real estate occupiers and the architects who create the buildings and plan the cities in which we work, live and play. For more information about RFP EcoBuild please visit www.ecobuildmagazine.com. Copyright for this article resides with RFP Media Services Ltd. If you would like to reproduce the article in any form please contact the Publisher at cs@rfpmagazine.com.