Covering city buildings in vegetation – creating “green roofs” and walls – could substantially save energy by reducing the need for air conditioning on hot days, say researchers.
Green roofs and walls can cool local temperatures by between 3.6°C and 11.3°C, depending on the city, suggests their new study.
Eleftheria Alexandri and Phil Jones at the Welsh School of Architecture, at the University of Cardiff in the UK, mimicked the microclimate around and inside buildings using computer modelling. They compared local temperatures when buildings were made of bare concrete with when the concrete was covered in vegetation.
Such green surfaces are already in use – roofs that are strong enough to take the additional load can be covered with mosses, turf and even trees. In Switzerland, roofs covered in alpine plants that require little soil are becoming increasingly common. Walls can also be greened, often by climbing plants planted at ground level.
Temperature drop
The researchers compared the effects of green surfaces in nine cities around the world, including subarctic Montreal in Canada, temperate London in the UK, humid Mumbai (India), and tropical BrasÃlia (Brazil). In all cases, they studied the month during which that city sees its hottest temperatures.
They found that green walls and roofs would cool the local climate around a building in all of the cities – and the hotter the climate, the greater the cooling effect.
If, for example, a group of buildings in Riyadh, Saudi Arabia, is entirely clad in vegetation, the gap between the buildings will become 9.1°C cooler during the day, according to the researchers' model. The gap's peak temperature of the day is brought down by 11.3°C. And in London and Montreal, the peak temperature drops by just over 4°C.
Greening the walls only, and not the roofs, results in smaller effects. Maximum temperatures in London and Montreal, for example, drop by between 2.5°C and just over 3°C between the buildings.
Green surfaces cool local temperatures in two ways. Firstly, the green surfaces absorb less heat from the sun. Hot surfaces warm the air around them, so by cooling the surface, the vegetation also affects air temperatures. Secondly, the plants also cool the air by evaporating water in a process known as evapotranspiration.
Lowering demand
Being dense regions of concrete and paved surfaces, cities and towns lose the cooling effects of vegetation. This generates what is known as the "urban heat island" effect.
Alexandri and Jones say their results suggest the urban heat island effect could be countered by introducing green roofs and walls in cities.
They point out that, other than making cities more comfortable and safer to live in, green roofs could also significantly reduce the demand for electricity – most of which is generated by burning fossil fuels and therefore contributing to man-made global warming.
In recent years, Europe and North America have been hit by severe heatwaves, the effects of which are often most extreme in cities. In 2003, a heatwave in Europe is thought to have killed 35,000 people and hundreds died this summer in Eastern Europe. Research has shown that the frequency of extremely hot days has nearly tripled in Europe since 1880.
Eliminating air-con
"In addition to the fact that they add a further insulation layer to the building, the green surfaces can decrease air conditioning demands inside the building," says Jones.
In BrasÃlia and Hong Kong, he and Alexandri found that the need to air-condition a building during the hottest month of the year is eliminated if it is given a green roof and green walls. Buildings in these cities would normally need air conditioning in the afternoon and early evening.
In hotter cities, such as Riyadh, the number of hours when air conditioning is needed would be cut from 12 hours to just 5.
Some air conditioners still use chemicals that deplete the ozone hole and demand for air-conditioners is expected to rise as a result of global warming, so green buildings could help counter this demand.
Journal reference: Building and Environment (DOI: 10.1016/j.buildenv.2006.10.055)
Climate Change – Want to know more about global warming: the science, impacts and political debate? Visit our continually updated special report.
Energy and Fuels – Learn more about the looming energy crisis in our comprehensive
Catherine Brahic NewScientist.com
full article
Friday 28 September 2007
CFLs to replace traditional lightbulb by 2009
In a drive toward more energy efficient lighting, Mr Benn said 150 watt bulbs would not be replaced by retailers from January next year.
Then from January 2009, 100 watts bulbs would be unavailable – followed by the disappearance of 40 watt bulbs in 2010.
Earlier this year Tony Blair signed up to EU plans that signalled the death knell across Europe of old style incandescent filament bulbs.
The aim is to switch people as quickly as is feasible to more energy efficient compact fluorescent lamps (CFLs), which consume a fifth of the energy used by old-style bulbs.
The Government calculates that if every British household were to replace three 60 or 100 watt light bulbs with CFLs the energy saving would be greater than the power used by the country's entire street lighting network.
But there is a price for consumers because CFLs are more expensive and require more energy to make.
Mr Benn told the Labour Party conference: "The major retailers and energy suppliers are now leading a voluntary initiative, with the strong support of the lighting industry and the Government, to help phase out traditional high-energy light bulbs. We need to turn them off - for good."
full article
Then from January 2009, 100 watts bulbs would be unavailable – followed by the disappearance of 40 watt bulbs in 2010.
Earlier this year Tony Blair signed up to EU plans that signalled the death knell across Europe of old style incandescent filament bulbs.
The aim is to switch people as quickly as is feasible to more energy efficient compact fluorescent lamps (CFLs), which consume a fifth of the energy used by old-style bulbs.
The Government calculates that if every British household were to replace three 60 or 100 watt light bulbs with CFLs the energy saving would be greater than the power used by the country's entire street lighting network.
But there is a price for consumers because CFLs are more expensive and require more energy to make.
Mr Benn told the Labour Party conference: "The major retailers and energy suppliers are now leading a voluntary initiative, with the strong support of the lighting industry and the Government, to help phase out traditional high-energy light bulbs. We need to turn them off - for good."
full article
Good Energy doubles ‘pay back’ to 9p a unit
On 1st October Good Energy the 100% renewable electricity supplier is launching its new ‘pay-back’ tariff to its customers generating their own electricity. Good Energy will pay 9 pence for every unit their customers generate.
Good Energy, in their on going work to nudge the Government toward supporting renewable microgeneration, have taken the rumour that the Renewable Obligation Certificates may be doubled some time in 2009 and decided to offer essentially a double ROC rate from 1st October to people who sign up with their Home Generation product. Juliet Davenport, Chief Executive of Good Energy stated why the company is launching the new Home Generation product. “Good Energy believes that climate change is the biggest challenge we face as a society. 30% of the UK’s carbon emissions come from our homes - this is where we need solutions and home owners using wind, solar and wood energy are providing those solutions. Good Energy wants to actively support these home owners producing their own power and by offering the highest payment for electricity generated at home, that is exactly what we are aiming to do.”
The move to increase the support for microgeneration has been welcomed by environmental groups, John Sauven Executive Director of Greenpeace, said“Good Energy is showing the way with their new Home Generation scheme. The government is dragging its heels on climate change and its support for small scale renewables is shameful. Microgeneration in mainland Europe is booming - if they can do it so can we. The UK government should now follow the lead of Good Energy.”
One of the barriers to wide spread micro generation by home owners is the low level of return on particularly photovoltaic solar generation. Income from home generation at the moment is in three parts, firstly the cost saving, depending on your energy demands, and with wind and solar your location, the average house hold can expect to save between £90 and £120 per year off their bills, the second part is the ‘feed in’ component of selling electricity back to the grid, the third part of the Renewable Obligation Certificates were by home generators are rewarded for generating carbon free power.
Chris Goodall, in his book “How to Live a Low Carbon Life” calculates that the average return on a 2 kilo Watt system, around 12 square metres of panels, is around 4% a year. He calculates this by adding up the average amount saved by home generation, around £120 a year plus around £24 earned by feeding electricity back into the grid at present feed in prices of 4p, plus around £72 of Renewable Obligation Certificates. This gives around £216 of savings and revenue for an installation cost of £5000. Put in straight forward terms its gives around a 4% return over the 25 year life of the system based on present energy costs, ROC allowances and price, and feed in prices. With the Good Energy scheme the slight increase in ROC equivalent payments, averaging around £158, the payback rises to 5%.
According to anecdotal evidence from Solarcentury installing a solar system on a house should not just be seen as an investment in cleaner energy but also an investment in the capital worth of the building itself. The Energy Saving Trust estimate that a solar home is worth 10% more than a traditional home, Jerry Newman, COO of Solarcentury told naturalchoices in a recent interview “We already have seen that a home fitted with solar achieved an 8% higher price that an otherwise identical adjacent home”.
Which is very valuable given the Government’s vacillation on supporting home generation. Going back to Chris Goodall’s calculation the installation of a solar system, which he prices at £5,000 is in reality closer to £8,000. The price is brought down by the assumption that a grant from the Low Carbon Building Programme which has now been capped at £2,500. The programme has been suspended, played around with and is in fact barely functioning with a mere £19 million behind it this year. Seen in isolation without the increase in value to the home itself microgeneration would remain the domain of the convert and not a viable option for many who remain Return on Investment driven.
Sadly at this moment in time, despite the huge increase in interest in sustainable and low carbon homes, the Government has still to lay out a clear system of support, at a grant level, a feed in payment level or at a ROC level. Hopefully Good Energy’s initiative will go some way to providing an incentive to policy makes to pull their heads out of the sand and get behind renewable and home micro generation.
Peter Shield naturalchoices.co.uk
Good Energy press release
full article
Good Energy, in their on going work to nudge the Government toward supporting renewable microgeneration, have taken the rumour that the Renewable Obligation Certificates may be doubled some time in 2009 and decided to offer essentially a double ROC rate from 1st October to people who sign up with their Home Generation product. Juliet Davenport, Chief Executive of Good Energy stated why the company is launching the new Home Generation product. “Good Energy believes that climate change is the biggest challenge we face as a society. 30% of the UK’s carbon emissions come from our homes - this is where we need solutions and home owners using wind, solar and wood energy are providing those solutions. Good Energy wants to actively support these home owners producing their own power and by offering the highest payment for electricity generated at home, that is exactly what we are aiming to do.”
The move to increase the support for microgeneration has been welcomed by environmental groups, John Sauven Executive Director of Greenpeace, said“Good Energy is showing the way with their new Home Generation scheme. The government is dragging its heels on climate change and its support for small scale renewables is shameful. Microgeneration in mainland Europe is booming - if they can do it so can we. The UK government should now follow the lead of Good Energy.”
One of the barriers to wide spread micro generation by home owners is the low level of return on particularly photovoltaic solar generation. Income from home generation at the moment is in three parts, firstly the cost saving, depending on your energy demands, and with wind and solar your location, the average house hold can expect to save between £90 and £120 per year off their bills, the second part is the ‘feed in’ component of selling electricity back to the grid, the third part of the Renewable Obligation Certificates were by home generators are rewarded for generating carbon free power.
Chris Goodall, in his book “How to Live a Low Carbon Life” calculates that the average return on a 2 kilo Watt system, around 12 square metres of panels, is around 4% a year. He calculates this by adding up the average amount saved by home generation, around £120 a year plus around £24 earned by feeding electricity back into the grid at present feed in prices of 4p, plus around £72 of Renewable Obligation Certificates. This gives around £216 of savings and revenue for an installation cost of £5000. Put in straight forward terms its gives around a 4% return over the 25 year life of the system based on present energy costs, ROC allowances and price, and feed in prices. With the Good Energy scheme the slight increase in ROC equivalent payments, averaging around £158, the payback rises to 5%.
According to anecdotal evidence from Solarcentury installing a solar system on a house should not just be seen as an investment in cleaner energy but also an investment in the capital worth of the building itself. The Energy Saving Trust estimate that a solar home is worth 10% more than a traditional home, Jerry Newman, COO of Solarcentury told naturalchoices in a recent interview “We already have seen that a home fitted with solar achieved an 8% higher price that an otherwise identical adjacent home”.
Which is very valuable given the Government’s vacillation on supporting home generation. Going back to Chris Goodall’s calculation the installation of a solar system, which he prices at £5,000 is in reality closer to £8,000. The price is brought down by the assumption that a grant from the Low Carbon Building Programme which has now been capped at £2,500. The programme has been suspended, played around with and is in fact barely functioning with a mere £19 million behind it this year. Seen in isolation without the increase in value to the home itself microgeneration would remain the domain of the convert and not a viable option for many who remain Return on Investment driven.
Sadly at this moment in time, despite the huge increase in interest in sustainable and low carbon homes, the Government has still to lay out a clear system of support, at a grant level, a feed in payment level or at a ROC level. Hopefully Good Energy’s initiative will go some way to providing an incentive to policy makes to pull their heads out of the sand and get behind renewable and home micro generation.
Peter Shield naturalchoices.co.uk
Good Energy press release
full article
Subscribe to:
Posts (Atom)
