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Solar Thermal Energy – The Neglected Renewable Energy in Australia

Posted by Barney Mezey in Climate Change | Climate Positive | Electricity Distribution | Electricity Supply | Energy Efficiency | Hot Water | Solar - (1 Comments)

Contrary to what the terminology suggests ‘solar thermal energy’ is not a recent development and it is certainly not something that has just been invented as another answer to reduce greenhouse emissions. According to the Renewable Institute for Sustainable Research, the first solar powered engines were constructed back in the 1860s by a couple of French mathematicians. During the past 30 years a number of solar thermal plants have been built and operated around the world to produce guilt-free electricity. However, the technology has been rapidly evolving in recent years and Australia has perfected the technology to make it commercially more viable.

Unlike wind power or solar photovoltaic panels, which generate electricity directly, solar thermal power uses mirrors to concentrate the sun’s energy onto a receiver and create heat, which can then be used to produce steam to run a turbine and generate electricity, in the same way as a conventional coal-fired power station. The other advantage of solar thermal technology is that it can be stored very efficiently in large tanks of molten salt and then be dispatched to generate electricity at any time of the day or night, making it in effect base load solar power.

The way solar thermal energy plants work is by focusing the glare of the sun’s rays on a central location –usually on a tall solar tower- to create heat, which is then turned into electricity. The concentrated heat is extreme between 500-2000 C and it could easily melt metal. Due to various heat exchange processes involved –which were further advanced in Australia- the water eventually turns to steam, powering the turbines at the base.

Various methods exist to concentrate the solar radiation, including parabolic troughs, power towers with mirrors that track the sun (heliostats), parabolic dishes, and Fresnel reflectors (these consist of multiple flat mirrors). Each technology differs in the way that it concentrates the solar energy, but they all track the sun to maximise energy capture and produce heat, which is then converted to electricity.

These technologies are at different stages of development and each has its own advantages and disadvantages. It is fair to say that parabolic troughs are the most mature, having first been installed at utility scale in the 1980s; although the other types may ultimately prove cheaper due to their inherent design advantages. These technologies have been successfully used in the USA and Spain since the 1980s. But the Australian National University has re-designed the dish for optimisation for manufacturing and mass production with mirror panels that should be able to concentrate the sun at least 2,000 times.


Solar Thermal Uptake in Australia

Australia has large areas of high solar intensity and little rain, where large concentrations of renewable energy power stations could be developed. In fact the Australian continent has the highest average amount of solar radiation per square meter per year of any continent on the planet ranging from 1500 to 1900 kWh/m2/year. In other words Australia is better-suited to this technology than any other country in the world, including Spain who is expecting to operate 60 solar thermal plants by 2013.

Peter Meurs (Managing Director of WorleyParsons-EcoNomics) has said that establishing advanced solar thermal centres could allow Australia to exceed the 20 per cent renewable energy target by:

• Facilitating the commercialisation of developing renewable energy technologies.
• Triggering the development of domestic solar thermal component manufacturing.
• Enabling Australia to become a world leader in these technologies.
• Allowing the construction of larger scale solar thermal power stations over time.

Wizard Power is also part of the same consortium who has been trying to commercialise big dish technology in Australia for the past five years. Their unique technology was developed by the Australian National University’s solar thermal group over the past 40 years who have perfected ‘the big dish’ and they’ve also figured how to best store the sun’s energy thermo-chemically. It appears that Wizard Power may be getting some support from the federal government in the form of $60 million towards a $230 million solar plant it’s building in South Australia. Wizard Power suggested Whyalla in South Australia as an ideal place to establish large scale solar facilities, because of the climate and the number of large scale resource projects requiring power. Australia’s very first solar oasis in Whyalla is going to provide enough electricity to power the town of Whyalla and also to provide power to the neighbouring steel works. In total it’s capable of powering approximately 9000 average homes or replacing something in the order of 17000 motor vehicles on the road each year in terms of carbon emissions.

There is no reason why Australia couldn’t match the Spanish government’s commitment who is expecting to cover 12 percent of its primary energy from renewable sources by the end of this year. Spain is the fourth largest manufacturer in the world of solar power technology and exports 80 percent of its production to Germany. Australia cannot quite export electricity to other countries but we could export our expertise in this technology to build solar thermal plants in other countries. At the same time there is no reason why 30 solar thermal plants could not provide 40 per cent of Australia’s renewable energy needs by 2020-according to WorleyParsons. But to achieve this goal, action must be taken today.

References:

http://www.npr.org/templates/story/story.php?storyId=13826548)
http://www.abc.net.au/insidebusiness/content/2010/s2925759.htm
http://ecogeneration.com.au/news/advancing_solar_thermal/002019/
http://ecolocalizer.com/2008/04/12/mega-solar-the-worlds-13-biggest-solar-thermal-energy-projects/
K. Lovergrove and M. Dennis Solar Thermal Energy Systems in Australia 2006 International Journal of Environmental Studies (www.tandf.co.uk/journals)

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What will make zero net energy office buildings affordable by 2020?

Posted by Bruce Rowse in Carbon Conservation | Climate Positive | Computers and Office Equipment | Control | Energy Efficiency | HVAC - heating, ventilation and air-conditioning | Hot Water | Lighting | Solar - (4 Comments)

A zero net energy office building is one which consumes no net energy. Its an office that uses very little energy, then has some form of renewable energy to generate all the power it requires.

With current off the shelf solar technology, presuming little or no shading, its possible to get around 100 kWh  of energy per year per square meter of solar panels at latitudes of around 40 degrees, more in sunny locations at lesser lattitude. For a single storey building, with a roof covered with solar panels, and little shading, keeping office energy consumption to 100 kWh/m2 is easy, and in fact I’ve audited quite a few small offices that are nothing special but only use in the order of 100 to 120 kWh/m2. But a grid connect solar system nowdays costs in the vicinity of  $700 to $1,000 per square meter, which is pretty  expensive, so there are very few zero net energy offices in existence.

Aggressive energy conservation and use of off the shelf technology (like skylights) can mean that office energy consumption is kept down to somewhere between 30 to 50 kWh/m2, meaning only half the roof needs to covered with solar panels, or allowing for some shading. For example our office uses only 30 kWh/m2/year, but is shaded in winter, we could make it energy neutral now just by covering around 2/3rds of the roof in solar panels.

So it is possible now, in 2009, to have a zero net energy office, but its not easily affordable, yet. And if your office is 3 storeys or higher, its becomes very hard to achieve no matter what your budget.

Technological advances however, are happening rapidly and I believe that by 2020 a zero net energy low-rise office may be affordable. And importantly this should be achievable by retrofitting an existing office building, with no need to especially construct a new building. Some of these technological changes are:

  • The emergence of LED lighting. Assuming by 2020 we have LED lighting of around 200 lumens per watt. Allowing for some daylighting, and good use of task lighting, it may be possible to have annual lighting use less than 8 kWh/m2/year.
  • Computer efficiency improvements. Assuming that with thin client architecture and high efficiency monitors by 2020 an office PC uses 15 watts, and that a 200 watt server can then serve 30 clients, computer energy use would be around 3 to 4 kWh/m2/year.
  • There are many likely pathways for HVAC, which will depend on climate. A likely pathway for temperate climates is 100% fresh air HVAC systems, with air to air heat exchangers, but also using legacy internal ducting to allow high flow full economy cycles. Fans will be highly efficient, and heat pumps will have high efficiencies at a range of loading conditions, with the conditioning of air separated from ventilation to lower fan energy use. Couple this with light weight retrofit phase change materials (PCM) to provide thermal mass (eg plasterboard with encapsulated PCM), white roofs (where there are no solar panels), glazing treatments and new insulating membrane technologies to improve the thermal performance of the building. Seal the building well, and combine with good use of sensors and intelligent control all of which limits HVAC energy use to say 15 kWh/m2/year.
  • Miscellaneous loads: high efficiency fridge at say 150 kWh/year; near zero standby loss hot water system; high efficiency multi function devices, totalling say 4 kWh/m2/year.

This will result in total office energy use of around 30 kWh/m2/year.

With aggressive energy conservation occupants should be able to to get down to say 15 to 20 kWh/m2/year.

Assume solar panel efficiency is more than double current efficiency and the installed price per watt of a grid connect system is one third of the current cost. This will provide 260 kWh/m2/year at a cost of say $500 per square meter.

A single story unshaded office where aggressive energy conservation is practiced will then need only 8% of its roof covered with solar panels, at a cost per square meter of building area of only $40.

A three storey half shaded office building would need most of its roof covered.

It should be possible to have a 7 storey building energy neutral if unshaded and the roof is covered with solar panels. Of course if additional solar panels can be added to walls it should be possible to get even taller energy neutral buildings.

By 2020 the net zero energy low-rise office building should be easily affordable, and in fact it may well be standard good financial practice to convert existing office buildings to energy neutral ones. So even building owners with no interest in acting to slow climate change will have energy neutral buildings. And most low rise office buildings then – whether they are 100, 50, or 1 year old –  could be energy neutral.

I say “should” and “may” because I still have some doubt as to whether a couple of the technologies that modify the thermal performance of a building –  particularly PCMs, and retrofit membrane’s that improve its insulation properties – will be affordable. But then again with focus a lot can change in 11 years, and as more of us demand better energy performance from our buildings I believe that this will spark the innovation needed to make zero net energy office buildings common place.

You can help make this a reality by acting now to make your building more efficient. Do what is affordable now. Then repeat regularly - technology is now advancing quickly. You’ll create the demand that will drive the innovation that will create the technology that will make energy neutral buildings common place.

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How efficient are centralised steam systems?

Posted by Bruce Rowse in Energy Efficiency | Hot Water - (2 Comments)

We have recently been working on a site with a centralised steam system. It has two natural gas fired boilers supplying steam to a number of plant rooms, with the steam used to generate domestic hot water and heating hot water amongst other things. So how efficient is this system? And are there alternatives to steam that use less energy?

The short answer is that the steam system is very inefficient. It could be replaced with a decentralised system using a combination of hot water boilers and, where process steam is needed, small steam boilers. This would halve energy use.

Centralised steam systems have losses designed into them that cannot be avoided. Firstly the boiler blow down results in energy wastage. Then, because of the high pipe temperatures, any heat losses from uninsulated pipe is higher than it would be if the temperature was lower. Failed steam traps waste energy by not using the steam before it turns to condensate. And leaks and steam vents waste valuable condensate. Finally because still steam will eventually condense and needs to be taken away by a steam trap then reheated the standby losses are high. All these losses add up to large inefficiencies.

Steam is a old technology, and its use should be limited to only where absolutely necessary. Using steam to generate hot water is very inefficient. Much more efficient would be to use a high efficiency condensing flue hot water boiler, a direct exchange boiler, which will use half the energy to generate the same benefit. Heat pumps could also be considered if a water temperature of no more than 60 degrees Celcius was required.

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