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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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What surface area is required to solar power the whole world?

Posted by Bruce Rowse in Solar - (8 Comments)

View “Todd’s Postereous Blog” to see a map of the world showing for each continent the area that needs to be covered with solar panels in order to meet all the world’s power needs. You might be surprised!

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How plummeting PV prices will greatly change the electricity distribution network

Posted by Bruce Rowse in Cogeneration | Electricity Distribution | Solar - (1 Comments)

I attended a workshop today in Melbourne run by iGrid, a consortium of universities and the CSIRO preparing a model of the intelligent energy grid of the future.

Its been identified that peak demand, which is rising faster than electricity consumption, is one of the most critical issues that a distributed generation network can address.

Dr. Muriel Watt, Chair of the Australian Photovoltaic Association and Project Manager with IT Power gave a presentation about the future pricing of PV, with  similar themes touched on by Michael Williamson from Sustainability Victoria.

Solar PV prices have historically decreased by roughly 20% for every doubling of global production. At current growth trends this means that the cost of PV generated electricity in Australia is likely to reach grid parity within the next five to ten years. “Grid parity” meaning that the cost of generating electricity from a PV system will be equal to the cost of buying electricity off the grid. This assumes some government support.

The $8,000 government rebate for a 1kW system has resulted in around 100,000 Australian households now having PV systems. As prices continue to lower it will become economic for business to also install PV.

As prices approach grid parity and take up of PV systems grows strongly we should see a significant reduction in greenhouse gas emissions. Most of these systems will be grid connect. Along with the uptake of other technologies, such as small scale co-generation, the electrical distribution grid will be transformed from one that provides for a one way flow of energy to one in which two way flows are experienced.

This in itself will generate other challenges, such as the need for energy storage in the grid. Several presenters discussed electric cars as a storage solution. Most cars are in use for less than two hours a day, and the rest of the day, if the appropriate infrastructure exists, could provide storage capacity to the electrical network.

There will need to be significant investment into the electricity distribution network to make it smart. Regulatory changes will be needed to facilitate this.

The upcoming “smart meter” rollout in Victoria, set to start over the next few months, is just one step in this direction. The distribution network itself needs to get smarter (so for example voltages can be adjusted), and the information collected by the smart meters should be made available to customers to result in a more effective demand side response, particularly if time of use pricing is introduced. There is opportunity for innovative new products to use this data to shift loads and influence consumer behaviour.

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Which Solar Hot Water Heating System?

Posted by Barney Mezey in Climate Change | Climate Positive | Energy Efficiency | Solar - (3 Comments)

(Part Two) The first part of this topic was published on the 8th of May.

Flat Plate Solar Collectors

Flat panel (aka flat plate) collectors work on the principle of copper pipes running through a glass covered collector, often connected to a water storage tank on the roof. The hot water can then thermosiphon itself in and out of the tank, thus heating the water. Finally the hot water is gravity fed into the house from the roof. This is an extremely efficient way of gaining and storing hot water and can be over 90% efficient in the right climate. The simplest combination is the close-coupled system (see photo below).

However, the water tank may be located in the roof space or on the ground as a separate unit in which case a pump is necessary to circulate the water. This is known as a split system. Flat panel collectors are still the most commonly used collectors in domestic hot water applications in warmer climates due to their affordability and reasonably easy installation. The collectors should last well over 20 years and can handle an operating temperature up to 80 degrees.

Flat Panel HWS

Flat Panel HWS

Evacuated Tube Solar Collectors

Evacuated tube collectors consist of glass tubes with a layer of heat absorbent coating inside them. As the tubes encasing the water pipes are a vacuum it greatly reduces heat loss. The thermal energy retention can be up to 97%. Copper pipes run through the centre of these evacuated glass tubes in a U-shape. These are all connected to a common manifold which is then connected to a slow flow circulation pump which pumps water to a storage tank below. The hot water can be used at night or the next day due to the insulation of the tank. Evacuated tubes are often used in commercial applications or in applications where hotter water is needed, since they are capable of generating temperatures above the boiling point of water (for example on dairy farms). While evacuated tubes have a long life similar to flat plate collectors, they are composed of fragile glass tubes which may occasionally need replacement.

Evacuated Tube HWS

Evacuated Tube HWS

Comparisons

As pointed out in Part One of this blog it is not a simple matter of using evacuated tubes or flat panels as each circumstance is different. Each collector design has its own merits. Both systems can save over 3 tonnes of GHG emissions per year and can reduce heating energy consumption in a home between 50%  to 80% especially when electric hot water storage systems are being replaced. In addition both systems can be up to 70% efficient when heating water and heat losses in the system are taken into account. So instead we should look at the benefits and the short comings of each system.

Evacuated Tubes

Advantages
  • No heat losses due to convection and conduction because glass collectors are hermetically sealed.
  • No change of performance during the service life of the collectors as there is no corrosion.
  • Thermal diode operation principle, the hot water flows one way only from the collector to the tank and never the other way around.
  • It is able to harness sunshine from all directions due to its cylinder-shaped glass tubes.
  • Well-suited for colder climates with reduced hours of sunshine, where frost may be a problem or where the roof is prone to overcast from clouds.
  • Freeze free so can be used in sub-zero temperatures and in the presence of snow.
  • Easy installation due to light weight and no maintenance needed afterwards.
  • Requires smaller roof area for installation.
  • It is less apparent on roof because of the absence of a water tank coupled to it.
  • Each glass tube is independent from each other so in case of breakage it can be replaced.
  • Minimum greenhouse emissions when combined with gas boosting.
  • Saves about 3 tonnes of CO2 annually when compared to electric storage.
  • Very low running cost when used with gas or off peak electricity.
  • On average it is about 5 years payback on investment.
  • Suited for commercial and industrial applications.

Disadvantages
  • Expensive to purchase due to more components, such as pump, separate water tank and associated plumbing and electrical work.
  • Less cost effective than flat panels based on initial investment.
  • Glass tubes could break easily in a hail storm or from falling branches.
  • In higher ambient temperatures it is less efficient than flat panels.
  • In direct summer sun it could be too efficient making the water too hot which results in wastage.
  • Evacuated tube collector’s aperture area is typically between 60 and 70% of the gross collector area (meaning that’s how much of the total area exposed to sun is doing useful work).
  • Some heat pipes are prone to cracking rendering the system useless especially at the braising points. These don’t like repeated heating and cooling down especially if it is very sudden.
  • The welding should be done with silver alloys to prevent this from happening.
  • Mainly made in China, thus not supporting Australia.

Flat Panels

Advantages
  • Operates extremely efficiently in warmer climates and in higher ambient temperatures especially when water tank is horizontal and adjacent to the collectors.
  • It can be between 44% to 76% more cost effective in warm climates than evacuated tubes.
  • Losses are minimised because of water tank being located next to collectors.
  • Thermosiphon operation minimises maintenance – no moving parts or distant pipes.
  • Simple to install as system can be purchased as one unit with collectors and tank together.
  • Affordable to purchase for the above reasons and because of less plumbing involved.
  • No electrical installation required in most cases where stand alone system is used (ie the tank is not separate from the collectors).
  • Space saving as water tank is located on roof and not in or around the house.
  • Robust construction.
  • Large collector area.
  • Flat plate collector’s aperture area is typically between 90 and 95% of the gross collector area.
  • Mostly made in Australia for Australian conditions, which supports the local industry and economy.

Disadvantages
  • Can corrode.
  • The air gap between the absorber and cover pane could result in heat losses during cold and windy days.
  • It can rob the water of built up heat if the collector becomes colder than the water temperature.
  • No internal method of limiting heat build up and have to use outside tempering devices.
  • In colder climates it may need extra protecting devices from frost or freezing.
  • It is more reliant on accurate northern exposure in order to operate efficiently.
  • Installation could be difficult due to weight and size.
  • Circulates water inside insulated areas. Prone to leakage, corrosion and restriction of flow due to possible airlock.

The graph below compares the three main types of solar hot water systems and their efficiency.

Solar Collector Efficiency Graph

Solar Collector Efficiency Graph

Explanation: Solar collector efficiency is plotted as a straight line against the parameter (Tc-Ta)/I, where Tc is the collector inlet temperature (in °C), Ta is the ambient air temperature (in °C), and I is the intensity of the solar radiation (W/sq. m.). Notice that inexpensive, unglazed collectors are very efficient at low ambient temperatures, but efficiency drops off very quickly as temperature increases. They offer the best performance for low temperature applications, but glazed collectors are required to efficiently achieve higher temperatures.

Summary

From the above descriptions and considering the merits and drawbacks of each system the following conclusion can be drawn. In warmer climates and most temperate zones, where there is good exposure to sunshine throughout the year, and the ambient temperature is fairly stable the flat panel collectors are recommended to be used. Also, if there is good uninterrupted northern exposure available the flat panel is more economic. The flat panel is extremely efficient and the systems can produce sufficient hot water for most households. The use of a flat panel system will result in up to 80% reduction of hot water cost when compared to electric storage units. These are also more affordable with a faster payback period on investment. They are designed and made in Australia for Australian conditions.

On the other hand the evacuated tube systems have an advantage of being able to operate in colder climates or where there isn’t enough sun light (ie. some alpine or mountain areas, prone to overcast or where there are more trees). These systems also work well in the presence of snow or sub-zero temperatures. The unique design of the glass tubes allows it to capture sunlight from various angles thus heating the water for longer periods. In some cases where very high water temperatures are required – even in warmer climates- the evacuated tubes have the ability to produce water at higher temperatures than flat panels. Being smaller in surface area these units could be more suitable where there is a lack of space. Again 80% reduction in hot water cost and GHG emissions are quite achievable from such a system.

Please take note of the references for the graphs and information in this article. Where possible we have used information stemming from government websites, academic resources, and manufacturers data. If you need more information or actual references please contact us.

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