Carbon Conservation & Energy Efficiency


Bruce Rowse & Team

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Which Solar Hot Water Heating System?

Friday, May 8th, 2009

(Part One)

One of the most energy intensive (and therefore costly) processes in any house is the heating of water. Heating water accounts to about 37% – 40% of the annual energy consumption in an average Australian household and about 20% of its greenhouse emissions. Therefore it is important to consider all the alternatives, such as using the heat of the sun in solar hot water systems.

The diagram below summarises the GHG emissions of each type of hot water system.

GHG emissions from hot water systems

GHG emissions from hot water systems

There are three main types of roof-mounted solar hot water heating systems used in Australia. These are: the unglazed polymer collectors which are mainly used in the form of black pipes or hoses for heating swimming pools, the glazed panels which are copper pipes insulated within a dark glass panel and the evacuated glass heat tubes which also have copper pipes running through them but are housed in a vacuum-filled environment. The tank maybe located on the roof together with the collectors or could be in a separate location. In passive systems, water flows unassisted between the collectors and the tank. In active systems, water is pumped between the collectors and the tank.

Throughout the day, a sensor monitors the difference in water temperature between the water in the storage tank and the water in the collector (typically mounted on the roof). At a preset temperature difference, the sensor triggers a pump to circulate the water through the collectors where it absorbs solar heat.

Below is a summary of the two types of commonly used domestic solar hot water systems. Both the flat panel and evacuated systems have several versions, where gas or electricity is used to boost the water temperature if it is not sufficiently hot coming out of the water tank. In most cases the sun is simply used to ‘preheat’ the water to higher temperatures (40-70 C) before it goes into a storage tank. A pump may be used to circulate the water from the tank to the collectors until it is used. In addition the flat panel systems may use a heat-exchange mechanism typically where the water may freeze.

Flat panel or evacuated tubes?

In recent years evacuated tubes have become more popular and affordable and together with the flat panels have become widely used in Australia, especially since generous government rebates have been introduced. However, it is still disputed which system is better than the other. Obviously the manufacturers of each type of system claim that theirs is better than the other (sometimes claiming 90% to 160% more efficiency than the other system). The following reasons have been cited: because it captures sunlight better, is better in certain climates, is more cost effective, has better output for dollar spent, has faster payback, is less prone to failure or damage, is cheaper to repair, requires less roof installation area, etc.

It is difficult to find impartial opinions on the subject. It seems that each system should be examined in its own context. The climatic conditions and application will determine the better collector. One of them may be the preferred choice over the other due to a number of variables, such as the environment, availability of sunlight, elevation, orientation, average outdoor temperature, greenhouse gas savings, ease of installation including existing plumbing, payback period, running cost, availability of natural gas to use for boosting water temperature, how well the hot water tanks are insulated and many other factors. So which one is better and how do they compare?

To be continued……..soon……….

Sunlight in a Cable

Wednesday, February 25th, 2009

We are all familiar with the concept of the traditional skylight or solar tube that directs sunshine through a duct or a flexible tube from the roof to a ceiling. This is an easy way to get natural daylight into a room but it is dependent on tube length and on a direct route between the roof top and the ceiling. There is another way known as ‘fiber optic solar lighting technology’.

Parans , the Swedish company behind the ‘sunlight in a cable’ concept, believes that it is possible to have sunlight in every single room of an indoor environment – even underground. The principle of the Parans’ system is simple; first the sunlight is collected by panels outdoors then it is transported through fiber optic cables into carefully designed luminaires located anywhere within a building including between floors.


The system consists of a light-collecting panel called a SkyPort that’s made up of a layer of movable and a fixed layer of lenses that track the movement of the sun through stepping motors controlled via a microcomputer. These can be mounted on a roof, facade or the ground just like other solar collecting devices; however glare shields may be used to throw direct sunlight onto its surface if the orientation is not quite perfect. The SunWire, consisting of a bunch of optical cables, then guides the sunlight indoors with minimum light loss. Very high quality light can be transported for up to 15-20 metres without major losses since the decrease of intensity for visible light is only 4.6% per metre.

The Björk luminaires are designed to give a spectacular sunlight experience both as strong light beams and as ambient light. The luminaires are made from thin sheets of semi-transparent acrylic. The feeling of natural light is immediate. The light intensity under one of these luminaires can be as high as 4000 lux when 100 000 lux outdoors (based on seven metres of fiber optic cable). UV and IR radiation are naturally blocked out by the Parans system making it the perfect solution for environments where these must be avoided. It is possible to ‘switch off‘ the system in case the darkening of a room is necessary for presentations etc.

While the Parans system works perfectly well in reasonable daylight conditions it is necessary to use artificial lighting during overcast days or when the hours of daylight diminish in winter. To counteract this there is a hybrid luminaire that incorporates T5 lighting technology, which dims automatically according to how much natural light is emitted.

However, the main focus of the system is to harness as much sunlight as possible before needing any artificial lighting thus reducing energy costs and most importantly greenhouse emissions. The only power the Parans system uses is 0.9W for the motorised panels and the microprocessor. Using the Parans lighting system can lower energy costs by 20-25% annually and probably around the same percentage of GHG emissions (based on brown coal emissions).

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