(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

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……….

For a small business such as ours maintaining a healthy cash flow is a must. Cash comes into the business when invoices are paid. A recent survey showed that Australian businesses were on average now waiting 58 days for invoices to be paid. This means that for most businesses the cash that will come into the business in April is dependent on what the business invoices now in February. There is lag between when the work is done and when it is paid for. Failure to invoice enough in February could result in a business running out of cash in April. And when there is no cash, there is no business.

Climate change is similar. The carbon we put into the atmosphere now influences the climate well into the future. However rather that a time span of weeks or months, its decades. Todays carbon emissions will influence the climate for decades to come. So to get a stable climate in the future we need to cut greenhouse gas pollution NOW.

Many years ago a friend “temporarily” left the shell of a model T Ford in my front yard as he had no space to store it. Its still there. I haven’t asked my friend to take it away because it reminds me that some of the carbon that car generated over its lifetime is still in the atmosphere driving climate change.

Since climate change is like cash flow, if we want a stable climate as we grow older, and for the sake of our children and grandchildren, we need to be acting now.