Power Up with Solar Thermal Energy
Financial Daily, May 20, 2011
By Sam Tan
The government has raised petrol prices several times recently, while unpredictable global weather is not helping, since it will mean poorer production of vital crops, and as a result, we can be sure that food prices will rise again this year.
Merely fretting over rising costs is counter-productive, so why not think ways to lower cost. For one, we can use the one naturally occurring, abundant and free resource—the sun—and the power of solar thermal energy to produce heat.
Solar thermal collectors in simple terms, collects heat from the sun for use in other forms. In their most basic form, flat plates collect heat which is then used for water heating water (or heat swimming pools in cold countries).
More advanced systems such as those already in widespread use in China and Japan are very efficient and require little sun to produce heat.
Again, as with most things ‘green’ nowadays, none of this technology is earth-shatteringly new, and in fact has been in widespread use for many years (though mainly in the West). It’s just that with climate change becoming an ever-more present danger, these technologies are advancing much more rapidly than ever before.
For instance, a type of solar thermal collector, called the evacuated tube collector, has proved to be highly efficient in capturing and storing heat even at very low temperatures. It is also becoming more available to common folks, since mass innovation and high demand is driving down costs.
The principle behind its effectiveness is quite simple, and is rooted in basic physics. Water normally boils at 100 degrees but in the mountains water boil at a lower temperature. The reason: lower pressure reduces the boiling point of water.
The evacuated tube collector takes advantage of this principle. The (glass) tubes are vacuumed, and in this vacuumed condition, the pressure inside the glass is extremely low. That means the boiling point of water is brought down to around 26 degrees Celsius. This is a very efficient way of obtaining heat.
Today, when we design new buildings and homes, we know that some of the key considerations include the way air will flow to facilitate ventilation. Ultimately, people look for comfort in a dwelling. And in a tropical country, it is about keeping cool without having to incur an exorbitant energy bill. So, when we design the structure of a building, we seriously consider basic factors like air flow and the siting of the most frequently used rooms. For example, bedrooms should face the rising sun and not the setting sun which means that such rooms will be cooler.
Hence, scientists, governments and businesses are beginning to realise that solar power can be used for base load power generation as well as peak power generation. More importantly, it has the potential to displace both coal and natural gas fired power plants. This is a real issue in Malaysia, since the vast majority of our power is produced using natural gas, oil and coal, which are expensive, short in supply and dirty. Using solar thermal collection in industrial cooling has allowed us to significantly reduce our energy cost.
Imagine big quantities of hot water made virtually free and used to produce cold water for your air-conditioned chiller.
Enter the absorption chillers.
An absorption chiller (or refrigerator) uses a heat source to provide the energy needed to drive the cooling system. Not surprisingly, absorption chillers are possible alternatives to regular compressor refrigerators because electricity is expensive, and the noise from a regular compressor can be quite inconvenient.
And in instances where there is surplus heat available (for example from turbine exhausts or industrial processes), then this proposition becomes even more compelling.
For example, a pulp and paper mill company which wants to reduce electricity costs may find it useful to harvest the excess extraction steam, instead of venting it to the atmosphere (thus wasting this latent energy).
An absorption chiller could utilise this excess steam to air-condition its office buildings, thus killing two birds with one stone, since its electricity costs are vastly reduced, and it need no longer spend money to cleanly rid the surplus heat.
Both offer equivalent cooling capacities, but by some calculations, the absorption chiller uses much less electricity to produce the equivalent cooling capacity of a conventional electric chiller.
Absorption chillers could be mated with solar thermal collector, and voila! Costs are lowered significantly.
In Japan, heating, ventilation, and air conditioning systems account for more than a quarter of the energy used in commercial buildings and nearly half of the energy used in residential buildings. I don’t have the details for Malaysia but we can’t be far off these statistics in the main cities of Kuala Lumpur, Penang and Johor Bharu.
Solar heating, cooling and ventilation technologies have the potential to significantly offset this energy usage. The sooner we recognise its potential, and utilise this already proven technology, the earlier we can help reduce our carbon footprint.