BY COMBINING RENEWABLE energy (RE) on the one hand and practicing energy efficiency (EE) on the other, owners of landed properties can easily achieve net zero energy today. This is good for the environment and at the same time, will save them some money.
Photovoltaic solar energy is obtained by converting sunlight into electricity using a technology based on the photoelectric effect. This is a type of renewable, inexhaustible and nonpolluting energy that can be produced in installations ranging from small generators for self-consumption to large photovoltaic plants.1
In Malaysia the capital cost of photovoltaic on roofs has dropped to a level where subsidies are no longer necessary to make them affordable. Table 1 provides a conservative reference guide to how much photovoltaic a homeowner will need, the approximate roof space required and the approximate capital cost based on monthly electricity consumption.
Table 1 assumes a conservative capital cost of photovoltaic, starting from a high estimate of RM6,000 per kWp for a small system, down to RM4,000 per kWp for a large system. If one’s negotiation and sourcing skills are good, the capital cost can be brought down even lower.
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In fact, prices for a photovoltaic system have been steadily dropping year-on-year. The lower the capital cost, the faster the payback, and with higher Internal Rate of Return (IRR). For those with cash sitting in fixed deposit accounts, the IRR is a good method to assess the benefits of installing a photovoltaic system. As seen in Table 1, even with the least favourable IRR, the option is still more profitable than keeping one’s money in a fixed deposit account. For a large system, one can easily make 500% more in returns.
Photovoltaic is sold via a term called kilowatt peak (kWp). Conservatively, 1kWp requires 10m² of roof space. With the diversity available in brands and the level of efficiency of the photovoltaic, it is not difficult to find one that requires 10-20% less roof space than those recommended in Table 1.
Installing a system that produces more electricity than the household consumes does not bring extra financial benefits to the household, however. The Net Energy Metering, the commercial deal offered in Malaysia for photovoltaic installation on one’s roof, does not pay for excess energy “exported” into the grid.
Exposing as much thermal mass to a cooling source such as cold air from nighttime to the early morning hours will extract heat out of these materials; and during the daytime, these materials will absorb heat, reducing the peak temperature indoors.
Table 1 assumes a conservative lifespan of 25 years, but the lifespan of a new photovoltaic system can go up to 30 years. However, the inverter system needs to be replaced every 10-12 years. An inverter is a device that converts DC electricity into AC to be used and exported into the grid. At present, an inverter is approximately 10% of the system’s capital cost, but it is projected to become cheaper in the next 10 years.
In summary, RE is already cheaper to use than electricity from Tenaga Nasional Berhad (TNB). On average, one will be paying less than 19 cents per kWh of electricity over a conservative lifespan of 25 years, and this is inclusive of inverter replacement costs. Current residential tariffs from TNB range from a low of 21.8 to a high of 57.1 cents per kWh.
Financial returns on EE are exponentially better than the use of RE. In short, nothing is comparable to switching off lights, fans, computers, televisions whenever they are not being used.
Still, the biggest energy cost saving is in reducing the need for air conditioners in homes. Instead, homes can be passively cooled by minimising heat gain from both indoor and outdoor sources, and through applied passive cooling strategies.
Minimising Outdoor Heat Gain
In a typical double-storey residential house, the roof absorbs the largest amount of heat. All buildings in Malaysia should have well insulated roofs. It is best to insulate the ceiling with a 50mm rockwool if the roof has an aluminium foil, or a 75mm variation if no aluminum foil is found.
To protect the windows from solar radiation, adjustable external louvers can be used; this prevents 100% solar heat gain. When one is at home, these louvers allow one to adjust the amount of daylight to illuminate the home, saving on electrical lightings which are hotter than daylight. Additionally, louvers are excellent as sun glare protection.
The external louvers can be paired with high-performance glazing that rejects solar heat. A high-performance glazing with low-emissivity (Low-E) properties rejects more heat than the best solar film used on cars. For a new construction, this also provides a cheaper, longer lasting and more cooling alternative.
For existing homes, however, it is probably easiest to apply solar film on existing windows. Do note that the quality and price range is very wide. If readers are interested, read up on these terminologies: Solar Heat Gain Coefficient, Shading Coefficient, Solar Transmission, Solar Absorption, Solar Reflection, Visible Light Transmission, Visible Light Reflection, Low-E, Light to Solar Gain Ratio and U-value.
Finally, one should open one’s home to natural ventilation only when the air outdoors is cooler than indoors.
Minimising Indoor Heat Gain
Sometimes, through our actions, we create heat indoors; any energy that is consumed will be transformed into heat. This is dictated in the 1st Law of Thermodynamic – energy cannot be created nor destroyed.
This law always applies, including a fan which, when in use, will convert energy into heat in a closed room. Conversely, the increase in air speed brings thermal comfort if we are in the room.
It is pertinent to note that 100% of energy used by electrical appliances is transformed into heat indoors. Inefficient equipment has twice the energy consumption rate compared to an energy efficient one doing the same task. For example, an energy efficient refrigerator offers the same space and cooling at a much lower cost. This in turn reduces both the cost of electricity and indoor heat.
To save running cost and reduce internal heat gain, it is advisable to invest in EE first before looking into RE. The financial returns of the former are greater.
In a tropical climate, choices are limited for passive cooling. The easiest is to make use of high thermal mass such as concrete, sand, stones, metal and water to store cooling from nighttime to daytime.
Exposing as much thermal mass to a cooling source such as cold air from nighttime to the early morning hours will extract heat out of these materials; and during the daytime, these materials will absorb heat, reducing the peak temperature indoors. More heat extracted during the nighttime makes for a cooler indoor space throughout the day.
Any indoor building material can be used as a high thermal mass material. For example, internal brick walls, concrete flooring, stone tables, clay pots filled with soil for indoor plants and a fish tank filled with water are good thermal mass materials.
All that is needed is for one to open the home for natural ventilation whenever the outdoor air is cooler for these thermal mass materials to be cooled down.
Finally, evaporative cooling can also be an effective strategy to keep the home cool during a hot day. However, the science of evaporative cooling must first be understood correctly. Otherwise, one may be left with a wet slippery floor, or one may even encourage harmful mould growth indoors.
If you are interested to learn more, read the author’s articles under his LinkedIn profile.