The construction industry has been talking about green buildings for a large part of the previous decade. India, and for about two decades globally. But, what is renewable energy and how is it linked to Energy Efficiency (EE)?
Renewable energy, also called ‘Alternative Energy’ or ‘Energy from nonconventional sources’ is the energy that comes from natural resources such as sunlight, wind, rain, tides and geothermal heat, which are renewable (naturally replenished) and, unlike energy from crude sources, do not take million of years to be created. When we harness these sources of energy, we save on various green house gas emissions, which in turn add to the energy efficiency of the overall project.
Until now, green buildings were isolated homes and offices. Research on technologies was limited and financial payback was very long. However, the scenario has been changing and people are waking up to the benefits of an energy-efficient buildings, which can generate cost saving for tenants in the long run. Various standards/certifying authorities have set guidelines for green buildings.
Energy Efficiency insists on using practical and simple solutions to increase the eco-efficiency parameters of a building. Waste water recycling and the thermal andelectrical performance of buildings are areas of immense potential. Resolving these parameters can massively improve the energy performance of any building.
Alternative energy forms such as solar and wind energy are available in abundance. However, certain systems and engineering inputs must be combined to facilitate the capturing and harnessing of their true potential. These technologies, when used as integrated design with buildings, lead to structures that are environmentally friendly and closer to Nature. By definition, a green building is the one that has a smaller carbon footprint, which uses less water, generates less waste, conserves natural resources, optimises energy efficiency and provides a healthier life in relation to a conventional building.
One of the most efficient ways of achieving EE is by conserving water. This is typically done in two ways—rainwater harvesting and sewage treatment.
This process implies the collection and storage of rainwater for either further use or recharging the water table. Rainwater is collected from the exposed surfaces of the building by a series of slopes, gutters, channels and holding tanks. Depending upon the percolation capacity of the soil, percolation wells are built. These are structures that help the rain run-off water to charge the water table. By this method, the water table is charged periodically, putting less strain on the natural water aquifers. This water can also be used for flushing and drinking needs, although it might require some treatment before it is fit for such use. In India there have been various successful case studies of this technique being applied. In Rajasthan’s Thar desert, these systems have been existent for centuries; some of them are now being archaeologically discovered and revived. The Tamil Nadu government made rainwater harvesting compulsory, as a result of which Chennai has seen a 50 percent rise in its water table.
Sewage Treatment Plant
Recycling water in residential or office buildings can help to prevent uncontrolled water wastage. In India, water once used goes into municipal drains. The hotel industry is an exception, since it is governed by various legislations. Sewage poses multi-faceted problems; especially in a developing country like ours, this could lead to water-borne diseases such as cholera and typhoid. Besides, releasing water in these drains usually leads to irreversible loss of precious water.
To counter this problem, a sewage treatment plant can be used. This, in principle, gets rid of all the impurities in the sewage and filters it into usable water, thus promoting the reuse of this resource.
The typical sewage treatment process involves the following:
Physical screening or sedimentation process for removal of solids: This is where large particles between 6–30 mm in size are screened, and the sewage or primary sludge is allowed to settle.
Secondary treatment/digester: The primary sludge is introduced to a digestion chamber where it comes in contact with bacteria aeration for several hours of aeration enables the bacteria to oxidise and break it down.
Final sedimentation: This is where the sludge passes though the final settlement tanks and settles down as secondary sludge. The clear water from above flows over for further treatment. Some of this secondary sludge is sent back to the secondary stage for more active treatment.
Tertiary treatment: Water is made usable by applying further treatments to remove still suspended impurities. This is executed by various mechanical means.
Solar and Wind Energy
Another way to harness renewable energy is to tap solar or wind power. Solar power can be used to drive a turbine for electricity generation or for incident radiation on photovoltaic cells, that can be used to generate electricity. Wind power can be used to drive turbines/generators for electricity production. This electricity can either be fed to individual consumers or directly to the grid. Both these energy sources can be exploited on a large scale and also at a domestic level. However, cost considerations often make it difficult for such facilities to be installed at an individual level.
Incedent Solar Radiation (Insol) and wind velocity are not same the world over. They differ from region to region. It is good to install these systems in isolation where the climate permits. But otherwise, inconsistent supply is the biggest impediment to a public-scale implementation of these technologies.
Spain, for example, is more blessed with Insol as compared to its other European counterparts. the country has installed a solar collector system capable of generating 11 MW of electricity. This system works on thousands of angled mirrors (heliostats) reflecting solar radiation on a central tower, which heats up its core. The heat is used to drive a steam generator and produce electricity.
If we look closer home in the wind-rich belts of Saurashtra and Tamil Nadu, we can see wind farms of installed capacity greater than 2,000 MW and 6,000 MW respectively. However, installing these aero generators at the domestic level is hindered by both high capital cost and inconsistent wind velocity, leading to a very long payback period.
The biggest challenge developes and designers is that they can do nothing to harness these abundantly-available resources for individual projects in India, because of issues with their dependability and very long gestation periods. On a larger scale this is the major downside of renewables. At a certain level, renewable power systems are difficult to sustain if a single type of system is used. The key lies in integrating both the systems and using a range of solutions, rather than depending on just one.
As India has a good blend of solar and wind energy, hybrid systems can be designed to consider both of them. Given our climate, a system with a 60–40 split of solar to wind respectively will be suitable and more efficient for installation over most of the country.
Solutions and Numbers
Windmills (aero generators) will have a small turbine attached to them. When the blades spin, they generate current. Solar power is captured by photovoltaic cells, which create a potential difference on receiving incident radiation, and hence generate electricity. Electricity from both these sources is then stored in a battery bank. An inverter is connected to this array of batteries, which provides output load as AC current.
A typical 3.45 KW design load system would have 2 KW assigned to solar and 1.45 KW assigned to wind turbines. At 250 sunny days per year and a wind speed of 5.5 m/s, this system will generate enough electricity to power the common areas of two typical 10-storeyed buildings. Faster financial paybacks are achieved by integrating this system into buildings, as the tenants can see immediate translation of electricity generated to savings achieved over grid power.
Renewable energy and energy efficiency are no longer restricted to mega and urban scale size domains. If used intelligently, these systems can help to reduce the carbon footprint of our buildings, and at the same time save some money and make for a stronger bottomline.