A 'Grid Interactive' Microgrid
Consider a village which has several small rain-fed water tanks and wells with a cumulative three days supply of normal daily water use. The village gets a water truck every day from the nearest town where there is a large water source. Since the road is long and prone to disruptions, the village does not get water for some days at a stretch. The people of the village have accordingly adopted a practice that the day their water supply does not come, each family reduces it's water consumption to drinking, cooking and essentials. Baths are postponed. The aim is to stretch the village tank reserves as long as possible to cater for longer disruption. This way the three day water tank reserves serve the village for 7 days. In 7 days, either the water supply resumes or evacuation of the settlement is organized after appreciating the size and extent of disruption.
An 'Off Grid' Microgrid Arrangement
If we substitute 'water' with 'power', the same practice is the fundamental basis of the microgrid approach. The wells correspond to the DG sets, rain is the equivalent of renewable energy generation and the water tanks are equivalent to energy storage devices. They are linked together by pipelines which serves each household exactly like generators, storage and consumers are connected by a local 220V/50 Hertz electricity transmission lines to form a microgrid. The water supply arrangement to the village by truck corresponds to the grid power supply - it may not exist in many cases in actual situation (an off-grid condition in power jargon). The practice of using water only for essentials on learning about water supply disruption is known as 'load-prioritization'. The duration for which the village can subsist after 'load-prioritization' is known as the 'Autonomy' of the village. The switch to usage of local water reserves on disruption of water supply from town is known as 'Islanding'. The switch back to supplied water on resumption of water truck arrangements is equivalent of 'Grid Restoration'. The act of using part of water supply to recharge depleted water tanks is exactly like recharging batteries or other forms of energy storage devices. If the village receives plentiful rain and a very large water tank is constructed to store the runoff, it may become perennially autonomous for water. Also it would be in a position to supply water to the town instead of importing it. This is a design decision. Similarly a microgrid can be perennially autonomous by design and export surplus power to the grid.
The concept is neither new nor original. In India we have been practicing this approach in various walks of life to overcome resource scarcity and uncertainty. It has worked well through the ages and is embedded in our culture.This is the approach adopted to electrify remote villages in India and neighbouring countries, Africa and Latin America. In the easiest terrain, it costs Rs 6-7 lakhs to build a km of low voltage distribution line of the kind which supply our homes. An entire village microgrid can be installed at a cost of Rs 4-5 lakhs per Kilowatt using solar panels and lead acid batteries. If LED bulbs and DC fans are used, A 2 Kilowatt microgrid is adequate for a village. A tubewell may require 6-12 Kilowatts in contrast.
Considering the fact that long distribution lines to villages rarely carry power for more than a few hours, the conductors are prone to theft. It makes no commercial sense to have them in first place as cost of establishment and maintenance is high, longer wires mean more resistive losses, more power theft and theft of power cables itself. The revenue from poor settlements just does not exist. As a result the microgrid model using prepaid metering is sustainable commercially and ideal for community development.
In my next post I will cover the advantages of microgrid approach in Government assets. Thank you for bearing with me.
No comments:
Post a Comment