Demand Side Management and Energy Efficiency
Electricity is used so widely because it can be used for transporting large amounts of energy at a high rate, and is easily converted into a number of common end uses such as mechanical movement, heat and light. However, at present, a major problem with electricity is that it cannot be stored economically. Thus, the generation of electricity has to be controlled and adjusted according to its end use rate. The power drawn by end users at a given time is known as the ‘demand’ on the system.
‘Demand’ refers to instantaneous requirement. As the name suggests, demand side management (DSM) involves controlling the demand created by the end users. What is the need of demand side management? The higher the demand, the higher is the amount of current required. The generation, transmission and distribution equipment have to be designed and sized according to the demand and this infrastructure has a maximum capacity which it can safely handle. An increase in demand thus puts strain on existing infrastructure, and new infrastructure may be needed to fulfill further increase in demand in the future. Setting up new infrastructure is a time consuming and extremely costly process. Also, due to the various types of power plants and differences in their behaviour, an optimal arrangement needs to be made to economically meet the demand as discussed in this post. During periods of high demand, the losses in the transmission and distribution lines are also high since the current is high and the losses are proportional to the square of the current. Thus, the demand is a crucial factor in determining the cost which the producers/transmission and distribution companies have to invest in both infrastructure and operations for meeting the end users’ requirements.
Energy conservation is also a factor. Higher demand essentially means higher power requirement, so a device operating at higher power requirement will consume more energy. Energy conservation has become increasingly important due to increased focus on environmental and resource considerations. So essentially, if a piece of equipment is operating for long periods at a high demand and if a DSM strategy reduces the demand level while maintaining the same output, then the energy saved = reduction in demand multiplied by hours of operation.
Demand side management strategies can be mainly divided into
behaviour change and equipment modification/replacement.
Influencing Behaviour Through Electricity Rates
Behaviour change involves changing the pattern of usage of
equipment so that the demand pattern gets modified. Strategies may include
actions such as shifting the usage of some equipment from one time of the day
to another, turning off inessential equipment during peak hours, use of locally
installed generating capacity to reduce drawl from the grid.
Utilities promote behaviour change by offering different types of rate options. Time of use/time of day rates are those in which electricity is priced differently at different times of the day. Prices can be several times higher during peak demand periods compared to non-peak periods. In some cases, based on other data such as weather/temperature conditions, the utility may specify critical demand periods and apply high charges to the electricity used in these periods.
(Source: 2019-20 tariffs for High Voltage consumers in Madhya Pradesh, India)
As seen above, the 10 PM to 6 AM period is designated as an off-peak period and the units consumed in this duration are billed with a 20% rebate on the normal per unit cost.
Another approach is a ‘curtailable’ rate category, for which a customer should possess some minimum ‘curtailable’ load which is required to be controlled - it has to be switched off during peak demand periods or during other emergency situations as declared by the electricity distribution company. This control can be either achieved by making an arrangement for the distribution company to directly control these loads from their end, or through a notice sent by the distribution company to the customer regarding curtailment. These rates may offer lower prices than standard rates or include some other feature as an incentive.
Energy Efficient Equipment
Efficiency of any process is a measure of the output obtained in comparison to the input provided. Energy efficiency is the ratio of the useful energy output obtained to the energy supplied for achieving the outcome. Energy losses occur in any type of equipment because of the inherent characteristics of the equipment - for example, an electric motor converts the electrical input into rotational motion; but in the process, there are factors like electrical resistance of the motor and friction between some parts of the motor, due to which all the energy supplied to the motor is not available at the output.
It is to be noted that efficiency improvement implies maintaining the desired level of output while reducing the input required. Proper performance, safety and reliability should always be given priority while considering energy efficiency measures, as saving energy will not compensate for the losses caused by the decrease in any of these.
Companies may undertake equipment replacement/retrofitting activities to reduce expenditure on energy bills. Apart from this, electricity distribution utilities may offer incentives for equipment substitution activities. Utilities may have a list of equipment which has demonstrated a certain level of efficiency, and may offer discounts to customers for purchasing such equipment to replace their less efficient existing equipment.
Readers in India might be familiar with the free/discounted LED bulb scheme which was launched in a number of states. Though the impact is low if a single house is considered in isolation (9W for LED lamp instead of 40W for incandescent bulb saves 31W, but requires around 35 hours of usage for savings equivalent to 1 unit; the savings are even less if say a 14W CFL is replaced with a 9W LED), the massive scale of implementation has an overall large impact. A report on this scheme, known as the 'Ujala' scheme, is available here.
In theory, launching such a program requires consideration of factors such as the demand and energy savings potential by use of the new equipment, cost and infrastructure required for manufacturing/importing the required equipment, useful life of new equipment to determine life cycle cost, strategy to be used (subsidies etc.) for promoting the use of the new equipment, cost recovery through scrapping of old equipment etc.
Other examples of recent demand side management programs in India include streetlight replacement in several cities, replacement of old agricultural pump sets with new energy efficient ones, and replacement of old, low efficiency 415V squirrel cage motors with high efficiency ones.
Given below is an example of equipment efficiency comparison. The image is a partial snapshot of the Indian standards for efficiency of electric motors. Other technical specifications such as operating voltage, intermittent/continuous operating characteristics etc. are also given to identify which motors will be covered by the standard. Only a few lines are given as an example; the actual standards contain ratings for standard size motors having rated output up to 375 kW.
(Note: As of 2020, IE4 efficiency motors are also available in India since the past 3-4 years, which are more efficient than the IE3 motors listed above)
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