Integrating renewables into mainstream

Making renewable energy (RE) a part of the energy mix alongside conventional energy is fraught with challenges. The fossil fuel-based system that attaches a high premium to the stability and predictability of the current flow is ill-prepared to integrate intermittence which is a hallmark of renewable energy. Keshav Chaturvedi looks at the issues, the challenges and the evolving measures to integrate renewables into the grid

Current systems, everywhere in the world, including India, are equipped to transmit huge loads of high-voltage electricity from a small number of production centres. The ideal mix in the conventional energy setup is the one where 60 per cent of the energy is sourced from fossil fuels (coal or gas-based power plants) and the remaining 40 per cent from large hydro power plants. This mix has provided stable and continuous power supply to every society and has become the model of development around the world.

The entire transmission system is geared to source energy from a handful of predictable large sources. This helps in planning and scheduling the power flow and prepare to deal with any gap in demand and supply. However, since the end of the 20th century, this system has been under severe pressure. Increasing awareness of climate change; impact of energy industry on the global climate patterns; and rising prices of fossil fuel have forced governments to look for alternatives that are clean and abundant. Therefore, there have been efforts to develop new technologies that could facilitate the energy evolution, uninterrupted transmission; equitable distribution; and demand side management – and therein lie the challenges.

Challenges of integration

Renewable energy (RE) sources like wind, solar, small hydro and biomass-based power plants have emerged as alternatives to enable improvement in power supply and fill the gap between rising demand and constrained supply. RE sources — sun, wind, water and organic waste — do not pollute the environment as they are natural elements. It is this fact however that makes their integration into the conventional energy system difficult.

Renewable energy generation, especially from wind, solar and small hydro, is dependent on natural cycles and it is difficult to make predictions about them on a long-term basis. Also, their production dips and rises through the day depending on the intensity of sunlight or the speed of wind.

Renewable energy generation, especially from wind, solar and small hydro, is dependent on natural cycles and it is difficult to make predictions about them on a long-term basis. Also, their production dips and rises through the day depending on the intensity of sunlight or the speed of wind.

Intermittent renewables, when connected to the grid, especially in large amounts, create challenges to power system operators. It has unexpected impact on the transmission system which makes the task of balancing demand and supply difficult for the systems’ operators, as they have to be on their toes to maintain stability and power quality all the time. Another factor is — renewables lead to higher unpredictability in net load variability and fluctuations which adds to the woes of the energy managers.

Smooth integration of variable renewables need to draw on a number of solutions. Ajit Pandit, Director, ABPS Infrastructure Advisory Pvt Ltd, says, “Integration of large-scale variable RE sources would require actions at multiple levels from various stakeholders, including RE generators, grid operator, transmission system planners, regulatory interventions and purchaser entities, etc. Better forecasting tools, improved visibility at State Load Dispatch Centre (SLDC), and a communication infrastructure would create the necessary ecosystem to facilitate smooth integration of such RE resources. However, a pragmatic approach deploying the combination of technical solutions, development of spinning reserves, and demand side response measures through smart grid controls and commercial mechanism needs to be adopted.”

Supply side management to smoothen out variability

Global studies into integration of renewables have shown that power fluctuations from variable sources can be better managed by enlarging the size of the balancing area. Variable outputs of individual wind farms, for example, can be dealt with by integrating a wider geographical spread. Connecting separate but contiguous renewable power areas will have smoothening effect. As the balancing area increases, the chances of ancillary services becoming available to handle the net load variability increases.

It is said that due to the intermittent nature of renewable energy, power system operators would need a backup to respond to fluctuations in supply. These backups are ancillary units that not only provide flexibility in a generation portfolio, but also provide an insurance against sudden drop in generation from variable sources.

The ancillary services can be divided into three types, depending on their speed of response. The frequency response reserves are primary generating units that are usually online and synchronised. They can ramp up or down production very quickly to meet sudden demands. The spinning and non-spinning reserves are secondary generating units and they may or may not be online but can ramp up or down their production within a relatively short time. The replacement reserves are offline and take a much longer time to come into action.

A study done by the European Network of Transmission System Operators of Electricity (ENTSOE) in 2010, however, said that as the share of variable renewable energy increases, the need for maintaining a larger ancillary service also increases. This creates a burden for utilities as it increases operational costs.

In the absence of adequate ancillary service and the insistence of government or any other national electricity authority to source power from renewable sources, utilities evolve a three-step approach to source electricity from variable sources. Either they accommodate variable supply at the cost of electricity from other sources; if accommodation can’t be managed, they curtail the surplus supply; and third, they transfer the surplus supply to neighbouring power systems.

The third option can be restricted if the region or a country has no national grid. In China, for instance, they don’t have inter-regional grid connections and no national grid either, which makes transfer of renewable energy to high-demand areas well-nigh impossible. In contrast, India is better placed due to the presence of a national grid and also national, regional and state load dispatch centres. So, the entire system can act in tandem to integrate supply from variable sources from different regions and multiple points.

While this structure is in place, the challenge that is emerging is of keeping pace with renewable energy growth. Pandit says, “The share of RE in the overall energy mix is 12 per cent in installed capacity terms and 6 per cent in energy terms. Experience in other electricity markets clearly establish that higher penetration of RE sources can be easily accommodated. However, the challenge in the Indian context is that the development of evacuation/transmission infrastructure is not able to keep pace with the pace of RE generation capacity addition in many states, leading to the bottling up of RE generation. To be able to accommodate a huge quantum of RE sources, we need to have the planning of RE transmission to be an integral part of our overall grid network planning.”

Aware of the growing need to integrate renewables in the system, the Integrated Electricity Grid code of 2010 made special provisions for wind and solar power. It said that system operators (State Load Dispatch Centre (SLDCs)/Regional Load Dispatch Centre (RLDCs)) shall make all efforts to evacuate the available solar and wind power and treat as a must-run station. However, the system operator may instruct the solar/wind generator to back down generation if grid security or safety of any equipment or personnel is endangered and solar/wind generator shall comply with the same.

Demand side management to deal with variability

A lot of efforts are being made to manage the supply side of renewable energy. Another very important issue is demand side management. As renewable energy is intermittent and the supply ebbs and flows during the day as well as at certain times of the year, utilities all over the world are working out strategies to align consumer behaviour with the supply pattern. In countries like Finland, where the entire system of electricity distribution and use is highly computerised, real-time pricing of power is used to engage residents and the industry sector in managing their respective demands.

However, in countries like India, this is not possible yet due to low penetration of ICT technology in managing the demand side. The government has launched an ambitious programme — Restructured Accelerated Power Development & Reforms Programme (RAPDRP) — to fundamentally change the entire distribution, generation and transmission scenario. Once it is completed, the entire system would be online and then high- end real-time measures can be undertaken to manage demand by factoring in variable supply schedules.

Another important factor that has emerged over the past decade is power-trading. Experts believe that a robust power- trading market can go a long way in integrating renewable energy into the present system. Ajit Pandit says, “Increasing share of RE in the overall energy mix would be driven by the RPO trajectory and rigorous monitoring of enforcement standards by the regulators. The robust spot electricity market would certainly help utilities to manage their variable RE sources procurement in an effective manner.”

But for that, renewable energy has to be connected to the grid in a big way and RE producers have to be registered on the power exchange. Executive Director, PTC India, Dr Rajiv K Mishra, says, “Renewable energy is still embedded in state utilities. Another factor is its infirm source of power and is dependent on natural cycles so their role in power-trading will remain limited at best.”

Finland-like spot market being used to source wind and hydro power throughout the Nordic region is a distant dream due to obvious problems as Dr Mishra says, “Thinking of using spot market to pep up RE use is too ambitious as we don’t have a spot market in India for any source of electricity.”