Electricity generation from renewable sources such as solar and wind offers numerous benefits to the country, but their intermittent and variable nature poses multiple challenges when their share in the grid exceeds beyond certain minimum levels. Without dedicated storage, renewable power generation plants are considered “non-dispatchable” as system planners and operators cannot rely on them to serve the continuously changing demand of electricity in their systems the same way they are accustomed to in the traditional grid. Below, we explore the viability of a facility, renewable power control center, between renewable generators and grid operators that can ease to a considerable degree the intermittency and variability of renewable power generation plants.
Renewable power generation technologies, especially those based on solar and wind, are making rapid inroads into the power grids around the world. In its flagship Renewables 2021 Global Status Report, REN21, a global leader in compiling renewable energy statistics and policy initiatives, notes that despite the COVID19-induced economic slowdown, 139 GW of PV and 93 GW of wind capacities were added in the global power grid during 2020 leading to a total PV capacity of 760 GW and 743 GW of wind capacity in the world. Total investment on renewable power projects exceeded USD 300 billion during the last year. Additions of renewable power generation capacity outpaced the collective additions of both fossil fuel and nuclear power capacity. The march of renewables now seems unstoppable as these plants have started to compete head-to-head with their conventional competitors even without any policy support.
We must note, however, that renewable power generation technologies are inherently different from the conventional fossil-fuel and nuclear-fuel based power generation technologies. In contrast to conventional technologies which rely on the stocks of exhaustible primary resources, solar and wind technologies base on natural flows of primary resources. Despite being ubiquitous, these resources are scattered, diffused, and also unpredictable and variable. Planning, decision-making, and financing frameworks and operational practices that have evolved around large-sized conventional projects in a centralized power supply and delivery system are not amenable for embracing small-sized, distributed, and diffuse-resource based power generation schemes.
Adding renewable capacity in the supply portfolio at any significant penetration levels poses both planning as well as operational challenges. Two key issues the planners face in developing long-term optimal plans are: first, how much firm capacity a candidate renewable power plant will contribute to their system to ensure that the finally selected portfolio is adequate for serving the forecast demand without violating reliability limits; and second, how much energy it will contribute in the forecast total requirement? Any miscalculation can easily lead to both allocative and productive inefficiencies for which the economy and consumers have to pay, and often dearly. These issues do not go away even if the planners succeed in coming up with a perfect generation portfolio; they just shift shoulders—from those of system planners to those of system operators.
Electricity demand in most grids follows a similar daily trend. From a minimum, it rises to a crest and then returns to the same minimum. The values of minimum demand, maximum demand, and the way it rises and falls can vary from day to day, season to season, year to year, and system to system, but the pattern is largely similar. In electric utility parlance, this is called load or demand profile or simply load curve. It is worth mentioning here that each point on this load curve for a given hour or shorter period in fact represents the midpoint of an envelope in which the actual demand may fall. The system operators’ whole function revolves around planning, scheduling, and then dispatching the resources at their disposal (mainly generation but could also include demand management) to serve the expected demand in the most economical way while maintaining the standards of reliability, quality of service, and environmental protection.
Economic considerations are arguably paramount, but three additional technical factors influence the scheduling and dispatch process. The ability of these resources to cater to intra-hour or sub-hourly fluctuation in demand (called regulation), ramping up or down to follow the demand as it rises to the maximum during the day and then falls back to the minimum (called load-following), and to assist in handling any contingency on the system triggered by the loss of a major source of supply, transmission line or component, or load. System operators employ a host of supply resources and some demand response services, to serve the anticipated demand in the face of dynamically changing operating conditions in their control areas.
The above situation changes when renewable plants are added to the system. In addition to the random variation in demand and system conditions, a new source of uncertainty surfaces. It’s the intermittency and variability of the primary energy resource, solar irradiance or wind speed, at the plant site. At low penetration levels, like the 4 to 5 percent we have in our grid at present, power and energy available from renewable plants can be treated as negative loads. System operators can ignore their capacity and serve the net demand in the system through some extra duty cycling of the available conventional plants without incurring any additional economic or technical penalties. But as their share in the grid rises like the 20 percent by 2025 and 30 percent by 2030 our country is considering such issues cannot be ignored as this can result in heavy technical and financial penalties.
What makes a power plant “dispatchable”? It’s the ability of the system operator to use and control it on command–turn it on or off, synchronize it with or de-synchronize it from the system, and raise or lower its output. Obviously, solar and wind power plants whose availability is uncertain as well as variable do not fit the above criteria. The simplest and easiest way to make these plants dispatchable is to add on-site storage to cover periods when the primary resource is either unavailable or available at reduced levels. The only issue is that it adds to plant’s costs, sometime, as much as 100 percent.
A variety of other techniques can be used to cover the uncertainty and variability of solar and wind plants. The requisite backup can be provided by building extra quick-start and fast-response conventional generation, by building additional flexibility in the grid, by building large storage facilities such as pumped-hydro and compressed air, by dispersing these plants over wider areas to spread the risk of unavailability, by seeking regional integration of autonomous grids, and by influencing electricity demand to align it with the timings of renewables’ availability.
Regardless of which option or combination of options is used, effective handling of the above challenges demands a cutting-edge weather and resource forecasting system to help planners in quantifying the availability of solar and wind resources and the patterns of their distribution and mutual correlation at various locations in the country. While for long-term planning historical statistics and satellite-based data may be adequate, these data are less useful for operational purposes which requires finer spatial and temporal resolution of resource availability and variability. A combination of physical and satellite-based data along-with sophisticated analytic modelling capability is essential to equip the system operators to commit, schedule, and dispatch available renewable capacity to derive maximum benefits from these resources.
Some basic forecasting capability is essential for any renewable power producer to offer the capacity and output of its plant (wind farm or PV park) to enable the system operator to include it in its schedule for dispatch. The scale, complexity, and sophistication of the forecasting system requisite to predict to any acceptable certainty its capability and expected production, is unrealistic in terms of cost and management. On the other extreme, expecting the system operator to develop and maintain such a system at its own end is also unrealistic as it would add another layer of complexity to an already complex function and may not be even perceived impartial by some grid participants. A new function in the form of a “renewable power control center (RPCC)” offers a useful means of performing the role of a middle entity—kind of an aggregator and interlocuter—between the renewable power producers and the system operator.
An RPCC can offer multiple benefits to the country in scaling up the deployment of renewable plants and their optimal utilization. Using a state-of-the-art weather and renewable resource forecasting system and by linking it with the data collected from plant sites, from within the grid, and from satellites, the RPCC can predict with a much better certainty, the availability and output of individual plants, and after some processing, offer it to the system operator for scheduling and dispatch. This arrangement holds a much greater promise for optimizing renewables’ contribution to the grid while mitigating to considerable degree the concerns about their intermittency and variability. This is not a novel idea as many other countries, realizing the scope of this arrangement, have either already developed such centers or are in the process of their development.
Such a facility, a pioneering one, has been functioning successfully in Spain since 2006. It’s considered the lynchpin of Spain’s power grid and has played a key role to Spain’s emerging as a world leader in developing and integrating solar and wind power generation in its power grid. This control center of renewable energies (CECRE) under Spain’s transmission system operator, Red Eléctrica De España, has been the main contributor to its serving routinely over 40 percent, and occasionally even up to 80 percent, of the country’s electricity demand via solar and wind generation despite the fact that Spain is not a renewable resource rich country; its interconnection with the other European countries’ power grids is also minimal as well as weak.
Another facility worth mentioning is the dedicated renewable resource forecasting and dispatch center that is being developed by Morocco’s transmission system operator ONEE with assistance from the World Bank on the model of Spanish CECRE. Morocco has an ambitious plan to develop renewable power generation and felt that a dedicated control center for forecasting of renewable energy generation potential on a long-term ahead to real time was worth the cost. The primary objectives of this center are real-time tracking of generation from individual renewable power plants, geo-spatial visualization of renewable energy generation, close coordination with the national load dispatch center for smooth grid operation, and act as a single source information repository and coordination point for renewable energy in the country. Some other countries, notably India and Saudi Arabia, are also seriously considering developing of control centers (or frameworks) for similar purposes.
The just released “Renewable 2021: Analysis and Forecasts 2026” report by the International Energy Agency (IEA) also confirms that power generation from renewable resources will maintain its thrust in the next 5 years and beyond also. IEA expects a further addition of 1,800 GW during 2021-26 to reach a cumulative renewable capacity of 4,600 GW globally. IEA feels that to achieve its suggested goals of “Net Zero by 2050″, countries will have to further accelerate renewables’ penetration in their grids and recommends relentless pursuit of their present efforts, need new policy initiatives, and further facilitating renewables’ grid integration.
Timely development of a centralized multi-source and cutting-edge weather and renewable resource data collection and forecasting system in the suggested control center can play a pivotal role in achieving the above goals in Pakistan too. This center’s access to primary resource availability data at various renewable plant sites, plant characteristics, real-time grid operating conditions, and assessing their consequent impact on supply-demand balance will equip the RPCC to offer the system operator a package of renewable capacity, energy, and ancillary services with a great deal of certainty compared with individual plant offerings. This will not only minimize the uncertainty and variability of individual renewable plants but will also help the country derive the maximum benefits from these facilities.
[box type=”note” align=”” class=”” width=””]The writer is a freelance consultant specializing in sustainable energy and power system planning and development. He can be reached via email at: msrahim@hotmail.com[/box]