Media is currently abuzz with reports of rapid inroads that renewable power generation technologies are making into the power sector of many countries around the world. Encouraged by these trends, our government is also set to increase their grid penetration from 4 percent at present to 20 percent by 2025 and 30 percent by 2030. Some enthusiasts are not happy with it and are urging the government to further upscale these to 100 percent citing examples of a couple of countries that have achieved this target already.
We explore below the viability of switching our power generation solely to renewables, identify the major constraints to achieving this ambitious goal, and highlight the enabling role that electricity storage technologies hold in the above transition. Though renewables possess tremendous potential for every sector of our economy, the discussion is restricted to their deployment in the power sector’s supply side only.
First of all, no country has so far achieved the target of 100 percent power generation from renewables in its system, though some are aggressively pursuing this goal. Even Denmark, whose example is often cited by avid proponents of renewables, has managed just over 50 percent of penetration in its grid and has set a target to reach 100 percent by 2050. Perhaps, they refer to the singular event that occurred between 2 and 3 am on the morning of 15 September 2019 when Denmark’s entire electricity demand was served by its own wind plants.
There are fundamental differences between renewable and non-renewable energy resources which must be kept in mind along with the complexities and constraints of the present power supply systems to realistically assess the scope, viability, and practicability of relying solely on renewables to serve electricity demand. The target is arguably achievable and desirable too, but may not be practicable any time soon unless cost-effective storage technologies become commercially viable and are deployed with renewable power plants to cover their intermittency and variability.
The world is definitely moving towards a total renewable electric system and we in Pakistan should also embrace these trends with open arms but it will be prudent to plan the transition carefully and use the time still available
Unlike the limited, and thus exhaustible, stocks of conventional fuels (coal, oil, gas, and nuclear), renewable energy resources (solar, wind, tides, waves, geothermal, biomass, etc.) depend on natural energy flows on a particular location. All of them are replenished by nature, though the times required for it may span from next instant to many years or even decades. Renewable resources are also abundant in nature and some are even ubiquitous, but they are dispersed, diffused, uncertain, and variable in time. Their conversion to electricity, therefore, is constrained not by technology but by the nature itself.
Physical systems in which power generated from renewable sources is to be used, also have unique characteristics. Electricity in the system must be produced and delivered the moment it’s demanded as its storage in any significant amount is difficult as well as expensive, if not impossible. Any imbalance between demand and supply must be managed instantly, to avoid serious damages to the system and catastrophic consequences for society. In power system operation, an hour is akin to a century as power systems are designed to deal with imbalances and disturbances within milliseconds.
Electric utilities serve the continuously varying consumer demand through a variety of techniques which make the power system one of the most complex and expensive undertakings in the world. Two of their salient features are worth mentioning. To serve consumer demand at all times, utilities ensure that they always maintain adequate generation, transmission, and distribution capacities in their systems (called “adequacy”). The second, and equally important, feature is to ensure that power systems are configured, designed, and laid out carefully and with sufficient redundancies to deal with any normal or abnormal disturbance in the system (called “security”).
When the share of renewables (solar and wind) in the grid rises beyond a system-specific limit (normally 5 to 10 percent), it starts to impact negatively on both the adequacy and security of that system owing to their intermittent and variable nature. Power production from a solar or wind plant can drop within moments from its full rating to almost zero due to a cloud moving over the solar plant or a sudden stopping of wind on the wind plant site. Even when available, power produced from these plants could fluctuate widely. Both these aspects make renewable plants non-dependable for serving consumer demand unless supported with suitable backup generation or storage.
As the electricity produced from renewable power plants is virtually free and eco-friendly, it’s tempting for electric utilities to increase their share in the grid as much as is practicable. However, their high investment costs and intermittent and variable nature have constrained most utilities from adopting them at a wider scale as they are required to maintain both the backup capacity and operational flexibility in their systems to continue to serve consumer demand reliably and economically. Things, however, have started to change lately.
The past couple of decades have seen order of magnitude reduction in the costs of both solar and wind systems and also in the battery-storage technologies. Both these developments are acting to ease the resource adequacy and operational flexibility constraints and are forcing electric utilities to rethink the scope and viability of renewable power technologies for their systems. The above two developments, especially those in the battery storage technologies, are proving “disruptive forces”, and are poised to reshape the electric utility business landscape completely in the coming years.
Unlike the other conventional electric storage options such as thermal mass, chemical, compressed air, pumped hydro, and conversion to other gases which require some minimum scales and special locations for cost-effective development, battery storage offers many advantages in terms of its location-independence, modularity, and portability. The only constraints preventing their wider deployment are their still higher costs and availability of raw materials needed for battery manufacturing.
The costs for utility-scale storage batteries have dropped by 90 percent since 2010 to reach USD 176 per kWh for a 4-hour pack in 2018. National Renewable Energy Laboratory (NREL) in the United States estimates the utility-scale battery storage cost to decline to USD 124 per kWh by 2030 and USD 76 per kWh by 2050. The results of a recent study at MIT in the United States (reported in IEEE Spectrum in September 2019), however, estimates that these costs must further decrease to around USD 10 or 20 per kWh to make them competitive for wider-scale deployment in the power grid. In other words, though we are on the right track, we still have a long way to go.
Shifting to a 100-percent renewable powered grid is, therefore, both plausible and achievable, but in the long run only. The key to achieving this highly-desirable goal, however, will be the cost-effective availability of storage technologies. The world is definitely moving towards a total renewable electric system and we in Pakistan should also embrace these trends with open arms but it will be prudent to plan the transition carefully and use the time still available to us to deploy the enabling systems and institutional capacity that is requisite to ease this transition.
Somewhere along this transition, but long before reaching the 100-percent renewable target, we may have to re-evaluate the continued viability of our conventional power supply system also. It may just be the time to castaway the existing model that relies on a centralized grid interconnecting large power plants through long-distance high-and extra-high voltage “ac” transmission lines. We may have to replace it with a more distributed “dc-based” micro and mini-grids linked together through a super grid. We are certainly entering into interesting but challenging times, so bon voyage.
The writer is a freelance consultant, specializing in sustainable energy and power system planning and development