Thanks to the National Solar Power Mission, the solar power capacity in the country is poised to increase in a rapid way in the next 4 to 5 years from the present installed capacity of around 3 GW. The new government has scaled up the target for solar capacity. The revised target is to achieve 100 GW of solar capacity by 2022 as compared to the earlier target of 20 GW envisioned by the Congress government. Though the target has been scaled many fold, how much of it would be actually commissioned – keeping in view the Indian ground reality it would be difficult to guess as of now. The Indian ground reality of topsy-turvy policies, state government priorities, land acquisition issues etc., may lead to derailment of capacity addition targets. Nevertheless, the decision of the new government on not to act on the ‘Anti-Dumping Duty’ (ADD) recommendation of the previous government has shown the new government’s commitment and vision for solar power.
Had the decision of high ADD imposed, there would have been severe setback to the capacity addition in solar. In fact, till the clarity on ADD came – many developers had kept their solar plans in abeyance as the projects which were awarded to them after tough competitive bidding would have become unviable – with increase in the cost of solar panels on account of increase in duty on imported cells and modules. With the clarity on AAD, the developers are back on their plans to complete their on-going projects at the earliest and are also looking aggressively for new bids. India can now look forward for rapid addition of solar capacity in the grid.
Though there is clarity on the policy front, one technical aspect that has the potential to derail the development of renewables, including solar power, emerges from the unpredictable nature of electricity from these renewables. Except Bio mass/gas, ‘Waste to Energy’ (WTE) and to some extent Solar Thermal with storage and ‘Run-of-River’ (RoR) Small Hydro power plants (SHP) with pondage, electricity from all other renewables viz. Solar Photo Voltaic (PV), Wind, RoR SHP etc. is solely dependent upon the vagaries of nature. E.g. energy from solar PV is dependent upon the presence of sun light, whereas energy from wind project is dependent on blowing of wind. Apart from the unpredictable nature, the electricity from these renewables is also prone to variability, which means the electricity from these renewables is non-controllable, i.e., the power output would be non-steady. For example, in case of solar PV, the energy output is directly related to the intensity of sun light termed as insolation – higher the insolation, higher is the output. Therefore, in case of solar PV, electricity starts flowing to the grid after some time past sunrise and ebbs out some time before sunset – typical time of electricity generation would be from 7 to 8 am in the morning to around 5 to 7 pm in the evening, with some variations in summers and winters. Further, the electricity from solar PV typically follows a bell curve with peak levels reaching in the afternoon from 11am to 12 noon to 1 to 2 pm. The output is also susceptible to any shade on the solar panels, and therefore is negligible during rainy days.
For the stability of power grid, it is pertinent that there is a balance between the demand and supply of electricity at all point of time. If the demand is more than the supply, the frequency would dip and vice versa. In extreme cases, it may lead to tripping of the entire grid unless load shedding is carried out. Typically, the Indian grid has two peaks – one smaller peak in the morning between 9 to 11 am, when the offices and commercial establishments start functioning, and a higher peak in the evening between 7 to 9 pm when the domestic & commercial lighting demand kicks in. The demand reaches its lowest point some time in between 2 to 4 O’clock in the night. This has been the general pattern in the Indian grid, with slight variations from state to state, depending upon industrial development and also with variations in weather. For optimum, economical and efficient operation of the grid, the peak demand should be met by peaking power plants viz. gas power plants, storage/pondage hydro power plants or pump storage hydro power plants etc. The base power which is required by the grid for nearly the entire 24 hrs should be met by base power plants viz., coal based thermal power plants, nuclear power plants – and to some extent also by large storage hydro power plants. The advantage of peak power plants is that they can be quickly turned on/off, reduce/increase output depending upon the requirements of the grid and thus the operator has control over their operations.
The generation from renewables is entirely dependent on the vagaries of nature and the operator has no control. Therefore, under the renewable power policy, energy from renewable sources is accorded a ‘must flow’ status to the grid and not to be backed down. Apart from environment consideration, the policy of not to back down power from renewables is also financially prudent – as the power from renewables have negligible variable cost. The danger to the stability of the grid arises from the ‘must flow’ status to these renewables, mainly solar PV and wind. If, at any point of time the power demand and supply in the grid are evenly matched – and at the same time the share of unpredictable power from renewables increases, then due to its ‘must flow’ status, power from base power plants viz., coal-based would be required to back down in order to stabilise the grid. This backing down can impact the base power plants (read coal based) by increase in their cost of generation, as the thermal power plants become less efficient on lower ‘Plant Load Factor’ (PLF). Variable Cost (VC) per unit and Fixed Cost (FC) per unit, both would increase – VC due to lower efficiency and FC as the fixed cost would be spread over lower units. This would ultimately increase the cost of electricity to the consumers and would amount to unintentional cross subsidising power from renewables. Backing down of base power plants (if it happens) would also point to insufficient management of the grid and lack of adequate planning.
As of now, the installed capacity of solar PV in India is around 3 GW, wind is at around 21GW and SHP around 3.8 GW, together they account for ~ 28 GW, which is ~ 11% of the entire installed capacity of India ~ 255 GW (as on Nov 2014). It is however, pertinent to note that due to low PLF (solar around 17 to 20% and wind around 20 to 26%) the energy contribution from these renewables to the grid is proportionately less than their percentage share in the installed capacity, at around 4 to 6% as against share of 11% in the installed capacity. Presently, there is not much impact on the stability of the grid on account of unpredictable power from renewables despite its ‘must flow’ status, though there has been state specific operational issues in some states – due to lack of adequate planning. As has happened in the state of Tamil Nadu, where due to inadequate evacuation system in areas with concentration of wind farms, the electricity from the wind farms could not be evacuated due to congestion in the evacuation lines.
Target of adding 100 GW of solar by 2022, however, may alter the present impact of renewables on the operation of the grid. Add to it another 60 GW of planned addition of wind power by 2022 and the scenario may change completely. Though, the entire target may not fructify – with the Indian ground reality, but even if 60% to 70% target of solar and wind is added to the grid – it may add additional renewable capacity of around 100 GW by 2022. In the same period, the planned tentative capacity addition of conventional power projects (mainly coal based & large hydro) is roughly pegged at ~ 138 GW, 38 GW in the remaining period of 12th plan (2012-17) and 100 GW in the 13th plan (2017-22). With the present installed capacity of 255 GW, the total installed capacity by 2022 may touch maximum ~ 493 GW (exist – 255 + conventional planned – 138 + solar & wind planned – 100). This is with assumption that the entire capex for conventional power projects would be commissioned as planned. With some of the ageing coal based plants getting de-rated/de-commissioned by 2022, the installed capacity could be considered around ~ 480 GW.
From the present installed capacity of ~ 28 GW, the total capacity of renewables mainly representing unpredictable power i.e., Solar PV, Wind & SHP would touch ~ 125 GW (considering de-rating of some of the exiting capacity) by 2022, taking the present share of renewables of around 11% in the installed capacity to around 26%, which would correspond to around 12 to 13% in energy content. Such a high percentage of unpredictable power in the grid with ‘must flow’ status may not be prudent to operate the grid economically. Though some of the power planners have been indicating that the Indian grid can sustain unpredictable energy content of up to 14 to15%, the same is doubtful as the bulk of the unpredictable ‘must flow’ power would come to the grid at non-peak hours – solar during day time off peak and wind during night time off peak. In comparison, the unpredictable power capacity (solar & wind) in China presently amounts to ~ 109 GW, which is only ~ 9% of the total installed capacity of ~ 1247 GW.
Some may argue that part capacity of the planned solar addition would comprise small kW size roof top installations which may not impact the grid, but one should not forget the fact that most of the roof top solar installations would take place in grid connected cities and would eventually replace grid power or feed-in to the grid (due to net-metering facility), depending upon the household consumption. The end result would be the same i.e., roof top installations would impact the grid the same way as large MW size land-based solar installations would impact. Only the off-grid solar installations would not have any impact on the grid, rather they would eliminate the need to stretch the grid to far off area not considered financially viable.
Experience of solar ramp up in some of the European countries is also worth taking into account. Germany, which has installed one of the largest solar power capacity of ~ 38 GW, largely of PV, due to lucrative Feed-In-Tariff (FIT), is suffering from the issues of grid stability. In the 3 year period – from 2010 to 2013 Germany added ~ 7 GW of solar capacity every year but did not plan for storage for sucking out the day time electricity from the solar PV. As a result, to stabilise the grid during day time when the solar PV starts pumping, Germany has to resort to exporting power to the neighbouring countries at cheaper rates. Though the combined share of solar & renewable in Germany in capacity amount to around 30%, their contribution in energy terms is only around 5%. Lately, new capacities in solar has started going down due to tightening of government policies – reduction in FIT and limit on the maximum installed capacity of solar utilities. In Spain, which at one point of time was at the forefront of the solar energy movement, the government has gone one step ahead and reduced the solar tariff from retrospective date. The reason for such drastic steps were a growing deficit – as the government didn’t pass to the consumers the high tariff being paid to the solar power developers resulting in ballooning deficit that needed emergent action in order not to derail the economy of the country.
The debate on the capacity of Indian grid to withstand the unpredictable energy/power content, it would be prudent to plan for sucking out the unpredictable ‘must flow’ power from the grid during off peak hours by suitable storage mechanism in order to utilise the same during peak hours. Different storage mechanisms available for storing bulk electricity are:
- Battery storage
- Pump storage hydro power plants
- Solar thermal with storage
Battery Storage: The conventional bulk storage batteries are not environment friendly and would also require change every 3 to 4 years. Life cycle cost would be higher – and therefore suitable only for smaller capacity off-grid utilisation. Recently there has been advancement in rechargeable bulk storage batteries wherein energy would be stored in liquid eliminating solid state interactions in conventional rechargeable batteries. The manufacturers are claiming life of 10 to 15 years and even of 20 years. However, they are very costly as of now and would add around 12 to 14 in per unit of electricity and thus financially prohibitive. Till this technology matures and the cost comes down, it would not be financially viable for large scale adoption.
Pump Storage Hydro Power Plants: Pump Storage Hydro Power plants (PSHP) can be one of the techno-economically viable solution for storing bulk excess unpredictable power. Though it would consume around 25 to 30% of the power to be stored, it would still be cost effective. However, a number of PSHP are already commissioned in India and a study would be require – whether their full advantage as pump storage plants is being reaped or not. Further, as the existing PSHPs in India are combination of conventional (or natural) hydro power plants and pump storage, pure pump storage hydro plants can be planned to utilise the excess unpredictable power being fed in the grid. In pure PSHP there is no need for natural gradient in a river, water can be pumped from a river or a water body to a water reservoir planned at a higher altitude in nearby hills by utilising electricity during off-peak hours. During peaks hours the water stored at higher altitude can be utilised for generating electricity. Such pure PSHP of smaller capacities in the range of ~ 100 – 200 MW can be located nearer to the cluster location of Solar or wind farms in order to avoid transmission losses. As the implementation period for PSHPs is very high as compared to other power projects, the action plan for such storage should start immediately.
Solar Thermal with Storage: Till date solar thermal power plants were not being looked as financially viable proposition in India due to various reasons ranging from technical to high cost. For the same capacity, as compared to ‘solar PV’ the ‘solar thermal’ units require more land and are costly. Solar PV units are modular and therefore can be set up in discrete units at the same location as compared to solar thermal – which requires construction of the entire plant capacity in one go. Implementation period for solar PV ranges between 6 to 9 months for a medium size plant whereas it takes 28 to 36 months for a solar thermal to be commissioned. Solar thermal requires a minimum threshold capacity of ~ 50 MW for Indian conditions, to be viable as compared to solar PV – where even a one kW capacity plant can be viable. Solar thermal requires boiler and turbine to generate electricity and thus issues of O&M are similar to coal based thermal power plants as compared to simplicity of O&M in solar PV. Availability of water is another issue, as most of the ideal location for solar plants – thermal or PV is water scarce areas. Solar PV doesn’t require much water apart from cleaning of the panels, which is not the case with solar thermal, which is heavily dependent on water for steam generation/cooling purpose which is akin to coal based thermal power plants. Despite many disadvantage vis-à-vis solar PV, solar thermal plants can be designed with storage which means that the excess electricity generated during off-peak can be stored and used during peak hours. Though the capital cost of solar thermal with storage would be higher but the life cycle cost would still be cheaper than other options for bulk storage of electricity. With increased focus on unpredictable renewables in India especially on solar PV, solar thermal with storage option definitely requires a serious look.
(The views expressed in this article are of the author and not of the organisation he belongs to.)
What are your views on this article? Please comment your feedback!
