By Sudhir Sharma

100% renewable energy (RE) is the new push of CSOs working in the field of Climate Change. I agree that we need to get to 100% RE if we want to save this world from drastic climate change. Decreasing RE prices (solar and wind) is giving this argument a more stringency. Some of the CSOs, especially in developed world, also are of the view that it is much easier to do so in developing countries, as energy infrastructure is not yet built in these countries then to uproot the fossil infrastructure built in developed countries. To make this effective it is important to understand the limits and needs to make the 100% RE a reality. This is a simple piece to explain why 100% RE is not as simple as portrayed by many.

I speak of solar and wind, the two RE technologies, that are seen as being the source of electricity replacing all fossil fuels. Why not Biomass, well biomass is like a fossil fuel source in terms of operations. The challenge with biomass is that it has its own implications re: deforestation, food production, as well as limitation on how much biomass production is feasible.

To explain things let us take a simple example of system that has constant electricity demand of, say 10 MW for all 24 hours of the day and 365 days a year. Yes, of course, electricity demand is not constant all through the day or in all season. But the simplification is only to bring out the challenges more starkly. Let us further assume for simplicity that sun shines from 6 am to 6 pm every day with same intensity, i.e., solar energy per square metre area of the solar panel is constant. Solar energy intensity per square meter of panel defines how much electricity can be produced by the solar panels. This implies that if a solar power plant of 10 MW is installed it can meet the electricity demand for 12 hours in a day. But what about electricity demand during the night? There are two options, either to invest in an additional of 10 MW solar plant and storage battery (to supply electricity in the night) or set up a 10 MW fossil fuel plant. The point thus is that to meet the demand either a much larger solar based electricity supply capacity has to be created along with electricity storage capacities compared to the demand or a fossil fuel back up facility would be needed to provide electricity when RE is not available.  For the first option one needs both electricity storage capacities plus cost of electricity price based on 20 MW solar plant plus 10 MW battery to be cheaper than a 10 MW fossil fuel power plant. Else one would say when a 10 MW fossil fuel plant can provide electricity for 24 hours, why do I invest in solar at all.

One could say that well neither 20 MW solar plant is needed nor a fossil fuel based back-up system if system in the area is connected to another area to tide over “time of availability” issue. Again to make things simpler, let us say there are two regions such that when it is night in one it is day in the other. The two regions could be connected, but still one would need to install 20 MW of solar capacity on the two sides, 10 MW to meet its demand and 10 MW to meet other sides demand. Yes, we don’t need the 10 MW of batteries, but we need a transmission system to connect the two sides. Whereas, in case of fossil fuel plant we still will need only 10 MW on each side and no transmission lines. Thus the system costs for a solar based electricity system are much higher compared to a fossil based system.

But things are not that simple, solar energy is not constant during the whole day and it is not always available for 12 hours a day. Even in a country like India, with weather being stable, the solar energy incident on solar panels varies across the day and during the year, which implies electricity produced during sunlight hours is not constant unlike fossil fuel based electricity plants that provide constant electricity output and are completely controllable. In case of solar energy, human beings have no control over electricity production. Further, some part of this variation is predictable so one can exactly estimate the energy that will be available from the solar plant though it varies. But some of it is unpredictable and this brings in uncertainty of knowing exactly how electricity demand would be met by the solar electricity plant. One can reduce the uncertainty but not eliminate the uncertainty.  Thus in case of our example of constant 10 MW demand, the solar power plant required even for meeting the demand in day time will have to be of bigger size then 10MW and would need a larger storage capacity. This further adds to the costs compared to the fossil fuel plants.

Thus what this implies is that a 100% RE system is not feasible without significant non-fossil based electricity storage capacities. Further, the investment required can’t be done on equal MW capacity basis. Therefore, stating that wind based electricity supply cost is of the same price as fossil fuel, is actually a wrong comparison and will not result in wind becoming the main source of electricity.

Let us take the example a bit further and add a complication. The diagram above gives the variation in electricity demand during the day. As is visible, the demand during the day is typically higher than in the nights though there are still strong variations, both, during the day and during the night. These variations add further complexities of managing the grid system. To make things easier to understand the implications let us say in our example the demand during day is at constant 20 MW and in the night constant 10 MW.  In such a system one could say that ok I meet the constant demand of 10 MW across day and night through fossil fuel, whereas, the day demand could be met through solar. Though, as mentioned earlier given the variations in solar energy one would still require certain redundant electricity production capacity to be created that can be immediately brought on to meet the gap left by solar energy. Thus the fossil fuel capacity will have to be more than 10MW.

BUT in this system RE is not 100%, it is only meeting at best 33% of electricity demand.

In case of wind the variability of electricity generation is much higher and predictability much lower. Further, even in best wind regimes, the utilization of the wind turbines to produce electricity is at best around 25 to 30% of time during the year. This implies that of the total 8760 hours in a year, a wind turbine produces energy for at most 2500 hours. As in the case of solar, in wind systems too one needs back up to meet the demand for the hours when wind energy is not available. Further, in case of wind, availability could be during low demand periods, which implies they can’t be utilized unless the base load power plant (plant that is operated to meet the constant load during 24 hours) is shut down. This increases the cost of system, as this implies that cost of power from base load plants is higher due to lower capacity utilization. So even if wind is cheaper it comes at increased cost of system, and, therefore might not be utilized. This is the case in Mauritius, where I was recently to discuss possibilities of increasing RE capacity in the system. The high wind speed regime is during the night, when the load is at the lowest. This implies that base load fossil fuel plants have to be ramped down to use wind energy, which is normally not possible, as most of the base load plants are coal based which can’t be instantaneously started and shut down. This implies to use the wind capacity in Mauritius, larger diesel or gas based back-up capacities will have to be set up, as they can be instantaneously brought on line. So taking our example, if 10 MW of wind was only available during the night, 20 MW of fossil fuel capacity needs to be installed to meet the demand during day. Further, as this capacity only operates for 12 hours, the cost of power from fossil system is higher, thus even if wind cost is cheaper the overall cost of electricity in the system is higher.

One could say in a large geographical domain where wind regimes might provide the possibility of smoothening the availability, wind could be continuously available as any other fossil fuel power plant. Though even such cases the capacities of wind based electricity would have to be much higher than that for fossil fuel based systems. It is quite possible but not that likely. Nonetheless building interconnected grids systems across larger geographical domains can increase the level of RE use. But this implies significant investments in grid infrastructure. Presently in India, wind capacity in Tamil Nadu is not fully utilized as it is availability is during periods of low demand period in the Tamil Nadu grid. Evacuation of the surplus wind capacity to neighbouring states for utilization is constrained by the transmission capacities. Thus the share of RE is combined grid of Tamil Nadu and neighbouring state could be increased but requires significant amounts of investments in transmission grids at the minimum. Again consider just the cost of wind electricity based on wind plants doesn’t reflect the true cost of using the wind capacity in Tamil Nadu.

Thus at present stage of technology development 100% RE is not feasible but yes one can work towards increasing the share of RE. At present RE can only be used to shave of demand from the load curve above the base loads. This too requires a lot of investment in the grid and RE generation management to ensure that RE injection in the system doesn’t lead to destabilization or break down of the grids as the capacities of RE plants increases.

Competitive prices of RE are a necessary condition but not sufficient to replace fossil fuels completely. But such comparison of price for competitiveness can’t be on the basis of MW to MW, as for RE to be able to provide 100% electricity requires much larger capacities and additional investments in storage capacities. Therefore, the current analysis that solar and wind are competitive to fossil based plants are actually not academically sound comparison.

In developing countries where the energy demand will grow to address the development gap, fossil fuel plants can’t be wished away as they would still be needed to meet the base load. Yes RE can be used to meet the level of demand above the base load in the new demand. Thus actually asking for developing countries to not build any new fossil fuel plants is akin to asking them to halt their development efforts and is completely an unacceptable demand to put on developing countries.

This is not to argue that 100% RE goal is not required. But to highlight that such a goal requires huge investments in developing storage technologies and technologies for smart grids. This lead has to be taken up by developed country investments in technology development and making them available to all the countries. This essentially means that we as CSO have to push for an early 100%RE in developed countries if we want the world to go 100% RE soon.

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