India's batteries are getting longer, not just bigger

**Akshara** (0:04)
In today's episode, we'll break down two important stories. First, we'll talk about India's batteries getting longer, not just bigger, and then we'll talk about the patient investor running out of patients. Welcome back to The Daily Brief by Zerodha, where we cut through the noise to help you understand what's actually happening in the most important stories from business and markets. I'm your host Akshara, and today is Wednesday, 24th June. Coming to the first story. So between May and December last year, India let 2.3 terawatt hours of solar electricity go to waste because the grid had nowhere to put it. Nearly 40 percent of that waste came in October alone when the sun was strong, demand was soft, and the coal plants underneath the system simply couldn't ramp down fast enough to make room. But you might already be familiar with this story because we've talked about the different versions of this problem countless times on The Daily Brief. Now, the obvious response is to build storage, and India has been trying to do that. The country added 4.6 gigawatt-hour of battery storage in the first three months of 2026, more than nine times what it managed in the previous quarter, taking its cumulative installed base to 5.9 gigawatt-hour by March. That sounds like a breakthrough until you set it against the target. The Central Electricity Authority reckons India will need 236 gigawatt-hour of batteries by 2031-32. So, we have built, in our entire history, a little over 2% of the batteries we expect to reach within 7 years. So the gap is enormous, and you probably already knew that too. But the more interesting story is hiding inside the engineering. Because somewhere in the last 18 months, without much fanfare, the kind of battery India buys has changed. Now, the grid has stopped asking, how many megawatts of battery do we need? And started asking, how many hours of stored sunshine do we need? So today, we talk about that shift. And to see it, you have to hold two numbers in your head at once. The first is power, measured in megawatts or MW.
It tells you how much electricity the battery can push out at any single instant. The second is energy, measured in megawatt hours or MWH. It tells you how long it can keep pushing before it empties. So divide the second by the first, and you get duration. For example, a battery rated at 500 MW or 1,000 MWh can deliver 500 MW for 2 hours. And the same battery can give 100 MW of power for 10 hours. Give it the same 500 MW of power, but 2,000 MWh of energy, and it becomes a 4-hour battery. So when India ran its first serious battery tenders, 2 hours was enough, but not anymore. And that's because of the nature of solar power. See, through the day, the sun is still doing much of the work. Because solar is cheaper than coal, we buy most of the solar during that time and run coal plants at a minimum rate so that supply matches demand. So this also means that the more we install solar and rely on it during the day, the less coal we need and the lesser we keep those plants running. But after sunset, solar falls away to nothing within an hour just as people get home and switch on lights, fans, air conditioners and stoves. Demand climbs at the exact moment the cheapest source of supply disappears, and coal plants are left to fill the gap. But now they're running at low utilization levels, and it's hard to ramp them up quickly. So for a couple of hours after sunset, the system is stretched. Now a two-hour battery solves this problem tidily. It charges through the day when power is plentiful and cheap, and then empties itself in that evening crunch period. And for the grid India had a few years ago, that was enough. Solar was still small, so the evening crunch was short and shallow, as coal plants were still carrying a lot of the burden in the evenings, leaving only a modest peak. So that was the thinking behind SEC as landmark March 2022 tender. 500 megawatt for two hours. But a two-hour battery was never a complete fix. It was a peak shaver, only clipping the very tip of the evening and nothing beyond it. So if the shortfall ever ran longer than two hours, the battery was already empty. And that did eventually happen. The more we depend on solar, the longer we need batteries for. But then solar grew, and the problem changed shape. The more we relied on solar, the less we leaned on coal, and the longer the crunch got, which only meant we'd need more and longer batteries. As solar has crossed 100 gigawatt, the evening peak has stopped being a single spike at all. It's now an elevated zone, stretching from roughly 5pm to 11pm in winter, and 7pm to past midnight in summer. A 2-hour battery can only shave the steepest point of that zone, and then it's empty.