11. Storage & EVs

Module 10 ended on a diagnosis: nearly every difficulty in running a grid traces to one fact — electricity is barely stored. Supply must chase demand every second because there is no buffer between them.

This module is about building that buffer. It has become the defining engineering and commercial problem of the 21st-century grid, and it is why a technology invented for camcorders now shapes national energy policy.

What storage actually sells

Start with a correction, because it prevents a lot of confused thinking.

Storage is not a source of energy. Every storage technology returns less than it receives — Module 1’s heat tax, collected on the way in and again on the way out. A grid made entirely of storage would produce nothing at all.

What storage sells is timing. And on a system where supply must equal demand continuously, timing is worth a fortune.

Look again at the duck:

total demand net load (non-solar plants) solar output

Solar on the grid: 100 units

Solar share of the day

32%

Belly (lowest net load)

12:00

Evening ramp needed

14%/h

Push the slider up. At midday there is more solar than anyone wants; by 7 pm there is none, and demand is peaking. Physically identical units of electricity, hours apart, with completely different values. Storage buys the cheap one and sells the dear one — and in doing so, it flattens the duck’s neck and reduces how much fast-ramping generation the system must own.

That is why storage economics is not about efficiency alone. A technology that loses 20% on the round trip but shifts energy from ₹2 to ₹8 is a very good business.

Batteries from zero

A battery converts chemical energy directly into electrical energy — no heat, no steam, no spinning magnet. Like solar, it sidesteps the entire Part B machinery.

Three components:

• The anode — the electrode that releases electrons while discharging.
• The cathode — the electrode that receives them.
• The electrolyte between them — and here is the crucial trick: it conducts ions but blocks electrons.

That asymmetry is the whole design. Chemistry wants to move charge from one electrode to the other. The ions can travel directly through the electrolyte. The electrons cannot — they are forced to take the long way round, out of the battery, through your phone or motor, and back in the other side. That forced detour is the current you use.

Why lithium

A lithium-ion cell is more elegant than most batteries, because nothing is consumed — the lithium simply commutes.

• Discharging: lithium ions leave the anode (typically graphite), travel through the electrolyte, and slot into the cathode’s crystal structure. Electrons take the external circuit and do your work.
• Charging: apply voltage and the process runs backwards, pushing the ions back into the graphite.

The ions shuttle back and forth, inserting themselves into host structures without destroying them. That reversibility is why the cell survives thousands of cycles.

Lithium is chosen because it is the lightest metal and gives up its outer electron readily, producing high voltage per cell and excellent energy per kilogram — which matters enormously in a vehicle, and rather less in a shipping container bolted to the ground.

Why they wear out, and why they occasionally burn

Degradation is not a manufacturing defect; it is chemistry. Each cycle causes slight structural damage to the electrodes, and a passivating layer grows at the anode surface, consuming a little lithium permanently. Heat accelerates everything, and so does sitting at 100% charge. Hence the standard advice — avoid extreme heat, avoid habitually charging to full — and hence why EV makers keep a hidden buffer at each end of the range.

Fires come from thermal runaway. A short circuit — from physical damage, a manufacturing flaw, or overcharging — generates heat; heat triggers reactions that generate more heat; those reactions release oxygen and flammable gases, which feed the fire. It is self-sustaining, hard to extinguish, and the reason batteries have battery management systems, fuses and cooling as standard. India’s cluster of electric-scooter fires in 2022 was a real safety failure that prompted tighter standards — worth stating plainly rather than glossing over.

The rest of the storage menu

Lithium-ion is not the only answer, and for the grid it is often not the best one.

Pumped hydro (Module 5) is still the giant — but you have to be careful about what you are measuring, because power and energy give opposite answers here. On power capacity, the rate at which it can deliver, pumped hydro reached 201 GW worldwide at the end of 2025 (International Hydropower Association, World Hydropower Outlook 2026). Batteries have now overtaken that: the world’s installed battery storage finished 2025 somewhere between 270 GW (Wood Mackenzie) and 302 GW (Energy Institute, Statistical Review of World Energy 2026), after the largest year of battery building yet. The two counts differ because the trackers include slightly different things — and where good sources disagree, it is more honest to quote both than to pick whichever suits your argument.

On energy — the electricity actually banked, waiting to be used — the ranking reverses, and not narrowly. All those batteries hold about 630 GWh between them (Wood Mackenzie, end of 2025). Pumped hydro’s reservoirs hold up to about 9,000 GWh (IHA): more than ten times as much stored electricity, out of a smaller power capacity. The difference is duration. A battery installation is usually built to empty in two to four hours; a pumped-hydro scheme is built to run for the better part of a day, and often longer.

So the accurate statement is the energy one: water uphill still holds the large majority of the world’s stored electricity. It is cheap per unit of energy stored, lasts half a century, and can run for many hours. Its limitation is geography: you need two reservoirs at different heights, and permission to build them. India has a substantial pumped-storage pipeline under construction precisely because the duck curve made it valuable again.

Grid batteries (BESS) are the fastest-growing category by a wide margin. Their advantages are siting flexibility — a container anywhere on the network — and speed: they respond in milliseconds, which makes them ideal for the frequency response and synthetic inertia that Module 10’s 🔥 block described. Their weakness is duration; economics currently favour a few hours, not a few days.

Sodium-ion swaps lithium for abundant, cheap sodium. It stores less per kilogram, which rules it out for aviation and hurts it in cars — but for a stationary installation, weight is nearly irrelevant. Watch this one.

Flywheels store energy in a heavy spinning rotor: superb power, tiny duration, seconds to minutes. Essentially bottled inertia — which is exactly the service a low-inertia grid needs.

Compressed air pumps air into sealed caverns and releases it through a turbine. Cheap in principle, geologically constrained, and thermally awkward, since compressing air heats it and expanding it chills it. Very few plants exist.

Gravity storage applies pumped hydro’s logic to solids — lifting heavy blocks with cranes or in mineshafts. Conceptually clean; its problem is that water is free and rock is not, so the economics are unproven.

The price collapse that changed everything

None of this mattered much until batteries became cheap. And they did, spectacularly.

Lithium-ion battery pack prices have fallen to around $108 per kilowatt-hour (2025) — roughly 93% below 2010 levels, according to BloombergNEF’s annual survey. The fall continues: about $139/kWh in 2023 and $115/kWh in 2024.

That single curve explains almost everything else in this module. It is why EVs stopped being a curiosity, why grid batteries became bankable, and why storage entered national planning. It is the same learning-curve mechanism that crashed solar (Module 7), and it gets a proper explanation in Module 12.

EVs, honestly

Now the hook question, and it deserves a careful answer rather than a slogan.

How an EV differs. A petrol car burns fuel in a small engine, converting roughly 25–30% of its energy to motion (Module 1) and losing the rest as heat, with a gearbox, clutch and exhaust in attendance. An EV has a battery, an inverter, and a motor that is typically over 90% efficient, with regenerative braking recovering energy that a petrol car throws away as brake heat.

The honest objection. “Your EV runs on coal.” In India, largely true — around 73% of generation (FY 2024-25). So does it actually help?

Efficiency alone cannot answer this. It is tempting to stop at “the power station plus the motor is more efficient than the little petrol engine”, and that is how the argument is usually made. But efficiency counts joules, and the atmosphere counts carbon — and coal is the dirtier fuel per joule. Burn a gigajoule of coal and you release roughly 95 kg of CO₂; a gigajoule of petrol releases about 69 kg (IPCC 2006 default factors). So coal starts about 1.4× behind, and an efficiency edge only wins if it is bigger than that. You have to do the sum in grams of CO₂ per kilometre, not in percentages.

So do it in grams. This is a well-to-wheel comparison, counting from the fuel through to the turning wheel. One honest caveat before the numbers: the two sides are not measured on quite the same boundary. The petrol figure includes the energy spent getting the fuel out of the ground and to the pump; the electricity figure is the grid’s emissions at the power station, so the diesel burnt mining and hauling the coal is not in it. The gap that leaves is small next to the one we are about to measure, but it runs in favour of the electric scooter, and you should know that before you trust the answer.

The electric scooter. Indian scooters use about 33 Wh per kilometre in city riding. Charging is roughly 90% efficient, and about a fifth of what a power station generates is lost in the wires before it reaches your socket — so 33 ÷ 0.9 ÷ 0.8 means roughly 46 Wh has to be generated per kilometre. The Indian grid emitted 0.710 kg CO₂ per kWh generated in FY 2024-25 (CEA CO₂ Baseline Database v21.0). That works out at about 32 g CO₂/km.

The petrol scooter. Burning a litre of petrol releases 2.31 kg of CO₂. At a real-world 45 km per litre that is 51 g/km out of the exhaust, and adding the energy spent extracting, refining and delivering the fuel brings it to roughly 62 g CO₂/km.

So the electric scooter emits about half — and a little more than half once you allow for the coal-supply emissions left out above. And the honest test of the hook: even on a grid that was entirely coal, at around 0.9 kg CO₂/kWh, the electric scooter would come out near 41 g/km — still comfortably under the petrol scooter. The margin is real, but it is not enormous, and anyone calling an EV on a coal grid “zero emission” is simply wrong.

Two effects widen it over time:

1. The grid gets cleaner every year; a petrol car never does. An EV bought today improves for its whole life as solar and wind grow. A petrol engine is as clean on day one as it will ever be.
2. Local air quality. Moving combustion out of dense streets and into a station with precipitators and stacks is a substantial public health gain in Indian cities, whatever the CO₂ ledger says.

The honest debits: manufacturing an EV — especially its battery — emits more than manufacturing a petrol car, so the EV starts life in carbon debt and must be driven some tens of thousands of kilometres to repay it. Mining lithium, cobalt and nickel carries real environmental and labour costs. Both are genuine, and both are reasons to build batteries better and recycle them, not reasons to keep burning petrol.

India’s electric transition looks nothing like the West’s

Here is where the Indian story diverges sharply — and, in this case, favourably.

Western EV coverage is about cars. India’s transition is overwhelmingly about two- and three-wheelers. Electric two-wheelers made up roughly 58% of all EVs sold in India in 2025, with three-wheelers about 34% — together over nine in ten. India also accounts for around 57% of global electric three-wheeler sales (2024).

Why this matters more than it sounds:

• The physics is friendlier. A scooter needs a battery a fraction the size of a car’s, so it is cheap enough to compete on sticker price, not just running cost.
• The use case fits. Short urban trips, predictable daily distances, overnight charging at home. Range anxiety barely applies.
• The impact is concentrated. Two- and three-wheelers dominate urban traffic and are disproportionate contributors to street-level air pollution. Electrifying them improves the air where people actually breathe.

Battery swapping is a distinctly Indian answer to charging time: instead of waiting, exchange a depleted pack for a charged one in a couple of minutes. It works far better for small vehicles, where packs are light enough to lift, and it suits commercial drivers — auto-rickshaws, delivery riders — for whom downtime is lost income. It requires standardised packs and someone to own them, which is a business problem more than a technical one.

Government policy has pushed through demand incentives (the FAME schemes and their successors) and manufacturing incentives (production-linked schemes for advanced cell manufacturing), aiming to make cells in India rather than import them.

🔥Vehicle-to-grid: the battery you already parkedAdvanced · optional

Most vehicles are stationary most of the time. That is not a criticism — it is an opportunity, because each of those parked vehicles contains a large, expensive battery doing absolutely nothing.

Vehicle-to-grid makes the charger bidirectional. Your car charges overnight when power is cheap and plentiful, and at the evening peak — while parked at home or the office — it feeds a little back. Multiply by a million vehicles and a country’s car parks become one of the largest batteries ever assembled, already paid for by somebody else.

The arithmetic is genuinely attractive. Even a modest fleet of electric cars represents enormous aggregate storage, sitting exactly where the demand is — at the distribution edge, which relieves congestion rather than adding to it.

The obstacles are real but unglamorous:

• Battery wear. Extra cycles age the pack, so owners need compensation and manufacturers need to honour warranties. Modern chemistries and shallow cycling make this less frightening than it first appeared.
• Standards. Bidirectional charging needs agreed protocols between vehicle, charger and utility.
• Metering and billing. Someone must measure what your car exported and pay you for it — the same net-metering question as rooftop solar in Module 7, but mobile.
• Willingness. Drivers must trust that the grid will not leave them with an empty battery.

For India, the interesting twist is once again the two-wheeler. A single scooter battery is small — but swappable-battery networks concentrate thousands of packs in known locations on known chargers. A swapping operator is, without particularly intending to be, a grid-scale storage company.

🔥🔥What a battery specification actually meansDeep · optional

Battery datasheets use a vocabulary worth decoding, because it explains why storage technologies are not interchangeable.

Energy vs power — Module 1 again. A battery has two independent ratings:

• Energy capacity (kWh) — the size of the bucket. Determines how long it can run.
• Power rating (kW) — the width of the tap. Determines how fast it can deliver.

A grid battery described as “100 MW / 400 MWh” is a 400 MWh bucket with a 100 MW tap: four hours at full output. The ratio matters more than either number. Frequency response wants a wide tap and a small bucket; solar shifting wants the opposite.

C-rate is that ratio expressed cleanly: charging or discharging at 1C means emptying the whole capacity in one hour; 0.5C means two hours; 2C means half an hour. High C-rates generate heat and accelerate degradation, which is why fast charging is hard on a pack.

Round-trip efficiency is energy out divided by energy in, compounding losses in both directions plus any standby drain:

Technology	Typical round trip
Lithium-ion	85–95%
Pumped hydro	70–80%
Compressed air	40–70%
Hydrogen (Module 9)	~30–35%

Depth of discharge and cycle life interact in a way that surprises people. A pack cycled between 20% and 80% will survive far more cycles than one repeatedly taken from 100% to 0%. Total lifetime energy throughput can therefore be higher from a battery you deliberately under-use — which is why EVs hide buffer capacity and why grid operators specify state-of-charge windows.

Levelised cost of storage. The figure that decides real projects is not $/kWh of hardware but cost per unit delivered over the asset’s life:

LCOS ≈ (capital + lifetime operating costs) / (total energy discharged over life)

This is why pumped hydro competes despite a worse round trip and enormous upfront cost: 50+ years of life and tens of thousands of cycles spread that capital across an enormous denominator. It is also why a cheap battery that degrades quickly can cost more than an expensive one that does not. Module 12 builds the same idea for generation, where it is called LCOE.

What comes next

Part D is complete. You know how the grid works, how it fails, and how storage is beginning to loosen the constraint that has shaped electricity since its beginning.

Part E asks the questions that decide what actually gets built. Not “does it work?” but “what does it cost, who pays, and who decides?” — starting with why India’s distribution companies are broke, and why that single fact explains more about Indian power than any piece of engineering in this course.