By CLN Energy Limited BSE SME listed, scrip 544347 Lithium battery manufacturer, Noida Published Updated
A battery energy storage system is bought from a specification sheet, but it is used for ten years or more. The points that decide those ten years are usually not on the first page of the brochure. Capacity in kilowatt-hours is easy to compare. The ten points below are what separate two systems that quote the same kilowatt-hours.
A system rated 100 kW / 215 kWh can deliver 100 kilowatts, and it can do so for about two hours. You should decide which of the two numbers your application actually needs. Peak shaving is a power requirement, because you need the kilowatts for short periods. Running a plant through a power cut is an energy requirement. Buying the wrong ratio is the most common and the most expensive mistake in this market.
| What the system is for | The number that matters | The question that sizes it |
|---|---|---|
| Peak shaving | Power (kW) | How high are the peaks above your target, and how long do they last? |
| Outage backup | Energy (kWh) | What load must stay on, and for how many hours? |
| Storing solar for the evening | Energy and cycle life | How much midday surplus is there, every day? |
| Replacing a diesel generator | Both | What does the generator carry today, at its highest and over a day? |
The C-rate tells you how fast a battery can be charged or discharged. A pack rated 0.5C gives out its energy over two hours. A pack rated 1C does it in one hour. If your load needs energy faster than the system is rated to supply, the shortfall reduces the cycle life. Ask for the rated C-rate and the peak C-rate, for both charging and discharging. Check both against your own duty cycle, not against the example in the brochure.
A cycle figure without its test conditions is not a specification. The figure should be written in this form: 6,000 cycles at 95% depth of discharge, 25°C, 0.5C/0.5C. Depth of discharge, or DOD, is how much of the stored energy is taken out in each cycle. You should also ask how much capacity the system is expected to retain at the end of its rated life. A battery that has come down to 70% of its original capacity still works, but it may no longer meet your requirement.
Cooling decides how the system behaves in an Indian summer. Air-cooled systems are simpler and cost less. Liquid-cooled systems hold the cell temperature more evenly, which helps pack life on sites where the ambient temperature is high and the system is cycled hard. Neither type is automatically the right one. Ask for the operating temperature range, and ask what the system does above that range. It may reduce its output, or it may shut down. Also ask what temperature the quoted cycle life assumes, and whether your site will actually hold that temperature.
| Air-cooled | Liquid-cooled | |
|---|---|---|
| Cell temperature | Varies more across the pack | Held more evenly |
| Complexity | Simpler, fewer parts | Pumps and a coolant loop, more to maintain |
| Suits | Lighter duty, smaller systems, milder rooms | Hard cycling, hot sites, larger systems |
| In our range | Rack and stackable systems | Cabinets of 100 kW / 215 kWh and 250 kW / 464 kWh, and the 5 MWh container |
Every kilowatt-hour you put into a battery comes back a little smaller. This loss is measured as round-trip efficiency, and above 90% is normal for a modern system. The figure is sometimes measured at the battery, and sometimes at the AC terminals after the power conversion system. These two are not the same number. Ask the supplier which one is being shown to you.
This point deserves the most attention when the system will be installed inside or beside a building. UL 9540A is the fire test that shows how a thermal runaway fire spreads in large-scale storage. IEC 62619 and UL 1973 cover the safety of the cells and of stationary batteries. Ask what fire suppression is built into the system. Aerosol based suppression is common in containerised and cabinet products. Also ask for the protection rating of the enclosure. Anything installed outdoors should be rated IP54 or above.
| Standard | What it covers | Ask for it when |
|---|---|---|
| UN 38.3 | Safety in transport | Always, for every system that is shipped |
| IEC 62619 | Safety of industrial cells and batteries | Always for stationary storage |
| UL 1973 | Stationary battery safety | Storage and backup systems |
| UL 9540A | How a thermal runaway fire spreads | Any system inside or beside a building |
The energy management system, or EMS, decides when the battery charges and when it discharges. It also decides how the battery works together with solar, the grid and a generator. Ask which operating modes it supports, and whether your own team can change them. Ask what data you can export, and whether remote monitoring is included in the price or charged as a subscription. If you cannot see the data, you cannot prove what the system is saving.
Requirements change over the life of a plant. Ask whether capacity can be added later, and whether new modules can be used alongside modules that are already several years old. Ask what such an addition does to the warranty. Modular and stackable systems are designed for expansion. A single monolithic system may not allow it.
Ask who will commission the system and who will service it afterwards. Ask where the nearest engineer is posted, and what response time the supplier commits to. Then ask how long spare parts will remain available, and for how long a module can be replaced with the same model. A system that will run for ten years needs a supply chain that can support it for ten years.
Ask for installations you can check for yourself. You should be given the customer name, the configuration, the year, and preferably a site you can visit. A completed installation is the one claim a supplier cannot create on paper. The installations of CLN Energy include 22,864 packs across the BSNL telecom network, 180 kWh behind a 100 kW UPS at the RailTel command control centre in Pondicherry, and a 20 kW hybrid inverter with a 69 kWh battery bank at a government school in Ballia for UP NEDA. Each of these has its own project page with the actual configuration.
There are seven points to cover on the first call. Ask for the power rating and the energy rating together. Ask for the C-rate for both charging and discharging. Ask for the cycle life with its depth of discharge and test temperature. Ask for the round-trip efficiency and the point at which it was measured. Ask for a UL 9540A report for the product itself. Ask what the energy management system allows you to change and to export. Finally, ask for installations that you can visit.
| Ask for | A good answer | A warning sign |
|---|---|---|
| Power and energy | Both, tied to your load profile | Only kilowatt-hours |
| C-rate | Rated and peak, charge and discharge | "High power" with no figure |
| Cycle life | A number with DOD, temperature and C-rate | "Up to" anything |
| Efficiency | Round-trip, and where it was measured | One figure with no boundary |
| Fire testing | UL 9540A report for the product | A company certificate |
| EMS and data | Modes you can change, data you can export | A closed box |
| Deployments | Customer, configuration, year, a site to visit | Logos only |
Storage in India has moved from pilot projects to national planning. Our article on why India needs energy storage now explains that shift, and gives the capacity the Central Electricity Authority says the grid will need.
Once the shortlist is settled, the next question is the budget. Our guide on what a BESS costs in India gives approximate ranges per kWh and per MWh for each system size. Please also read the VGF scheme and what it actually covers before anyone tells you that a subsidy applies to your system.
Commercial and industrial storage is covered on our energy storage website. That site holds the sizing and cost material, along with containerised systems, diesel generator replacement, UPS replacement and the all-in-one series. If your requirement is a battery pack rather than a complete system, our page on custom packs explains how a pack is specified.
Kilowatts are the power the system can deliver at one time. Kilowatt hours are the energy it holds. A 100 kW / 215 kWh system delivers 100 kilowatts for about two hours. Peak shaving needs power, and running through a power cut needs energy. A system sized for one of these will not perform well at the other.
Liquid cooling holds the cell temperature more evenly. This helps pack life on sites where the ambient temperature is high and the system is cycled hard. It is normal on larger containerised systems. Air-cooled systems are simpler and cost less, and they are suitable where the duty is lighter. The question to ask is what temperature the quoted cycle life assumes, and whether your site will hold that temperature.
Look for IEC 62619 and UL 1973 for the safety of the cells and of the stationary battery, and UN 38.3 for transport. UL 9540A applies where thermal runaway testing is required, which covers most installations inside or beside a building. Please ask for the test reports that cover the product you are buying. A general statement about the company is not sufficient.
The C-rate should match your duty cycle, and no more. A system that gives out its energy over two hours is rated 0.5C, and one that does it in an hour is rated 1C. Peak shaving and fast response need a higher rate. Shifting solar energy across the whole evening needs a lower rate. Buying a higher rate than the duty requires costs money, and buying a lower one costs cycle life.
Above 90% is normal for a modern lithium iron phosphate system, but you should check where the figure is measured. A figure taken at the battery terminals looks better than one taken at the AC connection after the inverter and transformer. The AC figure is the one that appears on your electricity bill.
Modular and stackable systems are designed for expansion, and monolithic systems often are not. Ask three questions before you buy. Can modules be added later? Can new modules run alongside modules that are several years old? What does either step do to the warranty on the original equipment?
Standards and government figures link to the organisation that publishes them. Figures about CLN products and deployments come from our own specification tables and project records, linked here so they can be checked. CLN Energy is among the lithium battery manufacturers in India building lithium iron phosphate packs in-house, at its Noida plant.
Looking for the batteries themselves? Battery energy storage systems (BESS) →
Our energy storage website sets out how to compare battery energy storage manufacturers in India and what an energy storage system costs per kWh.
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