# Size your BESS with ergOS and base the decision on your own data

> Start with what your site needs the battery to do.

Canonical: https://joulewise.com/insights/size-your-bess-with-ergos  
Publisher: jouleWise Advisory Services Pvt Ltd, Noida, India · Spain  
Reviewed: 2026-10-09  
Status: company page

## In short

“How big should our battery be?” sounds like a simple question. The answer changes depending on whether the priority is backup, peak-demand reduction, solar utilisation or shifting consumption to cheaper hours. ergOS, jouleWise's energy management and market optimisation platform for Indian industrial consumers, starts from how the battery will actually be used. It models dispatch across all 96 fifteen-minute blocks of the day, against time-of-day tariffs, power exchange prices, renewable output, banking rules and deviation penalties.
*Published 2026-10-09 · ergOS · energy storage*

“How big should our battery be?” sounds like a simple question. The answer changes depending on whether the priority is backup, peak-demand reduction, solar utilisation or shifting consumption to cheaper hours.

ergOS, jouleWise's energy management and market optimisation platform for Indian industrial consumers, starts from how the battery will actually be used. It models dispatch across all 96 fifteen-minute blocks of the day, against time-of-day tariffs, power exchange prices, renewable output, banking rules and deviation penalties.

The first step is to separate two numbers. Electricity, in kW or MW, is how much the battery can supply at any moment. Energy, in kWh or MWh, is how much electricity it can deliver over time. Both must match the application.

For example, supporting a constant 1 MW load for two hours needs 2 MWh of delivered energy. That is the starting point. Losses, operating limits, auxiliary consumption and battery ageing all raise the installed capacity required.

A useful sizing assessment connects four things:

- **Demand:** when electricity is used and how high the peaks rise.
- **Purpose:** which loads need backup and which costs the battery should reduce.
- **Charging:** when electricity is available, at what price and within what connection limits.
- **Lifetime performance:** how efficiency, cycling and capacity loss affect the result.

These inputs explain why two factories with similar monthly bills may need very different batteries. One might have a brief demand spike. Another may need sustained support through an evening shift. Size and operating strategy must be evaluated together ([National Laboratory of the Rockies](https://www.nlr.gov/reopt/curriculum/what-is-reopt)).

Billing units matter too. Many Indian industrial tariffs charge maximum demand in kVA rather than kW, so power factor affects how much a battery can cut that charge. Savings should be calculated in the same units your bill uses.

For Open Access consumers, the value goes further. A battery can charge from solar surplus or low Day-Ahead and Real-Time Market prices, discharge at peak, and reduce Deviation Settlement Mechanism (DSM) penalties. A simple tariff calculation misses most of this.

The same logic guards against oversizing. Extra capacity earns its place only when it delivers enough backup, savings or flexibility to justify its cost. If backup is your main concern, our article on [whether batteries can replace UPS systems and diesel generators](https://joulewise.com/insights/can-batteries-replace-ups-and-diesel) covers what to check.

This is where ergOS helps. Its optimisation engine treats the battery as one variable in your full energy portfolio, within state-of-charge limits, electricity limits, round-trip efficiency and degradation cost. Side-by-side scenarios, from DISCOM-only supply to fully optimised supply with exchange purchases and BESS, show the landed cost per kWh and the savings against your DISCOM baseline. The assumptions stay visible, so you can examine and refine them as better site data arrives.

**Explore with jouleWise:** Bring your load profile and backup requirements to an ergOS sizing session. [Book an ergOS sizing session](https://joulewise.com/contact)

**Try it:** [Value the scheduling in ergOS Studio](https://joulewise.com/studios/ergos)
## Related

- [Value the scheduling in ergOS Studio](https://joulewise.com/studios/ergos)
- [ergOS](https://joulewise.com/solutions/ergos)
- [Can batteries replace UPS systems and diesel generators?](https://joulewise.com/insights/can-batteries-replace-ups-and-diesel)

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