Free tool — planning estimate
BESS Calculator
Battery Energy Storage System (BESS) sizing tool — free, no sign-up
Estimate your battery power (MW) and energy capacity (MWh) in minutes — enter your generation and consumption figures to get started.
What's your goal? — you can pick more than one
Self-consumption: Store surplus generation to use it later instead of buying from the grid — exactly when "later" is depends on the site's profile (typically evening/night for solar, but not always).
Your generation asset(s)
Capacity factor (CF) is a suggestion based on type, not a fixed value — it depends heavily on region (e.g. higher solar irradiance in Africa/MENA gives a higher CF than in Northern Europe) and the specific site; edit it if you know a more precise number. Got more than one technology on site (e.g. solar + wind, or solar + biogas)? Add a row for each — daily generation is summed across all of them. Note that Biogas / dispatchable runs continuously rather than varying with weather, so it's excluded from the Grid Firming calculation below (firming exists to smooth weather-driven swings, which dispatchable generation doesn't have).
How much energy the site consumes, over whichever period you know it in (day / month / year — from your bill/meter). Used together with daily generation to estimate how much real surplus there is to shift with the battery.
▸Calculation assumptions
What share of the smaller of the two values (generation or consumption per day) the battery can realistically capture. Not 100%, because part of consumption already overlaps with generation in real time and doesn't need storing. Must be between 0 and 1 (0–100%).
How many hours per day consumption typically exceeds generation and needs to be covered by the battery. For solar this is typically evening/night (3–6h). For wind, or sites with 24/7 load, this window can be different — longer, split across several intervals in the day, not necessarily "evening." Estimate this based on your own site's profile. Must be greater than 0.
Indicative power estimate
2.92MW
Indicative capacity estimate
8.77MWh
How this is calculated
Self-consumption: Daily generation = power × CF × 24h. Daily consumption = annual ÷ 365. Capacity = min(generation, consumption) × shift factor (default 0.4). Power = capacity ÷ discharge window duration.
Frequently asked questions
What does the BESS sizing calculator estimate?
It gives an indicative power (MW) and energy capacity (MWh) estimate for a battery energy storage system, based on the sizing goal you pick — self-consumption, peak shaving / export limiting, grid firming / smoothing, or arbitrage / standalone BESS. It's a planning-stage estimate, not an engineering calculation.
How much battery storage do I need for solar or wind?
It depends on your generation profile and goal. For self-consumption, size storage to shift the surplus you generate but don't use right away (e.g. midday solar) to when you need it later. For grid firming, size storage to smooth short-term output swings from a weather-driven source instead of covering a full day of generation. Enter your own figures above and the calculator returns an indicative MW/MWh estimate for your site.
How do I calculate BESS size — power (MW) and capacity (MWh)?
As a rule of thumb, capacity (MWh) is roughly power (MW) × duration (hours) for a single use case, then combined across every goal that applies to your site. The calculator above does this automatically — enter your generation and/or consumption figures, pick one or more sizing goals, and it computes an indicative power and capacity estimate. Every underlying coefficient (capacity factor, shift factor, firming fraction, duration) is editable, so you can match it to your own assumptions.
What's the difference between self-consumption, peak shaving, grid firming and arbitrage sizing?
Self-consumption sizes the battery to shift surplus generation to when it's needed later (e.g. solar during the day, used in the evening). Peak shaving caps export at your grid connection limit instead of curtailing surplus. Grid firming smooths short-term output swings from weather-driven sources like solar and wind. Arbitrage/standalone BESS has no generation asset of its own — it's sized as an investment decision around charging cheap and discharging expensive, shaped by grid limits and market design.
Can I combine multiple sizing goals?
Yes — pick as many as apply to your site. When more than one goal is selected, the indicative power is the maximum across goals (it's rare to need every scenario's peak at the same instant), and the indicative capacity is the sum across goals (different goals typically fire at different times of day).
Does this calculator account for round-trip efficiency or usable capacity?
No — it calculates an indicative nameplate estimate from the coefficients you enter (capacity factor, shift factor, firming fraction, durations). Real-world usable energy is lower once you account for round-trip efficiency (typically 85–95% for lithium-ion) and depth-of-discharge limits, which vary by technology and manufacturer.
Where can I find BESS projects or systems that match my target capacity?
Browse active BESS listings on Wattilla and filter by capacity (MWh), power (MW), country and project stage — or post your own project or system for sale.
Looking for a BESS project or system?
Browse active listings by capacity, power, country and stage — or post your own listing free.