Open methodology / Model 1.1.0
The working is always open.
A daily simplified model, explicit costs and a result you can inspect. All financial outputs come from deterministic formulas; AI never invents your returns.
01 / Start with a fair baseline.
We compare your existing grid and actual diesel spending with the same business adding a battery. Your monthly input is imported grid energy from the bill. Outage energy that is already supplied by diesel is kept separate from non-outage peak grid demand.
New backup for previously unpowered load creates a service benefit, but does not displace diesel. Its recharge cost is included. The optional value of avoided production losses is shown separately and excluded from payback, NPV and IRR. It counts only the previously unpowered share of backup, never the load already served by diesel.
02 / Reserve backup first.
Usable AC energy = nominal DC capacity × DoD × discharge efficiency
Daily replenishable energy = min(usable AC energy, charge kW × charge hours × round-trip efficiency)
Backup energy = min(daily replenishable energy, outage hours × load kW, outage hours × battery kW)If the capacity you enter is already usable AC capacity, DoD and discharge efficiency are not applied again. Charging, outage and non-outage peak windows must fit within 24 hours. We assume at most one equivalent daily cycle, on your chosen operating days.
If battery power is below the outage load, backup benefits are zero unless you confirm that critical loads can be isolated and powered independently. After confirmation, only the power-limited portion counts. We do not estimate fuel savings from a generator running in parallel at low load.
Remaining capacity can serve peak grid demand, subject to peak energy and power limits. This is a representative-day allocation, not an hourly dispatch simulation or a guarantee of reserve availability in every event.
03 / Subtract the cost of charging.
Diesel kWh cost = fuel L/kWh × HSD price + avoidable variable maintenance
Diesel saving = operating days × displaced diesel kWh × (diesel kWh cost − charging rate / RTE)
Arbitrage saving = operating days × shifted kWh × (peak rate − charging rate / RTE)Arbitrage is disabled if the price difference cannot cover charging losses. Diesel replacement is allowed to show a negative economic saving when backup is expensive. Charging costs for newly served backup, annual battery O&M and replacements are also deducted.
Demand-charge savings default to zero because monthly billed demand cannot be reliably inferred from battery kW. Solar surplus is not treated as free energy; it requires an energy quantity and a verified export opportunity cost.
04 / Model all 10 years.
Capacity is degraded and reallocated each year, preserving backup priority. Grid prices, diesel prices and maintenance costs have separate editable growth assumptions. A paid replacement occurs at the selected year-end and restores initial capacity from the next year.
Cash flow₀ = −installed investment
Cash flowₜ = diesel savings + arbitrage savings − added backup recharge − O&M − replacements
NPV = sum(cash flowₜ / (1 + discount rate)ᵗ), years 0…10Simple payback uses undiscounted cumulative cash flow and linearly interpolates the first year that crosses zero. If that never happens, we show “not within 10 years”. A later replacement may reduce cash flow again; the full table remains visible.
IRR is the discount rate where ten-year NPV is zero. No sign change yields no IRR; multiple sign changes are flagged as potentially ambiguous. All figures are nominal local currency, unlevered and before income tax, without residual value. The discount rate is explicit, not a promised investment return.
Without a quote, capacity is sized for your selected backup requirement and charging power defaults to discharge power. We use the same operating cash flows to solve the highest installed total and PKR/kWh that meet 3, 5 and 7 year payback targets. No market equipment price is assumed; NPV and IRR require an actual installed investment.
05 / Keep uncertainty visible.
The sensitivity matrix recomputes the selected system with grid energy and diesel prices at −20%, unchanged and +20%. Capacity and all other assumptions remain fixed. Scenarios without a ten-year payback stay visible.
Suggested capacity is the energy needed to cover your selected critical load, allowing for the chosen losses. It is not a claim of economic optimization. Equipment warranty, safety, site design and reliability require project-specific review.
06 / Trace the data.
Every imported market observation has an original URL, source locator, data date and verification date. A missing value is not zero. Reference decisions are distinguished from verified current bills, and undated product documents remain undated.
Source entry points: NEPRA, K-Electric, OGRA. Private installed quotes and contact details do not enter public datasets.
Worked examples use synthetic inputs and the same engine as your calculation. Downloaded JSON includes the model version, input snapshot and dataset version. The first version has no product rankings or paid placements; future sponsorship must be labelled and cannot affect formulas or ranking criteria.
Your numbers come first
What does storage look like for you?
Use your bill, backup needs and installed quote.