Solar + BESS Sizing Calculator

Project type

Segment sets sensible defaults for tariff, load shape, and unit costs — everything stays editable.

Project name Location / State

Peak sun hours (kWh/m²/day) Grid connection

Electricity tariff (TNB RP4, from 1 Jul 2025)

Presets carry the July 2025 restructured rates. Verify against your actual bill — rates are editable below.

Tariff category

AFA fuel adjustment (sen/kWh, +/-) KWTBB RE fund (% of bill) Tariff escalation (%/yr)

Excess-solar export scheme

Scheme (Solar ATAP replaced NEM from 1 Jan 2026) Export credit rate (sen/kWh)

Consumption

Monthly consumption (kWh) Max demand (kW, blank = auto)

Load profile preset Weekend load (% of weekday)

Hourly shape (relative weights, 0–100)

Editing any value switches the preset to “Custom”.

Estimated max demand (weekday)–

Average daily consumption (weekday)–

Load factor–

Peak-period share (2–10pm weekday)–

Weekday load curve

Hourly demand, scaled so the month totals your input.

PV sizing method

Annual consumption offset (%)

Module & inverter

Module wattage (W) Module area (m²) Layout factor (walkways etc.) DC/AC ratio

Losses → performance ratio

Temperature (%) Soiling (%) Inverter (%) Wiring/mismatch (%) Shading (%) Availability (%)

Performance ratio (PR)–

Recommended PV system

– kWp

Modules–

Inverter AC capacity–

Roof area required–

Specific yield–

Annual generation (yr 1)–

Monthly average generation–

Consumption offset–

CO₂ avoided–

Typical day — solar vs load

BESS applications

The recommended capacity is driven by the applications you enable.

Solar self-consumption — store daytime excess for evening/night

Peak shaving — cap maximum demand (MD charge reduction)

ToU arbitrage — charge off-peak / solar, discharge 2–10pm

Backup / autonomy — ride through outages

Target max demand cap (kW)

Battery technical parameters (LFP defaults)

Depth of discharge (%) Round-trip efficiency (%) Max C-rate (charge/discharge) Cycle life (cycles @ rated DoD) Calendar life (years) Capacity fade (%/yr)

Override capacity (kWh nameplate, blank = auto) Override PCS power (kW, blank = auto)

Allow off-peak grid charging

Recommended BESS

– kWh / – kW PCS

Usable energy (DoD applied)–

Sizing driver–

Effective C-rate–

Est. cycles per year–

Expected life (cycle vs calendar)–

⏱ Charging & discharge times

Full charge at rated PCS power (grid)–

Charge from solar excess (typical day)–

Solar state of charge reached–

Typically full by–

Discharge duration at PCS power–

Off-peak window needed for grid charge–

Typical weekday — energy dispatch

Hourly simulation: solar serves load first, excess charges the battery, battery discharges per strategy, grid covers the rest.

Battery state of charge

Daily energy balance

Monthly energy — generation vs consumption

Capital & operating costs

PV installed cost (RM/kWp) BESS installed cost (RM/kWh) Other / grid works (RM) O&M (% CAPEX/yr)

Analysis period (years) Discount rate (%) PV degradation (%/yr) Battery replacement cost (% of today)

PV CAPEX–

BESS CAPEX–

Total CAPEX–

Year-1 savings breakdown

Financial results

Baseline annual bill (no system)–

Annual bill with solar only–

Annual bill with solar + BESS–

Year-1 total savings–

Simple payback–

Discounted payback–

NPV–

IRR–

ROI over period–

LCOE (solar)–

Battery replacement year–

Cumulative cash flow

Project summary

Assumptions & data sources

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⚠️ Feasibility-grade estimates for preliminary sizing only. Tariff presets reflect TNB RP4 (1 Jul 2025) and Solar ATAP (1 Jan 2026) as published; verify current rates, AFA, and scheme rules with TNB / Energy Commission before contractual commitments. Site survey, shading study, and PSS/harmonic studies required for detailed design.