Estimate Solar System Size from Monthly Units
This solar calculator turns a monthly kWh target into a planned inverter size (kW) and panel count. It is an independent MEPCODBill planning estimate for conversations with installers — not a roof survey, not net-metering approval, and not affiliated with MEPCO.
Start from units on a recent bill (or your own meter difference), choose sun hours and a realistic loss buffer for heat and dust, then review the recommended kW. For ROI context see solar panel ROI in Pakistan. Peak-hour export/import rules still matter — pair with the ToU calculator.
How the Tool Works (Step-by-Step)
- Enter monthly units you want to offset.
- Choose average daily sun hours for your season/region.
- Select panel wattage and a system-loss percentage (20% is a common planning default).
- The tool converts monthly → daily need, inflates for losses, divides by sun hours → kW, then divides by panel watts → panel count.
Inputs Explained
- Monthly units — target kWh/month from bills or the meter reading tool.
- Sun hours — effective peak-sun-hours estimate; winter/smog needs a lower value.
- Panel rating — DC watts of each module you plan to buy.
- System loss — buffer for heat, dust, wiring and inverter conversion.
The Sizing Formula (Plain English)
We do not treat nameplate watts as 100% delivered energy. Southern Punjab heat and dust often justify a 20–25% planning buffer. Final yield still depends on shade, tilt, inverter quality and tariff rules.
While international models like NREL's PVWatts use a 14% default system-loss assumption, high summer temperatures and dusty conditions in Southern Punjab can justify a 20-25% planning buffer. Final output still depends on panel quality, shade, installation angle, inverter performance, and tariff rules.
The Sizing Mathematics:
Daily Units = Monthly Units ÷ 30Target Generation = Daily Units ÷ (1 - System Loss %)System Size (kW) = Target Generation ÷ Average Sun Hours (4.5)Understanding Net Metering in Pakistan
Net metering is the regulatory mechanism that makes residential solar financially viable in Pakistan. It allows you to export excess solar energy back to the MEPCO grid during the daytime, essentially using the national grid as a massive free battery. At night, you import energy back from the grid. At the end of the month, MEPCO calculates the 'net' difference.
- Minimum capacity: Net-metering rules have historically referenced a minimum system size (often discussed around 3 kW). Confirm the figure in force with NEPRA/DISCO documentation and your installer — do not treat this page as the official eligibility checklist.
- Phase / meter type: Bi-directional green meters and phase upgrades are common prerequisites; verify what your subdivision currently requires before buying hardware.
- The peak-hour trap: Daytime export is typically settled differently from evening peak imports. Heavy peak use can still produce a bill even when monthly exported units look high — model this with the peak/off-peak calculator and check ToU rates on the NEPRA schedule.
Choosing the Right Inverter Technology
Once the calculator provides your required kW, selecting the right inverter topology is critical for uninterrupted power:
On-Grid Inverters
The most economical option. It syncs with the grid and supports net metering. However, as an anti-islanding safety feature, it shuts down entirely during load shedding. You will have zero power when the grid is offline, even if the sun is blazing.
Hybrid Inverters
The optimal choice for Pakistan. It supports full net metering AND connects to a battery bank. During load shedding, it seamlessly isolates your house from the grid and shifts your load to battery and active solar power.
When Results Differ from a Real Install
Roof shade, orientation, seasonal sun hours, battery hybrid design, sanctioned-load limits and changing net-metering policy all move the real answer. Use this number as a starting brief for a site visit, not a purchase order.
How this estimate works
Core logic
System kW ≈ (monthly units ÷ 30 ÷ (1 − loss%)) ÷ sun hours; panels ≈ (kW × 1000) ÷ panel watts
Assumptions
- Monthly units are a flat average target (from a bill or meter difference)
- Sun hours and system-loss % are user planning inputs (heat/dust buffer often ~20%)
- Panel wattage is the DC nameplate of modules you intend to buy
Limitations
- Rough kW sizing only — not a site survey, shade study, or installer quotation
- Roof orientation, tilt, inverter topology, batteries and sanctioned-load limits are not modelled
- Net-metering policy and peak/off-peak settlement can change the financial outcome
This calculator runs entirely in your browser. Inputs are not uploaded to our servers.
Sources & verification
Official sources sit above third-party summaries. Open these pages to confirm the current figure or process.
- NEPRA Tariff SchedulesTariff and ToU context for export/import settlement after sizing
Frequently Asked Questions (FAQs)
Do I need batteries if I get net metering?▼
No, batteries are not legally or technically required for net metering. An On-Grid inverter without batteries will sync with the MEPCO grid, export excess power, and financially offset your bill perfectly. However, without batteries, when MEPCO initiates load shedding, your entire home will lose power instantly.
How much physical roof space do solar panels take?▼
As a general rule of thumb using modern 540W to 580W panels, you need about 80 to 100 square feet of shadow-free roof space per Kilowatt (kW) of solar installed. Therefore, a standard 10kW residential system typically requires about 800 to 1,000 square feet of dedicated roof space.
Will solar eliminate my MEPCO bill entirely to zero rupees?▼
Solar can eliminate the cost of the 'units' you consume (resulting in zero units billed). However, you will still receive a physical bill and have to pay fixed monthly government charges, such as the PTV fee (Rs. 35) and any applicable meter rent or fixed capacity charges, which usually amount to a few hundred rupees per month.