Select your country, add every appliance you use, and get an exact panel count, inverter size, battery bank, and full installation cost in your local currency. Three usage scenarios show the difference between an oversized quote and what you actually need.
Peak load if all appliances ran simultaneously. The calculator applies realistic daily usage hours per appliance type to get accurate system size — not 8 hours flat for everything.
Step 3 — System Preferences
Essential load sizing recommended for most homes
How this calculator sizes your system: System kW = Daily kWh ÷ Peak Sun Hours ÷ 0.80. The 0.80 efficiency factor covers inverter losses (4%), wiring resistance (3%), temperature derating (8%), and dust losses (5%). Inverter sized to running load × 1.25. Battery uses actual DoD: 50% for tubular, 90% for lithium. These formulas follow NREL PVWatts and IEC 62109-1 methodology.
💰 Total Estimated CostAll-in installed price estimate
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Three Usage Scenarios — Oversize vs Realistic vs Optimised
Oversize — Every Appliance at 8 Hours Flat
This is what most online calculators give you. Every appliance runs 8 hours. Your dryer 8 hours. Your oven 8 hours. It produces an oversize system and an inflated bill. Shown only so you can spot this mistake in installer quotes.
System
0 kW
Panels
0
Daily kWh
0
Est. Cost
0
Do not use this figure. This is the number every cheap calculator generates. Your dryer does not run 8 hours a day. Neither does your oven, iron, or pool pump.
Realistic Daily Use — This Calculator's Recommendation
Each appliance gets a researched daily runtime based on IEA residential consumption data. AC 8hrs. Fridge 24hrs at 35% duty. Dryer 0.75hrs. Iron 0.5hrs. Pool pump 4hrs. Oven 0.5hrs. The system this scenario produces is what you actually need.
System
0 kW
Panels
0
Daily kWh
0
Est. Cost
0
The equipment report above is based on this scenario. Recommended for most households sizing a new solar system.
Optimised — Shift Loads to Peak Solar Hours
Run dryer, washing machine, dishwasher, and EV charger between 10am and 3pm during peak solar generation. Reduce AC by 1 to 2 hours with ceiling fans supplementing. This habit saves 15 to 20% on system size with no reduction in comfort.
System
0 kW
Panels
0
Daily kWh
0
Est. Cost
0
If you can shift heavy loads to solar peak hours, this is your right-sized system. Saves 15 to 20% on total installation cost vs Scenario 1.
Monthly Bill Saving
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on electricity
Payback Period
-
estimated ROI
25-Year Net Saving
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after system cost
⚠ Disclaimer: All costs are estimates based on 2026 market research. Actual prices depend on your installer, roof type, local permits, and equipment availability. Get minimum 3 quotes from certified installers in your country before committing. Panel and inverter prices fluctuate with exchange rates. Last updated May 2026.
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Sources & Methodology
✓
Formulas per NREL PVWatts and IEC 62109-1. Daily usage hours from IEA Residential Energy Consumption Survey 2024. Equipment pricing from multi-country solar market research covering 30+ countries, May 2026. Battery DoD values per manufacturer datasheets and independent lab test data.
Authoritative source for peak sun hours by location and the 80% system efficiency derate. System Size = Daily kWh / Sun Hours / 0.80 follows NREL PVWatts methodology. Used by solar engineers globally for residential and commercial system design.
International Energy Agency residential appliance usage hours. AC 8hrs, fans 10hrs, lights 5hrs, fridge 24hrs at 35% duty cycle, pool pump 4hrs, dryer 0.75hrs, washing machine 1hr, iron 0.5hrs. These are published consumption averages, not assumptions.
Formula set (engineering-grade):
System Size (kW) = Daily kWh ÷ Peak Sun Hours ÷ 0.80
Panel Count = System kW × 1,000 ÷ Panel Wattage
Inverter (kW) = Peak Simultaneous Running Load (W) × 1.25 ÷ 1,000
Tubular Battery (Ah) = Load (W) × Backup Hours ÷ (48V × 0.50)
Lithium Battery (Ah) = Load (W) × Backup Hours ÷ (48V × 0.90)
Battery Units = Required Ah ÷ Battery Ah per unit
⏱ Last reviewed: May 14, 2026
How to Calculate Solar Panel System Size — The Right Way
Why Every Solar Quote You Receive Is Bigger Than You Actually Need
Your electricity bill is high. A solar installer visits, adds up every appliance in your home, multiplies each one by 8 hours of daily use, and quotes you a system 40 to 60% larger than you need. You get two more quotes from other companies. They all say roughly the same thing. What none of them show you: a correctly calculated system based on your real daily usage is almost always significantly smaller — and cheaper — than what you're being quoted.
The mistake is the 8-hours-flat assumption. Your water pump runs 1 hour 40 minutes a day, not 8. Your iron runs 30 minutes. Your oven, 2 hours at most. Apply 8 hours to those three appliances alone and you add 8.4 kWh of fictitious daily consumption. At 5 peak sun hours that forces a 2.1kW addition to your system size before you've even counted the fans and lights. Across all appliances the inflation reaches 40 to 60% above what you actually need.
This calculator applies researched daily runtime per appliance type based on IEA residential consumption data. Your pump gets 1.67 hours. Your iron gets 0.5 hours. Your fridge gets 24 hours at 35% duty cycle. The result is a system sized to what you actually use — not what runs continuously for 8 hours.
Worked Example: 3-bedroom home, 2x 1.5-ton inverter AC + 6 fans + 10 LEDs + fridge + TV + router
Select your country above to see this example recalculated with your local sun hours, local appliance types, and local pricing.
The Formula: System Size (kW) = Daily kWh ÷ Peak Sun Hours ÷ 0.80
The 0.80 efficiency factor is not a safety margin — it is the measured real-world difference between rated panel output and actual AC electricity delivered to your appliances. It covers four unavoidable losses: inverter DC-to-AC conversion (∼4% loss), DC cable resistance (∼3% loss), panel temperature derating when surface temperature exceeds 25°C (∼8% loss), and dust and soiling (∼5% loss). Skip this factor and your system underperforms by 20% from the first day of operation.
Why Modern Inverter ACs Need Far Fewer Panels Than Older Calculators Show
Most solar calculators still use air conditioner wattage figures from non-inverter models made before 2015. A non-inverter 1.5-ton AC draws 1,600W to 1,800W. A 2026 DC inverter AC compressor adjusts speed to maintain temperature — it draws 900W to 1,200W running. In mild weather it runs at 600W. Only at peak summer heat does it approach 1,300W. Using the old figure overcalculates your panel requirement by 25 to 60%.
AC Size
Old Non-Inverter Draw
2026 Inverter AC (actual)
Overestimate Using Old Figure
1 Ton
1,400W
700–900W
+55%
1.5 Ton
1,800W
900–1,200W
+50%
2 Ton
2,400W
1,300–1,700W
+41%
3 Ton
3,500W
2,000–2,600W
+35%
This single correction drops the recommended system size for a typical home with two 1.5-ton ACs from 10kW (using old figures) to 6 to 7kW (using actual inverter AC wattage) — a difference of 25 to 40% of total system cost.
Peak Sun Hours — Why the Same System Produces Different Output in Different Locations
A 6kW system in a location with 6.5 peak sun hours generates 39 kWh per day. The same 6kW system in a location with 3.0 peak sun hours generates 18 kWh per day. This is why a system correctly sized for one location is completely wrong for another — and why any solar calculator that does not ask your location is guessing.
Peak sun hours are not daylight hours. They are the equivalent number of hours per day at full 1,000 W/m² irradiance. A location may have 14 hours of daylight in summer but only 5.0 peak sun hours because morning and evening light is too weak to produce full panel output. Always design to the conservative year-round value, not the summer peak, to ensure adequate power through winter months.
Region
Peak Sun Hrs (design safe)
6kW Daily Output
System for 20 kWh/day
Middle East & Gulf
6.0–7.0
36–42 kWh
3.4–4.2 kW
South Asia (tropical)
5.0–6.0
30–36 kWh
4.2–5.0 kW
Africa (sub-Saharan)
5.5–6.5
33–39 kWh
3.8–4.4 kW
South-East Asia
4.5–5.5
27–33 kWh
4.4–5.6 kW
Southern Europe & Oceania
4.5–5.5
27–33 kWh
4.4–5.6 kW
Central Europe
3.0–4.0
18–24 kWh
6.3–8.3 kW
Northern Europe & UK
2.5–3.5
15–21 kWh
7.1–10.0 kW
Select your country in the calculator above to use your location's exact peak sun hours in the calculation. The table above shows why a homeowner in the Middle East needs roughly half the panels of a homeowner in northern Europe for the same daily energy output.
Solar System Sizes, Real Costs, and What Each System Actually Runs
Standard System Sizes — What Each One Covers
Solar systems are sized in kilowatts (kW) of panel capacity. The right size for your home depends entirely on your daily energy consumption and your local peak sun hours. These two numbers drive the formula. The table below shows what each system size realistically covers for a typical home, and what it generates daily at 5.0 peak sun hours (select your country for location-adjusted output).
System Size
Panels (430W)
Daily Output (5 sun hrs)
Covers
Installed Cost
3 kW
7
∼15 kWh
Small home, essential loads
See calculator
5 kW
12
∼25 kWh
Medium home, 1–2 ACs
See calculator
6 kW
14
∼30 kWh
Medium-large home, 2 ACs
See calculator
8 kW
19
∼40 kWh
Large home, multiple ACs
See calculator
10 kW
24
∼50 kWh
Large home + EV or pool
See calculator
Select your country above and run the calculator to see your local currency cost for each system size based on verified 2026 market pricing for your region.
Tubular vs Lithium Battery — What the Numbers Actually Say
Most solar installers push tubular lead-acid batteries because the upfront price is 3 to 4 times lower than lithium. The 10-year cost tells a different story. The key difference is depth of discharge (DoD): how much of the battery's rated capacity you can actually use before it damages the cells.
Parameter
Tubular Lead-Acid (200Ah)
Lithium LiFePO4 (100Ah)
Usable capacity (DoD)
50% — 100Ah effective
90% — 90Ah effective
Cycle life
400–600 cycles (2–3 years daily)
6,000+ cycles (10–15 years)
Maintenance
Monthly distilled water top-up
Zero maintenance
Weight
∼60 kg per unit
∼12–15 kg per unit
Heat performance
Degrades above 40°C
Stable to 60°C
10-year replacement cost
3–4 full replacements
Zero replacements
For homes using battery backup daily — covering power outages or overnight loads — lithium consistently wins on 10-year total cost despite the higher upfront price. Tubular remains valid for homes where battery backup is only occasional. The breakeven point is typically 5 to 7 years of daily deep cycling.
Battery sizing formula: Battery Ah required = (Load W × Backup Hours) ÷ (Voltage × DoD). For lithium at 48V with 90% DoD and a 1,500W essential load for 8 hours: (1,500 × 8) ÷ (48 × 0.90) = 278Ah. At 100Ah per lithium unit = 3 batteries. The same calculation on tubular at 50% DoD: (1,500 × 8) ÷ (48 × 0.50) = 500Ah. At 200Ah per unit = 3 batteries but with only half the effective capacity of the lithium bank.
On-Grid vs Hybrid vs Off-Grid — Choosing the Right System Type
This is the most consequential decision in solar system design. It determines whether you have power during outages, how large a battery bank you need, and what your inverter must be capable of.
System Type
What It Includes
During Grid Outage
Best For
On-Grid
Panels + string inverter
Shuts off completely
Stable grids, net metering, bill reduction only
Hybrid
Panels + hybrid inverter + battery
Switches to battery instantly
Areas with regular outages, standard choice
Off-Grid
Panels + inverter + large battery bank
Fully independent
Remote locations, no grid connection
On-grid inverters are legally required to shut down during grid outages in most countries for utility worker safety. If power cuts are a regular occurrence in your area, an on-grid system provides zero protection. Hybrid is the correct choice for any home where outages are frequent.
⚠ Hidden costs that regularly appear in final invoices but not initial quotes: Special mounting structures when standard flat mount physically cannot work on your roof. Extended DC cable runs if the inverter location is far from the panels. Electrical panel and breaker upgrades required by local regulations. Earthing and surge protection systems. Grid connection or net metering application fees. Always request a fully itemised quote before signing any contract.
How to Choose the Right Solar System — Reading Your Result
What Your Calculator Result Actually Means
The system size this calculator gives you is an engineering estimate accurate within 10 to 15% for most homes. It is based on your actual appliance load and your location's peak sun hours. The next step is comparing it against installer quotes. If an installer quotes you 30% more than this calculator recommends, ask them to show their load calculation: which appliances did they include and how many hours per day did they apply to each one? The two most common inflation points are applying 8 hours to the water pump (actual runtime: 1 to 2 hours per day) and 8 hours to the iron or oven (actual runtime: 30 minutes to 2 hours per day).
If an installer quotes less than this calculator suggests, ask which appliances they excluded. Common exclusions are the water pump (high wattage inflates the quote), the geyser or water heater (high wattage, intermittent), and the clothes dryer. These may or may not be intended to run on solar depending on your system design.
How to Size Your Inverter Correctly — The 1.25x Rule
Inverter size is calculated from your peak simultaneous running load, not from the system's panel capacity. The formula: Inverter kW = Peak Running Load (W) × 1.25 ÷ 1,000. Add up every appliance that could run at the same time during normal use. Multiply by 1.25 for startup tolerance and safety margin. Modern hybrid inverters have built-in surge protection, so the old method of sizing to peak startup surge is no longer correct.
What you should not do: add up the startup surge of every appliance simultaneously. You will not start every AC, every pump, and the washing machine at exactly the same second. The 1.25x running load formula is what certified solar engineers use in IEC 62109-compliant system design. A quality inverter running at 80% of its rated capacity runs cooler, lasts longer, and handles occasional startup spikes without tripping.
When the Formula Does Not Apply — Three Edge Cases
The formulas this calculator uses work accurately for most standard residential setups. Three situations require professional adjustment. First: significant roof shading from trees, adjacent buildings, or rooftop structures covering more than 20% of the panel area reduces effective output by 15 to 30%. Add that percentage to the system size or install micro-inverters that handle shade on a per-panel basis rather than across the entire string. Second: extreme heat locations where panel surface temperature reaches 70 to 75°C in peak summer. The 0.80 efficiency factor includes a standard 8% temperature estimate. In extreme heat, use 0.75 instead of 0.80 for a conservative calculation. Third: three-phase commercial loads above 15kW require different inverter topology and must be sized by a certified solar engineer. This calculator is designed for single-phase residential systems up to 20kW.
How to compare solar quotes fairly: Divide any quote's total installed price by the system size in watts. This gives you the cost per installed watt — the only fair way to compare quotes on different system sizes. Select your country above to see the fair benchmark range for your market. Below the lower benchmark: verify panel certification grade and inverter warranty terms. Above the upper benchmark without premium brand justification: negotiate or get another quote. Always request an itemised breakdown: panel brand and wattage, inverter brand and model number, mounting type, wiring and protection components, installation labour, and connection and permit fees — all listed separately.
The Three Scenario Comparison — Why It Matters
The scenario tabs in the results section above show three different system sizes for your appliance load. Understanding what separates them is the most important thing you can take away from this calculator. Scenario 1 (oversize) is what most online calculators produce — 8 hours applied to every appliance. Scenario 2 (realistic) is what you actually need based on real-world usage patterns. Scenario 3 (optimised) shows what becomes possible when you shift heavy loads like the washing machine, dishwasher, and EV charger to peak solar hours between 10am and 3pm. In many homes, this habit change alone reduces the required system size by 15 to 20% with no reduction in comfort or convenience.
The difference between Scenario 1 and Scenario 2 in cost is typically 20 to 35% of the total system price. That gap represents real money spent on panels, inverter capacity, and mounting structure that serves no practical purpose in your home. The only beneficiary of an oversized system is the installer's revenue.
Frequently Asked Questions
Divide your daily energy use in kWh by your local peak sun hours, then divide by 0.80 for system efficiency losses, then divide by your panel wattage. Example: a home using 20 kWh per day at 5.0 peak sun hours with 430W panels needs 20 divided by 5.0 divided by 0.80 equals 5kW system, divided by 430W equals 12 panels. Use this calculator with your specific appliances and country for an exact figure.
System Size in kW equals Daily Energy in kWh divided by Peak Sun Hours divided by 0.80. The 0.80 accounts for four real-world losses: inverter DC-to-AC conversion losing 4%, DC cable resistance losing 3%, panel temperature derating losing 8% when surface temperature exceeds 25 degrees C, and dust and soiling losing 5%. Always use your city's conservative year-round peak sun hours, not the summer peak value.
Step 1: list every appliance and multiply wattage by realistic daily hours of use to get kWh per appliance. Step 2: add all appliance kWh to get daily total. Step 3: divide by local peak sun hours. Step 4: divide by 0.80 for system efficiency losses. Step 5: divide by panel wattage to get panel count. This calculator performs all five steps automatically when you add your appliances and select your country.
The 0.80 system efficiency factor accounts for the difference between rated panel output under laboratory conditions and actual AC electricity delivered to your appliances. Inverter conversion loses 4%. DC cable resistance loses 3%. Panel temperature derating when panels heat above 25 degrees C loses 8%. Dust and soiling loses 5%. Combined these four losses equal approximately 20%, which is why the factor is 0.80. Skipping it means your system underperforms expectations by 20% from the first day.
Inverter kW equals the peak simultaneous running load in watts multiplied by 1.25 divided by 1000. Add up all appliances that could run at the same time during normal home operation. Multiply by 1.25 for startup tolerance and safety margin. Modern hybrid inverters have built-in surge protection, so sizing to the running load times 1.25 is the correct engineering method. Do not size to the total startup surge of every appliance simultaneously.
Peak sun hours are the equivalent number of hours per day when sunlight intensity reaches 1000 watts per square metre. They are not daylight hours. A location may have 14 hours of daylight in summer but only 5.0 peak sun hours because early morning and late evening light is too weak for full panel output. The same 6kW system produces 39 kWh per day at 6.5 peak sun hours and only 18 kWh per day at 3.0 peak sun hours. Always design to your location's conservative year-round value.
On-grid solar connects panels and a string inverter to the utility grid. It reduces your electricity bill but shuts down completely during power outages for safety. Hybrid solar adds a battery bank and automatically switches to battery power during outages without interruption. Off-grid solar is fully independent from the grid and requires a large battery bank sized for overnight and cloudy-day power. Hybrid is the standard choice for homes in areas with regular power outages.
Battery Ah required equals load in watts multiplied by backup hours divided by voltage (typically 48V) divided by depth of discharge. For lithium LiFePO4 use 0.90 depth of discharge. For tubular lead-acid use 0.50. Example: a 1500W essential load for 8 hours on lithium: 1500 times 8 divided by 48 times 0.90 equals 278Ah. At 100Ah per lithium unit that is 3 batteries. The same load on tubular: 1500 times 8 divided by 48 times 0.50 equals 500Ah, requiring 3 batteries of 200Ah each.
Tubular lead-acid batteries provide 50% usable capacity and last 400 to 600 cycles under daily deep cycling. Lithium LiFePO4 provides 90% usable capacity and lasts 6000 plus cycles. Tubular costs 3 to 4 times less upfront. For homes using battery backup daily to cover power outages, lithium wins on 10-year total cost because tubular requires 3 to 4 full replacements over the same period. For homes where outages are rare, tubular remains a valid lower-cost option.
Yes during daylight hours with a grid-tie or hybrid inverter. Solar panels power AC units directly from approximately 8am to 6pm without drawing from the grid or battery. After sunset you need battery backup or grid power. A modern DC inverter AC draws 900 to 1200 watts running, not the 1600 to 1800 watts figure that older calculators use for non-inverter models. Using the outdated figure overcalculates your panel requirement by 25 to 60%.
Add up the running wattage of all appliances that operate simultaneously during peak home use. Do not include startup surges. Multiply the total by 1.25. Divide by 1000 to convert watts to kilowatts. Round up to the next standard inverter size available. Example: 2100W for two ACs plus 450W for fans plus 200W for lights and fridge equals 2750W running load. 2750 times 1.25 divided by 1000 equals 3.44kW, so a 4kW or 5kW inverter is appropriate.
Calculate your monthly electricity consumption from your utility bill in kWh. Divide by 30 to get daily kWh. Apply the formula: System kW equals daily kWh divided by peak sun hours divided by 0.80. A home consuming 600 kWh per month equals 20 kWh per day. At 5.0 peak sun hours: 20 divided by 5.0 divided by 0.80 equals 5kW system. The exact result varies by location because peak sun hours range from 2.5 in northern Europe to 7.0 in the Gulf and Middle East.
The fair cost per installed watt varies significantly by country due to labor costs, import duties, panel availability, and installer competition. To compare any quote fairly, divide the total all-in cost by the system size in watts. Select your country in this calculator to see the fair benchmark range for your specific market. Below the lower benchmark for your region: verify panel certification grade and inverter warranty terms. Above the upper benchmark without premium brand justification: get additional quotes.
Tier-1 solar panels from manufacturers including Longi, Jinko, Canadian Solar, REC, and SunPower carry 25-year performance warranties guaranteeing at least 80% of rated output at year 25. Actual degradation averages 0.3 to 0.5% per year, meaning panels still produce 88 to 92% of rated output after 25 years. Inverters last 10 to 15 years and are the most common replacement cost. Payback period ranges from 3 to 4 years in high-electricity-cost markets with good sun to 10 to 14 years in low-cost markets with limited sun.