Solar Hub
Panel output estimator, peak sun hours reference, and the system-sizing fundamentals that connect panels, batteries and inverters into a working off-grid or hybrid setup.
Last updated: May 2026
Panel Output Estimator
The starting point for any solar plan: estimate how many kWh your panels will produce per day, month and year. Enter panel wattage, panel count and your local peak sun hours, and the calculator returns kWh production plus an annual savings figure at your electricity tariff.
What you need before you start
- Panel wattage (Wp): on the datasheet - typical residential panels are 350 to 450 Wp in 2026.
- Number of panels: based on roof area or budget. A 10-panel 400 Wp array is 4 kWp nameplate.
- Peak sun hours for your region: see the reference table below. Northern Europe sits around 2.5 to 3.0; Mediterranean and US Southwest reach 5.0 to 6.5.
- System efficiency: 75 to 85% accounts for inverter losses, cable drop, soiling and temperature derating.
→ Open the Solar Panel Output Calculator
Returns daily, monthly and yearly kWh production plus estimated annual savings at your tariff.
Peak Sun Hours Reference
Peak sun hours (PSH) is the number of hours per day during which solar irradiance averages 1,000 W/m² - the standard test condition for panel ratings. It is the single most useful number for sizing a system: daily kWh ≈ nameplate kW × PSH × system efficiency.
PSH varies by latitude, weather and time of year. The values below are annual averages on a south-facing roof at typical tilt. Use the lower (winter) value when sizing for off-grid autonomy; use the annual average for grid-tied production estimates.
Europe
| Region | Annual avg PSH | Winter low | Summer high | Notes |
|---|---|---|---|---|
| Northern Scandinavia (Tromsø, Umeå) | 2.2 | 0.3 | 5.0 | Winter near zero; summer compensates partly |
| Southern Scandinavia & Baltic | 2.6 | 0.7 | 5.2 | Stockholm, Helsinki, Riga, Vilnius |
| UK, Ireland, Benelux, North Germany | 2.7 | 0.8 | 4.8 | Heavy seasonal swing; cloud cover dominant |
| Central Europe (DE, PL, CZ, AT) | 3.1 | 1.1 | 5.4 | Best production April to September |
| France (central) & Northern Italy | 3.5 | 1.5 | 5.8 | Good year-round production |
| Southern France, Northern Spain | 4.2 | 2.0 | 6.3 | Bordeaux, Lyon, Bilbao, Toulouse |
| Spain (central), Portugal, Italy (central) | 4.8 | 2.5 | 6.8 | Madrid, Lisbon, Rome - strong year-round |
| Southern Spain, Sicily, Greece | 5.2 | 3.0 | 7.0 | Highest in continental Europe |
United States
| Region | Annual avg PSH | Winter low | Summer high | Notes |
|---|---|---|---|---|
| Pacific Northwest (Seattle, Portland) | 3.5 | 1.0 | 6.0 | Strong seasonal swing; clouded winters |
| Northeast (Boston, NYC, Philadelphia) | 4.2 | 2.0 | 5.8 | Solid production; modest winter dip |
| Midwest (Chicago, Minneapolis) | 4.0 | 1.8 | 6.0 | Cold but clear winters help |
| Southeast (Atlanta, Charlotte) | 4.6 | 2.8 | 5.9 | Consistent year-round |
| Texas (Dallas, Houston) | 5.0 | 3.2 | 6.2 | Very strong; heat reduces panel efficiency |
| Mountain West (Denver, Salt Lake) | 5.5 | 3.5 | 7.0 | High altitude, low humidity, clear skies |
| Southwest (Phoenix, Las Vegas, Tucson) | 6.5 | 4.5 | 7.5 | Among the highest in the world |
| California (LA, San Diego, Bay Area) | 5.5 | 3.5 | 7.0 | Coastal fog reduces morning hours |
→ Full peak sun hours reference: 25 European cities, all 50 US states and 8 world cities with latitude, annual average, winter low and summer high values, calibrated to PVGIS and NREL datasets.
Pro tip
For grid-tied systems with net metering, size to the annual average PSH - excess summer production offsets winter shortfall through the grid. For off-grid or battery-backed systems, size to the winter low - that's the worst-case daily production the battery must bridge. Sizing to the annual average on an off-grid system guarantees winter blackouts.
System Sizing Cheat Sheet
The four numbers that drive every solar plan, with the formulas that connect them.
Daily kWh Production
kWh/day = panel count × Wp/panel × PSH × system efficiency ÷ 1000
Example: 10 panels × 400 Wp × 4.2 PSH × 0.80 efficiency = 13.4 kWh/day average.
Battery Bank Size (Ah)
Battery Ah = daily kWh × autonomy days ÷ (battery voltage × depth of discharge)
Example: 5 kWh/day × 2 days autonomy ÷ (48 V × 0.80 DoD) = 260 Ah at 48 V (~12.5 kWh nominal).
Depth of discharge for common chemistries: lead-acid 0.50 (safe), LiFePO4 0.80 to 0.90, lithium-ion 0.80.
Inverter Sizing
Inverter continuous W = sum of simultaneous loads × 1.2 safety margin
Inverter surge W = largest motor start × 3 to 7 surge factor (check appliance label)
A fridge compressor pulls 200 W running but can demand 1,200 to 1,500 W at startup. The inverter must handle the surge, not just the running load. Modern inverters list both continuous and 5-second surge ratings.
Simple Payback Period
Payback years = system cost ÷ (annual kWh production × electricity rate)
Example: €8,000 system ÷ (4,500 kWh × €0.30/kWh) = 5.9 years. Adding electricity-price inflation of 3% shortens this; financing interest lengthens it.
Pro tip
Sizing battery autonomy days higher than 2 to 3 rarely pays off for grid-tied homes. Beyond 3 days, the battery cost climbs faster than the avoided grid-import cost. For true off-grid cabins or RVs, 4 to 5 days is the practical maximum - longer autonomy turns into oversized batteries you rarely fully use, with measurable shelf-life losses.
System Components at a Glance
Every solar setup has these four blocks. Pricing in 2026 EUR per usable kWh of capacity; values shift quickly - check current quotes.
| Component | Function | 2026 price band | Lifespan | Failure mode |
|---|---|---|---|---|
| Panels | Convert sunlight to DC | €0.15 to 0.25 per Wp | 25 to 30 yr (~80% rated at 25 yr) | Soiling, micro-cracks, hot spots |
| Charge controller (off-grid) | Regulate DC to battery | €100 to 500 (MPPT preferred) | 10 to 15 yr | Capacitor aging in hot installs |
| Inverter (grid-tied or hybrid) | DC → AC for household / grid | €0.10 to 0.25 per W continuous | 10 to 15 yr | Heat-related capacitor / fan failure |
| Battery bank | Store DC for night / grid outage | €400 to 800 per usable kWh (LiFePO4) | 10 to 15 yr (3,000 to 6,000 cycles) | Calendar aging + cycle wear |
Charge Controller: MPPT vs PWM
For any panel over 100 Wp on an off-grid setup, choose MPPT (Maximum Power Point Tracking). MPPT controllers extract 20 to 30% more energy than older PWM (Pulse Width Modulation) controllers, especially in cold weather and partial shading. The price gap has shrunk to the point where PWM only makes sense for tiny systems (under 50 W).
Battery Chemistry Quick Pick
- LiFePO4 (lithium iron phosphate): 10 to 15 year life, 80 to 90% DoD, low fire risk - the default for new installs in 2026.
- AGM lead-acid: 4 to 7 year life, 50% DoD, low upfront cost - only economic if budget is the hard constraint.
- Lithium-ion (NMC): Higher energy density than LiFePO4, but worse cycle life and higher fire risk - rare in stationary storage.
Sizing Workflow
A linear way to size a system, in the order the numbers depend on each other.
- Estimate daily kWh consumption. For a home, check the past 12 months of utility bills. For an off-grid cabin or RV, list every appliance with its wattage and daily run-hours.
- Look up peak sun hours for your region. Use the annual average for grid-tied. Use the winter low for off-grid.
- Calculate required panel array (kWp).
kWp = daily kWh ÷ (PSH × system efficiency). Round up to the next panel count. - Size the battery bank. Multiply daily kWh by autonomy days. Divide by usable depth of discharge. This is your usable storage in kWh.
- Size the inverter. Sum simultaneous AC loads, add 20% safety margin, then verify the surge rating covers your largest motor start.
- Estimate payback. Divide system cost by (annual kWh production × electricity rate). Add a 3% per-year electricity inflation assumption for a more realistic figure.
Pro tip
Most over-spec'd home systems trace back to skipping step 1. Without an honest baseline of daily kWh use, installers default to "fill the roof," which oversizes the array, the battery and the inverter together - turning a 6-year payback into a 12-year payback. Pull the bills first.
Common Solar Mistakes
- Using nameplate kW for production estimates. A 4 kWp array does not produce 4 kWh per peak sun hour. After inverter losses, cable drop, soiling and temperature derating, real-world production is 75 to 85% of nameplate × PSH.
- Sizing off-grid systems to the annual average. Winter PSH is often 30 to 50% of the annual average. An off-grid system sized to annual average runs out of stored energy by January.
- Ignoring inverter surge requirements. A 2 kW continuous inverter that lists 4 kW surge won't reliably start a 1.5 hp well pump (often 5 to 7 kW surge). Read the appliance's locked-rotor amps, not just running watts.
- Mixing battery ages. Adding new cells to an old bank drags the new cells down to old-cell performance within months. Replace the whole bank when one cell drops out, or budget for a full swap from the start.
- Roof orientation off by 30°+. South-facing (Northern Hemisphere) gives reference output. East-west splits each lose 10 to 15% annually; pure east or pure west loses 15 to 25%. Verify with a satellite-based PVGIS or NREL estimate before committing.
- Forgetting temperature derating. A panel rated at 25°C cell temperature loses ~0.4% per °C above that. On a 65°C roof in Phoenix summer, real output is 84% of nameplate - not the 100% the brochure suggests.
All Solar Tools and Guides
Every solar utility on the site, with adjacent EV and electricity tools you'll often need in the same workflow.
Solar Calculators
- Solar and EV Glossary - 25 terms defined: kWp, peak sun hours, MPPT, DoD, C-rate, SoC, inverter, grid-tied, kWh/100 km and more
- Solar Panel Output Calculator - daily, monthly and yearly kWh from panel wattage, count and peak sun hours; estimated annual savings at your tariff
- Battery Bank Sizing Calculator - required Ah capacity, usable kWh and nominal bank size from daily consumption, autonomy days, voltage and depth of discharge
- Inverter Sizing Calculator - continuous rating, surge capacity, suggested standard inverter size and battery-side DC draw from your load, surge factor, voltage and efficiency
- Solar Payback Calculator - simple and inflation-adjusted payback period, first-year savings and 25-year net gain from system cost, annual production and your electricity rate
- Peak Sun Hours Reference - annual average, winter low and summer high PSH for 25 European cities, all 50 US states and 8 world cities; calibrated to PVGIS and NREL datasets
- Solar Panels for EV Charging Calculator - panel count, array size in kW, roof area and annual production to cover your EV's daily charging need from solar; inputs: daily km, EV efficiency, local PSH, panel wattage and system efficiency
- Solar Panel Layout Calculator - how many panels fit on your roof from usable area and panel size; array kWp, daily and annual kWh estimate, visual panel grid
Adjacent Energy Tools
- kWh to Euro Calculator - convert solar production into actual money saved at your electricity rate
- Electricity Cost Calculator - baseline household consumption you're trying to offset with solar
- Appliance Running Cost - identify the loads that dominate your daily kWh figure before sizing
- Power Supply Calculator - inverter and PSU sizing for AC loads
- Wh ↔ kWh Converter - battery datasheets often quote Wh; system designs work in kWh
EV + Solar Workflow
- EV & Energy Hub - charging, range, and cost tools that pair with home solar
- EV Charging Cost - compare grid-charge cost vs your solar production
- EV vs Petrol - pair this with solar payback for a full clean-energy savings picture
Wiring & Safety
- Wire Gauge Calculator - DC cable sizing between panels, charge controller and battery (voltage drop matters more at low DC voltages)
- Voltage Drop Calculator - long DC runs lose more than you expect; under-sized cable wastes panel output
- Fuse / Breaker Sizing - DC fuses protect battery banks from short-circuit currents
FAQ
What is the difference between peak sun hours and daylight hours?
Daylight hours count every minute from sunrise to sunset - including low-angle morning and evening light that produces only a fraction of full sun. Peak sun hours condense the same day's total solar energy into the equivalent number of hours at full 1,000 W/m² irradiance. A 12-hour daylight day in central Europe might equal 3.5 peak sun hours. PSH is the figure that maps directly to your panel rating - it tells you how many "rated" hours of production to expect.
Why is my real-world output less than panel wattage × PSH?
Three losses stack: inverter conversion (5 to 8% loss), cable drop and connector resistance (1 to 3%), and temperature derating (panels rated at 25°C cell temperature; real cells often run 45 to 65°C). Adding soiling, occasional partial shading, and reflection losses, real-world output typically lands at 75 to 85% of nameplate × PSH. Using 80% is a reasonable default for clean, well-oriented residential installs.
Do I need batteries to install solar?
No. Grid-tied systems feed excess production to the grid and pull from the grid at night or during low production - no battery required. They have the shortest payback because there is no battery cost. Hybrid systems add a battery for backup during outages and self-consumption optimisation. Off-grid systems have no grid connection and require batteries large enough for your worst-case autonomy. Pick based on your goal: payback only (grid-tied), payback plus outage backup (hybrid), or full independence (off-grid).
Why does LiFePO4 dominate new battery installs in 2026?
Three reasons. Cycle life: a quality LiFePO4 cell lasts 3,000 to 6,000 full cycles vs 300 to 600 for lead-acid - meaning 10 to 15 years instead of 4 to 7. Usable capacity: 80 to 90% depth of discharge vs 50% for lead-acid, so a 10 kWh LiFePO4 bank delivers more usable energy than a 14 kWh lead-acid bank. And safety: the iron phosphate cathode doesn't enter thermal runaway like nickel-based lithium chemistries. Upfront cost is higher per kWh, but total cost of ownership has favoured LiFePO4 since 2022.
How accurate are simple payback calculations?
Within about 15% for grid-tied systems in stable electricity markets. The biggest sources of error: electricity-rate inflation (rates have risen 3 to 8% per year across Europe since 2020), system degradation (panels lose ~0.5% per year), and changes to feed-in or net-metering policy. A more realistic payback adds an electricity-inflation factor and a small annual degradation term. For off-grid systems, payback is rarely the right metric - the system is replacing a non-existent grid connection or backup generator, not just electricity cost.
Does roof tilt matter as much as orientation?
Less than you'd expect on most homes. Within ±15° of optimal tilt (which is roughly your latitude for year-round production), the loss is under 5%. Orientation matters more: south-facing is the reference in the Northern Hemisphere; due east or due west typically loses 15 to 25% annual production. Steep roofs in northern latitudes favour winter production; shallow roofs favour summer. For grid-tied systems with net metering, year-round total matters most, so optimal tilt is close to your latitude - but most installs follow the existing roof angle and lose only a few percent vs perfect.