Solar Panel Output Calculator

What should I know about Peak Sun Hours?

'Peak sun hours' (PSH) is the key input for solar generation estimates, and understanding it prevents confusion when comparing solar output across locations and seasons. PSH is not the total hours of daylight — it's the equivalent hours of full-intensity (1,000 W/m²) sunlight. A real day might have 16 hours of daylight but only 4 of those at the equivalent of full intensity once you account for atmospheric losses, low-angle morning and evening sun, and cloud cover. UK average PSH: 2.5–3.5 hours per day averaged over the year, with significant seasonal variation (summer days can be 5–6 PSH, winter days as low as 0.5–1). Southern UK (Cornwall, Sussex) averages slightly higher than the Scottish Highlands. Europe varies widely: Southern Spain, Portugal, Greece, Southern Italy average 4.5–5.5 PSH; Central Europe (Germany, Netherlands) similar to UK at 2.5–3.5; Scandinavia lower. Middle East and North Africa (Saudi Arabia, Egypt, parts of Sahara) average 6–7 PSH — among the world's best solar resources. The US southwest (Arizona, New Mexico, Nevada, California desert) reaches 6+ PSH in some locations; northeastern US similar to UK. Australia averages 5–6 PSH for most of the populated areas. A worked example: a 4 kWp (kilowatt-peak) system in southern UK at 3.0 PSH average generates 4 × 3 = 12 kWh per day, or about 4,400 kWh per year — close to typical UK household electricity consumption of 2,500–3,500 kWh, so a 4 kWp system can offset most or all of a typical household's annual electricity demand on paper, though timing and matching to actual usage matters (see below). Manufacturers' figures sometimes assume STC (Standard Test Conditions) at 1,000 W/m² and 25°C panel temperature, which is optimistic — real-world panels typically deliver 80–85% of STC due to higher temperatures (which reduce panel efficiency) and inverter losses.

What's the difference between Self-Consumption and Export?

How much you actually save with solar depends critically on how much of the generated electricity you use directly in your home versus exporting back to the grid — and this is where many solar payback estimates go astray. Direct self-consumption: electricity you use the moment it's generated saves you the full retail electricity rate (around £0.28/kWh in the UK at the Ofgem cap in mid-2026) — this is a substantial saving. Export to grid: electricity sent back to the grid via the Smart Export Guarantee (SEG) pays much less — typical SEG tariffs are £0.04–0.15/kWh depending on supplier, so 25–50% of the retail rate. The economics strongly favour using your generation directly. Typical self-consumption rate for a household without battery storage: 20–35% — solar generates mostly in the middle of the day when many people are out at work, so most of it gets exported at the lower rate. Adding battery storage transforms this: a 5–10 kWh battery stores daytime generation for evening use, raising self-consumption to 60–80% and dramatically improving the savings. The investment in batteries (£3,000–6,000 typically) extends payback time but increases lifetime savings substantially if you have high evening electricity use. Other ways to increase self-consumption: smart appliances and timers that run dishwashers, washing machines, immersion heaters, or EV charging during the day; diverter switches that send excess solar to heat hot water rather than the grid. Working-from-home households naturally have higher daytime use and benefit more. Without battery storage and with mostly-out-during-the-day usage, the SEG export rate dominates the economics and payback can stretch to 10–12 years; with batteries and high self-consumption, payback can be 6–8 years. This calculator estimates total generation; the actual savings depend on your usage pattern.

What's the key thing to understand about Government Incentives?

Government incentives for residential solar have changed substantially over the past decade and vary by country. UK: the original Feed-in Tariff (FIT) scheme that paid generous rates to early adopters closed to new applicants in 2019, replaced by the Smart Export Guarantee (SEG) — which legally requires suppliers to pay something for exported electricity but at much lower rates (£0.04–0.15/kWh) than the original FIT. There's no longer a capital grant for residential solar in the UK, but the VAT on solar installations was reduced to 0% in 2022 (saving 20% on installation cost) and continues to be 0% for residential installations until 2027 at least — a meaningful saving on a £6,000–10,000 install. Some local councils still offer small grants or interest-free loans. EU: incentives vary by member state — Germany has historically had strong FITs (now reduced), Italy and Spain have generous current schemes including tax credits, France has 'autoconsommation' tariffs. US: the federal Investment Tax Credit (ITC) gives a 30% federal tax credit on residential solar through 2032, plus state incentives in many states (California, Massachusetts, New York have strong programmes). Net metering is widespread but rules vary by state and utility. Australia: state and federal Small-scale Technology Certificates (STCs) effectively give an upfront discount on solar installations. Beyond incentives, the most important economic factor is the high and rising cost of grid electricity itself — every increase in electricity prices improves the economics of self-generated solar. Energy security and climate concerns also push some households to install solar regardless of payback time. Check current incentives at the point of installation, as they change frequently. This is general information rather than financial advice; speak to an MCS-certified installer (UK) or equivalent for accurate costings for your specific home.

What's the key thing to understand about Safety and Regulations?

Most structural and electrical DIY work in England and Wales must comply with Building Regulations and is notifiable to local Building Control. Work that is not notifiable (like-for-like replacements, cosmetic changes) can be done without notification. Notifiable work done without approval is technically illegal and can cause problems when selling the property. Electrical work in most rooms requires a Part P competent person or Building Control inspection. Gas work must always be performed by a Gas Safe registered engineer — it is illegal for anyone else to carry out gas work in the UK, and using an unregistered installer invalidates both your home insurance and any warranty on the work. For structural changes (removing load-bearing walls, altering the roof structure), always get a structural engineer's assessment before starting, even for jobs that look straightforward.

Worked Example: Sizing a Solar Array to Typical Household Usage

A household uses 3,600 kWh of electricity a year and wants to size a solar array to cover a meaningful share of that from self-generation. A location in southern England gets roughly 3.2 peak sun hours a day on average across the year, while a 4kW array of panels at roughly 20% efficiency loses some output to inverter losses, shading and non-ideal orientation (a reasonable system efficiency factor is around 0.80-0.85). Expected annual generation = 4 kW x 3.2 hours/day x 365 days x 0.82 (system efficiency) = approximately 3,830 kWh/year That is more than the 3,600 kWh the household uses annually, but generation and consumption rarely align hour by hour — most solar output arrives at midday in spring and summer, while a large share of household demand happens in the evening and through winter, so even a system sized to match annual usage on paper typically only covers 30-50% of actual consumption directly, with the rest either exported (earning a lower rate) or needing grid import in the evening and winter, unless paired with a battery as covered in the battery storage payback guide on this site.

Approximate Peak Sun Hours by UK Region and Season

Peak sun hours (the equivalent hours of full-intensity sunlight a location receives) vary noticeably across the UK by latitude and by season, which directly scales expected solar generation for an identically sized system.

These figures are regional averages and can vary year to year with cloud cover, so treat them as planning estimates rather than guarantees. The large summer-to-winter swing is also why most UK solar installations generate the large majority of their annual output between roughly April and September, with winter months contributing comparatively little even on a well-sized system.