Output, Savings, and Everything You Need to Know
A 4kW solar panel system is one of the most popular choices for UK homeowners. It sits in the sweet spot between roof space requirements and energy output — large enough to make a genuine dent in your electricity bills, small enough to fit on most standard roofs without complicated engineering.
This guide covers exactly what you can expect from a 4kW system: how much it generates, how many panels you'll need, what you can save, and how to get the most from your installation.
How Much Electricity Does a 4kW Solar System Produce?
A 4kW solar system in the UK generates between 3,400 and 4,200 kWh of electricity per year under real-world conditions. Where exactly you land in that range depends on your location, roof orientation, and panel efficiency.
To put that in context, the average UK household uses around 3,500 kWh of electricity per year. A well-positioned 4kW system can cover close to 100% of that demand — though the timing of generation versus consumption means you'll still draw from the grid at night and during long cloudy periods unless you add battery storage.
Rule of thumb: A 4kW south-facing system in southern England generates roughly 850–1,050 kWh per kWp annually. In northern regions, expect closer to 700–850 kWh per kWp.
Output by Region
Your location is one of the biggest variables. Here's how annual output and estimated bill savings compare across the UK:
| Region | Annual output (4kW) | Est. bill saving* |
| South Coast (e.g. Hampshire) | 3,800–4,200 kWh | £760–£840 |
| South East / London | 3,500–3,900 kWh | £700–£780 |
| Midlands | 3,200–3,600 kWh | £640–£720 |
| North England | 2,900–3,300 kWh | £580–£660 |
| Scotland | 2,600–3,000 kWh | £520–£600 |
Output by Month
Solar generation is not spread evenly across the year. Summer months deliver significantly more than winter, but output continues year-round:
| Month | Monthly output | Daily average | Generation level |
| January | 25–40 kWh | ~1 kWh | Low |
| February | 40–60 kWh | ~1.5 kWh | Low–Medium |
| March | 80–110 kWh | ~3 kWh | Medium |
| April | 110–140 kWh | ~4 kWh | Good |
| May | 130–160 kWh | ~4.5 kWh | Good–High |
| June | 140–175 kWh | ~5 kWh | High |
| July | 135–170 kWh | ~5 kWh | High |
| August | 120–155 kWh | ~4.5 kWh | Good–High |
| September | 90–120 kWh | ~3.5 kWh | Medium–Good |
| October | 55–80 kWh | ~2 kWh | Medium |
| November | 30–50 kWh | ~1.3 kWh | Low–Medium |
| December | 20–35 kWh | ~0.9 kWh | Low |
How Many Panels in a 4kW Solar System?
The number of panels you need depends on the wattage of each individual panel. Modern panels are more powerful than those installed even five years ago, which means you can achieve 4kW with fewer panels and less roof space than before.
| Panel wattage | Panels needed | Approx. roof space | Panel type |
| 250W | 16 panels | ~32 m² | Older / budget panels |
| 350W | 12 panels | ~22 m² | Common mid-range |
| 400W | 10 panels | ~20 m² | Modern premium |
| 420W | 10 panels | ~20 m² | High-efficiency monocrystalline |
For a 4kW system using 400W panels, you're looking at 10 panels covering around 20 square metres of roof. That fits comfortably on most semi-detached or detached properties with a clear south, south-east, or south-west facing roof.
Roof orientation: South-facing is ideal, but east or west-facing roofs still work well — typically producing around 15–20% less per year. North-facing slopes are not recommended for solar installations.
How Much Money Can I Save and Earn?
There are two sides to the financial return from a 4kW system: the money you save by generating your own electricity instead of buying it from the grid, and the money you earn by exporting surplus electricity back to the grid.
Savings on Your Electricity Bills
Every kWh your panels generate and you use directly at home is a kWh you don't have to buy from your energy supplier. At current unit rates of around 24–27p per kWh, a 4kW system in southern England generating 3,800 kWh per year and achieving 50% self-consumption saves around £460–£510 per year on electricity bills.
Add battery storage and self-consumption typically rises to 70–80%, pushing annual savings to £650–£800 or more. Our customers' real-world results bear this out — one Hampshire household with a 4.2kW system and 10.5kWh battery paid just £64 across eight months.
The Feed-In Tariff
The Feed-In Tariff (FIT) scheme closed to new applicants in April 2019, so it's no longer available if you're installing solar for the first time. If you had panels installed before that date and are registered on the scheme, you'll continue to receive FIT payments for the remainder of your contract — typically 20 years from the installation date.
If your FIT contract is coming to an end, or if you're unsure whether you're registered, it's worth reviewing your options. The Smart Export Guarantee is now the main route for earning from exports.
The Smart Export Guarantee
The Smart Export Guarantee (SEG) replaced the Feed-In Tariff for new installations. Under SEG, energy suppliers are required to pay you for every unit of surplus electricity you export to the national grid. The export rate varies by supplier and tariff — currently ranging from around 5p to 20p per kWh.
Octopus Energy's Outgoing Octopus tariff, for example, currently pays 15p per kWh exported. For a 4kW system in southern England, you might export around 1,500–2,000 kWh per year (depending on how much you self-consume), generating £225–£300 in annual export payments on top of your bill savings.
Total return example: Bill savings of £500 + SEG export earnings of £250 = £750 per year from a 4kW system in Hampshire. At that rate, a typical £7,000–£8,000 installation pays for itself in around 9–10 years, with 15+ years of effectively free electricity beyond that.
Benefits of Investing in a 4kW Solar Panel System
A 4kW solar installation offers a combination of financial, environmental, and practical advantages that few other home improvements can match.
- Lower electricity bills from day one. Every unit of solar electricity you use directly replaces electricity you'd otherwise pay for at full price.
- Protection against rising energy prices. Once installed, your solar electricity costs nothing to generate. As grid electricity prices rise — as they have consistently over the past decade — the value of your generation grows with them.
- Income from exports. Through the Smart Export Guarantee, surplus electricity earns you money rather than being wasted.
- Reduced carbon footprint. A 4kW system in southern England avoids approximately 900kg–1,100kg of CO₂ emissions per year — equivalent to taking a car off the road for several months.
- Compatibility with electric vehicles and heat pumps. Solar pairs particularly well with EV charging and air source heat pumps, where daytime generation can directly power high-consumption devices at zero marginal cost.
- Increased property value. Multiple studies show that solar installations add value to UK homes, with buyers increasingly factoring in low energy bills when making purchase decisions.
- Energy independence. With battery storage, you can use stored solar electricity through the evening and overnight, significantly reducing reliance on the national grid.
- Choose the right roof orientation. South-facing delivers maximum annual output. South-east or south-west still perform well. If your best available roof faces east or west, discuss this with your installer — a slightly larger system may be warranted to compensate.
- Optimise the pitch angle. The ideal angle in the UK is 30°–40°. Flat roofs can use adjustable mounting frames to achieve this.
- Address shading before installation. Even small amounts of shade from a chimney, dormer, or nearby tree can disproportionately reduce output, particularly on systems without panel-level optimisers. Your installer should carry out a full shading analysis.
- Consider panel-level optimisers or microinverters. These reduce the impact of partial shading and allow individual panel performance monitoring, making faults easier to spot.
- Size your battery correctly. A battery too small won't capture all the surplus from sunny days; one too large may never fully cycle. For a 4kW system, a 5–10kWh battery is typically appropriate.
- Shift high-consumption appliances to daytime hours. Dishwashers, washing machines, tumble dryers, and EV charging all consume significant electricity. Running these during peak generation hours (roughly 10am–3pm) maximises direct use of your solar output.
- Use a smart tariff. Many energy suppliers now offer time-of-use tariffs with off-peak overnight rates as low as 7p/kWh. Combined with battery storage, you can charge the battery cheaply overnight and avoid any gap left by the solar during shorter winter days.
- Monitor your system. Modern inverters come with monitoring apps that show real-time and historical generation data. Checking this regularly means you'll spot any drop in performance quickly.
- Keep panels clean. In practice, rainfall keeps most panels reasonably clean, but if you're near a road, agricultural land, or have significant bird activity, an annual clean can recover a few percentage points of lost output.
How to Maximise Efficiency of Your 4kW Panels
Getting the most from a 4kW system comes down to both how the system is installed and how you use the electricity it generates.
At Installation
In Daily Use
Get Quotes on 4kW Solar Panel Systems
A 4kW solar system is a long-term investment. The technology lasts 25–30 years with minimal maintenance, and the financial returns compound as energy prices rise. Getting it right from the start — the right panel choice, the right installation, the right battery setup — makes a meaningful difference to what you earn and save over that period.
CRG Direct are MCS Certified solar and renewable energy specialists serving Hampshire, Portsmouth, Southampton, and the wider South and South East of England. Every installation comes with full aftercare and system monitoring support.
Use our Solar Savings Calculator to get a personalised output and savings estimate for your home, or speak to our team directly:
Call: +44 330 133 2497 Email: info@crgdirect.co.uk Website: crgdirect.co.uk