Installing solar panels is one of the most reliable ways to cut household energy costs and shrink your carbon footprint. With UK energy prices becoming increasingly unpredictable, solar PV offers the reassurance of more stable, predictable bills in the future.
One of the first questions people ask us at H2ecO is How many solar panels do I need? The truth is, there’s no single answer. It depends on your goals, your property, and a few technical considerations. In this guide, we’ll break it down and share our most common advice.
Let’s start with the question you should be asking:
Why Are You Considering Solar?
Most customers come to us with two main motivations:
- Reducing carbon emissions
- Saving money
Many want both, but often lean slightly more toward one goal than the other.
If your focus is carbon reduction…
You’re likely motivated by the bigger environmental picture involving concerns about climate change, rising sea levels, wildlife loss, and the future impacts on your children and grandchildren. For you, it’s simple: the larger your solar PV system, the cleaner the energy you generate, and the more carbon you offset.
Result: Install the largest system your roof space, budget, and National Grid approval allow.
If your focus is cost stability and savings…
You might be motivated by past experiences of energy crises or concerns about rising and unpredictable prices, especially if you’re on a fixed income. Here’s why a bigger solar PV system usually makes financial sense:
- Electricity use patterns matter more than past bills: Solar produces power mainly between 10 am and 2 pm. If you use energy outside those times, the panel output won’t perfectly match your consumption.
- Installation costs don’t scale evenly: Many costs (scaffolding, inverters, admin) are fixed, so a larger system costs proportionally less per kW.
- Future demand is likely to rise: With electric vehicles and heat pumps becoming more common, household electricity use is only going up.
- You can sell excess energy: Through the Smart Export Guarantee (SEG), you can sell surplus electricity back to the grid, earning credits that help offset winter bills.
Result: Again, the best financial approach is the largest system that fits, is affordable, and is approved.
Solar Panel System Design Considerations
If bigger is generally better, the next step is working out how to make that happen.
1. Panel Size and Roof Layout
While the above table gives you a rough idea of how long it will take to cover the cost of your solar panels through saved energy bills, how long it will actually be depends on a number of factors.
- Modern solar panels (2025) are typically just over 1m wide and 1.7–2.1m long.
- Panels can be mounted in portrait or landscape, close to ridge height and roof edges.
- Smart inverter systems can reduce the impact of shading from chimneys or other obstacles.
- If budget limits your initial install, position solar panels so it’s easy to add more later.
2. Grid Connection
- Up to 3.68kW can be connected without an application.
- Larger systems require approval, and we often see domestic approvals up to 10kW.
- Commercial applications can take up to three months and may involve site visits.
3. Planning Permission
In most cases, planning isn’t a barrier as the UK government actively supports solar. Read our blog on planning permission for solar panels here.
Calculate your solar panel needs
Here is a quick way to calculate how many solar panels you need. We’ll dig deeper into the specifics later on.
Find Your Annual Electricity Usage
- Check your electricity bills (paper or online) and look for total kWh used over the last 12 months.
- If you can’t find a full year of data, add up 3 to 6 recent months and multiply accordingly to estimate a full year.
- Alternatively, use a smart meter app or contact your energy supplier.
Estimate How Much Solar You Need
- One solar panel (350 W) produces about 265 kWh/year (under average UK conditions).
- Number of panels = Your annual usage (kWh) ÷ 265
Or calculate the system size:
- 1 kW of solar panels produces around 850 kWh/year in the UK.
- System size (kW) = Your annual usage ÷ 850
Consider Roof Space and Orientation
- Each panel needs about 1.6 to 1.9 m²
- 12 panels (4.2 kW) equals around 20 to 25 m²
- South-facing roofs are ideal, but east/west can also work with around 10% to 20% reduced output
Tips for working out solar panel usage
- If your energy use will increase (e.g., getting an EV or heat pump), plan for it now.
- If you want to cover 50% to 70% of your usage to reduce costs but not go fully solar, just adjust your panel count accordingly.
How Much Power Will Your System Generate?
The average home solar system in the UK typically produces 4 kW to 6 kW per hour in optimum conditions. This usually requires between 6 and 20 panels, depending on your home’s energy usage and roof space.
Energy usage is usually associated with house size – the more bedrooms you have, the more people in the house, the higher the energy needs. If you have gas heating, this can reduce your electricity usage, while if you are charging EVs, that would increase it.
| Property Type | Avg. Annual Use (kWh) | Panels for 100% Offset | System Size (kW) | Panels for 50% Offset | System Size (kW) |
| 1-bed flat | 1,800 kWh | 7 panels | 2.45 kW | 3–4 panels | 1.05–1.4 kW |
| 2-bed house | 2,500 kWh | 10 panels | 3.5 kW | 5 panels | 1.75 kW |
| 3-bed semi-detached | 3,000 kWh | 12 panels | 4.2 kW | 6 panels | 2.1 kW |
| 4-bed detached | 4,000 kWh | 15–16 panels | 5.25–5.6 kW | 8 panels | 2.8 kW |
2-bedroom house
A system of 6 to 10 solar panels is likely suitable for your standard UK, 2-bedroom home. Eight is a good average to work with, covering most of your typical energy needs like computers, running white goods, lighting, and heating.
3-bedroom house
For a 3-bedroom home, you may need 8 to 14 solar panels. Most setups fall between 10 and 12, which can vary slightly depending on your usage and home configuration (terraced houses may require fewer compared to detached homes, for example).
4-bedroom house
A 4-bedroom home requires more power and may need anywhere between 10 and 20 solar panels. Around 15 is a common estimate, depending on your home’s individual layout and energy usage.
Typical Household Electricity Demands
| Property Type & Age | Energy Efficiency (Median EPC Score) | Relative Electricity Usage* | Notes |
| Flat / Maisonette (modern) | High (Band C+) | Lower (e.g. below average ~2,500 kWh) | Shared construction boosts efficiency (Office for National Statistics) |
| Flat / Maisonette (pre‑1930) | Moderate (Band D/E) | Slightly higher than modern flats | Less insulation, poorer fabric |
| Mid‑Terrace House (older stock) | Low (Band D/E) | Higher (e.g. ~2,700–3,000 kWh) | Solid walls, limited insulation |
| Semi‑Detached House (mixed age) | Moderate (Score ~65) | Average‑high (~2,700 kWh/year) | Similar to mid‑terrace in efficiency (Office for National Statistics) |
| Detached House (older stock) | Lower (Band D/E or below) | High (~3,000–3,500 kWh depending on size) | More external walls, higher heat loss |
| Detached House (post‑2012 build) | High (Band B/C, score ~83) | Moderate (~2,500–3,000 kWh) | Built to newer standards (Office for National Statistics, Office for National Statistics) |
| Semi‑ or Detached House (pre‑1930) | Low (Band E or below) | Highest among similar‑sized dwellings | Poor thermal performance (Office for National Statistics, Office for National Statistics) |
*Note: These electricity usage ranges assume average occupancy (2–3 people), typical appliance use, and exclude significant electric heating.
Find the right solar panels for your home
Installing solar panels is an excellent way to bring certainty and savings to your energy costs, while contributing to a greener future. To make the biggest impact, it’s important to install the right number and configuration of panels. Working with an expert solar panel installer helps you get it right the first time.
At H2ecO, we’ve been working with renewable technologies for over 15 years. Our Dorset-based team is experienced, respectful, and easy to have around your home. So, if you’re looking for a reliable solar panel installer or have any questions, we’re here to help.
Contact us today to see what solar panels could do for you.
FAQs:
How many solar panels do you need for 4,000 kWh per year?
To generate 4,000 kWh per year, you’ll likely need 14 to 20 panels. Of course, this depends on the panel type and system design. This is enough for a higher-than-average household. Ofgem reports show that the average British house uses around 2,700 kWh of electricity per year.
How many solar panels do you need for 500 kWh per month?
To generate 500 kWh per month, you’ll usually need somewhere between 15 and 20 solar panels. Once again, this is on the higher side of consumption levels, around twice the UK home average.
How many extra solar panels do you need to power certain items?
Solar panels to charge a car
A standard electric car has a battery capacity of around 50–60 kWh. As such, an electric car charging system running on 6 to 12 panels can generate enough energy to cover most driving needs. This will vary depending on driving habits, time of year and sunlight levels.
Running a heat pump with solar panels
Heat pumps use electricity to warm your home. A standard solar setup with 10 to 16 panels should provide enough power to support your heat pump, at least partially. You may still need grid power at times, especially during winter, and if the rest of your home relies on your solar energy.
Solar panels for powering underfloor heating
A typical solar setup of 8 to 16 panels can help power most underfloor heating systems, especially in well-insulated homes. But in colder months, if there’s a shortage of direct sunlight, you may need to rely on backup energy. However, your solar panels will still contribute meaningful energy cost savings.
