There’s plenty of research to be done when looking for the perfect solar panel system for your home. One of the most important elements to get right is the system size.
One of the most popular capacities for UK home’s is a 4kW solar panel system. This is because it tends to be ideal for medium sized properties with 2-3 bedrooms. However, whether it is right all depends on how much energy your household uses.
In our guide to 4kW solar panels, we’ll take a look at what the system consists of, how much energy it generates, the costs involved, plus a few other things you should be aware of before you make a purchase.
What is a 4kW solar panel system?
A 4kW solar panel system is a renewable energy setup designed to generate electricity for your home using the power of the sun. The ‘4kW’ refers to the system’s power output under ideal conditions. You might also see it referred to as a kWp (kilowatt peak) system. Kilowatt peak is technically the nameplate rating of the theoretical peak output. When it comes to solar panels, these terms are often used interchangeably.
A typical 4kW solar panel system consists of several key components:
- Solar panels – Usually between 9 and 12 photovoltaic (PV) panels.
- Inverter – The inverter converts the direct current (DC) electricity produced by your panels into alternating current (AC) that your home can use. It’s thought your solar panel system should be around 50% larger than your inverter to perform efficiently.
- Mounting system – To secure the panels to your roof.
- Electrical components – Connecting everything up as it should be, including to your household system and to the grid. Includes items like isolator switches, connectors and cabling.
How many panels in a 4kW system?
The number of panels in a 4kW solar system can vary depending on the wattage of the individual panels. Here are a few common configurations to reach the 4kW capacity, give or take a few watts:
- 10 x 400W panels – This setup gives you exactly 4kW of power.
- 12 x 350W panels – This combination slightly exceeds 4kW, providing 4.2kW in total.
- 9 x 430W panels – This arrangement gives you 3.87kW, just shy of the 4kW mark but close enough.
- 9 x 450W panels – This configuration gives you 4.1kW of power.
What combination of panels you actually go for depends on a few things.
For example, if roof space is an issue you may have to go for larger panels to reach the desired capacity. More efficient panels will help you to produce more power in a smaller area, potentially reducing the number of panels needed.
That said, higher wattage panels often come with a higher price tag as they are more efficient and contain more advanced technology. For example, a 450W panel is likely to be around 20% more expensive than a 350W panel. Any price differences are also dependent on brand and the quality of the panels.
Either way, your solar installer will help you determine the best configuration for your specific circumstances to make sure you get the most efficient and effective system for your home.
Electricity generation from a 4kW system
Knowing how much electricity a 4kW solar panel system can generate in comparison to your household’s typical use is crucial. If a 4kW doesn’t produce enough energy for your house or produces way too much, you’ll be working with inefficiencies in terms of costs and system running. You don’t want this.
In the UK, a 4kW solar panel system typically produces around 3,400kWh of electricity per year. This is based on roughly 2.5 peak sun hours per day. In terms of panel efficiency, it means you’re getting around 85% of your system’s peak power output.
We can break this down further. Based on these figures, a 4kW system generates around 9.3kWh of solar electricity a day. With a UK average electricity household consumption of 6-10kWh per day, a 4kW system will be a good fit for most homes.
There’s an important note to make though and that’s on seasonal variation.
This electricity generation figure is an average. A 4kW solar panel system doesn’t consistently produce 9.3kWh per day throughout the year. In the summer, it’s likely to generate a lot more than this (which is where residential battery storage comes in handy) and in the winter a lot less at around 10-15% of annual production. Spring and autumn account for 20-25% each.
Individual variations come into play too, such as where you are in the UK and your roof orientation – south facing is best, with east or west facing roofs producing about 15-20% less energy.
How much of your home’s energy needs will it cover?
A 4kW solar panel system is well-suited for an average three-bed house in the UK. But what does this mean in terms of covering your everyday energy needs?
It’s true that 9.3kWh of electricity can power a lot of items in your home. To put this in perspective:
- A fridge uses around 150W per hour
- A TV is around 100W
- Powering a microwave for an hour will use 750W – of course you only use a microwave for a few minutes so usage will be way less than 750W
You then have your more energy hungry appliances such as:
- A washing machine – using between 600W and 2000W per hour
- A tumble dryer at around 2500W per hour
- EV charger – between 2.3kW and 7kW of electricity per hour
- Air source heat pump – can use between 0.8 and 5kWh of electricity
The theory is true and adds up but there are a couple of important things to think about here.
Your energy production and consumption needs won’t always align perfectly. Your solar panels can only power these appliances when the sun is shining and they are generating electricity.
During summer months, it’s entirely possible to go off-grid for days or even weeks at a time, especially if you pair your system with a battery storage solution. Stored power can then be used, for example, to charge your EV at night or power the dishwasher in the evening. Read about the best battery storage systems here.
However, the same can’t be said for winter. Because of the mismatch between solar generation and consumption, it’s likely that you’ll still need to rely on the grid, especially during non-summer months. Despite that, you can significantly reduce your grid dependency with a 4kW solar system.
You also need to consider inverter size. The inverter is the key piece of kit that supplies usable electricity to your home from your solar array. As mentioned, a typical inverter in the UK is undersized compared to the maximum output of your solar panels.
This is good as it allows the inverter to operate more efficiently most of the time and it’s also cost-effective as larger inverters are more expensive. However, it does mean that the immediate power available for your appliances is capped at the inverter’s rating. So, for a 4kW solar system with a 3kW inverter, you’ll only be able to send 3kW to your home at any one time.
Cost of a 4kW solar panel system
Now onto costs. If you’re considering a 4kW solar panel system, you’ll want to know how much you’re going to pay and other costs involved.
In the UK, you can expect to pay between £5,000 and £8,000 for a 4kW solar panel system. This price should include the PV panels, inverter, brackets and installation costs. Total costs for solar panels haven’t really come down in recent years – in fact, they’ve gone up a little despite the current 0% VAT rate on them. This is largely because of installation costs and labour, which can add up to £1,000-£3,000.
There are a number of factors that can influence the final price, including:
- Panel quality – Higher efficiency panels often come with a higher price tag.
- Roof complexity – If your roof is difficult to access or you have a flat roof for example, installation costs can increase.
- Inverter type – Microinverters can add to the overall cost but may improve system performance.
- Additional features – Options like monitoring systems or battery storage will increase the initial investment.
When considering the cost, it’s important to view it as a long-term investment. The savings on your electricity bills, potential earnings from the Smart Export Guarantee (SEG) and the increase in your property value can all contribute to offsetting the initial expense over time.
It’s always a good idea to get multiple quotes from reputable installers. This will not only help you find the best price but also make sure you’re getting a high-quality system that will serve you well for many decades to come.
How long before you get a return on your investment for 4kW solar panels
With a 4kW system, you can expect to save between £300 and £700 a year on your electricity bills. The exact amount depends on your energy usage patterns and how well they align with your solar generation.
You can also earn money through your solar panels under the Smart Export Guarantee (SEG). This is where you get paid for any excess electricity you generate and export to the grid. Rates vary by energy supplier (with Octopus Energy currently providing the highest rates), but you could earn an additional £80 to £150 per year.
Given these savings and earnings, the typical payback period for a 4kW solar panel system in the UK is between 8 and 12 years. After this point, your system will be generating ‘free’ electricity for the remainder of its lifespan.
Solar panels typically last 25-30 years, with many continuing to perform well beyond this. Over a 25-year period, your total savings could amount to £7,500 to £21,000, depending on future energy prices and your system’s performance. It’s worth remembering that as energy prices rise, your savings will increase proportionally. Your solar panels essentially lock in a portion of your electricity costs, acting as a buffer and protecting you from future price hikes.
Whilst the financial benefits are significant, the environmental impact of reducing your carbon footprint is an equally important return on your investment. By choosing solar, you’re not just saving money, but also contributing to a more sustainable future.
Space requirements and installation
A 4kW system usually requires between 16-24m2 of roof space. The exact area depends on the size and efficiency of the panels you choose – higher efficiency panels need less space as they provide more power for their size.
Most types of roofs are suitable for solar panels, but the ideal roof is south-facing with a pitch of about 30-40 degrees. You can have solar panels installed on flat roofs, which require special housing brackets to get the angle right and to secure them in place. It’s possible to get ground mounted solar panels too.
The installation of a 4kW system usually takes 1-2 days from scaffolding to testing and commissioning.
Do you need planning permission for a 4kW solar system?
In most cases, you won’t need planning permission to install a 4kW solar panel system on your roof. Solar panels are generally considered ‘permitted development’, meaning they don’t require planning permission as long as they meet certain criteria.
However, there are some exceptions:
- If you live in a listed building
- If your property is in a conservation area
- If the panels will protrude more than 200mm from the roof slope
It’s always wise to check with your local planning authority before installation, especially if you’re unsure about your property’s status. This can save you potential headaches down the line.
Pros and cons of a 4kW solar panel system
| Pros | Cons |
| Significant energy savings | High initial cost |
| Reduced carbon footprint | Weather dependent |
| Long term financial returns | Not consistent energy generation across the year |
| Increased property value | Aesthetic concerns |
| Low maintenance | Potential for overproduction (without battery storage) |
| Scalable with additional panels | Long payback period |
Should I pair a 4kW solar system with battery storage
Pairing your 4kW solar panel system with battery storage can significantly enhance its benefits.
A battery allows you to store excess electricity generated during the day for use in the evening or on cloudy days. This not only increases your energy independence but reduces your costs. By using more of your own electricity rather than buying it at 20-30p per kWh, you’ll save more on energy bills.
For a 4kW system, a battery capacity of 5-6kWh is often suitable. This size allows you to store excess solar electricity all year round, maximising the use of your generated power. This capacity is just an estimate though and you should always consult an expert to get the best size for your individual household needs.
Battery storage also comes with an additional cost of course. They tend to range from £2,500 to £6,000 depending on capacity and features. You’ll need to weigh these costs against the potential increased savings they bring. But the figures should work out positively for you over the long term.
Whilst not essential, battery storage can significantly enhance the performance and benefits of your 4kW solar panel system, making it a worthwhile consideration for many homeowners.
Is a 4kW solar panel system right for you?
As we’ve explored throughout this guide, 4kW solar panel systems offer a great option for many UK homeowners looking to embrace renewable energy. They give a good balance of cost and output for many UK households. It can significantly reduce your electricity bills and carbon footprint without requiring an excessive amount of roof space.
Deciding whether this size is the one for you depends on the main factors discussed, such as household size, your energy consumption and budget.
If a 4kW system doesn’t sound right for whatever reason, there are alternatives to consider including:
- Smaller systems (2-3kW) – If you have a smaller household or lower energy needs, these might be more suitable and cost-effective.
- Larger systems (5-6kW) – For larger households or if you anticipate increased future energy needs, these systems can provide more power.
- Solar tiles – If aesthetics are a major concern, solar tiles integrate more seamlessly with your roof but are typically more expensive.
With the information provided in this guide, we hope you’re better equipped to make the right decision for you on whether a 4kW solar panel system could be the right fit for your home’s energy.
