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Janet Richardson

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Sep 29, 2024

Read Time : 9 Minutes

A Guide to 4kW Solar Panel Systems for the UK

A 4kW solar PV system is the UK’s most common solar array. While some domestic and commercial solar systems come in larger sizes, a 4kW PV solar system can handle most of the energy needs of the average British home. Now, in terms of components, a 4 kW array will have a set of solar panels, a network of cables, and an inverter. The number in the name refers to number of electrical units the system can produce. Kilo means thousand and Watt is the name of a measurement of electricity. In the abbreviation kW we capitalise the letter W is because the term Watt is the surname of James Watt, who gave the unit its name.

The PV part of the abbreviation is short for photovoltaic and means 'energy created by light'. In the UK there are two basic gadgets that carry the name solar panels, PV or photovoltaic and solar thermal. PV cells generate electricity from the sun’s radiation. By contrast, Solar thermal panels, harness the power of the sun to heat water. In this article we’ll ignore solar thermal panels and focus of PV cells instead.

What can a 4kW Solar Panel System do?

As mentioned, a 4kW solar PV system is the average size for a solar array in the UK. Unlike smaller 2kW and 3kW systems, a 4kW solar PV solar system can produce enough electricity to cope with the power needs of a normal household in the summer but will likely struggle in the winter when the days are shorter and darker. That said, systems located in areas with less-than-optimal conditions and power-hungry households might need help from the grid even in summer.

In a perfect world a 4kW solar PV system would suit a two or three bedroom, eco-centric home or a smaller home with bigger electricity needs.

A 4kW Solar PV system could also power a small office, or another commercial property with lower energy needs. The system could also manage most of the strain of a bigger household depending on the power needs. It’s possible that while a 4kW PV array can cope with most of such a load, there’ll be time when the system needs to lean on the power grid.

Potential uses for a 4kW PV Solar System:

  • Two-to-three-bedroom home
  • Larger home with energy-efficient appliances
  • Light industrial unit or a small workshop
  • Small commercial premises like a retail shop, office, or storage facility
  • Holiday home, lodge or static caravan
  • Power source for an outdoor pool
  • Small off-grid holding

What appliances can a 4kW PV Solar System power?

Before deciding on the size of your array it’s important to work out the actual amount of power you need. Getting an electric meter or checking your energy bills is the simplest method to find out that information. You can use any itemised bill to find out how many units it takes to keep the power on each month. Don’t forget though, you’ll use more power over the winter thanks to its longer, colder nights.

A 4kW solar PV system can usually cover the demand of LED lighting systems, eco-friendly washing machines, TV's, efficient refrigerators and desktop computers. They may struggle with the demand of tumble dryers, dishwashers, electric heating systems and electric vehicles. As with all solar panels systems, it can be worth changing your current habits and using electricity appliances during the day when your solar panels are generating. 

Even if the solar PV system can't cover all the demand of thirsty appliances, they'll still help subsidise the electrical usage. 

Is there a way to make a 4kW Solar PV System more Efficient?

Solar systems are often modular and it’s uncommon to find two systems that have the exact same components. There are rafts of potential upgrades and gizmos that can affect the output and efficiency of an array.  However, there are also steps to take that can help you make the most of whatever system you have.  Let’s talk about upgrades first:

Upgrading your system

Adding devices designed to help your array collect the maximum potential power is one way to amp your optimal power.

Solar storage:
These devices are special batteries that collect any unused power your array produces and stores it away until it’s needed.

Micro investors:
These upgrades stop solar cells losing power to shade by opening alternative pathways for the collected energy to travel through.

Automatic solar trackers:
Solar power requires direct sunlight for peak efficiency; to make the most of this sunlight solar trackers tilt your panels to ensure they get the most sunlight.

Shielded cables:
Like everything else on the market, there are good cables, average cables and ugly cables. Having better cables won’t help you generate more power from your 4kW solar PV system, but it might stop you losing it through leakage. Investing in high-end wiring is one thing you can do to lessen the amount of energy that leaks away before it reaches your main inverter.

Now let’s discuss lifestyle changes

Not all changes you make to your energy supply have to be financial. The climate crisis is another reason often cited as the prime reason for moving over to solar. If you care about the state of the planet then there are plenty of steps you can take to make the most of your system. Little steps like swapping out all your bulbs for LEDs add up, but if you’re committed to a green future and prepared to make a few sacrifices here are a few ideas to help.

Use less heating:
There are lots of ways to achieve this goal without freezing. You can improve the insulation in your home, wear warmer clothes, and make sure you don’t leave windows and doors open.

Switch from baths to showers:
Everyone knows that baths consume more energy than showers, so if you haven’t changed your routine yet, now is the time to make the move.

Conserve hot water:
Electric kettles are terribly inefficient devices and not the most effective way to boil water. So, if you like a cup of tea or coffee, why not invest in a thermos flash and keep it near the kettle?

You can also make the most of the power you have
We’ll talk about eco-appliances in a moment, but if you can’t afford to invest in new white goods you can always get more from your old gadgets. Fridges, for example, are more efficient when they are full. It may seem daft to fill it up with Tupperware containers full of water, but you’ll get the last laugh when see how much power it saves you. Also, anything that relies on a fan or a vent will work better if they are clean and dust free. Taking the time to clear debris and detritus from the back of anything that makes a whirring noise is another solid investment of your time.

Efficient appliances:
Concern for the environment is a global issue. Today vast majority of today’s new technology comes with efficiency at its heart. Every year, new appliances become greener, leaner, and ever more efficient. Often the line between how much power we can generate, and use, is thin. If this is true in your case, then the simple act of updating your old appliances could be all it takes to make solar dream a reality.

Getting the best panels and system:

There are many solar panels on the market. Efficiency is the best benchmark and the arc is wide. Expensive monocrystalline panels promise rates of up to 25% while cheaper, thin film cells struggle to break double figures. With a 4kW PV solar system, chances are you’ll want the more efficient panels, but if you have lots of space then there’s potential savings to me made.

How much should you Budget for a 4kW PV Solar Panel System?

As a caveat, let’s clarify that there are many variables. Not all 4 kW PV solar systems are the same. You might find a bare-bones DIY kit with zero bells and whistles for around £3,000. Unless you know what you’re doing though, putting the system in yourself could end up costing more than a professional installation. Speaking of which, the cheapest system on the market will set you back around £5,000.

For a higher-end array expect to add another £2,000 to that number. Of course, there’s no real ceiling and prices can vary considerably. As with other solar systems 4kW arrays are modular, so if you do feel you need more power and you have the space then you can add more panels later, although this may necessitate a change of inverter.

How much Room does a 4kW PV Solar System need?

Depending on the styles of solar system and your panels the answer can vary. As a rough guide though, a standard 4kW solar panel system is comprised of 8-12 solar panels. This equates to approx.16-25m² of roof space. This example assumes you’re using more efficient monocrystalline panel. If you opt for cheaper less-efficient panels you’ll need more roof real estate.

You’ll also need space inside your home for the brains and gizmos that turn the power from the panels into electricity. Today’s inverters suitable for a 4kW PV solar system will fit inside the average airing cupboard. If you are opting for a 4kW array, then adding solar storage is a good plan. These fancy batteries are often bigger than inverters, so it’s wise to factor in at least double the internal space. We'll get to batteries later.

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What Components Comprise a 4kW PV Solar System?

A basic solar system features three or four distinct parts:

Solar array (solar PV panels)
In a solar system the panels collect the sun’s radiation. During the installation, engineers fit these glass-fronted panels to the roof on special racks. At present, there are three different variations on the market with more on the way:

  • Monocrystalline
  • Polycrystalline
  • Thin film

Let's measure the difference between these panels through efficiency and cost:
With an average of 18-24.5% efficiency monocrystalline panels produce the most power per square metre. These panels also command the highest price. You can identify them by their opaque almost black glassy appearance.

At 16-18% efficiency Polycrystalline cells are the second best at generating power. Their price point comes in a touch below their more efficient cousins. Polycrystalline cells have a blueish hue on their glass frontage.

Bringing up the rear with a mere 7-9% efficiency are thin film cells. Unlike their rigid ancestors, thin film cells, as their name suggests, are not made from glass and are also flexible. Although less efficient than the others, their low price makes these cells attractive to anyone with enough space to compensate for their reduced individual efficiency.

Inverter: the brains of the outfit
This gadget converts the power collected by the solar panels into electricity that's usable within your home or business. After it reached the inverter, your electricity can be used to power your home, sold on to the national gird, or stored in batteries.

Cabling
A solar array is an electrical circuit. To work it needs wiring. These cables run from the panels on the roof to the inverter, and into your consumer unit, which is connected to the national grid. The wiring will also connect to any solar storage facilities the system has.  

What is the Payback Period for a 4kW Solar PV System in the UK?

If you spend £6,000 on your new solar system, it’s possible to recoup your outlay in around eight years, but it can be significantly longer. There are two main ways your system can help repay your costs.

  • Savings on current energy bills.
  • Profit from selling unused units back the grid.

Now, it’s important to remember that how fast you see a return on your investment depends on many factors. You need to account for how much power your system can generate, which in turn is affected by events like shifts in the local weather. The time it takes to get your ROI back can also depend on the price you get from selling unused units. These prices fluctuate depending on which supplier you sign up with, so it’s a good idea to shop around before signing anything.

Your payback period will also be significantly effected by trends in your energy usage. The Smart Export Guarantee (SEG) is a tariff paid to you by your energy provider for each unit of electricity that you send to them. Any electricity generated by your system, that you don't use at the point of generation or send to a battery, will be sent back to the grid for the SEG. The SEG tariff ranges from 1.5 pp kWh (pence per kilo Watt hour) to 20+ pp kWh, but is nearly always less than you are paying per kWh for electricity from the grid. Due to this, if you are at home during the day and can use more of the electricity generated by your system, your payback period will be shorter than if you're out of the house during the day and sending more back to the grid. 

The suitability of your roof is also an important aspect to consider here. An optimal roof for solar panels is south facing, with a 35° degree pitch and no shade. With an east/west-facing roof, you can expect a reduction of approx. 15% in energy output compared to a south-facing system. As you can imagine, shade on the panels from trees, chimneys or nearby buildings will also negatively effect the output of the system, resulting in a longer payback period. Your installation company should be able to work out an approximate payback period based on roof specifics. 

Your geographical location in the UK will also effect the payback period. Southern regions generally receive more sunlight, increasing annual output, while northern areas may see slightly lower returns.

Geographical solar radiation

Other factors to consider:

  • Once you have recouped your ROI any excess cash generated is profit!
  • Your energy bills will be significantly reduced.
  • A solar array will shield you from growing energy costs.
  • Your initial investment on a 4kW system could be easier and quicker to recoup than a smaller system even if your outlay is higher.
  • You can upgrade your system whenever you need.
  • A 4kW system could reduce your carbon footprint by generating renewable energy, helping to avoid about 1.5 to 2 tonnes of COâ‚‚ emissions annually

Should you add a Battery to your 4kW Solar Panel System?

The typical price range for a solar battery in the UK is between £2,500 and £5,000. The price varies based on the capacity of the battery (how much electricity it can store) and the brand or type of battery. Larger batteries (9-15 kWh) cost more but can store more energy, while smaller batteries (3-7 kWh) are cheaper but store less. Lithium-ion batteries are the most common and efficient. Premium brands like the Tesla Powerwall range are more expensive but come with advanced features and longer warranties.

Adding a battery helps to increase the amount of electricity you consume yourself. They hold the electricity you can't use during the peak generation times for use on demand in the evenings or on cloudy days. Generally speaking, for a typical home, self-consumption of solar electricity is around 30-40% without a battery. With a battery, this can rise to 60-80%, depending on trends in your energy usage. 

A 4kW system might save you £600-1,000 per year on electricity without a battery. With a battery, that figure could rise to £960-1,360 per year, potentially adding 1,200 kWh/s of electricity that you consume yourself. This additional saving of £360-£400 per year can help reduce the payback period but this will depend on your SEG tariff and energy usage trends.

If you can only get a low tariff and you're out of the house a lot during the day, then a battery can shorten your payback period. Make sure to discuss this with your chosen installation company because the opposite is also true. A battery can be a bit redundant if you're in the house during the day or you get offered a high SEG tariff. For the record, the average SEG rate currently stands at 13p per kWh. 

It's also worth mentioning that a battery can offer a high degree of energy independence, which is especially important if you're in an area with frequent power cuts. Solar PV systems usually turn off during power cuts, to avoid sending electricity back down the wires where they be being worked on. That said, if you arrange it with your installation company, the system can be set up to work in times of power outage. 

Is a 4kW Solar PV System Worth it in the UK in 2024?

A 4kW system is generally worth it in the UK if:

  • You have an east-to-west through south facing roof. 
  • You can afford the upfront costs or finance it with a low-interest loan.
  • You use a significant portion of the generated electricity during the day or can take advantage of the SEG.
  • You want to reduce your carbon footprint and have long-term energy savings.

In Summary 

Energy Generation
A typical 4kW system in the UK can generate around 3,500 to 4,500 kWh of electricity per year, depending on your location (southern areas generate more due to higher sunlight hours). The average UK household consumes approximately 3,400 kWh annually, so a 4kW system could cover a significant portion or even all of your electricity needs.

Cost of Installation
The cost of a 4kW solar PV system in the UK typically ranges from £5,000 to £7,000, depending on equipment quality, installer, and roof complexities. The payback period ranges from 8-15 years. This varies considerably depending on electricity savings and available incentives like the SEG. 

Energy Savings
Based on current UK electricity prices (average is currently 24.5p), a 4kW system could save you up to £600 - £1,000 per year on your electricity bill, depending on how much solar electricity you use and how much you export back to the grid.

Incentives
Smart Export Guarantee (SEG): You can sell excess electricity back to the grid through the SEG. The SEG rates usually vary between 5p to 15p per kWh depending on your supplier.

Return on Investment (ROI) or Payback Period
A 4kW solar PV system can generate a solid return on investment, especially as energy prices rise. Over 20-25 years (the typical lifespan of a system), you could save £15,000 or more in electricity costs, making it a enticing long-term investment. 

 

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