How Many Solar Panels Do I Need?

When it comes to solar power, one of the first things you’re likely to ask is, “How many solar panels do I need to meet my electricity needs?” That answer can be reached by taking multiple steps, but we have broken down the process to bring accurate, tailored answers that apply to you.

1. Analyse Your Electricity Usage

Look at your electricity bills and find out how many kilowatt‑hours (kWh) of electricity per month or day you are using on average. Your rising bills are the main reason you’d consider getting solar panels.

In the UK, the average household consumes around 2,700 to 3,000 kWh per year, which is roughly 225 to 250 kWh per month.

In the US, an average 1,500‑sq‑ft house uses ~630 kWh/month, while an average 3,000‑sq‑ft house uses around 1,200 kWh/month.

Example: If you are using 900 kWh/month, that means you are using 30 kWh/day.

2. Identify Peak Sun Hours

The output of your solar system depends on the number of hours of full sunlight received, and this time of sun rays is referred to as the peak hour of sunshine. Most regions in the world receive 4-6 peak hours/day.

So, from our example above, if you require a 30 kWh/day and receive 5 hours of peak sunlight daily, your solar panel size should be a 6 kW solar array.

3. Adjust for System Inefficiencies

Even in a best-case scenario, solar power systems are not going to run at 100% efficiency. There are a number of factors that could affect your energy output, including inverter losses, wiring resistance, shading on the panels, dust and debris and even high temperatures. All of this will reduce the actual energy production of your system, which could be described as inefficiencies in the system.

Because of this, solar installers generally apply a derating factor to take into account this variability, and this can be applied as an expected multiplier for what you expect to actually get out of your solar installation. It’s generally a good approach to assume a 75%-80% efficiency rate when calculating how much solar you’ll need. This will vary depending on your specific situation, but as a good heuristic, if you take that 75%-80% efficiency, you’d want 125% of the expected energy usage you just created.

4. Choose Panel Wattage & Count

Solar panels typically range from 250 W to 400 W each. Here’s how it affects counts;

• Using 300 W panels: Divide 8000 W by 300 W/panel, and you have 27 panels.
• Using 400 W panels: Divide 8000 W by 400 W/panel, and you get 20 panels

5. Consider Roof Space & Orientation

Each solar energy panel occupies about 1.6–1.7 m². For instance, 20 panels require 34 square meters of roof space. This figure comes from multiplying the number of panels (20) by the space each panel occupies (about 1.7 square meters).

In addition to getting the actual figures on the space, you also have to make relevant accommodations to ensure full performance of the panels. These include ensuring:

1. Enough unobstructed area.
2. Optimal orientation (e.g., north‑facing in the Southern Hemisphere) and tilt.
3. Minimal shading for best performance.

6. Factor in Future Needs & Storage

When choosing and deciding the number of solar panels you need to invest in, don’t just consider your present needs, but also what you may incorporate or add to your space in the future.

For instance, you may have to size a slightly larger system to accommodate higher loads, if you’re planning to:

• Charge an EV,
• Add a heat pump or,
• Install battery storage.

Take Note: Simple Quick-Step Formula

As a general rule of thumb, keep these calculations in mind to help you decide the capacity and sizing needs of your solar panels.

1. Daily energy usage (kWh) ÷ Peak sun hours/day = base system size (kW).
2. Divide by efficiency factor (e.g., 0.75) = adjusted kW.
3. Convert to watts and divide by panel wattage = panel count.

Additional Considerations

Other parameters to consider when deciding on how many solar panels you need include;

• Panel efficiency: High-efficiency (monocrystalline) panels produce more per m² but cost more.
• Inverter sizing: A bit bigger than the array to work at its most efficient and live the longest .
• Local climate: The more sun, the fewer panels required.
• Numbers: On average, it costs about 4,500–7,000 sterling pounds for a 4 kW system in the UK. Payback is 8–14 years.

Investing in Solar Panels

If you researched the benefits of solar energy and you are going for it, estimating “how many solar panels do I need” involves assessing your energy usage, determining sunlight availability and adjusting for system inefficiencies. Further, you want to choose panel wattage and count them, confirm roof suitability and plan for future energy demands.

While you can use our online calculator for rough estimates, consulting a local installer is essential. They can assess your location, roof conditions and usage profiles to provide a customised system that meets your needs efficiently and cost‑effectively.

UK Solar Incentives: What You Should Know

If you’re installing solar panels in the UK, you could benefit from the Smart Export Guarantee (SEG), a government-backed scheme that allows households to earn money by exporting excess electricity back to the grid.

What is it?

The SEG requires licensed electricity suppliers to pay homeowners for any surplus solar electricity they export.

Who qualifies?

Most systems under 5 MW (including residential setups) that use certified equipment and are installed by a Microgeneration Certification Scheme (MCS)-registered installer.

Why it matters:

While the old Feed-in Tariff (FIT) scheme has ended, the SEG helps shorten payback times and increases the long-term value of your system.

Additionally, you may be eligible for zero VAT on solar panel installations in the UK (valid through March 2027), reducing upfront costs.

Ready to go solar? Start with your bills and sunlight data, then build from there. The payoff in savings and sustainability can be well worth it!

Common Questions

Do I Need to Reinforce My Roof for Solar Panels?

Not usually, but it depends on the condition of your roof.
Most modern roofs in good structural condition can support the additional weight of a solar panel system without reinforcement. A typical residential solar panel adds about 10–20 kg per square metre, which is well within the load capacity of standard roofing in the UK.

However, you may need reinforcement if:

• Your roof is over 20–25 years old
• You notice sagging, leaks, or visible structural issues
• Your roof is made from less common materials (e.g., slate, wood shakes)

Before any installation, a structural survey or roof inspection by a qualified installer will identify if reinforcement is necessary.

What type of roofing works best for solar panels?

Solar panels can be mounted on most roof types, but the easiest and most cost-effective installations are usually on:

• Pitched tile or composite shingle roofs
• Standing seam metal roofs (ideal for clamps)

More complex materials like slate or clay tiles may require specialised mounting hardware and careful handling to avoid damage.

How Do Solar Panels Work?

Solar panels convert sunlight into electricity. They use photovoltaic (PV) cells made from semiconducting materials (like silicon) to absorb solar energy and release electrons, creating a flow of electricity.

The electricity generated is direct current (DC), which is then converted into alternating current (AC) by an inverter. AC power is what your home appliances and the grid use.

Are solar panels environmentally friendly?

Yes. Solar energy is renewable, reduces reliance on fossil fuels, and cuts carbon emissions significantly. A typical UK home solar system can offset 1–1.6 tonnes of CO₂ per year, equivalent to planting dozens of trees annually.