How many solar panels do I need?

           Determining the number of solar panels needed for your home requires considering several factors. These include the size of your house, average energy requirements, annual electricity usage, the amount of sunlight in your area, and available roof space. 

By understanding these factors, you can estimate the appropriate solar array size, maximise the potential of solar energy for your home, and optimise cost savings.

What to consider to find out how many solar panels you need

More UK citizens are considering solar as an alternative power mode, especially in light of Europe's energy crisis. To help you make an informed decision, let’s look at all the factors that play into determining the right solar panel system for you:

• The size of your house

      Larger homes typically require more energy to power all the appliances, electronics, and lighting. However, a bigger house also usually translates to a larger area of roof space available for solar panel installation. If you have a spacious roof, you may be able to accommodate more solar panels, which can generate a higher amount of electricity to meet your energy needs.

• Your average energy requirements

       
       Even living in similar homes and environmental conditions, different households can have vastly different usage patterns. For example, you may have a much higher bill if you often work from home, or have more family members. Appliances, such as an air conditioner, electric oven, electric stove, electric water heater, clothes dryer, or swimming pool pump can significantly increase your usage. Not withstanding the fact that every appliance has its own level of efficiency.

That being said, the average UK home consumes roughly 3,600kWh of electricity per year.

If you have energy-efficient appliances, LED lighting, and good insulation, your energy requirements may also be lower compared to a home with older, less efficient appliances. By assessing your average energy requirements, you can estimate the capacity of the solar panel system required to cover your electricity needs.

• Your annual electricity usage
  
  
  

      Once again, only you can determine your true energy needs. Start by examining your monthly electricity bills to gauge your typical energy consumption and take note of the kilowatt-hours (kWh) used each month. 

You should note the total number of “Kilowatt Hours (or kWh) Used” somewhere in your bill. For accurate calculations, also note the exact billing cycle (monthly, quarterly, semi-annually). To find your daily average, divide the total kWh by the number of days. Further divide it by 24 to find your hourly usage in kW.

It is especially important to plan your energy production for the medium to long term so that you can ensure uninterrupted supply throughout the year. Keep in mind that your usage may also vary greatly from season to season. Most households use less energy in Spring and Autumn when the weather is mild.

• The amount of sunlight in your area
  
  

       The amount of sunlight in your area plays a significant role in calculating how many solar panels you'll need. Regions with abundant sunshine can generate more solar energy, allowing for greater electricity production. 

For example, the UK receives roughly 500 to 1,100kWh/m² of direct normal irradiation (DNI) per year, depending on the location. The DNI of an area is the the amount of solar radiation received per unit area.

Areas with less sunlight or more cloudy days may require additional solar panels to compensate for lower energy generation. It's essential to consider the local climate and solar irradiance levels in your region when estimating the number of solar panels needed. However, even factors like the angle and direction of your roof impact the maximum sunlight your panels can absorb.

How big is a solar panel?

       The physical size of a solar panel can vary depending on the manufacturer and the specific model. Most standard solar panels used for residential installations have dimensions of approximately 2 metres by 1 centimetres, with a depth of around 4 centimetres. These dimensions are known as the "form factor" and are standardised for compatibility with mounting systems. 

The surface area of a typical solar panel is around 2 square meters or more. However, it's worth noting that the wattage and power output of a solar panel isn’t always directly related to its physical size. Higher wattage panels may have a slightly larger form factor but offer greater energy production potential. Today, you can get residential panels as large as 3.1 square meters, but these are still rare and often impractical.

How heavy is a solar panel?

      The weight of a solar panel can vary depending on the size, type, and manufacturer. On average, a standard residential solar panel typically weighs between 20 to 25 kilograms (40 to 50 pounds). This weight range applies to traditional crystalline silicon solar panels, which are the most commonly used type. 

Some newer panel technologies, such as thin-film solar panels, can be significantly lighter. Thin-film panels can weigh as little as 3 to 5 kilograms (6.6 to 11 pounds). However, these panels aren’t generally available commercially.

When considering solar panel installations, it's essential to factor in the weight to ensure proper structural support and safe mounting on the roof or other mounting surfaces.

The output efficiency of solar panels

      The output efficiency of solar panels refers to their ability to convert sunlight into electricity. It’s an essential factor to consider when determining the energy production potential of a solar panel system. 

Efficiency is measured as a percentage and represents the ratio of usable electricity output to the amount of sunlight received. Higher efficiency panels are more effective at converting sunlight into electricity and can generate more power within the same surface area compared to lower efficiency panels. 

Most solar panels on the market today have an efficiency range of 15% to 22%, with top performers at just over 23%.

The type of solar cell technology used, the quality of materials, and manufacturing processes all influence the efficiency of a solar panel. Monocrystalline solar panels typically have higher efficiency levels, reaching up to 22%, while polycrystalline panels tend to have slightly lower efficiency, around 15% to 17%. Thin-film solar panels have lowest overall efficiency, typically ranging from 10% to 12%. That’s why crystalline panels account for over 90% of the solar panel market, with monocrystalline accounting for the vast majority.

Choosing higher efficiency panels can be advantageous when you have limited roof space or specific aesthetic requirements. However, it's important to note that higher efficiency panels often cost more money. Finding the optimal solar panel system for your energy needs often involves a delicate balance between output efficiency, cost, and roof space.

How much roof space do you have?

       The size and orientation of your roof might just be the most important factor in determining the maximum capacity of your solar panel system. To assess your available roof space, you'll need to consider factors such as obstructions (chimneys, vents, skylights), shading from nearby structures or trees, and the overall shape and dimensions of your roof. 

Typically, solar panels require about 100 to 400 square feet of roof space per kilowatt (kW) of installed capacity. By evaluating your roof's dimensions and available space, you can determine the maximum number of solar panels your roof can accommodate and make informed decisions regarding system size and energy production potential. 

The optimal configuration may require a system that uses differently-sized panels arranged in somewhat complex patterns. For example, a gable or hip roof may require you to install panels in unique configurations on all four major surfaces to capture sunlight throughout the day.

How many solar panels are needed to power a typical house?

       Although it depends on many other factors (which we’ll discuss below), we can estimate the number of solar panels needed for different home sizes. In the UK, the average consumption is only 3,600 kWh per year, thanks to the widespread use of conventional gas. 

That means only around six panels are needed for the average home.

      To show you how this can change, let’s consider a 450W panel, like these 430W to 450W Commercial Series A Panels by SunPower.  With an average efficiency of 22.2% and 5 daily sunlight hours in the UK, each panel will generate an average of roughly 0.56 kWh per day or 205 kWh per year. That means you’ll need roughly 18 panels to power a typical UK household.

However, to illustrate how much energy consumption can vary around the world, according to the Energy Information Administration, the average US household uses 10,632 kilowatt hours (kWh) on average per year.

How do I calculate the right solar array size?

      Calculating the right solar array size for your home involves considering all the factors we’ve discussed above. To determine the appropriate size, follow these steps:

1.  Assess your energy consumption: Start by analysing your past electricity bills to understand your average monthly and annual energy consumption in kilowatt-hours (kWh). This will serve as a baseline for estimating the minimum solar array size required. As we saw above, the typical UK household requires roughly six panels.
   
   
2. Solar production per kilowatt installed: Evaluate the amount of sunlight your location receives throughout the year. DNI for the UK ranges from around 500 to 1,100kWh/m². That translates to roughly between 800 - 1,200kWh/kWP.
   
   
3. Factor in system efficiency and losses: Take into account the efficiency of solar panels and the losses due to shading, dust, and system inefficiencies. These factors can impact the actual energy output, so it's important to include a buffer when calculating the solar array size.
   
   
4. Calculate system size: Divide your annual energy consumption by the average annual solar production per kilowatt installed in your area. This figure, typically expressed in kWh/kWp, provides an estimate of the required system size in kilowatts peak (kWp).
   
   
   

Can I power my house with only solar power?

      Many individuals understandably have the misconception that solar panels won’t work in the UK due its cloudy climate. However, that isn’t the case. In fact, household solar panel adoption in the UK is soaring. The UK still receives 60% of the sunlight source that’s found at the equator. Solar panels also work under cloudy conditions, although they may lose between 20% to 90% of their production capacity, depending on how cloudy it is.

So, while the UK might not be the ideal climate for solar panel systems, it’s still feasible. This is particularly true in the South of the country, where sunny weather is more common. However, it does mean that UK residents need to plan their solar installations carefully to maximise production and combine it with a charging battery storage system to capture excess energy during peak times.

Following the above calculations, you’d need roughly 18 450W panels to replace the average UK home’s energy intake. The average UK home (terraced house) is roughly 1087 sq. ft. in size. We’ll be conservative and estimate an average of 400 sq. ft. in available roof space. 

Considering a typical solar panel is roughly 21 sq. ft. in size, you’ll still be able to fit 19 panels. That’s just enough to accommodate the 18 panels needed, even if you consider the drop-off in energy production due to the UK’s climate.

Summary

      When calculating the number of solar panels required, factors such as house size, energy consumption, sunlight availability, and roof space must be taken into account. By considering these factors, homeowners can make informed decisions about their solar panel investment and achieve a sustainable and efficient renewable energy solution, reducing their carbon footprint and reliance on traditional energy supply systems.