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What size solar panels do I need – Your questions answered

By becoming a person who has a solar panel system fitted you’re not only doing your bit to help the planet by choosing sustainable energy, you’re also going to save money on your household bills and improve your energy efficiency. 

Whether you’ve already taken steps to start your solar journey, or you’re at a stage where you want to find out everything you can about solar panel systems before you commit, you’ve come to the right place. 

A common query we receive is ‘What size solar panels do I need?’ Our handy guide aims to clear up any uncertainties you have ahead of installing solar panels, and to make sure you get the right system for your needs.

There are a few factors you’ll need to consider ahead of purchasing a solar panel system to ensure it meets the requirements you need. Read on to find what size solar system you need.

Calculating your energy needs

The size of the solar panel system you will require is dependent on some key factors, and the aim is to balance the power going into the solar panel with the power going out over a period of time. 

It’s important to try and estimate the amount of power you need your solar panel system to generate before determining how many solar panels to have fitted. There are three elements to a solar panel system to take into account:

Power generation – the solar panel

Power storage – the solar battery

Power use – the energy you need to run your household from solar energy

To calculate power generation and how many solar panels you need, you can refer back to your past utility bills, and apply a simple calculation. Multiply your household’s hourly energy requirement by the peak sunlight hours for your area and then divide this by the solar panel’s wattage. 

To find a range, use a low-wattage (150W) example and a high wattage example (370w). Note that some other factors will need to be taken into account such as how much sunlight your panels are exposed to, the size of your roof and whether you have battery storage.

Finding your average use – Look for Kilowatt Hours (kWh) used, then make sure to note the time period the bill represents, normally 30 days. If your bill doesn’t show kilowatt hours, look at your meter readings and subtract the previous from your most recent. 

Using your energy bills to determine your daily use will then help to find how much energy you need your solar panels to generate daily. 

As an example, if your monthly energy consumption is 124kWh in January, then you will use 4kWh daily. For the solar system to be effective for your needs, it should generate an average of 4kWh each day. This figure can also be referred to as the expected daily solar system power output. 

The average daily energy usage is your target daily average for you to calculate your solar needs. By using this calculation it will generate the number of kilowatt-hours you need your solar system to produce if you want to cover 100 percent of your energy needs.

Finding the required solar system size

Once you have determined your energy usage needs, you will be much better placed to calculate the size of your solar system. Factoring in your roof space and the amount of sun hours in your area are also important measures when deciding what size solar panels you require.

Solar panels generate different amounts of energy depending on their wattage size and rating. A 250 watt solar panel will generate up to 250 watts per sun hour.  

The capacity of your roof will also impact the amount of individual solar panels you can install, and subsequently how much energy you can generate. Different solar panels also have different dimensions, depending on the installation you choose. 

If you are planning to install 16 250W solar panels, for example, you would require a roof surface area of 25.6m². 

Calculating sunlight hours

Solar panel systems aren’t designed to run at full efficiency at all times, which is why it may be useful to invest in a solar panel battery, however, this does mean you should cushion for 25% when calculating how much energy you will use on a daily basis.

Daylight hours are a very minor factor when finding out what size solar panels you need, as this varies slightly depending on your location within the UK, and the time of year. 

This doesn’t mean your energy production will be lower if you live somewhere with less daylight hours, but you may need to add more solar panels in order to generate the amount of energy you need to power your home.

To roughly estimate the size of solar panels you need you can divide your daily kWh usage by the number of peak daylight hours in a day. This will leave you with a rough figure of the amount of energy you need to produce in kilowatts to fuel your home.

What size charge controller do I need?

As well as determining the size and amount of solar panels you require, it is also important to factor in the other aspects of a solar system that are needed to ensure it is running effectively. 

A charge controller manages the power going into the battery bank from the solar array. It ensures that the system and batteries in the solar panel don’t get overcharged during the day when they are being used, and the power doesn’t run back into the solar panels overnight and drain the batteries. 

Sizing charge controllers is fairly straightforward. Charge controllers are sized depending on your solar array’s current and the solar system’s voltage. By rule of thumb, you want to make sure your charge controller is large enough to handle the amount of power that is produced by your solar panels. 

Typically, charge controllers are sized at 12, 24 and 48 volts. Amperage ratings can be between one and 60 amps and voltage ratings from six to 60 volts. 

So, as an example, if your solar system’s volts were 10 and your amps were 12, you would need a charge controller that had at least 12 amps. However, you’ll need to add an additional 25%, bringing the minimum amps this charger controller must have to 15 amps. 

What size inverter do I need for solar panels?

The function of a solar inverter is to ‘invert’ the direct current (DC) output into an alternating current (AC). This means the energy from your solar panels can be used to operate the electrical devices in your home. 

Your inverter will roughly need to be the same size as your solar panel system, for a 6 kilowatt solar panel system, you would need a 6kW inverter

Choosing the right sized inverter will play an important role in overall electricity production for your solar panel system. 

Just like solar panels, the size of an inverter can be rated in kilowatts (kWh) and the size will be determined by your electricity usage and the size of your solar panel system. The inverter needs to have the capacity to handle all the power the solar panels produce. If you are installing a 5 kilowatt system, the proposed inverter will need to be around 5,000kWh, give or take a small percentage. 

The key factor is that the size of your inverter should be able to handle the peak wattage that your household appliances require when all running at the same time. 

What size solar panel system do I need?

You can expect a fitted solar panel system to produce between 9 and 11kWh per square feet each year. This means if you have a 1kw system covering 86 square feet you can use around 850kWh of electricity per year.

If you’re ready to start your journey to a more sustainable way of life or have further questions about what size solar panels you need, get in touch with our team of solar experts today.