Solar panels can be installed anywhere — from homes to schools, office spaces, hospitals, and beyond. So, before asking the number of solar panels required, it is essential to understand your goals.

Goals may vary. Maybe you’re looking to switch to renewable energy sources to reduce environmental impact. Saving money on electricity can be another such goal. In institutions like hospitals and schools, electricity usage is high. They set up solar panels to minimize direct electricity use.

A good start would be fixing your goal and then pondering concerns like the number of solar panels, power generation, set-up costs, and beyond.

The article is a compilation of multiple factors you must understand before installing solar panels. Let’s dive right into it.

Solar Panels for Houses

A typical house requires between 20 to 25 solar panels to power a home’s hundred per cent electricity needs.

However, the number of solar panels also depends on factors like.

  • Weather
  • Geographical location
  • Your daily energy consumptions
  • Panel efficiency

The factors mentioned above will also determine the price you’ll pay for solar energy.

How to Calculate the Number of Solar Panels You Need

It is essential to know how to calculate the number of solar panels you need, whether you want it for a house or a whole building.

There are three critical factors around which the calculation of the number of solar panels revolves.

  1. Panel Wattage
  2. Solar Panel Efficiency
  3. Annual Energy Usage
  4. Production Ratios

Let’s get into the parameters one by one.

Solar Panel Wattage

Roof Solar PanelsSolar panel wattage is commonly called the ‘power rating’ of a solar panel. It is the amount of power a solar panel can generate if the temperature and sunlight are ideal.

Typically, power ratings to solar panels vary between 250 to 400 watts. The power rating of a solar panel is inversely proportional to the number of panels required. In other words, the greater the power rating, the lesser is the number of solar panels needed to achieve desired energy output. Let’s consider the average wattage of 350 kW

Solar Panel Efficiency

The solar panel efficiency measures a solar panel’s capability of converting direct sunlight into solar energy, considering ideal sunlight and temperature conditions. If a solar panel has an efficiency of 15%, it implies 15% of sun energy successfully transitions into usable energy.

The number of solar panels required follows the same relationship to efficiency as the power wattage of a solar panel. In other words, if two panels with different efficiencies are placed under direct sunlight, the solar panel with higher efficiency will generate more power.

Most solar panels available in the market have efficiency ratings between 15% to 20%. Many manufacturers produce solar panels with an efficiency rating of 22%, but the maximum efficiency recorded is 23%.

Annual Electricity Usage

The annual electricity usage is the measure of electricity used over twelve months. It is measured in kilowatt-hours (kWh). The measurement of yearly electricity usage depends on the appliances present in your home and the frequency.

Everything from refrigerators, geysers, television, air-conditioners, lights, electric fans, and beyond are the appliances that consume energy. The UK Power declared that the average high consumption scale for electricity is between 4,300 kWh to 7,100 kWh annually.

To create an ideal scenario, let’s take the average annual consumption as 10,000 kWh. To get a precise calculation of your yearly electricity consumption, view your last year’s electricity bill.

Production Ratio

The production ratio is measured by a solar panel’s system. It is the total energy output of a system in kilowatt-hour to the actual system size. The ratio number depends on the sunlight your solar panel system receives.

The geographical location and the sunlight received are interdependent. The production ratio is also directly affected by factors like roof orientation, shade, roof tilt, and positioning of your house. The type of equipment the installer uses also affects the ratio.

The Number of Solar Panels You Need: The Math

The calculation of the number of solar panels depends on the three key factors – production ratio, annual energy use, and panel wattage.

The formula is:

(System Size ÷ Production Ratio) ÷ Panel Wattage = Number of Solar Panels Required

Using the average numbers in the formula,

10,000/1.3 or 1.6/350 = 21.9

21.9 falls in the range of 20 to 25 solar panels. For a household, 20 to 25 will properly support yearly electricity needs. In the same way, if you want to calculate the number of solar panels for an institution, calculate the annual electricity bill of an institution.

In conclusion, an 8 kWh solar panel system will provide adequate electricity for the whole year.

Solar Power for Different System Sizes

In our previous calculations, the 8 kWh solar panel system came out to be the ideal condition. However, production ratios differ. Production ratios depend directly on the amount of sunlight a place receives. It flickers between 1.3 to 1.6 depending on the city you live in, in the UK.

The table below displays various solar panel systems, and the production ratio used is 1.6. Since we live in times of high consumption, 1.6 is ideal. 350 watt is taken as the perfect panel wattage in the table.

System SizeNumber of Panels NeededEstimated Annual Production
4 kW136,400 kWh
6 kW199,600 kWh
8 kW2512,800 kWh
10 kW3216,000 kWh
12 kW3819,200 kWh
14 kW4422,400 kWh

Remember, the panel efficiency determines the space solar panels will take up on the roof. The table below will show you the space a solar panel system will take.

The annual electricity usage is the most fluctuating parameter out of all. Many households have more oversized consumer products. A central air-conditioning system or a heated swimming pool increases annual energy usage significantly.

System SizeLow Power Panels (Sq. Feet)Average Power Panels (Sq. Feet)High Power Panels (Sq. Feet)
4 kW240203179
6 kW367305269
8 kW490406358
10 kW612508448
12 kW734610538
14 kW857711627

It is essential to calculate the energy consumption of individual products to estimate the correct solar panel size. Also, a specifically designed roof will alter the size of the system. Considering an average household in the UK, the measure used is 65 by 39 inches or 5.4 feet by 3.25 feet.

Solar Panels Required for Common Appliances

After knowing the impacts of solar panel requirements based on different appliances, one thing is evident that add-on appliances will alter the numbers of solar panels you install.

Solar Panels on RoofAn intelligent way to make solar energy more efficient is by pairing an electric vehicle with solar panels. Combining solar panels with electric cars helps to reduce the carbon footprint, although it should be planned and consulted.

If you’re finalizing the installation of a solar panel system, it must be calculated and accurate. Everything from add-on appliances, annual electricity consumption caused by general devices must be considered.

Of course, it is possible to have a solar panel system beforehand and then get more panels installed to meet the electricity needs, but that is a waste of time and money. Start questioning how many solar panels you would need for every appliance at your home. That will give you a reasonable estimate of the number of solar panels you need overall.

See the table below to know the number of solar panels required for different electric appliances.

ProductAverage Annual kWh RequiredEstimated No. of Solar Panels Needed
Air Conditioning Unit6002
Central Air Conditioning215<1
Electric Vehicle1,0003
Heated Swimming Pool3,00010
Hot Tub (Outdoor)3,30011

How Do Solar Panels Work?

Solar panels do not have an efficiency of more than 15% to 20%. Very rarely do they touch 23%. This means, only 15% to 20% of sunlight received overall gets converted into usable energy.

A common question arises: how do solar panels work? Let’s understand the basic steps of how solar panels generate power.

  • The sunlight comes in contact with the panel, which creates an electric field.
  • The generated electricity goes to the edge of the solar panel and gets absorbed by the conductive wire.
  • The solar panels are connected to an inverter. The conductive wire drives the electricity into the inverter, where DC electricity is converted into AC used to power homes and buildings.
  • A separate wire flows the AC electricity from the inverter to the electric panel, called the breaker box.
  • The breaker box that receives the AC electricity distributes it to various parts of the building and home.
  • Excess AC electricity flows from the utility meter to the electrical utility grid. The meter runs backwards, and excess electricity is stored for future use.

The Theory Behind Solar PV Cells

The solar panels have many small photovoltaic cells. It is capable of converting sunlight into electricity. These cells are made of silicon or other semiconductors. Semiconductors are capable of conducting electricity, creating an electric field through the electrical imbalance.

Home Solar PanelsIn the first stage, when sunlight hits the photovoltaic cell, the cell absorbs photons while freeing a few electrons that move in the cell. In a solar cell, positive and negative charged semiconductors are sandwiched together, which creates an electric field.

The free electrons then attain motion due to the electric field towards the conductive wire. The flow of electrons is termed as energy current, and the strength of the current determines the capability of the solar cell to produce electricity.

Further, the electrons strike metal plates to create an electric current, which flows into a series of wires. The wires drive the electric current, which is DC. The inverter acts as a hub to convert the DC into AC.

The DC reaches the breaker box to supply electricity to numerous parts of a building or a house. The unused electricity passes through the utility meter and propels the meter to go backwards. Excess electricity gets stored in the utility grid.

When your electricity consumption exceeds what your solar panels are delivering, the electricity is drawn from the grid. Primarily, electricity is used from the grid during nights when there is no sunlight or during monsoons.

Manufacturers have only been able to create solar panels with an efficiency between 15% to 20%. However, many solar panels come with efficiency levels higher than 20%. The key is to strengthen the energy current, which will increase the electricity produced.

Frequently Asked Questions (FAQs) on Solar Panels

Are There Electricity Bills for Solar Panel Systems?

Electricity bills will arrive monthly. However, the bills will be negligible, close to zero, at times even in negative integers. If your electricity bills are high despite a solar panel system, you must re-evaluate the size of your system.

The primary reason for a high electricity bill despite a panel system is the extra add-on appliances like a central air-conditioning system or a heated swimming pool. Evaluate how many solar panels each device would require, and adjust as soon as possible.

What Are the Disadvantages of a Solar Panel System for a Household?

Even though solar energy is renewable, it fails to align with our lifestyle at times. There are two demerits of solar panel systems.

  1. They have high upfront costs. The costs increase as you look for solar panels with higher efficiency. Also, the charge of installation and the arrangements required to run the system successfully costs money, effort, and time.
  2. Solar energy is intermittent, which means you cannot expect sunlight twenty-four hours a day. Weather conditions and geographical locations also affect the sunlight you receive.

Is It Worth Installing a Solar Panel System?

The worth of installing a solar panel system depends on your annual electricity bills, geographic location, and your want to be eco-friendly. The only issue with a solar panel system is the high initial costs of setting up. However, it’s a one-time investment. The monetary savings that follow are worth it.

A wise way to make it worth it would be to follow the calculations as mentioned earlier and make an informed decision based on the analysis.

Final Takeaway

It’s great if you’re planning to install solar panels at your home or institution. However, calculate accurately the number of solar panels you will need.

To calculate the number of solar panels, you need three key factors: annual electricity usage, power wattage, and production ratios.

The production ratio is complex to calculate since it depends on factors like your geographical location, roof type, size of panels, and beyond. However, the ratio flickers between 1.3 to 1.6.

Typically for a household, an 8-kWh solar panel system would be ideal. Calculate the system requirement for a building in the same way, and you’re all set!