How many solar panels do I need?
The idea of installing solar panels at home has probably crossed your mind more than once recently due to the volatility of energy prices. It is well-known that these come with countless advantages besides the positive impact on the environment, and the possibility to generate substantial savings since day one is on top of the list for most homeowners who have decided to take this step.
As with every project that involves a significant amount of money, there’s some planning to do before proceeding with the installation itself. To begin with, it’s essential to assess how many solar panels you need to power your home and whether the conditions your roof and surrounding environment offer are optimal for PV efficiency.
In order to arrive at a conclusion that seems logical and feasible, you should take into account factors such as your energy consumption patterns, as well as your location and roof orientation.
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How to calculate the number of panels you need in the UK?
According to Ofgem, the non-ministerial government department that regulates the networks of gas and electricity in the UK, the average electricity consumption level is 2700 kWh/year. This is the typical consumption observed in households of 2 or 3 people.
Ofgem also stipulates that any annual electricity use around 1800 kWh is considered low, while any annual electricity use around 4100 kWh is considered high.
You’re probably wondering how many solar panels are needed to power a house with each of these electricity consumption levels. At Otovo, we have defined 3 different system sizes capable of addressing these. The minimum number of solar panels to power a system for your house should be 5; a system composed of 5 solar panels should be capable of generating enough electricity for a family with a lower consumption, as it is expected to produce around 1828 kWh/year, with slight variations depending on your exact geographical location. This figure, just like the others that will be presented throughout the article, already takes into account the actual performance ratio of the solar panels, not their estimated total production (which is 2150 kWh/year for 5 solar panels).
A system of 10 panels can produce around 3655 kWh/year, thus suiting any household with a medium annual electricity consumption. Finally, we have systems composed of 15 panels, which can produce around 5483 kWh per year and are ideal for any household whose consumption is above the average. The number of panels impacts the cost of the system, along with other factors.
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How does your location impact the number of solar panels you need?
Your location will always be essential in determining how much solar you need and the expected output of your solar panels throughout the year, as these depend on the amount of sunlight they receive. Even though a PV system can also deliver without direct sunlight, it is evident that solar installations in locations that benefit from sunnier weather will be capable of reaching higher outputs.
For example, a 10 panel system installed in Dover will produce around 3910 kWh per year, more than enough to fulfill the electricity demands of a household with an average electricity consumption level in the UK. A system of the same dimension in Glasgow is expected to have a lower output, circa 2975 kWh per year. This output is still within the threshold of the typical UK household, but it is clear that the difference in kWh/year is considerable between the two locations.
Let’s take as an example a family whose electricity use over the whole year is around 1900 kWh. Now, let’s calculate how many solar panels that family would need if living in Dover or in Glasgow. If they lived in Dover, a PV system composed of 5 panels should be enough to address their electricity demands, as the expected output of a system of that dimension is 1955 kWh/year. However, if they lived in Glasgow, the most sensible thing to do would be to upgrade their system, as the minimum number of solar panels (5) would only be capable of producing an estimate of 1530 kWh/year.
Roof orientation and angle
The ideal orientation for all solar panels installed in the Northern Hemisphere is south. Having them east-facing or west-facing is also good, as they will produce more at some point of the day but underperform at some other point. If facing east, panels will perform better in the morning. If facing west, panels perform better in the late afternoon.
Calculating the ideal angle of a solar installation follows a similar procedure. As a rule of thumb, the best all-year-round angle of your panels should be close to the latitude of your location. You can make some minor adjustments aiming for optimal efficiency during specific seasons: panels can perform better with a steeper inclination (+15º) in the winter. During summer, the opposite is true, as your panels can perform better if you subtract 15º to your all-year-round angle.
The wattage of your solar panels and the importance of batteries
Besides the location factor and the size of your solar array, the quality of the components of your PV system will also play a crucial role in determining the annual output. The calculations we made above started from the premise of using solar panels of 430W, which are available at Otovo. These are capable of delivering a greater output than others, such as the 410W panels, whose wattage is closer to the industry average and can also be found in our inventory.
We mentioned before that a system of 10 solar panels in Dover is capable of producing 3910 kWh kWh/year. A system of this size will produce around 3750 kWh/year if it is composed of 410W panels instead.
How batteries can optimise for efficiency
The decision to include solar batteries or not can also have a say in the number of panels you need to power your home. Why is that? Because no matter how many solar panels you have, they’ll only be able to produce while there’s sunlight - whether it’s direct or indirect sunlight. The average peak sun hours in the UK is lower than in other European countries (between 2 and 3), and a majority of the population is not at home while the panels are producing more electricity, meaning they’ll not be able to generate savings from their PV systems unless there’s a battery attached.
Let’s consider a family in Dover whose electricity bill is £100/month. If this family installs a system of 10 panels, each capable of reaching 430 watts, then it will be able to generate savings between £34000-£46000 over the span of 30 years. With a system of the same size, but with panels of a lower caliber (385W), these figures will lower to £27000-£36000 over the same period.
This comes as good news, especially for all homeowners who cannot afford having bigger installations due to the limitations offered by their roofs, as it becomes evident that it is possible to generate significant savings with solar by upgrading the quality of the components of the PV system.
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