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How Many Solar Panels Do I Need? (2021 Size Guide) | Next Day Solar

Posted by Asher Budwig on
How Many Solar Panels Do I Need? (2021 Size Guide) | Next Day Solar

How many solar panels do I need?

Your 2021 Size Guide

  • Define your goals 
  • Understanding your energy consumption
  • Panel generation
If you’ve got this burning question, you may be at the beginning of your journey into renewable solar energy, or you might be evaluating a quotation you’ve received, and trying to work out whether you’ve been quoted for too many or too few panels on your roof. In this article we will tackle some of the important questions you will have, and you’ll come away with a clear picture of what will be right for your home or business. 

Step 1 - Lets define your goals… 

Investing into your own renewable energy system, for your home or business, is very different to investing in the stock market. At the outset, you’ll have a very clear picture of what it will cost, and certainty on what your return on investment will be (i.e the amount of energy you’ll be generating each year, and its financial equivalent if you had to buy it at today’s rate). Whilst most investors hope to get in and out quickly, with solar you need to be looking at the +10 year horizon if you are financially motivated by this. So if return on investment, time to payback is top of your agenda, you’ll be focussed on ensuring you’ve got the least number/cheapest panels and kit, that can generate the most energy, to reduce your energy bill as much as possible, and increase the speed in which your system has paid for itself. 
Equally there are some who are very keen to do their bit for the environment. Whilst its possible to sign up to an energy firm today, that buys credits for green energy that is ‘renewable’ the reality is that the energy you directly consume, has more than likely come from a coal fired power station, or one of its dirty equivalents, and therefore in generating your own energy, you are reducing your requirements from the grid, reducing the need to burn coal, and taking steps toward a cleaner greener future. If this is you, then you’ll want to consider what your energy requirements are, and size your system to ensure you can cover this, along with a buffer for variations in the season and natural environment. 
Now we’ve dealt with the financially driven, the environmentally driven, there is a third camp that I believe exists. The‘makes sense’ camp. If you sit in this group, you’ve got a property, its got a fantastic roof to generate solar, and your keen to get as many panels up as possible, and generate as much energy as you possibly can, so you can cover your energy needs & push energy back to the grid, and get paid for it. You’ll be enhancing the visual appearance or green credentials of your property or workspace. You’ll be less financially constrained, and likely want to ensure the solar installation looks the part, as well as doing your bit for the planet. 
Finally, you might be considering Solar, as a property developer, to ensure you are compliant with the current and future building requirements that will come into force. 
As a re-cap
Every new home built in England will require renewable energy technology for the property to achieve the stricter SAP calcs (homes will be a minimum of 31% more energy efficient than current Regulations). For a standard Notional House of 85m² this will equate to 2.6kWp of solar with a gas boiler, roughly 6 x 400w panels. 
If this is you, it will be a very simple case of ensuring you’ve got just enough solar to cover your compliance. You’ll probably have little care for the rest of the system and wish to ensure its as cost efficient as possible. 
For more information on the changes to building regulations coming into force in June 2022 read here : 
Now we’ve tried to establish some of the goals for those looking into solar, let's start to help you answer some of the questions you have about what is the right number of panels for you. In all scenario’s its important to get a decent grasp of how much energy you are using. 

Step 2 - Lets get to grips with your energy consumption. 

Any solar PV installer, will always be asking you (and if they don’t you should be concerned) what your current consumption is. You can easily read this off a recent energy bill, or by taking some simple meter readings yourself every day or every week over a standard period of usage (i.e don’t do it when you’ve got the family over to stay). 
Energy meters are counting your ‘watts’ consumed. Energy consumed is measured in kWh, 1kWh is 1000 watts consumed for 1 hour. The average UK home consumes roughly 4500 kWh per year, or 12.3kWh per day. If you’ve got a smart meter you’ll be able to check really easily what your current consumption is. A smart meter is free from most energy suppliers, so I’d highly recommend requesting one, to get a better handle on your bills and consumption. 
To get an even more basic understanding of how much energy some of your appliances might be using you can use a simple energy meter, this will help you establish how many watts some of your most regularly used appliances are consuming, it can be useful to try and identify any pieces of equipment that you might want to upgrade to a more energy efficient version, or just to get a grasp of what 100 watts or 50 watts ‘looks like’. 
The orange juice is using just under 100w, where as a nutri bullet will use over 1000 watts. 
It’s important to identify your annual energy consumption, as your ‘grid dependency’ or the % of energy you’ll be needing from the grid is a calculation that needs to know your annual usage. 
As you’ll see from the table below, which relates to an industry standard (MCS) way of calculating the amount of energy a system may generate, you’ll need to input your annual energy consumption here. 
C. Estimated PV self-consumption - PV Only
Assumed occupancy archetype
In half the day 
Assumed Annual Electricity Consumption kWh
Assumed annual electricity generation from solar PV system, kWh
Expected Solar PV self-consumption (PV Only) 
Grid Electricity independence / Self-sufficiency (PV Only) 
Now that we’ve established what type of ‘solar consumer’ you want to be, and we’ve got a grasp of how much energy you are using, let's get back to the discussion on panels. 

Step 3 - Panel Generation 

No solar panel is 100% efficient, so its important to state that a 360W panel, is unlikely to generate 360watts of energy reliably all year round for lots of reasons we will cover below but mainly 
  • Depends on Temperature, more efficient in colder climates
  • Depends on angle toward the sun, defined by your roof or other mounting surface. 
  • Depends on orientation (i.e south/north/east/west) 
  • Depends on systems used to take the energy generated and convert it to something you can use 
So how many panels should you have ???
  • The honest answer is as many as you can fit. Simply put, the panels themselves are likely to be one of the cheapest parts of your system/install, and equally solar energy benefits from large arrays, which are able to generate lots of power, fewer panels means less energy, and if you are going to the trouble of putting a system in, go as big as you can afford and fit. If you are in any doubt about having excess energy, you are likely able to sell it back to the grid for something so your investment isn’t wasted. You can also use excess energy to heat your hot water tank with clever things such as below which diverts any excess energy, before pushing back to the grid. 
  • Cost may be a big factor, panels typically start at around £150 for a good 360W+ panel, and upwards from there. A top end 400W+ panel is likely to set you back around £200. 
  • Its important to ensure your property is right for solar panels, as the last thing you want to do is make the valuable investment and find out your system is facing the wrong way. Due South is best, East/West systems work well, North systems should be largely avoided unless on very flat roofs. Homes toward the South of England generally get on average a’bit more sun than their northern counter parts, as the link below clearly illustrates. 
  • Finally, when requesting a quote from any MCS certified installer, you’ll be provided a performance estimate which will evaluate your consumption, your predicted generation, which is based on (Location/Angle of panels/size of array) and more. You’ll then get to decide if you want to add batteries to the system to improve its independency from the grid. At this point you can talk to your installer about any tweaks in less or more panels. 
If you have any further questions, or are thinking about installing PV on your property feel free to reach out to our team. 

Thank you 

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