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Solar energy and battery technology have helped shape our modern world for the better. With global warming causing significant changes in the world’s climate, this technology has proved that humans can use ingenuity and work with the elements to create something that can positively benefit everyone.
Businesses, in particular, have a huge role to play in curbing greenhouse emissions. While the carbon footprint of large-scale industries is undeniable, the Small and Medium-sized Enterprises (SME) sector is also equally responsible for generating much of the emissions that are worsening the problem of global warming.
This is why it has become apparent that for us to improve and heal the climate, we must strive to do better and adopt technologies that help us achieve this ambitious goal. Not to mention, the modern customer has also become environmentally aware, with many seeking to do business with SMEs that champion “green initiatives”.
Fortunately, this is also a win-win situation for businesses. Having an effective Battery Energy Storage System (BESS) paired with or without solar PVs can not only help reduce grid demands but can also save businesses money down the road.
As of 2025, millions of homes and businesses benefit from using solar energy in the UK, and according to a statistic by the National Grid, the UK is set to see a 5x increase in solar PV generation by 2030.
If you are an SME looking to adopt solar technology, now is as good a time as any. However, transitioning to BESS-derived power requires some research. Every business has unique needs, and to get the most out of your BESS investment, it is important that you effectively figure out the requirements for your business and learn how to size a BESS.
Read on to learn more about the basics of battery energy storage systems, cycle life, battery checks, and how to size a BESS for an SME:
Before we dive into the best practices for sizing a BESS for your SME, let’s talk about a few important terms that we will be using throughout this guide:
Energy requirements are calculated in kilowatt hours. This is commonly referred to as kWh. The kWh figure is the total amount of usable energy the battery can store. You may have seen this term used for phone batteries as well. In simple terms, it shows how much the battery can store and provide once it is charged.
For example, a business may be powered by a 3, 7, 8, or higher kWh battery. This depends on the type of business, its needs, the requirements during peak hours, and the footfall of customers during different time periods.
The power rating is calculated in kilowatts or kW. The power rating is the maximum instantaneous charge or discharge power that the battery and its inverter can deliver. This is important in sizing because it enables you to acquire the right components that can not only provide uninterrupted energy but also sustain the required load.
The “C-rate” is a measure of the speed at which a rechargeable battery charges or discharges. This rate is important to understand because it allows users to get an idea of how the battery will perform during application.
The C-rate is expressed as a number. For example, a 1C rate means that the battery will be fully charged or discharged in one hour. A 2C rate battery will take half an hour, and a 0.5C rate battery will take approximately two hours.
So, the higher the C-rate, the faster the battery will charge and discharge. On the other hand, a lower C-rate will charge and discharge slowly, but it will use less power.
However, faster isn’t always better. A higher C-rate battery will likely heat more since it uses more power, which can result in more wear and tear and battery degradation. This is why higher C-rate batteries are only specifically used in certain scenarios where higher demand is expected.
Think of a battery as a reservoir. In this analogy, the energy stored can be thought of as water and the outlet or wire system is the faucet. When you use the battery, the water starts going down until it is completely depleted.
The Depth of Discharge, in this sense, is simply the fraction of the total capacity used in a cycle. For example, a DoD of 80% means that 80% of the total capacity is used and 20% is left in the battery or “reservoir”.
Battery manufacturers highlight a battery’s DoD so that users know how much power they can safely draw from the battery without causing significant degradation. A recommended DoD of 80% means that 80% of its total energy can be used before recharging is needed.
100% DoD is not recommended because that means that the battery is completely depleted and can cause stress on the components inside the battery, which can lead to a shorter lifespan.
The charge cycle or cycle life is the number of charging or discharging cycles the battery can endure before its capacity degrades to some threshold, often to 80% of its original capacity.
One charge cycle happens when you charge a battery in a way that totals 100%. For example, if you charge a battery from 20% to 100% then you have basically charged it by 80% (100 – 20 = 80). However, if the battery falls to 80% and you charge it again to 100%, it will charge by 20% which will equate to one charge cycle (80%+20%).
Charge cycles are important to understand because they allow users to know the overall efficiency and performance of the battery and can help them figure out the expected lifespan according to their specific usage.
Batteries use chemistry as power. A lot of the components used in batteries are prone to degradation by their very nature.
For example, lithium-ion batteries, while very promising and relatively stable, are prone to degradation over time, regardless of charging cycles. This happens due to ageing or external factors such as exposure to extreme heat or cold temperatures.
Inefficiencies in the system can result in losses from heat, conversion, wiring quality, resistance, and other factors. This is referred to as the round-trip efficiency losses.
The energy stored in the battery goes through multiple components; this “trip” can cause losses due to heat and resistance, which must be accounted for to figure out the overall performance and economics of the battery.
Sizing is an important part of BESS because it allows users to effectively figure out the right system for their needs.
Sizing can help SMEs shave peak load hours and use strategies such as charging during off-peak hours and discharging during high tariffs to save money.
A properly sized battery storage system can not only help SMEs make the most out of their investment and enhance their ROI, but it can also enable them to continuously save money on electricity costs, even during high-demand hours.
Here is a step-by-step checklist for effectively sizing battery storage for SMEs in the UK:
Just as you would conduct a financial audit of your business, a professional installation company like Calder Electrical can send out trained technicians to conduct an electrical audit of your property.
This audit can help reveal the property’s total power consumption in kW and how big a system you would require to meet the energy demands. This can be done by analysing historical loads and studying peak hour patterns for a particular area.
The more data gathered, the more accurate the audit will be, which will ultimately lead to a sound financial investment for your business.
The next step is to define how many hours you would want the battery to run. Some businesses won’t require a longer backup system, but most businesses will aim to at least shave off most of the peak-hour tariff during high-demand hours.
For example, if you determine the peak hours for your area, you can get a good idea of how long you want the battery to run.
If the peak hour lasts for 2 hours and you want the entire 2 hours to be covered by the battery, then this would give you a great starting point for figuring out the total kWh required for your SME.
Once you have the total hours and the energy load of your property, you can begin with power sizing. Power sizing is simply the maximum discharge rate you need and is calculated in kW.
Energy sizing is done in kWh, which accounts for the duration that we figured out in step 2. You can compute the two figures together to figure out the total requirement. For example, a 100kW system for a 2-hour backup would mean that you would need a 200kWh system. A headroom of 10% to 20% is added to this amount to account for some occasional high-usage scenarios.
A professional technician can help you determine the total C-rate requirement in the audit. Many commercial BESSs use 0.5C as a good starting point. A 0.5C rate means that the battery will take 2 hours to fully discharge.
Keep in mind that a higher C rate will enable faster discharging, which might be great for high loads, but it will also put a lot of stress on the battery, which will ultimately degrade it faster. Conversely, a lower C rate is relatively “gentler”, but it will require a larger capacity to provide the same power.
The final step for sizing accounts for all the factors that will affect the performance and economics of the battery. This includes figuring out the following:
By following these steps, you can effectively come up with an adequately sized battery that can help you achieve your energy needs without problems. This audit can be done by yourself, but please keep in mind that it will take a lot of time and knowledge to accurately figure out the right size of the BESS for your SME.
This is why we recommend that you pick a good installation company like Calder Electrical to do all the mental gymnastics for you. A certified installation company will use its experience, accreditation and adherence to best practices to give you a BESS solution that you can rely on for the long term.
Sizing is just part of the equation in planning a transition to a BESS for your SME. There are several factors that go into the implementation of such a project – from choosing the best location to assessing the energy needs and picking the best hardware for the job.
Your best bet at starting right is to go with an effective installation company that can assess your business’s needs and come up with a viable BESS solution that can power the SME for the long term.
A professional team can help you with various aspects of the project, the most important of which is site selection. Selecting a location for your battery storage project is even more important if you plan to pair your BESS with a solar PV, which would require you to find a location that has ample direct sunlight.
The land should ideally be flat and south-facing and should receive at least 4 hours of unobstructed sunlight every day. For an effective BESS installation, you will need to ensure that the system has easy access to the grid.
A professional installer can also help you source the right equipment at the best rate and give you a complete package that provides your business with an uninterrupted supply and potentially large savings over the years.
Once you find a good installation partner, you can also count on them to provide you with maintenance services. BESS require monitoring and tweaks to ensure that the system is running smoothly and is tuned to the needs of your SME.
By conducting regular maintenance, technicians can ensure that you continue getting the most out of your investment, secure a great ROI, and power your SME when it matters the most, like during outages or peak hours.
Calder Electrical Services provides a wide range of solutions to help you play your part in making the world a more sustainable place.
If you wish to have solar panels installed on your residential or commercial property, our experts can conduct a site visit to determine your requirements and propose the best type of solar system for your needs.
We also offer solar battery storage installation so that you can minimise any wastage of the energy you create. This will help lower your energy bills and make you more independent from the grid.
We have been providing electrical services to residential, commercial, and industrial properties for over 40 years and are specialists in all aspects of electrical installations, maintenance, and testing.
All our work is fully insured and meets the current regulations and standards set by the NICEIC. Also, all the notifiable work is signed off by the local authorities.
Contact us here or call us at 0800 612 3001 to get in touch with our professional electricians for more information on solar panels, battery storage solutions, and how to size a BESS for an SME in the UK.
Photo by American Public Power Association on Unsplash
