11 Points to Check Before You Buy
You know the basics of solar power and the benefits it brings, but do you know what you should be asking before you buy? And what to look for in the answers to spot a fake?
Solar panels are one of the most cost effective upgrades you can make to your home. They cut your bills, lower your carbon footprint and reduce your reliance on the National Grid.
When done right, solar can go on to save you money for decades. However, the rush in demand within the solar industry has led to a rise in the number of fast talking, inexperienced solar sales reps, selling low quality, low efficiency and poorly fitted solar PV systems.
This guide will give you the most important questions you need to ask your installer before signing your contract, and how to know whether the answers they give are true or showing red flags.
“What energy price did you use to calculate my savings?”
Why It Matters
Some installers will use inflated prices (30p/kWh or higher), not aligned with current market rates, to make savings seem larger than they are. You need to know what price is being used to estimate your returns, using a realistic and transparent model.
| Ask | Red Flag |
| The exact tariff they are using for your calculations | “Energy prices always go up” |
| What happens if prices fall? | No explanation on assumptions |
| Can they provide a version based on your actual bill? | Vague or generic savings claims |
If your installer is not using figures based on your actual bill, your usage and tariff, the savings they give you may be inflated and incorrect. Look for an installer that is a member of EPVS (Energy Performance Validation Scheme). EPVS independently verify all estimates and return figures, ensuring they are accurate and explainable.
“Did you include inverter or battery replacements in your long term calculations?”
Why It Matters
Your solar inverter will need replacing every 10-12 years, depending on brand, while your solar panels last a minimum of 25 years with most going on to perform efficiently for up to 40 years. Most solar batteries last around 10 years, so they will need to be replaced periodically. Without accounting for these replacements, your return on investment may be overinflated and too good to be true.
| Ask | Red Flag |
| When will replacements be needed? | “The system just runs forever” |
| Typical costs for replacement inverter and battery | No lifecycle cost modelling |
| Whether these costs are built into the savings estimates | No mention of future maintenance costs |
Return on investment is only correct if you include the full lifecycle of the solar inverter and battery. While solar panels can last up to 40 years, you will only get the full benefit of the savings if your inverter is working too.
“Will you check if I need planning permission or a grid application?”
Why It Matters
Most homes will not require planning permission as solar panel installation is allowed under Permitted Development Rights. If your home is in a conservation area or is a listed building, you may require Listed Building Consent, which at SolarTherm UK we can help you complete the application to your local planning authority.
Applications to the Distribution Network Operator (DNO) are completed according to the size of your system. If your system is below 3.68kW per phase your DNO will be informed after installation via a G98 form and if your system is above 3.68kW per phase approval will be acquired before installation via a G99 request.
| Ask | Red Flag |
| Confirmation on DNO application (G98/G99) | “You’ll be fine” without checking |
| Planning advice if you’re in a conservation area or listed building | No mention of DNO notifications |
| Whether your installer will handle the paperwork for you | No written confirmation |
DNO approval is required before exporting any excess electricity back to the grid. If you don’t have DNO approval, you system has not been checked that it can be safely connected to the grid and you won’t be able to receive payment for any electricity you export.
“Who will install my solar PV system, and how experienced are they?”
Why It Matters
A bad installation can cause leaks, poor output and become a fire risk, resulting in costly repairs and replacements. Your system is only as good as the person installing it, so make sure they carry all the correct accreditations and qualifications. At a minimum, your installer should be MCS accredited to ensure safety and quality of your system.
| Ask | Red Flag |
| In-house installers | “We use subcontractors” |
| How many systems they have fitted | Shrugs or vague claims |
| Photos or references from past jobs | No evidence of past installs |
Even if you have the best kit installed, if your installer is not qualified your system will likely still be poor. Warranties usually require installation by an accredited and qualified installer to be valid, so cutting corners can cost you more in the long run.
“Are you fully insured – and what actually happens if something goes wrong?”
Why It Matters
Solar panels go on your roof and are part of a larger electrical system. If something gets damaged or something goes wrong, you need to know where liability lies and who you call on for a solution.
| Ask | Red Flag |
| Ask about their public liability and professional indemnity certificates | “We’ve never had a problem” |
| Whether roof or structural damage is covered | No documentation |
| What happens if issues arise months after installation | Limited workmanship warranty |
If they are not insured, it is your property and equipment that is at risk. Insufficient insurance cover can leave you with costly repairs at your expense if something goes wrong.
“Will my system work if there is a powercut?”
Why It Matters
If one of your goals from installing solar is to have backup power in the event of a grid failure, you need to ensure your installer fits a system that is suitable for home backup and has an Emergency Power Supply (EPS) fitted. Most solar PV systems will shut down during a grid failure to allow engineers working on the grid to work safely and without risk of electrocution. To maintain power from your solar PV system you will need to have a battery storage system installed that has EPS compatibility.
| Ask | Red Flag |
| Backup capable inverter | “Yes, probably” |
| Battery with emergency socket | No technical explanation |
| A clear yes or no answer | Confused response |
If you don’t have battery storage, you won’t have EPS. You also need to let your installer know the level of EPS you require, from a single socket to keep devices charged to full home backup, as different levels require different systems and electrical connections.
“Will the system be battery ready – even if I don’t want one now?”
Why It Matters
Adding in a battery later can become expensive if your system isn’t fitted ready for one. Your installer needs to know any plans for system expansion or if you plan to add battery storage, an EV charger or heat pump in the future to design a system that is not only large enough for your current needs, but compatible for future upgrades.
| Ask | Red Flag |
| Hybrid inverter or battery ready system | “You’ll need a full upgrade” |
| Space reserved for a battery in future | No flexibility built into design |
| Wiring designed with a battery in mind | “You don’t want one anyway” |
Build your system for today but plan it for tomorrow. As long as your installer knows your future plans, your system can be fitted to be compatible with future upgrades.
“What size system and configuration do you recommend?”
Why It Matters
A tailored system design is crucial for efficiency. Buying an off the shelf solar PV system may not be big enough for your property, or may be too big incurring higher costs and a longer pay back period unnecessarily.
| Ask | Red Flag |
| How they calculated the optimal system size | “This fits on your roof and generates more than enough” |
| Why they chose that brand over another | No explanation of why that brand was chosen over another |
| What monitoring solutions are there to track your energy production | The system doesn’t need a monitoring platform |
You don’t just want a high power system, you want a system that works for your home. Balancing performance and cost to maximise savings and minimise your payback period.
“What are the total costs and payment terms?”
Why It Matters
Make sure you know what is included in your quote and if there is anything else you will need to pay for separately.
| Ask | Red Flags |
| What is included in the quote – ask for an itemised list not just an ‘installation’ cost | “Everything you need is there” |
| Are there any financing options? | “We require cash upfront” |
| Are there any additional or optional costs I might encounter later – such as scaffolding, monitoring subscriptions or upgrade fees? | “There shouldn’t be anything else” – without confirmation in writing |
A clear, itemised quote protects you from hidden extras and ensures you know exactly what you’re paying for.
“What warranties are included – and who honours them?”
Why It Matters
A solar PV system is a long term investment, and warranties protect you if something fails unexpectedly. Not all warranties are equal. Some apply only to parts, others only to labour and some are offered by the manufacturer not the installer. If your installer disappears, you need to know your warranties still stand. Clear, written warranty documentation is essential for long term peace of mind.
| Ask | Red Flag |
| What are the lengths of the product, performance and workmanship warranties? | “Everything has a long warranty, don’t worry you are protected” |
| Who provides the warranty – the manufacturer, the installer or a third party? | Installer avoids clarifying or only offers their own “in-house warranty” |
| Is the workmanship warranty insurance backed, and what happens if your company ceases to trade? | “We’ll always be here”, with no insurance backed guarantee |
A reputable installer will always provide warranty certificates and explain exactly who to contact if something goes wrong.
“What aftercare and maintenance support do you provide?”
Why It Matters
A solar PV system has minimal ongoing maintenance, but that doesn’t mean it should be ignored once installed. Monitoring, system checks and occasional cleaning all help ensure your system stays performing at its best.
| Ask | Red Flag |
| Do you provide a post installation handover and explain how to monitor my system? | “It’s all straightforward” with no demonstration or guidance |
| What support is available if I have questions or issues in the future? | No dedicated customer service, just a sales number to call |
| Do you offer maintenance or health check services and how often should they be done? | “You’ll never need maintenance” or a refusal to discuss long term care |
A good installer won’t just install your system — they’ll stay with you throughout its lifespan to ensure it keeps performing as expected. A reputable installer should offer clear support pathways, help you understand your monitoring app, and be available if something goes wrong months or even years after installation. Good aftercare protects your investment and maximises your long-term savings.
Ready to Start Your Solar Journey?
Now you know what to ask, you’re ready to start your solar journey. You don’t need to be a solar expert, you just need to be asking the right questions from your solar installer – after all, they are the expert and should be able to answer all your questions.
These 11 points will help you cut through all the sales talk, show you what to look for in your quote and spot a good installer from a bad one. At SolarTherm UK we’re always here to help guide and advise, whether you just want to check information you’ve been told or you want to book in for an installation.
Contact SolarTherm UK today for a free, no obligation quote and design, tailored to your property, usage and future energy needs. No hard sell, just honest, expert advice.
Your home. Your energy. Your future.
