The Questions Every Homeowner Should Ask Before Buying Solar
The other articles in this series make a case: that domestic renewable systems have become genuine energy infrastructure, that the rules governing them are worth understanding, and that the difference between a good installation and a merely working one is largely about what you designed for. This article turns all of that into something you can actually use: a list of questions to ask before you sign, and — more importantly — the reason each one matters.
I want to be clear about how to use this. The point is not to walk in with a script and interrogate an installer until they crack. The point is that the questions are a competence probe as much as a fact-finding exercise. A good installer will welcome most of these and answer them fluently, or tell you honestly where the edge of their knowledge is. A worrying one will get defensive, hand-wave, or reach for reassurance instead of explanation. You are gathering two things at once: information about your system, and information about whether the person selling it to you understands what they are selling. Both matter, and the second one is harder to get any other way.
I have grouped the questions by theme, given each a plain reason, and put a stripped-down printable checklist at the very end that you can take to a quote.
Grid connection and export
This is the area most likely to hide a decision you did not know you were making, and the one I most wish I had understood earlier.
“Is my installation being done under G98 or G99, and why?” This tells you whether your system is being notified to the network operator after the fact, or applied for and approved before installation. It reveals whether the installer knows which side of the line you are on, and it flags whether there is a DNO application in your project’s critical path that could affect timelines. If they cannot answer this, that is itself the answer to a different question, about them. The full explanation is in the G98 vs G99 article.
“Who submits the DNO application or notification, and will I get a copy?” The paperwork should describe your actual installation and should end up in your hands. You want to know the notification or approval is real, not assumed, and you want the document, because you will need it if you ever expand, sell the house, or have a dispute. A system whose grid paperwork you cannot produce is a system nobody quite finished.
“What is my export limit, and is the system export-limited?” You should be able to state your export limit as a number. If the system is export-limited — capped at, say, 3.68 kW — you need to know, because it shapes both your grid relationship and your economics. This is not a setting to discover later; it is a ceiling you are agreeing to now.
“If I want to add more generation or storage later, what does that do to my grid connection?” This forces the future into the conversation. The answer reveals whether the current design leaves you room to grow within your existing connection, or whether the first expansion re-opens the whole G98/G99 question. A good installer will have thought about your headroom. A poor one will not have considered that there might be a “later.”
Battery chemistry and safety
Batteries are the component with the most safety weight and the most variation between products, and the questions here matter for both your wallet and your house.
“What battery chemistry is this, and why that one?” Different lithium chemistries trade off energy density, cycle life, thermal behaviour and safety differently. You do not need to become a chemist, but you want to hear a reason for the choice — thermal stability, longevity, safety margin — rather than “it’s what we fit.” The reasoning tells you whether the choice was made or merely defaulted into.
“How many charge cycles is it rated for, and what capacity remains at end of warranty?” A battery’s honest cost is per usable kilowatt-hour over its whole life, not the sticker price. Cycle rating and end-of-warranty capacity (often expressed as a percentage of original capacity retained) let you work out whether the battery will still be worth having in ten years, or quietly fading. This is the number that separates a cheap battery from a false economy.
“How aggressively will the system cycle the battery, and can I control that?” Every full cycle ages the cells. A system chasing small savings by cycling hard can shorten the battery’s life in ways that no single day’s bill reveals — a trade I deliberately guard against in my own battery optimiser. You want to know whether the cycling strategy is sane and whether you can influence it.
Inverter and sizing
The inverter is the brain and the bottleneck, and its sizing is the ceiling you are most likely to hit first.
“What size is the inverter, and how much headroom does it leave above my current load and storage?” As I argued in the hindsight article, an inverter sized to exactly today’s need is a ceiling that makes your first expansion a replacement rather than an addition. You want to know how much room is left, and whether a slightly larger unit now would save a forklift upgrade later.
“Is it a hybrid inverter, and can it be commanded programmatically?” A hybrid inverter manages solar and battery together. Whether it can be commanded — charge, discharge, hold, on a schedule, via a clean interface — determines whether you can run a real smart-tariff strategy or are stuck with crude built-in timers. If you want automation, this is a purchasing decision, not a later tweak.
“What is the round-trip efficiency?” Every kilowatt-hour that goes into the battery and comes back out loses something on the round trip. That loss is a permanent tax on everything the battery does for you. A few percent difference compounds over years, and it is worth knowing before you buy.
Backup, black start and resilience
This is the area most people assume is handled and most often is not.
“When the grid goes down, does the system keep any power on — and which circuits?” Most grid-tied systems shut off entirely when the grid fails, for anti-islanding safety, leaving you dark next to a full battery. If backup matters to you, you need to know whether the system supports it, which circuits are covered, and how the changeover works — because retrofitting it means rewiring at the consumer unit. Ask before, not after the first power cut.
“Does the system support black start?” Black start is the ability to bring itself back up from nothing — to start from a fully dead state without needing the grid to bootstrap it. For a system you are relying on for backup, this is the difference between resilience and a system that only works when it was already working. It is a genuine engineering property, and asking about it by name tells you a lot about whether the installer thinks in those terms.
“Can a generator or alternative source be connected during a long outage?” Even if you never do it, the provision for a generator input is cheap at installation and expensive later. Asking flags whether the design leaves the option open.
Cabling, earthing and fire safety
The unglamorous, safety-critical layer. Mistakes here are the ones that actually hurt people.
“What size are the cables, and do they leave any capacity for expansion?” Cable sizing is a safety matter first — undersized cable is a fire risk — and a future-proofing matter second. Cable run with a little headroom, in conduit that is not full, is what makes future additions a pull rather than a rebuild.
“How is the system earthed, and does it meet the requirements for this type of installation?” Earthing for generation and battery systems has specific requirements, and getting it right is fundamental to safety. You are not expected to audit it yourself, but asking the question — and hearing a confident, specific answer rather than a vague one — is a meaningful competence signal.
“What are the fire safety provisions for the battery — location, isolation, ventilation, and detection?” Battery location is governed by safety rules about where units can be mounted, how they are isolated, and how a fault is contained and detected. This is not scaremongering; it is the single most safety-relevant siting decision in the whole system. You want to hear that it was thought about deliberately.
Firmware, monitoring and support
The parts that determine whether the system is a living platform or a sealed box, and whether it stays good over its life.
“How does the system receive firmware updates, and who is responsible for them?” A modern inverter and battery run software, and that software gets updates — for bugs, for safety, for new tariff features. You want to know how updates arrive, whether they can break a working configuration (a lesson I learned the hard way with automatic updates in my homelab), and who owns the problem when one goes wrong.
“What remote monitoring is provided, and can I get the data myself, locally?” There is a large difference between a vendor cloud dashboard you can look at, and open local access to your own data. If you want real observability and integration — Home Assistant, your own dashboards, your own optimisation — you need local data access, and that depends on which equipment you buy. Ask before you are locked into a cloud garden.
“How long is the manufacturer likely to support this product, and what happens if they exit the market?” Renewable hardware is a long-lived asset in a young, churning industry. A manufacturer that disappears can leave you with orphaned firmware, no warranty, and an integration that stops working. You cannot eliminate this risk, but you can weigh it, and asking shows the installer you are thinking in the right timeframe.
Warranties and the boring paperwork
Where the real long-term value hides, and where the cheap quote often turns out to have been cheap.
“What are the separate warranties on the panels, the inverter, the battery and the workmanship — and who honours each one?” These are usually different warranties of different lengths from different parties. The battery might be ten years, the inverter five, the workmanship something else entirely, and each is honoured by a different entity — manufacturer or installer. You need the whole map, because a warranty is only as good as the party standing behind it and their likelihood of still being there.
“What happens to my warranties if the installer goes out of business?” Installer-backed warranties and workmanship guarantees are worth exactly as much as the installer’s continued existence. Manufacturer warranties usually survive; installer promises may not. Knowing which is which tells you where your real protection lies.
“Will I receive full documentation — the certificate, the DNO paperwork, the commissioning report, and the settings that were configured?” You should end up owning a complete description of your system: what was installed, how it was configured, what grid settings were applied and why. This is the artefact that lets a future installer safely modify it, and its absence is the undocumented black box that the whole first article in this series warns against.
Integration and the future
The questions that decide whether the system grows with you or fights you.
“Can this system coordinate with an EV charger?” An EV is the biggest movable load in most homes, and a charger that can be load-managed and can coordinate with the battery against one tariff is worth far more than two systems that fight over the same cheap half-hours — exactly the problem I flagged between my own charger and battery. If EV charging is anywhere in your future, raise it now, because it influences equipment choice.
“Is the system designed for a smart, half-hourly tariff?” On a time-of-use tariff, the value of a battery comes almost entirely from exploiting the price spread, which requires programmatic control at the tariff’s granularity. A system designed only for flat-rate operation leaves most of that value on the table. Say up front that you intend to run a smart tariff.
“What is the realistic upgrade path — more panels, more storage, backup — and what does each one require?” This is the summary question that ties the whole checklist together. The answer reveals whether the system was designed as a platform or a finished object. A good installer can sketch your upgrade path and what each step costs. A poor one has never thought past commissioning.
The installer, directly
Finally, a few questions about the people, because — as the first article argued — the knowledge gap is really about them.
“What are your relevant qualifications and certifications for this specific work?” Solar, battery and grid-connection work has specific competency requirements beyond general electrical qualification. You are entitled to know what the people doing the work are certified for, and a good installer answers this without a flicker of defensiveness.
“Have you installed this exact combination of equipment before?” Experience with the specific inverter, battery and configuration matters, because the interactions between components are where the difficulty lives. First-time-on-this-kit is not disqualifying, but you deserve to know it.
“Can you explain a non-obvious setting you’ll configure — say, the export limit or a grid-code parameter — and why?” This is the direct competence probe. You are asking them to explain a real decision in their own words. Fluency here is worth more than any certificate; the inability to explain a grid setting is exactly the failure this whole series is about.
How to actually use the checklist
Do not fire all of these at one person in one sitting; you will exhaust everyone and learn less than you think. Instead:
- Lead with the future questions and the “why” questions. They surface competence fastest and are hardest to bluff.
- Listen for the shape of the answer, not just the content. “I’ll check and confirm in writing” is a good answer. “Don’t worry about that” is a bad one, regardless of what follows.
- Get the important answers in writing. Export limit, warranties, DNO process, upgrade path — these should end up in the quote or a follow-up email, not just spoken across a kitchen table.
- Compare quotes on the answers, not just the price. As I argued in the first article, price tells you almost nothing about the variable that actually matters. The quality of the answers to these questions does.
The printable checklist
Here is the stripped-down version. Print it, take it to your quotes, and note the answers.
SOLAR & BATTERY — QUESTIONS BEFORE YOU SIGN
Installer: ____________________ Date: __________
GRID CONNECTION & EXPORT
[ ] G98 or G99 — which, and why?
[ ] Who submits the DNO application/notification? Do I get a copy?
[ ] What is my export limit? Is the system export-limited?
[ ] What happens to my grid connection if I expand later?
BATTERY
[ ] What chemistry, and why that one?
[ ] Cycle rating, and % capacity retained at end of warranty?
[ ] How hard does it cycle the battery? Can I control it?
INVERTER & SIZING
[ ] Inverter size, and headroom above today's load/storage?
[ ] Hybrid inverter? Can it be commanded programmatically?
[ ] Round-trip efficiency?
BACKUP & RESILIENCE
[ ] Any power kept on during an outage? Which circuits?
[ ] Does it support black start?
[ ] Can a generator be connected during a long outage?
CABLING, EARTHING & FIRE
[ ] Cable sizes — any capacity for expansion? Conduit not full?
[ ] How is it earthed, to what requirement?
[ ] Battery fire safety: location, isolation, ventilation, detection?
FIRMWARE, MONITORING & SUPPORT
[ ] How do firmware updates arrive? Who owns update problems?
[ ] Remote monitoring — can I get my data locally?
[ ] Likely manufacturer support lifetime? What if they exit?
WARRANTIES & PAPERWORK
[ ] Separate warranties: panels / inverter / battery / workmanship?
[ ] What happens to warranties if the installer folds?
[ ] Full documentation: certificate, DNO paperwork, settings, why?
INTEGRATION & FUTURE
[ ] Can it coordinate with an EV charger?
[ ] Designed for a smart, half-hourly tariff?
[ ] Realistic upgrade path, and what each step requires?
THE INSTALLER
[ ] Relevant qualifications for THIS work?
[ ] Installed this exact equipment combination before?
[ ] Can they explain a non-obvious setting — e.g. the export limit — and why?
RULE OF THUMB: "I'll check and confirm in writing" is a good answer.
"Don't worry about that" is not.
Summary
- These questions are a competence probe as much as a fact-finding exercise. How an installer answers tells you as much as what they answer.
- The highest-value areas are grid connection (G98/G99, export limits, DNO paperwork), future headroom (inverter sizing, upgrade path, EV and tariff readiness), and the boring paperwork (separate warranties, full documentation) — because these are where the invisible, expensive decisions hide.
- Safety questions — battery chemistry and cycling, earthing, cable sizing, fire provisions, backup and black start — matter for your house and your family, and asking them by name signals whether the installer thinks rigorously.
- Lead with the future and the “why” questions, listen for the shape of the answer, and get the important ones in writing.
- Compare quotes on the answers, not the price. The cheapest quote is a question, not an answer.
- Take the printable checklist to every quote and record the responses. The act of asking changes the quality of the installation you get.
Next, and last, in the series: what enterprise IT taught me about designing better solar systems — why buying a solar installation is surprisingly like designing an enterprise datacentre, and why you should think of renewable energy as infrastructure rather than an appliance.