How to compare solar quotes without getting misled (neutral, practical)

Solar quotes are easy to compare badly.

Two installers can both offer “10 panels and a battery”, yet the real difference can be scaffold, roof risk, export caps, paperwork, and what happens if something fails in year 7.

If you want a fast reality check for your postcode first (yield, tariffs, and typical savings), start here: Find your postcode

This guide shows you how to compare quotes like an adult:

• how to normalise them so you are comparing like-for-like
• what questions force the hidden exclusions to surface
• how to sanity-check performance claims without being an engineer

It is deliberately neutral. No brand recommendations, no sales pitch.

Quick answer

Assumptions and variability

• We refer to energy (kWh) and system size (kWp) and inverter power (kW), plus SEG, DNO, and G98/G99 (see Glossary).
• This is about domestic rooftop solar quotes for typical UK homes, not commercial installs.
• We assume you are comparing reputable installers and want to choose the best overall package, not the cheapest headline.
• What varies most in real installs is roof access/scaffolding, shading complexity, export limits, and electrical upgrade needs.
• We do not assume batteries are always worthwhile. Battery value depends on your usage shape, not on marketing.
• For how SolarByPostcode estimates yield, tariffs, savings, and payback by location, see: Data sources and methodology

Step 0: what you should collect before you compare anything

Before you even look at quotes, get these inputs. They turn “opinions” into something testable:

1) Your annual electricity use (kWh) from your bill or account
2) A rough sense of when you use electricity (daytime-heavy vs evening-heavy)
3) Any obvious constraints: shading, flat roof, listed/conservation, leasehold

If you do not know your annual kWh, start here:
- How much electricity does the average UK home actually use?

If you are unsure whether your roof constraints could trigger extra permission steps, keep this open too:
- Planning permission and conservation areas: when rooftop solar needs extra checks (UK)

Step 1: build an “apples-to-apples” comparison sheet

Quotes are usually written in a way that makes them hard to compare. Your job is to extract the same fields from each and line them up.

Copy this table into your notes and fill it in for each quote.

Category	What to record	Why it matters
Panels	Brand + model, wattage (W), count	“10 panels” can mean very different total kWp and quality tiers
System size	Total DC size (kWp)	This anchors output potential and price sanity checks
Inverter	Brand + model, AC size (kW), phases	AC size affects clipping, export, and upgrade options
Battery (if any)	Brand, total kWh, usable kWh, warranty cycles	“10 kWh battery” is often not 10 usable kWh
Export limit	Any export cap stated (kW)	This can change your savings more than panel brand
Monitoring	App access, data ownership, offline fallback	You want monitoring that still works if the installer disappears
Scaffold	Included? assumptions?	Scaffold is a common “surprise extra”
Roof works	Tile replacements, felt issues, remediation terms	Roof risk is where cheap quotes get expensive
Electrical	Consumer unit changes, isolators, cable routes	Small line items can become big ones on install day
Paperwork	MCS, DNO submission, handover pack	This is what makes SEG and warranty claims smooth
Payment terms	Deposit %, stage payments, cancellation terms	Terms tell you as much as price does

If an installer cannot give you this cleanly, treat that as information.

Step 2: ignore panel count. Compare kWp and roof realism instead

The most common quote comparison mistake is “£ per panel”.

What you actually want to compare:

• Total system size (kWp) and whether it realistically fits your roof
• Layout quality: neat array, sensible spacing, and honest shading treatment
• Whether the design respects constraints: vents, skylights, dormers, conservation visibility, flat-roof ballast zones

A quote that squeezes more panels in by ignoring roof realities is not “better”. It is a future snag.

If you want a quick local sanity check on typical yield (and what an extra 1 kWp often buys you in your area), run your postcode first:
- Find your postcode

You can also use postcode examples to keep yourself honest across the UK, because the same kWp can behave differently in different places:
- High-yield south west examples like TR1 (Cornwall) and PL1 (Plymouth)
- Mid-band examples like BS1 (Bristol City of) and LE2 (Leicester)
- Lower-yield northern examples like AB10 (Aberdeen City) and EH1 (City of Edinburgh)

Step 3: understand inverter sizing in one minute (so you do not get fobbed off)

You will usually see two different “sizes” in a solar system:

• Panel system size (kWp): the DC rating of the panels combined
• Inverter power (kW): the AC power the inverter can output

These are not supposed to match perfectly.

A slightly smaller inverter than panel kWp can be normal. Panels rarely hit nameplate output in the UK, and a touch of “DC oversize” can improve shoulder-season output. But it can also be abused to make a quote look better on paper.

What to ask:

• “What is the panel kWp and what is the inverter kW?”
• “Do you expect clipping in summer, and roughly how much?”
• “Is the export capped to a lower figure than the inverter could deliver?”

If the installer only talks about panel count and refuses to talk about inverter size, that is a signal.

If you want the plain-English physics of why rated output is not what you see in real life, this guide is the anchor:
- Why solar panels never hit their rated output in the UK

Step 4: export limits and DNO reality can make two quotes incomparable

Many quotes quietly assume you can export freely.

In reality, the grid operator (your DNO) may limit your export, or require a different approval route under G98/G99. This can change:

• your maximum export power
• whether you need pre-approval
• how long the grid paperwork takes

If one quote assumes “no export limit” and another assumes “export capped”, you are not comparing like-for-like.

This is the guide that explains it properly and is worth reading before you decide:
- DNO, G98/G99, and export limits: why your inverter may be capped

What to ask each installer:

1) “What export limit are you assuming for my address?”
2) “Is this a G98 notify-after install, or G99 pre-approval?”
3) “If export is capped, do you propose a limiter, and is it included?”

A quote that refuses to state the assumed export limit is not a complete quote.

Step 5: performance claims are only as good as their assumptions

Most quotes contain an annual kWh forecast. Treat it like a claim in a debate.

A good forecast shows:

• the assumed orientation and tilt
• the assumed shading and how it was assessed
• whether losses are included (inverter, temperature, wiring)
• whether the number is “P50-ish typical” or an optimistic best case

A weak forecast is just one big number.

The two most common ways quotes inflate the “savings” story

1) Assuming high self-use without explaining how
If the quote assumes you will use 60 to 80% of your solar at home, ask how. For most homes, self-use depends on being at home in the day, or actively shifting loads.

2) Using an export rate that is not your reality
If the export rate is inflated, battery payback suddenly looks magical.

If you want a grounded explanation of how overcast UK days and seasonal shape change the story, these are the best companion reads:
- Cloud cover vs solar output: what actually happens on overcast UK days
- Temperature losses in UK solar panels: how heat quietly eats your kWh

Step 6: batteries are where people get misled most often

Batteries are not “good” or “bad”. They are situational.

A quote should clearly state:

• battery model and usable capacity
• warranty terms (years, throughput, cycles, exclusions)
• what the battery is supposed to do in your life (evening cover, peak shaving, backup)

If the pitch is “battery = always worth it”, treat that as marketing, not analysis.

Practical questions that cut through the fog:

• “What is the battery’s usable kWh?”
• “What is my assumed evening usage that the battery will cover?”
• “What happens in winter when solar is low? Does the battery still add value?”

If your home is evening-heavy, batteries can help. If your home already uses a lot in the day, a battery may do less than you think.

If you want to understand how usage shape drives value, these two are the relevant anchors:
- Daytime vs evening electricity use in the UK: why it changes solar savings
- Can solar cover 100% of a UK home’s electricity? What is realistic?

Step 7: paperwork is not boring. It is your protection

Two core paperwork items matter for normal UK homeowners:

• MCS certification: often needed for SEG export payments and to keep things clean for future buyers
• Handover pack: inverter commissioning, test results, schematics, warranty documents, and how to access monitoring

If you have not read this, it will save you from common nonsense:
- MCS certification in the UK: what it guarantees (and what it doesn’t)

What to ask:

• “Will I receive the MCS certificate, and who submits it?”
• “What exactly is included in the handover pack?”
• “Who do I call in year 8 if something fails?”

A quote that is vague about paperwork is telling you how the aftercare will feel.

Step 8: the fastest way to compare quotes is to email back 10 questions

You can paste this into an email. A good installer will answer cleanly.

1) What are the exact panel and inverter models, and the total system size (kWp)?
2) What is the inverter AC size (kW), and do you expect any clipping?
3) What export limit are you assuming for my address, and is this G98 or G99?
4) Is scaffolding included, and what access assumptions are you making?
5) Are any roof repairs excluded or “subject to survey”? What would trigger extra cost?
6) Are consumer unit changes included if needed, and what electrical work is assumed?
7) If a battery is included: what is usable capacity, and what is the warranty in plain terms?
8) What assumptions drive your annual kWh forecast (orientation, shading, losses)?
9) What paperwork will I receive (MCS, DNO, test results, schematics, warranties)?
10) What are the payment terms and the cancellation policy?

If one installer answers properly and another evades, you have learned something without needing to argue.

A practical way to “cast the net wide” without repeating the same examples

Quote comparison advice can feel abstract, so use different UK contexts as anchors:

• Dense city/leasehold reality: SE1 (Southwark) and UB5 (Ealing) in London
• Standard suburban family-home reality: LE2 (Leicester) and BS1 (Bristol City of)
• Coastal and high-yield reality: TR1 (Cornwall) and PL1 (Plymouth) in South West England
• Darker winter, export story changes: AB10 (Aberdeen City) and EH1 (City of Edinburgh)
• Wales and NI context reminders (different admin cultures, same homeowner logic): CF10 (Cardiff) in South Wales and BT1 (Belfast)

You do not need to overthink it. The point is to keep your examples grounded, and not always reference the same three postcodes forever.

Red flags that deserve a hard pause

If you see these, slow down:

• “No mention of export limits” (or “export is always fine”)
• “Savings claim without stating self-use and export assumptions”
• “Battery payback claim without your usage shape”
• “Scaffolding excluded or vague”
• “Roof condition ignored”
• “Warranty language that conflates product warranty with workmanship”
• “No clear plan for MCS, DNO paperwork, and handover docs”
• “Pressure tactics, artificial deadlines, or refusing to itemise”

Bottom line

A good quote is not the one with the best headline number.

A good quote:

• makes the assumptions explicit
• includes the boring but expensive stuff (scaffold, electrical, paperwork)
• tells you the export limit reality
• gives you a design that respects your roof, your planning context, and your life pattern

If you do those things, you can choose confidently even when two prices are close.

Next reads

• Solar system sizing in the UK: choosing the right kWp without wasting money
• Solar panel cost in the UK: what you actually pay and why quotes vary
• MCS certification in the UK: what it guarantees (and what it doesn’t)
• DNO, G98/G99, and export limits: why your inverter may be capped
• Solar warranties and insurance in the UK: what is covered, what is not, and who to call first
• Do solar panels increase house value in the UK? The boring truth (and when it backfires)

Run the calculator for your postcode

Once you have normalised your quotes, the final sanity check is to see how the numbers behave in your local context: yield, tariffs, export assumptions, and payback.

Run the calculator for your postcode