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The most common solar regrets (and how to avoid them before you install)

A UK-focused guide to the solar mistakes homeowners most often regret: overpaying, oversizing, ignoring shading, misunderstanding SEG export, buying the wrong battery, and trusting optimistic assumptions. Includes a practical pre-install checklist.

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By: SolarByPostcode

The most common solar regrets (and how to avoid them before you install)

Solar regrets are rarely about solar “not working”.

They are usually about buying the right idea in the wrong way.

The good news: most regrets are predictable, and you can avoid them with a few simple checks.

If you want a quick postcode-level baseline for expected output and savings where you live, start here: Find your postcode

This guide is UK-specific. It is not a sales pitch. It is a map of the mistakes people keep repeating.

If you want the economics foundation first, read the cluster flagship:

Quick answer: the top regrets in UK solar

TL;DR: the biggest regrets are not about panel brands. They are about assumptions: price, shading, sizing, and how much solar you actually use at home
  • Overpaying for the install (and realising later the “premium” was mostly marketing).
  • Believing a single payback number based on optimistic self-use or export assumptions.
  • Ignoring repeatable shading and discovering winter performance is much worse than expected.
  • Oversizing and exporting too much at a lower value than expected.
  • Buying a battery for the wrong reason (to “make solar work” rather than because it truly fits the home).

Assumptions and variability

  • We talk about system size in kWp, power in kW, and energy in kWh, and we reference SEG export payments (see Glossary).
  • We assume a typical UK grid-connected home solar system, not off-grid setups.
  • We assume you want a decision that stays sensible even if energy prices, export rates, or your usage pattern change.
  • What varies most between homes: shading and roof layout, your self-use share, install price and roof complexity, and whether export is limited by DNO rules.
  • If you want the modelling assumptions behind SolarByPostcode pages (yields, rates, and savings calculations), see: Data sources and methodology

Why solar regrets cluster around a few predictable mistakes

Most regrets come from one of these:

  • a hidden constraint (shading, roof complexity, export limits)
  • a wrong assumption (self-use share, tariff, “average UK payback”)
  • an overpriced upgrade (battery, “premium” kit, unnecessary extras)

So the goal is not perfection.

It is to remove the avoidable mistakes before you sign.

Table 1: The most common UK solar regrets (and the prevention moves)

Regret What happens in real life How to avoid it Best guide to read
Overpaying You learn later that a comparable system was available for much less, with similar output. Compare like-for-like quotes and treat “premium” claims as hypotheses to verify. How to compare solar quotes (UK)
Believing a single payback number The payback “works” only under optimistic assumptions (high self-use, high export rate, no shade). Use a payback band and sanity-check self-use and export assumptions. Solar payback periods (UK)
Ignoring shading Summer looks great, but winter output is disappointing because shade is repeatable when the sun is low. Treat shading as a first-class constraint, especially winter shade. Shading and solar panels (UK)
Oversizing You export a lot more than expected and the “extra panels” deliver less value than the quote implied. Size for realistic self-use and export value, not for a perfect annual kWh number. Oversizing your solar system (UK)
Buying the wrong battery The battery feels nice, but the economics do not justify the cost for that household pattern. Treat batteries as timing tools. Justify them separately from solar. Solar batteries (UK)

The rest of this guide unpacks each regret in a practical way, with “what to ask before you buy”.

Regret 1: Overpaying for the install

This is the most common regret because it is invisible at the moment you buy.

Solar will still generate. The system will still “work”.

But you might discover later that you paid for:

  • sales commission and padding
  • unnecessary kit upgrades
  • a design that looks impressive on paper but does not deliver proportionate value

The simple prevention move

Do not compare “a solar quote” to “another solar quote”.

Compare like-for-like:

  • same kWp size (see Glossary)
  • same assumptions about export and any battery
  • same roof scope (scaffolding, access, roof complexity)
  • same warranty and workmanship commitments

Then check whether the expensive quote is more expensive for a real reason.

Useful reads:

Regret 2: Believing a payback number built on optimistic assumptions

The classic regret is not “solar did not save money”.

It is:

  • “The payback they implied depended on assumptions that were never made explicit.”

The two most common hidden assumptions:

1) Self-use share: how much of your solar you use at home rather than export
2) Export value: what rate you actually receive under SEG (see Glossary)

If the quote never asked about your daytime usage, but the payback assumes high self-use, treat it as optimistic.

If you want the clean model behind this, read:

The prevention move

Use a payback band:

  • pessimistic (low self-use)
  • middle (typical)
  • optimistic (high self-use)

If it only works in the optimistic case, it is not a robust decision.

Start here:

Regret 3: Underestimating shading (especially winter shade)

Shading regret is painful because it often shows up after the excitement phase.

In summer, almost any system looks decent.

In winter, a small, repeatable shade window can do outsized damage because:

  • the sun is low
  • shadows are long
  • generation is already lower, so losses feel larger

The most common “I wish I knew” shading moments:

  • a tree that barely matters in summer but bites hard in winter
  • a chimney shadow moving across a key string
  • neighbouring roofs or dormers creating predictable morning or afternoon shade

Prevention read:

The prevention move

Before you buy, do one honest check:

  • stand where the panels will be (or use roof photos) and identify any objects that will cast shade when the sun is low
  • treat winter as the worst-case season for shade, not summer

If you are already near the margin, your quote should acknowledge shading explicitly, not hand-wave it.

Regret 4: Oversizing and exporting too much at a lower value than expected

Oversizing regret usually sounds like:

  • “We have loads of generation, but the savings are not as big as the system size suggests.”

That happens when too much of the extra solar ends up exported.

Export is not worthless, but it is often lower value than self-use because:

  • self-use avoids your import unit rate
  • export earns your SEG rate

If you want the clean explanation:

The prevention move

Size in this order:

1) your roof constraints and shading reality
2) realistic self-use (daytime usage)
3) export value as a bonus stream

Reads:

Regret 5: Buying a battery to “make solar work”

A battery can be great.

But the most common battery regret is buying it for the wrong job.

A battery is a timing tool:

  • it moves solar generation into the evening
  • it does not create extra energy

Common battery regret patterns:

  • paying for capacity you rarely use
  • expecting a battery to turn the UK winter into summer
  • buying a battery before understanding your own usage pattern

Read before you decide:

If you are trying to increase self-use without a battery, start here:

Regret 6: Not understanding export limits and the DNO process

This regret is less common, but it can be nasty when it hits.

Some systems are capped on export due to grid constraints, and the details depend on the DNO and whether you fall under G98/G99 (see Glossary).

If your plan depends heavily on exporting large amounts, you should understand this before you buy.

Read:

The prevention move

Ask a direct question in writing:

  • “Will export be capped, and if so, at what limit, and why?”

Then evaluate whether the design still makes sense without best-case export assumptions.

Regret 7: Missing the “boring paperwork” that protects you later

This one shows up when you need to:

  • claim on a warranty
  • sell the house
  • set up SEG export payments
  • prove the install was done correctly

In the UK, the paperwork that matters most is usually tied to MCS and handover documentation.

Read:

This is not about “tick-box compliance”.

It is about whether you can prove what was installed, by whom, and under what terms.

Table 2: The “no-regrets” pre-install checklist (copy/paste for your notes)

Use this list before you sign anything.

Category Questions that prevent regrets Why it matters
Roof reality What repeatable shading exists, especially in winter? Which roof faces are actually usable? Shading and layout errors are hard to “fix later” without cost.
Sizing Is the system sized for realistic self-use, not for a perfect annual kWh story? What happens if export is capped? Oversizing can push value into lower-value export.
Assumptions What self-use share was assumed? What import rate and SEG export rate were assumed? Most payback disappointment is assumption mismatch.
Quote hygiene Can I compare this quote like-for-like with others? What exactly is included (scaffolding, monitoring, warranties)? The same “kWp system” can be priced wildly differently.
Battery decision Is the battery justified on its own, or is it being used to cover weak solar assumptions? Batteries are often oversold as “required”.
Paperwork and future-proofing Do I understand MCS paperwork, SEG setup needs, and what happens if I sell the home? This is what protects you when something goes wrong later.

A final timing note: the “wait” regret is real too

Some people do everything right, except they wait.

They wait for:

  • perfect subsidies
  • perfect battery tech
  • perfect electricity prices
  • perfect certainty

Meanwhile, they lose years of generation.

If timing is your sticking point, this guide slots directly after this one:

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