ESOS
Asks what you did about the savings you identified.
Compliance & deadlines
The deadlines that put a date on your roofs
Most organisations don’t decide to look at rooftop solar. Something makes them look - a compliance deadline, a published plan with a date on it, or a funding round whose rules decide what qualifies.
Start here
Which obligation describes you?
ESOS for large private undertakings. Welsh public sector net zero for public bodies. PSDS Phase 4 for England heat capital via Salix - portal closed; watch for the next round.
All three ask the same question, and none of them answer it.
Welsh net zero
Asks what your plan cost.
PSDS
Asks what carbon your grant buys.
Every one of them ends up pointing at the roofs - and none of them tells you which roofs are worth the capital.
Track A
ESOS - large private-sector undertakings
5 Dec 2026
Progress update 2
5 Dec 2027
Phase 4 notification
Passed 5 Dec 2024 action plan · 5 Dec 2025 progress update 1
ESOS deadlines fall on 5 December. Phase 4 will carry its own action plan and progress-update cycle on the same annual pattern; dates follow once GOV.UK publishes the guidance.
-
1. What happened
In force Phase 3 participants who notified compliance must file an annual progress update against action plan commitments by 5 December 2026, signed by a board-level director via Manage your ESOS. GOV.UK - ESOS guidance
-
2. Where estates actually are
Many Phase 3 action plans committed to explore rooftop solar and never acted - assessing twenty or fifty roofs is real work, and capacity was short. Under the 2023 amendment regulations, high-level recommendations must be publicly disclosed. The Environment Agency publishes compliance notification data as open data.
-
3. What it does to the solar case
An ESOS assessment must identify cost-effective savings across at least 95% of total energy consumption, and a compliant audit must include site visits. On a forty-site estate a lead assessor cannot survey forty roofs, so rooftop generation is treated generically or left out. The progress update then asks what you did about the solar commitment in your action plan - an obligation to be specific about roofs while making that impractical to produce.
-
4. What you can’t answer from this alone
Which of those roofs carry a case - an ESOS audit was never designed to tell you.
Phase 3 qualification was assessed at 31 December 2022. GOV.UK has not yet published the Phase 4 qualification date. Secondary sources give 31 December 2026 - treat that as unconfirmed until GOV.UK states it.
Phase 4 — confirmed, intended and postponed →
5 December 2027
Phase 4 notification of compliance
Confirmed by GOV.UK. Full Phase 4 guidance and the updated reporting system are planned to be in place by early 2027.
Changes intended for Phase 4
Subject to parliamentary time and scrutiny
- Removal of Display Energy Certificates and Green Deal Assessments as compliance routes
- Progress against action plan commitments to be included in the ESOS assessment
- Where commitments have not been met, participants must provide an explanation
Postponed to Phase 5
Will not go ahead in Phase 4
Refocusing the scheme to cover net zero as well as energy efficiency, and aligning qualification thresholds with SECR. Both postponed to Phase 5.
Do you qualify? Four tests →
Phase 3 criteria, assessed at 31 December 2022. A large undertaking is any UK company that either:
Employee test
Employs 250 or more people
Financial test
Annual turnover over £44 million and balance sheet total over £38 million
Groups
Corporate groups qualify if at least one UK group member meets the definition
Overseas parents
UK establishments of overseas companies are in scope if any part of the global group’s UK activities qualify
Find a lead assessor — seven approved registers →
All seven registers listed on GOV.UK
01
Association of Energy Engineers
ukaee.org register
02CIBSE Certification
Low Carbon Consultant register
03Elmhurst Energy Systems
Find an assessor
04Energy Institute
energyinst.org/industry/esos
05Energy Managers Association
EMA ESOS lead assessor
06ISEP
ESOS lead assessors register
07Quidos
esosregister.com
GOV.UK removed the Institution of Chemical Engineers from this list on 16 February 2026. Check the source page before relying on it.
Which regulator applies — enforcement links →
England
Environment Agency
Wales
Natural Resources Wales
Scotland
SEPA
N. Ireland
NIEA
Offshore
Secretary of State, DESNZ
Track B
Welsh public sector - net zero by 2030, reported annually
-
1. What happened
In force Welsh public sector bodies were asked to publish plans by March 2023 and report emissions annually against a published plan. GOV.WALES - reporting guide
-
2. Where estates actually are
Audit Wales examined 48 larger Welsh public sector bodies. Of those that responded to its call for evidence, only two felt they had fully assessed the financial implications of meeting the 2030 ambition. The finding is about costing and capacity, not ambition. Audit Wales report
-
3. What it does to the solar case
Bodies know they should decarbonise; what they report not having is a full assessment of the financial implications and the specialist capacity to produce one. On most public estates, roofs are the largest single unpriced asset class.
-
4. What you can’t answer from this alone
Which roofs on the estate carry a capital case - annual carbon reporting was never designed to rank them.
Funding
Public Sector Decarbonisation Scheme - heat first, portal closed
-
1. What happened
In force DESNZ capital via Salix for low-carbon heating in public-sector buildings - not standalone solar. Applications must propose low-carbon heating for all buildings; fossil-reliant technologies are ineligible. Fabric and efficiency measures - including solar that reduces heat or electrical demand of the heated building - may ride along under a whole-building approach. Each building needs end-of-life fossil heat plant (generally 10 years or older). Passed Phase 4 portal opened 9 October 2024 at 2pm; closed 25 November 2024 at 2pm. Salix - Phase 4
-
2. Where estates actually are
Funding profile 2025/26 £86m · 2026/27 £427m · 2027/28 £427m. Ranked on grant carbon cost (cap £510/tCO2e), not first-come first-served. Minimum recipient contribution: 12% of total project costs (the cost of a like-for-like fossil plant replacement). Grant Offer Letters are issuing; no successor window announced. Salix - Phase 4 funding
-
3. What it does to the solar case
PSDS will not fund solar on its own. But the low-carbon heating it does fund raises the building’s electrical demand. Once that load is higher, more of the roof’s generation stays on site instead of exporting - so the same array, on the same roof, answers a different question. Any assessment made before the heat system changed is out of date.
-
4. What you can’t answer from this alone
The buildings in a PSDS bid are the buildings where the solar case has moved most - and they are rarely the ones anyone goes back to re-run.
PSDS delivery rules and funding profile detail →
Delivery deadline
Projects must be delivered by 31 March 2028. Grant end dates are 31 March 2026, 2027 or 2028 depending on the offer.
Money cannot move
Once agreed in the Grant Offer Letter, grant funding cannot be moved between financial years. Unspent allocation in a year is lost.
DNO engagement
Applicants must assess current and required electrical capacity and engage the Distribution Network Operator early - heat-pump loads often need it.
Planning year & locked profiles
Use 2025/26 as a no-spend planning year if needed; spend in only 2025/26 and 2027/28 is not eligible. Requested funding profiles cannot be amended once submitted.
Where we come in
A deadline without a ranked roof list is still a guess.
We do not file your ESOS return or write your net zero plan. We tell you which roofs are worth the capital - on identical assumptions - so the next step is specific. Start with a Full free report (one off).
Deadline first. Rank the roofs second.
Context
Standards, and what they do and don’t cover
Installer quality
MCS
The UK quality mark for small-scale renewables. Confirms an installer meets a standard; does not confirm a particular roof is a good investment.
Grid
Your DNO
Grid connection capacity is where projects most often stop, and it is not something an installer’s proposal can promise on your behalf.
The gap
None assess the roof
Whether a specific roof is worth the capital sits with you - not with MCS, the DNO, or the compliance scheme.
Before you accept a proposal
Independence changes the assumptions, the sourcing, and the reliability of the verdict a board is asked to approve.
FAQ
When is the next ESOS deadline?
If you qualified for ESOS Phase 3 and submitted a notification of compliance, the next deadline is the annual progress update on 5 December 2026, signed by a board-level director via the Manage your ESOS reporting system. The Phase 4 notification of compliance deadline is 5 December 2027. GOV.UK - ESOS
Does ESOS apply to public sector organisations?
Public sector organisations do not usually need to comply with ESOS. Welsh public bodies follow a separate track: public sector net zero by 2030 with annual carbon reporting. GOV.UK - who qualifies
What happens if I miss an ESOS progress update?
Your environmental regulator is responsible for compliance and enforcement and may issue civil sanctions including financial penalties. See the Environment Agency enforcement policy, annex 2 section D, and published civil penalties on data.gov.uk.
Can a desk-based feasibility assessment be used for ESOS compliance?
No. An ESOS-compliant energy audit must include site visits and lead assessor sign-off. A Stage1Energy assessment is a desk-based feasibility screening and cannot be submitted as an ESOS energy audit. GOV.UK - ESOS audit criteria
What is a grant carbon cost, and why does it matter for PSDS?
PSDS Phase 4 funds low-carbon heating projects - not standalone solar. Within that scheme, applications are assessed on grant carbon cost - how much direct carbon is saved by the grant funding alone - and sorted into tiers. The maximum acceptable figure is £510/tCO2e over the project lifetime for grant-funded measures. Lower costs improve odds of funding. Salix - key changes
Where do I find an ESOS lead assessor?
GOV.UK lists seven approved registers (AEE, CIBSE, Elmhurst, Energy Institute, EMA, ISEP, Quidos). See the registers section above and check GOV.UK for the current list.