Installer guide · 10 min read

Solar EPC Contractors: What They Are and How UK Installers Work With Them

By Roman Steer-Love, co-founder of TNW Marketing · published 23 October 2026

Short answer: a solar EPC contractor is a company hired to do the engineering, procurement and construction of a solar system under one contract. It designs the system, buys the panels, inverters and mounting, builds it, tests and commissions it, then hands it over, which is why EPC deals are also called turnkey. This is not the Energy Performance Certificate, the A to G energy rating of a building. Compared with a normal design and build installer, an EPC contractor usually signs up to a performance specification, a fixed price, bonds and damages for delay or underperformance. An installer can also work on EPC projects as a subcontractor without taking that risk itself.

Solar EPC: the two meanings

Searches for "solar EPC" mix two unrelated things. In property, an Energy Performance Certificate rates how energy efficient a building is from A to G; GOV.UK says a commercial building needs one when it is sold, let or built, and each certificate is valid for 10 years. Solar panels can improve that rating, but that is not what this guide is about.

In contracting, EPC means engineering, procurement and construction. NEC's guidance note on EPC contracts defines it this way: the contractor is appointed to design and plan the scheme to meet the client's objectives, procure the plant, materials and subcontracts, and construct, test and commission the work. The client gives an output or performance specification, and the contractor hands over a finished, working asset.

EPC vs design and build vs subcontract

The line between design and build and EPC is the risk, not the work. JCT describes its Design and Build Contract as for projects where the contractor carries out both the design and the construction. An EPC contract does the same but usually adds performance tests, bonds and damages that a smaller rooftop job for a factory owner may not carry.

The standard contract forms

• FIDIC Silver Book. FIDIC's Conditions of Contract for EPC/Turnkey Projects, second edition 2017, reprinted in 2022 with amendments. FIDIC says not to use it if tenderers lack time or information to check the employer's requirements, if much of the work cannot be inspected, or if the employer means to supervise closely, and recommends its Yellow Book for those contractor-designed works instead.
• NEC4 Engineering and Construction Contract (ECC). NEC's own note says the ECC can range from no contractor design to full design responsibility, so it can be used as an EPC contract, with Option A (priced contract with activity schedule) or Option C (target contract with activity schedule). Secondary Option X17 (low performance damages) links payment to performance tests.
• JCT Design and Build Contract. The current DB 2024 edition, with matching Design and Build Sub-Contract documents (DBSub/A and DBSub/C). A client may amend it to add performance terms.
• NEC4 Engineering and Construction Subcontract (ECS). NEC says it uses the same definitions and procedures as the ECC, giving the main contractor back-to-back protection, and can include any level of design.

What a solar EPC contract usually contains

SolarPower Europe's EPC Best Practice Guidelines (version 2.0) set out typical terms. They were written with utility-scale and commercial and industrial plants in mind, so expect smaller rooftop contracts to carry lighter versions. The ranges below are the guideline's, not a UK standard.

Two points matter most for an installer's cash flow. Bonds are usually issued by a bank or other financial institution as irrevocable, first-demand guarantees, so you need a provider willing to issue them. And the guideline treats Provisional Acceptance as the end of construction and the start of a two-year warranty in which the contractor must prove a minimum level of performance.

When and how an installer subcontracts to an EPC contractor

Subcontracting suits an installer with good crews but no appetite for bonds and performance risk. SolarPower Europe's guidelines expect EPC contractors to use subcontractors, for example for civil and electro-mechanical work. Before you sign:

1. Read the main contract terms passed down. Back-to-back subcontracts can pass down damages, performance tests and warranty periods.
2. Pin down design responsibility. Both the JCT and NEC subcontracts can include design; agree exactly what you design and what you build to someone else's drawings.
3. Check payment and retention. When you are paid, what is held back and until when.
4. Check insurance requirements. Design responsibility may need professional indemnity cover; see our sister site's solar installer insurance guide.
5. Agree handover documents. Test results and records that feed the main contractor's acceptance.
6. Sort the tax set-up. Subcontract installation work is likely to fall under the Construction Industry Scheme and may use the VAT domestic reverse charge; see our guide to VAT, CIS and the reverse charge on commercial solar.

Moving up to EPC: what changes

Taking the main contract means taking the risk with it: a fixed price, bonds, a liability cap that may reach the full contract price, and damages if the system is late or underperforms. MCS certification covers electrical technologies such as solar PV up to 50kW, so on larger jobs quality is proved through the specification, testing and documents rather than MCS (our sister site covers MCS certification). Public buyers advertise EPC-style work through tenders and frameworks; see commercial solar tenders. Investor-owned systems are covered in our commercial solar PPA guide.