How to choose the right solar EPC partner

Choose a solar EPC partner on evidence: comparable projects it still operates, a financial model you can challenge, engineering you can check, and a clear owner for problems after commissioning.

No two proposals are built the same way, so lining them up fairly is hard without specialist help. A weak choice tends to surface once the plant is running, when output falls short of the proposal or a fault turns out to belong to nobody. Putting either right can bring costs that were never in the quote and interrupt your operations.

A partner worth appointing shows the working behind every figure, set out plainly enough for you to test at your own desk. Years after handover, who will you call? A plant can run for 10 to 20 years or more, and what it saves over that time depends on how well the company you appoint now looks after it.

1. Have they built plants like mine?

The proof that an EPC has built plants like yours is three or more comparable plants whose owners still use it for service. Comparable means the same kind of business, a similar size and a similar electrical setup, including any battery and the municipal connection. Start with this check, because it narrows the field fastest. Its references should include the hard parts of your job, such as a battery fitted while a factory kept running. Experience on large solar farms may not cover them.

What to look forRunning plants you can visit, with output records their owners will share.

2. Do past clients keep them on after handover?

Past clients who keep an EPC on after handover are among the strongest references it can offer. Ask for its list of completed plants, marked to show the ones it looks after today. Owners who stay are showing that they trust the EPC, and an EPC that still runs plants it built years ago has lived with its own design and workmanship ever since.

What to look forA high share of its plants still in its care, including the oldest ones.

3. How much do they ask about my business?

An EPC that works as an adviser spends most of the first meeting asking about your business. It wants to know your operating hours, production patterns, critical loads and expansion plans, any generators or solar already on site, and whether you would rather pay cash or finance the plant. Then it walks the site. A quoted saving or plant size that arrives before anyone has seen your bills or your site is a guess.

What to look forA proposal that names your problem first, such as high daytime electricity costs or backup for critical loads, and sizes the plant to solve it.

4. Have they analysed my meter data?

You can tell an EPC has analysed your meter data when its proposal shows charts drawn from that data and traces the system size back to them.

That list is your load profile, recorded every half-hour or more often. From it an EPC can see when the site uses power, when demand peaks, how the tariff and its demand charges fall on your usage, and how much of the solar output the site will use. If a battery is proposed, it should be sized from the same data for a stated purpose. Figure 1 shows a week of that data at a business where we operate the solar plant.

Figure 1. A metered week of demand and solar output at a Gauteng business

The navy line is what the site used, half-hour by half-hour, from Monday 7 to Sunday 13 September 2026. The green area is what its 170 kWp solar plant produced: at the weekend, more than the site could use. On the overcast Monday the plant produced 67% less than on the Friday, and the site’s highest half-hour of grid demand reached 105 kW. On the other weekdays it stayed between 45 and 80 kW, and came between 07:00 and 08:30, before the sun was strong. Source: Focal Energy metering of a plant we operate (the site is not named), 5-minute readings averaged to half-hours.

What to look forYour site’s own peak days and daily load shape, shown in the proposal.

5. Does the savings figure hold up when I test it?

A savings figure holds up when the EPC writes down every input behind it, and a re-run on cautious inputs still leaves a plant worth buying. Few of these checks have as much money riding on them. Start with the yield, which should be stated as P50 and P90 figures.

Then ask for the rest of the inputs, each with its source:

• The irradiance data behind the yield estimate.
• The tariffs, and how fast they are assumed to rise.
• Panel degradation.
• Battery cycling, where there is a battery.
• Downtime and curtailment.
• Operating and maintenance costs.
• Finance costs.

In Gauteng, ask directly about export and self-consumption. Count export income as zero until your municipality has approved feed-in and is paying for it. Across the plants we operate, solar typically covers 30 to 50% of a site’s consumption without batteries. Ask what share the proposal assumes, and how much of the solar output the site will use itself, its self-consumption share.

Solar can trim the demand charge as well, but treat that saving as an extra, on its own line next to an energy-only business case. Demand is billed on the busiest half-hour the tariff counts in the month, and on some tariffs over the past twelve months. One overcast afternoon at the wrong time can leave that peak close to where it would be without solar, as on the Monday in Figure 1.

On the plants we operate, solar’s cut in billed demand is typically about 10%, but it runs from roughly 5% at some sites to 25% at others. If the plant only pays its way once the demand saving is counted, its return is at the mercy of the weather, so question that figure hard.

What to look forThe cautious re-run in writing, before you sign.

6. Can the engineering be checked?

Design documents drawn up for your site make the engineering checkable. Ask for:

• A single-line diagram of the electrical design.
• Exact model numbers, with datasheets.
• The inverter’s NRS 097-2-1 certificate, the grid-interface type test the national specification requires for every grid-connected inverter.
• The system size in kWp DC alongside the AC rating.
• The exclusions, listed up front: waterproofing, lightning protection, roof access and a roof-specific mounting system.

The cost guide explains why quotes that state the size or the exclusions differently cannot be compared. The documents are the visible part of the design work, which covers cable sizing, earthing, protection and load flows, the roof structure, the existing electrical equipment, grid requirements, battery integration and safety.

Then come the independent checks. Ask to see each one:

• A structural assessment, confirming the roof can carry the extra load of the panels and mounting.
• A wind loading assessment, confirming the mounting and its fixings will hold against the wind loads on your roof.
• A lightning and surge risk assessment, which sets the protection the plant and the building need.
• Sign-off by an ECSA-registered electrical engineer.
• The electrical certificate of compliance (CoC), issued by a registered electrician after the installation has been inspected and tested.

What to look forDrawings and calculations complete enough that nothing rests on trust.

7. What will the plant need from my building over the years?

A rooftop plant needs a sound, watertight roof for as long as it runs, safe ways for people to reach it for cleaning and repairs, and protection from lightning and theft. A good proposal plans for all of it before anything is fixed to the roof. Ask to see:

• A survey of the roof’s condition and remaining life. If the sheeting will need replacing while the panels are on it, re-roof first: lifting an array off and putting it back is a project of its own.
• How each fixing through the roof will be sealed, and who answers for a leak, for how long.
• The lightning and surge risk assessment from check 6, done for the roof with the array on it, because a rooftop array changes the building’s lightning exposure. Southern Gauteng averages 10 to 15 ground flashes per square kilometre a year.
• Safe, permanent access to the roof, and walkways between the rows, so that nobody stands on panels or brittle sheeting.
• A water point within hose reach of the array, for cleaning. Most of Gauteng’s rain falls between October and March, so dust can sit on the panels through the dry winter.
• A ventilated, shaded and lockable home for the inverters.
• Security for the panels, inverters, batteries and cable.

Plan security into the design. The insurer King Price recommends tamper-resistant fasteners on the panels, locked enclosures for inverters and batteries, and keeping ladders and tools out of reach, because opportunistic thieves use any they find. Ask whether the monitoring would show a missing string the same day.

What to look forThe roof work, maintenance access and security priced in the proposal.

8. Do they ever advise me to buy less?

Sometimes the right advice is to buy less, even when that shrinks the EPC’s own contract. It might mean a smaller battery than you had in mind, an array capped where extra panels would stop paying for themselves, or a load that is cheaper to handle another way. If every option you are shown lands at the top of your budget, ask what a smaller plant would earn.

What to look forAdvice that shrinks the order when the numbers say it should.

9. Who fixes things once the plant is running?

The EPC that built the plant should fix things once it is running: it monitors the plant, finds and repairs faults, and handles warranty claims, with a named person who calls you. You should never be sent to the inverter manufacturer or the battery supplier to sort out a fault yourself.

Make sure the handover pack is in your company’s name. It should include:

• The certificate of compliance, with its test report.
• As-built drawings.
• The commissioning report.
• The warranties, registered against the equipment’s serial numbers.
• The municipal approvals.
• An owner-level login to the monitoring.

With those in hand, the plant keeps most of its protection even if the company that built it closes.

What to look forA named contact and a service agreement that runs for years after handover.

10. Can they show me their processes?

An EPC should be able to show you written processes and checklists for procurement, design reviews, quality control, commissioning, documentation, safety and changes to scope. Good processes mean every electrician’s work is checked, recorded and handed over the same way on every job.

Commissioning is a good place to start. It should follow IEC 62446, the international standard for testing grid-connected PV, and end in a written report that you keep. Ask whether it also covers these checks, which matter once the plant is running:

• The inverters’ reactive-power settings, so the plant brings your power factor closer to 1.
• A baseline reading of every string.
• A check that the grid meter and the plant’s meter agree.

What to look forA sample commissioning report from a past project, and the checklist behind it.

11. Does the proposal explain itself in plain language?

A clear proposal opens with a summary a non-engineer can act on: the equipment and the reason for it, the expected saving and its basis, the main risks, and the plan for faults. The datasheets belong in an appendix, for whoever checks the design. Be wary of detail that seems meant to end the conversation.

What to look forStraight answers to your follow-up questions, in plain words.

Sources

• Electrical Installation Regulations, 2009 (Government Notice R.242, Gazette 31975, 6 March 2009), regulations 2, 6, 7, 9 and 11, Department of Employment and Labour.
• ECA(SA): “PV installers must be electrical contractors” (12 August 2022); “How long is an electrical certificate of compliance valid for” (21 November 2022); installer verification statement, reported by Green Building Africa (8 April 2026).
• NRS 097-2-1:2024, Edition 3 (via sseg.org.za); AMEU/SALGA standard SSEG requirements (February 2020).
• City Power SSEG booklet (15 November 2024) and SSEG FAQ (27 March 2025); ITWeb, “City Power hits back on solar registration process” (22 April 2026). City of Ekurhuleni, Annexure E25 (approved 29 May 2025), SSEG general information sheet (undated, read September 2026) and 2026/27 Annexure F (24 June 2026). City of Tshwane SSEG FAQ; Gauteng Provincial Gazette 217, LAN 648 (18 June 2025).
• PV GreenCard programme website and directory (read 28 September 2026).
• CSIR Energy Centre for GIZ, with SALGA, “A guideline for cost-efficient procurement of photovoltaic assets for municipalities”, issue 02 (October 2021): commissioning to IEC 62446, the guaranteed performance ratio to IEC 61724-1 with independent monitoring, the example payment schedules and retention.
• Sungrow manufacturer warranty, APAC (May 2021); JinkoSolar limited warranty (19 September 2025); Sunsynk manufacturer’s warranty terms, Africa (December 2022).
• Buyer guidance on deposits: the South African buyer guides audited on 28 September 2026.
• Morné Gijben, “The lightning climatology of South Africa”, South African Journal of Science 108(3/4) (2012): ground flash density from the South African Weather Service network, 2006 to 2010.
• Liesl Dyson, “Heavy daily-rainfall characteristics over the Gauteng Province”, Water SA 35(5) (2009): Gauteng’s October-to-March rain season.
• Sparks Electrical News, lightning protection and the South African standards (2025): the SANS 62305 lightning-protection suite and its risk assessment.
• King Price’s theft-prevention advice, reported by MyBroadband (31 October 2024).
• DC:AC ratio, exclusions, waterproofing, walkways, roof access and inverter housing: the commercial solar cost guide. The share of a site’s consumption that solar covers without batteries, typically 30 to 50% across the plants we operate, and the typical reduction in billed demand, about 10% in a range of roughly 5 to 25%: Focal Energy operating experience. The eleven checks, the independent-check list and the five questions: Jonathan de Vrye.