Quick answer
When a solar farm changes hands, the buyer inherits the grid connection agreement and all the compliance evidence behind it. Technical due diligence checks that the paperwork is complete, the site still performs the way its studies claim, and the protection settings match what the network operator approved. Problems found before completion become price adjustments or seller obligations; the same problems found after completion are the buyer's cost.
Key takeaways
- Most solar farms are built by developers and sold to investors; the buyer inherits the compliance evidence, gaps and all.
- Five checks worth commissioning: paperwork, grid compliance, protection settings, power quality, and a site walk-down.
- A problem found before completion is leverage; the same problem found after completion is the buyer's cost.
Solar farms change owners more often than most people realize. The companies that build them are usually developers: they take a site through planning, grid connection, and construction, then sell the finished farm to an investor and move on to the next project. It is a normal, healthy part of the industry.
But every sale raises a question the new owner has to answer: is this site actually compliant, properly connected, and performing the way the seller's paperwork says it is? The work of answering that question is called technical due diligence, and this post explains what it involves, why buyers commission it, and what happens when it turns something up. We do a lot of this work; one investment client alone has around a billion pounds of renewable assets moving through acquisition at the moment.
What you actually buy when you buy a solar farm
You are not just buying panels and land rights. A grid-connected solar farm in the UK operates under a connection agreement with its local network operator, and behind that agreement sits a stack of technical evidence: studies proving the site meets the grid's engineering rules (chiefly a standard called G99 for generation connections), protection settings agreed with the network, and test results from the day the site was commissioned.
All of that transfers to you with the site, and so does the responsibility for it. If a compliance question comes up two years after you buy, it is your problem, not the developer's.
The trouble is that three things tend to slip during a sale:
- The paperwork is incomplete. Commissioning records, study files, and as-built drawings often arrive with gaps, and what the seller hands over does not always match what the network operator has on file.
- The site has changed. Inverters get swapped, strings get reconfigured, firmware gets updated. Any of those can move the site away from the performance the original studies described.
- The people are gone. The engineers who made the design decisions have moved on with the developer. Nobody on your side was in the room.
The studies a buyer should commission
Technical due diligence puts fresh eyes, and fresh measurements, on all of that. A typical scope, scaled to the size of the site:
Paperwork check. Compare what is in the sale documents against what the connection agreement requires: which studies should exist, whether they do, whether commissioning tests were witnessed and accepted, and whether anything on site changed afterwards. This is desk work, and it usually decides how much of the rest is needed.
Grid compliance check. Confirm the site still performs the way its approved studies say it does: how it controls voltage, responds to frequency changes, rides through faults, and manages reactive power. This is the core of what our power systems consultancy models for buyers, using the same simulation tools the original connection studies should have used.
Protection check. Verify the protection settings on site match the schedules the network operator approved. Protection coordination is one of the most common places we find the site and the paperwork have drifted apart.
Power quality check. Measure the site's electrical behavior rather than trusting inherited assumptions. Harmonics are a frequent sticking point for renewable connections, and equipment swaps since commissioning can change a site's harmonic behavior. In the UK these checks have formal names you will see in the site's paperwork: a G5/5 harmonic assessment, plus P28 and P29 studies covering voltage flicker and voltage unbalance. Ask for them, and if the site has changed since they were done, re-run them against fresh measurements. Where problems show up, root cause analysis separates equipment issues from network ones.
Site walk-down. Physically compare the site against the as-built drawings. Undocumented modifications are not rare, and every one puts a question mark over the studies that assumed the original design.
Why bother, if the site was signed off once already?
Because the sign-off belongs to the past, and the risk belongs to you.
Whether a formal re-study is strictly required at the point of sale depends on the agreements involved, and it varies case by case. What does not vary is where problems land. The connection agreement's obligations travel with the asset. Lenders and insurers increasingly want current technical evidence, not inherited paperwork. And any claim you might have against the seller has a deadline on it. Buyers who verify early keep all their options. Buyers who file the documents away and move on tend to discover problems after the remedies have expired.
There is also a blunter reason: sometimes the site was designed wrong in the first place. Our consultancy team regularly works on installations where genuine remedial engineering, not just paperwork, was needed to get the site properly compliant and connected. Those problems did not stop the original commissioning. They surface later, under a new owner, at the worst possible time. Found during due diligence, the same problem becomes leverage: a price adjustment, a seller obligation, or a planned fix. It is the same lesson that runs through why grid connection projects get delayed: the expensive version of a problem is the one you find late.
A buyer's quick checklist
Before completing on a solar farm, your technical advisor should be able to answer yes to all six:
- Do we hold the complete set of compliance evidence, and does it match what the network operator holds?
- Has anything material changed on site since the studies were done?
- Do the protection settings on site match the approved schedules?
- Does measured performance, including harmonics, sit inside the agreed limits?
- Does the site physically match the as-built drawings?
- If any answer is no, is the gap priced in, fixed, or contractually the seller's problem before signing?
Acquiring solar, wind, or storage assets? Our power systems consultancy runs the studies buyers rely on, from grid code compliance checks to protection and harmonics. Start a consultation or email sales@renewable-d.com.
Frequently asked questions
What is technical due diligence for a solar farm?
An independent engineering review of a solar site before purchase. It checks the grid connection paperwork, protection settings, electrical performance, and whether the site as built matches the site as documented, so that problems surface while they can still be priced into the deal.
Do compliance studies transfer to a new owner?
The connection agreement and its obligations transfer with the site, and the original studies remain its compliance evidence. The real question is whether they still describe the site accurately, especially if equipment has been replaced or modified since commissioning. Buyers, lenders, and insurers increasingly want that verified rather than assumed.
What studies should a buyer commission when acquiring a solar farm?
At minimum: a review of the compliance evidence against the connection agreement, checks of grid code performance (voltage, frequency, fault ride-through, reactive power), a protection settings review, and a power quality assessment (in the UK: a G5/5 harmonic assessment plus P28 and P29 studies for voltage flicker and unbalance). A site walk-down against the as-built drawings catches undocumented changes.
