LONGi Solar Panels in the UK

A LONGi Hi-MO X10 panel sells to UK buyers at between £85.00 and £123.20 excluding VAT, which is 17.5p to 25.4p per watt, and the advertised "30 year warranty" is 30 years on the power output and 15 years on the panel itself. Those are two separate promises in two separate clauses of LONGi's own warranty document, and the gap between them is where almost every misunderstanding on a British solar quote lives. On top of that, the exact full black model that UK distributors sell as a Hi-MO X10 is not named in any of the three warranty documents LONGi publishes for this market. All of it is checkable in about ten minutes, and this page shows you where.

Who LONGi are, and what Hi-MO means on your quote

LONGi Green Energy Technology Co., Ltd is a Chinese module manufacturer, and that exact company name is what appears against its panels in the MCS Product Directory. It does not sell to British homeowners and it does not install anything. It sells modules through distributors, who sell to the installer who turns up at your house, which means the only LONGi document you will ever be handed is the one your installer chooses to hand you.

On its own European site LONGi says it has "broken the world record for cell efficiency 19 times since 2021". Midsummer Wholesale, which describes itself as an Authorised Distributor of LONGi products for Europe, calls it "the world's leading solar technology manufacturer since 2000 and the largest producer of monocrystalline silicon wafers". Those are the manufacturer's and the distributor's claims respectively, and neither is the number that matters to you.

What matters is which generation is on your quote, because the warranty follows the generation and not the brand. Three show up on British paperwork:

• Hi-MO X10 is the current residential range, built on LONGi's HPBC 2.0 back contact cells with an n-type TaiRay wafer. Model codes begin LR7 or LR8. Midsummer's own product page notes the X10 "is divided into four series: Explorer, Scientist, Guardian and Artist".
• Hi-MO 6, also badged X6, is the previous residential back contact range, model codes beginning LR5 or LR7 with HT in the middle. Still widely stocked and still quoted.
• Hi-MO 7 and Hi-MO 9 are the larger utility and commercial modules, codes like LR7-72HGD and LR8-66HYD. They turn up on domestic quotes for big roofs and ground mounts.

The generation also decides the panel's physical size, which decides how many fit on your roof. Our guide to solar panel dimensions in the UK covers why a 540W panel is not simply a better version of a 480W one.

What a LONGi panel costs in the UK right now

Checked live on 3 October 2026, LONGi residential panels sell to UK buyers at between 11.8p and 25.4p per watt excluding VAT, and the spread sits inside the same brand rather than between brands. Two sellers, same day:

Two things to hold on to. The Midsummer figures are the prices its site shows before you log in, and the page itself says "don't forget to login to your account or you won't see your trade prices", so an installer with an account pays less than £123.20. And the three X10 lines are the same generation of the same brand at 17.5p, 19.8p and 25.4p a watt on the same afternoon, a spread of 45% from cheapest to dearest. Panel list prices in this market are a starting position, not a value.

Set it against the whole job. The Energy Saving Trust puts a typical 4.5kWp UK installation at around £7,600, using about 12 panels over 20 to 30 square metres, and that page was last updated on 1 October 2026. Ten of the 480W full black X10s is 4.8kWp for £950 of panels, so the modules are roughly 12% of what you pay. At £123.20 each the same ten panels are £1,232, or 16%. Scaffolding, labour, the inverter, the mounting system and the installer's margin are the rest. Our guide to UK solar panel costs breaks the other 84% down line by line.

The 30 year warranty is two warranties, and only one of them is 30 years

LONGi's Limited Warranty for Hi-MO X10 Solar Modules, dated April 2026 and downloaded from LONGi's own European warranty page on 3 October 2026, gives a 30 year performance warranty and a 15 year product warranty. The datasheet prints it plainly for anyone who looks: the LR7-54HVH page on eu.longi.com carries a spec block reading "15 Y Product Warranty" next to "30 Y Performance Warranty", under a badge that just says "30 Year Warranty".

The two clauses promise different things:

• The product warranty covers the panel and its cables being "free of defects in material or workmanship". That is the one that pays out if a panel delaminates, cracks or fails. On the X10, it runs 15 years.
• The performance warranty only promises output. For the X10: at least 99% of nameplate power at the end of year one, then no more than 0.35% decline a year, reaching at least 88.85% at the end of year 30.

So from year 16 to year 30 you hold a guarantee that the panel still makes 89% of its rated power, and no guarantee at all that it has not physically failed. That is not unusual, and it is not a criticism of LONGi. It is the structure of nearly every module warranty in the market, and it is why a brochure's single headline number is close to meaningless. The same split, with different years, shows up on the Aiko panels you may have been quoted as the alternative.

It also means the three generations are not interchangeable. Reading all three Limited Warranty documents on LONGi's European warranty page the same morning:

Read the Hi-MO 7 and Hi-MO 9 rows against the top one. A Hi-MO 7 panel carries a 12 year product warranty and guarantees 87.4% of its power at year 30. A Hi-MO 9 carries the same 12 year product warranty and 88.85% at year 30. The X10 adds three years of product cover (15) at the same 88.85% output floor. All are sold as LONGi, and on the price table above the Hi-MO 7 is the cheapest panel per watt by a wide margin. That is what the extra money buys, and it is a reasonable thing to buy. It is not reasonable to be sold it without being told.

On the Hi-MO X6, the word after the model code changes the term

The X6 warranty document splits its model list in two, and often the only thing separating them is the series name printed after the code. LR5-54HTH Scientist gets 25 years of product warranty. LR5-54HTH Explorer, the identical code, gets 15. Most Scientist and Artist variants sit in the 25 year table and every Explorer and Guardian variant sits in the 15 year table, but the 72-cell LR5-72HTH and LR7-72HTH Scientist and the LR8-66HTD Scientist are 15 years too. Check the exact code.

Midsummer's listing for the Hi-MO X6 HTH 540W is a clean example of a distributor getting this right. Its spec table reads "Product warranty 15 years" and "Warranty on output 25 years", which is exactly what the X6 document says for an Explorer grade panel.

There is one more wrinkle worth a look if your quote names a dual glass X6. The X6 document gives a 30 year performance warranty, rather than 25, to six model codes: LR5-54HTD Explorer, LR5-54HTDB Artist and LR5-72HTD Explorer (86.9% at year 30), and LR8-66HTD Scientist, LR5-72HTDR Guardian and LR7-72HTDR Guardian (88.9% at year 30). Six codes out of more than thirty. If someone has told you your X6 array has a 30 year output guarantee, that is the list it has to appear on.

The full black panel on many UK quotes is in none of the three documents

LR7-54HVB, the all black monofacial X10 that UK distributors sell as the residential flagship, does not appear in LONGi's X10 warranty document, nor in the X6 one, nor in the Hi-MO 9 and Hi-MO 7 one. Checked by searching the model lists in all three PDFs on 3 October 2026. The X10 document names 14 codes: LR7-54HVH, LR7-54HVD, LR7-60HVH, LR7-60HVHL, LR7-60HVD, LR7-72HVH, LR7-72HVHF, LR7-72HVD, LR7-72HVDF, LR7-72HVDA, LR7-72HVDE, LR8-66HVD, LR8-66HVDF and LR8-66HVDE. HVB is not among them, and neither are HVBB, HJBB or HJD, the other full black and HIBC codes in the current range.

Meanwhile Midsummer's product page for the "Longi Hi-Mo X10 HVB 485W All Black Mono", model LR7-54HVB-485M, prints a spec table reading "Performance Warranty, Product Warranty, 30 years, 30 years". Thirty years of product warranty, for a code that is not in the 15 year table or any other table on LONGi's warranty page. The prose on the same page is more careful: "The Hi-MO X10 comes with a 30 year performance warranty."

There are innocent explanations. Warranty documents lag product launches, a distributor may hold a separate written undertaking, and the HVB may be covered by a revision not yet published to the public page. None of them help you in year 14. The fix takes one line in an email: please send me the LONGi warranty document that names the exact model code you are fitting, and confirm the product warranty term in years. If the answer arrives and your code is in it, you have what you need. If it does not, you have learned something useful before you paid.

When the warranty clock starts, and whose warranty it is

All three documents start the clock on the earlier of two dates: delivery to the Initial Customer, or six months after the panel left the factory. Verbatim, the warranty start date is "the date of delivery to the Initial Customer or 6 months after the modules are shipped out of the production plant, whichever is earlier".

Two consequences follow, and neither is obvious.

First, panels that have sat in a warehouse arrive with time already spent. A module shipped in March and fitted in November has burned six months of its term before it generated a kilowatt hour. On clearance or heavily discounted stock, ask for the shipment date in writing and treat the saving as a shorter warranty rather than a bargain. It is the same clause that bites on inverters, and our guide to UK solar inverters covers the equivalent trap on the other half of the system.

Second, the Initial Customer is not you. The documents define it as "the Buyer or Purchaser as identified in the Sales Contract for the purchase of the Solar Modules, regardless of whether they are the end-user of the modules or not", and name "the sole and exclusive beneficiary" as that buyer, "or the successor or assignee of the Buyer or Purchaser as confirmed by the Supplier in writing". The buyer under the sales contract is your distributor or your installer. You are a beneficiary only if LONGi has confirmed the assignment to you in writing, which in practice nobody arranges. The warranty is routed through your installer, which is another reason the question "will this firm still be trading in ten years" matters more than the brand on the panel.

Four clauses worth ten minutes before you sign

These are in all three documents, and each one changes what a claim is actually worth.

• You pay the labour. "Costs incurred due to dismantling, repacking, installation or reinstallation the module(s) and other related expenses shall be borne by the customer." LONGi compensates documented shipping on a valid claim. Getting a scaffold up and an electrician on your roof is yours. On a mid roof panel that can cost more than the panel.
• A replacement does not reset the clock. "Any repair or replacement of the affected module(s) shall not renew or extend the applicable warranty period." A panel replaced in year 13 of a 15 year product warranty carries two years, not fifteen.
• The cash remedy is depreciated. LONGi can choose to refund residual value instead of replacing, calculated as "current market price (price-per-watt) * nominal power * left-over service life / Limited Performance Warranty period". With panels at roughly 20p a watt and falling, a 485W panel failing at year 20 of a 30 year performance warranty computes to about a third of 485 times today's price per watt. Not the £123 you paid.
• Bifacial rear gain is not warranted. The performance warranty "only applies to the actual power output of the front-side of the modules". If you are quoted dual glass bifacial panels on the basis of extra output from reflected light, that extra is not part of the guarantee.

Are LONGi panels MCS certified?

LONGi modules are listed in the MCS Product Directory, and you should check your own model code rather than take anyone's word for it, including ours. Searching the directory's product data on 3 October 2026 returns LONGi Green Energy Technology Co., Ltd as manufacturer and BABT/TUV as certification body for the ranges a British homeowner is likely to be quoted: LR7-54HVH 460M to 500M under certificate BABT8771-56/00, LR7-54HVB and LR7-54HVBB under BABT8771-60/00 and BABT8771-64/00, LR5-54HTH 405M to 450M under BABT8771-33/00, LR5-66HTH 495M to 550M under BABT8771-41/00, and LR8-66HYD 625M to 670M under BABT8771-59/00.

Every one of those records shows a certification period ending on 1 August 2026, and that date is not a coincidence. MCS 005 Issue 4.0, the updated Solar PV Product Standard, became mandatory that day. MCS said so in its own announcement of 30 July 2026, re-read live on 3 October 2026: "the update to MCS 005 will mean a significant number of solar PV products will no longer be MCS certified from 1 August, which presents a risk to the wider supply chain." It added that "the withdrawal of these products is not due to any identified safety concerns with the products", and granted a six month grace period that "will apply from the date of certificate withdrawal on 1 August 2026 and will run until 1 February 2027", during which "MCS certified installers may use grace period products in MCS certified installations".

So the practical question on a quote today is not "is this brand certified" but "is the exact model you are fitting certified to Issue 4.0, or is it grace period stock". If your installation completes after 1 February 2027, that distinction decides whether you get an MCS certificate, and the MCS certificate is what your supplier asks for when you apply for Smart Export Guarantee payments.

Two honest notes on method, because the directory is easy to misread. Searching it for the word "LONGi" returns nothing useful: the search matches model numbers, not manufacturer names, so you have to type the code from your quote, such as LR7-54HVB-485M. And the directory's own "currently certified" flag came back the same for every panel we queried, including brands with certificates running to 2030, so that flag proves nothing either way. Read the certification dates on the listing, and ask your installer for the certificate.

What the efficiency actually buys you, measured on your own roof

The top X10 module is 24.74% efficient, and on a typical British roof that buys you about 3% less space rather than any extra electricity. Check the efficiency first: an LR7-54HVH-505M measures 1800mm by 1134mm, which is 2.0412 square metres, and 505 divided by 2,041 watts of sunlight landing on it is 24.74%. The 480W version of the same panel is 23.52%. Efficiency is not a separate feature, it is the wattage and the dimensions stated a second way.

Now the part that gets sold hardest and matters least. The MCS standard that governs the generation estimate on your quote, MIS 3002, calculates annual output as installed capacity in kWp multiplied by a location factor from a table, multiplied by a shade factor. Three inputs, and panel efficiency is not one of them. Two 4.8kWp systems have the same estimated output whether the panels are 20% efficient or 25% efficient. Efficiency decides how much kWp fits in your available square metres, nothing else.

Put real numbers on it. The 480W X10 full black needs 4.25 square metres per kWp. The 540W Hi-MO X6 needs 4.40. The newer, dearer, higher efficiency panel saves you 3.4% of your roof area, and costs 38% more per watt comparing Eco Wizard's X10 with Midsummer's X6 list price, and 78% more comparing the two at Midsummer alone. That trade is worth making on a small or awkward roof where the kWp you want genuinely will not fit. On a standard 1930s semi with a clear south facing slope, you are paying a premium for space you were not short of. Our guide to solar panel efficiency in the UK works through where the premium does pay.

For the output itself, use the location factor. MCS's irradiance dataset at 35 degrees and due south gives 984 kWh per kWp a year for London, 935 for Birmingham, 865 for Manchester, 833 for Glasgow and 1,130 for Brighton, the highest zone in the country. A 4.8kWp LONGi array on an unshaded Birmingham roof estimates at about 4,490 kWh a year, and the panel brand does not change that figure. How much electricity solar panels produce in the UK has the full zone table.

The rest of the datasheet, briefly

From the LR7-54HVH and LR7-54HVB datasheets on eu.longi.com, read on 3 October 2026. The 54 cell residential X10 is 1800 by 1134 by 30mm and weighs 21.6kg, which is a normal two person lift and a normal roof load. It is 108 half cells in a 6 by 18 layout behind single 3.2mm coated tempered glass in an anodised aluminium frame. Power tolerance is 0 to plus 3%, so the panel can only be over its label, never under. Temperature coefficient of power is minus 0.260% per degree, which is good and matters on the handful of genuinely hot British afternoons. Front load rating is 5400Pa, rear 2400Pa, hail resistance 40mm stones at 27.54 metres a second, operating range minus 40 to plus 85 degrees, maximum system voltage 1500V DC, protection class II, IP68 junction box.

One specification to check against your own quote: both 54 cell X10 datasheets state a fire rating of IEC Class C. Midsummer's page for the larger X10 HVD 530W dual glass says that model "achieves a fire rating class A test report". Fire classification varies by construction within the same product family, so if a fire rating has been used to sell you the panels, ask which rating applies to the exact model on the quote.

The back contact design is a real engineering advantage rather than marketing. Moving the contacts to the rear removes the busbars from the front of the cell, which is why these panels look uniformly black, and LONGi's claim for the X10 is that it keeps 70% of output when shaded and runs up to 60 degrees cooler under shade than a conventional module. If shading is your actual problem, read that claim alongside solar panel optimisers, because panel level electronics and shade tolerant cells solve overlapping parts of the same problem and you rarely need to pay for both.

So should you accept the LONGi quote?

Yes, on the hardware. LONGi panels are mainstream, well made, properly certified and competitively priced, and a Hi-MO X10 is among the best modules you can put on a British roof. The caution is not about the panel. It is about four numbers on the paperwork that the brand name hides.

Ask for these before you sign anything, in writing, and the quote stops being a leap of faith:

1. The exact model code, not "LONGi 480W". LR7-54HVB-485M. The code is what the warranty document, the MCS listing and the datasheet are all keyed on, and nothing can be checked without it.
2. The LONGi warranty document that names that code, and the product warranty term in years. If the code is not in the document, say so and ask again.
3. The MCS certification status of that model, and whether it is certified to MCS 005 Issue 4.0 or sitting in the grace period that closes on 1 February 2027.
4. Whether the price is supply and install at 0% VAT, or a box price plus labour. Zero rate VAT on energy saving materials runs to 31 March 2027 and then goes to 5%, not 20%, and it applies to the installation rather than to panels you buy yourself. Our page on VAT on solar panels explains who qualifies.

And one piece of arithmetic to do yourself. Take the per watt price in the table above, multiply by the array size you have been quoted, and compare it with the total. If the panels are 12% of the bill, the brand on them was never the expensive decision. The installer was. For the wider comparison, choosing solar panels in the UK puts LONGi next to the other brands on British quotes.

Frequently asked questions