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longi himo4 solar panel product photo

The Longi HiMo4 comes with a 12-year warranty (Image credit: Longi)

Longi Solar’s HiMo4 range of panels are some of the best solar panels available in the UK today. These solar panels are built using monocrystalline PERC half-cut cell technology – where the solar cells are cut in half, improving the solar module’s performance and durability. Along with several enhancements added, these panels can achieve up to 20.9% efficiency. 

Longi HiMo4’s solar panels are available in 60-cell, 66-cell and 72-cell formats, built on gallium-doped silicon, which reduces light-induced degradation and increases performance. 

The gallium-doped silicon solar panels are far superior to the regular P-type silicon modules often used by lower-end suppliers. The annual degradation of the Longi HiMo4 is 0.45%, whereas P-type solar panels will see annual degradation of 0.55%-07% per annum. This means that your Longi HiMo4 solar panels will only lose 11-13% of their power after 25 years, comparable to premium solar panels. 

The power rating for the Longi HiMo4 is impressive at 350W-380W – especially in this price range. It comes with a 12-year product warranty and a 25-year performance warranty. 

Overall, Longi performs much better than many other solar panels in the same price range and even competes with far more expensive models. The Longi HiMo4 offers good value for money and excellent performance. 

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Technical information

The Longi HiMo series utilises high-efficiency PERC cell technology in both half-cut cells and bifacial modules. The bifacial modules are the most popular in-ground mount for commercial installations. The HiMo 4-range modules are available in 60-cell, 66-cell and 72-cell formats, built on gallium-doped silicon in order to increase performance and reduce the degradation of cells from 0.7% to 0.45% per annum. This means that your Longi HiMo4 will only lose 11-13% power after 25 years, comparable to more expensive N-type solar panels. 

  • Range: 19.5%-21.0%
  • Efficiency: 350W-580W
  • Warranty: 12-year product warranty, 25-year performance warranty
  • Cost per panel: £100 – £165 

Key features

Highlights: Uses monocrystalline PERC gallium-doped silicon cells which are a good cost-effective alternative to more expensive N-cell solar panels. 

Key benefit: 84.8% remaining power after 25 years, comparable to more expensive panels.

Warranty: There is a 12-year product guarantee as well as a 25-year performance guarantee available. 

Cost: £100-£165 per panel, excluding the cost of installation and labour. 

Pros and cons

While the Longi HiMo4 isn’t the most expensive solar panel on the market, any investment in solar panels is quite significant for the average homeowner. It’s important to weigh the pros and cons carefully. 

The benefits of the Longi HiMo4 include:

  • Cost: Starting from as little as £107.40 per panel, Longi HiMo4 solar panels are very affordable, with good performance. 
  • Performance: Most solar panels priced at the lower end of the market guarantee about 80% power after 25 years, but Longi promises 84.8% power after 25 years. 
  • Reputation: Longi is a Bloomberg 1-rated company and a participant in China’s Top Runner Program (a government scheme with the goal of boosting solar panel efficiencies). As a stable and trusted brand, they’ll be around for a long time. 
  • Efficiency: With an efficiency of up to 20.9%, Longi is one of the most efficient lower-priced brands on the market. 

There are a few disadvantages to consider: 

  • Introduction of N-type: Longi is introducing a next-generation N-type solar panel, which may replace the HiMo4 range in the near future.
  • No UK office: Longi doesn’t have a local presence in the UK, which means that support is offloaded to third parties.

How the Longi HiMo4 solar panel works

longi smart soldering diagram

Longi uses smart soldering technology (Image credit: Longi)

Longi Solar, together with Shin-Etsu Chemical Co, started mass-producing new gallium-doped silicon cells in 2020 to combat the effects of light-induced degradation in P-type PERC silicon solar panels. 

This form of light-induced degradation causes a 2-3% loss of power within the first few hundred hours of operation as oxygen is left over from the manufacturing process. Over the remaining life of the panel, losses drop depending on the quality of the crystalline silicon. 

Many solar panel manufacturers use boron-doped P-type silicon wafers, which are less stable and more prone to light-induced degradation. Gallium-doped silicon reduces the damage significantly, retaining close to 85% of the original power rating after 25 years of use. 

Longi Solar also uses “smart soldering technology”, using a triangular shaped micro busbar flattened at both ends. This reduces the inter-cell gap, increases the surface area and boosts efficiency. 

The triangular segmented ribbon maximises the absorption of sunlight and boosts efficiency by 0.3%.

Longi HiMo4 add-ons

Longi doesn’t sell specific add-ons for the HiMo4, but several compatible add-ons can be purchased via your solar panel installer. Longi HiMo4’s standard solar kit comes with solar panels, micro inverters with monitoring tools and accessories, and racking materials. 

How does the Longi HiMo4 compare to other solar panels? 

Longi offers the HiMo3 panel, which is even more affordable than the HiMo4 model, but it’s much smaller and less powerful. It has a 10-year warranty and six busbars, as opposed to the eight busbars fitted to the HiMo4. The HiMo4 is larger, produces more power and comes with an additional two years in product warranty, which justifies paying a little bit more. 

The closest competitor to the Longi HiMo4 is Trina Solar. Trina Solar offers an 80.7% output in year 25 and a 10-year product guarantee, which is slightly lower than the Longi HiMo4 but not as favourable as the likes of Panasonic. 

Panasonic solar panels are pricier than Longi, but with a 90.76% output power in year 25 and an efficiency of 19.4%. Trina Solar’s 365W TSM-DE06X beats Panasonic with a 20.6% efficiency

You could also consider JA Solar’s JAM60S20 solar panels, which offer a great price but drop to 82% power after 25 years

The Longi range of solar panels (Image credit: Longi)

What does the Longi HiMo4 cost?

While the Longi HiMo4 is one of the most affordable solar panels on the market, its performance is on par with some of the more expensive modules in the UK.

NameOutputCost per panel
Trina Solar TSM-DE06X365WFrom £208
Longi HiMo4325WFrom £107.40
Panasonic HIT N 245W245WFrom £250

Maintaining the Longi HiMo4

The Longi HiMo4 doesn’t require a lot of maintenance. Regular rainfall should be more than adequate for keeping the solar panels clean. However, if you notice soiling or debris blocking the solar panels, you should rinse them from the ground with a regular garden hose. 

If you cannot reach the solar panels with a hose, you can wipe the surface with a soft sponge or cloth and water. Do not use soap or chemical cleaning agents, and take care when climbing on the roof. 

If performance doesn’t improve after cleaning, get in touch with a professional Longi technician. 

What the professionals say

“Longi Solar Panels are a great reliable option for a customer looking for an affordable mid-range panel from a company with a solid financial backing and reputation.”

“If you are considering Longi Solar panels, we recommend them, especially if you are looking for solar panels on a budget without sacrificing on efficiency. In addition to their value based price point, their modules are typically high-watt, which adds additional savings due to smaller bill of materials and installation costs.”

“Longi solar panels are tier one and so should be reliable, and I would not have a problem with installing them on my roof. They will also appeal to people who are interested in panels that should lose little in capacity over the years but don’t want the expense of purchasing premium panels. While many companies have run into financial difficulties after rapidly expanding, Longi’s financial position appears reasonably sound. While I don’t have any solid evidence, I suspect they will be around for a longi time. I can feel it in my gut. Specifically, my longi intestine.”

Customer reviews

“Having had no issues from the previous panels, and with good reviews of the Longi panels, I am confident that they will perform well.

LATER: After one year in service, the panels are performing well and generating up to their maximum.”

“Once again, only on a two-week sample, but so far, they are working great. My panels are facing north, and even at 8 pm at night, it produces 3kw. I will rate again at a later time.”

“Although I had wanted to use LG panels, they were not easily available through Ahlec Solar, although I have been reassured these Longi 370 watt models should more than satisfy our needs for many years to come. Panels are producing plenty of power, and combined output for September was an impressive 1.266 MWh with June and July only just dipping under 1 MWh.”

Our methodology 

While compiling this review, we consulted hundreds of customer reviews, professional write-ups and recommendations, technical papers, and media articles related to the Longi HiMo4 to form our opinion. We created a scoring system (totalling 100 points) to rate the Longi HiMo4 against. 

During our research, the total score was comprised of: 

  • The power rating of the solar panel for a total score of 10 points;
  • The efficiency of the solar panel for a total score of 15 points; 
  • The pricing of the solar panel per panel for a total score of 10 points;
  • The length of the warranty for a total score of 10 points;
  • The level of service and support for a total score of 5 points;
  • Durability of the solar panel for a total score of 15 points;
  • The design of the panel for a total score of 5 points;
  • The overall performance of the solar panel for a total score of 15; and
  • Online ratings and reviews for a total score of 15 points. 

More on solar panels

Read our guide to the best solar panels in the UK in 2022 or learn about how solar panels work. You can also find out if the economics add up for you in our guide which asks: are solar panels worth it?