Solar PV Knowledge Bank

Best Solar Panels

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Spirit’s solar panels

We are independent installers of solar panels; we’re not tied to any individual panel manufacturer. We have therefore chosen a range of manufacturers to work with, based on the quality of their product, their warranties and the support that they provide. We are therefore in a position to recommend the best solar panels for your project and source them at a very competitive price.

Choosing the best solar panels for your project

Overall, we believe the best solar panels on the market are made by SunPower. They are superior in efficiency, lifetime output, and aesthetics. They also have a fantastic 25 year warranty covering product defects, performance and the service costs of changing a panel.

LG is similar in efficiency to SunPower and also offers a 25 year warranty.

Another leading name is Panasonic (previously Sanyo), which like SunPower, utilises a different technology with a much higher efficiency (see below). With the exception of these panels, most solar panels are assembled from solar cells made in a relatively small number of factories in Asia, and, in our view, one panel is pretty much like another. Indeed, even many of the German panels are made from cells made in China and ‘packaged and branded’ in Germany. Thus while your warranty will be with a German company, the German product is pretty much identical to its Chinese counterpart, but more expensive.

Since many of the Chinese suppliers have a global presence, and re-insure their warranties with German insurance companies, you may as well buy Chinese solar panels if you are not going for the very high efficiency ones. As the technology is advancing so rapidly, the 'best' makes and models are constantly in shift so it's a case of assessing each project individually and recommending the best currently available panels at the best price. 

Which solar panel?

In general there are five main considerations in choosing a panel:

  1. Efficiency measured in watts per square metre.

  2. Cost per watt.

  3. Performance warranty and degradation.

  4. Strength of the manufacturer – will they be around to honour the warranty?

  5. Colour and size.

In the table below we have summarised some of these factors by different types of cell technology.

Panel type Module efficiency (W/m2) Relative cost Typical performance guarantee Typical product guarantee Typical colour 
HIT (heterojunction with intrinsic thin layer) 190 - 200 High 10 years: 90% 25 years: 80% 25 years Black cell with silver frame
Monocrystalline with integrated back contact 205 - 215 High 5 years: 95%    25 years: 87% 25 years Dark blue cell with black frame
Monocrystalline 170 - 210 Medium-High 10 years: 90% 25 years: 80% 10 years Black cell with silver/black frame
Polycrystalline 165 - 170 Low 10 year: 90%   25 years: 80% 10 years Blue cell with silver/black frame

The key considerations in choosing a panel are as follows:

1. Efficiency, measured in watts per square metre (W/m2)

In other words, how much space do you need to get a given level of output?

As you can see from the table, HIT & monocrystalline panels are the most efficient on average. However, there are also some very high efficiency pure monocrystalline panels available.

They use a different patented technology, which gives approximately 20% more power per square metre than the bulk of the solar panels on the market. From the table you can see that this technology yields around 200 W/m2 compared to around 165 W/m2 for standard polycrystalline panels. The downside is that they currently cost around 50% more per watt – so for a 4 kWp system you will pay around £750 more if you choose mono/hybrid panels.

If you are wondering whether to buy high efficiency or not, ask yourself what you are trying to maximise: the total power you can squeeze out of your roof or your financial return? If your objective is simply to maximise the power output from your available roof space without regard to budget, especially if your roof space is limited, then you should choose high efficiency panels. Otherwise we would recommend focusing on financial return and aesthetics as the primary factors to focus on. To compare financial return you need to estimate the performance of the panels over their life, in the field. One important point is that mono/hybrid panels (e.g. SunPower) tend to have a lower degradation level implicit in their warranty - roughly 0.6% per year compared to the standard 0.9% per year (see point 3 below).

For more information on the most efficient solar panels, see below.

2. What is the cost?

The Chinese panels are generally the least expensive and offer the best value, combining good efficiency and a strong warranty with insurance backing, so if cost is the primary concern then this is the recommended route. An exception to this rule is that if the installation costs are high e.g. complicated roof, then it may be more cost-effective overall to use higher efficiency panels as it will minimise the other costs.

As all of our systems are bespoke designed, we are able to advise on, and fit, almost any panel that is commercially available. If you are looking for a panel from a specific manufacturer please ask as we can probably source it for you. And if you want a comparative quote between two systems, all you have to do is ask…

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3. Performance degradation and performance warranty

The performance of solar panels is expected to decline over their 25 year life. The standard performance warranty guarantees that a panel will produce at least 80% of its initial output after 25 years and at least 90% of its initial output after 10 years.

Some manufacturers do slightly better than this, by offering a ‘linear guarantee’; the effect of which is that the 90% guarantee is made at 12 years rather than 10, and the final guarantee is about 81% after 25 years.

SunPower and LG have the best warranties on the market. First of all they guarantee that you will receive 90%+ after 25 years, rather than 80%, with linear degradation over the life. This leads to about a 12% output increase over the life (not 12% a year, 12% over 25 years). Also SunPower guarantees to cover the cost of actually getting the panels off the roof, rather than just replacing them. The fact that it offers this with confidence over 25 years is testament to how little can go wrong with a solar panel!

4. Strength of manufacturer

In the unlikely event that it will need to be called upon, do you feel comfortable that the 25 year guarantee will be upheld by the manufacturer? There are many solar panel manufacturers and there is generally an over supply of solar panels across the global market. Some of the players may not be around to honour their warranties in the long term and it is therefore worth giving thought to who the stronger players are. It is also worth choosing a manufacturer offering insurance of their warranty. We feel comfortable with all of the manufacturers whose panels we supply but the only thing that we can guarantee about the next 25 years is that the sun will rise in the morning!

5. Colour and size

Finally, although the vast majority of panels are virtually identical in size, the dimensions of some solar panels may work better on your roof than others. Also, you may have a preference for the colour of the cells (essentially blue or black) and the frame & visible backsheet (silver or black).

The most efficient solar panels

We are often asked for the most efficient solar panels on the market. Not only do high performance solar panels tend to be superior in quality with superior warranties, they also achieve a greater output per square meter.

The solar cells that make up a solar panel are ultimately confined to a physical limit in the efficiency that they can convert sunlight into electricity. This limit, as applies to the single p-n junction silicon cells found in commercial panels, is approximately 32% (equivalent to 320 W/m2 as standard test condition is 1000 W/m2).

In reality, achieving this level of efficiency in a solar panel is not possible due to losses associated with practical issues such as reflection off the front surface and light blockage from the metallic top contacts. Consequently, the standard efficiency for commercially available panels comes in at around 16-17%. There are some manufacturers who do a little better than this, however. Here is our list of the most efficient solar panels on the market:

  • Top of the list for high efficiency solar panels is SunPower, the long-time global PV leader based in Silicon Valley. SunPower produces a range of residential solar panels with efficiencies exceeding 20%. Its most efficient panel, the 360 Wp X22 series, has an average panel efficiency of 22.2%, making it the most efficient commercially available panel there is.
  • Best of the rest status belongs to the consumer electronics giant, LG. LG's NeON® R series of panels range in power up to 365 Wp with a top efficiency of 21.1% (these panels are larger than those of SunPower). 
  • Finally, the last worthy mention goes to Panasonic, whose innovative heterojunction cell technology once dominated the high efficiency solar panel market. Their new HIT N330 panel still comes in at a very respectable 19.7% efficiency.

More information is given on our page dedicated to high efficiency solar panels.

What are Tier 1 panels?

You may have heard of 'Tier 1' panels. Indeed many projects specify that Tier 1 panels must be used. In case you are wondering what Tier 1 means, here is a quick explanation...

As a means to introduce some form of differentiation between the many solar module manufacturers on the market, Bloomberg New Energy Finance developed a tiering system that reflects the 'bankability' of manufacturers. Bloomberg determines this criterion based on their database of past photovoltaic projects (over 1.5 MW) financed by banks. The tiering is reviewed every quarter as new information is added to the database.

Bloomberg defines Tier 1 module manufacturers as "those which have provided own-brand, own-manufacture products to six different projects, which have been financed non-recourse by six different (nondevelopment) banks, in the past two years". Bloomberg does not publish a Tier 2 or 3 list.

It is important to note that the classification is purely a measure of industry acceptance, and is not a guarantee of product quality or financial stability. As such, we do not limit our offering to Tier 1 panels exclusively; however, we only quote for products from reputable manufacturers and that suit the requirements of each individual project.

Bifacial solar panels

A technology on the rise - bifacial or double-sided solar panels expose cells on the front and back of the panels to capture reflected light. While this isn't practical when mounted flush against a roof, this can lead to increased output on flat roof and ground-mount installations. Find out more in our bifacial solar guide.

Black solar panels

Many of our customers ask for black solar panels, to the extent that we think black solar panels deserve a paragraph of their own.

In the absence of an economical alternative to standard frame panels (e.g. solar tiles/slates), we believe that the most cost-effective aesthetic choice available to customers is an 'all-black' panel installed in-roof. All-black panels use black monocrystalline cells and have a black frame and back-sheet, giving them a neater finish. They contrast particularly well with dark slate and concrete tile roofs.

Our favourite black solar panels for in-roof applications are those of JA Solar and Viridian Solar (below).

Viridian panels

Installing panels in-roof, however, is only really suitable for new builds or properties undergoing roof refurbishment. So when it comes to on-roof installations, our favourite black solar panels in terms of looks are probably LG's Cello modules. By replacing the conventional three busbars running over each solar cell with twelve thinner wires, these LG panels achieve an improved look that appears completely black at a distance.lg neon 2 black

Learn more in our blog post on black solar panels.