What is the Most Efficient Solar Panel?

One of the most common questions we are asked is “what is the most efficient solar panel?”  Here’s our guide to the best of the best.

More efficient photovoltaic systems produce more electricity from every square meter of roof space, so they are an attractive means of using space in the most efficient manner possible. Greater electricity production means more carbon savings, which is great for the planet. You’ll also have more electricity to do what you want with – whether that is using directly in the home,  storing the energy in a battery, or putting in to an electric vehicle.

High efficiency panels are a bit more expensive than conventional modules, as you might expect from a high-end product. However, there a number of good reasons why you might want to opt for the very best possible products, which we outline below.

High Efficiency Panels for Electric Vehicles

Choosing high efficiency panels over standard ones increases your generation from your available roof space.  For a typical home, this might increase your installed capacity from 3.5kW to 4 kW, in the same area.

It might not sound a lot, but that could be an extra 500kWh of electricity generated over the course of the year.  Put all that into an electric vehicle, and that’s 1500 miles of carbon-free travel.  Every year for 25 year lifetime of the system.

We’re experts at designing systems that allow you to capture this benefit – either through a smart EV charger such as the Zappi, or by integrating with a battery.

What do Joju Solar offer?

At Joju, we’re technology agnostic, so we’re happy to specify any solar panel you wish.  However, we are big fans of SunPower – their dominance of the above table is a clear demonstration of their quality.  We’ve been official Sunpower partners ever since they became available in the UK in 2011.

SunPower have made an all-back-contact cell, which mean that both the +ve and –ve electrical connections are on the rear of the cell. That means no collector wires on the front surface, which increases the area available for collecting the sun’s energy.  We also think it makes them look super neat, with a more uniform look to their front surface.

Another reason we like SunPower is due to their industry leading warranties. SunPower panels have a 40-year performance and product warranty. No other manufacturer comes close to offering the same security. You can see why SunPower are comfortable offering this – they are particularly robust and have a low failure rate. In fact, we have never had any performance issues with our SunPower modules.

As well as having the highest rated efficiencies, SunPower panels do very well in the real world. We have over 10 years of generation data from our SunPower installations so we can assess how they perform. Our Head of Engineering James Page has published the results of his study and found that as well as doing what they say on the tin – SunPower panels perform particularly well at low light levels. This means they perform well across the year, even in winter when the solar resource is lower.

Lastly, and it might seem like a minor point to some, but SunPower panels look really good. They have attractive black frames and the lack of wires on the front of their cells to give the panels a uniform and sleek appearance.

High Efficiency Modules for Commercial Buildings

Commercial properties tend to be less space limited than domestic properties, so there isn’t always the same need for high efficiency modules in this setting.

However, we are seeing customers choosing high efficiency modules for their commercial buildings, for the following reasons:

• CSR reporting is becoming ever more important, so generating as much renewable power as possible is helpful here.  The more electricity that is produced on site, the more your Scope 2 emissions can be reduced.
• The economics of solar power on commercial building is excellent, and installing high efficiency modules is a way of maximising your overall benefits, whilst still achieving a hurdle rate for investment.
• The long-term warranties available for products like Sunpower make them an attractive option from a risk perspective.

How we choose solar panels

Having outlined the different categories of PV panels, the question is how to choose the product to use.  This is easy – our experts select the best product in each category, so you don’t have to.  We do this by assessing across multiple criteria.

Brand value – In order to choose a trusted product, we choose from well-respected brands.  Most people purchasing solar panels wouldn’t recognise the names of the manufacturers, as they are not usually household names.  Fortunately, the research organisation company Bloomberg New Energy Finance analyse the market each year, and produce a list of high quality (so called Tier 1) modules.  They assess bankability – which brands of panels are used in (large scale solar) projects that banks are investing in.   If banks are willing to put their money at risk on a product, it’s a good measure of quality, as they will have done their due diligence.  Joju only use Tier 1 products.

Module testing – Industry trade magazine Photon International run a large test site monitoring the performance of different brands of solar panels.  We check the outdoor performance of our chosen modules so we know they perform well in real life.

Warranties – the length of warranty is also an important indicator of quality.  Most modules come with a 25-year product warranty (guarantee that the module won’t break), although some manufacturers such as Sunpower offer a 40 year product warranty.  On top of this, the modules come with a performance warranty, guaranteeing a certain percentage of output after 25 years.  Typically manufacturers guarantee that the module will be producing 80% of its nameplate efficiency after 25 years, although some manufacturers will offer higher values.  We also check that these warranties are insurance backed by European insurers.

Installer feedback – We rely on feedback from our installation teams about the product they are installing.  Historically, we have stopped installing some brands, as our installers felt they were too flimsy.

Ethics and sustainability – these are important considerations for us as a green business in choosing the products we offer.  We ensure all our modules are guaranteed conflict metals free.  We’ve also written about wider ethical and sustainability issues in more detail for Ethical Consumer magazine.

Efficiency – Efficiency is more important in choosing the category of solar panel (cheap solar panels vs. high efficiency panels), as within each class there is little variation between similar modules.  Cheap solar panels will give you the lowest system price, whereas high efficiency panels will maximise generation and income over the system lifetime.