There are thousands of technologies out there, and quite often the best panel changes project by project. We use 6 key factors solar panels you should use to determine which panel is best for your project:

  • The application (where you’re putting the panels).
  • Rated efficiency and power.
  • Size.
  • Cost.
  • Warranty and degradation rates.
  • Manufacturer’s strength and reliability.

The application

The application of solar panels is perhaps the most important factor to consider. Are you looking at integrating it on to a building? If so, you may consider solar slate or in-roof technologies. Does it matter how it looks? You may want to look into Thin Film PV for building cladding. Are you looking to maximise power output? Potentially look into newer, monocrystalline PV.

We typically select the technology following a site visit and discussion with the owner. This lets us get an eye in for what technology is best, and lets us optimise the other factors.

Efficiency and power

Rated efficiency and power lets you know how much space your solar system will take up. For example, a single panel output could be anywhere from from 150 to 400 Watts, while all being roughly around the same size (1.5m x 1m). This means that a 4 kilowatt PV system would take up 15m² if using 400W panels, compared to a whopping 40m² if using 150W panels.

Roof-mounted solar
Ground mount solar

Rooftop solar ( left) is often made up of higher efficiency panels than solar farms (above), as space is more of an issue


Cost is key in choosing the right panel, and often ties in with the power output of the panel. The more you spend on your system for similar power outputs, the longer it will take to break even on the investment. On the flip-side, cost can show quality. Is it actually worth spending over £300 for the SunPower’s 400W panel? We find that usually it’s a balance for each system, and use modelling software to figure out the best panels for each project. From our experience, it’s generally not worth going really cheap on solar panels unless you’re looking at economising a very large system.

Warranty and Degradation

This is where warranty and panel degradation rates come in. Panels are almost always warrantied to 25 years for faults and rates of degradation. This is shown by ‘performance guarantee’ in panel tech specs, as a percentage of power rating available after a number of years. Higher quality panels will degrade to 90% of power output after 10 years and 80% after 25 years. So if the panel doesn’t meet this guarantee, you’ll be able to get a replacement from the manufacturer.

Manufacturers Strength

However, a warranty is meaningless if the manufacturer isn’t around – and 25 years is a long time, which is why the strength of the manufacturer is also important. To give a measure to this, Bloomberg have released a simple grading system which looks at the manufacturers financial stability. Solar panel manufacturers with a ‘Grade 1’ rating are considered not risky, and able to honour warranties. Unfortunately, being a Grade I manufacturer doesn’t always mean the panels are quality, so use with discretion.

We typically opt for panels made by Grade 1 manufacturers. because these are often the largest panel manufacturers, they have the most cost-effective offerings which can be the best value for money. That said, we do offer certain products from other manufacturers – particularly with building integrated PV and monocrystalline cells. To provide extra security, we often organise extra insurance for clients on these systems.

We’ve put together a quick table below to show how some common solar module technologies compare on these points.

Panel type
Module efficiency
Relative cost
Typical performance guarantee
Typical Warranty Length Notes
170-400 W/m^2
90% after 10 years; 80% after 25 years
25 years
Highest efficiency, premium cost. Often solar companies’ flagship panel.
170-250 W/m^2
90% after 10 years; 80% after 25 years25 years
Cheaper to manufacture than monocrystalline. Commonly used in projects where space is less of an issue
Amorphous (thin-film)
100-120 W/m^2
90% after 10 years; 80% after 25 years25 years
Extremely thin cells make for highly flexible modules, ideal for building facades.
200-400 W/m^2
90% after 10 years; 80% after 25 years25 years
Extremely thin cells make for highly flexible modules, ideal for building facades.