Buying Guide

The Future Is Electric

It is now quite possible to become almost entirely self-sufficient in your energy requirements. Up until recently, solar panels have not been a good investment as the returns could not cover the installation cost. Now, with the introduction of tax-free, inflation-linked government incentives, solar panels have become an excellent investment opportunity.

The Sunday Times listed solar panels as one of their top 5 investments last year. With the continued economic downturn, government sponsored feed-in-tariffs and with energy price inflation running into double digits, producing your own power is looking more and more attractive.

Solar Panels

Panel Types

There are 4 ways that commercial solar panels can be manufactured.

1. Monocrystalline

These are the most common and are made from silicon wafers cut from a single crystal, hence the name. They are more expensive than polycrstalline panels but they produce more power and tend to maintain outoput over the years better than polycrystalline panels

2. Polycrystalline

As the name suggests these panels are made up of silicon wafers pressed from crystal fragments. They are cheap to manufacture but do not have the same life expectancy or power output as monocrystalline panels, although production techniques are improving so it is possibl;e that they may be worthwhile in teh future.t

3. Thin Film

This is a technique where a compound is coated on a base (usually glass). They have long life but the power output is not great. They are however cheap so if space is not a problem then they might be worth considering.

4. Hybrid

One panel in particular, the Panasonic, produces considerably more power, because these panels combine two types of technology. They use the usual solar cells built from silicon wafers and combine these with a thin film of sunlight reactive material that produces extra electrical output.

Panel Efficiency

The efficiency of solar panels is a measure of how compact they are and has nothing to do with the power they produce or their electrical efficiency. The efficiency figure tells you how much power is output per square meter, so more ‘efficient’ panels use less roof space.

If you do not have enough roof space for a full 4kW system and you want to maximise the power output, a more ’efficient’ panel will on average allow you to install more wattage. However, all panels are different shapes and sizes and one panel may fit more on your roof than another and be a better choice. Only a proper survey will be able to identify the best configuration.

Temperature Coefficient

Other factors affecting how much power a panel produces is the temperature coefficient. This measures  how the power output reduces as the panel gets hotter.  The power rating of a panel is calculated at a temperature of 25 degrees  and for every degree hotter than this the power output drops by the temperature coefficient which ranges from 0.3% (best) for Panasonic to 0.38% (worst) for SunPower.

Power Tolerance

Another factor is power tolerance which is a % figure showing how the stated power output can vary.  Usually this is around 3% so a 100W panel would be in the range 97% - 103%.  This can have a considerable effect as the total power output is only as good as the weakest link the chain.  One poorer performing panel in a string of panels reduces the total power output.  This is built in to the government SAP calculations.
Some are worse than others, notably the Panasonic panels have a greater variability (+10%/-5%).  If you are lucky you get a really good performing array, on the down side there is a chance that a poor panel could bring the whole array down by up to 5%.


Generally, most panels perform in a very similar way and the only real gauge is how they perform once installed. We look carefully at published real data and would recommend the HJ Solar or Yingli  panels for performance and cost effectiveness.  If you want the best performance then Panasonic is still the only choice.  Sharp and Schott are average but not as cost effective as HJ and Upsolar.  SunPower are fairly average performance and overpriced, though if space is tight worth considering. 


Grid Tie Inverters

Grid Tie Inverters

The inverter usually lives in your loft and is responsible for converting the DC electrical power from the panels into a usable domestic AC supply.


Unlike panels the efficiency of the inverter is important for power output. The higher the efficiency then the less power is wasted in the conversion process. This efficiency is measured as a percentage with the best invereters now over 98% efficient and the worst around 92% efficient. Be careful, there are often 2 figures mentioned. Maximum efficiency is often quoted but is rarely achieved, a more realistic figure is give by the Euro Efficiency measurement which calculets the performance in a more real world way.

Life Span

Inverters will need replacing. Panels can go on for a long tiome, early manufactured panels, made about 40 years ago are still running but with a recued output (about 2 thirds). Inverters however don't really degarde they suddenly fail. As many of those on sale have not had the test of time their comparative reliability is not known. Lifetimes are expected to be around the 12-15 year mark,. so their will be a replacement cost at some point but it should be sub £400 for most domestic installations by then.

Well Known Manufacturers




Solar Mounting Systems

Mounting Systems

Mostly manufactured from aluminium and zinc alloys this part of your installation will be tough and long lasting. They will probably still be stuck together long after the building beneath them has disintegrated. Once the panels active life is over, you will probably be able to replace the panels using the existing mounting system. If not, you will have to remove the mountings and dispose of them. They should have good recyclable value.


The three manufacturers below are the biggest and probably the most expensive. They are excellent quality though there are many alternatives, all probably just as good for the purposes of mounting solar arrays.


Schuco logo

Altec Lansing


Solar Installers

To qualify for the Feed-In-Tariff installers must be registered under the Microgeneration Certification Scheme (MCS) that carries detailed guidelines about the quality and specifications of any installation. The UK government also used the opportunity of this regulation to ensure that installers operated under strict insurance, health and safety and fair trading standards.


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Panel Information


Until recently, Panasonic (formerly Sanyo) was the ferrari of the solar panel world but under challenge from the innovations of the Chinese manufacturers like Yingli.

Technical Brochure


HJ Solar are solid workhorse panels with good performance even under lower light conditions, so well suited to the British climate. Best value until price drops from Yingli in recent months. Very competitive.

DataSheet 250W Panels


Yingli Solar Logo

Yingli is the only manufacturer that produces every component in-house from silicon wafers to the finished solar panels. Very efficient panels with the most recent production reaching over 20% efficiency for the first time.

Company Profile


Yingli Solar Logo

Jetion are similar to HJ Solar but performance very slighly under from our experience in UK conditions and marginally more expensive, although they are not as quick as HJ Solar to adjust prices they intend to stay competitive.

DataSheet 250W Panels


Yingli Solar Logo

Good performance and until the start of 2012 a compact panel but now looking a little overpriced under the wave of new competition.

DataSheet 250W Panels