Photovoltaic Systems Explained

It is not surprising that many people do not realise there is more to a photovoltaic system than just the solar panels. Whilst the PV panels are the main component of a PV system and the most visible because they tend to be roof mounted there are more components involved in creating fully functional PV systems.

So let's take a look at a typical UK photovoltaic setup for a residential building. This system is grid tied which means that it is connected to the national grid in order to export excess electricity generated back to the grid. You can get stand alone systems that are usually connected to lead acid batteries in order to charge them and use the electricity later, such as at night. We are only going to look at a grid tied system because this is the option most people will have with their installation.

Tip: You can claim the governments feed-in tariff (that's the solar panel grants they offer) for both grid tied and off grid photovoltaic systems.

Components Of A Grid-Tie PV System

If like most people who are installing a solar PV system are going to be paying a solar installation company to do the work then it is not that important that you are familiar with the ins and outs of a typical system. However it is useful to know where your money is going and what it is being spent on.

Photovoltaic Solar Panels

The photovoltaic solar panels are generally the most expensive component in your system. These are the panels you see on the roofs of houses and are the things that actually turn light into electricity. There are many different types of panel that range in size, power output and efficiency. The type commonly used in the UK and indeed around the world is Crystalline Silicon (c-Si) based.

Your chosen installer will usually have a preferred panel that they use based on cost, performance and experience with using that specific make and model. Depending on the size of your installation there may be as few as 5 or 6 panels or over 20 panels in the array.

The size and therefore number of panels will usually be limited by the size of your roof, more specifically the south facing aspect of your roof. If you happen to have a large roof you may be able to have an array of panels that generate under 4kW.

Generally you will need to use all the same make and model of panels that have the same power output. You will also need to have the panels all on the same part of the roof rather than having some on one part such as an east facing roof and the rest on the main south facing area. It is possible to mix and match technologies with the right equipment but as a rule they will all be the same.

PV Roof Mounting Kit

You will need a way to connect the panels to the roof and this is done with a solar roof mounting kit. There are a few different types of PV mounting system but you will generally tend to see on-roof solar mounting systems being used that allow the panels to sit above the tiles. A few tiles will need to be removed whilst installing the mounting system to your roof but the installers will make the roof weatherproof afterwards.

DC Isolator

A DC Isolator is needed between the connection to the array and the inverter. Essentially it is just a switch that enables the connection from the panels to the inverter to be isolated. There are various types to handle different amp ratings but you should expect this component to account for a tiny fraction of the overall cost.

Inverter

Grid tie inverters are usually the second most expensive component of a solar photovoltaic system after the panels themselves. The inverter accepts the direct current (DC) generated by the solar panels and converts it to an alternating current (AC) that can utilised within the home or exported back to the grid.

Inverters generally work up to a maximum wattage and have a specific efficiency. The inverters that can handle a higher wattage are more expensive. In the process of converting DC to AC some of the electrical power is lost. Some inverters are more efficient than other and can convert more of the energy into useable electricity. Efficiency ratings tend to be in the 95 percent plus range.

AC Isolator

An AC isolator switch is also needed for the same reason as the previously mentioned DC isolator. The AC version sits between the grid tie inverter and the rest of the AC side of the system.

Generation Meter

An Ofgem approved generation meter will be needed to measure the amount of electricity you use and export back to the grid. Meters can be purchased from about twenty UK pounds.

What Makes Up The Cost Of A Photovoltaic System?

At least half of the cost of photovoltaic systems is taken up by the panels themselves. You can find out more about how much photovoltaic solar panels cost and what sort of price you can expect to pay. The larger the array the greater the percentage of the cost the panels will make up. This in fact is a good thing as larger systems are more cost effective as the extra cost of labour and scaffolding becomes less of a significant factor.

The next significant slice of the cost is the labour and scaffolding. You will need an MCS certified installer to install your solar system so that it can be registered to claim the feed-in tariff payments currently being offered through a government scheme.

After labour costs the inverter is the most expensive part of the system with costs usually between one and two thousand pounds. This is followed by the mounting kit, the rest of the components make up only a fraction of the overall cost.