Renewables Series: Solar Photovoltaic Systems

06/Apr/2016
Ellie Parker

From wind turbines to solar panels, the UK’s interest in renewable energy sources is increasing and PV systems are fast on their way to becoming a mainstream source of electricity. Despite Government changes to limit the cost of spending on renewables, e.g. by reducing solar subsidies for homeowners and small businesses as of January 2016, the number of solar installations continues to grow. According to DECC, 'As of the end of February 2016, overall UK solar PV capacity stood at 9,213 MW across 867,876 installations. This is an increase of 62% (3,526 MW) compared to February 2015.’

But what is a PV system?

A solar PV or Photovoltaic system is a system whereby solar panels (or tiles) are installed to generate a useable energy supply for a residential property or commercial unit. Despite its increase in popularity amongst homeowners, PV systems still only account for a small percentage of the energy generated in the UK today, which could be due to a number of factors – the price of purchase and installation, the pay-back period, or even just the upheaval of having a new system installed. However, the UK is bound by an EU directive to produce 15% of its energy via renewable sources by 2020 so, in recent years, Government has introduced incentive schemes such as Feed-In Tariffs to increase interest in renewable technologies – although these tariffs have since been subject to cuts (as seen in the table below). 

So how do solar PV systems work?

A residential PV system converts sunlight into electrical energy via the photo-electric effect and comprises a number of components including: 

  • Solar panels (or a ‘PV array’, often building-mounted) or sometimes tiles
    Solar panels contain a number of semi-conducting cells, usually made from silicon, which convert solar energy from the sun into a flow of electrons and, therefore, an electric current.
  • Solar inverter
    An inverter converts the direct current (DC) output of a solar panel to alternating current (AC) which can be used to power the property, or can be sent back to the grid.  
The efficiency of a PV system is dependent on a number of variables including location, panel orientation and, of course, weather conditions. Take, for instance, the heat map below detailing the solar potential of the UK. As you can see, the further south you are, the higher the density of solar radiation which makes for a more efficient PV system. 

 

 

It is important as well to note that solar panels work best when facing due south to ensure they are exposed to the light for the longest period of time. Although it is not essential for panels to be oriented in this way (your roof may not be oriented as such), the efficiency of the system will obviously suffer if the panels are frequently left in the shade (e.g. if your property is surrounded by tall trees or buildings. Furthermore, as you might expect, changeable weather conditions in the UK can make it difficult to predict the energy output of a PV system; however, it has been argued that the high wind speeds in the UK can help to cool down a PV system, thus increasing its efficiency.   

 

Figures and trends

In 2012 it became mandatory for an Energy Performance Certificate (EPC) to be issued on or before the commission of a PV installation. This can be seen by the dramatic increase in PV systems recorded in 2012 (in the graph below). A recent study of EPCs undertaken by members of the NHER Accreditation Scheme shows that, after a dip in 2013, PV installations have increased in residential properties and only time will tell if this trend will continue into 2016.  

In addition, the graph shows a peak in 2015 with 3.6% of EPCs for residential properties recording the presence of a PV system; an increase that was likely driven by controversial Government plans to cut solar subsidies from January 2016. When these cuts were first proposed, many believed they would ‘kill off’ the renewables market, but current figures suggest that the industry is still very much alive. This comes despite a ‘pause’ to the Feed-In Tariff Scheme from 15th January – 7th February 2016. It is important to stress, however, that, as solar panels are becoming more popular, PV systems are coming down in price. For instance, a solar PV system that cost £10,000 in 2012 might only cost £5,000 today. 

To put this into perspective, we have put together a payback model showing you the payback period of a standard 4kW system installed on a south facing roof at a cost of £5,000 (this takes the new Feed-In Tariff rates into account): 

 

 

As you can see, the cost of the system is recouped in 9 years and 2 months – after this, the money brought in by the Feed-In Tariff is yours to keep and can go a long way towards your yearly bill. In this case, the net benefit in pounds over 20 years is £8,093. In addition to this extra income, it is important to remember that renewable systems like this are a great way of cutting your carbon footprint. In fact, over a 20 year period, this PV system saves 34 tonnes of carbon dioxide.   

 

 

What are the benefits of solar PV?

  • Environmentally friendly
    Solar PV systems provide a way of harvesting energy that is freely available, without producing harmful emissions. So, if you’re conscious of saving the planet, installing solar PV is a great way to cut your carbon footprint. 
  • Save money in the long term
    Solar panels can be expensive to buy and install; however, once you have paid off the initial set-up costs, it is possible to make great savings on your energy bills in the long term. 
  • Feed-In Tariffs (FITs)
    You could be eligible to take part in the UK government’s Feed-In Tariff scheme. The scheme pays you for the electricity you generate whether you use it yourself or export it back to the national grid. As of 14th January 2016, a new FIT scheme was put in place with lower tariffs. This came as a blow to both homeowners and installers; however, whilst the initiative still exists, an incentive remains (albeit a less attractive one).
Please click here for more information on Feed-In Tariffs, or click here to learn more about solar PV systems. 

Comments

 

1. Payback time should also consider savings made by substituting PV generate electricity for grid supply. This is conditional on using electricity during daytime when many people are at work. Increasing use of smart energy management systems will help get greater benefit from PV.
2. At present FiT assume that 25% of generation is put back into the grid. Devices exist that will detect when this happens and divert the surplus to an immersion heater in the domestic HWC until the stored water reaches a set temperature and only then expert the energy to the grid. This produces a saving on the energy (gas) used to heat DHW.
3. Shading - this problem can be partially solved by using an array with miniature inverters on each panel so that when shade only the output of the shaded panel is affected.

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