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FAQs – Solar PV

How do solar PV panels work?

Must solar panels face due south?

Are all solar PV panels the same?

What are the components of a solar PV system?

What is the life expectancy of a solar PV system?

Can I use solar PV to power my home?

Feed in Tariffs have been reduced – how can I maximise the benefit of my investment in solar PV?

Can I use Solar PV to power my business?

We are building a new home – can we install our PV panels and use the free electricity during its construction?

Do I need planning consent to install solar PV.

How will I know how much electricity my panels will produce and what savings I will make?

Is there any limit to the size of a solar PV installation?

How do solar PV panels work?

Each solar PV panel is made up of one or two layers of semi-conducting materially, usually silicon, in a “cell”. When exposed to light, the cell releases a small amount of electricity. By combining several cells into a “panel” and a number of panels into an “array” enough electricity can be gathered to be useful to either power your home or business, or sold to the national grid.

Must solar panels face due south?

Solar PV panels need direct sunlight to generate electricity so a southerly aspect is ideal. Arrays facing to the east and west will also generate electricity for the times of day that they face the path of the sun.

For similar reasons an array should be positioned so that no overhanging structures or vegetation shade the panels.

Are all solar PV panels the same?

 No, solar PV panels come in a variety of forms.

There are two main types of solar cell which differ in the arrangement and number of silicon crystals. Polycrystalline panels are made from wafers created by cutting thin strips from a solid block of silicon. These are relatively cheap to manufacture and historically have had lower efficiencies than other panel types however technology has improved to increase it so to be nearly in line with other panel types. Polycrystalline panels usually have a blueish tint.

Monocrystalline cells are usually black and have a single silicon crystal. They are efficient and perform better in low light conditions than polycrystalline panels.

What are the components of a solar PV system?

A complete solar PV installation will usually comprise several solar panels to form an array, an inverter to convert the DC electricity generated by the panels in to usable AC electricity and a generation meter to tell you how much electricity the system has created.

Inverters come in a variety of forms depending on the size of installation and where the array is located.

  • A “string” inverter will convert the energy from multiple solar PV panels which are connected in line. The disadvantage of a string inverter is that if a single panel is partially shaded it will restrict the amount of electricity the entire array will produce.
  • An alternative to a string inverter is to opt for a system using “micro-inverters”. These are just small inverters with a separate one, commonly integrated, for each panel in the array. This allows every panel in an array to generate independently of the other panels making them ideal for situations where there may be partial shading.
  • “Solar optimisers” are similar to micro inverters in that one is required for each panel however these control the flow of the DC current from each panel to a single inverter that acts for all the panels in the array. As with micro-inverters, they offer higher system efficacies than by means of a string inverter and are ideal for use where shading of the array could be an issue. An additional benefit of solar optimisers is that they can provide real time performance monitoring of every panel in an array.

What is the life expectancy of a solar PV system?

Solar PV panels come with two warranties, a Performance Warranty and a Product Warranty.

The Performance Warranty will detail the reduction of efficiency of the panel over a 20 or 25 year period. Commonly this is stated as a percentage figure that the panel is guaranteed to produce at given points in the life-time of the panel. Most quality panels will provide a guarantee that the performance will not drop below 80% of its original efficiency at the end of the given period.

Though the life expectancy of a solar PV panel is to be expected to be beyond 20 years, product warranties for the physical construction of a PV module are generally for 10 to 12 years.

The efficiency of string inverters reduces over time and have a life span from 10 to 15 years. This being shorter than that of the panels it will be necessary to replace a string inverter to maintain the overall output of an array.

As the loads passed through micro-inverters and solar optimisers is far lower than that of a string inverter, there is not as significant loss of efficiency over time and will have a life expectancy in line with that of the panels in the array.

Can I use solar PV to power my home?

Yes, all the electricity you generate is free and can be used to run your household appliances from light bulbs to the dish washer, a hair dryer to a heat pump! A typical 4kW domestic array with a southerly unshaded aspect in the north of England will generate around 3,500kWh of free electricity every year. The average UK home consumes around 4,000 to 4,500kWh of electricity so a PV array can make a significant contribution towards this.

It of course must be remembered that peak times for electricity consumption are the evening and winter months when the sun is not shining and the panels may not be generating as much electricity.

Any electricity you do not use through the Feed in Tariff scheme is sold back to the National Grid though this will not be as finically beneficial as if you use your self-generated free electricity. Small changes in routine such as using the dishwasher during the day rather than overnight will maximise the benefit of installing a solar PV system.

Feed in Tariffs have been reduced – how can I maximise the benefit of my investment in solar PV?

Though Feed in Tariffs have substantially fallen since their introduction in April 2010, there is still a good case for installing solar PV.

The simplest way of maximising your return is to use as much of your self-generated electricity as you can. As the Export Payment for most domestic installations is a “deemed” figure you do not forgo any loss in your FiT payments no matter how much self-generated free electricity you use!

Electricity prices have risen by around 66% since the introduction of the Feed in Tariff scheme 2010. As it continues to rise and you use your self-generated electricity the return on your solar PV array will only improve.

A simple and cost effective way is to add a “solar switch” to your solar PV system which will divert any self-generated electricity from your solar PV array to an immersion heater in your hot water tank. For a typical household, this will provide all domestic hot water from the middle of Spring to the middle of Autumn making a saving of around £100 against the cost of heating by a gas boiler.

Battery storage is now becoming a viable proposition for many to store their excess generated electricity rather than export it to the grid. The rising cost of electricity and a fall in the price of batteries due to improving technology brings ever closer the day when adding a battery to a solar PV installation makes absolute sense.

Fervo will be pleased to advise you on how best to maximise your returns.

Can I use Solar PV to power my business?

For businesses using large amounts of electricity solar PV can make a significant reduction to running costs as well as reducing carbon emissions. With options for mounting panels on all types of structures or mounting on land there are few instances where a solar PV array will not be of benefit.

We are building a new home – can we install our PV panels and use the free electricity during its construction?

Yes, you can but may not be advisable. Unfortunately, recent changes to the rules for registering for the Feed in Tariff have made this a complicated matter.

As part of your application to register for the Feed in Tariff you must provide your chosen Feed in Tariff licensee with an Energy Performance Certificate (EPC) for your home. The EPC assessment is only undertaken on completion of your project and should assume no solar PV system is installed. The EPC must therefore be dated before the commissioning date of the solar PV installation.

This means whilst the solar PV array can be installed as part of your building project it cannot be connected to your electricity supply until after your EPC has been issued, post completion of the build.

In practical terms for an “in-roof” array on a new build property, the panels will need to be installed as part of the main roof construction works with the inverter and generation meter capped off from the connection to the mains. Following issue of the EPC the connection to the mains can be made and the solar PV system commissioned.

If this procedure is not followed the array for the purposes of the Feed in Tariff will be classed as “second hand” and not eligible.

Fervo will be pleased to discuss how best a solar PV array can be incorporated into a new-build property and the timing issues for the installation.

Do I need planning consent to install solar PV.

In most domestic situations for roof mounted solar PV no planning consent is needed as it falls under Permitted Development rights. This is not the case for listed buildings or properties forming part of a scheduled monument. For properties in Conservation Areas or part of a World Heritage sites panels should not be installed to the highway frontage.

Planning permission is required for any ground mounted array except for small arrays (9m²) within the curtilage of a domestic property and 5m from a public highway.

Planning consent is required for solar PV installations to commercial properties.

How will I know how much electricity my panels will produce and what savings I will make?

Fervo undertake a detailed assessment of the location where a proposed array is to be installed noting alignment, aspect and any issues of shading that could impinge on the performance of an array. Using historic weather data, a calculation is prepared that will estimate how much electricity the array will produce over 12 months. A Performance Estimate will be provided detailing all of this and what financial benefits will arise from your proposed installation through the Feed in Tariff scheme.

Is there any limit to the size of a solar PV installation?

Apart from having the necessary space, no is the simple answer but there are matters to consider.

To install a solar PV array with an output over 3.68kW consent is required from the District Network Operator (DNO) who manage the local electricity infrastructure.

How much of the self-generated electricity you are going to use and how much you are likely to export is also a factor to bear in mind. If you are not going to use a great deal of the electricity generated by your solar panels the financial return may not be attractive. Fervo will discuss this with you and prepare a Performance Estimate outlining the likely financial benefits your proposed solar PV array will provide.

If you have any other questions regarding Solar PV or would like to discuss how you can incorporate Solar PV into your project, please contact us