Photovoltaic (PV) FAQs

Where can solar panels be installed?
Solar panels can be installed on the roof, on the side of a building, on the ground or on a pole. The most cost effective installation will usually be on a roof, but if shading or lack of space is an issue, then ground-mounted systems are an alternative.

Is my roof suitable?
Ideally, at this latitude in the UK, your roof would be oriented south and have a pitch of 35 degrees. However, it is possible to install solar systems onto many surface types (pitched and flat roofs, walls, gardens, pergolas etc) with orientations from west to east and pitches from 0 to 90 degrees with varying levels of efficiency loss.  It is important not to have too much differential shading on the panels; however, certain panel types and/or the use of multiple inverters/optimisers can overcome this issue.

How long does it take to install a PV system?
A typical residential roof installation can be completed in 1-2 days. The number of panels and type of installation will affect the installation process.

How does shade affect the performance of a PV solar system?
PV systems are composed of individual cells in a panel and each panel is connected in series to create a system. One of the leading causes of power loss in a solar PV system is when part of the panel or array becomes shaded. If any individual cell's performance is degraded by shade, the performance of the entire panel will fall to a point relative to the worst performing cell. Likewise, in a string of panels, the entire string suffers performance reduction to that of the lowest performing panel. Ideally, a solar installation should be designed in a way such that none of the panels are even partly shaded at any point of the day.  However if this cannot be achieved, here at Eco Hi Solar we use any one of several inverters, dual MPPT inverters or micro-inverters/optimisers to overcome this problem.

What are the different types of PV panel?
There are many types of panels, but the most common are: -

a) Mono-crystalline - these cells are single crystal silicon cells made from a polycrystalline starting material.  They have a higher efficiency, between 15-20% and can be round, semi-round or square cells, the latter being the most efficient.  They have an anti-reflective coating, which gives them the dark blue/black colour.

b) Polycrystalline – these are made from polycrystalline silicon and have a slightly lower efficiency between 13-16% with the anti-reflective coating. They are cheaper per watt than mono-crystalline panels. They are easy to spot because they have an uneven color, usually blue.

c) Thin film – these are made by depositing a thin layer of very finely powdered, high light-absorbing amorphous silicon, copper indium diselenide or cadmium telluride on a substrate. They have considerably reduced raw material consumption because the amount of semiconductor required is only a fraction of that required for crystalline panels.  The weight therefore is less and module sizes can be larger than for conventional panels. Despite their relatively low efficiency, the energy yield under certain conditions produces good output values at high operating temperatures and with more diffuse or low light, i.e. the decrease in performance at higher temperatures is less than with other technologies.

d) Hybrid cells : HIT solar cells - these cells are a combination of a crystalline and a thin-film solar cell.  HIT stands for heterojunction with intrinsic thin layer, and this refers to the structure of these cells. These are high performance cells and compared to crystalline cells they give a greater energy yield at higher temperatures and utilize a wider part of the light spectrum. When operating a PV system with HIT modules a 7-10% increase in annual yield has been shown, but this needs to be set against the cost of the system.

What are solar inverters?
A solar inverter is the link between the PV system and the AC mains system. Its task is to convert the solar DC electricity generated by the PV system into AC current, and to adjust this to the frequency and voltage of the building’s electrical system.

What is a grid-tied solar system?
Most PV systems in the UK are grid-tied systems, meaning that any electricity generated is fed into the mains system. Most homes in the UK operate a single-phase system where we are limited to delivering a maximum of 16A to the grid. In parctice we can install systems on single-phase properties well in excess of 4kWp using grid-limited inverters.  Larger systems (e.g. on farms or industrial units) can be up to 3 phase, where systems up to 12 KW and larger can be installed.

What is an off-grid solar system?
An off-grid solar energy system is where there is no connection to the National Grid. This type of installation requires a charge-controller, a bank of batteries and in most cases an inverter, so that electric power requirements can be met at night or during cloudy conditions if the system is not also grid-tied.

What are micro-inverters?
Micro-inverters convert DC current from a single solar panel into AC, in contrast to centralized inverters, which convert power from multiple solar panels. Duo inverters that connect to 2 solar panels are a recent innovation. The advantages of micro-inverters are several; they may be safer for the installer because they eliminate high voltage DC in the system and in instances where shading is an issue, individual inverters do not disproportionately reduce the output from the entire array. Access for future maintenance may, though, be awkward since the micro-inverters are located behind the PV modules.

What maintenance is required?
Solar PV needs little maintenance, as there are no moving parts. You will need to keep the panels relatively clean and make sure trees don't begin to overshadow them. The panels should last 25 years or more, but the inverter is likely to need replacing some time during this period, at a current cost of between £500 and £900.

Is Planning permission required?
In England and Scotland, changes to permitted developments rights for renewable technologies introduced on 6th April 2008 and 12th March 2009 respectively, have lifted the requirements for planning permission for most domestic microgeneration technologies.

Permitted developments: http://www.planningportal.gov.uk/planning/

Battery storage systems

The average home fitted with a solar PV system in the UK exports approximately 50% - 70% of its power to the grid. (Graph coutesy of PowerFlow):

Grid-coupled systems: a Lithium Iron battery stores excess solar energy which can be used at any time. The FIT is not affected. If there is a power cut the PV system can still charge the battery. Recommended for households consuming > 4000kWh per year which are typically unoccupied during the day. Multiple batteries can be installed.

 

Hybrid-systems (DC-coupled): the battery can either exist within the inverter or as a separate unit inline with your existing inverter. The excess solar energy is stored as DC. The inverter converts it back to AC. If there is a power cut you cannot access the energy in the battery.

Off-grid systems: here there is no grid connection. Solar energy is stored in batteries which is then used either directly by DC appliances or converted by an inverter for use in AC appliances. The FIT is not available for these systems.

Can I heat water with my PV system?

Yes. We can install a unit (e.g. Immersun or iBoost etc) which diverts excess solar generated energy, over and above that being used by the household aplliances, to the immersion heater in your hot water cylinder.