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3 Solar
42. Energy from the sun has been harnessed for thousands of years. Scotland has one of the best conditions in Europe for making use of solar energy. This may seem surprising, as solar radiation levels are relatively lower than in other European countries. This is, however, offset by the fact that we heat our homes for more months of the year, allowing better utilisation of available solar energy overall. Solar energy can be utilised in several ways, including passive solar design, solar hot water systems and photo-voltaic cells ( PV), which generate electricity from solar radiation, this section will focus on the latter two as issues of sustainable layouts and making best use of resources can be found in other planning guidance, eg PAN 67 and PAN 68.
43. The amount of electricity that can be produced from solar panels will vary with the intensity of sunlight, the type of technology being used, and any overshadowing by trees or buildings. However, even on the cloudiest days energy comes from indirect sunlight, called diffuse solar radiation. On a cloudy day PV cells can produce up to 30% of the power output of a sunny day. However, there is still an inevitable mismatch between peak availability and peak demand of energy. This shortfall can be overcome by combining solar energy with a complementary technology such as wind which has a different seasonal pattern.
44. Both energy and carbon emissions savings can be made with solar technologies. The average domestic solar hot water system can reduce CO 2 emissions by 0.25-0.5 tonne per year, depending on the fuel replaced, and provide almost all of a home's hot water during the summer months.
45. Solar PV is currently one of the most expensive technologies, however, prices of solar power systems have steadily fallen over the past decade and are anticipated to continue to fall as the technology advances and economies of scale occur. Solar systems are therefore predicted to become a more familiar feature in the environment.
Existing Planning Controls
46. In some cases, providing that solar panels are not of an unusual design, or sited on a listed building, or in a designated area, they can be regarded as permitted development and thus do not require to seek planning permission. The GPDO Class 2 explains permitted development rights in relation to additions or alterations to dwellinghouse roofs. Class 23 of the GPDO will be relevant for industrial and warehouse developments.
Types of Systems
Solar Hot Water Systems
47. Solar hot water systems have been available in the UK since the 1970s and the technology is now well developed with a large choice of equipment to suit many applications. Solar hot water systems are mainly used for domestic water heating but can also be used in other settings such as light industrial, agricultural use and swimming pools. In the UK, an average household will reduce its annual energy consumption levels for providing hot water by approximately 50% after installing a solar hot water system.
48. Solar hot water systems work on the principle of water being pumped through the solar panel and heated by solar energy when the sun is shining. This heated water then usually flows through a heat exchanger, warming the stored water in the hot cylinder. In effect this serves to pre-heat the water so that less energy is required from traditional sources such as the boiler. The collectors are silent and generate no emissions.
49. The key component in a solar hot water system is the collector. There are two different types of solar collectors; flat plate systems and evacuated tube systems:
Flat Plate Collectors
These are the simplest and most common form of solar hot water heating panels. They are made from a sheet of metal painted black which absorbs the sun's energy. The metal sheet is embedded in an insulated box and covered with glass or clear plastic on the front.
Water is fed through the panel in pipes attached to the metal sheet and picks up the heat in the metal. These types of systems are sometimes described as having a similar appearance as a sky-light, although they tend to be larger than a typical skylight. Flat plate collectors can be positioned on roofs or walls.
Evacuated Tube Collectors
These are made of rows of parallel, transparent glass tubes. Inside each tube is a flat or curved metal plate, attached to a pipe.
They are generally more efficient because heat loss by convection is negligible compared to the flat plate collector system. They therefore tend to need less area, but can be more expensive.
Photo-Voltaic ( PV) 50.PV systems convert solar radiation into electricity. The greater the intensity of the light, the greater the flow of electricity. PV solar panels may vary in appearance, but they are generally dark in colour and have low reflective properties. They can also vary in size and are usually grouped together to form a PV array to meet the required output of electricity. A typical PV array on a dwellinghouse will cover an area of between 9-18m 2. They have no moving parts, generate no noise or emissions, and can be integrated into all types of buildings - houses, commercial and public buildings. |  |
Stand-alone
51. The issue of stand-alone or grid-connected systems is only relevant for PV systems which generate electricity. The use of PV for street lighting, parking meters, and road 'furniture' lighting is increasing as it reduces costs of mains connections and cabling. PV is also widely used to provide power for communications and monitoring systems in remote areas. Stand-alone systems will require associated equipment such as a battery to store energy during cloudy periods and an electronic controller to manage the energy from the array to the battery and the load.
Grid-connected
52. A PV array fitted on a building can be connected to the local electricity supply network and export any excess electricity produced to the grid, with the agreement of the network operator and an electricity supplier. Conversely, when demand is high extra electricity can be purchased from the grid through an electricity supply company. However as yet, most PV installations do not sell back to the grid. This may change as more systems are installed and seeking to sell to the grid and the combined input becomes a more attractive proposition to energy suppliers.
Building Integrated Systems and Building Attached (Retrofit)
53.PV solar panels can either be mounted on structures or free-standing, and come in a range of forms such as modules, laminates and solar tiles. PV solar panels or tile systems can be used in place of, or in addition to, traditional roof or façade materials. They can blend in with the built environment to minimise the aesthetic impact on the building. These types of products can serve a dual function: as building material and as a source of renewable energy. They may be installed on existing structures, although costs may be lower if they are integrated into the design of new structures.
Cost and Maintenance
54. Solar panels have proved to be very reliable and can have a design life of 25 years or more. Costs vary due to a range of factors such as size of collector, type of roof and geographic location. Solar panels generally require very little maintenance other than ensuring they are kept relatively clean, checking that shade from trees has not become a problem and where applicable inspecting the battery packs.
Siting and Design
55. Solar panels can be used on roofs, windows and walls. Roof panels are typically more economical for small systems, however, they can suffer from snow coverage in winter. Wall mounting is usually used where there are larger areas to cover, they can benefit from a boosted effect of snow reflection from the ground in winter, however, their positioning can be susceptible to shade.
Orientation
56. Most solar panels will be fixed in a position to provide maximum capture of solar radiation. Installers will calculate the best orientation but generally, in the UK, the panel should face roughly south, towards the sun, and at a tilt of between 30-50 degrees from
the horizontal. Solar panels can be used for a building with a roof or wall that faces within 90 degrees of south, as long as no other buildings or large trees overshadow it. Where a south facing roof is not available or if an installation is not acceptable due to its impact on the character of the building; stand-mounted solar panels may be put up in a more optimal location.
57. Whilst it will generally be preferable for solar panels to be mounted to the rear of the property, it must be recognised that applicants will seek to put them on south facing roofs
to maximise solar gain, regardless of whether this is a front or rear elevation. Solar panels can come in all different colours to suit the architectural design from contemporary
designs to those attempting to match traditional tiles or slates. In contemporary designs consideration can be given to emphasising the sustainable elements and matching other roof materials to the solar panels.
58. Another consideration is that the roof must also be strong enough to hold the weight of the panels, especially if the panel is going to be placed on top of existing roof coverings.
Overshadowing
59. If the surface of the solar panel is in shadow for parts of the day, the output of the system decreases. Shadows from buildings, trees or other structures can significantly reduce performance. However, building design and site conditions may help to optimise performance. Planners and developers should take reasonable steps to minimise overshadowing of the solar panels for example positioning to avoid the shadow of a chimney stack. Developers and planning authorities should also try to ensure that new buildings or extensions do not overshadow existing solar panels on neighbouring buildings.
Rooflines
60. Different roof designs may have more potential to conceal solar panels from view for example, valley roofs, double pitched roofs, roofs contained within parapets, low-pitched roofs not easily seen from the street, flat roofs and platformed roofs.
61. The visually acceptable levels of roof coverage will vary with the technology, for example solar tiles, which have a similar appearance to traditional roof coverings, may cover a large percentage of the roof, whereas conventional flat plate collectors that look similar to roof lights will generally need to cover a smaller percentage of the roof, particularly where they are installed in traditional tiled roofs. Wherever possible solar panels should be flush with the roof and mounted at the same angle as the roof to minimise contrast.
Natural Heritage
62. The key natural heritage issue will be the landscape impact. Solar panels are an appropriate development within natural heritage designations as long as the siting and design advice is followed. Further information about natural heritage can be found in NPPG14 and PAN 60.
Historic Environment
63. Installation of a solar panel on a listed building or on another building or structure in its curtilage is likely to require an application for listed building consent. This will be so, even if specific planning permission is unnecessary. A high level of design quality will be required on listed buildings, in conservation areas and on scheduled ancient monuments. Sensitive siting and design will also be required if an application is submitted for the installation of solar panels close to a listed building or scheduled ancient monument. Historic Scotland will provide advice on solar panels proposed for scheduled monuments. Advice on Listed Buildings and Conservation Areas is given in their Memorandum of Guidance within Appendix 1, section 1.7.1. Solar panels have been successfully installed on even A-listed buildings.
Siting Opportunities
64. There are many situations in the built environment where solar panels can be installed to generate and promote renewable energy. Planning authorities will be aware that the levels of energy generated by PV schemes may be low but should recognise their value in terms of raising awareness to the technology.
65.PV cells can be added to the outside of existing buildings or south-facing roofs or walls. Service station canopy roofs can present a good opportunity for the installation of PV, particularly as it is frequently difficult to see the roof covering from the ground. PV can be used in a variety of roadside applications including motorway sound barriers, street lighting and street furniture. Planning authorities should consider how they can promote the use of solar panels on larger installations.
Case Studies
Midlothian: Crichton Castle
Crichton Castle, a scheduled monument in Midlothian is the first property in the care of Historic Scotland to be powered by renewable energy. Eight PV solar panels were installed which provide enough power to run lighting and a fax machine in the small shop and ticket office associated with the castle. The solar panels are about three square metres in size and are positioned on a roof slab on top of the remaining part of the original 14th century tower, where they are not visible to visitors.
The solar panels were chosen as an environmentally-friendly option which would not damage the structure of the ancient building. The panels replace previous systems of gas lighting and, more recently, a petrol generator. The latter had an adverse effect on the tranquillity of the monument and required regular deliveries of combustible fuel. The option of bringing a mains electrical supply to the site was ruled out on the grounds of cost and probable disturbance of important archaeological remains.
Aberdeen: Bridge of Don Academy
Aberdeen City Council has constructed one of the largest solar panel installations in the UK to heat the community swimming pool at Bridge of Don Academy. The 180 square metre installation covers the entire roof of the pool with 60 state-of-the-art, low maintenance solar hot water panels, using evacuated tube technology. The panels are not visible from ground level. Solar water heating was considered for this project due to the large area of suitable roof space which would allow a large solar array.
The City Energy Conservation Department has started work on a carbon emissions reduction pilot in the school. For educational purposes, the project will have a public display facility, which will show throughout the year the level of solar energy input to the pool.
Motherwell: UK's First Wind and Solar Powered Bus Shelter
A state-of-the-art bus shelter, has been located in Airbles Road, Motherwell, as part of a pilot scheme promoted by North Lanarkshire Council and bus shelter company Adshel. It is the UK's first wind and solarpowered bus shelter, using these sources of renewable energy to power the interior courtesy light in the shelter and to illuminate the advertising panel, which requires a power supply of 200 watts. The solar panel is located on the roof of the shelter, while the 5m high wind turbine pole is discreetly positioned in foliage two metres from the shelter. A battery stores the power generated by the solar panel and the wind turbine, which produces energy even on calm, cloudy days. A gentle breeze will generate some power, while a strong breeze with a wind speed of 22mph will generate 340 watts.
As well as increasing passenger safety it reduces the disruption normally experienced when roads are excavated and power cables lain.
Edinburgh: Dumbeg Park
Assist Architects, won an open design competition to develop a sustainable housing development for Prospect Community Housing at Dumbeg Park, Westerhailes, Edinburgh. This development of 18 flats and houses incorporates solar hot water panels as well as utilising passive solar gain. Whilst the angle of the roofs on which the solar panels are positioned is not at the maximum tilt to maximise solar energy, a lower pitch was chosen on aesthetic design grounds.
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