LAWR

February 2014 Local Authority Waste & Recycling 21 LANDFILL MANAGEMENT ground-mounted solar generation on landfill sites - specifically to do with differential settlement - have proved a stumbling block in the past. Differential settlement occurs at varying rates across an area as a result of the variations in the depth, type, method of waste disposal and decomposition rate within the underlying landfill. Its effects would in the past normally have resulted in damage to solar panel frames and foundations, ultimately leading to failure of the panels themselves as well as creating an unsightly layout. It would previously also have been hard to anchor the structures, since former landfill sites are often covered by an engineered cap in order to prevent the ingress of water and the escape of landfill gas. Now, however, new technological advances in panel mounting and framing systems give landfill operators a way around these problems. Juwi, for example, a German company and one of the world's leading solar PV suppliers, has developed a bespoke design for frame-mounted solar arrays on landfill sites using a telescopic racking system that keeps panels flat and level. Its mounting mechanisms can be applied with minimal impact on the integrity of the underlying engineered cap and without applying undue loading to the landfill system itself. The solution has been successfully deployed on a number of solar farms which have been developed on closed landfill sites in Germany. Persuasive commercial arguments There are many persuasive commercial arguments in favour of extending the role of former landfill sites to include the generation of solar power. The first and most obvious arises from the fact that many former landfill sites had a connection to the electricity grid in order to export electricity from landfill gas engines and, as landfill gas generation diminishes, grid capacity potentially becomes available. The availability and capacity of an existing grid connection is normally a significant factor in the development of a large-scale solar PV facility and could therefore considerably reduce both cost and timescale. The connection could potentially be optimised by using the solar farm to generate and export electricity during daylight hours while still utilising the landfill gas engines at night time. Former landfill sites may well contain slope angles that favour the southerly orientation required for optimal performance of solar panels, as well as the large spaces ideal for the cost-effective development of a large scale solar facility. Previous landfilling operations probably also mean that issues associated with overshadowing by vegetation, buildings and overhead wires can normally be avoided. Sites are often securely fenced, a pre- requisite for solar farms that contain thousands of valuable solar panels and where access needs to be controlled to what is essentially an electricity- generating facility. Site monitoring and security may already be in place, while highway access for construction traffic and deliveries is also normally very good. Former landfill sites often avoid areas of landscape value or sensitivity, and are usually well screened from sensitive receptors such as residential properties. There are of course planning issues involved in developing a solar farm on a landfill site which require the normal close engagement with the local planning authority and the Environment Agency or Natural Resources Wales. The key issue is usually landscape and visual impact. The raised profile of a former landfill site, while necessary to promote surface water run-off and minimise water ingress into the former landfill, may mean that a proposed solar farm may be visible over a wide area. The impact of this and possible mitigation such as site layout and landscape planting will require careful assessment, often utilising modern computer modelling. The construction of the solar panel array must take into account the unique considerations of building on a former landfill site. Maintaining the integrity of the landfill cap and the gas management system are primary concerns. The construction considerations include limiting the depth of excavation (depending on the depth of the restoration soils), avoiding the use of heavy equipment on certain areas, restrictions on laydown areas, maintaining erosion and surface water run-off controls, soil and/ or groundwater testing if hazardous materials have been landfilled, robust health and safety measures and capping system repair plans. There are a number of site development, ownership and operating models that can be tailored to suit individual circumstances. If 'client owned,' the landfill operator/owner serves as the developer, financier, builder and owner of the PV system – enjoying all the direct benefits including electricity generation revenues but accepting all the project risks. Under a 'land lease' model, the client selects a vendor to be responsible for the design, finance, building, ownership, operation and maintenance of the system. The vendor assumes all risks but claims much of the project revenue. Under a Power Purchase Agreement (PPA), the client buys the electricity generated by the PV array from the developer/owner at a predetermined rate. The client gains from the predictable price of power, while the project owner gains a fixed revenue stream to finance project development, installation and operation. This arrangement may be attractive where a landfill site has no grid connection (or one with insufficient capacity) but is located close to a material recovery facility or other similarly power- hungry facility. Extending the role of former landfill sites with the addition of large scale solar PV facilities can bring big potential benefits. Before you go too far, though, it will pay to get the right expert knowledge and technical support on your side. Wasted effort and unnecessary costs and delays can be avoided by gaining a detailed understanding of the planning process, the business and financial issues, and the engineering aspects of combining solar generation with landfill management. Adrian Lea is technical director at Wardell Armstrong.

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