Connecting renewables

by agwelch

Coverage of British Power International’s POC-MAST from Energy Engineering 60

The locating and making of a grid connection has always been a headache for the solar PV and onshore wind industry. In chasing the most advantageous resource and avoiding the planning permission difficulties that come with proximity to centres of population, developers often site solar and wind farms in relatively remote locations.

To connect a wind or solar PV site to the grid, developers can run a cable from their site to a grid substation, but the further the distance between the two the more costly this option becomes. If there is not a nearby substation, there may well be overhead conductors running in proximity to the wind or solar PV site. However, connecting to such overhead lines has not been an easy task, typically requiring the replacement or, at the very least, the extensive modification of existing towers in order to accommodate the grid connection. This work can last over a year, involve complex consent agreements with landowners, local authorities and network operators, and see costs spiral into million of pounds.

In an effort to make grid connection less time consuming, less expensive, and generally less painful for onshore renewable energy developers, electricity sector consultancy British Power International has developed a connection solution that eliminates the need to replace or significantly re-engineer existing towers.

The company’s POC-MAST (patent pending) product negates the requirement for a new junction tower allowing the developer to connect directly to the overhead line. The POC-MAST is installed adjacent to the existing tower at a distance of between five and ten metres and connection is made via low tension cross leads. The POC-MAST is suitable for overhead line distributed generation connections operating from 11kV to 132kV.

POC-MAST

Bob Ford, head of design projects at British Power International (BPI), explains that the consultancy began work on the POC-MAST after a client with a large solar PV farm approached the company looking for a more cost-effective means of connecting to the grid at 132kV. “Traditionally to do that connection you’d have to replace an existing tower which requires a lot of temporary work to maintain one live circuit; is dangerous from a health and safety perspective; and would require a great deal of planning permission, organisation, and deep excavation for foundations,” he says. “Our solution is much cheaper and can be installed with the minimal circuit outage conditions as you don’t need to divert the circuit or the existing tower on the overhead line.”

The overhead line design team at BPI devised the POC-MAST with health and safety and speed of installation in mind. The modular POC-MAST comprises multiple polygonal sections of folded sheet steel that can be connected together to achieve the desired height. The POC-MAST’s base accommodates the base flange and hinge arrangement and is connected to the mass concrete foundation by cast in-situ holding-down bolts. In addition BPI as developed an alternative foundation using screw-anchor assembly.

Ford explains that the POC-MAST can be installed and connection achieved by a four-man team within three days. The traditional connection method involving the modification of the existing tower, on the other hand could take up to a year. “We have developed a hydraulic system to lift the POC-MAST so we can fully construct and ‘dress’ (that is put the insulators and other equipment on) at ground level so nobody is working at height,” he adds. “Using an hydraulic ram we can lift the POC-MAST within 20 seconds and once the POC-MAST is raised a team on a cherry picker use cross leads to connect the POC-MAST to the overhead line.”

Depending on the connection configuration most overhead line connections can be achieved in less than one day meaning a significantly shorter period of circuit outage than in a conventional connection.

One key element of the POC-MAST’s design is that, whatever the weather conditions, it will transfer minimal mechanical load to the existing towers – and it is, in fact, this aspect of the system which is subject to an international patent. Given that many of the existing transmission towers, especially in the 132kV field, date from the 1930s and 1940s ensuring they are not placed under an excess strain is particularly important.

Whilst the fundamental design of the POC-MAST will not differ from site to site, Ford explains that each POC-MAST will be designed to be site specific according to prevailing weather conditions and the particular tower it is connecting to, this is contained in a complete design pack. Additionally, the POC-MAST is designed for minimal visual impact: its standard finish is in galvanised steel but the POC-MAST can be coloured if necessary to make it less conspicuous in the landscape.

BPI completed the installation of the first POC-MAST for its original client in August 2014; the product is now operational and has proved to be very successful. In March 2015 the mast was named Business Innovation of the Year by Construction News in recognition of the product’s major potential in the renewable energy sector.

In addition to the design of the POC-MAST BPI also provide a complete design service for the adjacent substation.

Building on this initial success, Ford explains that the company is now tackling business development and attempting to communicate the advantages of the POC-MAST to renewable energy developers. “We want to set up meetings with solar and wind farm developers to educate them that you aren’t necessarily stuck with a 12 to 18 month connection solution – our product can be up within three months or just a matter of days if planning permission has already been granted,” he says. “This gives the developer much more autonomy to plan and use sites that they would not necessarily have been able to use.”

“The traditional connection methods have been with us since the beginning of overhead lines and it really is time to look at new methods,” concludes Ford. “Our technology is cost effective, time saving, and health and safety focussed – overall a much better solution.”

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