Solar panels at Blackrock Mayo (photo: Noel Gaughan)

THE LIGHT on Blackrock Mayo was first exhibited on 1 June 1864. It comprised a wide oil burner and a 1st Order dioptric revolving optical apparatus supplied by Chance Brothers of Birmingham. The initial character was one flash every 30 seconds.

In 1908 the candlepower of the light was increased by replacing the wide burner with an incandescent paraffin vapour burner, which remained in service until 1974.

In the early 1970s Irish Lights were in discussion with the Atomic Energy Research Establishment at Harwell in England with a view to providing Blackrock with a nuclear powered light. However, it was determined that the station was unsuitable for the intended light because of its elevation above sea level.

At a height of 86 metres above Mean High Water Springs, Blackrock Mayo is the second highest of all our lights, and the modifications necessary to spread some of the beam downwards would have reduced the intensity of the light too much. Because of this the optic originally intended for Blackrock was installed on Rathlin O'Birne, and the semi-automatic acetylene gas powered optic originally intended for Rathlin O'Birne was placed on Blackrock Mayo.

This acetylene gas light, with a new character of one flash every 12 seconds, was installed at Blackrock in late 1974. The pressure of the gas was used to rotate the lens and that same gas was then fed to the burner to fuel the light. Having been tested and accepted from AGA Navigation Aids Ltd, and again tested at the Lighthouse Depot, it was only when the optic was installed and lit on Blackrock that the Principal Keeper noted that it was a fine light if only the character was that of Blackrock and not Rathlin O'Birne. Following the decision to relocate the optic nobody had remembered to inform AGA of the change.

It was arranged for Jim Parkins, then working for AGA, to travel from England to Blackrock to adjust the rotation to produce the correct character. Subsequently the Lightkeepers were withdrawn and the station became unwatched.

During the past few years all of our gas buoys have been modified to electric light, powered by batteries charged by solar panels from the sun's rays. During the past year we have applied this technology to stations like Vidal Bank, Green Island, Copper Point, and Dun Laoghaire West Pier. Our only previous solarisation project at a major lighthouse was Rathlin O'Birne which received its solar powered light in 1994.

Beginning in April 1999 we have also converted Blackrock Mayo to solar power. In preparation for this one of the two original Keepers' dwellings on the rock was renovated during 1998, as reported in Beam 1998-9.

The new solar-powered optic supplied by Pelangi International was first exhibited on the night of 2 August 1999. It comprises a revolving pedestal on which is mounted eight flat faced lenses arranged in the shape of an octagon. Inside the lens is mounted a lampchanger holding two 35 watt Ceramic Discharge Mastercolour single tubular lamps-a main lamp and a standby. The pedestal has a rotation period of 96 seconds, which provides one flash every 12 seconds, the same character as the gas light.

The range of the new apparatus is 22 nautical miles (nm) in the white sector and 16nm in the red sector, which is just 2nm shorter than its gas predecessor. In the event of this optic system failing an emergency light is provided by two ML300 lanterns, fitted with 10 watt bifilament lamps mounted on the tower balcony handrail.

When this new optic was unwrapped and put on test at the Lighthouse Depot, it was found to have some teething problems. To enable Irish Lights staff to fully check the optic and gain some knowledge of the system's operation, its designer and manufacturer was invited over from England.

By coincidence, the designer was none other than the forementioned Jim Parkins who 25 years earlier had corrected our problem with the new gas light. Having moved on from gas to electricity he now works for his own company designing optics and control systems.

There are 144 lead-acid battery cells in the solar power system to provide the power for the optic and other systems at the station. Each cell provides 2 volts with a capacity of 550 Ampere-hours (Ah). These cells are split into two banks of 72 cells to provide two solar batteries. Each bank comprises 6 strings of 12 cells connected in parallel. Therefore, each battery provides 24 volts with a capacity of 3,300Ah. With the two banks connected together we have a total solar battery capacity of 6,600Ah. (This means it will give 66 amps for 100 hours or 6.6 amps for 1000 hours before being considered to be flat.)

The batteries are charged from the sun's energy. A large metal stand holds 24 solar panels aligned in a south-facing direction. These 24 panels are divided into four arrays of six panels, each rated at 12 volts, 50 watts. Each array is connected as three strings of two panels in series so that each can provide 24 volts, 150 watts.

Two arrays are then connected in parallel to provide a maximum charge current of approximately 24 amps to each battery. This charge is fed to the battery through a solar regulator box which controls and monitors the voltage of each battery.

Should the battery voltage drop below a preset level the regulator will disconnect the battery from the systems it supplies, allowing it to charge up from the array without supplying any power to the lighthouse systems. If, for any reason, the battery should go flat, there is another smaller battery charged from a diesel generator on station which will automatically take over the task of supplying power to the station's systems. All going to plan, this should never happen.

The interconnection of the 24 panels and 144 battery cells may seem complicated but its main purpose is to provide a certain level of redundancy. We can, for example, lose power from one 3,300Ah battery and still supply the light from the other battery. Or we can lose several solar panels and yet still charge the batteries, though at a lower level.

It is planned in the coming years to install similar systems at many of our main lighthouses including Bull Rock, Inishtrahull, Skelligs, and Inishtearaght. It should make the stations more economical to run due to a much reduced requirement for diesel and all the services required to get the diesel fuel to the station.

Theoretically, stations with solar powered systems will require fewer visits and less maintenance than those with diesel generators. However, having said that, it is more difficult and time-consuming to identify and rectify a faulty battery than a faulty diesel generator.