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News Release from: Saft Industrial Batteries | Subject: Bullero island
Edited by the Engineeringtalk Editorial Team on 27 March 2002

Island batteries are long-term survivors

Specialist photovoltaic rechargeable nickel-cadmium batteries still going strong nine years after they were installed on a remote island in the archipelago of Stockholm.

Specialist photovoltaic rechargeable nickel-cadmium batteries still going strong nine years after they were installed on a remote island in the archipelago of Stockholm Saft Sunica batteries enable a hybrid photovoltaic and wind power system on Bullero, the main island of a national park in the archipelago of Stockholm, to provide a reliable supply of electricity for visitor facilities and the park ranger all year round

The Sunica batteries, which are designed specifically for photovoltaic applications, are still going strong nine years after they replaced the previous lead-acid batteries and will not need replacing for many more years.

Bullero island is very remote from the nearest electricity grid and in 1986 the cost of installing an undersea cable to provide power for the visitor facilities and the park ranger, who lives on the island all year round, was estimated at around $100,000.

Instead in 1988 a low-cost combined PV (photovoltaic) and wind hybrid system was installed.

This was upgraded in 1996 with more PV modules and a new combined regulator and monitoring system.

The PV modules are mounted on an old airforce tower.

The installed peak power is 1.45kW.

The modules are connected by a 100m cable to the batteries located in a battery room next to the park ranger's house.

A system voltage of 48V was chosen to reduce the losses in the cable.

A Rutland Furlmatic 1800 wind generator, with a nominal power of 0.25kW is installed on a mast at the back of the house.

During the short periods when there is both low insolation and weak winds, a backup petrol generator, with a nominal power of 0.75kW, is used to charge the battery bank.

A single NSCi microprocessor charge control system controls the power coming from the PV, wind and the backup generator, and provides a data-logging system.

The battery comprises Saft Sunica rechargeable nickel-cadmium batteries with a nominal capacity of 571Ah at 48V.

The system voltage of 48V DC is converted to 12V DC before being fed into the house.

The electricity powers lighting, a refrigerator and freezer, a radio, a television and a 1kVA inverter for a few small appliances which need AC power.

Photovoltaic systems require efficient batteries with a long cycle life and a potential for both shallow and deep cycling.

The Saft Sunica nickel-cadmium batteries installed on Bullero island are designed specifically to offer a number of key advantages in this type of application, namely: constant charging efficiency over time; continuous operation at any state of charge; minimal self-discharge rates; a high available performance even at very low states of charge; sustained efficiency even at high or low temperatures;and a long cycle life even when the charge/discharge cycle involves 100% depth of discharge.

Sunica batteries feature pocket plates, shock-resistant polypropylene casing material and a special spill-proof vent.

An extra electrolyte reserve ensures almost supervision-free service and a long interval between topping up.

They also benefit from the long service life of nickel-cadmium technology, with no risk of the 'sudden-death' failure found in lead-acid batteries, and are expected to have a lifetime of up to 20 years.

The batteries on Bullero island were installed in 1993 when the previous lead-acid batteries had reached their five-year design life.

They were not new then, but were transferred from another PV application on Sweden's west-coast (a demonstration project for desalination with reversed osmosis), even so they should still give many more years service in this location.

The performance of the hybrid power system on Bullero island was monitored closely over a three-year period between 1997 and 1999.

With an average power consumption of 17,461Ah and an average energy production of 18,676Ah (from PV, wind and back-up generator) the system is clearly well designed to meet the energy demand from users, especially as only around seven percent of the energy was delivered from the backup generator. Request a free brochure from Saft Industrial Batteries ...

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