These bulbs are made to operate in 12.0 volts and not on typical battery voltage (about 12.6 Volts for a fully charged 12V battery). According to one authoritative source, life expectancy is decreased to 50% by 5% over voltage (eg: 0.6V on 12V) and by about 75% by 10% over voltage.
On a 'normal' solar system this is usually not too big a problem because with line losses, the operating voltage on load at night will probably be down to around 12.4 volts or less. On the other hand, if you turn on these lights during the day (when the solar panels are charging), or if you have a wind, hydro or generator back up at night, you could be subjecting the bulbs up to say 15.0 volts!
If you run your halogens off a relatively cheap/old transformer type converter from 240V, you can get over voltage if one bulb burns out or you use less wattage bulbs than specified by the transformer.
Replace any failed bulbs promptly!
We install solar systems in Northern NSW and Southern QLD.
QLD: Gold Coast (from Coolangatta to Southport), Nerang and Hinterland (Beaudesert) and out West (Warwick, Stanthorpe, Killarney)
NSW: Northern NSW (Tweed Heads to Yamba, including Evans Head, Byron Bay and Ballina); the Far North Coast Hinterland (Grafton via Lismore to Murwillumbah) and out West (Casino to Tenterfield, including Drake and Tabulam, as well as Woodenbong and Bonalbo)
For larger system we also go up to Brisbane or down to Coffs Harbour and even Glen Innes. Other places by arrangement.