A solar-powered energiser with an automatic night mode for electric fences has had its New Zealand launch.

Hamilton's Gallagher Animal Management Systems spent two years developing the PowerPlus S50 solar-powered energiser - the big brother to the S17 model.

When night falls the unit, which monitors light levels, automatically lengthens its pulse rate to save power during the time animals are less active. That extends battery life and ensures a strong voltage during daylight hours.

The S50, launched in the US in January, can store half joules of energy and power up to 8km of multi-wire fence, or the equivalent of an 8ha block.

The S50, which sells for about $650, is much larger than its predecessor and produces three times as much energy.

Gallagher product manager Carl Sheridan said the self-sufficient, portable unit would appeal to lifestyle farmers who wanted a simple, efficient and cost-effective system to power their fences.

It was also ideal for larger-scale farms which had areas without mains power.