The S20 solar energizer is a portable, super tough energizer that comes with a rechargeable battery and in-built solar panel. Powers: 1 kilometre / 3 acres Contains: 0.2 Joules of stored energy Suitable: for short term, portable fencing Gallagher's solar energizers are fully self sufficient energizer and use solar power to charge your electric fence. These units can be used in permanent electric fencing, where there is no access to mains power and also for portable, short term animal control.