... Greenpeace is 100% right on this one.
Broadly decentralized energy production and infrastructure will make Israel much less vulnerable to localized attacks, whether on the gas processing facilities or on centralized power plants. You can bet that Hezbollah and Iran are planning a variety of attacks, ranging from terror attacks and hijacked shipping to missile strikes against cities, the power grid, power plants, gas facilities, etc.
A more decentralized power generation system, particularly one that could rely on solar/wind for a higher % of its requirements while continuing to use gas for off-peak hours, could be made much more robust in the face of attack or natural disaster (e.g. a major earthquake).
Greenpeace is right to bring the security implications of current plans to the attention of Israel's leaders and to encourage them to take action BEFORE the threat ripens, rather than afterward.