Solar Systems on Common Property.

1 unit of our 8 unit complex has solar hot water fitted, with body corp approval and associated bi-law, and now others in the complex wish to determine how they will progress from their current electric hot water systems when required. The bi-law created only covers the one unit with the solar system fitted, not any of the other 7 units, and we need to find a suitable path to accomodate everyones needs.

Considering that the roof and walls of the complex are common property, just how prescriptive can unit holders be about what type of unit is fitted and it's positioning (for example-requiring no external hot water tanks on the roof, and that any panel or evacuated tube collectors are not to be elevated, in order to not interupt our ocean views)?

One unit holder has decided to pursue the heat pump option, but insists it be located outside on the ground on common property, as the manufacturer purportedly asserts that external placement of the heating unit provides optimum efficiency. One consideration is that heat pumps reportedly make a noise like a refridgerator, which would require additional consideration before placing a unit outside. All hot water system tanks are currently located within each unit's garage. Is it reasonable to require the hot water system tank be moved externally to common property in these circumstances (any external solar panels or tubes will be on common property on the roof of the units)?

If external hot water tanks are approved to be fitted to the roof, who is liable should the weight of the associated unit (up to 400kg) cause structural damage or leaks internally?

Is the existing bi-law giving approval to the current solar hot water system able to be easily and cheaply modified to include the remainder of the units in the complex?

Cheers.