HONOLULU -- On a hot sunny day in the islands, crews from solar help are busy installing a solar water heater on the roof of an older Pauoa home.

"These are our main bread and butter. This is what we usually do. It's very high efficiency. It saves you about 40 percent on your electricity bill ad also it's the cheapest to buy and has the most dramatic effect initially," said solar help installer Jeff Augustine.

It's also a step in the right direction of a greener future for Hawaii which is also the intent of the law that went into effect in the New Year -- one that requires new homes to have solar hot water heaters.

"Currently, one in four homes use solar. We need that number to 100 percent," said Jeffrey Mikulina, with Blue Planet Foundation.

While the new bill means more solar panels will go in, it could also mean less business for some of Hawaii's small solar companies.

Owners of new homes used to have the choice of when to add solar.

"The homeowner has the option to put in solar before or after they move in," said Steven Yamase, with Solar Help Hawaii. "The remaining people who don't put in solar now can use us because we do one home at a time."

Now, because the systems will come with house, the number of new home solar hot water installations will cool for many island installers.

But, there is hope hot water systems will, in turn, heat up sales of other clean energy systems.

"Building new homes with solar, those homeowners will experience what clean energy is like and then go further, put in PV system or clean energy system," said Mikulina.

"As it becomes more standard, people will think about it more and putting more energy into it. I think it's a good route to go," said Jeff Augustine, Solar Help installer.