Eleven years ago, when Hawaii became the first state in the nation to require installation of solar water heating systems in new single-family homes, the mandate to increase tapping one of the state’s most abundant renewable energy sources and thereby reduce dependence on imported oil was greeted with green-minded applause.

But tacked onto the mandate, signed by then-Gov. Linda Lingle, were exemptions that are hampering the measure’s envisioned progress. And despite repeated calls from environmentalists and others, state lawmakers have flatly failed to close an apparent loophole in the law.

And so it is that a recent First Circuit Court ruling, which brought a temporary halt to the issuing of exemptions, serves as an encouraging sign. After several years of essentially rubber-stamping approvals to make way for more fossil-fuel-fed water heating systems, the state is being forced to apply more rigorous criteria in review of exemption applications.

A few of the law’s exemptions, such as waiving the solar requirement for homes in forested areas that get scant sunshine, are sensible. But an option that allows application for an exemption to install a gas-demand water heater if a gas appliance is already in the home has rightly touched off anger among clean-energy advocates.

Despite the Legislature’s written directive that variances “will be rarely, if ever, exercised or granted,” the state Department of Business, Economic Development and Tourism (DBEDT) has approved nearly 100 percent of all variance requests for tankless gas water heaters.

To date, that adds up to more than 6,500 exemptions statewide, including many for homes in the first phase of Ho‘opili’s vast development being built on Oahu’s sun-drenched Ewa Plain.

The court case resulted from a lawsuit filed by Earthjustice attorneys on behalf of Hawaii Solar Energy Association and the Sierra Club of Hawaii, arguing that DBEDT’s exemptions were contrary to the law’s purpose of promoting the environmental and consumer benefits of solar water heating.

In response to the ruling, DBEDT — with the attorney general’s guidance — should quickly rework its exemption application review process to set the bar much higher to reflect the state law’s intent.

It seems that driving the effort to bypass solar is a preference among home builders for gas heaters as a means to keeping up-front costs down. Installation of the average gas tankless water heater is $1,500, while a solar water system can add up to $6,000 to the price of a new home.

Even so, a solar water heater is recognized as a hugely efficient — and cost-saving — strategy. In the long run, it can result in greater utility-bill savings and serve as a step toward better protection of the environment from climate change threats.

Hawaii’s preference for solar is hardly revolutionary. California recently adopted an even more ambitious agenda: a first-in-the nation plan to require most new homes in the state have rooftop solar panels starting in 2020.

It applies to most single-family homes as well as multi-family residential buildings up to three stories, including condos and apartment complexes. And while the move is expected to add on average about $9,500 to the cost of new houses, it’s projected to be offset by the solar-energy system’s long-term savings.

Given the high cost of housing, Hawaii may not be ready to go that far. But we shouldn’t head in the opposite direction.

In 2015, following the Lingle administration’s clean-energy lead, Gov. David Ige signed into law a bill directing utilities to pursue a path toward generating 100 percent of electricity sales from renewable resources by 2045. Hawaii stands little chance of actually meeting that deadline unless we’re willing to make the investment now.