The value of building permits issued to the top 25 solar companies on Oahu fell to $370.3 million in 2013, down 20 percent from $466.5 million in 2012, according to city and county data compiled by industry veteran Marco Mangelsdorf.

The total number of PV permits issued on Oahu fell for eight consecutive months from May through December on a year-over-year basis, according to Mangelsdorf, president of Hilo-based ProVision Solar.

The 1,140 permits issued in December for PV projects was 41 percent fewer than the 1,925 permits issued in December 2012.

Of the top 15 PV companies in the state, only four experienced an increase in the number of PV permits issued in December: Hawaii Energy Connection, SolarCity, EcoSolar and Hawaiian Island Solar.

Mangelsdorf said he expects the number of PV permits issued in January will be about 50 percent fewer than in January 2013.

"The skies are gray and getting darker over Oahu solar contractors," he said.

The Hawaii solar market was dealt a blow early last year when the state Department of Taxation put in place new rules that effectively reduced the ability of homeowners and businesses to claim multiple tax credits for the same PV installation. Tax Department officials said they believed that in some cases the tax credits were being abused.

That was followed by Hawaiian Electric Co.’s move in September to revise its requirements for homeowners seeking to hook their PV systems into the utility’s grid in areas with high penetration of PV panels.

HECO said it made the changes to deal with potential safety and reliability risks in areas due to excessive solar power generation.

In some cases, homeowners in areas saturated with PV panels have been told they may have to pay for equipment upgrades if they want to connect to the grid. HECO also has undertaken studies about the effect of solar energy on the grid, which has caused delays for some utility customers who want to install PV systems.