The installation of solar photovoltaic panels across areas served by the Hawaiian Electric Companies rose last year at the slowest rate since 2010, the utility reported Wednesday.

There were 17,609 photovoltaic systems with 129 megawatts of generating capacity installed on Oahu, Hawaii island and Maui County in 2013, up 39 percent from the previous year. That followed annual increases of 136 percent in 2012 and 143 percent in 2011. PV generating capacity in 2010 rose 33 percent across the utility’s service area.

The cumulative amount of PV installed in all years through 2013 totaled 300 megawatts of generating capacity, including 221 megawatts on Oahu, according to HECO. That means about 10 percent of all HECO customers on Oahu have PV systems, by far the highest percentage of any utility across the country. In Maui County the figure is 8 percent, and on Hawaii island it is 7 percent, according to HECO.

Several factors weighed on PV installations last year, according to industry observers.

HECO in September revised its requirements for homeowners seeking to hook their PV systems into the utility’s grid in areas with high penetration of PV panels. 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.

In addition, the Hawaii solar market suffered a setback 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.

Other data suggest that PV installations may continue to slow in 2014.

Building permits issued for PV systems, an early indicator of future installations, fell on Oahu for eight consecutive months from May through December on a year-over-year basis, according to city and county data compiled by industry veteran Marco Mangelsdorf. For the year, 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, Mangelsdorf said.