With three months to go, 2012 was already a record year for U.S. solar photovoltaics installations – and there could be a lot more on the way.

A new quarterly report by the Solar Energy Industries Association and GTM Research, released Tuesday, said 684 megawatts were installed in the quarter ended Sept. 30, down slightly from a huge second quarter but up 44 percent over the same period last year. It was the third-largest quarter ever for U.S. solar and boosted 2012′s newly installed capacity to 1,992 MW – beating the whole-year record of 1,885 MW from 2011.

And it’s the fourth quarter when the installation totals typically really go crazy, the SEIA said in a statement, so look for a much bigger 2012 end-year total:

• Historically, Q4 has been the strongest for PV installations in the U.S. In 2010 and 2011, Q4 represented 41 percent and 42 percent of annual installations, respectively. U.S. Solar Market Insight forecasts a similar Q4 bump in 2012 with approximately 1,200 MW to be installed. That would not only account for 38 percent of this year’s forecasted total, but would be the largest single quarter on record for the U.S. PV market by far. SEIA and GTM Research expect 2012 growth to top 70 percent with a record 3.2 GW of solar installed – enough to power more than half a million average U.S. homes.

Residential solar was particularly robust in the third quarter, growing 12 percent over the second quarter with a record 118 MW of installed capacity. More and more, those systems were leased, not bought.

“During this quarter, residential PV markets in Arizona, Colorado, California, and Massachusetts saw third-party systems range from 57 to 91 percent of total residential system installations,” the SEIA said in a statement.

The new report mirrored government data released two weeks ago that showed homeowners benefiting from continuing plunging costs for installed solar – and costs were falling even faster for utility-scale systems:

• System prices for PV projects in the U.S. continued their downward trajectory in third quarter 2012. Average residential system prices dropped quarter-over-quarter from $5.45 per watt to $5.21 per watt nationally while average non-residential prices declined 15 cents per watt, falling to $4.18. Average utility system prices, which are currently at $2.40 per watt, continue to see the greatest reduction in prices of the three market segments covered, falling by 30 percent since third quarter last year.

But will that all change with tariffs on Chinese solar PV imports kicking in? Nah, the report’s executive summary said:

• As the International Trade Commission (ITC) has issued its final decision in the antidumping (AD) and countervailing duty (CVD) investigations against Chinese c-Si cell manufacturers, GTM Research maintains that tariffs will not have a material impact on pricing in the U.S. Many manufacturers continue to obtain U.S.-bound cells via tolling from Taiwan with an estimated cost impact of less than $0.10/W. This does not necessarily prohibit Chinese manufacturers from pricing modules below their domestic competitors.

California led the way in the state breakdown of installations, with 193.6 MW, barely edging out Arizona, which had 192.1 MW of new installed capacity in the quarter, the vast majority of it at the mammoth Aqua Caliente plant in Yuma County. New Jersey was far behind in third, with 69 MW.