The number of UK homes installing solar panels has fallen dramatically since the start of August, following a cut in subsidy rates by the government.

Figures published on Friday show a huge rush by householders aiming to install panels before a 1 August government deadline, followed by a huge drop. There was nearly three-quarters less capacity installed in the past six weeks than the equivalent weeks in 2011 for the feed-in tariff scheme, which pays householders for generating green energy.

The solar industry said the fall did not undermine its claims that panels still represent an attractive finanical investment of around 10% annually, saying its message that installation costs were falling was failing to get through to consumers.

Paul Barwell, the chief executive of the Solar Trade Association, told the Guardian: "The returns are certainly still there [despite the tariff cuts] because the costs have continued to come down. While a 4kW system has dropped in cost from around £9,000 in April to £7,500 now, tariff drops are a problem for consumers because that's what they see. August is generally a poor installation month anyway because people are away from their homes."

He added that he didn't expect to see a "cliff-edge drop" when the next cut – a much smaller one of just 0.5p rather than 5p as seen in August – comes in November.

On average, 2,872kW of solar panel installations smaller than 4kW were fitted in the past six weeks, versus 10,789kW on average for the same weeks in 2011.

Under the rule changes in August, the length of the payment period was also cut from 25 to 20 years, although there was a small sweetener in the form of a rise from 3.2p to 4.5p for each kWh of energy exported to the national grid.