The number of people contacting the state's consumer watchdog about solar electricity systems increased from five a month in 2007 to 183 a month this year.

Largely about faulty units, poor installation, service delays and difficulty in cancelling contacts, the complaints have pushed solar power systems into the top five products reported to Consumer Affairs Victoria, alongside furniture, white goods and clothing.

The more serious complaints have been made over sales of defective equipment and failure to honour contracts - allegations that led the watchdog last week to issue a warning about Melbourne supplier Sunburst Solar.

It follows prosecutions of two solar companies earlier this year, one of which was fined $60,000 for consumer law breaches.

The increase in complaints has come as the popularity of solar systems has surged. Driven by government incentives, the falling costs of solar panels and rising electricity prices, more than 126,000 systems were sold in two boom years.

Sales fell in 2013 as government incentives were wound back. But calls to the watchdog remain as high as they did during the peak, with more than 2000 a year.

Consumer Affairs Victoria director Claire Noone said the watchdog was cracking down on rogue suppliers. The warning about Sunburst Solar came after it was contacted about the company 60 times this year.

Ms Noone said consumers reported difficulties connecting their system to the grid and alleged the company provided faulty panels and inverters, failed to reimburse shortfalls in feed-in tariff incentive payments and could not be reached for warranty claims.

''We're concerned that Sunburst hasn't provided adequate detail about the warranty offered on its products and we're concerned that they haven't honoured warranties when consumers have reported faulty products,'' Ms Noone said.

''We want to alert consumers to concerns about their business practices. We're still considering what action we might pursue.''

Sunburst issued a statement through its lawyers saying it was committed to addressing any complaints. ''Sunburst Solar is not aware of any client with an outstanding complaint or issue relating to any installation or agreement … and would encourage any client with such a grievance to contact the company, at which point a solution and rectification will be forthcoming,'' it said.

ASIC records show that Sunburst chief executive Robin Grainger is a director or shareholder in a series of other solar or energy companies. There is no suggestion any of the other businesses have acted inappropriately.

The Consumer Affairs warning follows legal action against two solar companies earlier this year.

Solareco Pty Ltd was fined $60,000 last month for making false representations and Ballarat-based Bailey Designed Engineering was forced to close after losing a series of legal battles over faulty equipment.

Ms Noone said solar suppliers flooding the market in recent years led to some aggressive marketing tactics, misleading practices and substandard products, but was not a reflection of the whole industry. ''We're not saying it isn't a reputable industry, but certainly it's relatively new,'' she said.

Clean Energy Council policy director Russell Marsh said the organisation was committed to raising standards and had introduced a code of conduct to highlight top-performing solar suppliers.