Industry experts say the government registry through which solar subsidies are paid has all but ground to a halt, leaving consumers who've forked out for the green energy option facing a choice of either a long wait or cutting their losses and accepting a lower rebate.

A stronger than expected boom in solar installation last year has flooded the market with renewable energy certificates - tradeable credits that the government awards to people who install solar systems. These can be sold to electricity suppliers at a guaranteed price of $40 per certificate - but only if they are traded on the government's registry.

The oversupply of certificates has pushed down the market price to about $31, meaning trade on the government registry is virtually paralysed with a backlog of more than $280 million worth of certificates.

''It does mean that if people took at face value they would get $40 and put them in the (government) clearing house, they will wait a long time,'' said John Grimes, chief executive of the Australian Solar Energy Society. ''The message to those people is that really there is no guarantee that those certificates will ever be cleared out of there. I certainly don't see the price of certificates rising to $40.''

The delay is also hitting installers, who often take the certificates off the buyer's hands in return for an up-front discount. One major firm, which did not want to be named, told The Age it was pulling its certificates out of the government registry and selling them on the market at an estimated drop in value of $1 million.