Campaigners say they fear that a "gold rush" in planning applications from solar firms and landowners will scar the Cornish landscape.
Protestors are worried the cessation of a five-megawatt ceiling on government subsidies and lower panel prices has caused interest to rocket.
The county already has 12 solar farms with permission granted for a further 24.
The largest existing solar farms currently have about five-megawatts capacity – enough to supply about 1,000 homes.
One application in the pipe-line is for a five-megawatt farm on land at Lanthorne, Tideford Cross Lane, Tideford, South East Cornwall. If council chiefs grant planning permission, 20,876 panels will cover 17.25 hectares of farm land.
Earlier this week, St Germans/Tideford Parish Council voted not to support the application and also a separate application for a wind turbine at Bake Farm, Trerulefoot, near Saltash.
Nigel May, spokesman for Save Landscape in Cornwall (SLIC), said he feared solar farms would be springing up all over the county, ruining the countryside.
He said: "There's a real gold rush attitude to starting up solar farms because of the amount of money to be made – between £500,000-£750,000 a year I believe.
"The proposed site is much larger than any other equivalent five-megawatt solar farms applications which are normally for around 25 acres.
"This solar farm would be in a designated Area of Great Landscape Value and will have a detrimental impact on the character of this well-loved countryside by industrialising what is a rural landscape."
Mr May said he had no objection to alternative forms of energy being explored on a small scale, but felt the county could not afford such large- scale operations.
The site in question is north-west of Tideford, near Tideford Cross, and consists of two separate areas divided by Tideford Cross Lane. Currently the land is used mainly for livestock grazing.
Rows of panels would be encased in an aluminum frame mounted on a galvanised steel frame with an overall maximum height of approximately 2.3 metres.
Each panel would be either matt blue or black in colour and not reflective.
The panels would be angled at 25 degrees from horizontal and orientated in a series of linear arrays facing south to maximise energy output.
Tim May, chairman of St Germans/Tideford Parish Council, said the vote to reject the proposals was carried unanimously.
He said: "Around 50 people attended the meeting to object – normally we get two or three, so it shows the level of local feeling against it."
According to the planning application lodged with Cornwall Council, the land is owned by John Blake of Dean Street, Liskeard.
Agents acting for Mr Blake are David Jarvis Associates based at Swindon, Wiltshire.
The firm declined to comment to the Western Morning News.