The fund gives people access to interest-free loans of up to £10,000 for a range of renewable technologies such as a wind turbine or a solar water heating system.
Aiming to reduce the dependency on fossil fuels, more than 1,000 loans have been handed out to homeowners since the project was launched in April 2011.
First Minister Alex Salmond announced the Home Renewables Loan Scheme would be given additional funding while visiting the Western Isles as part of a series of travelling Cabinet meetings.
Speaking after a visit to a home on Lewis where the family received a loan to install a wind turbine and air source heat pump, he said: "Scotland is going greener and the wide take-up of small-scale renewables appliances in households will be vital for us to become a low-carbon economy. There has never been a better time to save energy and go green.
"Since April, 2011, more than 1,188 loans have been issued to householders across Scotland and in particular more than 53 loans across the Western Isles, islanders are clearly leading the charge in choosing efficient green energy.
"I am delighted to allocate further funding of £4 million to this successful interest-free loans scheme, so that even more Scots like the Smith family can reap the benefits of low carbon technologies, cut energy bills and emissions, support jobs and the local economy."