When Sutherland crofters were asked to support a wind farm on land they had an interest in more than 10 years ago, Tom Robinson decided to get behind the project.

It led to him becoming a director of the Kilbraur Co-operative and buying shares. He has since also responded to the share issues for three of the other Scottish co-operatives. "It has worked out excellent," he says. "There was one year when we only got 7.6%, but then you look at an Isa paying 0.1%. One year it was 10.6%."

On tying up the cash for 25 years, he says some of his shares have been bought for grandchildren, but adds: "If somebody wants to pull out because they have hit hard times, they can apply to the co-operative board which will offer the shares to other shareholders."

Investors attracted to renewable energy and looking for good returns have subscribed £132,000 to the latest Scottish wind farm co-operative share offer in its first week.

They should earn profits well above the payback on most conventional investments – though their cash could be tied up for 25 years.

The Spirit of Lanarkshire Wind Energy Co-operative launched its public share offering last week to raise up to £2.7 million for stakes in two local projects being developed by Falck Renewables Wind, near Coalburn and Strathaven.

Uniquely in the UK, the sponsor, Energy4All – established in 2002 in Cumbria – is owned by the nine co-operatives it has set up, including five in Scotland.

Investors in one of the earliest co-operatives, at Kilbraur in Sutherland, were guaranteed returns of at least 6.5% a year by Falck, depending on electricity sales during each year, and have seen returns above 10%.

Jim Lee from Hamilton, chairman of Spirit of Lanarkshire, said: "Individuals, businesses or any organisation may invest between £250 and £20,000 by purchasing shares.

"Priority is given to residents of South Lanarkshire and, if these wind farms perform as well as existing Energy4All Scottish co-ops, we can all expect to enjoy an average annual return of around 8.5%."

On the first week's subscriptions, Lee said: "This is a great start and very encouraging news. We very much hope that this initial momentum can be maintained and we will be working hard to get the message out there.

"The share offer gives everyone in South Lanarkshire and beyond the opportunity to become a member of the new co-operative."

The wind farms are Nutberry Hill, near the village of Coalburn, with six 2.5MW turbines, and West Browncastle, near Strathaven, with 12 turbines planned. It is the first time in Scotland that two wind farms have been part of the same co-operative, which suggests that anyone investing will get the benefit of revenues generated from both sites over the life of the projects.

While the share offer is open until next March, those investing early will benefit, as funds raised by September – up to £1m – will be invested in Nutberry, allowing members to start earning profits from this date.

The co-op says it "intends to repay members' original investment after 25 years, however it may be possible for members to withdraw their capital before then on request".

Last month, Australian renewable energy firm CBD launched a four-year "mini-bond" offering investors a fixed rate of 7.5%, to finance UK solar and wind farm projects.

However, such bonds are unlisted products, so cannot be bought and sold on the London Stock Exchange (like retail bonds, corporate bonds and Government bonds).

Lending to companies, even in listed bonds, also means investors are not covered by the Financial Services Compensation Scheme.

The Dutch ethical bank Triodos is midway through a share issue to the public, raising capital which it says will "allow it to lend more to sustainable enterprises pioneering a greener, fairer economy".

The bank has 26,500 shareholders throughout Europe, and there is no transaction fee during the offer period which runs until July 25.

However, not all co-operative lending has gone to plan.

Some 7000 savers who loaned money to the Co-operative Bank, attracted by a high rate of return on its bonds and the bank's "ethical" credentials, are now facing big cuts in their income and a possible loss of capital under the bank's controversial refinancing.