The three schemes at Cruachan, Galloway and Lanark, have a combined output of 562MW. The largest of the three, Cruachan in Argyll, has enjoyed its best performance in 10 years, with production rates at an all time high due to recent investment.
The £20M will be used to carry out a range of civil works at each of the sites and to maintain and upgrade operational equipment. Some of the plants were originally designed in the 1920's and this investment will ensure continued high performance in the coming years.
ScottishPower's commitment will also mean that both Lanark and Galloway will still be in operation when they celebrate their centenary years in 2027 and 2036, respectively.
Frank Mitchell, Generation Director at ScottishPower, said: 'In a climate of global volatility in the wholesale energy markets, hydroelectric plants are proving to be an extremely efficient method of generating electricity as input costs are relatively low. With no signs that the global markets will level off any time soon, hydro will continue to be an important aspect of our generation business and this is reflected in our investment.
'Hydro is also very versatile and can be brought on-line quickly when required, so is an essential element in guaranteeing secure supplies of power across the entire network.'
