Passage: "For decades, many small islands depended on diesel generators that ran only a few hours each night. Fuel had to be shipped in by boat, so electricity was expensive and stopped whenever storms delayed deliveries. Solar panels combined with batteries are changing this. Once installed, they need no fuel, and the batteries store daytime energy for use at night. The equipment still costs money to buy and maintain, but several island communities now enjoy power around the clock for the first time." According to the passage, why was electricity on many small islands expensive and unreliable?