Read the passage and answer: Although solar power once seemed impractical for everyday use, advances in technology have changed that. Modern solar panels are far more efficient and affordable than earlier models. As a result, many homeowners now install them to reduce electricity costs. What is the main idea?

The passage traces a change: solar power was once impractical, but technological advances made panels more efficient and affordable, so homeowners now adopt them. The main idea ties these together — improvements have made solar power practical and affordable for homeowners. The other options are supporting details or partial points (old panels were inefficient, electricity is costly) that don't capture the full message. The word 'although' sets up the central contrast between the past and the improved present, which the main idea should reflect.