I’m sorry you are experiencing issues with reliable power. That is something no aspiring IELTS candidate should have to deal with. All you can do is do your best. One thing you could do is break down a study plan into “days” – day 1, day 2, day 3 etc. Then study that day’s materials whenever you get the opportunity.
Study plans do not have to be rigid. Adopt a study plan that meets your needs and accessibility issues.