Every qualifying person (citizen, legal resident, TBD) would have a baseline exemption. As you point out energy requirement varies by geography, and the exemption would also have to be geographic sensitive.
More importantly, such an energy based tax system would result in the vast majority of tax being remitted by business and institutions, not individuals. Businesses would not be able to avoid taxation through accounting tricks, but at the same time the cost to business of paying tax would be eliminated because it requires no bookkeeping. Like all taxes on business, this reflects in cost of products and services. Less energy intensive products and services become more competitive on cost.
More importantly, such an energy based tax system would result in the vast majority of tax being remitted by business and institutions, not individuals. Businesses would not be able to avoid taxation through accounting tricks, but at the same time the cost to business of paying tax would be eliminated because it requires no bookkeeping. Like all taxes on business, this reflects in cost of products and services. Less energy intensive products and services become more competitive on cost.