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Solar with battery storage- run off the sun during the day and batteries at night. What holds me back is the initial investment; the batteries are freaking expensive.
In the USA; when fuel costs are factored in, Natural Gas is the cheapest way to go. Actually costs less to run my house (and a neighbor's) for less than the local power utility- to the tune of $10/month. An awful long time to pay it off though.
Diesel and Propane are close in price for operations, and gas/petrol is the least efficient.
For us tinkerers out there (eg CodeWitch)... an old diesel genset could be converted to run on many different oil-based fuels such as heating oil, kerosene, vegetable oil.
Disclaimer: I work for Generac/Pramac
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