Tanks can be heated at night (or midday), when electricity is cheaper and, in my case, when non-renewables are contributing less to the grid.

This is one of the bigger myths used to sell tankless. Modern water heater tanks are well insulated; losses are usually quoted as less than 10%.

From a cost perspective, the slight efficiency increase of tankless never pays back over the cost of the unit, and unfortunately, usually the more frequent repairs. The big benefit is the 'unlimited' hot water.