Examples of such investments are electric vehicles, heat pumps and energy efficiency measures. In the case of electric vehicles, the limits on range and refuelling time have imposed inconveniences which have had a great impact on the commercial viability of electric vehicles for many years - to a degree where range and charging time are the two main parameters in R&D on electric vehicles. In the case of energy efficiency investments or conversions of heating systems, the economic benefit of making the switch may be so low that it is barely worth considering. Unlike machines, humans tend to have a minimum threshold for effort versus payoff.