It seems obvious; energy harvesting is intermittent, so combine different types to make it continuous and therefore much more useful. Coordinated multimode EH could largely overcome intermittency and increase power density and cost-effectiveness with less or no energy storage required. Indeed we see it in a crude way with the combination of photovoltaics and wind turbines on both road furniture and seagoing boats. Add to that buoys at sea and autonomous underwater vehicles that both garner wave and solar power. Again one works in bad weather and the other in good.
So what became of the dream of something the size of a cigarette packet providing three or four types of energy harvesting for general use? It has proved tougher to do as a commercial offering than had at first been realised. Acceptable broad band piezoelectric vibration harvesters have not been forthcoming for mass usage. Thermoelectrics is also designed to purpose rather than general purpose as needed in a universal product. For providing the most useful power, photovoltaics needs to have greater area than that available on a cigarette-sized package so back to the drawing board. Indeed, charging mobile phones on the move now looks like succeeding not with energy harvesting but with ubiquitous contactless charging stations to the widely agreed Qi standards. That is planned to be embedded in Starbucks tables: it recently started to appear in new cars for charging mobile phones and the like.
Multiple energy harvesting is not yet getting major commercial traction but the need is so strong and it is so feasible we are sure success awaits. For example, the different modes can work alternately as with an electric car charging its battery by photovoltaics and wind turbine when parked, by energy harvesting shock absorbers and photovoltaics when going along and by electrodynamic regenerative braking when slowing down. Sometimes they can be optimally matched.
Electrodynamic energy harvesting is the most fertile technological option in its scope, such as energy range, versatility, price and options for shape. The variations are proliferating.
The end game for multi-mode harvesting in one package could be smart materials exhibiting several EH properties. The University of Bolton in the UK is developing flexible plastic film layered to create hybrid piezo photovoltaic harvesting (HPP). This can blend into many forms of structure such as curtains, airships and sails.
For more, see the IDTechEx overview report on energy harvesting from microwatts to tens of kilowatts off-grid which covers the whole subject with forecasts and timelines - Energy Harvesting: Off-grid Renewable Power 2015-2025.
Top image: Small wind turbines in Minhang (Shanghai), China. Source: Anthony Ivanoff (talk), Wikipedia