Mark Greenaway writes about writes about robots being designed to remove weeds from farms. This seems like a bad idea given that we currently have an energy crisis due to CO2 emissions from power plants causing environment change (including reduced water supplies), and coal and nuclear power plants requiring water to produce electricity (pity about the reduced water supply). Introducing robots that require either electricity of petrol for operation and also maintenance (which probably requires plastic parts on occasion) seems to be more of a problem than a solution.
Fortunately there is already work in progress on training sheep to eat weeds. Given that we already raise sheep for wool and food it makes more sense for them to eat unwanted vegetation (weeds in a vineyard is the example given) than to grow grass specially for them.
Also Mark says that the recent increase in oil price is not good news. What would be ideal is a slow steady increase in petrol prices that allows individuals and companies to change to more efficient vehicles (smaller and slower vehicles, hybrid vehicles, and more use of public transport) and also allows governments to make changes (such as building new public transport infrastructure). Having the oil remain cheap until it starts to run out doesn’t do anyone any good (apart from the short-term interests of oil companies).
If only we could make the robots run on weeds. :)
More seriously, though: if you intended that as a serious proposal, you would need to carefully consider the relative cost of a robot versus a sheep, and the rate and efficiency with which they remove weeds. You should also consider that not every farmer with a weed problem wants to raise sheep.
Furthermore, while you do raise some reasonable concerns about the energy efficiency of robots, from the perspective of the farmer it only matters how much the energy costs: how many weeds will the robot eliminate for how much electricity/gas/$ALTERNATIVE_FUEL.