Whatever the future energy mix, it's becoming apparent that coal and gas are both hugely consumptive and not entirely great for the environment--even if they provide large swathes of the world with their energy.

Renewable energies like solar, wind and hydro on the other hand supply only a small proportion of the world's population, yet they're vastly cleaner. The challenge is scaling them up to such an extent they can be truly useful.

But how do you make use of nature's own energy? One option is solar roads--using heat from the criss-cross of asphalt in every nation to generate electricity.

The theory is this: In hotter climates particularly, roads and parking lots get really hot. Oppressively, uncomfortably so if you're unlucky enough to be walking along one on a hot day, with extra heat radiating from the black ribbon of asphalt under your feet.

According to Oilprice, scientists at Worcester Polytechnic in Massachusetts propose burying water pipes an inch or so beneath the road surface.

Heat absorbed by the dark road surface then heat the water, which in turn can be used to generate electricity. As a side-benefit, the transfer of heat from road to water also helps cool the road surface, extending its potential life.

Water heating is used in many current solar generation applications. The difference here is that it's visually no more intrusive than the existing road already is. No fields would be filled with solar collectors, for example.

Rajib Mallick, the associate professor leading the team of researchers, says the team's "preliminary results provide a promising proof of concept for what could be a very important future source of renewable energy."

Don't get too excited though--there are a few hurdles to overcome.

The first is finding investors for a system with untried, unknown potential returns. Some scientists speculate that the heated water simply wouldn't be hot enough to generate high levels of energy, making return on investment too low.

And it'd be quite some investment - not just installation costs for the water piping and electricity generators, but the cost of fully re-surfacing any road where the system is installed. To ensure that return on investment, you'd be talking significant stretches of highway.

It could, potentially, be a technology worth pursuing on private land, but it seems like there are too many hurdles to see widespread adoption of solar road technology.


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