From LOW-TECH MAGAZINE
Most of the talk about renewable energy is aimed at electricity production. However, most of the energy we need is heat, which solar panels and wind turbines cannot produce efficiently. To power industrial processes like the making of chemicals, the smelting of metals or the production of microchips, we need a renewable source of thermal energy. Direct use of solar energy can be the solution, and it creates the possibility to produce renewable energy plants using only renewable energy plants, paving the way for a truly sustainable industrial civilization. A large share of energy consumed worldwide is by heat. Cooking, space heating and water heating dominate domestic energy consumption. In the UK, these activities account for 85 percent of domestic energy use, in Europe for 89 percent and in the USA for 61 percent (excluding cooking).
Heat also dominates industrial energy consumption. In the UK, 76 percent of industrial energy consumption is heat. In Europe, this is 67 percent. I could not find figures for the US and for the world as a whole, but these percentages must be similar (and probably even higher on a worldwide scale because many energy-intensive industries have been outsourced to developing countries). Few things can be manufactured without heat.
The importance of heat in total energy consumption sharply contrasts with our efforts to green the energy infrastructure. These are largely aimed at renewable electricity production using wind turbines and solar panels. Although it is perfectly possible to convert electricity into heat, as in electric heaters or electric cookers, it is very inefficient to do so.
It is often assumed that our energy problems are solved when renewables reach ‘grid parity’ – the point at which they can generate electricity for the same price as fossil fuels. But to truly compete with fossil fuels, renewables must also reach ‘thermal parity‘.
Though today in some locations it may be as cheap to produce electricity with wind or solar energy as with gas or coal, it still remains significantly cheaper to produce heat with oil, gas or coal than with a wind turbine or a solar panel. This is because it takes 2 to 3 kWh of fossil fuel thermal energy to create 1 kWh of electricity, so it is at least 2 to 3 times cheaper to make heat by simply burning the fossil fuels directly than to use an electric renewable technology at grid parity.
This means that solar panels and wind turbines will have to become two to three times cheaper than they are today in order to reach thermal parity with fossil fuels. This might sound reasonably possible, especially if you expect fossil fuel prices to rise. But consider this: even though they are intended to replace fossil fuels, renewable energy sources like wind turbines and solar panels are in fact dependent on a continuous supply of fossil fuels.
Solar panels and wind turbines do not need fossil fuels to operate, but they do need fossil fuels for their production. You won’t find any factory manufacturing PV solar panels or wind turbines using energy from their own PV solar panels or wind turbines. Why not? Because it is very inefficient (and thus utterly expensive) to convert electricity into heat. Yet to make solar panels and wind turbines, to produce steel and silicon for instance, heat is what is most needed. This means that the production costs of solar panels and wind turbines will be affected negatively by rising fossil fuel prices. an essential element of electric cars and renewable electricity storage, and for many other modern green technologies, like LEDs and heat pumps. They require heat for their production, and this heat can be delivered at least 2 to 3 times cheaper by burning fossil fuels than by using wind turbines or solar panels (cheap electricity from hydropower plants is also an option, but has limited potential). This is a fundamental problem, because we will have to produce new wind turbines and solar panels every 20 to 30 years, and new batteries every 5 to 10 years.
Renewable source of heat energy
The missing element in our sustainable energy strategy is a renewable source of thermal energy. Geothermal energy produces heat, but its potential is limited to regions that have volcanoes. Biomass is another option, but it faces many problems. If we were to try to provide an important share of heat demand by burning biomass, we would quickly come up against the limits of what the planet can produce. There is only one source of heat energy left, and it is a powerful and inexhaustible one: solar energy.
We tend to see solar energy as yet another way to generate electricity, using photovoltaic panels or solar thermal power plants. But solar energy can also be applied directly, without the intermediate step of generating electricity. Basically, harvesting direct solar energy can happen in two ways: by means of water-based flat plate collectors or evacuated tube collectors, which collect solar radiation from all directions and can reach temperatures of 120 °C (248 °F), and by means of solar concentrator collectors, which track the sun, concentrate its radiation, and can generate much higher temperatures. These can be parabolic trough systems, linear concentrating Fresnel collectors, parabolic dish systems or solar power towers. Almost all of these technologies were developed at the turn of the 20th century.
The problem is that we mostly use this technology for the wrong purpose. In today’s solar thermal plants, solar energy is converted into steam (via a steam boiler), which is then converted into electricity (via a steam turbine that drives an electric generator).
This process is just as inefficient as converting electricity into heat: two-thirds of energy gets lost when converted from steam to electricity. This is one of the main reasons why the use of solar thermal energy to produce electricity is only cost-effective in deserts…
Complete article here ~~