Your choices so far:
1 Process heat (> 1000 °C)
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| Biomass (digestible sludge) | District cooling | Comfortable indoor climate |
| Biomass (fermentable sludge) | District heating | Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| Water | Fuel: Solid | 1 Process heat (> 1000 °C) |
| Wind | Local cooling (ind. house) | Transport |
| Residual oils/fats etc | Local heating (ind. house) |
For processes occurring above 1000 °C such as glass melting, steel reheating for rolling, the burning of ceramics like building brick in tunnel furnaces or cement in cement kilns; fossil fuel firing by natural gas, LPG or oil together with electricity are today the major sources of energy supply.
When discussing the potential to replace these fuels with renewables, the very first thing to keep in mind is that through all ages up until and including the mid 1800's, industrial manufacturing was based exclusively on the use of wood and charcoal as fuel. The very simple fact that all building materials – cement, steel, brick, glass, tiles... – used in the palace of the doge in Venice or in the castle of Versailles was produced in wood-fired furnaces prove that there are no thermodynamic hindrances to use wood and charcoal as fuels to produce the same things today. Similarly, the fact that cast iron stoves were produced already during the 1700's contradict the misconception that steel production requires fossil fuel. Rather the other way around: With modern process technology, there are no real hindrances for us to re-introduce several of the "traditional" fuels back into the heavy process industry.
Of course this should not be done un-critically: Modern blast furnaces are simply too big to be run if charcoal would replace the metallurgical coke, just to mention one example. There will also be a number of examples where the products of today are so advanced that the demands on process control, be it for temperature or for furnace atmosphere, simply makes a change of energy carrier impossible. Finally, like for temperatures exceeding 2000 °C, replacing electricity in plasma torches by oxy-fuel fired wood-powder burners would simply be stupid.
But for a number of processes and especially for those producing relatively simple bulk products such as standard cement or building brick or container glass, the arguments against a re-introduction of renewables to replace fossil fuels need to be critically revised.