Energy and climate change

 

 

I can imagine groans ” not another post on climate change”. Although climate change is real and happening I want to talk more about some encouraging developments. It is generally agreed that energy is the root of the problem. Mankind has progressed by burning fossil fuels but this cannot continue. But perhaps we need to recast this by asking ourselves what energy we need. Essentially we burn fossil fuels to heat spaces or generate electricity. Leaving aside space heating for the moment lets think about electricity which is a medium of transferring energy.

Electricity is far more in that it is a nearly ideal form of transferring energy. It is efficient, clean quick and capable of transmission over long distances. Electrical technology is fairly well understood and electrical equipment is widely used. Electricity does have one major drawback: it cannot be readily stored. The modern electricity grid matches supply and demand on a second by second basis. In the UK there is only one big storage system and that is pumped water in North Wales. The idea is that water is pumped by electric pumps from a low reservoir to a high one. Then the stored energy is released by allowing water from the high reservoir to flow to the low through electrical generators.

It is just becoming technologically feasible to have grid scale battery storage. A 100MW battery system is operating in Australia. A more speculative possibility is that vehicle batteries could be used as electricity supply buffers. Although discussed no such system is in operation. There is speculation the electric vehicle pioneer Tesla is about to announce plans for use of vehicle batteries to offset fluctuations in electricity usage. Another supply offset occurs with interconnectors between counties. Such interconnectors are in use and are increasing but are necessarily on a very large scale. They exploit the fact that different places use electricity at different times.

It is important to realise that electricity storage possibilities don’t increase non carbon energy supply but they increase the flexibility of supply. This is important because the lead low C energy sources of wind and solar are highly variable. Wind power is particularly interesting because its cost has now fallen to fossil fuel levels. Solar is still more expensive than fossil fuel.

The outsider in many ways is nuclear. The stability of nuclear production for baseload supplies is valuable. Nuclear stations need to run continuously. The problem is that large nuclear stations are very expensive to build although once built they are cheap to run. One possible route forward is to build small modular nuclear stations ( SMR ) which would be factory made in quantity rather than monolithic one off stations as current practice.

Space heating can be considered somewhat separately although there are strong links to overall energy uses. The main technical difference is that whereas electricity generation by thermal means needs high temperatures, space heating doesn’t. Space heating, the internal heating of homes and offices requires modest temperatures. Electricity is both directly applicable and indirectly by powering heat pumps. A heat pump can be thought of as a refrigerator in reverse. The pump is electrically powered but takes its heat from the air or the ground. Very roughly for every unit of electricity the pump supplies about four units of heat. Heat pumps are a well established but little used technology.

There has been a lot of talk of the hydrogen economy. Hydrogen is a gaseous fuel and there is ongoing investigation into using to partly replace natural gas. At present hydrogen is expensive but it could be made by electrolysing water. This means passing electricity through water to break the water up into its constituents , hydrogen and oxygen. One big problem is that hydrogen is rather tricky to handle. It cannot be easily liquefied and is normally stored as compressed gas. For use in vehicles compressed hydrogen can be used in a fuel cell to produce C free electricity. Fuel cells are known and used but their technology is immature.

As far as vehicles are concerned there is another way of looking at the problem. Petrol is a very concentrated form of energy. The weight of petrol to drive a vehicle a long way is modest. Vehicles can be refuelled with petrol in minutes. In contrast batteries are very heavy for the amount of energy they contain and recharging is relatively slow. The recharging rate is being increased but we are still looking at tens of minutes. Charge density in batteries looks much more difficult and despite immense efforts improvements are slow. It seems likely that the energy density of batteries will always be low compared with petrol.

There have been efforts to develop a liquid fuel which is both low C and as dense and easy to use as petrol. The only liquid fuel replacement which has found large scale use is alcohol. Alcohol can be a fuel in its own right or it can be  blended into petrol in low proportions. .Alcohol can be made by fermentation and then distillation( rather like spirits for drinking) but this is fairly expensive and requires a fermentable feedstock.

In conclusion it seems that a ferment of investigation and innovation is occurring. Right now wind turbine generated electricity looks the best way forward with the electricity used to charge batteries for vehicles as well as myriad other uses. Batteries are on the fringe of being adequate both for vehicles and grid storage.