Presentation by Mark Whitby, BEng, FEng, FICE, Hon FRIBA of Whitbybird Ltd to the SGR Conference on Saturday 22nd October 2005

In the debate about energy and the security of supply it would appear that almost every possible scenario has been covered from every viewpoint and persuasion. However, to my mind there is a gap which possibly has more to do with economists than engineers but nonetheless, as an engineer, I attempt to explore it.

Over the next 20 years and more we are inevitably going to continue to burn fossil fuels and the question is not only about how much we use but also how wisely we use it. After all, whilst we can each question the number of journeys we make as individuals, some journeys will be essential and, likewise, some consumption of power in the home necessary. What we will all try to do, I hope, is to reduce our needs, and some of this reduction will come at the expense of spending more energy to create a more benign environment. A classic example is insulating one’s home, where a little energy spent up front will go a long way in reducing long-term consumption.

What has been interesting for me as an engineer is the balance point at which investing energy in making a building more sustainable uses more energy than would be delivered by a similar investment of energy in a renewable generator. You will notice here that I am talking in terms of energy. It could be money – the economist’s measure of value – but, if we are looking at the earth being able to tolerate a finite amount of emission over a period of time, then we had best stick to the energy-side of the equation.

What is obvious is that, whilst we can make a zero-energy property, to do so could be at the expense of the environment, as the energy consumed might have been invested better. Or, conversely, had those last units of energy been invested in an alternative generation system, that system would have delivered more renewable energy than the losses associated with not investing the energy in the property.

Imagine a new village with a thousand dwellings: we can choose to make them efficient or super-efficient with the increased costs for super-efficiency being x, or, alternatively, we could buy that community a share in a wind farm that makes up the difference and leave them as just being plain efficient.

For an engineer, the question is how do we determine this balance point? For instance, the energy payback for a wind turbine is between 25:1 and 40:1, which means that within the 25-year life of the turbine, we are going to get back each year between 1 and 1.6 times as much energy as originally invested in building the turbine. The implication of this is that if the energy-saving device you wish to build into your home doesn’t save, in energy terms, at least one times the energy invested it may have been better to use that energy in an alternative way.

Of course, this only makes sense if you can invest in an alternative renewable source, and whilst your investment in the turbine makes sense on day one, if your house is to last a 100 years and the turbine only lasts 25, the equation can become distorted by the need to reserve some of the energy being produced for reinvesting in maintenance and replacement.

But let’s stop here for a second and look at that argument from the opposite point of view.

Whilst ultimately simplistic, this is fundamental good house keeping, or, more to the point, good investment practice. All the housing developers I work with are mad about capex, the rate of return on capital expended, which means how little money do they have tied up in unsold property compared to the profit they are making on sales?

Each project the developer looks at, he asks how much money do I need to invest before I get a return and what is the rate of return. He may have a very big development but if he can deal with it in small bits his risks will be lower and he can work to a tighter margin. Alternatively, if the development involves major commitments to infrastructure in advance his risks will be high and he will have to have better margins.

We can look the same way at the energy we spend and examine the ‘capex’ of energy. What are the different rates of return on energy invested in generation?

Scaling the argument up we can start by looking at good clean hydro-power. It takes five years to build and will produce 200 times the energy invested in a life of 100 years, i.e. for every one unit in, we get two back per year. However, it takes five years to build. So, if we were investing one unit a year over ten years, after five years we would get our first functioning hydro station with an output of ten units per year, and, a second after ten years. Using the same argument we had for the house, we choose to reinvest the ten-unit per annum output from the first hydro station in another station, giving us another, much larger, station built from 50 units with an output of 100 units per annum. So, by the end of the ten-year period, we have a production capacity, for an investment of ten units of energy of: 10 + 10 + 100 = 120 units per annum.

Alternatively, imagine we were investing in a nuclear power station, which would take ten years to build, last 20 years and yield 40 units of energy for each unit of energy invested; i.e. two for every one unit invested. The equation, based on exactly the same energy spend as our hydro-electric scheme, is a simple 20 compared to 120. Clearly, it is in the interests of society to find as much hydro as we can in looking for the responsible expenditure of our remaining allotted energy share.

But let’s go one step further on.

Wind turbines generate between 1 and 1.6 units of energy per annum for every one invested and are built in six months. Let’s keep the sums simple and imagine this is a year (perhaps they are off-shore). After the first year we have invested one unit that delivers a return of one over the second year. We reinvest this new output along with the second unit of borrowed energy so that the total production capacity at the end of the second year is three. Over the next year we invest another unit of borrowed energy but reinvest the output of the original three to give three more turbines and achieve an output of seven units at the end of third year.

For the next year, we reinvest the output of the seven, to give us seven more, which, together with another one unit of borrowed energy totals 15. At the fifth year, on the same basis, the 15 give 15 more, which, plus one more borrowed unit is 31. At the end of the sixth year, it is 63, at the end of the seventh year it is 127, at the end of the eighth year it is 255 and at the ninth year it is 511 and finally, at the end of the tenth year we have a return of 1023 from the same ten units of energy invested in the nuclear power station: a 50 times better investment.

The current debate focuses around the need for action now, while things are still okay, on the basis that nuclear has such a long lead in and construction time. The reality is that there is no need to panic. The renewable systems have gone through the proving stages and their rapid deployment, on an exponential level is the challenge for engineers. We have been there before.

The nuclear lobby are surely joking.

**Mark Whitby** is a founder and director of the engineering design practice **whitbybird ltd**