Energy Conservation and Management

I suggest that energy management, conservation and storage are at least as important as generation in transitioning to a sustainable energy economy.

The development of wind farms and solar parks and other forms of sustainable generation is important, but it is easier to utilise energy from weather dependent sources if demand is low and managed and fluctuations in availability can be buffered with storage.

Reaching this conclusion (which I don’t claim to be original) was a two stage process. I first became interested in wind and solar systems around 2007, (just before the financial crisis) partly to find a use for data and programming skills learnt in the oil and gas industry and partly a desire to be the energy equivalent of Tom and Barbara Good (characters in the 1975 BBC sitcom in which the lead characters attempt self-sufficiency in Surrey). Being cautious by nature I investigated solar PV by creating a very small off-grid system based on a 4.5 watt panel, 3 amp hour lead acid battery and an LED light. During the day the battery charged and by night the LED light illuminated alfresco dining. Over a year, I learnt that at 51N, solar does not do much in winter and even in summer clouds significantly reduce clear sky solar irradiance. Wandering around the garden with a wind speed meter convinced me that an urban valley is not a good place to put a small wind turbine, even if I could convince the neighbours and the council it was a good idea. The conclusion f this stage was that it was better to buy electricity from a company with wind turbines and solar panels in optimum locations, such as offshore and on ridges.

The second stage started with a load of data, Excel, and Visual Basic, later to be replaced with Python. The objective was to understand the potential of wind and solar sources. A lot of time was spent fitting Weibull Distributions to wind speed data and a simple model of clear sky solar irradiance. The latter was based on simplified sun-earth geometry, the work of the Meinels from the early 70s which provided an estimate of direct normal irradiance and some crude observations of diffuse irradiance made in a local park. At this time I started trying to create a simple mode of cloud sky irradiance (this is still work in progress). There were several conclusions from this phase, the first being that offshore wind is a better source of energy than onshore wind, however, I know from my oil and gas days that working offshore is significantly more expensive than onshore. Economics may be inconvenient, but they can’t be ignored. Secondly, was the problem of seasonality. It’s a gross oversimplification, but at 51N, solar panels do not produce much energy in winter and summer winds are gentler than those of winter (the energy available from wind is proportional to the cube of its velocity). Thus a sustainable energy economy needs diverse sources, not an option for many urban households.

As an aside, much as I love software and data, its good to try and link what one sees on the screen with the effects of wind and sun which one feels in the face. I attempted to bridge this by cycling around the the town and surrounding countryside with a wind speed meter. If on the seafront, the wind was blowing smoothly at 10 m/s, on the roofs of multi story car parks in the town there would be long period gusts, depending on the direction my backyard could be calm and on the surrounding hills, the speed would still be 10 m/s, but with significant turbulence.

Having gently shelved the idea of putting PV panels on the roof, I concentrated on reducing household energy consumption. When we started, the house was lit by incandescent light bulbs and whilst we were not extravagant with energy, we did not think much about it. A quick win was swapping the incandescent lamps with CFL, this alone took consumption down from 20 – 25 kwh/day to less than 10 kwh/day. As things like computers have died, we opted for energy efficient replacements and in the last year, some CFL’s have been replaced with LEDs with the result that we now consume less than 5 kwh/day and have relatively low electricity bills. For heating, we have opted for the counter intuitive solution of reverting to open fires. Our gas central heating system is not yet zoned, by only heating one room, albeit inefficiently, the the amount of energy consumption for space heating has dropped. None of this has required major capital investment, but has given a better outcome than a roof full of PV panels. Technology has also changed, once I used a big PC to do sums and software, this also acted as a space heater, increasingly I now use a Raspberry Pi, excluding the attached monitor, this take about 3 watts of energy. This is where the doctrine of unforeseen consequences kicks in, I sometimes light a fire to keep warm in winter.

Wind and solar are both climate weather dependent energy sources. Solar works well in winter under the clear skies of a hot desert, less so in the cloudy ones of a winter in a temperate maritime region. Wind energy arrives in pulses, sometimes days apart, sometimes weeks, the pulses being stronger in winter than summer. I have no experience of grid management, but my understanding of demand is that it is low at night, rises during the day and peaks in the early evening when families, cook meals, children do homework and many people watch television or interact with screens. It would seem that grid management would be easier and generation more efficient it the load was constant. Thus if every new building incorporated a few hours of storage capacity the peaks in demand would be flattened and it would be easier to incorporate sustainable energy sources such as wind and solar.

Similarly, demand can be managed, a trivial example is our washing machine, we always run this around 09:00 in the morning for no very good reason, however, if the washing machine is part of the internet of things then something could make a decision on when was the optimum time, say in the middle of the night when demand is low or sometime when the wind is blowing and wind farms are productive. I do not minimize the problems of this approach, not least of ensuring that the machine is loaded and the door shut. Also, it is important to define the boundaries of the systems being controlled. There are at least two configurations, the first is at the level of the home where the home accepts a maximum load that they will impose on the grid, maybe, in return for a lower tariff. Alternatively, there can be central control by the grid operator. This taken to its illogical conclusion could spark a debate on civil liberties and washing machines.


About SolarBucket

I trained as a mechanical engineer in the 1970's and then spent most of the following 25 years doing sums and software for Oil and Gas Exploration. Current interests are the study of wind and solar resources.
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