Buckets are not only for beer

At university during one of the oil price shocks we were sent off to investigate the potential of chicken poo as an energy source, with hindsight, I now realise that this was just a subtle marking scheme.  In the first years of the 21st century we were going to save the planet by strapping wind turbines to our chimney pots.  Despite the general tone of this blog I support the concept of a sustainable energy economy, but building one is a big, big challenge.  As I stare out of the window, I can neither smell chickens or see a wind turbine, but there may be some rooftop PV lurking in the shadows.

Wind and solar installations are energy conversion systems, for example wind turbines take something that blows your hat down the street and turns it into electricity which you can use to light your home.  Baz Luhrmann has remarked on sunscreen.  Whilst you can learn much about wind and solar energy by staring at maps and graphs, messing with models and prototypes is also instructive and much more fun and this was where the Solar Bucket started around 2007.

The Solar Bucket, so called, because for a short time some of the bits were located in a bucket before being moved to a large sandwich box.  The concept was simple, a 4.7 watt solar panel charged a 3.2 AH lead acid battery during the day, overnight the energy stored in the battery was used to power something.  Initially, the something was a couple of 10 watt resistors, whilst these provided a steady load, they were a bit boring, so after a few months an old computer case fan was installed.  This was a bit more entertaining, but failed to grab the interest of either my family or neighbours, the breakthrough came with a 12 volt LED light which was bright enough to read a newspaper and more appropriate to my family, light the outdoor dinner table so that we could see what we were eating.  The energy yield was determined by giving the battery an hour to stabilize at dawn and dusk and then measuring the voltage, the battery having been previously calibrated.

A more detailed description can be found here:

The Solar Bucket

This page also contains links to results and discussion.

Compared with virtually anything found in a school lab, this was a crude bit of equipment, but over the period 2008/2009 generated enough data to produce this.

Underlying this graph is a learning curve and in particular how to manage the battery.  The battery was much too small and probably suffered damage from overcharging during the summer months, only later did I learn enough about power electronics to give the battery some protection and also a bigger battery would have helped.

Whilst undeniably crude, this experiment taught me some useful lessons.  Close to the top of the list is the challenge of seasonality.  We're 50 degrees north of the equator, so the sun is low in the sky in winter and often hiding behind cloud, so unless a solar energy system is going to be stupidly large you are not going to get through winter without either a backup or a complementary technology, such as a wind turbine.  Next, was the importance of energy management, the LED light worked because it was efficient and was able to use the energy in the form which it was available , i.e. 12 volts DC.  Whilst its possible to provide a range of low DC voltages with reasonable efficiency, there are higher losses associated with moving to 240 volts AC which is what many domestic devices expect.  Most important is the opinion that storage is the missing link in the sustainable energy economy, this is especially true for solar energy systems because the Sun does not shine at night and some summer days can be a bit dreary also the demand for power rarely matches the supply.

A couple of pictures show the reality:

This is my favourite picture of the Solar Bucket.  The panel was easily restored to functionality with a yard broom but without this simple maintenance the energy yield would be zero on a snowy day.  Bird poo also made a return visit to renewable energy.

This is the computer case fan, the blue LED's gave a frisson of excitement to task which often involved standing in the rain.

I recommend this experiment to politicians and policy makers.