Olive - 1 - Description

For a long time I have been interested in relationship between sustainable energy sources, climate and terrain.  An attempt to produce a megalithic chunk of software using downloaded data was instructive but failed to produce anything useful.  Software like pet dragons acquires names and this code was called Druid.  Rather than give up on the concept I recently adopted a completely different approach.  The concept was to build some simple equipment and to take one or two short data-shots each day from my back yard.  Over a period of a year this would produce a few hundred data points which hopefully would provide enough samples to draw some conclusions but not so much that it could not be assimilated.  Because hardware was involved, the name changed to Physical Druid and the equipment was called Olive.

Olive attempts to measure solar irradiance.  The sensors are two very small horizontally mounted solar panels.   Because they are flat they have a good cosine response.  During a data-shot one of the sensors is shaded from the direct rays of the sun and therefore only receives diffuse irradiance, the other is not shaded and it's output is a combination direct and diffuse irradiance.  Combining the output of the two sensors it is possible to estimate direct normal irradiance.

The current produced by a photocell is proportional to the irradiance it receives.  A resistor is connected across each cell and the voltage across the resistor is also proportional to the irradiance.  The voltage across the resistors is only a few mV which is too small for the analogue-to-digital converter on the Arduino Nano so a TS358CD op-amp is used to get the output into the range 0 - 5 volts.  The Arduino Nano is a brilliant piece of equipment, I first used it on a small dynamometer and found it easy to use for both control and measurement and it works well with Olive.  The Nano connects to a Raspberry Pi model 2 which acts as data logger powered by a 20,000 mA power bank.  A data-shot consists of approximately 16,000 observations over an eight minute interval.  During a data-shot a photo of the sky is taken with my mobile phone.

The observing site is real-world rather than ideal.  Olive sits on pillar on the wall which separates my back yard from the street, the quality of the measurements will improve as the sun gets higher in the sky.  On the plus side, Olive is a good conversation starter.

Data from Olive is fed to an evolving suite of programmes on a Raspberry Pi 3, I'm still figuring out how to use the stuff.  The basic presentation consists of a plot of the sensor output, a cropped and resized version of the phone photo, a graphic showing the attenuation of the irradiance by any passing cloud.

To give the observations some context, some data from the Global Forecast System has been added.  The objective is to attempt to explore the results using machine learning methods.

Doris B - Diodes and dynamometers

If simplicity is a virtue then my first attempt at making a dynamometer could be regarded as sinful.  This more successful machine consists of a wooden pulley bolted to a bicycle hub generator.  The pulley is turned by fishing line attached to a weight, a 10 watt resistor acts as a load.  An Arduino measures the voltage across the resistor and senses the rotational speed as the weight falls, all this provides enough information to estimate the input and output power which in turn suggests the efficiency of the system.

The generator turns out AC but to charge batteries it is necessary to convert the output to DC.  When developing anything, a good rule is "first make it work, then make it work better".  Initially, a standard silicon bridge rectifier was used.  This had a voltage drop across the diodes of 0.7 - 0.8 volts.  I flirted with the idea of smart diodes based on mosfets but this required greater knowledge and skill than I possess.  A simpler alternative was a bridge rectifier made up of Schottky diodes.  These have a voltage drop of around 0.2 volts.  The effect was to increase the power available to do something useful as shown in the graph below:

For a given speed, the output is roughly 0.3 watts higher with the Schottky diodes, they also increase the system efficiency by about 10%.

The diodes are rated at 100 volts to accommodate the generator when it goes open circuit.

The next step is to use the dynamometer to investigate the use of pulse width modulation to manage the load.  The objective is to use the power curve to optimise the relationship between the rotor and the generator.

Doris B - The experience box

I was in a bar chatting to one of my sons (he's 31).  There's some overlap in our work experience and we were talking about product development and he came up with the description "first we make things, then we break them" which is a variation on one of my mantras "if you want to learn fast, make mistakes fast".  This gives me great faith in the next generation.

Oddly, I've just cleared some space in my work room by dumping less than successful bits of wind turbine into a box.  This includes three rotor designs, two generator, several attempts at making drag buckets and does not include several Meccano constructions which have been dismantled.  Work had been progressing steadily but I came to the conclusion that the generator I was using was probably 15 years old albeit in good order.  It might have benefited from being stripped down and the bearings cleaned but I was uncertain about the state of the magnets.  As I'm about to invest some time and energy in this project, I thought it would make sense to start with a brand new one.  The new one is slightly smaller and lighter than the original, so the bucket carrier and the dynamometer ring will have to be remade.  A slightly tedious task but an opportunity to remove some defects.

The dynamometer is very simple, it consists of a length of fishing line wound onto a pulley, the line runs through a pulley/block on which a weight is hung.  As the weight descends, it turns the generator.  The Arduino works out the rotational speed and the energy generated, the rotational speed is also a measure of how fast the weight is falling allowing the input energy to be estimated which in turn allows the efficiency to be estimated.

Doris B - Trial Assembly

10-April-2019 - Completed the partial assembly of the Doris B5/6 small vertical axis wind turbine this morning before giving it a trial outing on the Downs later today. 

The objectives of the initial trials are to determine if it rotates in a wind of 5 m/s and does not disintegrate at 10 m/s. If it survives, the next step will be add some instrumentation and to try and figure out how it works. The design is based on some maths, guesswork and wishful thinking. There have been four previous versions, mostly made of Meccano and sawn up bits of plastic pipe, this one is mainly made of wood. This is not a finished design but part of a process of learning how to make small wind turbines for rural and urban environments, hopefully the design will evolve. The objective for this series is an output of 2.5 watts (similar to a standard USB port) at 5 m/s.