**3.1 Case 1: invention of a new hydro mechanism for sun tracking**

A new hydro-mechanism for interconverting linear and rotary motion was invented—and is described in a South African patent by the Cape Peninsula University of Technology (CPUT) [29]. The primary motive of the invention was to create a mechanism that would be deployed in a novel single axis sun tracking device that relied on mechanical energy to turn a domestic home solar energy collecting surface during the day, and return it to a morning position any time before daybreak. **Figure 3** shows the mechanism being used in conjunction with a photovoltaic panel.

## *3.1.1 Design processes*

The approach used was a slight modification of the Remo Reuben open process in **Figure 2**. There was branching at the stage of evaluating alternative concepts, which led to other, very different products altogether—discussed in Refs. [30, 31].

#### **Figure 3.**

*The hydro mechanism driving a sun tracking PV panel (watch online video at: https://www.youtube.com/ watch?v=79CKBxt\_h-I).*

### *3.1.2 Identification of need and formulation of engineering problems*

A need for a new single axis sun tracking device, suitable for sub-Saharan Africa conditions of bi-hemispherical location, low credit and disposable incomes, and an inadequate technical skill base had been established in Ref. [32].

The product design problem and its sub problems were defined as: "Design a single axis sun tracking mechanism and its coupling means to a domestic home flat solar collector, so that the latter will be able to receive more energy from the sun, and therefore through the appropriate conversion process, yield more output than when in a fixed orientation."

The sub problems, imposed by constraints discovered during identification of the 'Need' were:


#### *3.1.3 Solutions: evolution of the gravity driven hydro-mechanical tracker*

Many solutions were investigated. Some were tried up to manufacture stage, and then discarded. Here, only significant ones are described in chronological order up to the prototype milestone. The reasons for discarding or modifying them are given.

### *3.1.3.1 The initial concept: solar-thermal hydraulic (STH) system with mechanical clock control of valves*

A STH powered, spring controlled system was envisaged as in **Figure 4**. A hydraulic head *h***max** was to be provided by a liquid in shaded tank '**A**', connected to spring bank *k* through a one way valve **V1** and a cylinder-piston assembly. The piston rod would be a cylindrical rack, which energises the compression spring at the other end. The rack would drive a gear train to which, the frame holding the solar collector would have been coupled. At the end of the cylinder, was to be a one way valve **V2,** leading to an un-shaded small tank '**B**'. In late evening, with **V2** closed, and the piston at extreme western position, the panel would be facing west. **V1** would be actuated to open by the closure of **V2**. Liquid would flow into the cylinder, and compress the spring bank to the maximum (at which point a head *h***min** would act on the piston) while reorienting the panel to face eastward for the next day. In the morning, valve **V2** would be actuated by a clock signal to open. Valve **V1** would simultaneously close. During the day, the **V1**-**V2** link would be automatically deactivated to enable independent operation of **V2** without opening **V1**. Then, a clock mechanism would intermittently open **V2** allowing a precise liquid weight to flow into un-shaded tank '**B**' and then close for a definite period. This would relieve the spring bank a distance *x*, and in turn rotate the solar collector a definite angle westward—hence tracking the sun in this direction.

In due course, the liquid in tank '**B**' would vaporise and condense in shaded tank '**A**' so that the hydraulic head in '**A**' gradually rose during the day in preparation for a night

**75**

*Mechanical Engineering Design: Going over the Analysis-Synthesis Mountain to Seed Creativity*

return action. The panel tracking axis could be rotated about the piston-cylinder axis for correct installation at different latitudes by graduated scales in a plane perpendicu-

This concept required use of a low boiling point, low enthalpy of evaporation but high density liquid. The low enthalpy would give sufficient daily solar assisted evaporation rates while the high density would enable storage of enough mechanical energy to compress the spring and turn a collector whose centre of gravity would most likely be offset from the axis of rotation. Such a liquid was actually identified among the refrigerants (R140a) but it was expensive in Cape Town. Being a chlorohydro-carbon (CH3-CCl3), it was banned in some African countries. Although there were other issues, this alone was sufficient to disqualify the concept. However, many

After discarding the concept of using a chloro-hydrocarbon, water was considered. The immediate problem however, was that it was less dense and had a much lower vapour pressure at the envisaged working temperatures. Most importantly, its enthalpy of evaporation was an order of magnitude higher than that of R140a. These limitations were to be overcome in a series of solutions still using STH principles (i.e., evaporate the liquid, raise it to some height and condense it there to provide a head that will reset the mechanism at the end of the day). A summary of the salient 'solutions' up to the time the STH system was

• Evacuation of the system so that the boiling point could be lowered significantly to say, below 60°C. This was in attempt to raise the vapour pressure at a working temperature of between 30 and 40°C in the evaporator tank '**B**' of **Figure 4**.

• A redesign of the evaporator '**B**' to a flat plate solar collector, possibly able to evaporate at least 5 kg of water on a 'typical' Cape Town winter day. This was to be supplemented by provision of hybrid heating using say, biomass below the

• A redesign of the condenser tank '**A**' and its condensation means to use

evaporative cooling so that a smaller unit could be used. This was followed by elevating the tank to an appropriate height and by design of a vapour evacua-

*DOI: http://dx.doi.org/10.5772/intechopen.85174*

of its elements were carried to the next concept.

*Concept number 1: solar-thermal-hydraulic (STH) system.*

evaporator—in case the day was very cloudy.

tion and piping system from the evaporator.

*3.1.3.2 Concept 2: solar-thermal hydraulics (STH): water replaces R140a*

lar to the figure.

**Figure 4.**

discarded is given below.

*Mechanical Engineering Design: Going over the Analysis-Synthesis Mountain to Seed Creativity DOI: http://dx.doi.org/10.5772/intechopen.85174*

**Figure 4.** *Concept number 1: solar-thermal-hydraulic (STH) system.*

*New Innovations in Engineering Education and Naval Engineering*

when in a fixed orientation."

which machine elements?

and install the mechanism?

*clock control of valves*

the 'Need' were:

user?

are given.

The product design problem and its sub problems were defined as: "Design a single axis sun tracking mechanism and its coupling means to a domestic home flat solar collector, so that the latter will be able to receive more energy from the sun, and therefore through the appropriate conversion process, yield more output than

The sub problems, imposed by constraints discovered during identification of

• What motion transformations would the mechanism have to effect—and by

• How would the motion transformation be controlled, and how much energy would

• Which materials and manufacturing/assembly methods would be used to make

• What operational and maintenance tasks would be expected of the owner/

Many solutions were investigated. Some were tried up to manufacture stage, and then discarded. Here, only significant ones are described in chronological order up to the prototype milestone. The reasons for discarding or modifying them

*3.1.3.1 The initial concept: solar-thermal hydraulic (STH) system with mechanical* 

A STH powered, spring controlled system was envisaged as in **Figure 4**. A hydraulic head *h***max** was to be provided by a liquid in shaded tank '**A**', connected to spring bank *k* through a one way valve **V1** and a cylinder-piston assembly. The piston rod would be a cylindrical rack, which energises the compression spring at the other end. The rack would drive a gear train to which, the frame holding the solar collector would have been coupled. At the end of the cylinder, was to be a one way valve **V2,** leading to an un-shaded small tank '**B**'. In late evening, with **V2** closed, and the piston at extreme western position, the panel would be facing west. **V1** would be actuated to open by the closure of **V2**. Liquid would flow into the cylinder, and compress the spring bank to the maximum (at which point a head *h***min** would act on the piston) while reorienting the panel to face eastward for the next day. In the morning, valve **V2** would be actuated by a clock signal to open. Valve **V1** would simultaneously close. During the day, the **V1**-**V2** link would be automatically deactivated to enable independent operation of **V2** without opening **V1**. Then, a clock mechanism would intermittently open **V2** allowing a precise liquid weight to flow into un-shaded tank '**B**' and then close for a definite period. This would relieve the spring bank a distance *x*, and in turn rotate the solar collector a definite angle westward—hence tracking the sun

In due course, the liquid in tank '**B**' would vaporise and condense in shaded tank '**A**' so that the hydraulic head in '**A**' gradually rose during the day in preparation for a night

*3.1.3 Solutions: evolution of the gravity driven hydro-mechanical tracker*

• What would be the source(s) of energy in the mechanism?

be required for both transformation and control?

**74**

in this direction.

return action. The panel tracking axis could be rotated about the piston-cylinder axis for correct installation at different latitudes by graduated scales in a plane perpendicular to the figure.

This concept required use of a low boiling point, low enthalpy of evaporation but high density liquid. The low enthalpy would give sufficient daily solar assisted evaporation rates while the high density would enable storage of enough mechanical energy to compress the spring and turn a collector whose centre of gravity would most likely be offset from the axis of rotation. Such a liquid was actually identified among the refrigerants (R140a) but it was expensive in Cape Town. Being a chlorohydro-carbon (CH3-CCl3), it was banned in some African countries. Although there were other issues, this alone was sufficient to disqualify the concept. However, many of its elements were carried to the next concept.
