Lessons to be Incorporated
Access to a good supply of timber is easy in the Solomon villages. Usually however it has been 'milled' by hand with a chainsaw.
The problem is with its quality - straightness, sizing, and cross-sectional accuracy. Especially the hardwoods required extensive clamping while nailing.
Accurate geometry of the rails is crucial
For the full trays to run easily the rails must be straight and level. This requires planning, careful construction: plus square, straight, properly-sized timber right from the start.
Correcting sloppy milling on the building site has its limits and usually requires extra work or tools/ equipment not usually available to local carpenters.
Depth of drying during processing
Practical experience suggests that drying more than 30mm of cocoa in a tray requires twice-daily stirring. This was true even with a mesh bottom in the trays. However, for copra it is expected there to be a better flow of air from underneath.
Therefore to improve drying of cocoa it is recommended that the trays have a galvanised sheet steel bottom to better transfer heat to the under side of the layer. Regular stirring will remain important.
Wheels on the drying trays
Acquiring suitable wheels for the prototype proved expensive and difficult. Fitting them to the wooden trays allowing access through the walling was equally awkward.
In order to make such a tray-based design more suitable for rural builders the use of wheels has been avoided. What is now recommended is that the rails are made from vassa timber (hardwood) and a vassa skid-strip is fitted to both bottom edges of the drying trays.
The increased friction will not greatly impede normal operation. If suitable wheels (castors) can be found just two could be fitted centrally to the frame under each tray.
Vassa timber is commonly available and very weather-durable. It is also very hard, thus providing a good sliding surface. The cost-saving, and ease of construction and repair relative to finding, fitting, maintaining (and keeping) of wheels easily outweighs the extra effort of sliding the trays. Application of candle-wax or coconut oil over the sliding surfaces would be advantageous in this case.
Roofing type
In the prototype the roofing material of choice was a transparent, corrugated fibreglass sheeting purchased locally from Bowmans. This product has since become very expensive and difficult to obtain in the Solomons. It also proved rather fragile while fitting. What is recommended instead is to use ordinary corrugated iron sheets with the undersides (only) painted black. This is much cheaper, more robust, and a much more familiar material to rural builders. It also means that painting the insides of the drying chamber black may be omitted, further reducing construction costs and effort.
Although this changes the mechanism of the drying process it is not expected to noticeably alter the practical outcomes. Iron-roofing has been used successfully in PNG solar driers of the same scale (Tony Jansen, APACE - pers comm).
Another potential advantage of iron roofing is that its lower cost allows more flexibility in the dimensions of the building; (e.g. larger driers; extra floor space for rock beds for heat storage).