Solar concentrator for heating processes

I am new in the community. Do you think it is possible to build a solar concentrator for the injection mould machine?

Project is based in East africa, Malawi by an NGO

Thank you!

Hi Kevin,
Welcome to the community.
Are you thinking of something like these GoSol concentrators?
I am sure that something could be devised – either by using direct heat, or by using a suitable heat transfer medium (e.g. vegetable oil)

@wellsforzoe – Have a look at this post, that I just came across:

Hi from a solar thermal-based recycling project (November 2018)

They have a photo of some kind of parabolic trough tube heater.

@thegreenengineers – I guess if they have enough electric power for an extruder motor, and a controller, there will also be enough power for some band heaters.
Solar thermal might be more useful with manual (or pedal) powered machines.

The easiest for solar direct sun beam heating i think is the extruder. Direct the beam at the barrel. Now using a PID controleryou have 2 options of control of temeprature
1. Use the PID controller that when off something such as a piece of aluminum or something falls infront of the beam thus blocking the beam from the barrel. when on that peiece of metal is brought back up allowing the beam to continue hitting the barrel.
2. connect the PID controller to the motor. Because you have power going in as watts you also have power going out in watts as far as the energy put into the plastic to get it to glass transition temperature or higher that is leaving the barrel. Thus the PID controller will turn on the motor when it is to hot. and turn off the motor when it is to cold thus maintaining the temperature. however this option requires some design criteria as if you make the watts coming in using solar to high and the motor to slow or to underpowered the motor will never turn off and you will have thermal run away until you reach equilibrium with the enviroment. This will surely overheat the plastic destroying the polymer chains inside the plastic (essentially burning the plastic).

@wellsforzoe I was surprised that you wanted to build the injector first. While it is one of the easier machines, it produces fairly small items and does not consume much plastic (probably less than 150 g per shot). You also need the capability to make molds, which can vary in difficulty.

Integrating the injector design with a solar concentrator has some challenges. If you are going to try for direct heating then you will need to configure the injector cylinder accordingly, you will also have the sunbeam in the same place where the operators are working to fill and compact the plastic in the cylinder.  If you go with the remote collector and hot circulating fluid, you will need to design a heat exchanger at the cylinder and you have to come up with a hot fluid pumping approach. Both can be done, it just means some engineering needs to happen to come up with a modified or new design.

By comparison the compression oven should be easier to adapt to solar heat and there are similar designs already out there from the baking application.

@frogfall  thanks for pointing out the kenya-project… I will check that!
@s2019 I have no experience with injection moulding whatsoever… why do you think I should modify the injection mould machine? Which tweaks did you think of?
Thank you guys for the support!

It may be worth writing down some top level requirements to establish the scale of what you are trying to do. I’m guessing you will end up modifying the basic injector concept significantly. It may also be worth keeping a hybrid concept as a possibility where some of the power and control are electric. PV solar panels are relatively inexpensive.

Good luck

@wellsforzoe I suggest you look at the pilot project in Kenya for some perspective on how Precious Plastic can play out in an East African environment. I’m sure @mattia-io and @davehakkens can pass on some valuable advice, if asked.

I’ve no experience of Malawi, but I visited Southern Tanzania about a decade ago, and remember seeing some of the problems that are probably inevitable in a country with a relatively under-developed technological infrastructure.


I would not call me and @frogfall arguing an active forum, but I’m glad we inspired you. And don’t forget your part, by starting an interesting topic 😉


Your idea goes way beyond just plastic, because it’s scaleable. Up AND down…

Might even work for metal… or chocolate…


If you can do the CAD and some actual testing can be done (preferably somewhere there’s actually some solar energy to use) the numbers will show which is the right way to go…


Keep us posted on your progress, but first enjoy your holidays.

An active mind also needs to recharge every now and then….

Wow guys that is a really active forum. I like that very much!
I am still on holidays and stumbled upon all this project “by accident”.
I have no prototype or designs to share yet but in 2 weeks I should be able to develop  some CAD-illustrations.
I like the very simple idea of a trough-heater-design with a blind to open&close but also the me complex idea with veg. oil sounds not bad.
I will start the easy way and test it I guess… But I think the vegetable oil idea with a large trough solar concentrator should be implemented for the whole container as it seems rather inefficient to use electricity for small scale processes like this one.
I assume that electricity cost would be as high in large production numbers as getting new parts from China all along (which is not the idea here – I know… But it seems many projects here have the goal to make just “something” out of the waste”… I want to use this method to make parts which we Mar with cnc and lathes at the moment…)
Thank you all for your support and ideas!

I agree, but in my experience ‘solar ovens’ tend to be build for ‘slow cooking’ at fluctuating lower temperatures.

So in terms of low-tech, safely, ‘slow cooking’ plastic in such a setup, the maximum temperature of the oven would be the temperature needed for melting the plastic, while for this setup to consistently work this melting temperature would have to be the minimum temperature of the oven.


A transfer medium (like the vegetable oil you mentioned) could be heated beyond the minimum melting temperature (without danger of burning plastic) if only to use it to au-bain-marie fry/melt the plastic and press it in an unheated mould.


This also reduces the influence of ‘clouds’ as there would still be a base temperature stored in the oil, instead of the ‘power’ being shut off entirely.

And at night, simply heat the oil over a fire and the system still works…


Or in short:

A medium you CAN heat beyond the safety temperatures for plastic for a more consistent ‘melt’. In a simple setup (like a solar oven) you can only ‘turn down’ the energy, you can’t ‘turn it up’, so you need to build for overcapacity and store the heat in a medium.


Make any sense?

My ‘technical’ English still needs some work 😉





I guess that as long as you have some method of measuring barrel temperature, a movable heat shield might allow sufficient on/off control to maintain the right conditions.  Ultimately that could be automated – but I’d tend to go for a simple, cheap, and reliable manual method to start with.

Indeed @frogfall, Solar ovens (also parabolic trough reflectors) work the same way, and they can be scaled.

Temperature control is going to be a problem though unless you use the created heat indirectly.

Actually, the GoSol devices could be overkill.  A simple parabolic trough reflector, arranged along the barrel, might possibly supply enough heat to hit moulding temperature.  Have you had any thoughts about suitable schemes that you’d like to share?