Grain Mill

Introduction

Grain milling is part of a value chain of transformation of agricultural products. It is one of the most common and most frequently demanded productive uses in rural areas.

Without electricity, grain mills are often driven by diesel motors, for example, in the so-called multi-functional platforms.

Although demand may be highest during the harvest season, grain milling is required throughout the year as many households keep a stock of grain.

Technologies

There are several technologies available, and they can be grouped into technologies

• concerning the way the product is milled
• concerning the way the motor is driven

Mill technologies

Hammer mills etc.

Drive technologies

DC grain mills

These are the so-called « solar » grain mills. For the sake of this article, a solar grain mill is a grain mill that is driven by direct current. The grain mill is used in a solar system that consists of the basic components (PV panels, batteries, charge controller, load). Common voltage levels are 12 V and 24 V.

Advantages:

• General advantages of decentralised solar systems: usable wherever the resource is available, can be sized to the need, etc.

Disadvantages:

• Relatively high start-up currents require a start-up resistor which may brake easily.
• The start-up current also means that the load (the mill) cannot be directly connected to the charge controller, but must be connected to the battery. The battery is thus not protected against deep discharge. Users must be trained to switch off the mill as soon as the charge controller indicates a deep discharge.

Technically, one could solve this problem by including a shunt that is governed by the load contact of the charge controller and that disconnects the mill as soon as the charge controller switches off the load. However, DC shunts are very expensive.

• Requires battery maintenance.

AC grain mills

These are grain mills which are operated at 230 V. Basic models can be found with suppliers of agricultural equipment. These grain mills can be operated on the national grid or on minigrids.

In addition, these grain mills can also be driven with solar energy. This use case would require an inverter and batteries.

Diesel-driven grain mills

These can, for example, be found in multi-functional platforms. In this case, the diesel motor drives the grain mill via a transmission drive.

Practical Experiences

Senegal

PERACOD currently has two DC-driven grain mills in operation. These grain mills were bought locally. After initially receiving quotes for a product that seemed suitable, another product had to be bought since the provider could not deliver the product the project had originally aimed at.

After installation, problems occurred with the starting resistor, which broke and had to be replaced several times. Also, users manipulated the system, leading to several failures. The grain mills have had a disappointed performance ever since installation. A detailed technical monitoring is under way in order to study the problem further.

One of the first conclusion of the project was to not underestimate the amount of work necessary in the beginning to make the productive use work.

Please see a presentation here on some issues with solar grain mills in Senegal.

Pitfalls

Product alteration

Grain mills may alter characteristics of the good that is milled.

The size of the resulting powder may be different from the size people are used to from other milling techniques. This can result in changes in the way the product can be used for food preparation and / or changes in taste.

In addition, grain may become hot in the grain mill and thus change its taste.

Types of grain that can be milled

Grain mills must be adapted to the type of product to be milled. There are several grain mills which can be adapted to different goods, for example, wheat, maize, or sorghum. Be careful when choosing a product and test it before deployment.

Impact

Grain milling can greatly ease workload on women, as women are usually in charge of milling by hand with the help of a mortar and pestle.