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An Off-grid Solar Photovoltaic Electric Pressure Cooker system that costs only $200 in Malawi

8th October 2021

By Robert Van Buskirk, Lawrence Kachione and Gilbert Robert (Kachione LLC, Malawi)

An introduction by Simon Batchelor, MECS Research and Innovation Co-ordinator. 

This is the first in a series of three blogs by the Kachione team who are pioneering Solar Home Systems inclusive of cooking.

While MECS continues to lobby for more integrated planning of modern energy that leverages the access gains in grid electricity to include energy-efficient cooking appliances, there remains the challenge of reaching the 760 million people without access to electricity. Mini grids and Solar Home Systems (SHSs) are key technologies for delivering electricity access for those who are in ‘off-grid’ areas.

To date, Solar Home Systems have barely been considered as a possible means of providing clean cooking, since their deployed cost was so high and they generally deliver minimal power which is suitable for lights and phone charging.  Nevertheless, the sector has evolved and become more efficient in getting SHSs to the rural areas. This combined with the significant reduction in price, which seems to have reached a major tipping point in 2021, makes higher powered SHSs that includes an energy-efficient cooking appliance more cost-effective for households. Our colleagues at Kachione LLC in Malawi, guided by Robert Van Buskirk, have used a MECS challenge fund grant to make significant steps forward in developing higher powered SHSs and in this blog Robert describes the Direct DC Solar (DDS) option.  We acknowledge the importance of ensuring that technological advances are linked to socio-cultural practices, and the DDS system does mean that people might have to start cooking in the mid morning.  However, the Kachione team has put in place processes which include very deep discussion on this aspect with customers and wider community consultations before rolling out the product.  Robert also mentions larger systems in the blog below that might be used by businesses; allowing them to cook during the day and sell in the afternoon.  In a subsequent blog, Robert will describe how they address aspects related to energy storage and reliability, and how they see a procession of upgrades including lighting, home appliances (phone and TV), irrigation pumps, cooking and even electric vehicles, and how this integrated system will ultimately fulfill the needs of consumers in different aspects.

When you read Robert’s blog below, keep in mind that the Solar PV panels last 15 to 30 years, and EPCs last between 5 to 15 years.  This means that what Robert describes as a system price includes (potentially) 15 years of cooking without any need for additional fuel! Kachione are deploying these systems in areas where people collect wood, and research to date suggests such communities and households are reluctant to switch women’s (unmonetized) labour in collecting wood to a monetary outlay from the family.  So, for instance, mini grids often struggle to convince people to pay regularly for cooking energy, when that energy could be collected from the surrounding forests. Kachione has managed to reduce the system cost to a level so low, and made it so aspirational, that early adopters in the communities are already willing to purchase the system with an upfront payment after harvest season, when households have disposable cash. Robert and Kachione LLC have plans for scaling the approach and this will be discussed in the third blog in this series.

Narrative by Robert Van Buskirk: 

One of the cheapest configurations of a Solar Home system for off-grid electricity is one where the solar panel electricity is delivered directly to the appliances with no battery or controls. This electricity has been called “Direct DC Solar” (DDS) electricity.

To date for cooking, DDS electricity has been applied mostly to slow cooking and water heating in an effort to keep costs as low as possible. Published analyses on DDS cooking typically describe systems with panel capacities ranging from 100 to 500 Wp.

We at Kachione LLC recently pushed DDS cooking to the next level by testing whether it can be used to power the recently developed eWant 24VDC, 500W 5L EPC. As shown in Figure 1, we connected the EPC to two 280W 60-cell solar panels that were connected in parallel.

Figure 1. An eWant 5L electric pressure cooker (EPC) connected to two 280W solar panels that are connected in parallel such that the current is doubled for the same voltage.

We found that the cooker operated well, though at somewhat lower voltage and power than recommended by the EPC manufacturer. This is because the solar panels were not quite matched to the current requirements of the EPC. While the solar panels theoretically provided a total of 560Wp, the current supplied was closer to15 amps rather than the 20 amps required by the cooker at 24V.

This mismatch means that a different, 48-cell configuration for the solar panels should be used to better match to the 24 VDC power needed by the cooker. The 60-cell panels that we used in this test operate at maximum efficiency near 30 volts.  Nonetheless, 60-cell panels are what we have in stock at the moment, so we conducted our DDS tests with 60-cell panels.

Figure 2. Low-power Direct DC Solar (DDS) cooking of rice in an eWant DC EPC.

We note that even with the moderate current and voltage mismatch, the eWant DC EPC still operates well.  As shown in Figure 2, we were able to cook brown rice in the EPC without a problem. Similarly, the cooker also used for cooking beans, which went well. In this particular configuration, the EPC operated between 16 and 20 volts, averaging about 18V.

We believe that with better-matched 48-cell solar panels we can get the DC EPC to operate much closer to its ideal 500W operating condition without significantly increasing the total panel power, thus creating a DDS EPC system that needs less than 600Wp of total panel power.

We note that currently, we can import solar panels at the container scale to Malawi at a cost of about $0.25/Wp, while we think we can import the eWant DC EPC at a cost of about $35 or less. This means that the wholesale cost of a DDS eWant DC EPC system is $35 + $150 + (miscellaneous costs for plugs and wiring). Thus an off-grid solar EPC system is now possible in Malawi for a wholesale cost of only $200. 

More Solar Panels to Increase EPC Power and Reliability

To compensate for the mismatch between our solar panels and the DC EPC, we also tested operation of the EPC with several panels connected in parallel. We expect to power DDS kitchens with multiple panels that are connected in parallel over the next year, . These solar-powered kitchens will be used by village women cooperatives. In such kitchens, multiple solar panels can power multiple EPCs which are then used at slightly different times of the day to cook different dishes on an overlapping schedule. The greatest power consumption of an EPC is during its heat-up phase, and once the EPC contents are heated, the average power consumption typically drops. This allows a second EPC to be turned on for cooking the next dish before the first dish has fully completed. Because the EPCs are less costly than the solar panels, it makes sense to use several EPCs with several solar panels in DDS operation so that the power from the solar panels can be utilized to the fullest extent.

Figure 3. Cooking Malawian Nsima (corn meal porridge) with DDS power supplying an eWant 500W 24VDC EPC.

Figure 3 shows a cook making the traditional Malawian and Zambian corn meal dish Nsima (which is called Ugali in Tanzania, Uganda, and Kenya). In Malawi, Nsima is by far the most commonly consumed food and is responsible for the largest share of household cooking energy use. We observe that Malawians prefer to cook Nsima with the EPC unpressurized.  This does not seem to be a significant impediment for use of the eWant EPC as this particular dish cooks rather quickly with most of the energy used to heating the food to boiling temperature.

We at Kachione, LLC are confident that a 600W DDS EPC system that costs between $200 and $300 will sell rapidly in rural Malawi. Malawians value making investments in solar panels for their house. With cost-efficient distribution to rural villages it will be possible to provide a DDS EPC cooking system for a price that is substantially lower than the regular retail price of solar panels. This should allow DDS EPC systems in Malawi to sell like ‘hot cakes’ in 2022, once an efficient distribution system can be put into place. 

A key problem with DDS EPC systems is that they only cook when it is sunny. While this may be a concern in the short-term, over the long-term, households will very likely buy extra solar panels and long-lasting batteries to increase the availability of solar electric cooking on partly sunny or cloudy days. Such investments to improve reliability can be added incrementally to a DDS EPC system at a similar cost as the initial system purchase.

The implications of this new cost-saving technological development of DDS EPCs in Malawi are huge. It will enable us at Kachione LLC to surmount the modern energy cooking affordability barrier for even some of the lowest income households in rural villages, thereby making affordable, clean, electric cooking truly available and accessible for all! Even for households living on $1/capita/day!


Featured image: Photo by Jadon Kelly on Unsplash.