By Dr. Simon Batchelor (Loughborough University / Gamos Ltd.).
A working paper is an assessment of a 5 litre electric pressure cooker for possible use on solar home systems. As said in previous blogs, there has been discussion for the past few years, on how to get a direct current cooker that might match a solar home system or a draw from a battery storage system without the need for an inverter. The potential market for off-grid solar home systems that can deliver DC electrical cooking, centres on three ideas:- Efficiency (and simplicity) of the system, Lower power demand leading to lower discharge rates from batteries; Cost effectiveness resulting from the above features. A DC appliance could potentially exploit those efficiencies and savings.
An early working paper the CREST team at Loughborough documented the functions and safety features of a range of commercial electric pressure cookers and stated concerns over the safety of the 12V and 24V DC Tesga/BES EPCs. The challenge then was that there were no other makers of a DC EPC, and thus began a journey and which it feels with the publishing of this working paper we arrive at a good rest stop.
Since 2020 we have worked with Foshan Shunde Ewant Electrical Technology Co Ltd, who actually deliver very good larger EPCs, for them to provide a DC EPC. They did so and it was available for testing in the early part of 2021. As our specification suggested they made an EPC that would work at 24V DC. It was a safe and well made EPC as this blog and working paper explained, but it was small. With a pot of 2.5 litres it effectively had a working volume of 2 litres. It has a role to play in the ecosystem of off-grid systems, but since the main potential for the DC versions of EPCs are in the rural areas, and rural dwellers tend to have relatively large families and households, the size of the pot was thought to be a stumbling block to extensive and widespread use.
Going back to eWant we asked if they could supply a 5 litre pot, with appropriate power draw of around 500W. Their designers set to task, and adapted an appliance from their existing AC line, and voilà – we now have a 500W, 5 litre, 24V DC EPC.
The working paper and associated infographic describes its performance. The unit behaves as one would expect, heating constantly until pressure is reached, then self-switching off based on a pressure switch, returning to heat occasionally to maintain pressure. It also has a keep warm function. The lid has a locking pin preventing opening of the unit during the pressure phase. It also has safety weighted valve. An air gap provides good insulation for cooking during the pressure phase. The handle on the lid remains cool enough to touch. The unit can fry onions and cook with an open lid at 140 to 180 degrees C. It does not have a lid locked sensor and can cook without a lid on any setting. Its efficiency and cost per capita meal is of the same order as AC EPCs (at an assumed tariff).
As a DC appliance it is a very welcome addition to the toolkit of off-grid appliances that can work on solar home systems where there is no grid connection. It can be considered an energy efficient appliance, that utilises pressure cooking to reduce cooking times for ’long cook’ foods such as beans.
Featured image: The eWant 24V DC 5 litre electric pressure cooker (image credit: Simon Batchelor, 2021).