Update 19.03.2019: The result of this work has been published in an IEEE article titled Using Solar Electric Cooking to Kickstart Universal Energy Access in the Developing World.
February 27, 2019: From now on, when people talk about “solar cooking” or “solar cooker”, ask whether they mean “solar electric” or “solar thermal”.
Up to now, when we say “solar cooking”, normally people understand it as “solar thermal cooking”. What else can it be? However, the price of solar panels cheaper than a glass door and output over 300W, it is time to revisit our long held understanding about solar cooking, and new possibilities it opens up in more effectively decarbonising our economy and combating global warming.
If there is any doubt, here is a simple instruction to build your own in an afternoon.
The making of a basic solar electric cooker
A solar electric cooker (or kettle, steamer, frying pan etc.) includes a solar panel, a heating element, and a food container. It is quite easy to build.
The mainstream solar panels in 2018 are between 280 to 350W (operating ay about 30-32V, 8-11A) with size from 1.65mx0.9m to 2.0mx1.0m, which is about the size of a door. The container for our DIY project can be a glass bottle with a capacity of about 1 liter. Any metal wire can make a heating element provided it is of the right thickness and length, not necessarily nickel-chromium wire. Let’s just buy the iron wire from a neighbourhood hardware store. You need other things such as high temperature tape, connectors, and preferably also a high current electrical switch. you also need some basic electrician tools, including a wire stripper and a multi-meter.
As a minimum, we just need to wind the wire round the bottle, using the high temperature tape to hold the wire onto the bottle surface. The circuit is built by connecting the solar panel, the wire, and the switch into a loop which is joined with mating connectors. The length of wire should be determined that gives resistance of about 3-4 Ohms with the help of the multi-meter. I used one with diameter of about 0.6mm and the length needed is found to be about 6m. There are easy to build variants based on the bottles and insulation material at hand. I’ve made a few solar cooking appliances recently. By the way, one of these was actually made 10 years ago for use with a 100-200W human powered generator and documented in my paper to the 1st IEEE Humanitarian Technology Conference Titled “New Village Gadgets”. Now solar panel can do the job of power generation without our sweating.
That’s it. On a sunny day, these simple gadgets can boil a bottle of water or food in about 20 minutes, or fry an egg in a couple of minutes.
Siu-Cheung MOK
Design enhancements
Given the simplicity of the basic construction, it is up to us to make improvements and customization to suit our purpose or usage environment. I’ve added heat insulation using a silicon sheet, then a cotton cloth and fix it to the bottle surface with a few pieces of head-tie. You might also want to add a handle and decorations as you wish. In developing countries, insulation material for firewood stoves are often good candidates.
I want to park my solar panel while not using it, so I added two coasters on a long side of the panel such that my 20 kg panel can be moved around easily without using a strong mounting rack for permanent installation. This simple act helped save the panel from typhoon No. 10 as Super Typhoon Mangkhu (23rd September 2018) hitted Hong Kong.
Another improvement is adjustable inclination angle which is difficult or at least expensive for fixed mounting. I do this with two planks of different lengths, which can be placed beneath the solar panel to give low and high angles of inclination. If the solar panel is facing the sun within 20 degrees accuracy, it can still deliver over 90% of the ideal output. So positioning the panel with the planks is giving performance almost 90% as good as a perfect sun tracking mechanism but at almost no cost.
According to the specific situation, users can adapt and enhance, or otherwise build a customized solar cooking system for themselves.
Before you start, note the precautions !!!
Think through the dangers and the corresponding methods to handle them before you start.
Anything powerful is also likely to be dangerous if not handled properly. The solar electric cooker involves high current, high temperature, and possibly also high voltage.
Siu-Cheung MOK
High current can melt wire insulation or create spark during connection. So silicone wire of 20# gauge or thicker should be used to handle the high current while the silicone insulation can withstand high temperature. Some connectors have protective sheath which can stop sparks from going outside and prevent a fire. A better way is to add a electrical switch. It also helps prolong the life of the connectors.
To deal with dangers of heat, insulation material should be able to withstand sustained temperature of 150 degrees Celsius, at least for the layer close to the heating wire. Most synthetic fabrics melt when in contact with the heating surface whereas cotton and linen might catch fire. There are many good insulation material of industrial grade with guaranteed fire-proof characteristics but tend to be more expensive and hard to get in small quantities. Silicone sheet is a common heat insulation material in kitchens today, which is preferred. As a general rule, do not use the solar electric cooking appliance near material that may catch fire or give out toxic substance when overheated.
Normally, voltage below 36V is considered safe. If you experiment with electronic devices such as step up voltage converter or DC-AC inverter, make sure you know what you are doing and as much as possible, do not work alone.
Potential hazards can’t be listed exhaustively. Just be sure to be mindful when working with electricity and powerful tools. But don’t let the above warning deter you from actually doing. When you are aware of the dangers, they are not that dangerous. May your upcoming solar electric cooking be safe, successful and satisfying.
Importance of DIY solar electric cooking in decarbonisation
The IPCC report on 1.5 degrees temperature rise has shown the urgent need to reduce our emissions in order to avoid the disastrous consequences of runaway global warming. Yet the current international emissions reduction commitments points to a horrible 3 degrees temperature rise above pre-industrial levels by end of this century, and the behaviour of the general public makes a 4 degrees rise more likely. So we should work out very aggressive approaches if we want to avoid massive species extinction and millions of climate refugees in the next few decades.
Solar electric cooking is, in my opinion, a very effective use of the limited production of solar cells to cut our green house gas (GHG) emission. The firewood stoves they replace currently emit several tonnes of CO2 and GHG with tonnes of CO2 equivalent emissions annually. With almost a half billion firewood stoves in use, replacing them can quickly cut our emissions in the order of Giga-tonnes CO2 equivalent (GtCO2 eq). It can also help reverse deforestation, which can strengthen the resilience of our ecosystem and safely capture carbon in the woods. Take our current annual emissions to be about 50 GtCO2 eq. , this single point of attack to our emissions can start immediately and potentially gain us a few % points in our GHG emission budget, which is very attractive.
As a rough estimate, a 300W solar panel used in solar electric cooking to replace a woodfire stove may cut down GHG emissions of 2-5 tonnes of CO2 equivalent each year. The same panel used to displace electricity generation from a coal-fired power utility can generate about 400-800 kWh annually and cut emissions of about 0.3-0.6 tonnes of CO2 equivalent. So deployment of solar panels in solar electric cooking represents several times more effective deployment of our solar panel production in reducing our emissions.
As we are now losing hard in the emissions control battle, we must weigh the relative benefit of displacing what kind of energy systems and applications for our best advantage. When and as our energy applications are widely electrified, it is most effective to focus in improving the emissions of our power generation means. At this moment, solar panels cuts little carbon emission in displacing nuclear or gas power but can create big impact in directly replacing existing inefficient energy applications. If we can consciously channel more solar panels towards effective applications such as electric cooking, we can get much better results in our decarbonisation pathway and increase our odds of avoiding uncontrollable global warmng and extreme weathers.
The virtues of solar electric cooking
Our carbon and GHG emissions are increasing despite advances in technology and civil movements. There are many obstacles we need to overcome including high cost, technical hurdles, user training, administrative delays and inefficiencies. Solar electric cooking may be immune to most obstacles. The number one virtue is that it eliminates a substantial amount of greenhouse and toxic emissions at very reasonable cost, which is desirable for all parties concerned.
Technically, it is based on proven solar panels with over a billion units in the field, can be bought at low price, and with sufficient production capacity as the market takes off. Unlike most technologies featured in the news and popular science documentary, there is no uncertainty about availability of solar panels. More importantly, the technology is not monopolized by a single company. While a company may have proprietary technologies and strong patent profile, other companies may have their own to compete in the market, while major players also have cross licencing arrangements. Regardless of the underlining technology, all deliver their energy as a low voltage direct current (DC) through two conducting wires. Users and entrepreneurs can adopt it without worries of supply interruption or fuel cost hikes.
The maturity, affordability, and easy handling characteristics of solar panels enable the general public to build our own energy systems. Solar electric cooking can accommodate fluctuations in power generated without resort to expensive and/or unproven solutions. Its deployment is not bound by technical, economic, nor administrative obstacles. In fact, its cost advantage over fire-wood stoves can provide economic basis to fuel its rapid market expansion.
Clean cooking has actually been identified by the United Nations as one of the “high impact opportunities” in sustainable development which can kill several birds with one stone. The target to deliver 100 million improved clean cookstoves to developing countries by 2020 is well on track to be achieved. The supply side of improved cookstoves are split among many players of incompatible designs, which makes sharing of design knowledge and scaling up difficult. With the arrival of affordable solar electric cooking, the solar panel and resistive heating are quite generic to allow development of compatible products and transferable skills, and hence rapid market expansion. We have good reasons to be optimistic and aim even higher to achieve universal energy access in the coming decade.
As a strategic move in decarbonisation, solar electric cooking provides a much needed one-time opportunity for us to greatly cut down the short-lived GHG emissions and black carbon which can quickly reduce global warming effect, giving us some leeway to juggle with our tight carbon budget. Hope this can become a beachhead in the fight-back against global warming to make subsequent work easier. Hope also that this life-saving opportunity is not wasted, and we build on it to launch other longer-term and bigger impact decarbonising initiatives.
What if there is no sunlight?
The simple answer is: Use what you are using now.
We all know that there are times of the day and weather conditions when a solar panel has low or negligible output. But even if we can use it 50-70% of the time, it can cut more than 1 tonne CO2 equivalent emission annually per stove displaced, which is still far more effective than the same panel used to displace other energy production means or energy applications.
Solar electric cooking is not perfect, and it can’t replace all other means of cooking, nor should we aim at this. But it can create tremendous advantages while it is applicable and appropriate. With the high emission reduction achievable by investing little more than the cost of the solar panel, it is a very nice complement to existing cooking methods in developing countries.
Making it work
Given the huge potential for solar electric cooking to quickly cut our emissions and combat global warming, it is worth our efforts to make it work.
Let’s see how it can be done. Following are some possibilities. They are by no means exhaustive or the best, but are nevertheless practicable and serve to get things started.
Minimize barrier to adoption
The solution need to be easy to implement and enable self-maintenance by eliminating hard-to-get components. The DIY solution outlined above is a first step towards this end by re-using commonly found bottles and use iron wire instead of nickel-chromium wire. It should be further simplified and better presented for people in the developing world. Drawings should be better than words.
It is important to get things started quickly. We don’t need a perfect DIY solution. Business will jump in when they see the market growing large enough to justify mass production. Nevertheless, the DIY solutions will keep merchants honest because if their offerings are not good value for money, we can always fall back on our DIY solutions at minimal cost.
Advancing Global Goals
The solar electric cooker has many attributes that enable it to create value in a humanitarian project to advance the Global Goals. It provides clean energy (7:affordable & clean energy) for cooking at a fraction of previous price and helps cut household air pollution (3:good health), resulting in reduced medical & fuel cost (1:no poverty, 2:no hunger). The financing, distribution and support of such systems can create local employment (8:decent work) for either men or women (5:gender equality). Additionally, there is significant GHG emissions reduction (13:climate action) and long term restoration of forest and ecosystem (15:life on land).
By working towards the Global Goals, there are ample opportunities to work together with like minded people and organizations to reinforce each other, as well as gaining government support, making it a value-added-component instead of a cost item in a humanitarian project.
Doing it in scale
The big cost advantage will be drown in overheads if this is done one by one. Shipping a single piece of solar panel is very expensive and may easily break during transportation while delivering a whole pallet of 20 or 30 pieces do not cost much more and chance to break is greatly reduced. Doing it in groups also enable mutual support and exchange of ideas to improve on the implementation and usage, thereby making the project more successful. Further down the road, it is possible to ship a whole container of solar panels and related material to further reduce the cost of deployment.
Doing it together
Solar electric cooking is a powerful means of decarbonising our economy and thus combat global warming, yet it is simple enough for us to participate. The key to success lies not in everyone trying to invent a even better design, but bringing it to the communities through the collaboration of people taking up different functions. A multi-function team can provide support with sound financing, helping people in various stages of adoption, and developing local entrepreneurs to expand the scale over time.
As we work together, we can improve on each others’ ideas quickly and avoid expensive mistakes. My ideas may be biased and overly optimistic. If so, we need to know as soon as possible so that we can quickly adjust and start moving along more productive avenues. Devil’s advocate badly needed. As we identify effective means to realize the high emission reduction potential of solar electric cooking in real world projects, we should share and expand the success to build a strong beachhead against global warming.
As we work together, an idea that doesn’t fit in our own community may help another community go a long way. By exchanging ideas and helping out for other communities, we can do much better as a whole. For example, I won’t expect widespread use of solar electric cooking in Hong Kong. But it is easy to get all kinds of materials here to experiment on the design and serve as an information hub to support deployment elsewhere. The carbon footprint of Hong Kong is about 6 tonnes per-capita for electricity and transportation. Some estimate total carbon footprint of Hong Kong people including travel and importation of goods to be about 30 tonnes per person. So I can balance my share of carbon footprint by helping deploy about 10 solar electric cooking sets in a sunny country that is currently using traditional wood or charcoal stoves. This would be much easier and effective than doing it in Hong Kong.
Using this extended carbon footprint accounting, decarbonising becomes much easier. For those of us in developed countries, helping a village to use solar electric cooking would balance the emissions budget of our whole family or more. This is quite practicable. Our friends in developing countries can also play an active role in fulfilling commitments in cutting carbon and greenhouse gas emissions at speeds much faster than expected of them, inspiring those countries lagging behind to catch up. As we expand our works, we can make that simple calculation on our achievements and see to our satisfaction concrete evidence of fighting back global warming!
We can all be winners.
Siu-Cheng MOK
Source: Siu-Cheng MOK
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