Monday, May 03, 2010

West Africa Cashew By-Products Project Assessment Trip

In late March ATDT representatives were sponsored by the ACi to visit West Africa to observe the end of the 2010 cashew harvest, and see first hand what the issues surrounding cashew byproducts are in this region. We flew into Accra, Ghana to meet the project organizers then planned to quickly head out for Burkina Faso by plane – but two days of late harmattan (sand storms) kept us grounded so in desperation we hired a car and driver and spent the next 2.5 days speeding the length of Ghana as we tried to make up for lost time. We took the opportunity to visit Ghana’s largest cashew operation, MIM Cashew, where we received an excellent introduction to cashew processing from managing director Lars Wallevik – pertaining to byproducts, they are just getting ready to introduce a cashew apple schnapps (very modern equipment), and while they burn some cashew nut shells to fuel their boiler they are unhappy with the amount of air pollution caused by the unburned CNSL. We also stopped at two agricultural research stations, in Bole and Wenchi, where we saw many varieties of cashew apples, heard about research on grafting and other agroforestry improvements, simple wine and alcohol production trials, and experiments to use dried cashew apple pomace for animal feed. Unfortunately, we didn’t have time to visit the Benedictine monastery in Techiman, where they are said to sell processed cashew apple products. Nowhere in Ghana did we get to observe fresh cashew apples (or any cashew apple product) for sale, but it could be that we were travelling too quickly; we did take every opportunity to sample the fruit and indeed found them too fragile to transport far, extremely juicy and sweet, and causing a bite of astringency at the back of the throat.

We were met at the Burkina Faso by our able escort/driver Sekou, and now that we were in French speaking territory our translator Maria Mathess proved especially invaluable. We appreciate all the help from the Ouagadougou PDA/GTZ office (the Agricultural Development Programme) – particularly Philippe Constant and Andrea Wilhelmi-Some – as we galloped from one meeting or production facility to another in Banfora and Bobo. From the second we entered BF we occasionally encountered children selling cashew apples from baskets on their heads, so we were able to use our “community engagement” tools to inquire how people value the fruit – all of the ones we tried were fibrous and the only way of consuming them seemed to be to suck out the juice and spit out the rest. As we visited several cashew production facilities (such as Sotria-B) we received the same request – help is needed particularly in extracting value from the oily shells (~25% CNSL by weight), since there is presently no way to burn them cleanly; each operation has a similar field of accumulating shells, and everyone would benefit from their efficient use. All over this portion of Africa fuel (such as wood and charcoal) is in short supply and so it is criminal that trees must be cut down when shells are so energy rich and plentiful. Later we found that a government research institution in Bobo (IRSAT, with GTZ/FAFASO) has an active program to extract the CNSL and use the remaining dry nut shells for fuel for improved cooking stoves – in cashew growing regions all over the world there is a need for simple extraction methods (and adequate markets for the CNSL), as well as ways to cleanly combust un-extracted shells for those instances where CNSL extraction is not feasible.

We also visited several cooperatives (like Association Wouol and Coopake) where cashews and dried mangoes are processed, and sampled some of the very first dried cashew apples in this region – these organizations desire new products to benefit their members so proved very receptive to learning about cashew apple products that have proven popular in other parts of the world (particularly Brazil). With Rakesh Gupta (TechnoServe) we met with representatives of DAFANI, a juice manufacturer eager to add new juice mixtures to their line, and perhaps install a biogas fermenter to capture value from their waste pulp. We spent considerable time at L’Union Yanta, both at their plant and in their cashew orchards, learning about the community that supports them. We visited a nearby home where a meeting had been organized for us to talk with families – always an important part of EWB assessment trips – and regaled several generations with our stories of cashew apple uses around the world. As always we asked “What can we do for you?”, and typically found that expanding the uses of cashew apples is probably a marketing rather than a technology problem – all the right information conceivably already exists, now how do we get it to the people who want it? Recipes, solar fruit driers, simple juicers, cooking demonstrations, technical information transfers, and so on might all be part of a comprehensive effort to encourage greater utilization of this valuable resource. And, as in most areas of the world where cooking is done with biomass, fuel is one of the largest daily expenses so access to the energy in the nearby nut shell middens would be appreciated – the best forms might be briquettes or charcoal, both areas of active interest to those developing improved stoves all over the world. For larger scale applications - say to produce process heat for industry or to provide rural electrification - gasification of shells in a reactor is the cleanest and most efficient method.

In conclusion, as we travelled we found encouraging signs everywhere – uses for cashew byproducts are of interest to everyone (and the internet is full of activities in other countries as well – waste is in no one’s best interest, so attracts attention) – and we saw or heard of examples of most of the possible uses we imagined ahead of time. The fact that commercialization of many of these has not already occurred suggests that there are hard problems to be overcome, particularly if we are to make good use of the shells. But then the expertise of ATDT members wouldn’t be needed if everything was already figured out…

Its a shame not to have more space for trip photos - you can find additional ones here!

Short video of my experiment comparing the pyrolysis (on a bed of hot charcoal, with forced air) of U.S. English walnut shells, and Burkina Faso CNSL saturated cashew nut shells. In both cases the pyrolysis gases burn nicely, and the CNSL does not seem to interfere - when they are added gradually to existing combustion. Inside a gasifier fully loaded with cashew shells we hope that the CNSL will not drain too quickly into the combustion zone as the shells preheat, resulting in noxious smoking.:

YouTube has many many videos of cashew processing throughout the world, including Thailand, Guinea-Bissau, Sri Lanka, Benin, India, Vietnam, Indonesia, Brazil, Philippines, and more. They show different levels of automation, and many discuss cashew apple utilization as well!

Tuesday, April 13, 2010

Intro to the Cashew By-Products Utilization Project

Cashews are one of the favorites of the world’s nuts, but very few people know much about the rest of the story… the tree is closely related to the mango and a cousin of the poison ivy, it produces a fruit which is technically not really a “fruit” but an engorged stem, the “nut” (really a seed) develops outside the fruit, up to 20% of the shell weight is a valuable industrial chemical, it is raised in countries all around the globe, and the Bill and Melinda Gates Foundation has recently taken a special interest in improving cashew production methods in Africa. Through the African Cashew Initiative, their generous funding seeks to extract more value for Africa from the cashew crop – presently raw nuts are shipped abroad for roasting and packaging, when these operations could be performed locally, benefitting the communities where the nuts are grown. A specific goal is to find more uses for by-products – like the fruit and nut shell – so that small farmers can obtain additional income, improving their quality of life; EWB-SFP has committed to helping find or expand uses of these valuable resources.

Cashew trees originated in Brazil and were spread by early Portuguese traders (often simply to prevent soil erosion), but they often forgot to spread the word that the “cashew apple” is as delicious and nutritious as the nut – the juice is extremely popular in South America, and in Central America often the nut is discarded as not particularly useful but the apple has an important place in markets. All kinds of prepared foods – jam, chutney, drinks, dried fruit, candy, etc. – are consumed in other cashew producing countries (such as India and Vietnam), but what happened in Africa? Sometimes information just doesn’t flow evenly, and we hope that with some encouragement the situation will change. Of course if it was as easy as that no outside technical assistance would be needed, but in sooth the cashew apple is very soft when ripe so does not transport or store well, and it contains tannins that must be removed because they give it an astringent flavor.

Making full use of the nut shells has its tricky parts too – while the oil in them (CNSL) is valuable for use in polymers, coatings, and auto brake components it is also noxious (it causes a skin rash much like that from poison ivy) and difficult to extract. Again, sometimes we need to move technologies around the world, adapting them to new circumstances – our challenge is to do it in a way which is most appropriate for Africa. With or without the oil, the shells have a high energy content, making them suitable for providing process heat for industry or fuel for improved household cooking stoves… except that the simple technologies needed to turn them into charcoal or briquettes don’t exist there yet, and when burned in a typical way the oil produces an unacceptable amount of very unpleasant/acrid smoke. For now the landscape is littered with huge piles of messy shells, while scarce wood resources are consumed in their place.

What can ATDT do to improve the situation? As always, we’ll first seek to become minor experts in apple and shell uses around the world (we always do our homework), learning how these problems perhaps have been overcome in other places, and we’ll visit West Africa to see what the people and communities there value. Without meeting our local partners (GTZ manages the program, but there is a whole suite of professionals from TechnoServe, the African Cashew Alliance, Costco, and similar involved) and our end customers (the small farmers and cashew processors who would benefit from new ways to utilize these “waste” products) we can’t determine what paths might be best. We also have members who have recently visited Brazil and Vietnam, to examine their situations and see what we might learn from them.

Next: results of the site visit to West Africa!

Wednesday, November 11, 2009

The Case for Tiny Wind

We have been working with the Appropriate Infrastructure Development Group (AIDG) on small wind generators for their clients in Guatemala, and recently were fortunate enough to be able to use a wind tunnel at NASA Ames in Mountain View, California - to characterize two turbines that we have been developing. Tyler describes the experiments here, and now we continue with some more general discussions.

Working squeezed/scrunched up in the belly of the Army Aeroflightdynamics Directorate 7’x10’ wind tunnel gives one lots of time to think about the world and our place within it, and how these “tiny” wind generators (the term “micro” has already been claimed for systems up to 5000 watts) can help contribute to an improved quality of life for some. Remember the target market is people who either have zero access to electricity, or who perhaps depend on charging worn out car batteries in distant grid connected towns – you pay bus drivers to transport your battery back and forth – to get a trickle of power. How people use that first few watt-hours of high quality energy they have access to fascinates me, since while we sometimes have an impression that everyone else wastes scarce resources too, in reality people with scarcity tend to know the value of conservation and wise use best – especially when their costs are high.

Extending their day by a few hours with an efficient light is usually the first use – most unconnected places seem to be close to the equator where the days are always short, and recurring costs for candle/kerosene lighting are cumbersome/prohibitive – allowing people to read, do homework, and maybe even earn extra income. Charging batteries – for flashlights, the radios all campesinos carry to the fields, and cell phones – is another priority, hopefully reducing the number of discarded disposable ones that litter the ground. Both of these applications require very little energy – for us it would be worth just pennies worth a day, but for people who all year around are used to calling 6 pm bedtime… priceless! And yes, one of the first appliances to appear is the ubiquitous television, often for soap operas and soccer matches, but also news and education.

Just a hundred watt-hours a day will do all kinds of things when the appliances

s are efficient, and in a breezy location it shouldn’t take an expensive turbine to provide this. As a slightly technical aside, it is best to remember that people use energy to do things while we have a tendency to express the output of wind generators (and photovoltaic panels, and microhydro installations, and nuclear power plants) in units of power (watts). The wind tunnel tells us how many watts we might generate at a given wind speed, but winds fluctuate so we can’t count on getting that much all of the time. Commercial turbines are almost invariably rated just in watts, and you always have to ask “At what wind speed?” – and you’ll quickly find that they choose to rate at some phenomenal (and usually unrealistic) value, like 25 miles/hour (~11 meters/sec). Southwest Windpower ( has now started doing the right thing by helping you estimate how much energy (in watt-hours… each one of these helping to perform a useful task, such as a one watt LED lamp aiding a kid do homework for one hour) you might expect to generate from their products, after making some assumptions about your local wind speed distribution.

This brings us to the question “How do we extract power (and energy) from the wind – which comes originally from the sun?” The maximum power available from the wind, per square meter of turbine swept area, can be easily calculated from the equation

Power = ½ rAV3

where r is the density of air, A is the swept area of the turbine, and we see that the power increases as the cube of the windspeed (doubling the windspeed gives 8 times as much power), so that while there is lots of power produced at high wind speeds there is almost none available at very low speeds. Our Lenz blades sweep out an area of .75 m2 (the Savonius configuration we tested is .45 m2) and we know that we can only realistically have a fraction of the energy the wind contains – Albert Benz said that 59% is the maximum, but more like 30-40% is typical for small tubines like ours. So the amount of power you can tap into depends on how much the wind blows, and with like so many other things (like per capita income) the averages provided to us by the government don’t always do us enough good – some days it doesn’t blow, some days it blows too much, and luckily some days it blows just enough for your turbine to fill up your batteries for the coming week. That’s the concept of the distribution (vs. and average), and luckily the wind speed variability tends to follow a Weibull distribution (, a statistical function, where just two variables describe the distribution. These are the average wind speed and a number related to the general amount of time with no or low winds (the shape parameter), and this site does a much better job of explaining it than I can here – and they allow you to type in your power vs. wind speed data (such as from wind tunnel testing), plug in a shape factor, and get the anticipated energy output (say in watt-hours/day) at your target location. Now you can buy the right number of storage batteries to get you through the wind-less doldrums, and compare the cost of your tiny wind system with your other electricity alternatives – including continuing to charge your car battery for the equivalent of $3/kW-hr, and waiting a long time for the grid to arrive.

Taking the raw wind tunnel data Tyler showed (torque and power vs. RPM) we can determine the maximum amount of power a given blade set or configuration can extract from the wind at each speed and plot it – that upward curved shape is very important because it tells us that not much power is available to us at low wind speeds (say, less than 10 mph) Our experimental method did not include a generator to turn the winds power into the electrical power we need to run appliances, and there will be losses in this conversion process – we expect it to be ~75% efficient - so we have to take this into account, giving us the ability to get about 25% of the energy embodied in the wind – not bad if the resource is free.

As mentioned, a single “power rating” for a turbine is not very useful (and only meaningful if the wind speed it was measured at is associated with it), but people are used to hearing just one number so we may need one. Catapult Design will tend to rate these turbines (a set of blades plus the associated generator) at more realistic wind speed values, like 15 mph (7 m/sec), and then we’ll do our best to try and characterize the wind resource at a specific locale. If we choose to rate at 15 mph, for example, then the real power output of the Lenz blades is ~30 watts, and the wind will need to blow at that particular speed for ~3.5 hours/day to provide 100 watt-hours of energy per day to a family or small business. Blowing at half that speed for twice as many hours does not do us much good, since the blades of VAWTs often don’t start turning until 8 mph, and at 10 mph we might have to rate these tiny turbines at only a watt or 3. For estimation purposes, Weibull wind speed distributions with very low shape parameter values would be an example where it blows very little, much of the time.

Its unfortunate that life is never as simple as it needs to be – it seems like that if a family wanted to consider buying a tiny turbine at X dollars, to decide whether it is worth it they need that power performance curve for it, decent information on their local wind conditions, and some idea how much electricity is worth to them (for example based on how much they are presently using and the cost for charging that car battery, or how much more they want to use – say if their neighbors pay them for charging cell phones). Now if we just knew the probable lifetime and annual maintenance costs we could start to understand the cost of each future watt-hour… what an exercise, and don’t forget that investing in all forms of renewable energy is tantamount to buying at one time all the electricity you will use for the rest of your life, which is not an easy decision to make.

An interesting resource for evaluating the performance (energy generated per unit time) and financial characterisitics of a wind investment can be found here: and while you have to play some tricks on it to simulate this size of wind generator (technically it would be rated at ~200 W at a traditional wind speed like 25 mph) in an off grid location where electricity is presently very expensive to acquire. It is a good tool for showing what steps are required for determining fiscal suitability, and along the way it will teach you a little about wind energy - for example, at my home in Berkeley it says that I should expect an average wind speed of 10 mph and a Weibull distribution shape parameter of 2 (I may disagree, unless they mean at the sailing marina). It is not detailed enough to take into account our specific turbine characteristics, like efficiency and cut in speed, but nevertheless is is interesting to consider their estimate of 75 kW-hrs per year of energy generation for this turbine and location. My utility bill says that last month I used 127 kW-hrs of electrical energy (needing 175 watts of power capacity), for the privilege of which I paid a grand total of $16, or ~$.13/kW-hr. Clearly a turbine providing only 75 kW-hr/year would give me $10 of energy annually and just meet a minuscule part of my demand - hog that I am, with all my phantom loads from consumer electronics - but if my cost of electricity was instead several dollars per kW-hr instead of a fraction of one then the situation changes, and tiny wind may make sense for my family or business.

Friday, August 01, 2008

EWB-SFP and the UCB/Google Pre-Engineering Camp

Part of EWB's mission is to educate and encourage the next generation of engineers in a way that leads them to want to be involved in technical humanitarian activities - it can take up to a generation to change society (to recycle more, use efficient light bulbs, reduce individual carbon footprints, have broader horizons than just your own country, etc.) so the best time to start is now. Google has graciously funded, University of California (Berkeley) is hosting, and EWB-SFP is teaching engineering topics to 30 gifted high school students this summer - we have projects on developing world fuel efficient stoves, pico wind energy (Guatemala), solar water pumping, and designing a water distribution system (Tanzania). Work sessions take place at UCB but we also have off site workshops for more detailed experiences.

As an example, Charlie Sellers' two 5 student stove teams are investigating options for cooking stoves in places where there is not nearly enough fuel for everyone - the refugee camps in Darfur are a good example of this so it is appropriate that one of the stoves being tested is our own Berkeley Darfur design! Their goal is to document experiments where they compare a typical 3 stone fire with various improved stoves burning a wide variety of fuels - such as ordinary wood, charcoal, paper pulp and sawdust briquettes, walnut shells, and more. There is no better way to test a new stove than by tending a fire in it for awhile - a real mother and cook has to tend sick children while cooking, and if the baby is sick then she has even less time to spend on a clumsy stove.

Wood is so scarce around these denuded camps that even saving half the wood compared to simple stoves may not be sufficient (but it sure helps) - the world is just starting to consider whether we need to re-think our approach to helping in large emergencies/disasters like this by providing instead densified waste biomass (a fancy term for briquettes of non-woody materials), either for the latest generation of improved stoves (like the sheet metal one for Darfur) or for briquette specific stoves like fan assisted gasifiers. Whenever there is a tsunami or major earthquake, enormous amounts of supplies are rushed in by select NGOs because other kinds of aid can't respond fast enough to replace an entire destroyed infrastructure - it is not the intention to replace everything for the long term, but immediately provide basic human needs like clean water, sanitation, shelter, and cooked food. We're not talking big screen LCD televisions here, just enough to stave off hunger and disease until the needs of millions of people can addressed more completely. As such, emergency stoves and fuel can be airlifted in, alleviating suffering and reducing the immediate impact on the local environment - these inexpensive stoves might only last until the emergency is over, but they may change the way they view stoves and cooking for the rest of their lives.

The students are creating presentations for Google HQ where they analyze how people cook, what they need out of their stoves, and which fuels might be best suited for a range of situations. One of the biggest challenges in the field is to overcome the natural resistance to change - if their mother did not cook with a new stove design or fuel, then the present generation of cooks might not want to either. Technology "fixes" which are not introduced appropriately are usually doomed to fail quickly - as soon as the engineers disappear the benefits don't seem nearly as apparent, spare parts and maintenance efforts are nowhere to be found, and people just plain have a tendency to prefer or to revert to old ways.

For a view of what things looked like, here is a preliminary Youtube video (Pat Coyle is behind the camera) of the day Alex Brendel visited to explain his briquettes made from waste such as paper, sawdust, and even algae. And here are some photos!

A visit to The Shipyard on Saturday gave an opportunity to try another type of improved traditional stove (the Justa, for Central and South America) and see a range of larger biomass gasifiers - including one that will run a car just on walnut shells. We cooked on the Justa, which seemed to take only a few sticks at a time to cook for everyone, with zero smoke coming out of the chimney. Everyone's experiences were accompanied by data taking, so that results could be graphed in Excel spreadsheets - the temperature of the water as it came to a boil, the amount of fuel used per minute to cook, and the temperature of the chimney gases.

Saturday, December 08, 2007

Experiences Using a Hand Crank Generator for Fan Stoves

Charlie Sellers and Brad Ballard

January 2008

For about four months I have had a hand crank powered LED flashlight that I have been very impressed with (, and other retailers such as REI sell it for less - ~$50) – it can either be charged by its AC adapter or by turning a hand crank, the high performance LED is extremely bright, the flashlight has several intensity settings, it lasts longer on a full charge than I can easily measure, and my model is heavily rubberized for ruggedness and waterproof characteristics. It is by far the best of the many LED flashlights that I have tried, including both moving magnet and straight battery powered ones – this one seems very bombproof and efficient; several of us have been very pleased with it.

Brad’s flashlight broke after it was submerged in water so we had the opportunity to disassemble it and both investigate its construction and measure its electrical characteristics, and then use it to power the commercial WoodGas campstove. A very successful experiment showed that we had plenty of power for the fan - this is all contrary to my previous comments, because it uses a well designed generator that is well matched to this particularly efficient stove fan – it supplies the correct voltage and it has enough battery life,

Upon opening the broken unit we were very impressed with most of its construction – the 2 beautiful circuit boards were ruined by the exposure to water, the LED turned out to be the very high intensity 1 watt Luxeon Star warm white model (, with a forward voltage rating of 3.42 V, 350 mA – USD $9 each when purchased separately), the batteries were very low capacity (three 1300 milliamp-hr NiMH batteries with a total parallel rating of 3.6 VDC, while good rechargeable AA batteries have 2500-2700 mA-hr of capacity each, at the same 1.2 VDC) but adequate, the generator was a nice sintered NdFeB magnet version somewhat like those used to drive HDD and CD/DVD drives in computers, and all the electronics were surface mounted (the most modern method); there was nothing to complain about except for the 2 nylon gears, that might wear out too quickly with hard use.

We removed the obviously ruined main circuit board (which

contained somewhat unnecessary

control/indicator functions like switches and status

LEDs) and then rewired it so that we had access to the unadulterated output from

the generator’s alternator – this is a 3 phase motor connected to a resistor

bridge circuit board, which then produces a simple DC output. We could then use the manual crank to produce an incredibly bright light output, or connect it directly to other loads. At the leads we measured a voltage of ~4 VDC and ~250 mA at ~1 turn per second – approximately supplying the 1 watt that the LED is rated at (and we could power the LED without the removed circuitry – from the bridge we got a smooth 4 VDC for the LED or for other purposes). We don’t know yet how many mA-hrs of energy each turn of the crank generates.

The commercial TLUD WoodGas’s stove fan also requires only about 1 watt at 2.5 – 5 VDC (quite efficient - it is designed for 2 AA alkali batteries, but I usually use 3 NiMH AA batteries to achieve a similar voltage, or alternatively I sometimes use for testing a variable voltage power supply for up to 5 VDC – above that the motor sounds unstable). We used the simple hand crank mechanism (with just the 3 phase power converted to single phase) to power the WoodGas fan, both with and without the LED in series (together, for amusement only and to limit the voltage). Lo and behold, this hand crank generator powered the fan beautifully! Fortunately the voltage was approximate matched to that needed by the WoodGas fan. At ~1 crank/sec we got good flame (no smoke) from the stove and easily cooked quesadillas quickly. When we got down to the “charcoal stage” (after the obvious yellow flame disappeared) we inserted a device to occlude all of the secondary air holes at the top (a trimmed stainless steel hose clamp, spring fit – doubling the primary air flow at the bottom of the stove) and again easily cooked another batch of quesadillas. We thought that the mostly constant cranking was a little tedious, and that a treadle powered mechanism (like an old sewing machine) would work better; this company also sells a foot generator for 12 VDC power output to any device.

Now that we had prowled the interior of one, we could hack my own functioning one to power a commercial WoodGas stove – I just took the necessary screws out, attached wires to the LED, used 6 ft. of wire to allow for powering the stove from a distance, burned a hole in the flashlight casing to pass the wires out, and soldered a new power plug on the end. Now I can use the 3 intensity settings with the fan (the setting for pulsing/blinking the power might just work to save energy using a fan stove…), and the batteries charge if there is extra cranking. Trying it on a stove with wood pellets it performed beautifully, with the voltage/power evened out by the battery circuit – always constant and just enough. One minute of cranking from completely discharged batteries seems to yield from 1 to 14 minutes of fan time, depending on the setting. With a full charge (from the AC adapter, or an unknown amount of time spent cranking) we can expect to get many hours of operation, and by installing a simple switch we can turn off the LED while the stove is on

Initial experiments put the stove fan in series with the LED, then in parallel, but finally the best circuit is to isolate the fan from the LED with a simple switch (single pole, double throw) so that the two can be operated independently – a full charge then powers the fan at very high rpms for +2 hours, and with this particular flashlight we have more fan speeds than the WoodGas stove has usually. This stove is designed for 2 AA alkaline batteries and has 2 settings, but the 3 AA rechargeable NiMH batteries that I normally use with a speed controlling rheostat are better (a PWM controller is even better - both environmentally, and it permits both a higher fan speed and a longer run time – though the motor is not designed for these rpms) – and this flashlight approach permits even more variations (including the pulsed mode).

It is still unknown how many turns of the crank it takes to power this stove for a meal – if you charged it fully (AC or by hand), the 3 AA batteries are somewhat anemic (you can easily buy ones with twice the energy capacity of these) so few hours of operation result – you can calculate this, and maybe my flashlight version is just outdated. And remember that you cannot extract all of the energy from any battery:

Charging with the AC adapter was a tad curious – it seemed to take too many hours before it indicated that there was a full charge. Further experience showed that a one hour charge (from a dead discharge state) resulted in 30 minutes of full fan power (or at "low" LED power of closer to 14 hours - the obvious reason for more like 14 hours, a clear reason to use a higher efficiency motor or better fan blade design, such as the Philips stove uses) – any project would want to analyze the situation further, since every load is different.

An ultimate WoodGas batch of fuel might be 400 g of wood pellets (as are used in North American pellet stoves), which requires ~20 minutes to burn completely at the full fan speed (stove firepower is generally correlated with fan speed) – several hours of energy then corresponds to a number of batches of fuel with this stove, a very considerable amount. More typically, batches of ordinary fuels (wood chips, pine cones, nut shells, etc.) are closer to 100-150 g so this same amount of battery energy would not result in nearly as much total energy output – the denser the fuel (in g/cm3) the better this type of stove performs for the user.

In conclusion, an efficient and rugged hand cranked generator can easily power a efficient fan motor for biomass cooking stoves – provided that they are electronically voltage matched (a simple circuit can do this) and that the generator is of this quality. Other applications (such as for off grid operation of medical instruments) can similarly be supplied with power, but a decent knowledge of the requirements – e.g. volts, amps, watts, LED lumens, and mA-hrs of energy storage – is recommended.

Friday, October 26, 2007

LEDs and Other Technologies for Producing Light

Whenever I come across a technology that is not well summarized on the web I feel an urge to take all the information accessible and blog on it - so everyone else does not have to fight as hard to find all the links, and get all the necessary information... like I did. Lighting, by whatever method, is one of the handful of areas that we involved with appropriate technology need to be familiar with - in addition to quality shelter, decent sanitation, clean water, efficient cooking, secure production of food from their agricultural efforts, and good health. This week I became particularly interested in lighting again (I pushed compact fluorescent bulbs since the early '80s, when they were expensive and regularly problematic - now they are cheap and mainstream) after I recently did a workshop on photovoltaics (see the post below) for emerging economies - high grade electrical energy is hard enough to produce that you want to consider what might be the best lighting for your electrical system. In remote locations electricity (from sources like solar, hydro, wind, etc.) is so expensive that the lifetime cost of electrical devices is far more important than their purchase price - operating costs (for lighting, something resembling the cost per lumen) are the largest proportion.

The trouble I found was that it is presently too complicated to compare different kinds of lighting products - especially if we want to focus on the quality of light instead of just the quantity (or the cost, or combinations of various parameters). The most common types of light bulbs available to consumers are the incandescent, the fluorescent, and (just recently) the LED (light emitting diode - I believe in anticipating the future, since technology never seems to stand still) - there are many other types like metal halide, sodium vapor, kerosene lamps and other combustion based, neon, high intensity discharge, sulfur, etc. but these are mainly used for industrial applications or are not electric). I thought that lighting selection for energy efficient applications (like ones powered by alternative energy) was as simple as "light output per watt of electricity" but have just found out that life is not that easy - other things come into play if you really want "good light". First, let's define some basic lighting terms:
  • lumen - a measure of the amount of light produced, but it does not describe how well that light suits the eyes of human beings.
  • luminous efficiency - what portion of the emitted electromagnetic radiation is usable for human vision.
  • candle power
  • CRI - the color rendering index compares a light source to daylight in the way that it makes a colored object appear; higher CRI values mean that things look closer to how they do at noon, in natural sunlight (CRI = 100). Lower CRI values are acceptable when colors are not important, like for street lighting, while very high values are desired when you want a retail item in a store to look its very most colorful.
  • lifetime - an ill defined term to describe how long a product is expected to last in service, but usually it is only for ideal conditions (moderate temperatures, not too much switching, etc.), and this number does little to describe how many parts will vary (the statistics of reliability and lifetime - mean time between failure, distribution of failures over time, etc.)
  • color temperature - a rough comparison of how the frequency distribution of the light compares to that of a "black body".
  • environmental sensitivity - how stable a product is as the temperature of use changes; some technologies for example don't perform as well when the temperature is cold.
Every time we need light we tend to need a certain combination of these things - just cheap lumens are no good if we want light of reading quality, and efficiency doesn't make much sense if the lifetime of the bulb is too short...and in reality there always seems to be trade offs. Life would be relatively easy if we could just choose one parameter as "most important" when we are selecting a bulb, but I have found that there is unfortunately more too it than that - if you are looking for an easy solution then stop here.

Most of us are familiar with the venerable incandescent bulb - a hot tungsten filament that gives off mostly heat, but some light as well (I think of them as "resistive" bulbs because when current flows through a wire with a high resistance it gets hot, and it also happens to glow somewhat in the visible spectrum) - and also fluorescent bulbs - either in linear tube or "compact" varieties - where the bulb is cooler and more efficient (less heat, more light). Compact fluorescent lights (CFLs) have recently become very popular with the gov't and media, but when they were first offered they did not seem to be a very realistic alternative to incandescents - now their combination of characteristics is such that several countries have banned resistive bulbs with the expectation that consumers will buy CFLs instead and thus reduce the need for additional electrical power plants. Prohibition will have the usual problems - fewer choices will mean some disgruntled users, since incandescents have their benefits for some applications. Light emitting diodes (LEDs) are a newer form of "solid state" light - sort of the opposite of silicon-based solar cells, where when light falls on special semiconductor devices we get electricity. In an LED an electrical current causes energy transitions in these more exotic semiconductors, and then light is emitted - with much less heat produced as an unwanted/unnecessary byproduct. But LEDs are a newer technology, so they are still under development - much like CFLs were in the 1980's when they were more expensive than we would have liked - but luckily technology advances in response to our needs, and this will happen with LEDs as well. If we can just be patient, and encourage the technology by investing in new products, we'll soon have better solutions... and then the next improved lighting technology will start to evolve (such as microwave sulfur lamps, or electroluminescent wire - if its not just a Burning Man thing). Such is the nature of science.

So this week I invested in my very first LED bulbs, trying various different styles (5 different ones) - all "Edison" socket ones, like fit household fixtures. It was fascinating how different the bulb appearances were - unlike incandescent bulbs the exterior of each one of these was completely different! This alone would confuse many consumers so I predict that these differences will eventually go away - consumers want to compare apples with apples, so only minor differences in appearance may be acceptable if the other properties are the same. And the color of each was different - their specifications should have indicated that they would be (and they might be - to a more knowledgeable consumer), but I just assumed that they would combine different types/colors of LEDs so that all would be (more or less) equivalent and optimal for the human eye. Nope, each one looks different to me, but because I am technically colorblind I don't assume that my color judgment is worth a damn.

I was surprised to find that they are many things, but not necessarily more efficient than CFLs for alternative energy (or other) applications - my lights, ranging from 1.3 to 3 watts for a total of 12.5 W, cost $84 and have a rated total output of just 285 lumens (both the wattages and the lumens seem to be approximate though), leading to a very pricey 23 lumens/watt. Individual bulbs were as efficient as 40 lumens/watt but they are not marketed according to to this measure. For comparison, common CFLs now cost $2-$4 for an 11 W bulb, which puts out approximately 600 lumens - an efficiency of 55 lumens/watt; one of those bulbs then puts out twice as much light as all my new LED bulbs, at twice the average efficiency, for a tiny fraction of the bulb cost! But I am simplifying too much here - other 11 W CFL bulb models may not be as efficient or long lasting, very few of them can be used with a dimmer, they tend to decrease in intensity a little over time, etc. And we have only compare cost and efficiency, not all the other factors which may also impact your decision. The table here does a much better job of assessing just the luminous efficiency comparison for various lighting technologies, showing that incandescents are ~2.6% efficient (it depends on the wattage - efficiency of these and fluoescents tends to increase with wattage), CFLs are ~8% (the latest T5 straight tubes are more like 15%!), and present LEDs are up to 10% efficient but results in laboratories show the potential for more like 22%!

Now we can start to see that LEDs will tend to be better for small output bulbs (such as those that are typically used in alternative energy systems where the cost of each extra installed watt of capacity approaches $20, and they are generally suitable for developing countries where there is not such a tendency to "over illuminate" homes), and where they will be valued because they are unbreakable, dimmable, longer lasting, and available in so many colors and configurations. And, while CFLs are a mature technology that is well on its way to predominance, LEDs are still improving so their future efficiency and costs are yet to be seen. Now I feel better about my new investment in them - I am cutting edge. In the developed world we are seeing LEDs used just for their color variety - in traffic lights, billboards and other forms of advertising, nightclubs, art installations, etc. - and it may be some time before plain white ones are used for lighting alone, since incremental efficiency improvements are not as highly valued.

The bottom line? Be prepared to ask a lot of questions if you want the very best light technology for your application. Incandescent bulbs have a long history so people are familiar with them and they are perfect for some applications, fluorescents of various types are the near future and will continue to get better with time, and LEDs will be coming down in price at the same time as they are improving their light quality and efficiency. And there will always be something that is next.

Sunday, September 30, 2007

Green Empowerment Workshop - PV/RE in Developing Countries

Heather recently sent around an email saying that there would be an Oakland photovoltaic/renewable energy workshop that would focus on sociocultural issues of developments as well - exactly the direction that I'm headed toward now that I have decided that the "technology" part contributes only maybe 10% to the probable success of the project. Human dynamics, cultural differences, education, planning, maintenance, risk management, etc. seem to make up the rest of any possible local solution. Green Empowerment seems to focus on bottom up development (vs. big plans and big money), allocating most of their funds for local NGOs. They lead tours, advise, install, and teach good things like principles of solar cells for electricity (e.g. lights) or water pumping, and pico/microhydroelectric.

The 2.5 day workshop included both technical aspects - everything that you could imagine about planning a PV system - plus a discussion of things that went awry in countries all over the world (cultural issues). Unlike many humanitarian aid projects, solar power installations require a moderate amount of technical skill in the community - some solid state physics, decent electrical practices, and a good sense of maintenance/troubleshooting if the project is to succeed for years. The global PV industry (now in almost every country) still sells mostly "components" and then users have to specify what they need to provide enough power, order the right pieces (there is lots about all this in the GE handouts for the class), wire it all together, test if for mistakes, and train the populace - not particularly a consumer friendly process. And there are all kinds of assumptions that need to be made in sizing a system (too big is to be avoided because of $), but in the end you round up number in the number of solar panels and batteries so it doesn't really matter that you have uncertainties. Except that the cost can be higher.

Demos and hands - on sessions gave people experience with all the components, and with wiring them all together, and I'll be building my own tiny system soon. There might be +10 years until household solar is mainstream (I remember trying to promote compact fluorescents, CFLs, 25 years ago, when their quality was poor), but I saw the need for a handful of engineered widgets that might help hurry solar measurements along. LED lighting is going to be the next big thing (look at the lumens per watt table in the middle), and research is making them better everyday. Exciting to be on a steep curve for a new material - commercialized but still under intense development. The auto and industrial markets are going to be first adopters, because they measure costs much more carefully - watch their $/lumen costs. And here are 120VAC LED Edison bulbs ($1-$2/lumen). But using auto LED lights in other applications is hampered because they require special sockets - has anyone seen socket adapters to convert 12VDC "twistlock" or "bayonet" car lamps into household screw "Edison" bulb bases? A little adapter can be co-injection molded (to insert the metal parts) that should only cost $1 - but is it really needed by the people in the field? I think options will be needed because auto lamps are available in a variety of low wattages, they are dropping faster in price than residential bulbs, there are many incentives for improvement, there will soon be an incredible number on the market (economies of scale), etc. Let the auto industry do the work and home PV systems will benefit for free.

Also, a few more diagnostic tools may be needed - some manufacturers build more features into their best products, but for example is there a tiny, cheap power meter that can be used for various purposes? A kW-hr meter is not needed to charge homes for the exact amount of electricity they use, but it would be handy to see how the PV load is distributed throughout the community, and over time. Or battery characteristics - state of charge, health, input and output, etc. Someday the best of these parameters will be clearly shown on a standard panel (like consumer electronics now) that makes solar easy, but for now a little cheap datalogging and some USB connectivity wouldn't hurt.

And, the more I look the more I find - industrial lights (floodlights, streetlights, traffic lights) are here and I am still trying to figure out why a traffic light seems to cost so much less (in $/lumen/watt, or similar units) than %$#@&! consumer models.

One thing that will take time to seep into the mentality for PV installations everywhere is the drive for quality that system manufacturers in other industries (automobiles, computers, DVD players, medical instruments, and similar complex things) now use to increase reliability and prevent consumer problems. From the start of a project new ways to determine risk (system too large or small, things that might happen to break the system, quality of components...) should be identified and then slowly reduced. This kind of thing is what can be missing when things are manufactured in developing countries, where quality is a new concept (the last thing to learn in every new business). But QC tools are everywhere - new types of connectors (so no mis-wiring), error proofed maintenance, more robustness, better instructions, community participation, an overall rise in familiarity with technology, etc. will eventually make solar as easy as connecting up to the big grid (plugging into a wall socket) right now - and for now we can just try to facilitate this change.

next post - I'll try to review the recent book "White Man's Burden", which postulates that grassroots efforts like these are the best solutions - and big aid projects are doomed because they provide none of the right incentives.