Dear Friends, Family and Compatriots:
After 7 years of hard work, finally, it looks like 2022 will be our "break-out" year where we test our ability to grow rapidly.
I am glad that all of you have been so patient with me over the past 7-8 years as we have been trying to grow and as we have been trying different designs and technologies to see which products can provide the greatest benefits to whom.
We now have a great set of products: (1) Long lasting "forever" lights, (2) Solar-electric cookers, (3) Solar Pumps, and (4) Solar Electric Vehicles.
And since the last letter in November, we have done two key things that lay the foundation for rapid growth in 2022.
First we have upgraded and consolidated our designs for using Lithium Titanate batteries (which are a type of Lithium battery chemistry that lasts ten times as long as Lithium ion).
And second, we have secured >$100k in low-interest loan financing to provide the capital we need to invest in expansion.
Let's discuss these two items in turn:
Designing and assembling affordable batteries that can last 10 years or more!
In creating solar batteries that last 10 years or more, we have three key cases: (1) Batteries in the range of 3V to 6V that are used for lights and cell phone charging, (2) Batteries in the range of 12V to 30V to be used for other electrical loads and for cooking, and (3) Batteries with voltages greater than 30V that are used for solar electric vehicles.
While we are using Lithium Titanate (LTO) battery chemistry for all three types of batteries, the issues of battery configuration, control and protection differ significantly for all three types.
Long-lasting batteries for lights and cell phone:
How do we maximize the affordability of batteries for lights and cell phone? For the last six months, we have been using small cylindrical cell batteries and making a durable light from two of these small batteries connected in series, and charged with a small solar panel. These small solar lights cost only $5 to $10, which makes them very affordable. But to make the lights affordable, they are made rather small. Most of the material cost of these lights is the long-lasting batteries.
But, if we get a different configuration of battery (with the same LTO chemistry) called a "pouch cell," the cost per unit energy stored can drop by more than half. One cylindrical cell with about 3 watt-hours of energy costs $2 ($0.67 per watt-hour), while one pouch cell with 24 watt-hours of energy costs less than $6 ($0.25 per watt-hour). Obviously, it is better to give people battery storage that is more than two and a half times cheaper if we can, so we have to convert from cylindrical cells to pouch cells.
We figured out how to do that on this trip. There are two tricks that we had to use to convert to the lower-cost pouch cells for lights and cell phone charging.
The first trick was figuring out how to use only one pouch cell to power lights and cell phone charging even though one cell has only 2.4 volts. Lights need 3 volts and phone charging needs 5 volts.
The solution is to use a cheap voltage converter that is used in phone power banks to convert Lithium-ion battery voltage of about 3 volts to cell phone voltage of 5V. These voltage converters cost only $0.30 and are highly affordable. And even though they are designed for voltages higher than LTO batteries (i.e. 3V), many such converters still convert voltages as low as 2V because they are designed to fully discharge a Lithium-Ion battery. This 2V minimum discharge voltage is close to perfect for a LTO battery cell.
The second trick was figuring out how to get the solar panel voltage to effectively match the voltage of a single LTO pouch cell. There are two obvious approaches, and one less obvious approach, and it winds up that the less obvious approach is the best approach.
The first obvious approach is to find 3V solar panels that effectively match the voltage of the LTO cell. The key problem with this approach is that such low voltage panels are typically more expensive per watt of power and are made of epoxy or plastic which degrades in the hot sun. Higher voltage glass and aluminum panels are cheaper per watt and longer lasting.
The second obvious approach is to use another voltage converter between the glass solar panel and the battery cell. We tried this approach. It is not great. The voltage converter is a bit more expensive than the power bank converter, and the converter is somewhat unreliable. We can't use an unreliable converter in a light system that is supposed to last 10 years.
The third approach is to rewire the solar panel to decrease the voltage by half and double the current. This is actually pretty easy to do and takes only 15 minutes. A common 10W solar panel is 9 volts, so the rewiring converts it to 4.5 volts and doubles the current to about 2 amps. The maximum voltage of the battery cell is about 2.8 volts. It is not a perfect match, but good enough for us to wire up some diodes and resistors to do the charging voltage adjustments at almost 50% efficiency. An efficiency of 50% is not too bad for inexpensive low-voltage, very-low-power circuits.
We made several test prototypes of this third approach, and they seem to work great. But we have only a couple of hundred LTO pouch cells in stock. Now that we know that these are the best solution for solar lights and phone charging, we need to order thousands more. We will do that over the next month.
Using LTO pouch cells to make 12V and 24V batteries:
Because LTO pouch cells are the least expensive form of LTO battery, we want to use them to make bigger batteries that can serve bigger loads at voltages that are larger than 2.4 volts per cell.
To do that you connect several cells in series--where the positive of one cell of connected to the negative of the next cell. When you do that, the voltages of the individual cells add together, and the voltage of the assembled battery is the sum of the voltages of the individual cells. Five cells times 2.4 volts per cell is 12 volts. And 10 cells times 2.4 volts per cell is 24 volts.
For solar electric cookers, it is good to have a 24 volt battery because reasonably fast cooking requires about 500 watts of power. With a 24 volt battery, you can get 500 watts with 20 amps of current which you can do with a reasonable size of wire. If you try to do 500 watts with power that is 12 volts, you need 40 amps of current which can burn up many sizes of wire.
So we have been making 10-cell batteries to power cookers. When you male a battery, you also have to add circuitry to make sure all of the cells stay in the right voltage range. For LTO batteries that is between 1.8 volts to 2.8 volts per cell. We are a little conservative and try to keep most cells between 2.0 and 2.6 volts per cell. Now we can buy controllers that cost $20 to $30 that do this, but this starts doubling the coat of the battery, so we are developing our own low-cost tricks for keeping all of the cell voltages in the right range. These cost about $10 per battery which helps keep the overall battery cost extremely affordable.
So how do we do the electronics? Well, first to keep the top voltage within range we put a voltage converter between the solar panel and the battery. There are inexpensive $4 converters that can supply 10 to 20 amps that have a screw adjustment that allows you to set the maximum output voltage of the converter. This is called an "adjustable step-down buck converter." So that takes a care of the high voltage.
Secondly, for the low-voltage, there are $3 adjustable discharge controller which can turn off the output at an adjustable output voltage, allowing the output to turn back on at an adjustable voltage that is one to a few volts higher than the turn-off voltage.
And last but not least, we put some diodes across the terminals of each cell such that for below 2.6 volts per cell, the diodes don't pass any current, but at and above 3.0V the diodes pass a lot of current. This makes it so that the cell discharges current if it starts getting overcharged. This helps prevent any particular cell from getting overcharged.
During this last trip, a Stanford Electrical Engineering doctoral student, Skyler S. came to Malawi for two weeks to help work out and test this set of LTO battery solutions, which has been a huge help. So we are now done answering most of the controller/assembly design questions.
So now it is time to implement!
And for that, our low-interest loan scheme described in the last friends and family letter in combination with donations which pay off the loans over the long term. This can be used to create optimal financing for expansion.
Low-interest loan allows us to expand by more than 200% in 2022
Because of the progress that we made in 2021, we were able to get an extra $30k of donations. But rather than just be satisfied with just a $30k expansion, I made a commitment to raising an extra $30k/year for the next six years so I could financially "leverage" the increased donation revenue to get a much larger expansion investment loan.
I then went to Craig H who has been helping me find finance for my Africa projects over the last almost 30 years, and asked for a loan that I would pay off from a combination of donations and customer revenues/sales over the next six or seven years. He agreed, and now we have >$100k to invest in expansion over 2022.
What will we be able to with that extra >$100k?
Well now, we should be able to distribute the following:
> 3000 Forever light systems
> 10 solar electric vehicles
> 300 solar electric cookers
> 200 solar water pumps
The exact distribution numbers will depend on how things unfold over the course of the coming year. With only $30k we would only have been able to do the lights.
In addition, we will start developing partnerships with other local distributors in Tanzania, Uganda, Cameroon, and Togo/Ghana to see if our strategy of providing low-cost solar panels plus cookers plus LTO batteries is replicable throughout the continent. This might set the stage for a much larger expansion in 2023.
Focusing on cost-efficient expansion:
For my part I will be focusing on trying to make this expansion as cost-efficient as possible.
The hope is that if I can get the impact per dollar of donation and per dollar of loan as high as possible--and higher than anybody else--then it will be that much easier to raise more donations and loan financing in the years to come. And hopefully that will allow us to get solar electricity--including solar electricity for cooking--to millions of people in low-income Africa over the coming decade.
I am currently about half way through my current trip to Malawi. Now that most of the technology problems are solved, the next set of things to work on include accounting, organizational procedures and processes, and data collection (both on customers installed and monitoring of system performance).
Solar system distribution in Malawi starts after harvest at around April and continues until the start of the next rainy season in December. So between now and April we need to ramp up so that we can distribute many hundreds of solar products each month. While this is a lot of work, it should be fairly straightforward to organize once the next batch of materials and products arrive in Malawi in about May.
In love and struggle,