Tech Update: Pico-hydro system developments

Sam Redfield, Project Manager of AIDG’s pico-hydro program in Guatemala was just accepted for MIT’s International Development Design Summit in Ghana this summer! Here is an account of some of his work at our new facility in Guatemala. Keep an eye out for the build manual he is producing for the Five Gallon Bucket Generator!

Sam Redfield

Hi everyone. I’m back in Xela, home of AIDG’s offices and research facility in Central America. Big things are happening down here. This January we moved into a beautiful new compound. Rising above the neighboring buildings, the new office resembles a pagoda. Its red corrugated roof flanking three stories of golden clapboard walls is something of an enigma in a neighborhood dominated by low concrete block houses. In addition to much needed additional office space, we now have a new fabrication shop, electronics and water lab and, under construction, housing to accommodate several interns and visiting researchers. The new office is full of light and the staff and interns that work here are noticeably happier with the new work space. In what can be chilly mornings in a city perched at roughly 7000 ft., it’s nice to work in a place where the brilliant morning sun comes in through the windows and warms the space.

New AIDG Compound

I have returned to Xela to continue my work on the pico-hydro system that I field tested in La Florida last year. Pico-hydro systems are small hydroelectric generators that produce less than one kilowatt of power. We are looking at using the generator to provide basic lighting, cell phone charging and ultra violet water purification in under served communities. Housed in a five gallon bucket, and employing a modified car alternator driven by a turbine, the generator promises the potential of cheap clean energy to those without access to the electricity grid.

Pico-hydro test in La Florida in 2008
Pico-hydro test in La Florida in 2008

The Permanent Magnet Alternator

Last year, we established that the generator was viable as a single point power source that could be installed quickly with limited resources and could produce consistent power with modest water usage. Still unresolved were issues of cost, longevity of service and overall performance for electrical output. The generator was built using a rather expensive modified GM alternator produced in the States for the home brew wind turbine market. This modified alternator, called a permanent magnet alternator (PMA) produces energy at low RPM’s and works well in small-scale hydroelectric systems. In addition to the price, (more that $300.00 U.S.), the alternator would have to be shipped to its destination country, adding additional cost. The PMA was by far the generator’s most expensive component and the only element in the system that would need to be imported, so we looked to it to reduce the generator’s overall cost.

My solution was to modify the Nippo Denso alternator produced for Toyota’s 22R engine. They key was using low-tech mods that could be cheaply and easily reproduced in a basic machine shop. The Nippo Denso alternator, found in most Toyota pickup trucks and many sedans in developing countries, might just be the most common alternator in the world. They are often shipped to developing countries to be rebuilt for the market in the US and other developed countries. Where in the States these alternators are simply replaced with rebuilt alternators when they fail, in developing countries there is extensive infrastructure to rebuild them. They are available in quantity in Guatemala and are cheap.

My design for the Toyota based PMA uses only the alternator casing and the stator (the wire coils that surround the rotor inside the alternator). For the conversion, the rotor is completely rebuilt with powerful neodymium magnets and the stator is rewound with thinner gage wire. Non-functioning Toyota alternators can be had for about $20.00 US in Guatemala if bought in bulk. The magnets are the only part of the new alternator that may need to be imported.

Left: rebuilt rotor with permanent magnets. Right: Toyota rotor.

Left: Rebuilt permanent magnet rotor. Right: Toyota rotor.

Toyota based permanent magnet alternator
Toyota based permanent magnet alternator

Our new hydro test bench

Last year we lacked the facilities to do extensive testing of the PMA and could only determine that, yes, it worked and that it produced energy at low RPM’s. But we couldn’t determine which gauge windings of the stator would produce the most power given the bucket generator’s RPM ranges. We needed more controlled study conditions, particularly as field tests were difficult to repeat (distance to test site, variability of water flow, etc.).

This past month, we set up both a hydro and a PMA test bench. The hydro test bench simulates the head and water flow rate that determine the output of a small hydroelectric system. By varying the head and flow in the test bench, we can simulate the various conditions under which the bucket generator operates and rate its performance under different loads.

Bucket generator connected to hydro test bench
Bucket generator connected to hydro test bench

We can’t directly measure the RPMs of the bucket generator when it is hooked up to the hydro test bench, but we can estimate this number using the PMA test bench. Simply put, we find the number of RPMs in the PMA test bench that replicates the current produced by our bucket generator in the hydro test bench, and thereby get an estimate of the bucket generator RPMs. Using the PMA test bench we can only investigate which windings offer us the highest current at the appropriate RPMs for the system.

PMA test bench
PMA test bench

Direct comparison of the GM and Toyota PMAs is difficult due to differences in configuration, size and layout of the 2 systems. That said we were able to determine that the Toyota PMA offers performance in the same general range of the GM system and at a fraction of the cost. If manufactured in bulk, the Toyota PMA would come in at around $120.00 U.S. and the entire bucket generator could cost about $160.00 U.S.

Currently, we are trying to determine which wind of the Toyota PMA will give us the maximum current at the RPM ranges of the bucket generator system. At our maximum available head on the test bench, about 90’, we were able to produce over 1,200 RPMs and 90 watts. We expect to get more than 100 watts in the field at slightly higher heads. We don’t know yet what the maximum output will be.

This spring, we’ll be installing at least two of the bucket generators in Haiti to power ultra violet water purification equipment. A portion of the funding for this project was generously provided by St Peter’s Church in Weston. AIDG’s Haiti office is partnering with local NGOs, including our good friends at SOIL, to address the lack of clean potable water in their service areas. Each ultra violet purification device draws about 30 watts. With the generator, we expect to be able to power three or more UV devices at 100’ of head and 50 gallons a minute of flow. Currently, sites surveys are being conducted in Haiti to determine head and flow conditions and find suitable sites that provide year round consistent water. These long term test sites will provide data on performance as well as service and maintenance needs of the system.

Sam Redfield
AIDG
Quetzaltenango, Guatemala

Related posts:
Sam Redfield on Pico-hydro at La Florida
Parts List for Five Gallon Bucket Hydroelectric Generator