The goal of this group is to minimize the amount electricity the community uses from the current grid system. This can be approached in two ways: we can reduce the amount of electricity used and we can obtain electricity from another source. By lowering the amount of electricity used, less electricity is needed. The electricity needed is provided by purchasing electricity from the current source or by producing electricity using a new technology. Basically, we hope to generate electricity and then use it efficiently.
The citizens of San Pablo, Tacana, Guatemala have expressed interest in working to provide a grid-free solution for generating electricity. With the procurement of computers and microwaves, the community has increased their reliance on electricity. Although they already have electricity provided through the grid, they want to explore ways to generate electricity for themselves in a more environmentally friendly way. San Pablo already attempted to install solar panels but were unsuccessful in their efforts for reasons which are still unknown. Because of this, the citizens want an alternative method for generating electricity.
We contacted the group that went down to San Pablo in December to obtain the data they collected. We received pictures and videos from the trip but have not received any flow rates or other measurements taken. Their contact is San Pablo has not replied either.
Options for Reducing the Amount of Electricity Used:
– Turn off lights and appliances when they are not being used (for example: during the day or when the room is empty)
– Use more efficient lights such as CFLs or LEDs that use only a fraction of the electricity
Alternative Methods for Producing Electricity:
There are three main methods for generating electricity by “alternative” methods. These are solar cells (also called photovoltaics), wind turbines, and micro hydro (or water).
There are already solar cells in place in the village. From the photographs we can see some external damage. However, we do not know why these are not functioning or why no one has tried to fix them. One of the first actions in arriving in San Pablo should be to examine these panels to see if they can be repaired. Hopefully, they can be repaired and made functional. This would allow the village to generate electricity by using existent technology and materials and allow them to recoup (through savings) some of the money invested in these devices.
Wind turbines are also used to generate electricity using a blade that spins a generator. A concern for the Tacana region is a species of endangered bats that are endemic to the region. We are worried that wind turbines could further endanger the bats through collisions with the blades.
Water: (Micro Hydro)
There are a multitude of streams present in the surrounding area. Most of these have a low volume of water but are present year round. In addition, there are a number of waterfalls and sharp hills in the region that create large vertical drops, creating fast moving water over a short period of space. This is ideal for creating a micro-hydro device which needs a constant water source to turn the wheel or turbine.
Proposed Solutions for Micro Hydro:
A micro-hydro technology uses water to generate electricity. However, unlike large hydro applications, the stream or water supply is not contained in a dam. This reduces the impact on the environment by allowing wildlife and debris to pass through without becoming stuck in a pool to decay. There are three main micro-hydro technologies used. These are the power bucket, the water wheel, and the vortex.
The power bucket uses a simple bucket in which water is spins a pelton wheel (described below). The water is piped from the stream into the bucket. The water enters the bucket from four separate holes on the top. This works to distribute the load and reduce the torque on the shaft. The water hits the wheel causing it to turn before flowing out of the bottom of the bucket to return to the stream.
The water wheel works by turning a large wheel that is attached to a generator. In this case water is again piped from the stream, however, for this application it is then released over the wheel. As the water falls it hits the wheel causing it to turn.
The vortex works by diverting a large amount of slow moving water from a stream. This water is channeled through a concrete pool shape to form a vortex or whirlpool. As the water exits through the whirlpool it turns the large turbine present in the middle.
Once we had researched the main methods used in micro-hydro we had to decide on which device to make. In an attempt to avoid our own bias, we used a decision matrix which ranks how well each device is for the listed attribute and weights how important each of these attributes are.
|Decision Matrix to Determine the Best Micro Hydro Technology|
|Weight||Water Wheel||Vortex||Power Bucket|
|Ease to Build||9||8||2||6|
|Water Flow Adaptability||8||6||5||8|
Based on this decision matrix the power bucket is the best fit for this application. Therefore, we will design and build the power bucket.
Basics of the Power Bucket:
The power bucket uses a pelton wheel such as the one shown below. The water enters the PVC pipe and follows the circle of the pipe before exiting the other side. This pushes the pipe forward causing the wheel to turn.
- We compared using straight PVC pipes versus elbow PVC pipes. The elbow PVC pipes worked best in capturing all of the water (in the straight pipe the water flowed out the side).
- We tested the size of the piping by comparing 3/4″ elbows with 1″ elbows. The 1″ elbows spun the wheel faster because we were able to direct the water to a certain portion of the pipe rather than hitting the entire pipe (created the effect of the pelton wheel).
- We tested the ideal number of elbows on the pelton wheel. For this test we tried 6, 10, and 12 elbows. The wheel with 10 elbows created the highest voltage (keeping everything else the same). Theoretically the 12 should allow us to harness more energy but we think that they were spaced so closely that the water was leaving the pipe and hitting the one behind it, creating a resistive load on the wheel.
Final Recommendations for the Pelton Wheel:
– Use 10 1″ PVC elbows on a 7″ grinder disc.
- We started with a 3/4″ garden hose. We reduced the end of the hose with a nozzle to create a higher water pressure (which in turn increases the force of the water on the wheel causing it to spin faster).
- We began with a 3/8″ nozzle but it wasn’t creating the pressure we wanted so we reduced it to a 1/8″ nozzle. This increased the voltage by over an order of magnitude.
- When using this system in Guatemala the flow rate and pressure will depend on the flow rate of the stream used. Calculations will need to be made to determine the height and size of the piping used.
Final Recommendations for the Water Pressure
– Reduce the nozzle to increase the force of the water – in our case 1/8″ nozzles worked best.
– Obtain water flow data to determine the height drop and size of piping needed.
Effect of reducing nozzle shown below:
GENERATION OF ELECTRICITY
- We tested three sources for generating electricity: a car alternator, an AC motor, and a DC motor.
- Car Alternator: We were able to generate a voltage with the car alternator but there were complications in creating a permanent magnetic (we tried 2.5 V and 12 V batteries). Ultimately, although we were creating electricity it was a very small amount. A car alternator is designed for higher RPM than we are able to generate with a power bucket.
- AC Motor: With the AC motor we were able to spin the wheel really fast (judging from the sound). Before we were able to get a reading, however, the AC motor burnt out (there was a burned electrical smell). If we were to use an AC motor, more research would need to be done to find a more appropriate one.
- DC Motor: This provided the highest reading. It has the further advantage that no batteries or additional supplies are needed to create a magnetic field. If used the electricity could be used directly to power lights. However, an inverter would have to be added for use in AC applications.
Final Recommendations for Generation of Electricity
– Use a DC motor (size and voltage will depend on the application)
The three sources are shown below. From left: car alternator, AC motor, DC motor.
Our tests were done using a common household water faucet; because of this, we were able to calculate the maximum possible power using known values for the pressure and flow rate of the faucet. In a real world application these would vary with the source and water head. This maximum potential power only applies to hydro generators hooked up to faucets of the same nature (30psi at 2.5GPM).
Actual measured power (using a 2.5Ω load resistor)
Since we know the power output of our bucket and the maximum possible power invested in the faucet, we can calculate the efficiency (shown below).
Ultimately the power bucket can be used to power high efficiency LED bulbs or trickle-charge a car battery. The size of the bucket, amount of pressure head, and flow rate of the water source are all limiting factors to the amount of power that can be generated.
Below is a chart comparing the power consumption of different technologies to the output of our power bucket (on a common household water faucet). A logarithmic scale is used to to prevent the smaller scale outputs from being illegible.
Below is a linear scaled version of the same chart (showing applications with minimal power consumption).
Cost (Environmental and Monetary):
To calculate the cost of the power bucket we made some informed estimations. Using the cost of the supplies and power generated, we calculated the cost and CO2 emissions for our device. This data was then compared to other sources used to generate electricity (photovoltaics, wind turbines, and conventional fuel sources such as natural gas, coal, and nuclear). In all calculations the lifetime of the power bucket was assumed to be 5 years (being used 90% of that time). Please keep in mind that these calculations, while quantitative, are estimates. The calculations are shown below.
COMPARATIVE COST OF ELECTRICITY
COE = total cost / (power*lifetime*duration of use in day)
CARBON DIOXIDE EMISSIONS
Carbon dioxide is a main contributor to global warming. Our project aims to provide a low-carbon source for generating electricity. To evaluate the performance of our device in reducing carbon dioxide emissions, we looked at two separate areas: the carbon dioxide released in producing the power bucket and the carbon dioxide released during use of the power bucket. These two calculations were then combined to get a better understanding of the full impact of the power bucket of carbon dioxide emissions.
Carbon Dioxide Emissions From Production
CO2 = CO2 in initial materials/total kWh
Assumptions: Buildings used to house power plants are made of 100,000 tons of cement and last for 50 years.
Know: Embodied CO2 in primary production (Source: CES EduPack)
- Cement: 1 lb CO2: 1 lb cement
- PVC: 2.4 lb CO2: 1 lb PVC
Carbon Dioxide Emission During Use
CO2 = CO2 from fuel/total kWh
Total Carbon Dioxide Emissions
CO2 = CO2 from production + CO2 from use
Our graphs show that while our micro-hydro bucket performs favorably in CO2 emissions during use, it does not do well in comparison to other power sources in terms of CO2 released in production and the comparative cost of electricity.
Conclusions and Recommendations:
- We made electricity!
- The micro-hydro power bucket is not a viable option for San Pablo. It does not produce enough electricity to power the appliances used in this village.
- The power bucket could be implemented for lighting and other small power needs in villages with no electricity.
- We recommend trying to fix the solar panels already in place in San Pablo.