Global Alternative
Power Solutions
Purdue University
Partnering with La Universidad de Antioquia
For the benefit of Km-18 in Caucasia, Columbia
Purdue EPICS
Spring 2013
Introduction
In 2012, EPICS of Purdue University was commissioned to develop an alternative
power solution for Km-18, a school in Caucasia, Columbia. That fall, the Global Alternative
Power Solution group (GAPS) was created to meet this problem.
Communication with the school revealed that a typical monthly power bill was
between $74 and $77 US dollars a month. Without sacrificing design, we needed to produce
a system that could match their payments a month or save them money.
We knew from further communication that several systems were essential to meet
the basic needs required for a typical school day: the refrigerator, the computers (5
computers are running daily), fans (9), the air conditioning, the lights, and additionally a
water pump which is external to the school building, which supplies drinking water to the
institution. Moreover, appliances that are not essential but the school wants to work are:
the printer and photocopier, used in the administrative area.
Blackouts were a common problem in Caucasia, ruling the grid power to be entirely
too unreliable. Blackouts could be as brief as 5 to 10 minutes, or in the cases of rain or high
winds last up a full school day or more (8 hours or more). In these cases, students and
administrators may not convene that day or leave early. The lack of use of certain devices
such as the printer or copier could result in a lack or shortage of academic materials for the
students. Additionally, between 38 and 50 students are fed at least one meal at the building
each day. Obviously the lack of dependable power was affecting the education and general
quality of life for the students at Km-18 and the eradication of this problem will provide
them with enough electrical security to leave the school year uninterrupted for years in the
future.
Pictures were sent to the team showing the school, its resources, and a little of the
surrounding area. Through these, we learned that there was a small grassy area to the left
of the school and the school itself was positioned to the south facing the road. This meant
that the sun passed directly over the school from right to left.
Integration Plan Layout
1. Work Done in Previous Semesters
2. Systems Considered
a. Budget
3. Battery Decisions
4. Constraints
a. Specific ones to mention:
i. Safety
ii. Batteries
iii. travel/cost
iv. maintenance
v. cloud cover/outside forces
vi. power at school increases
vii. economy goes down
viii. acceptance of the system
b. decisions concerning constraints
c. trees
i. needs to be addressed separately due to size of issue
d. how to get it to school
e. who to buy parts from
5. Assumption list
6. Communication list
7. Post-Delivery
a. our role
b. effects
Solar Power System
Shortly after its introduction, GAPS developed an idea for a power system for the
school and determined a solar solution to be the most efficient power system available.
Although batteries and panels are expensive, we believed that our system could save the
school money and produce more reliable power. This system was to rely on absorb glass
material (AGM) batteries to store the energy captured from the solar panels. These
batteries don’t require maintenance and are cheaper than their gel alternative. These
batteries are also able to withstand greater temperature variations, which was also a large
factor in the decision making process. These batteries would be housed in battery banks
and would be attached to an indeterminate amount of solar panels.
After deciding on solar power for our system type, we needed to get more specific
and developed 3 system types and 3 locations to propose to the school in Columbia.
Ensuring that we had multiple options for our consumer was important to us in order for
Km-18 to maintain a positive outlook on the project. Giving the final decision to them kept
them in the drivers seat, guaranteeing that they got the final say and received exactly what
they asked for.
As far as positioning, we had one system that was elevated where a tarp now hangs
over the middle of the play area. This was unfavorable with the school due to the tarp’s
function as a block from the sun while still letting sunlight through. Mounting the system
over this area would leave it completely shaded and might also make maintenance difficult.
The next system was elevated over the grassy area to the left of the school, and one
system was grounded in the grassy area.
Upon presenting our options, the final grounded version was settled upon and our
work continued from this decision from the school.
From here, we developed 3 systems that utilized and produced different levels of
power.
Full System Abstract
This system can provide use of 750 kWh per month, or 24 kWh per day. If this
system is chosen, it has the ability to power:
 Air conditioning
 Computers
 Lights
 Kitchen appliances
 Fans
 Refrigerators
The full system is much more expensive than the half or quarter systems at an initial
cost of $25,690. It is also more expensive over time, as it has more parts involved in the
design that could potentially break. Over 20 years, this system is estimated to cost $33,500
with this accounting for one panel and one battery replacement, in the event of an
accidental breaking. This system only has 1 day of reserve power, as it is meant to power
more electrical items than the other two systems. Negatively, it also takes up the most
space due to, again, its higher number of parts. The lack of a backup in case of a malfunction
in the panels or depletion in the battery reserve also makes this system a gamble. It was
created to allow the school to be entirely independent of the grid. Lastly, because of the
larger amount of panels and batteries, this system also requires the most maintenance over
time.
There are, however, some benefits to this system. It will allow the school to be
entirely independent from the grid. Due to this, the school will no longer have a monthly
energy bill and their energy source will be much more reliable. By overestimating their
power needs for this system, they also will have room for expansion. This system is
guaranteed to run everything the school has currently running, and we are confident in the
full system’s ability to handle more electrical devices that the school may acquire in the
future.
Overall, it is our belief the design for the full system is not the most beneficial choice
of the three we have conceptualized for the school. It is the most costly option and gives
them more power than they asked for or need. The amount of power this system provides
is more fitting for an average American home to live independently from the grid, but not
for a rural Columbian school. The school will not only require less energy in general, but
also only requires energy during the school week. We have estimated the school is paying
$18,000 over 20 years. Since this amount is already proving to be too much money, it is
unrealistic that they will be able to pay nearly twice that much money for this full system.
Half System Abstract
The half system was envisioned to ideally power the listed necessities from the
school and what was considered non-essential would be powered with the grid.
This system can provide 750 kWh a month (375 kWh from the panels and 375 kWh
from the grid). It is equipped to provide reserve power for the duration of one full day. The
initial cost is moderate at $14,845 and the projected upkeep cost for 20 years is $16,750.
With the addition of an estimated monthly grid bill, the total upkeep cost is estimated to be
$25,750.
If the half system is chosen, it has the ability to power:
 1 refrigerator (8 hours)
 12 light bulbs
 9 fans
 water pump (4 hours)
 2 computers
 10 monitors
This half system consists of 8 batteries, 2 inverters, 2 charge controllers, and 14 solar
panels.
Comparatively, the half system would have much lower initial and upkeep costs. The
initial cost would nearly be halved from the full system. The half system would also require
less space due to the decreased number of components. However, the grid would still rely
on the grid, and therefore would need to pay a monthly bill. The half system would be more
expensive than the quarter system but would be more comprehensive in terms of power
output. While calculating the power consumption, it is possible that we could have
underestimated the impact of factors such as frequency of grid failure, trees, cloudy
seasons, etc. Therefore, the half system would provide a greater safety net in the event that
these assumptions are not adequately prepared for.
Quarter System Abstract
After reviewing our system types, we realized that by overestimating the school’s
power needs for each system, we were actually able to power everything the school
requested electrical power for just with the half system. Because of this phenomenon, we
decided to create a third system size that would meet half of the school’s power demands
through the solar panels and the other half covered by the grid power.
This system can provide 187.5 kWh per month, which amounts to roughly 6 kWh
per day. This initial cost is significantly lower than the other aforementioned systems at
$11,330 and the estimated upkeep for 20 years is also significantly lower at $10,288.
However, this cost does not take into consideration the monthly cost of the grid.
If the school were to choose this system, it would adequately be able to supply
power to:
 Refrigerator (24 hours)
 12 light bulbs (8 hours)
 9 fans (8 hours)
 Water pump (8 hours)
 2 computers (4 hours)
 10 monitors (4 hours)
Additional desirable time or addition of other items would involve the use of the grid.
The most desirable aspect of this system is the lower cost. It has both the lowest
initial cost, which Purdue will fund, and the lowest upkeep cost, which the school would be
funding, as compared to the other systems. Additionally, this quarter system is around
$8,000 cheaper over a 20-year period than the grid tied system the school is currently
using. Since the school specifically stated that money was one of the major reasons they
were looking for alternative ways to get power, we made sure to include a system that was
substantially cheaper than what they were paying for now. An important fact to note about
this system is that it will not supply enough power to run all the appliances in the school.
To supply the remaining components, the school must rely on the grid for this additional
power. This means that those appliances connected to the grid will have the same
reliability problems that are occurring with the current system. The school will also have
an additional upkeep cost consisting of the monthly grid bill.
Assumptions
To be able to commence with project work, many assumptions had to be made
about the school. These assumptions are essentially the groundwork to all the systems that
we developed. It was necessary for GAPS to make these assumptions because some
essential information wasn’t able to be gathered.
One large problem we encountered were the trees surrounding the school. To
combat this problem we wrote a program that gives as close an estimate of daylight hours
as possible based on the variables of tree height, the height of the solar panels, and the
distance between these variables. From this, we were able to determine that the panels
should be slightly elevated in order to absorb the most sunlight as is attainable.
We are also assuming that the batteries will need to be changed every 5 years, as is
the recommended span on these batteries according to our research. This estimate has
been evaluated and added into the total cost over 20 years.
Extensive research was conducted on the weather in Caucasia. Initially, the
information we gathered showed that Columbia has 70% cloud cover anywhere from 45%
to 90% of the time. This was a huge obstacle we had to work around. With so much cloud
cover, it would be impossible for our system to charge the battery bank. After making this
discovery, we started researching how the solar panel’s efficiency changed with cloudy
skies. We found the efficiency decreased anywhere from 50% to 90%. If we had to factor in
a 50% to 90% decrease in the amount of power we would be able to generate, the scale and
cost of the project would be too great to make it useful.. I could not find any other climate
data that was as precise and thorough as the NASA data we were already working with.
After rechecking initial assumptions, we realized that we were calculating in cloud cover
when NASA had already done this before posting their results online. NASA calculated the
average number of kilowatts per hour that can be produced and it is from these numbers
that we went forward with the rest of our calculations.
Power Modeling
In order to produce our power estimate, our team went through an extremely iterative
process. First we began with a cost model. When this became too complicated to be useful,
we inquired further of the school as to which devices they are using and how often the
power is out. Based on an electric bill, appliance listings, and the qualitative information
sent to us, we as a team estimated a power outage range from 1/6 to ½ of the time,
producing a power demand between 320 kWh and 750 kWh, including a buffer zone for
growth. We verified this range based on two new cost estimates and created system trends
to give our project partners the best possible information.
System Trends
Basic Premises for understanding trends
-Panels are sized to supply a day’s worth of power in 4.3 peak sunlight hours.
-Battery banks are designed to power the system for one day
Based on these trends and the cost models the following trends were gathered.
Cost per kWh Capacity
Installation Cost, Dollars, USD
40000
35000
30000
25000
20000
One day bank
15000
Half day bank
Two day bank
10000
5000
0
0
5
10
15
20
kWh / day Capacity
25
30
35
The above graph plots, based on a kWh demand, the initial implementation cost of a system
capable of supplying a day bank, a half day bank, and a two day bank respectively. This
graph can be used a number of ways. First, based on the kWh wished to power and the size
of the battery bank, the user can achieve an estimated cost of the batteries and panels of
the system. For instance, if you wanted to power only a refrigerator with a two day bank it
would cost approximately $3,000 USD. Alternatively, at a given minimum price you can
find the options available. For instance, at $10,000 the user can power a 7.5 kWh / day
Capacity with a two day battery bank, a 14 kWh / day one day bank, or a 17.5 kWh / day
with a half day bank.
5 Year Part Replacement Cost / kWh
Capacity
Replacement Cost, USD
25000
20000
15000
One Day
10000
1/2 Day
2 day
5000
0
0
5
10
15
20
kWh / day Capacity
25
30
35
This chart demonstrates the net costs after five years of usage necessary to maintain the
system for another five. In this particular chart, the primary replacement cost is in
replacement batteries.
10 Year Cumulative Part Replacement Cost /
kWh Capacity
45000
Replacement Cost, USD
40000
35000
30000
25000
One day bank
20000
Half day bank
15000
Two day banks
10000
5000
0
0
5
10
15
20
kWh Capacity
25
30
35
This chart includes both the five year and the ten year cost necessary to bring the net cost
maintenance cost for 15 years. This includes two battery bank replacements and one
replacement of inverters and capacitors.
15 Year Cumulative Part Replacement Cost /
kWh Capacity
Replacement Cost, USD
70000
60000
50000
40000
One day bank
30000
Half day bank
20000
Two day bank
10000
0
0
5
10
15
20
kWh Capacity
25
30
35
Finally, this chart displays the 15 year costs based on the net replacement costs needed to
keep the system running for 20 years. In all these charts, it is assumed that the current
technology of batteries is constant over the next twenty years.
Constraints
In order to ensure the best possible system, we felt the need to brainstorm all of the
aspects of our system that had the potential of failure. We call these possibilities
constraints of our system. These potential problems would either drastically change our
design or cause the system to completely malfunction. We then researched these problems
and came up with solutions to each one of them, which were later communicated to the
specific teams that could implement them. The ultimate goal of this brainstorming and
research is to solve problems our system will have before they actually happen to insure a
long and efficient life for our system. The constraints that we deemed most important are
listed below.
1. Safety – This system will be implemented at an elementary school, meaning we
had to ensure the system did not harm the children and the children did not harm the
system. We also needed to make the system safe for the people who will maintenance it.
We propose putting the system in some sort of enclosed area with a locking door or gate.
This enclosure could outline the panels themselves, the batteries, or both. It’s also
necessary to put all wires leading from the system to the school underground so the
children and animals do not interfere with them. Warning signs in Spanish around all the
potentially dangerous areas of our system would be implemented. An instructional
demonstration would also teach the teachers at the school how to properly and safely
handle the equipment so they can then pass that knowledge onto the students.
2. Trees – Because our system is solar powered, anything that blocks the sun could
potentially cause our system to be less efficient or even completely useless. We received
detailed pictures around the school showing the current status of the trees in the area.
There are no trees directly to the east or west of the school, but there are numerous trees
to the north and south. More information was attempted to be gathered from the school
regarding the typical shade of the planned area of instillation, but a response was never
received. Because of this, we created the computer program to estimate the daylight hours
we could expect with our variables. To keep the expense low, it isn’t possible to lift the
panels off the ground significantly, but even a small increase greatly rises the efficiency of
the system. Arranging the panels in such a way so they are in the spaces where the sun
shines the most will help to keep the cost low and the efficiency high, but we will not know
what the optimal configuration is until we get more onsite information. This is also only a
short-term solution because of the continual growth of the surrounding trees. We will have
to make the school aware of this problem and tell them how to deal with the growing trees
over the next 20 years.
3. Delivery / Cost – Since we are designing this project in the United States, but
building it in Columbia, there are various problems that we will have in implementing our
design. We chose to use a local company in Columbia to purchase the solar panels called
Hybrytec. This company was chosen because it has reasonable prices for the purposes of
this endeavor and we would spend less money by negating an oversea shipping cost. Also,
if part of the system breaks, it would be easier for the school to get replacement parts from
a company in Columbia. We also have to work out how to get all of the components (the
system and structure components) from the places they are manufactured to the school.
Possible means of transportation have been discussed such as by boat, trucks, or
attempting to persuade the company to deliver them for us.
4. Maintenance – The system requires a certain amount of maintenance. If it does
not get this routine maintenance, it may malfunction and parts could even be destroyed.
Information on the maintenance work and contact information of the companies we
purchased components from were included into the Integration Plan. The most important
thing we can do is to highlight the importance of this system to the school so they will be
motivated to maintain it.
5. Outside Factors – This includes things beyond our control such as cloud cover, the
government, guerilla interference, etc. There are countless problems that can go wrong
because of things beyond our control, but we came up with both the most important and
plausible problems that our system could encounter and brainstormed solutions to those
problems. We propose to make the system blend in to the surrounding buildings. There
was also an idea to promote the system within the community so the community will better
protect it from any harm that others might want to cause it. This promotion could be done
through the churches, or any other community based organization.
6. School’s Power Demand Increases – If our system cannot power the entire school
or at least have plans to get power to the entire school, it is useless to the school. We have
planned for school expansion and have factored into our calculations an increase in their
power demand sometime in the next 20 years. For the short term, we have found the
maximum amount of power our system can power, and it is already well over the school’s
current power needs. We will also provide examples of appliances that they could
implement in the school that will not exceed the power supply our system can deliver. For
the long term, we will provide instructions on how to expand the system in the integration
plan, including contact information for the companies to purchase and install more
components. A feedback system may also be utilized that will notify the school how much
power they are using and how much they could potentially use. This would ensure the
school always knows what their capabilities and limitations are.
7. System Malfunctioning – If one part of the system breaks, it could be very hard to
find the part that is broken. Any part of the system could break at any time, so it is
important to have some sort of feedback system to alert the school of any problems. We
propose to integrate a display that will present the status of the system either by LED lights
or something else entirely. An auto shutdown function may also be desirable because if one
part of our system breaks, it could potentially break another part. For example, if the
charge controller breaks, the influx of charge could destroy the batteries.
8. Acceptance of the System – It is important for us to convince our project partners
that our system will help them by supplying them more reliable power and saving them
money. It is important to ensure that our system will be used how we intend it and not
scrapped for parts after implementation. To make sure the system is used properly, we
have been continually improving communication between our team here at Purdue and our
project partners in Columbia. This was accomplished by sending more emails, as well as
Skype conferences to the school communicating our design in exchange for their feedback.
Tree Program
Hannah Lundell wrote the code for a C program to give an accurate estimate of the
amount of daylight hours expected based on the height of trees, height of the solar panels,
and the distance between the two. This is done by finding the height between the top of the
solar panels to the trees and taking the inverse tangent of that height and the distance
between the solar panels and trees. This is done to find the angle. The angle is then
converted into degrees (C computes trigonometric functions in radians) and multiplied by
2. This is to replicate trees being on either side of the solar panels with the solar panel
exactly in between the two trees. This angle is then subtracted from 180 to find the angle
in between (not sure how to describe this…). This is then multiplied by 12/180 to find the
approximate daylight hours expected.
Battery Decisions
At the beginning of the semester, our decision of using AGM batteries needed to be
verified. Hannah Lundell was the lead battery expert on the Sustainability team and she
researched different kinds of batteries to find which would work most efficiently for a solar
panel system. She found that the optimal choice was an AGM battery, which was verified
by the GAPS project leader, Steve Kalacinski, and the Sustainability team leader, Chris
Bosma. This type was ultimately chosen due to the lower price, the sizeable lifespan, their
availability in Columbia, their ability to weather the elements, and low maintenance. We as
a project team are buying the batteries from a local company in Columbia called Hybrytec.
Recommendations
To preserve the integrity of the system and to promote safety with the school, we
are recommending constructing a fence that blocks off access to the panels. In this way, we
can assure that the solar system will continue to work correctly and it will keep the
students safe out of the way of the equipment.
We are also recommending an education program to teach the students how the
system works. We are hoping this will further promote safety, as well as provide a positive
educational experience with the technology that we are giving to them.