Introduction:
The goal for the solar sub-team of the Honduras project was to design a robust and sustainable solar system that would be able to provide power to the health clinic that is to be built in Honduras. The solar system to be implemented will be used to power a vaccine fridge, fluorescent lights, two laptops, and any other possible AC appliances. In designing the power for our system, the first main question that had to be answered was whether the major components in the project will be AC powered or DC powered. It was decided that the fluorescent lights and vaccine fridge will both take
DC power. This will eliminate the 25% efficiency loss that is associated with using an inverter. Also, this makes the system less prone to failure, since if these components depended on AC power, failure of the inverter will cause the entire system to fail. Almost all our parts will be provided by a solar vendor in Honduras by the name of Insagro Solar
( http://www.insagrosolar.com/ ).
Components:
DC fridge
We originally considered using the Sunfrost DC vaccine fridge. However, because of shipping costs and customs cost, we decided that the Sundazer solar fridge will be more viable. The Sundazer fridge will be provided by Insagro
Solar. This fridge is rate to consume 348Whrs of 12 V DC power per day when the outside temperature is 42.3⁰C (110⁰
F). Because of the thick insulation, this fridge is much more efficient than standard small sized AC fridges, which would usually consume over 1000 Whr per day. According to a Sundazer representative, this fridge also meets the World
Health Organization’s requirements for vaccine fridges.
Lighting
For lighting the clinic, we decided to use fluorescent lights because of their high efficiency and long lifespan.
Specialized DC ballasts are necessary to power fluorescent lights using DC power. Insagro solar can only provide 10 W,
360 Lumens light bulb, which would not be bright enough examining a patient or office work. Thus, we decided to also order some 30 watt Thin-lite, which uses standard F32T8 fluorescent tubes. These 30 watt lights can generate 2850 lumens and will be used in rooms that require bright lighting.
Batteries
We decided that deep cycle batteries would be the best option for our needs. Insagro solar has 6 V, 225 Ahr, deep cycle batteries available. They have a life span of 790 cycles.
Charge Controller
Insagro solar would provide us with 6 x 20 A charge controllers. Each charge controller will handle 2 solar panels. The charge controller will use three LED lights to display different states of charges of the battery. Different combinations of lights will indicate charge levels of >75%, 25-75%, <25%, and <10%.
Inverter
For the inverter, Insagro solar was able to provide us with a Xantrex 3000 Watt inverter. This inverter will only be able to provide 2500 watts of continuous power. This inverter is large enough to power tools and large appliances.
Currently it will only be used to power a UV water filter and the laptop computers. The laptop computers may also be powered by using a DC/DC inverter. However, this inverter will allow room for expansion and may be used to power a donated ultrasound machine or fetal monitor.
Solar panels
Insagro solar will be supplying our team with 75 watt Isofoton solar panels. These panels will also have a 10 year warranty
.
Calculations:
Solar Irradiance
The solar irradiance for Las Mercedes was obtained through a modeling software called Homer. From Google
Maps, the longitude and latitude of Las Mercedes was found to be 14⁰ 16’ North and 87⁰ 34’ West. Table 1 shows the values for the solar radiation at different months of the year and also the average clearness index. Figure 1 shows the total daily radiation per day and figure 2 shows the average value of solar radiation per m 2 .

Table 1: Total Solar irradiance and clearness index for different months at Las Mercedes
Month Jan. Feb. Mar Apr May Jun Jul Aug Sept Oct Nov Dec Mean
0.510 0.559 0.585 0.580 0.538 0.506 0.508 0.514 0.506 0.497 0.495 0.497 0.525 Clearness
Index
Daily
Radiation
(kWh/m 2 /d)
4.244 5.108 5.857 6.127 5.741 5.367 5.386 5.414 5.135 4.649 4.190 3.984 5.099
Figure 1: Total Daily radiation per day
Figure 2: Average solar radiation per m 2
The values for solar irradiance were used by the program to calculate the output of the PV arrays based on the power rating of the solar panels.
Load calculations
Table 2: Components list with watt ratings and hours of operations
Components Quantity
Sundazer fridge 1
Sunday 10 W lights 12
Thin lite 30 watt lights 17
UV filter 1
Watt rating
(Watts)
60
10
30
30
Total load
(Watts)
60
120
510
30
Hours of operation
7
6
3
2
Laptops 2 21.5 43 3
From the values calculated in Table 2, we also estimated the times when the different appliances would be on and input that data into HOMER. Figure 4 is a graphical representation of the load profile in a typical day.
Table 3:

Hour
00:00 - 01:00
01:00 - 02:00
02:00 - 03:00
03:00 - 04:00
04:00 - 05:00
05:00 - 06:00
06:00 - 07:00
07:00 - 08:00
08:00 - 09:00
09:00 - 10:00
10:00 - 11:00
11:00 - 12:00
12:00 - 13:00
13:00 - 14:00
14:00 - 15:00
15:00 - 16:00
16:00 - 17:00
17:00 - 18:00
18:00 - 19:00
19:00 - 20:00
20:00 - 21:00
21:00 - 22:00
22:00 - 23:00
23:00 - 00:00
0.630
0.690
0.120
0.120
0.120
0.120
0.000
0.000
0.030
0.060
0.030
0.043
0.060
0.043
0.043
0.060
0.630
Load (kW)
0.060
0.000
0.000
0.060
0.000
0.000
0.060
-
-
Components on
Fridge
Fridge
-
-
Fridge
-
UV filter
Fridge
UV filter
Laptops
Fridge
Laptops
Laptops
Fridge
30 W lights, 10 W lights
30 W lights, 10 W lights
30 W lights, 10 W lights, Fridge
10 W lights
10 W lights
10 W lights
10 W lights
-
Figure 4: Load Profile at different hours of the day
Table 4: Total and Excess electricity for different solar panels
Number of solar panels Total electricty production (kWhrs)
11
12
1411
1539 256 (17%)
From this data, HOMER calculated the 2.95 kWh per day. The total DC load serviced in a year will be 1077 kWhrs.
System Sizing
Solar panels:
After the load profiles have been entered, HOMER was used to run a simulation of the system.
We found that the optimal number of solar arrays need for the system would be 12 x 75 Watt solar panels. The system would also be functional with 11 x 75 Watt solar panels.
Excess electricity produciton (kWhrs)
146 (10%)

Figure 5: Monthy electric productino with 12 solar panels.
Batteries
We found the optimal number of batteries to be 8 batteries. The autonmy of the system would be 52.7 hours, under full load and the annual throughput of the batteries is 947 kWhrs. Thus the battery lifespan is calcualted to be 7.2 years.
Figure 6 shows the battery bank state of charge. The battery bank does not fall below 76%(Figure 7), which will further prolong the life of the batteries.
Figure 6: Battery Bank state of charge at different horus of day and different months
Figure 7: Frequency for state of charge
Calcuation for finding lifespan of batteries.
8 batteries x 225 Ah x 6 Volts x 790 cycles x .80 = 6825600 Whrs
= 7.2 years

Lighting:
Based on standard lighting conditions found online(Table 5), we caculated the number of lights necessary to light different rooms. Figure 8 shows the locations of the lights in the different rooms of the clinic and Table 6 shows the calcuated brightness at different rooms.
Table 5: Standard lighting conditions for different rooms
Room
Office
Kitchen
Living Room
Lumnes/ sq ft
30
18.5
4
Figure 8: Locations of different lights in the clinic
Table 6: Lighting conditions for different rooms in the clinic
Room
Kitchen
Lumens/sq ft
12.4
Delivery Room
Labor Room
Office
27.5
27.5
22.5
Exam
Recovery
Residential
Storage
Waiting
19
3.4
2.7
2.3
1.4