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 (

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

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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 m2.

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
Clearness Index / 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
Daily Radiation
(kWh/m2/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 m2

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 / Watt rating
(Watts) / Total load
(Watts) / Hours of operation
Sundazer fridge / 1 / 60 / 60 / 7
Sunday 10 W lights / 12 / 10 / 120 / 6
Thin lite 30 watt lights / 17 / 30 / 510 / 3
UV filter / 1 / 30 / 30 / 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 / Load (kW) / Components on
00:00 - 01:00 / 0.060 / Fridge
01:00 - 02:00 / 0.000 / -
02:00 - 03:00 / 0.000 / -
03:00 - 04:00 / 0.060 / Fridge
04:00 - 05:00 / 0.000 / -
05:00 - 06:00 / 0.000 / -
06:00 - 07:00 / 0.060 / Fridge
07:00 - 08:00 / 0.000 / -
08:00 - 09:00 / 0.030 / UV filter
09:00 - 10:00 / 0.060 / Fridge
10:00 - 11:00 / 0.030 / UV filter
11:00 - 12:00 / 0.043 / Laptops
12:00 - 13:00 / 0.060 / Fridge
13:00 - 14:00 / 0.043 / Laptops
14:00 - 15:00 / 0.043 / Laptops
15:00 - 16:00 / 0.060 / Fridge
16:00 - 17:00 / 0.630 / 30 W lights, 10 W lights
17:00 - 18:00 / 0.630 / 30 W lights, 10 W lights
18:00 - 19:00 / 0.690 / 30 W lights, 10 W lights, Fridge
19:00 - 20:00 / 0.120 / 10 W lights
20:00 - 21:00 / 0.120 / 10 W lights
21:00 - 22:00 / 0.120 / 10 W lights
22:00 - 23:00 / 0.120 / 10 W lights
23:00 - 00:00 / 0.000 / -

Figure 4: Load Profile at different hours of the day

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.

Table 4: Total and Excess electricity for different solar panels

Number of solar panels / Total electricty production (kWhrs) / Excess electricity produciton (kWhrs)
11 / 1411 / 146 (10%)
12 / 1539 / 256 (17%)

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 / Lumnes/ sq ft
Office / 30
Kitchen / 18.5
Living Room / 4

Figure 8: Locations of different lights in the clinic

Table 6: Lighting conditions for different rooms in the clinic

Room / Lumens/sq ft
Kitchen / 12.4
Delivery Room / 27.5
Labor Room / 27.5
Office / 22.5
Exam / 19
Recovery / 3.4
Residential / 2.7
Storage / 2.3
Waiting / 1.4