Expanding the solar electric at a clinic in Haiti

KeithWHare

Over a year ago, we started looking at options to expand the solar electric system at a clinic about 10 miles east or Port au Prince Haiti. The clinic is operated by a USA based non-profit called Healing Art Missions (https://healingartmissions.org).

I've posted about this system several times in the past. For more details see:

• Original installation in 2010 -- http://forum.solar-electric.com/discussion/7795/off-grid-system-in-haiti
• Adding a well and a pump -- http://forum.solar-electric.com/discussion/14846/well-pump-at-a-clinic-in-haiti
• Replacing the original batteries -- http://forum.solar-electric.com/discussion/21172/update-on-a-pv-system-in-haiti
• Discussions of expanding the system -- http://forum.solar-electric.com/discussion/350738/adding-an-air-conditioner-to-an-off-grid-system-at-a-clinic-in-haiti

Last week, we installed an additional PV array, installed two Midnite  Solar Classic 150s, replaced the battery bank, and ran power to the new surgery room air conditioner.

The PV array installed in 2010 consists of twelve 130-watt Kyocera KC130 panels wired in three strings of four panels. Each string potentially produces about 70 volts and 7.39 amps.

The system is wired for 24 volts DC because in 2010 we were able to get a Magnum MS4024 inverter in Port au Prince. Changing to a 48 volt system would require replacing the inverter and modifying wiring in the Midnite E-panel on which the inverter hangs. Every time I think about the benefits of 48 volts, I also think about the complexities in getting there and decide that 24 volts will work for a while longer.

The driving force for this upgrade was adding support for an air conditioner in the surgery room. We found a company in Port au Prince that sold and installed a Panasonic 12000 BTU mini-split (Part numbers CS-S12PKV and CU-S12PKV). This is an inverter unit with a soft start. It requires 240 volt, 60 cycle AC.

The MS4024 inverter outputs 120 volt, 60 cycle AC. We have a 120-240 volt transformer already in use to power the pump. We talked about whether the system could handle both the pump and the air conditioner at the same time. The water is pumped to a 600 gallon tank on the roof of the clinic so it only pumps every day or two. The surgery room air conditioner will be used a couple of mornings a week. Because of this, it was acceptable to install a switch so that either the pump or the A/C is powered, but not both at the same time.

We added eight 305-watt PV panels. The panels are JA Solar JAP6(K)-72-305/4BB with the specifications:

• Maximum Power: 305 watts
• Voc/V: 42.27 volts
• Vmp/V: 36.72 volts
• Isc/A: 8.84 Amps
• Imp/A: 8.29 Amps

I ran the numbers for several configurations. Nine panels would have been a little too much power for a Classic 150 charge controller. Six panels wasn't as much power as I wanted. The compromise was eight panels wired in four strings of two panels per string. This gives us 2440 watts in the new PV array in addition to the 1560 watts in the original PV array, for a total of 4,000 watts.

Two arrays require two charge controllers, so we replaced the original Outback FX60 charge controller with two Midnite Classic 150 charge controllers.

We also changed out the twelve Trojan T105 6-volt batteries for eight Trojan L16H-AC 6-volt batteries. The L16H-AC batteries are 435 amp hours at the 20-hour rate. They are wired in two strings of four batteries for a 870 amp hour battery bank. We used 4/0 battery cables and a 300 amp T-fuse on each string.

The installation went well and I was pleased with how the system was working when I left last Monday. I will post pictures in a couple of minutes.

Keith

KeithWHare

The combiner boxes, charge controllers, and the inverter. The left combiner box was installed in 2010. The right combiner box was installed this year.

KeithWHare

The new battery bank. The cage keeps hands out of the batteries and provides some security. All cables are 4/0.

KeithWHare

The 2010 array in the background faces slightly east of south. The new array in the foreground faces more directly south. The clinic is at about 18 degrees north latitude. The new panels are mounted a little shallow, but still should produce plenty of power in December. Additional masonry will be added to the back and front of the new racks for additional weight, but not as much as was used for the original array. The sun is never low enough for the water tank to cause shading problems.

KeithWHare

The transformer, pump controller, and Pump -- A/C transfer switch. The edge of the doorway is really straight -- the picture is slightly warped because of my cell-phone camera.

Photowhit

KeithWHare said:

I ran the numbers for several configurations. Nine panels would have been a little too much power for a Classic 150 charge controller. Six panels wasn't as much power as I wanted.

Keith,
I plugged in the numbers for a 3x3 nine panel configuration into the Midnite string calculator here;
http://www.midnitesolar.com/sizingTool/displaySizing.php

While it comes up as excessive, it is within what they would recommend. It looks odd, but Midnite is fine with having an array up to 1.2x the panels rated wattage. this has to do with the panels rarely (and in Haiti, never!)producing their panel rating in Standard Test Conditions. If you plug in the numbers it will say Excessive, but the first note says to add a 2nd controller above 1.2...


If you look at the info sheet for the JA Solar JAP6(K)-72-305/4BB here;

http://www.solarclaritycaribbean.com/wp-content/uploads/2015/12/JAP6-72_4BB.pdf

You can see why, Look below the STC numbers at the top and you will find the NOCT (Normal Operating Cell Temperature) values, or the expected output. They are;


So the expected output of 221.43 watts for 9 panels would fall within the Classic 150's capacity. That said it's always nice to run below the full capacity on electronics.

Well Shoot, I read "Every time I think about the benefits of 48 volts, I also think about the complexities in getting there and decide that 24 volts will work for a while longer. " So I went and did all this thinking you were here for advice. I see it's all nicely installed, Thank you for helping out! They seem to be a magnet for natural disasters. I'll leave this up and perhaps someone will gain something from it.

KeithWHare

According to the data I downloaded from the Classic 150 attached to the 2440 watt array, the peak input power to the Classic last Wednesday was 2,488 watts. This was the first day on the new batteries and we tested the air conditioner for a couple of hours. The early afternoon was clear and the sun is directly overhead at this time of the year so the sunlight may exceed standard test conditions even under the normal operating cell temperatures.

I had thought about the trade offs between higher voltages and warmer temperatures in the electronics. Since cold in this area of Haiti is 70 degrees Fahrenheit, lower voltages seemed like a good idea to help extend the life of the electronics. For the small sample of data I have, peak voltage in from the panels was 84.4 to 85.9 volts.

Photowhit

When full, a charge controller can 'see' short circuit numbers.

BTW - I like the added spacing and short heavy connectors for the battery bank! It does look like there is uneven resistance between the 2 battery strings. (Different cable length)

KeithWHare

The cable lengths on the two strings are the same (within a small margin of error). I color coded the strings so I could double check and explain the length issues. (My nephews Matthew & Aaron brought a variety of tape colors with them.) The violet string has an extra 16 inch cable on the negative side. The blue string has an extra 16 inch cable on the positive side between the fuse blocks.

The six-inch 4/0 cables between the batteries do not have a lot of flex, so that pretty much controls the battery spacing.

jonr

I recommend using a clamp DC ammeter to check balance between parallel strings.