Solar Two - Solar Food Dryer & Vacuum Sealing

We attempted to build a solar food dryer, using the sun energy to hygienically dry fruits in Cambodia. We have search through the internet and came across a design which we can try out.

We bought wood and cut the to shapes and assemble them together. Finally, we painted it and allow it to dry before using it.

Sun energy is collected through the transparent plastic and heats up a wire mesh inside. Air intake from the front sucked in and heated up by the wire mesh, the hot dry air rises because of convection in the dryer and flow into the drying chamber behind. The fruits prepared for drying are placed on trays to be dried in the chamber. On a hot day, the temperature in the chamber reaches about 50 degress Celcuis and humidity falls to below 30%. Drying takes about 3 days.

The temperature and humidity of the drying chamber was measured from night time till the next evening. It was noted that the humidity at night reaches above 80% while its temperature drop to below 30 degress Celcius. During the day, the temperature in the chamber increases to above 50 degrees Celcuis and the humidity falls close to 30%. Drying of the fruits takes place only during the day time.

The result was partially successful. Somehow we could not get complete drying of the fruits. Probably due to condensation of moisture at night.

Hence for the next improvement to the design, we must introduce continuous drying process through the night which we will require some heating process.

In conjunction with the solar dryer, we design a vacuum sealing machine to store the dried fruits in a vacuum sealed plastic bag. The machine does not use electricity but working on the priciple of a reverse bicycle pump for sucking the air out of the plastic bag and using fire from a candle stick to seal the plastic bag.

Solar Two - Fire Store Construction

On request from the orphanage, we build a fire stove for them. We got all the children in the orphange to help in carrying the bricks for the stove. We visted one of the villager's house to study how a fire stove is constructed. We came back using a double walled stove to prevent heat lost to the outside wall when fire is lit.

For the top, we constructed a mould and later put cement into it and allow them to dry before removing them. The hole size is determined by using their largest cooking pot.

We prepared the ground where the stove is to be placed and began brick laying.

We have a specialist who is good at mixing cement, sand and water in the quickest possible time.

Finally, we could see the shape of the fire stove. We place the pre-fabricated top onto the base of the fire stove and to complete the job, plaster the bricks to provide a good finishing touch.

Solar Two - Clean Water for an Orphanage

We installed a water filtration system for another orphanage in Cambodia. We used an ultra-membrane filter with pore size of 0.1 micron. It is able to remove bacteria and give clean water. It requires a minimum water presure of 2 bar to operate, hence we need to install an electric water pump before the filter so that it has enough pressure to operate the filter. A setback of this system is it requires regular back flushing in order to clean the filter to prolong the filter's life. Once the filter to clog up, it is time to replace a new filter. Suitable for making rainwater drinkable.

Solar Two - Rainwater Harvesting

We experimented and constructed a rainwater harvest system for the orphanage at Prey Veng.

Back in the laboratory, we experimented using the heat gun to seal plastic sheets together for making the rainwater collector. We also build a huge water bag to collect the 1 tonne of rainwater.

We brought all the materials to the orphanage and constructed the rainwater harvesting system. We used a monkey ramp to drive the iron picket into the ground. The plastic sheets were spreadout and tightly secured to the iron picket with steel wires.

The design need some fine tuning as we did not expect the rain in Cambodia to have very strong wind. One day when it was raining heavily, the strong wind blew and tore the plastic sheet which is used to collect the rainwater. We recommend them to build a proper roofing system instead of spreading a wide plastic sheet in the open. This approach will be able to withstand the strong wind when it rains.

Visited a Boarding School in Pontianak, Indonesia

In 2005, I visited a boarding school in Pontianak, Kalimantan, Indonesia. I followed a church group who were visiting the school. My role was to study if it is possible to help them make their well water drinkable using a simple water filter system. I brought water samples back for testing and found that the water was acidic. This requires an additional process of neutralisation to raise the pH level of the water to 7.0 before filtering.

Also notice that the water was greenish in the toilet and latter realise that it was due to the acidity in the water attacking the copper pipes.

I did not recommend to install a simple water filter system as they need to address the low pH first.

Solar One - Security Lighting

In April 2005, I designed and installed a security lighting system for an orphanage powered by a 500W photovoltaic system. The lamps are turn on nightly to ensure the ophanage is well lit and also prevents thieves from breaking into the orphange to steal things.

In order to keep the total power consumption low, high efficiency LED Lamps were used. Each lamp comprised of 3 Luxeon Star 3 watts LEDs driven by a constant current circuit at 400mA. The lamps were operating at 12Vdc. The lamps housing is IP44 comformance, meant for outdoor use. It is important in Cambodia because at night, there are alot of flies attracted to the light and they will try and enter the lamp unit, thus destroying the leds and its electronics.

We have to digg trenches to lay conduits and cables all over the orphanage compound for the installation of 24 lamps at different locations. Since we are covering long distances in the cable laying, sometimes more than 400 meters, we have to use a higher operating voltage other than 12Vdc. We operated at 24Vdc to overcome the losses from the voltage drop along the cables. Also, we used thick copper cables, 6mm diameter, to minimise voltage loss. Hence we have to connect 2 LED lamps in series so that it can operate at 24Vdc.

The controls for the solar charging is design around a charge controller from morning star. Simple to use and reliable. It has a build-in meter for charging and load current readings and also the battery voltage. This makes it convenient for testing and troubleshooting. The whole security lighting at the orphanage is divided into 4 zones and the switches are placed at the control box. In the morning, it is easy to switch off all the lamps because it is located at a central location. We used 4 lead acid batteries, each having a capacity of 120 AH. This provides enough stored solar charge for up to 3 days operation even on cloudy days where solar charging is minimum.

The mounting of the solar panels was a challenge. We finally were able to mount it on a pole using available resources such as dinning tables, stack up, from the orphanage.

The solar charging and discharging cycle is shown in the graph. When the sun rises, charging begins at around 7 am and peaks at 1 pm and begins to decline after 5 pm. At night at 7 pm, the lamps are switched on and the discharge cycle of the batteries begins. The terminal voltage of the battery never falls below 25 volts. Hence the system is balanced, i.e. day time charging is sufficient for the whole night operation.

Once completed, we switch on the system and it works as planned. The orphanage was litted by solar one!