Activating Plan B

There is a saying - "we ought to prepare for rainy days". This is especially fitting when it comes to solar energy harvesting in Singapore. Not only rainy days but cloudy days as well.

Singapore is a tropical island country surrounded by sea located near the Equator. Most of the days are sunny, hot and humid except at the end of the year in November and December which is so called the monsoon period when heavy rains and thunder storms are common in the afternoon.

I have 3 x 30W Mono crystalline panels, 1 x 42Ah and 3 x 9Ah SLA batteries connected in parallel for a total of 69Ah capacity. I am running a 3W LED lamp for few hours at night, a 15W Solar fan running 8 to 10 hours overnight, a 6W LED strip running occasionally and a 2W handphone charger.
With my batteries, I should have 828Wh (69Ah x 12V) if fully charged, so they should be able to power my loads continuously for about 32 hours or 4 nights without charging if I run them 8 hours per night.



Under normal weather condition, that is mostly sunny with occasional one to two days of rain and cloud in between, my setup should be adequate. However, the reverse happens during this 2 weeks whereby most of the days are raining and cloudy with 1 to 2 sunny days in between.
Eventually after almost 2 weeks of working, my system sounded the first low voltage alarm at around 6.30am Saturday morning. I looked at the battery voltage and it was at 10.4V. I quickly switch off my fan to prevent the batteries from over discharge. The batteries were at 11.9V the night before.

Now I have 2 options. One is to expand my solar capacity to cater for rainy and cloudy days. Another is to use an AC battery charge to charge up the batteries.

If I opt for the first option, I think I would need to at least double my panel capacity from 90W to 180W, which means it would impact my ROI (Return on Investment) for at lease a few years. The other disadvantage of this option is that it would be over capacity during sunny period.


So I opted for the second option which is my plan B. Then I started to look at SLA battery chargers. The price ranges from S$18 to almost S$50. I am reluctant to spend extra money on charger and also have the fear that poor quality charger might damage the battery. I also read that we should not use charge meant for charging car battery to charge SLA battery, otherwise, it may cause gassing and explosion.

Then I remembered I still have an 10A PWM Solar charge controller laying around after I switched to the MPPT controller. This would be an ideal charger as it is designed to charge SLA batteries. I also have a Philips power adopter which I use to charge my Philips electric shaver.

The Philips power adopter output is at 17.2V which is well within the input range of the PWM charge controller. I then connected the output of the Philips power adopter to the panel input of the PWM charge controller and observed that the red panel LED lighted indicating that it is receive power from the "solar panel". I measured the voltage of the "panel" input and it read 11.89V. I measured the battery output and it read 11.86V. The charging green LED also blinking indicating that it is charging the battery.

The Philips power adopter is rated at 9W. I do not know how much charge it will put into the batteries. But so far it has been able to maintain the voltage above 12V with current weather condition of frequent rains. With that little extra electricity it consumes, I think it is worthwhile to go for the second option and implementing Plan B. I have decided that I would always use the AC charger to charge the battery if the voltage is below 12.6V.

With this plan B, it gives me the peace of mind that I will always have enough energy to power my loads in all weather condition and can sleep soundly without being wake up in the middle of the night by the low voltage alarm again.

Update: The Philips power adopter with it's 9W power is not enough to buffer me through a few consecutive days of cloudy sky and heavy weekends usage during the Christmas period. I ended up ordering a 2A battery charger from DealExtreme which should tide me through longer rainy days. The learning point is to get a charger that is sufficient to charge your battery than what you will consume for the whole day.

Review of my 15W Floor Standing Solar Fan

I bought a DC 12V Solar fan on 24 Nov 2013.
I have been using this fan for close to 2 weeks and I think it's time to write a short review of my Solar fan.

A little background on why I bought this Solar fan first. My solar power system consists of 3 x 30W panels hooked up in parallel. I have 3 x 9Ah and 1 x 42Ah 12V batteries connected in parallel also totaling 69Ah capacity. I have a 30A MPPT Solar charge controller connected between the solar panels and the batteries.

I used to power my Mitsubishi floor standing fan through a 300W DC to AC inverter. The AC fan together with the inverter consume about 55W of power.

I calculated that if my batteries were fully charged, I would have 828 Watt Hour (Wh) of energy for my usage (69Ah x 12V). With my intention of powering my floor standing Mitsubishi fan for 8 hours a night, I would need 440 Wh of stored energy (8hr x 55W). So my batteries are sufficient to power my Mitsubishi fan for almost 2 nights if they are fully charged.

The problem I encountered is that although my batteries capacity is sufficient, they do not get charge up fast enough. I observed that it took about 4 days to fully charge up the batteries with good sunlight. That works out to be around 200Wh per day. Though my panels are rated at 90W in total, I hardly get the full 90W energy. The most I observed is 65W from the display of my MPPT controller during peak sunlight and most of the time it is at around 15W to 30W.

This means that if I on my Mitsubishi fan for 1 night, I would have to wait for 2 days before I start to use it again in order not to deplete the batteries too much. So my next option would be to increase my solar charging capacity to at least twice the current capacity (90W), or to reduce my power consumption.

Increasing the charging capacity by twice would cost twice as much to get a 15W Solar fan. I am reluctant to get the 15W solar fan initially because I felt that it would not be as powerful as my current 55W Mitsubishi fan. But after thinking about the hard work of having to mount another
3 x 30W panels and the cost of them, I decided to give the solar fan a try.
The solar fan consumes merely 15W at high speed. This means my 828 Watt Hour batteries would be able to power it for around 55 hours or almost 7 nights if I use it for 8 hours per night. This would allow ample time for my batteries to get charged up without depleting too deeply.



How does it perform?
I got the fan from Tanericash on 24 Nov 2013, Sunday night around 8pm. A quick test at his place to make sure that the fan works and it sounds powerful enough.
I got back home around 9pm and quickly setup and connect it up for testing.
My wife was a bit surprise as from the appearance of the fan, she did not expect it to perform as powerful. But I quickly noticed that the wind at full speed was not as powerful as the wind of the Mitsubishi fan at speed 2. It is quite noisy and the noise gives the impression that it is powerful.

I had a feeling that the fan blades are too small and slim to produce strong winds. So I took the Mitsubishi fan blades and installed onto the solar fan. But the Mitsubishi fan blades are too heavy for the small DC motor that it not only turn more slowly but consumes more power (20W).

I continue my search for a suitable fan blades and then came across a Toyomi AC fan with 5 blades. I tested the fan at OG and found the wind to be quite powerful. I called up Toyomi agent and was quoted $18 for the fan blades alone. So I search in Gumtree and manage to get a used Toyomi fan at $15.

I replaced the original fan blades with the Toyomi fan blades. The performance of the fan improves and it runs much more quiet. The wind power is still lower than the Mitsubishi fan at speed 2. It is acceptable during this time of the year when the temperature is cooler.

So my conclusion is that if you are using you AC fan normally at speed 1 or 2, you may find this solar fan suits your needs. If you are a person who need fan speed at 2 or 3 to be comfortable, you may find this DC Solar fan is under power.

Update: I was a little bit disappointed with the power of the solar fan, so I actually tried to look for DC motor to replace the original solar fan motor.  I also searched the Internet to see whether there are more powerful solar fans available. While I was searching, I noticed that my solar fan input accept voltage ranging from 12V to 18V. It struck me that may be I could increase the voltage to increase the power. I have bought a power booster previously for charging my electric shaver which requires 17.2V input. So I connected the power booster output to the solar fan and to my delight, the fan speed increases and the wind becomes very strong, although it ended up using more power (around 30W). I then tune the output voltage of the power booster to 14.5V so that it uses less power and yet providing the powerful breeze I needed.

Now, it consumes about 23W on low speed and 26W on high speed. I am very satisfied with the solution although it consumes slightly more power than the original setting, it achieves the amount of air flow I require for sufficient comfort level.