More on the Pilot Solar Power Setup

The panels are not secured and simply  laid down flat on top of the roof.  Good thing that the roof inclination is not very steep and no chance for the panels to slide down.  I hope to attach them to railings before the typhoon season.  I don't like the idea of putting them on the roof to be honest.  I think I'm putting some stress on the roof and wood trusses underneath when I am up there working on the panels.

I was not using MC4 connectors in the pilot setup.  What I did was to bend some of the strands of the #12 AWG wire enough to make contact with connectors that came with the panels.  To secure the connection and as crude weather seal, I wrapped them with electrical tape. One pair of wire for each panel, therefore I've got 4 wires going down from the roof.

The PWM charge controller has three pair of terminals.  One pair each for the PV, battery and load.  Wires or cables are inserted on slots on one side of the controller.  Inside the slots are metals to clamp to wires when the screws on top of the controller are tightened.  The two #12awg from the PV fits nicely on those slots but making it three could be a challenge.  As for the battery connection I used the common automotive two terminal connector as in the picture.  I defined the terminal near the lock tab as the positive and used female one for all my batteries.  This means the connector from the controller is a male.  Nothing is connected on the load terminal of the controller on my initial setup.

The inverter is directly connected to the battery using the  thick wires that came with it.  Just plug and play as the wires has eye terminals on both ends and colored red and black.  On the AC side, I made an extension with plugs on both ends.  One side plugs into the AC output of the inverter while the other end plugs into one of those wall sockets inside the house.  The next step is to open the breaker box to turn ON the house circuits the I want to be powered up.

Parts List
     2x     100W solar panels
     1x     30A PWM charge controller
     1x     100Ah deep cycle battery
     1x     1000W pure sine wave inverter
     4x     5m #12 awg

Calculated (sunny day) capacity = 200 * 0.5 * 6hrs = 600Whr
Calculated battery capacity = 100 * 50%DOD = 50Ah or 600Whr @ 12V


Total cost ~ 18,000 Php

My (pilot) Solar Power Setup

(Note : Ideas and calculations are all mine.  If you will be setting up your own system based on what was written here, I take no responsibility for any failure.  Not to discourage you or anything but mainly for safety since working on this stuff can burn your house or injure a person most likely to be you.)

Solar Panels
A 100W panel generates around 5A peak.  In my setup, this occurs between 11:00AM to 1:00PM and at this time of the year.  I actually have two units so it is 200W total capable of pushing 10A of current.  As early as 7AM, the PVs generates about 1A rising gradually until it peaks around noontime.  It is a downhil afterwards until it is back again to 1A at 4-5PM.  If I have to estimate the number of hours when the panels generate power, it would be around 8 hours but with substantial current flowing in the inner 6 hours of this period.  In my last post, I calculated the theoretical generated power of a 200W panel in a day which is about 600W-hr.  I believe this is a good estimate based on my monitoring data.

The above information by the way is when the weather is good and sunny.  Unfortunately, this is not always the case and it is the nature of weather to be somewhat fickle minded.  I have some observation data but to make things very simple I have a rule of thumb that whenever it is cloudy, the generated power is 50% and 25% of the maximum when it rains.  Therefore if it is cloudy the 600W-hr becomes 300W-hr and drops further to 150W-hr if it is rainy.

Charge Controller
Current measurements are taken from the LCD display of the 30A PWM charge controller.  I am not sure about the absolute accuracy of the readings but I'd be happy if it is better than 10%.  This is a cheap unit but is smart and it seems to do its job quite well.  The seller warned me not to disconnect the battery while the panels are connected.  I've violated this unintentionally a number of times and controller is still alive which makes this unit a sturdy one as well.  Aside from the PV current, it also monitors the A-hr generated that I find handy.

Deep Cycle Battery
I bought a 100Ah battery for this off grid setup.  This means I have around 600Whr of energy to spend while the sun is out.  That is at 50% DOD and provided the battery was able to reach a full charge during the day.  The only possible indication of this event is when the controller displays 14.5V for the battery voltage and the charging current cycles between zero and maximum or some value in between. This could mean that the PWM switching mode takes over to trickle charge the battery.  On weekends when there is no office work, my observation is that at dawn the battery reaches a voltage of 13V+ which then goes down to an average of 12.2V the following morning.  Less final voltage of course when the weather is not so good which is around 12.7V to 12.9V.  There was only one morning when I saw it at 12V but was never less than this value.

Inverter
The inverter which I've been using for a month now is low cost (cheap) 1000W unit.  It can drive our 8.5cuft refrigerator, 50inch LCD TV and even my electric drill.  It complains when it is asked to power a grinder, though.  But for LED bulbs, electric fans and charging gadgets, this is more than fine.  The only gripe is the idle consumption which I estimate to be 10W. This is equivalent to 20Ah lost daily assuming the inverter is connected all the time.  I hope this is not a fixed offset  and drops to close to zero when a load a connected.  I need to buy a wattmeter for confirmation.

Loads
As mentioned previously, my setup has been running for a month now.  At the moment, the refrigerator is still unplugged and we failed to watch Miss Universe 2017.  We are still in test drive mode while closely monitoring our consumption because we are completely off grid.  No rice cooker and no ironing of clothes.  Just bulbs for lighting, occasional electric fan, wifi router, diy stereo and gadgets charging.

... but NO electric bills to worry about.

Solar Power Ideas

(Note that ideas expressed in this post are from my own understanding.  More like brainstorming on the concept of an off grid system.)

INPUT

200W panel capacity for practical purposes is actually 100W.  So that is 50% off the rated value.  Based on Wikipedia, the Philippines gets an annual sunlight of 2,000 to 2,4000 hours.  Choosing the mean of 2,200 hours we get therefore an average of about 6 hours sunlight daily.  A 200W panel therefore can supply about 600W-hr of energy per day.

200W * 50% * 6hrs = 600W-hrs

STORAGE

Batteries rated capacities are specified in Ampere-hours (Ah).  Therefore for a 100Ah battery with a load that draws 100A, it should be able to last for an hour.  If the load is 50A, 2 hours...so on.  I believe that is the ideal case with no losses and other factors.  But draining the battery is not a good idea since it will shorten the usable life.  50% DOD or less is oftentimes recommended. DOD or depth of discharge is the amount of energy drawn from the battery.  In the case of the 100Ah battery, instead of drawing 100A for an hour, we should should cut the time or the current to half to satisfy the 50% DOD criteria.  The energy we can extract from the battery is 600W-hrs.

12V * 100Ah * 50% = 600W-hr

12V * 100Ah * 40% = 480W-hr  ;if 40%DOD

*Learned this late, that batteries are normally 20hr rated.  Therefore a 200Ah battery could supply about 5A for 20 hours.

OUTPUT and LOAD

Load calculation is quite tricky since there are factors that needs to be managed.  Basically it is just the Time and Power but consumption is almost always varying for a 24 hour period.  For example during the day when people are awake, they could be charging their gadgets, watch TV or playing on their PCs.  During the night when there could be less human activity, perhaps one or two bulbs is ON or the electric fan is providing some needed cooling so that people are comfortable in their sleep. Therefore to be able to manage the available and stored energy, it is necessary to have an energy usage budget.

Ideally during the day, we should have enough power from the panels to keep our appliances and gadgets working while charging our batteries for night usage.  If we draw more power than what the panels can supply, the battery is there to the rescue.  But then remember this is the opposite of what we should be doing and if we are do this long enough such that the battery has no chance to charge, we end with no power left to consume during night.

At 40% DOD wherein we got 480W-hr available out of the 100Ah battery (that is assuming we have a full charge before nightfall) we can have a load of 48W from 6PM to 4AM the next day.  Say we've got two LED bulbs of 9W each that is continuously ON the whole night, the battery has more than enough juice for this purpose.  That is 18W from 6PM to 6AM is 216W-hr or less than half of the stored capacity at 40% DOD of the 100Ah battery :).
As an extreme example, if we watch a 100W TV from 6PM to 12PM, we consume 600W-hr and although the battery at that point could still be alive, we run the risk of over discharging it which is detrimental to its health.

I believe that knowing the amount of power available and having an energy budget and load management plan is a must specially on an off-grid solar power setup.