Category: Solar

Force Charing Pylontech Batteries

We had an issue with our house backup batteries where one of the BMS (Battery Management Systems) on the battery told the Schneider Hybrid XW Pro inverters to halt operation due to an overage in the charging amperage. After carrying out some battery diagnostics and reporting back to Pylontech, it was found that one battery unit had cells in an imbalanced state. Pylontech has agreed to replace the unit but it was also suggested to Force Charge the batteries.

The procedure of force-charging the batteries apparently should be performed around every six months or so. Force charging essentially applies a charge to the batteries until the batteries reach the desired constant voltage, and then the batteries are kept at that voltage for around 8 hours. Under normal operation, the inverters and the BMS will coordinate the charge cycles.

Before force charging we had to ensure the following voltage settings are correct under both inverter’s battery settings.

As another precaution, I waited for the batteries to be normally charged at 100%. This is normally performed at around 8pm every evening in my office after peak hours. I also temporarily stopped the automation (cron jobs) that is responsible for manipulating the recharge and grid support SOC (state of charge) settings throughout the day. Both grid support and recharge SOC are set to 100 so that the battery has room to charge and is kept at 100%.

> solarUtil.sh -r 100 -g 100
set Grid Support SOC to 100
set Recharge SOC to 100

We do not want to mess around with other charging parameters while performing a force-charge.

Once this is done we had to change the Charge Cycle from External BMS to 3 Stage on the Master inverter only. The available options are shown on the left. Once force charging is completed we can switch it back to External BMS.

With this configuration, we will only use the Master inverter to perform the force charge and leave the Slave configuration untouched.

Finally to trigger the force charge, we set the force charge parameter in the Control section of the Master inverter’s configuration to bulk.

We leave these settings for about 8 hours or so and then we change the Charge Cycle back to External BMS and re-enable the automation of the cron jobs for normal operations.

Panel Snow Coverage

Today is January 13, 2023. We had an icy snow storm last night that lasted until this morning, and I was curious what the roof condition was like. Just how much of the panels were covered in snow?

Our peak energy production was at around 11am when we generated a little over 800Wh, which is inlined with what we kind of get on a cloudy, misty, winter day. In contrast, the best we got so far was on January 7th at 1pm. We generated 5,494Wh. That was a sunny day with no snow coverage on the panels.

A quick drone survey of our roof this afternoon at around 3pm.

I was kind of impressed that we got that much with so much of the panels covered. Watch the above video to see just how much of the panels are covered today. Our total production for today is only about 3,400Wh.

Below are the stats per panel.

Per panel generation statistics for today.

As you can see above, every panel contributed even the covered ones! There will be two sunny days over the weekend, so we will see!

Update: 2023-01-14

I did another roof survey with my drone, seeing that today it was a sunny sky day.

Roof survey on Jan. 14 (day after storm)

We have generated over 10,000 Wh of energy today about 3 times more than yesterday. The survey was conducted when it was still -6 ºC outside, so way below freezing.

Length of Days Throughout the Year

Winter has arrived, and our solar production is seeing a sizeable drop in production. Although the month of November is still incomplete, here is our current solar production history so far:

We were operating at 50% utilization when on of our SolarEdge inverters went down in June, and as pointed out earlier, November is only about 75% completed as of the time of the writing of this post.

Even with the above discrepancies in mind, we can see a gradual reduction in generation from the summer months. From a peak of over 2500 kWh in July to just around 1230 kWh in the month of October. That is half of our peak from July. Based on the November trend, we will have even less.

These reductions got me curious to the length of day variation through the year, and I found this handy chart:

Number of hours when the sun is out throughout the year

The above chart is customized by our home location of course. From trough to peak, there is a difference of about a 6.5 hours! I must say, I knew there is a difference between the longest and shortest days, but seeing number was a bit of a shock. These short days are made worst by lowest sun elevation on our Southern horizon during the winter months.

It will be interesting to see how much power we end up generating during December which will be our lowest generating month, per the above chart.

Solar with Snow

The past few days we have met our first signs of Canadian winter. Although winter has not officially arrived, we have received at least a couple of snow dustings that resulted in enough accumulation on the roof to cover the solar panels.

I wanted to record our observation with this “new” experience in terms of the impact to power generation. Below is a chart on solar power generation in the past few days with different weather conditions during the shorter days of our Canadian autumn.

Solar power generation from Nov. 07 to 18 with different weather

Our highest recorded power per day is around ~110 kWh during a nice sunny, long, summer day in June. We are now facing shorter days with the panels active from around 8am to a little after 3pm, as the chart below shows.

Solar generation through out the day during Nov. 17 (partially cloudy)

Below you will see what my roof looks like today on November the 18th. Click the video below to see the entire roof.

Partially covered roof on a cloudy November 18th (click to play)

You can see that we have some panels that are fully exposed, and some that are partially covered. The solar optimizers are optimizing away during these times, and when the sun comes out, we can still sometimes generate above 3500W of instantaneous solar power.

During these dark and short days, we are now definitely eating into our stored electrical credits from Alectra Utilities.

XWPro Configurations

This is going to be a fairly technical post on the topic of my Conext XWPro battery inverter configurations. I am writing this post primarily to document my experience and my current rationale, and for my future, forgetful self.

Previously I had my Grid Support SOC (State of Charge) and the Recharge SOC set to 40%. With these settings, the battery will be used (anytime during the day and night) until it discharged to 40%, which will initiate a charge cycle that will charge the battery back to 100%. Under normal circumstances, the battery will typically discharge during a very cloudy day, but mostly in the evenings and at night.

I had the above settings because I stupidly thought I should stay off the grid as much as possible. The intent is to try to charge the batteries in the evening during off peak hours, and not to use the grid at all during on peak hours. These settings certainly accomplish this, but at the expense of shortening battery life. Another big downside with this approach is that charging the battery through the Conext XWPro inverters only achieves around 83% efficiency. This observation is based on my real-time data observations from the actual inverters.

Yesterday I noticed that my batteries are reporting a State of Health (SOH) drop to 99% instead of 100%. This was a bit alarming given only 6 months of uses. I also realized from the Alectra invoices that Time of Use (ToU) is not a factor in Alectra’s billing calculations. All of this resulted in a shift in my thinking. We will now use the grid as our primary battery, and preserve our Lithium Ion as our backup batteries only. Time shifting of loads will no longer be my primary concern since it is no longer worth it with zero benefits.

To do this, I have set the Grid Support SOC to 90% and the Recharge SOC set to 85%. This way immediately after a charge cycle, the battery will be used a little bit to draw down from 100% to 90%. This has two benefits in my opinion. The first is to get some charge flow through the batteries, so it is not only sitting there. The second is that it leaves a 10% SOC gap. If we have a power failure during a sunny day, there is space for the excess solar production to go without tripping the solar inverters.

The 5% gap between Grid Support and Recharge is currently a guess. My thinking is that over time the charge on the Lithium batteries will leak and it will trigger a recharge cycle. Of course I did not want to set the Recharge the same as the Grid Support, because this will cause a constant recharge loop which defeats the purpose of preserving battery life. I do not know how long it will take to naturally draw down from 90% to 85%. This is why it is still a guess at this point. If there is no leakage, which is great news because it shows how good the batteries are, then I will have to trigger a recharge cycle at least once a month just to keep the charge flow within the battery’s chemistry.

For now I will live with the new settings and see how often the battery cycles. If it only cycles once every one or two months, then that is perfect. If it does not cycle through more than three months, then I may have to add the monthly charging cycle logic into my custom controller.

Electricity Bills & Natural Gas Rates

Since our solar installation, and our live commissioning of our net metering with Alectra Utilities, our last payment to Alectra was in May, 2022. Since then, we have not paid a dime to Alectra, but instead we are sitting on a nice credit as the attached snapshot of our bill showed:

As the above bill indicates, we created 372 kWh during the 30 days of this last bill that we received. I was also surprised by the fact that during the summer months, we were still able to generate excess while running our AC without compromising our comfort requirements. The extended summer days and the higher angle of sun’s elevation were very conducive to solar production.

I also noticed our natural gas prices increased by 110% from the same time last year. Below is directly from the Ontario Energy Board (OEB):

Our goal now is to try to switch our heating source from natural gas to electric, so that we can use our excess electricity for this winter’s heating needs. This makes total sense, since our electricity is almost free, while natural gas is not!

There are reports out there saying the rate increase is significantly less. This is because they are comparing against the July, 2022 rates and not the October, 2021 rates, so read carefully.

I went on Amazon and purchased three of these electric based heaters.

De’Longhi Slim Style HCX9115ECA Convector Panel Heater

At time of purchase, they were $219 CAD each. We tried the cheaper ones, but their fans were simply too loud. These ones are nice and quiet with a very user friendly interface.

The master plan is to set the house thermostat to 18ºC, so that it acts as a backup heating source. While these electric panels will try to heat the house during most of the winter days. We will see how this plan goes. I would consider this to be a win if we can reduce our natural gas consumption this winter by more than 50%, which will effectively normalize the rate increase. In the end, these electric heaters may not be enough. Time will tell.

I also investigated the possibility of installing a centralized heat pump, but current technology is limited to -20ºC outside temperature. I decided to table this for now until the technology matures a bit more. I want a solution that can transfer heat from -30ºC outside to indoors.

Our next plan is to research our water heating needs and to see if there are any electric based tankless solutions out there.

Wish us luck and I’ll keep everyone updated!

Update: November 14, 2022

Previously I got the rates from the Enbridge web site. Below is an actual excerpt from my Enbridge bills. However you compare, the increase is significant.

April vs July Gas Rates in 2022 from my invoices

Update: November 26, 2022

Found this CTV article.

First Hydro Bill with Solar

I cannot believe that I am actually excited to receive a bill! Our first bill from Alectra Utilities covering the consumption period since our net meter was installed on May 4th has arrived.

Our July Alectra Utilities Bill Extract (click to enlarge)

This bill covered almost two and half months. As you can see from the above extract, we have given back a total of 2,763 kWh and used 1,621 kWh yielding a net of 1,142 kWh, which Alectra credited back to us at $0.115 / kWh.

The surprise is that this credit can be used to offset both the delivery and other added surcharges. It looks like we still benefit from any other regulatory and provincial rebates and they are incremental to our credit.

The net result of all of this is that not only did we not have to pay any electricity from May 4th until July 14th, a period which definitely covered some heavy air conditioner usage, we also generated $61.80 worth of credit on our account.

So, how much did we save? I looked back at our bills for the same period from last year (2021), and found:

From	To	Amount
2021-04-15	2021-05-13	$132.18
2021-05-13	2021-06-11	$196.41
2021-06-11	2021-07-14	$240.17

Amounts From Last Year’s Bills (from 2021)

Although we do not have perfect alignment for comparison since I cannot find a bill in 2021 that matches the May 04th starting period, I think it is clear that we have saved approximately $450.

Of course it is not only about the money, but this bill has confirmed that our solar system has the ability to not only to stay away from grid electricity (after netting everything out) but also to give some back even during the peak summer months. This is also a confirmation that our Toyota Prius Prime (a hybrid plugin vehicle) is now also indirectly funded by solar. We were not certain about this when we first design the system, so I am ecstatic to have this final confirmation!

Live Monitoring of Electricity Consumption in Ontario

Today I came across Gridwatch. This is an interesting web app that provides a live monitoring of Ontario’s current electrical production and consumption.

As the screen capture shows, we have a heat warning today. This situation is currently being shared by UK and Europe, where they are experiencing temperature in excess of 40ºC, clearly much worse than we have it here.

The hype of these high temperatures in the media caused me to wonder what is our current electrical consumption?

Which lead me to do a quick search on Google, and resulted in me finding the Gridwatch web app, and its home page:

Gridwatch Home Screen (click to enlarge)

Aside from how much electricity we are using, the most interesting part is the CO2e number which is currently at 81g/kWh. Since my solar installation, I have generated 6,450 kWh of electricity through the use of my solar panels from April 12 to today. Do some simple math, this means I have prevented 522 kg (~1/2 tonne) of CO2 emissions.

In a previous post, I mentioned that an average person in Canada uses around 14.2 tons of CO2 per year. From this perspective, we are just placing a dent on our overall CO2 footprint. However in this Reuters article, it claims that we have to remove 1 billion tonnes of CO2. If we do some rough math, the average per capita onus is (1 billion tonnes / 7 billion people) = 143 kg. Given our household is 4 people, we have an obligation to remove 572 kg of CO2 to meet the goal of 1 billion tonnes of CO2 worldwide removal.

I say we are pretty close! Okay, we can obviously do more and we will.

Frequency Shift Power Control

If you follow my posts in the Solar category, I mentioned Frequency Shift Power Control. What is this? I will try to answer it in this post and explain why this is important in the context of full house backup and grid connectivity is lost during a power outage.

There are two types of inverters in my house. The Schneider inverters are the hybrid inverters that charge and discharge the battery and manage the battery power in conjunction with grid power. During normal operations when the grid is connected, the Schneider inverter can consume or send electricity to the grid.

The other type of inverter is the SolarEdge inverter, which is a solar inverter. Its job is to convert DC power from the solar panels into AC power which your house needs.

Having both hybrid and solar inverters connected on a common AC bus is known as AC coupling.

First, let me explain how it works when the grid is happy and we have connection. The solar power from the solar inverters will do the following in priority:

Power the house; and send excess to
Charge the batteries; and send excess to
Send back to the grid

If there is not enough power from solar, then power is supplemented by the batteries or the grid depending how you configure the Schneider inverters. I will not get into how Schneider inverters are configured here.

Now when the grid is out (power outage) and the batteries are fully charged, the solar power has no where to go. To regulate solar power production, the hybrid inverters will communicate to the solar inverters via Frequency Shift Power Control. The hybrid inverters will intentionally shift the output power frequency from its normal 60Hz to something like 61Hz. This is done slowly. The solar inverters detects this anomaly and either throttles its power output or stop producing power completely. Once power regulation is completed, the hybrid inverters will shift back to 60Hz.

The solar inverters will come back online after an arbitrary down time. For SolarEdge, I have observed this to be around 5 to 10 minutes. The idea of having this down time is so that batteries can be discharged while powering the house and create more head room for new solar energy. Unfortunately the SolarEdge down time is not long enough, at least not for my house and my battery storage system. Once solar power is restored, you can end up in a cycle if the batteries are still topped up. The hybrid inverters will again shift its frequency to force the solar inverters to reduce or stop producing power. The cycle repeats until the grid comes back on.

Instead of a repeating the cycle every 5 to 10 minutes, it is better to manually turn off the solar inverters and wait for the batteries to draw down until you have enough head room for the batteries to absorb the solar energy again. For example, you may want to draw down the batteries from 100% to 80%, and then turn back on the solar inverters. In this scenario, excessive solar power can then be used to charge the batteries.

Another matter to pay attention to is UPS (Uninterruptible Power Supply) units. Certain models are very finicky to frequency shift and will actually shutdown instead of continuing to supply power. This is very frustrating as it cuts power to the very items that you are trying to protect from outages.

I had UPS units spread through out the house prior to our solar installation. Now I am simply going to replace these with surge protection power bars.

First Hand Supply Chain Impact

Our last power outage on May 21st, caused one of my two SolarEdge inverters to stop generating power. This effectively caused 50% of solar panels to be ineffective. Considering that the system was recently commissioned fully on May 4th, it was a bit frustrating to go through this. At least the other SolarEdge inverter is still generating power from the remaining 50% of my panels.

Upon a remote assessment of the inverter by SolarEdge, they determined on the 25th that the inverter requires replacement. As of this writing, I have not been given a formal response by SolarEdge that explains why the inverter cease generating power. I assume it is a quality issue on their end, and something from the grid outage during the storm fried something in the inverter. For an inverter that was less than 2 months old, this was slightly concerning.

It took SolarEdge from May 25th to June 10th to ship a replacement. Today is June 15th, and the UPS tracking number still shows “Label Created”.

Apparently recent supply chain issues has caused much shortages resulting in the delay.

Kudos to New Dawn who was able to source another inverter and they promptly installed the inverter today. All is good now.

In summary, we had 50% of our solar panels not producing power for 24 days (from May 21st to June 15). SolarEdge to this day still has not met its warranty commitments because its replacement unit is still in “transit”. If it was not for New Dawn being creative, I would still be out 50% of my solar capacity.

If you are using SolarEdge for off grid applications, perhaps it is wise to store an additional unit if you think solar generation is critical to your livelihood.