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Help Me Improve My System

BubbaDX

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Jan 23, 2020
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Sorry for the lengthy post but I am hoping someone can tell me if the energy I am getting out of my battery bank is what I should expect to be getting. My questions are two fold: 1) Is the data my home energy monitor giving me what I should expect to get from my system? 2) What can I do to improve my system?

Here is what I have currently:

10 solar panels, configured in 2 arrays. All are 300 W panels.
Midnite PV combiner box
Midnite Classic 150 charge controller
AIMS 10K Inverter
8 BYD 24v batteries configured as 2 serial, 4 parallel, 48 volt battery bank.
Emporia Vue home energy monitor

My house is running a split power setup. All of the heavy hitter appliances like the furnace, dryer and stove are on a breaker panel running on grid. The power to this panel comes from Ameren UE, the utility company. The rest of my house, including the AC, is coming from a separate breaker panel that is fed from either the utility or my solar system. So it can run either on or off grid depending on a manual transfer switch. So it's a manual process to switch to off grid or on grid with a complete outage for all of my appliances. I am OK with that but plan to purchase an automatic transfer switch in the future, they are just so darn expensive.

My inverter feeds a breaker panel that is used strictly as a feed for the power to my house. The only other breaker in that panel feeds the Emporia Vue energy monitor. Since this monitor is fed by power from the inverter, it's only on when I am running my house on energy from the battery bank. When I am running everyhting on-grid, this energy monitor is powered off because the inverter goes into power saver mode and waits for a load.

I have done a couple experiments with running every thing off grid and so far, if I don't run the AC I can go almost 24 hours before my battery bank is depleted. However, I have not tried this exact experiment yet when I have good sun. That should extend my time off-grid by several hours. My last experiment was yesterday, and this was the first time running off-grid when I had the Emporia Vue energy monitor to show me exactly what it was getting out of the inverter. Yesterday at noon I cutover to off-grid power and ran for 8 1/2 hours before my battery bank reach 50.4 volts and I switched back to the utility company for power. I think that was pretty good considering I lived life as I normally would, including running the AC. I left everything on so the septic aerator run 1/2 of that time, it runs 30 minutes out of every hour. My well pump, septic pump, AC, 3 computers, TV, everything ran flawlessly for that entire time. I closely monitored by battery bank and cutover to the utility as soon as I seen my battery bank hit 50.4 volts. I could probably have run longer, but that is the value I chose to stop the experiment. 8 1/2 hours without attempting to conserve engery I think is pretty good.

When reviewing what my energy monitor shows me, I am a bit perplexed at the data but I assume it's accurate. The Emporia Vue shows me that yesterday during this experiment I used 179 Ah and 21 kWh of energy. I know this is an open ended question, but do you feel those numbers are pretty good for the setup that I have?

I know there are some things I need to change. First, I need more panels. I cannot produce as much energy in a day as what I normally use. According to my Ameren UE electric bill, when not running the AC I consume approximately 10kWh of energy per day. So that is my goal to produce from my panels, but so far I have only been able to produce 7.1 kWh in a single day. So that is the first thing I think I need to fix. The second thing I need to fix is my BMS, I have none. I know I need one and I plan to install one, but have not a clue what I need. I have been reading and honestly and just as confused as when I started this adventure last fall. Third, I need (want) an automatic transfer switch so I can simply kill the utility power into the ATS and cutover to off-grid power.

So in your opinion, how do those numbers from the Emporia Vue look? Is the 21 kWh from the 8 BYD batteries good? Is that number even accurate (I tend to think it is but have doubts)? I attached screenshots from the Emporia Vue so you can see what I see. It does have more detailed graphs and I can even get a download of the raw data if needed.

My second question is what can I do better? Please, no flaming I know I am derelect of knowledge about solar energy but I am trying to learn. The inverter and solar panels were here when I purchased the place. I trashed the rest of the system and replaced it because the batteries were garbage and the charge controller they were using was only good for AGM or lead acid batteries. The Classic 150 can make much better use of the power from the PV than the old Schneider CC they were using before.

Did I miss anything, I am sure I did? Any feedback is welcome, I am open to ideas.
 

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I think I may have made my post too complicated. That or I put it in the wrong place. I would like to know if you think the energy I am getting from the 48V battery pack is about what that is expected. I think the 21kwh was pretty good, but I would of course like it to be more. I can attach a schematic of my system if that would help. I have one diagram I made in Visio that I can export to PNG and attach here.
 
Hi. First: You need to have a BMS of course. Even tough your system is 50.4Volts a single cell could be to low, and even worse, when you charge up your system, a single cell could go to high, and go hot. BMS doesn't need to be complicated, you connect it to the 0Volt on your battery, and then connect your 0Volt on the load side to the other side of the BMS. Will Prowse has some excellent videos about that. A BMS also "balances" cells' meaning, the cell with the most voltage is transfering some energy to the cell with the lowest voltage.

If your batteries are 16 cell serial LiFePO4 batteries your system can go down to 48V with load. There are just some 5-10% of energy from your "limit" (50.4V) and down to 2.8V per cell (2.8 * 16 = 44,8V) when the battery is without load, but with a load the Voltage is going down, so maybe you have even 20% left when you got it at 50.4V.
Take a look at this:
 
...
8 BYD 24v batteries configured as 2 serial, 4 parallel, 48 volt battery bank.
...during this experiment I used 179 Ah and 21 kWh of energy.
Something sounds wrong... 179 Ah x 48V = 8,592 Wh.... where did the other (21,000 - 8592 =) 12 kWh go?
 
Something sounds wrong... 179 Ah x 48V = 8,592 Wh.... where did the other (21,000 - 8592 =) 12 kWh go?

This was measured on the AC side not the DC side. I ordered a meter for the DC side but it went out of stock before they shipped it. This particular meter is wired into the AC panel fed by the inverter.
 
Watts are watts. The DC side should be higher, but only by the inefficiency of the inverter. That is AC watts = DC Watts / inverter efficiency.

Possibly I'm just not understanding what was actually measured.
 
The Emporia Vue home energy monitor has a sensor on each 110 AC feeds into the breaker panel from the inverter and the app adds them together. It has other sensors that can be added, but I only have the 2. I attached an example of how it's setup. Mine is setup just like this example. Once again, the attachment is not mine but from the Emporia webiste. It shows how their monitor is installed.

I will be adding another monitor to the DC side, just no real slick solutions like what is available for the AC side. I ordered one from China but it went out of stock and I am still waiting for it to ship. I expect

As for the BMS I am probably going to purchase the Chargery BMS16 to balance the cells in my batteries.
 

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Okay! My bad... I get it...they're not two separate measurements... 179 Ah x 120V = 21 kWh of energy. Okay... so back to your original question

...do you feel those numbers are pretty good for the setup that I have?...

Let's see... you said you had 4 parallel banks of two 24V batteries making a 48V system. You didn't supply the amp hours or watt hours for the batteries so let's see what we can find online:

This post says:

NOMINAL VOLTAGE IS 25.6V
FULLY CHARGED IS 29.2V
FULLY DISCHARGED IS 20V

This link says they're 3 kWh. So 8 batteries x 3 kWh each equals a total of 24 kWh of batteries. You used 21 kWh of energy, 21/24 = an 88% DoD.

With two in series the voltage would be 58.4 to to 40V.

LiFePO4 is fairly flat lined at the nominal voltage and voltages are bad way to determine SoC unless they've been sitting a while...but (58.4-50.4) / (58.4-40) = 43% DoD. Which is about half the power measured and most likely shows why voltage is a bad way to get the SoC. That you got at least 88% power out of them seems to indicate they're performing as advertised.
 
Thanks for the replies. I hope to get a measurement of watts and ah from the DC side very soon so I can compare the measurements upstream and downstream of the inverter.
 
OK I finally have something I think will allow me to monitor the DC side. Hopefully I can get that installed and working soon. I also ordered 6 new panels to replace 4 mismatched panels in my system. This should give me a good boost in the power I can pull also. Hopefully those will be here in a few weeks.
 
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