to understand the monitoring data

[Jeff King]

page 2 of monitoring SBMS0 I want to understand. I do not have the numbers reset each day,

If I subtract PV1 number for "day 2" from the PV1 number for "day 1", I get the total amount of PV generated?

if I take the difference from one day to the next for PVtoLoad and the difference for BattLoad from one day to the next, add these two differences together, I get the total load for one day?

if that is all correct, then I have two methods to track the total PV and total load per day:

1. log the readings from page 2 each day, do not use the reset daily option, and substract one day from the prior, add the delta for PVToLoad and the delta for BattLoad to get total load.

2. use the reset daily option, log the readings and those will be the load and production per day

do I understand correctly?

[Dacian Todea]

Jeff,

Yes if you do not want to reset that energy counter (can be done automatically at midnight by setting that in the Time and Date menu) then  you can calculate by subtracting the value form yesterday from the value shown today.

1. Yes you can do that if you want. But load is basically all it comes from PV as all energy is either used to recharge the battery (that is discharged by the load) or used to directly power the Load so if you ignore then 2 to 3% loss due to battery cycle efficiency all PV energy is used by the Load.  

2. The energy is already a log data so not quite sure I understand the question.  SBMS0 measures the current and battery voltage then calculates power. Then the power and current are integrated over time and that is how energy in Wh is calculated and displayed on page 2.  There will be nothing to log from page 2 maybe one snapshot just before midnight as the total energy generated over the 24h period.

So page 1 provides you with live data for power and page 2 has the accumulated (integration of power over time) data for energy.

[Jeff King]

This is a new setup for me. So I do not know all the system capacities as of yet, this is why I am trying to understood PV production and total load.

What you said is correct in that eventually all PV generation goes to load.  However, that doesn't tell what the PV system is "capable" of delivering.  Right now, my PV shuts off charging when gets to upper cell voltage. So, system could put out more. I guess to learn more about the upper PV limits I need to add more load. Some sort of "safe" incremental load that I could add a little more each day or week.  When I say "safe" I mean something that wont be harmed if low voltage cutoff. For example, my fridge is 12V compressor, but I would like to avoid having it shut down due to load voltage as I don't want to lose the valuable ice cream stock or let the beer get cold.

And related is what is my total load, and how much more load can I add and the PV system can keep up?

Of course all of this is seasonal, more sun during summer, weather related, less during clouds and this is RV, so if parked in trees I'll get shaded.

And for #2: I understand now. If I set the counters to reset every day (at midnight), then I would have to take a reading just before midnight to get total PV and total load for a 24 hr day.  This is why I currently do NOT have that option set, so the numbers just accumulate daily, growing ever larger. So, I have to take readings each day and then substract the difference to get daily PV or daily Load. 

[Dacian Todea]

Jeff,

Unless you intentionally try to keep the battery from being full you will not be able to see how much the solar PV can produce. It is normal that in an offgrid system you will not be able to use all PV available energy (not even close).

Yes your system will need to be sized for worst month of the year in therms of solar and so in all other months there will be a lot off excess (unused PV energy) and that will be normal.

In my case is fairly extreme as I have a large PV array to heat the house in winter so in summer only about 10% of the PV solar energy is used 90% remains unused in my system.

During the day when it is sunny you can do more maybe electric cooking or any other energy intensive activities.

Yes you can do manual subtraction or you can just manually reset the counter any time you want. The PV energy and battery output energy are stored anyway permanently in the About screen so you will have the production over the life time of the system.

In any case over a 24h period the PV energy is basically the same as load usage as yes you may have charged the battery with part of the energy but then you also discharged the battery.

So say you start at midnight with battery at 70% then after 24h the battery is back to 70% then load was basically the amount generated by PV is just that some energy went directly from PV to Load and some first went to battery and from there to Load but since LiFePO4 is very efficient >98% typical you can ignore that small loss in to battery.

So over time PV generated energy is the same as energy consumed by Load. Then for battery just energy getting out of battery is counted (as of course all that energy will need to be put back in to battery plus 1 or 2% more) and so that battery energy just tells you how much of the energy went trough battery.

To give you two extreme examples say you had no loads during the day so you where just charging and say PV panels put 1kWh in to battery then at night you have a 200W load say a large light source working for 5h so 1kWh total then next day again solar will charge back the battery putting in the missing 1kWh.

In this case from a 24h period you will see 1kWh from PV array and 1kWh from battery meaning the Load used 1kWh but all energy went trough battery load was not powered directly from PV at all.

Then another example say you have a load that works continually for 24h with constant consumption (not sure what say a LED light that is always ON) and this load uses 1kWh over 24h so 1000Wh/24h = 41.666W will be what Load power is.

Then say there is a large PV array and it will charge the battery in 4h then what energy counters will show is PV energy will be 1kWh and Battery energy will be 1000Wh - (4h * 41.666Wh) = 833.33Wh

So what you will see in page two is 1kWh from PV and 833.33Wh from battery then you know PV directly provided energy to load 1000Wh - 833.33Wh = 166.67Wh and the rest of the Load energy went trough battery so total Load is same as PV 1kWh and that is always the case your load say you count that for one month will be the same as PV generated energy.