I have recently added solar panels to my electrical installation on my yacht. My question is relatively simple. If my daily solar yield exceeds my daily total electrical consumption, why am I seeing slow but consistent discharge of my battery bank
The system consists of 3 Lynx Distributors, Lynx Shunt VE.Can, Quattro 12/5000 Inverter/Charger, Cerbo GX and a Smart Solar MPPT 100/50. The battery bank is a 900Ahr lithium LiFePO4. The 3 batteries are connected to the first Lynx Distributor, which in turn is connected to the Lynx Shunt followed by the remaining two Distributors which deal with all the loads and chargers. The Cerbo GX monitors it all.
On the battery side of the shunt, there are no other connections other than the batteries
The solar panels went live on the 19th April, the battery bank was recharged from the shore power on 1st May, and on 3rd/4th May I went sailing and hence the consumption spike. The slight increase in power consumption after I went sailing is due to leaving the DC powered freezer switched on in addition to the DC powered fridges and AC powered drinks cooler.
Not possible, you’ll have to check again, but ofc you shouldn’t forget that you’ll have some loss with charging/discharging the batteries, some more, some less.
As you can see from the graphs, it is happening. Furthermore, it is also back up by interrogating the individual battery BMS (via Bluetooth) which confirms that the batteries are indeed discharging slowly over time.
I do take you point regarding natural losses during the charging/discharging process but the difference of 800W (between solar and consumption on a daily basis) seem a lot to write off to this process.
I can also confirm that the charging parameters for both the Quattro and Smart Solar have been changed to match the battery chemistry. (lithium)
On average, the yacht while unattended uses 1Kwh and the solar panels are producing anything between 1Kwh - 2.1Kwh (Today it was 1Kwh used and 1.8Kwh produced
I do not know exactly what is counted in consumption but my guess is it does not include system overhead. For example the idle load of the Quattro 12/5000 is 30W x 24hr = 720 Wh. It probably also does not include conversion losses on the Quattro either, plus cable losses etc. Coincidentally this is close the the 800Wh you mention above (although you label it as W, it is Wh). Suggest this is the difference.
Thanks for your suggestion. I didn’t realise the Quattro’s consumption was that great. Cable runs I don’t think are that much of an issue - the batteries are within 1.5 metres of the Lynx Distributors, and the Quattro & Smart Solar is around 60cm away.
Your first image shows me that the Inverter is idling at 22W but here I see even higher values. Up into the 60-ish watts. And it’s not just the inverter. There’s the Cerbo GX and connected display as well. Both contributing to the DC load as well.
If the losses are up to 30W per hour for the Quattro, why is this power drain not recorded by the Lynx Shunt, and therefore become a part of the total power consumption?
The dc power drawn by the Quattro is recorded by the Lynx Shunt. The trouble is, we do not know exactly how the aggregated total figures are arrived at so exactly what they show. Are they useful consumption by loads or total consumption including system losses.
Very confused now. If the shunt is truly recording all the consumption for all sources, including losses from the Quattro, and if I believe the input total from the Smart Solar MPPT is also correct, then I should not see a discharge from the battery bank since, in general, the input exceeds the output on a daily basis. As an example, 24hours ago, the battery bank was at 74% and now it’s at 63% despite (supposedly) having 1kwh taken out and 1.2Kwh put back in.
If you look at your overnight usage when there is no solar, 21:00 to 06:00, 9 hours using about 40W = 360Wh. = 28Ah at 13V. This equals 3% of your battery. Yet when you check the SOC graph, over this 9 hour period it has fallen about 8%. Clearly there is a mismatch between load and what the battery is discharging. Have a look at your data and see what the power / current flows were during this period. During the night when the consumption is shown as 40W is the shunt showing about 3A (matches 40W) or 9A (matching rate of rate of SOC fall).
If you look at your chart between the hours of 09:00 and 15:00 the SOC was pretty flat, i.e. there battery was neither charging nor discharging, so the battery current would have been zero. During this time you had a load of around 50W so 4A. Your solar was producing around say 120W or 10A. 6A should have been going into your battery but it was not. This is the same 6A discrepancy noted above during the night. The system believes it has a 70W power draw that is not listed in the consumption figures.
Do you have a SmartShunt or BMV712 on your DC loads to measure them using the DC Energy Meter functionality. If not, the DC loads value is simply a calculated value based on the known measurements and is not entirely accurate. This is why night time is useful when there is no charging, the actual system load is then the same as measured on the Lynx Shunt.
Go back to your data for prior to solar when you were on shore power, did your consumption and import balance then, i.e. is this a new issue after solar, or was it there before and you did not notice.
Perhaps some more information over the day shown would be useful. Provide plots of the battery voltage and current, solar output voltage and current, DC loads and ac loads. Do some calcs on the raw data to see if they agree or not. Do you have a clampmeter that reads dc amps because that would help troubleshoot.
3 thoughts.
The solar is being measured because the SOC flattened off, but it should be increasing. Are you sure that there is no parallel path for the solar negative to bypass the shunt such as through a ground wire direct to the battery.
Is the Lynx Shunt properly set to 900Ah battery capacity so the SOC is following the charge current correctly.
Carry out a zero current calibration on the shunt per the manual, i.e. power down absolutely everything and check the shunt shows zero current when no current is flowing.
Thank you for taking the time to generate such a detailed reply. It’s greatly appreciated.
Replying to your 3 thoughts first,
There is absolutely no way for the solar to bypass the shunt and go directly to the batteries. The only connections from the batteries are to the Lynx Distributor, which is then connected to the Lynx shunt. The shunt in turn is connected to 2 further Lynx Distributors and all DC loads, chargers and the Quattro are wired to them.
Yes, the Lynx Shunt is correctly set to 900Ah (See photo above)
I have considered a zero current calibration, but that would require some considerable wire disconnection so as to ensure its accuracy. The manuals don’t really recommend this recalibration, but I might still give it a try.
Unfortunately, I don’t have a Smartshunt or a BMV712. Just the Lynx 1000 Shunt, and the Cerbo GX. The Quattro also has a battery monitoring feature, but the Cerbo GX is set to Auto and it favours the Lynx Shunt.
Here is a graph which displays in more detail the current and voltage of the system for the last 24hours. As predicted, it would appear that the average current draw is 9-10A during the night.
I will check the data prior to the installation of the solar panels. I wasn’t all that worried when the whole system was permanently connected to shore power since the batteries were always held at 100% and the loads drew power from the shore power.
During the day, the solar panels do recharge the batteries (sun dependant of course) - a 2KWh solar output day is enough to to power the static loads and top up the batteries by approx 5% - the last few days the solar output has fallen short of that.
Certainly you have an average consumption of around 2kWh but the total is reporting only 1kWh. I have never paid any attention to these because I always look at the system information itself. I think it comes down to how the boxes are calculated on the summary chart or if these have an error in or as already hypothesised are they trying to calculate useful load and remove system losses. I can not explain this
I agree with the feeling about zero error, in 4 years of helping moderate Victron Community I think I have seen 1 genuine calibration drift on any of Lynx Shunt, SmartShunt and BMV Monitors. Additionally, seeing the data, a calibration error should carry through to the kWh figures.
