I've been meaning to ask about this... my system is set to the default 4% battery cutoff.
It works fine, always stops at 4% charge.
But every morning, I find it's dropped further... I've seen it at 1%, 2% & 3%. Due to the dongle being replaced recently, I'd lost about 10 days of data. But it's happened the last 2 nights again.
Is this normal behaviour?
Anomnomnomaly That depends on your settings. If they effectively halt charging then parasitic power (the power the batteries themselves use) can take the SOC lower. Furthermore, if the batteries are at 4% at midnight and the temperature of the batteries falls overnight then, again, the SOC may drop. The battery firmaware 'should' force a small charge to protect the batteries if they fall to the protection level. I assume that you do not have an overnight off peak tariff to charge the batteries as you are leaving them at reserve. This is something you should consider for the winter period when generation is low and usage is high - leading you to have no charge in the mornings.
We are currently on a fixed rate tariff until Sept. So that has protected us from the price increases... But no cheaper night rates for battery charging.
I've experimented with putting some charge into the battery overnight, to about 60%... but there's no savings to us doing it that way... Just ensuring the battery gets a regular charge every week at least. Not enough generation to fully charge the 5.2kwh battery. I think the best we've managed in an entire day was just over 5kwh from the panels and we used at least 50% of that as it came in... putting just over 50% into the battery.
As the days get longer, the sun higher... we'll see more and more generation... we've got a roof that's only a few degrees of due south with no shading at all... Ideal for the system.
The battery has a buffer built in so the 4% default reverve is actually something like 11% so you shouldn't need to worry about damaging the battery with it falling to 1% visible to you. THe BMS will kick in to protect the battery if it needs it. You are right to limit chagring from grid whilst you are on a simple tariff as inverter losses will actually make your costs increase (10-15% depending on ambient temps).
Anomnomnomaly we've got a roof that's only a few degrees of due south with no shading at all
Yes this time of year is the poorest for solar generation. You don't say what size battery you have but it will be worth checking what tariffs are available to you now. Even if your existing contract has a penalty to get out of it, it's still worth looking. If you know your daily consumption and could meet that purely or mainly from battery charged off-peak, it would mean that you have all your electricity at the off-peak rate rather than your current fixed rate.
Everyone's lifestyle and PV system are different, but it's still worth looking at what tariffs are available. If nothing else, it will help you to understand what you should be looking for when your current contract ends.
Tim It's a 4kw + 5.2kwh, depending on what appliances we use... we average between 11-15kwh a day... maybe as much as 19kwh if we use the dishwasher, washing machine & tumble dryer on the same day.
We use most energy in the evenings... not more than the rest of the day combined, just a higher average... There's 2 of us here all day. The few times I've got the battery charged to 50% or more... it's lasted us maybe a couple of hrs or so because it inevitably coincides with cooking dinner and we're pretty much all electric aside from central heating and hot water.
Since having the system installed and first commissioned on the 11th Jan we've generated about 132kwh and imported another 40kwh from the battery against 443kwh from the grid.
So we're running at about 28% from solar/battery right now... not bad for mid winter.