Precursor to setting up Solar Assistant automations for SunSynk inverters

[klondike]

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Precursor

Before you can put specific numbers into the automations you need to gather information such as your battery capacity, charge rate and export rate. My examples all assume Octopus Flux but the same principals will apply to other tariffs probably except times and maybe other factors need taking into consideration.

My personal aim is to charge the battery at cheap rate overnight based on solar prediction such that it has sufficient power to last until supplemented by solar generation ideally leading to a filled battery by 4pm ready to take maximum advantage of the higher export rate and leaving sufficient battery to last through until the 2am charge period starts next day. The ideal here is that the battery is almost down  to the minimum 20% state of charge required to supply the household load. Obviously such perfection can't be met due to solar and load unpredictability. Slight deviations will reduce return but only by coppers at most. As this runs 365 days a year though even coppers amount to pounds a year so getting close is good. The high solar production days result in export at a lower than maximum rate but that is all extra return and offsets any non optimal days. Overall you are either using free or low rate electricity with the bonus of selling free solar electricity back to the grid. Those with bigger systems will have differing need but will still want to force charge and export at specific times.

In the event that you cannot fully fill your battery from the typical low charge rate of 20% in 3 hours you will need to know what maximum charge rate your battery supports. It may also be the case that your inverter doesn't have the power to fully charge your battery or batteries in the 3 hours available although hopefully the installers will have ensured that you can.

You should also check that you can discharge your battery from full down to the minimum level you have set to sustain your house needs from 19:00 through to 2:00am assuming that you are using Octopus Flux.

Obviously all those times may be different with other tariffs.

Getting the charge and discharge rates
If you have been running Solar Assistant you can calculate these rates directly from the State of Charge graph under the Charts tab



Position the cursor at the start of the charging period and note the time and state of charge then reposition to the end and note the numbers there. From this you can calculate the change in SOC and the time it took in minutes. From that you can calculate the rate per hour.

You can do the same for rate of export. This won't be so accurate as at night you just have the grid charging the battery and satisfying house load which over that period at night is probably stable from night to night. During export you will maybe still have solar and perhaps more variation in load. Absolute accuracy is not needed as the automations can be fine tuned later to suit your circumstances.

An average daily rate of usage can be seen either from your Octopus usage or under Solar Assistant



Use that to come up with an approximate percentage charge of your battery to last from the 5:00am end of  cheap charge rate to when solar begins to charge your battery. The SOC chart will help you again here. This is something that will need changing from season to season. Effort and return are both reduced by setting a compromise value.  Too high and you will be exporting power at around 9p that you bought for 15p. Too low and you will miss out on some of the 27p export you would otherwise have been able to make.

Similarly the SOC needed to last from the end of export at 7pm through to the cheap charge period at 2am. Again a compromise value will need to be  set.  Too low and part of the evening will be importing at the day rate. Too high and you are reducing the time on 15p charging from power you could have exported at 27p.

Best not get too paranoid over any of this - you are still getting free energy from your solar panels and should that not cover your household needs at least some and probably all will be satisfied by 15p power from your battery.

Battery charge rate and Export power

You need to be super careful here as you could damage or shorten the life of your battery or exceed the power you are allowed to export.

Check your battery documentation. I'll neither advise nor recommend any changes to your installer settings. I found that mine had entered values for a single 5kWh battery when in fact I have two in parallel so I did make changes.

In the UK, the G98 regulation sets the export limit for micro-generation systems such as rooftop solar—up to 16 A per phase, which equates to approximately 3.68 kW per phase.

If yours is G99 your DNO should specify what you are allowed to export.

You will find the battery charge and discharge currents via the Configuration tab



Scroll down a little to Devices.

On the Status line there is a hyperlink to Settings

Amongst the many items on this page over to the right are the battery grid charge and maximum selling power



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