Managing the Inverter from the App

General Everything Else
1

Managing the Inverter from the App

Preamble

As a new user I have been puzzled as to how to control the system from the App. This document sets out my understanding of what is going on and what the fields in the App mean.

Don’t take this as gospel: there may well be mistakes. If you find one, please point it out and I’ll revise this document.

Priorities

The inverter uses a set of priorities in meeting load on the system:

  1. use PV if it is available;
  2. if there isn’t enough PV, meet the balance of the load from the battery provided the battery is permitted to discharge and subject to limits on the rate of discharge;
  3. take the electricity from the grid.

There is also a set of priorities in using the PV:

  1. meet the load;
  2. store in the battery any surplus in excess of the load provided the battery is permitted to charge and subject to limits on the rate of charge;
  3. export the surplus

Eco Mode

While Charge Mode is set to Solar and Discharge Mode is set to Dynamic, the inverter is put in Eco Mode. Eco Mode applies the priorities set out above.

The system allows you to define up to 10 Charge Periods and 10 Discharge Periods. During these periods the battery will be charged or discharged at specified rates.

Setting Charge Mode to Solar + Grid causes Charge Periods to take effect. We say that the Charge Periods are then in force. While a Charge Period is in force, the battery cannot discharge and the only charging which takes place is that specified for the Charge Period. Outside Charge Periods the system remains in Eco Mode.

Setting Discharge Mode to Scheduled causes the Discharge Periods to take effect. The Consumption Type is set automatically to Home Demand. We say that the Discharge Periods are then in force. While a Discharge Period is in force, the battery cannot charge and the only discharging which takes place is that specified for the Discharge Period. Outside Discharge Periods (and also Charge Periods which are in force) the system remains in Eco Mode.

If you have set Discharge Mode to Scheduled you can then change Consumption Type from Home Demand to Full Export. This turns off Eco Mode. BEWARE OF DOING THIS: THE ONLY CHARGE AND DISCHARGE WHICH WILL TAKE PLACE ARE THOSE IN CHARGE PERIODS WHICH ARE IN FORCE. Otherwise, Full Export appears to behave in much the same way as Home Demand.

To sum up, provided you haven’t set Full Export, the system runs in Eco Mode except when a Charge Period or a Discharge Period is in force. You can configure Charge Periods for times when you want to charge from or discharge to the grid and disable them by switching them off using Charge Mode and Discharge Mode. Once you have done this, you don’t have to worry that the Charge Periods and Discharge Periods are hanging around and will suddenly come back and bite you. Relax: you’ve turned them off. Eco Mode is in force.

Battery Reserve

There is one parameter in the App which affects the system at all times, including during Eco Mode:

  • Reserve

Reserve is a % limit on how far you wish to allow the battery to be depleted.

Batteries differ in their declared maximum Depth of Discharge (DoD): Generation 1 batteries have a maximum DoD of 80% while for Generation 2 it is 100%. Needless to say, there isn’t any difference between the cells in a Gen 1 battery which you buy today and a Gen 2 battery which you buy today (but there might be between a Gen 1 battery which you buy today and one which you bought 3 years ago).

The rules about maximum DoD are managed behind the scenes and you don’t need to worry about them. Reserve is an additional safety margin which you can choose to leave above the internally-applied maximum DoD.

Two further parameters are shown in the App at all times:

  • Charge Power
  • Discharge Power

These fields are only used while a Charge Period or a Discharge Period is in force. We therefore defer discussion of them.

Charge Periods

When Charge Mode is set to Solar + Grid, three extra fields appear:

  • Start Time
  • End Time
  • Charge Up To

Also relevant is the always-present field

  • Charge Power

Start Time and End Time define the start and end of the first Charge Period. There can be up to 10 of these, but numbers 2 - 10 can only be seen and configured from the Remote Control, which is accessible through the Web UI.

Charge Up To is a limit on the maximum % to which the battery can be charged while a Charge Period is in force. This limit does not apply while a Charge Period is not in force (e.g. because Charge Mode is set to Solar).

Charge Up To is a global limit which applies to all Charge Periods. From the Web UI you can specify additional limits which apply to that specific Charge Period, e.g. AC Charge 1 Upper SOC % Limit. During a Charge Period both the global limit and the specific limit apply, so the lower of the two takes effect.

Charge Power is the rate at which the battery will be charged while a Charge Period is is in force and the charge level is below the limit(s) which apply. This can be modified by the Remote Control parameter Battery Charge power %, but we shall ignore this.

While a Charge Period is in force, the battery is either:

  • charging at the Charge Power (using surplus PV which is available after meeting Load, with the balance coming from the grid); or
  • Idle, once the battery charge has reached the lowest limit which applies.

Note that:

  • while a Charge Period is in force, the battery cannot discharge;
  • while the battery is charging, it does so at the fixed rate specified as Charge Power.

These consequences follow:

  • while a Charge Period is in force, if the Load can’t be met from PV, the balance will be drawn from the grid. This applies not only while the battery is charging but also when it isn’t;
  • after charging has finished (or throughout the Charge Period if the charge level at the start is above the lowest charge limit), any surplus PV is exported rather than being stored in the battery.

This last point may come as a nasty surprise if you have a Charge Period in force during daylight. It conflicts with Eco Mode’s priorities, but Eco Mode has in effect been turned off.

Discharge Periods

When Discharge Mode is set to Scheduled, three extra fields appear:

  • Start Time
  • End Time
  • Consumption Type

Also relevant are the always-present fields

  • Reserve
  • Discharge Power

Start Time and End Time define the start and end of the first Discharge Period. There can be up to 10 of these, but numbers 2 - 10 can only be seen and configured from the Remote Control, which is accessible through the Web UI.

Irrespective of any previous setting of Consumption Type, the action of changing Discharge Mode from Dynamic to Scheduled causes Consumption Type to be set to Home Demand.

Changing Consumption Type from Home Demand to Full Export turns off Eco Mode. Completely. The battery will be Idle except when charging during Charge Periods and discharging during Discharge Periods. The rate of charge or discharge will never be changed automatically to store surplus PV in the battery or to discharge from the battery to meet Load. YOU HAVE BEEN WARNED.

Changing Consumption Type from Full Export to Home Demand turns Eco Mode back on. Eco Mode is also turned back on if you change Discharge Mode from Scheduled to Dynamic.

Reserve is also used outside Discharge Periods. It is the minimum % of the dischargeable battery capacity to which the battery can be discharged. If it is set to 0%, the battery will be discharged to its permitted maximum Depth of Discharge but not beyond.

Reserve is a global limit which applies to all Discharge Periods. From the Web UI you can specify additional limits which apply to that specific Discharge Period, e.g. DC Discharge 1 Lower SOC % Limit. During a Discharge Period both the global limit and the specific limit apply, so the higher of the two takes effect.

Discharge Power is the rate at which the battery will be discharged while a Discharge Period is is in force and the charge level is above the highest limit which applies. [This can be modified by the Remote Control parameter Battery Discharge power %, but we shall ignore this.]

While a Discharge Period is in force, the battery is in one of two states:

  • discharging at the Discharge Power; or
  • Idle, if the battery charge is at or below any limit which applies.

Note that:

  • while a Discharge Period is in force, the battery cannot be charged;
  • while it is discharging, it does so at the fixed rate specified as Discharge Power.

There are significant losses during discharge (10% or more). These are shown as part of Load. They make it hard to be precise as to what happens during discharge. Broadly speaking:

  • the first call on PV is to meet Load;
  • if net Load after PV < Discharge Rate, the surplus is exported
  • if net Load after PV > Discharge Rate, the deficit is imported from the grid

As the battery cannot be charged while a Discharge Period is in force, any surplus PV which is not used meeting Load will be exported, subject to the internal limits on the rate at which the inverter can deliver AC.

Once discharge from the battery at Discharge Power has finished (because some limit has been hit), the battery is Idle but export continues of surplus PV.

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Correction to when Charge Periods are In Force

I wrote that setting Charge Mode to Solar + Grid caused Charge Periods to be in force between their Start Time and End Time. This turns out to be true only if Battery Charge is less than or equal to Charge Up To.

At the start of a Charge Period, if Battery Charge ≤ Charge Up To, the Charge Period comes into force, Eco Mode is disabled and the battery can no longer discharge. Load is met from PV and the grid. Charging (from surplus PV + grid) begins at the Charge Power unless the charge already exceeds the upper limit for that individual Charge Period. This is specified in a Web UI parameter, e.g. AC Charge 1 Upper SOC % Limit. If so, the battery becomes Idle.

At the start of a Charge Period, if Battery Charge > Charge Up To, the Charge Period does not come into force. If Eco Mode was On, it remains in force and Load is met from PV and the battery.

If a Charge Period comes into force and charging begins, it stops once Battery Charge reaches either Charge Up To or the Web UI upper limit for the individual period. Once it has stopped, the battery becomes Idle for the rest of the Charge Period.

If the battery becomes Idle during a Charge Period, load is met from PV + the grid, but any surplus PV cannot be stored and so is exported.

Full Export

I have installed an inverter and a battery as part of a move to decarbonise. I’ve also installed solar panels and a heat pump. I’m on Cosy Octopus with off-peak periods from 4 - 7 am and 1 - 4 pm and premium pricing from 4 - 7 pm.

I have therefore approached the GivEnergy system from the point of view of someone with a large load (for now). My aim is to minimise the cost of the electricity which I buy. So I want to use as much as possible of the PV which I generate. This usually comes in the middle of the day when I need less heating because of solar gain. So I need to store the PV.

Over a 24-hour period if I don’t generate enough PV, I need to supplement it with electricity bought from the grid. It’s obviously better to do this during off-peak periods, so during those periods I aim to charge up or, if not actively charging, meet the Load from the grid.

Some users of the GivEnergy system will be in a very different position. Those without solar panels have no interest in storing surplus PV which they’re not using: they have no PV. Their interest lies in buying electricity at off-peak prices and selling it back to the grid at premium prices.

I have been puzzled as to why Full Export is so called. It occurs to me that it describes what users without solar panels want to do: hold in the battery all the charge that is there until the start of the Discharge Period. Then discharge it for export. This is what is achieved by turning off Eco Mode (which is what Full Export does). It stops the charge in the battery from being used to meet Load outside the Discharge Period.

Once the Discharge Period starts, the battery discharges at Discharge Rate. Load needs to be met (and includes the losses from converting the battery charge to AC). If PV is available, it meets or contributes to meeting the Load with any excess being exported (subject to the limit on how much AC the inverter can produce). If there isn’t enough PV to meet Load, the balance of Load is met out of the Discharge Rate with the remainder being exported.

So even with Full Export, the actual export rate will typically be lower than the Discharge Rate.