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TonyM1958 edited this page Feb 5, 2024 · 20 revisions

This is a schematic diagram of the arrangement of components if you have a hybrid inverter:

image

Click here to download a PDF file containing a high resolution image.

This shows:

  • The major components (Smart Meter, Generation Meter, Inverter, Main Load (e.g. your consumer unit and attached loads)
  • High Voltage batteries such as HV/Mira, ECS or EP. EP can have up to 4 parallel connected batteries.
  • Primary solar panels, connected directly to the hybrid inverter. These are not present for a battery only (AC) inverter.
  • Secondary generation sources, such as separate solar inverters, previous FIT installlations, solar panels with micro-inverters or a wind turbine with a grid tied inverter. Often, these will have their own generation meters (not shown)
  • Optional components, such EPS for backup power and/or an EV Charger, connected so it does not discharge the battery. The diagram shows EPS using the internal change-over switch. More information on EPS is available here
  • Within the major components, the arrangement of internal subsystems (AC to DC converters, DC to AC converters etc)
  • Approximate efficiency or power consumption of the subsystems. The figures given are based on H1-6.0-E and HV BMS v2 and may differ slightly for other inverter or batteries. In practice, inverter operating power is drawn from multiple sources and varies with operating mode and PV generation. The value shown is when no PV generation is available.
  • Where the main sensor parameters are collected from. You can look at the data from these in the Fox ESS Cloud. This data is used to populate the Fox apps and Energy Stats.

The diagram is for a single phase system, showing the L connections in brown. The topology of a three phase system is very similar with R, S and T connections instead of the single live phase. Neutral and Earth connections are not shown.

You can follow power as it flows down a path, based on work mode and use the efficiency figures in this diagram to work out approximate system efficiencies and understand where losses are incurred.

For example, when charging the battery:

  • Grid power is drawn via the AC connection into the inverter and converted to DC with an efficiency of around 97%. This sets the DC charge power that is available via the BAT connection to the BMS.
  • The BMS consumes around 30w from this power and uses the remainder to charge the batteries.
  • The battery has an internal resisitance (this results in heat generation when charging). Around 96% of the energy sent to the BMS gets stored as residual energy in the batteries.

When discharging the battery:

  • DC power is taken from the battery. Battery discharge losses also heat the battery and the energy available is around 96% of the residual energy that is removed.
  • The BMS takes 30W from the battery power and makes the remainder available to the inverter via the BAT connection.
  • The inverter converts the DC power to AC via the Main DC-AC converter, with an efficiency of around 97%.
  • The inverter consumes 120W of the power generated.
  • The remainder is provided via the AC connection and generation meter to power your main load and/or to export to the grid via your Smart Meter.

This is the model used to determine the system performance when using charge_needed()

Battery Losses

Batery losses are modelled using an ideal battery with an internal resistance that results in power loss both when charging and discharging the battery. Typically, the internal resistance of a battery is around 0.072 ohms (basd on HV2600). So, if you have 2 batteries in series, the total resistance is 0.144 ohms. 6 batteries is 0.432 ohms etc.

Battery losses depend on the charge / discharge current being used. The power lost is I squared R (current squared x internal resistance). Here are 2 examples of working out the charging losses:

SCENARIO A)
4 x HV2600 v2 batteries, being charged at 6kW to add 8kWh to the residual energy:

  • The inverter consumes 120W of the grid power, leaving 5.88kW of AC power
  • The DC battery charge power is 5.704kW after AC-DC conversion.
  • The BMS consumes 30W, leaving 5.674kW for battery charging.
  • With 4 x 54v, the nominal battery voltage is 216v, so the charge current is (5674W / 216V) = 26.3A.
  • The internal resistance is 4 x 0.07 = 0.288 ohms.
  • The power lost when charing is (26.3A x 26.3A x 0.288) = 199W.
  • The power added to the battery residual energy is (5674 - 199) = 5.475kW.
  • The battery loss is 199/5674 = 3.5%.
  • The battery efficiency is 96.5%.
  • The overall losses are (6000 - 5475) = 525W and the overall charging efficiency is (5475 / 6000) = 91.3%.
  • Adding 8kWh to the battery residual energy takes (8000Wh / 5475W x 60) = 88 minutes.
  • The overall energy losses are (525W x 88 / 60) = 0.770kWh

SCENARIO B)
The same 4 batteries are charged with the maximum charge current set to 13A:

  • The charge power is 216V x 13A = 2.808kW.
  • The BMS consumes 30W, leaving 2.778kW.
  • The power lost charging the battery is (13A x 13A x 0.288) = 49W.
  • The power added to the battery residual energy is (2778 - 49) = 2.729kW.
  • The battery loss is 49W/2778W = 1.76%.
  • The battery efficiency is 98.2%.
  • The input power is (2808W / 0.97 + 120W) = 3.015kW.
  • The overall losses are (3015 - 2729) = 286W and the overall charging efficiency is (2729 / 3015) = 90.5%.
  • Adding 8kWh to the battery residual energy takes (8000Wh / 2729W x 60) = 176 minutes.
  • The overall energy losses are (286W x 176 / 60) = 0.839kWh

Battery efficiency and absolute losses appear marginally better with the higher charge current, but this is only due to the inverter operating power being included over a shorter time. In reality, the operating losses are incurred regardless of the charging time so the difference in overall efficiency is negligible. The same amount of charge is added in both cases, so there is no difference in battery throughput. Still, some regard lower charge current as beneficial to the battery health.

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