TIME OF USE CORRECTLY SETTING BATTERY CONTROL PARAMETERS

Transcription

1 CORRECTLY SETTING BATTERY CONTROL PARAMETERS

2 Fronius International GmbH Version 02 05/2018 Business Unit Solar Energy Fronius reserves all rights, in particular rights of reproduction, distribution and translation. No part of this document may be reproduced, in any form whatsoever, or stored, processed, duplicated or disseminated with the aid of electronic systems, without the written consent of Fronius. You are hereby reminded that the information published in this document, despite the greatest care being exercised in its preparation, is subject to change and that neither the author nor Fronius can accept any legal liability. Gender-specific wording refers equally to the male and female form. 2/14

3 CONTENTS 1 INTRODUCTION BATTERY CONTROL PARAMETERS Battery power limits without parameters Permitted battery restrictions Maximum charging and discharging limits Specifying the charging range Specifying the discharging range Specifying a defined charging power Specifying a defined discharging power PV power reduction APPLICATIONS Time-dependent electricity tariffs Locking the battery during low-tariff times Limiting the discharging power in the low tariff Charging the battery during the low-tariff period for use during the high-tariff period (3 tariff zones) Fully charging the battery during the medium-tariff period (3 tariff zones) Capacity reservation for power limitation Time-dependent capacity reservation for emergency power SUMMARY LIST OF FIGURES /14

4 1 INTRODUCTION Photovoltaic systems are largely equipped with electrical storage devices to increase the degree of selfconsumption and autonomy. High self-consumption means consuming as much of the energy produced as possible at source, while autonomy means drawing as little energy as possible from the grid, i.e. being as self-sufficient as possible. To achieve these goals, a Fronius Smart Meter is installed on the household connection. This device measures how much power is fed into the grid and how much is drawn from the grid. If more power is generated by the PV system than is consumed in the household, this results in surplus PV power. If more power is required than is generated by the PV system, electricity is drawn from the grid. In the standard configuration, the surplus PV power is stored in the battery. The household is supplied with this stored energy if too little or no PV power is available. 1) PV production 2) Household consumers 3) PV surplus 4) Electricity sourced from the grid 5) Battery discharging 6) Battery charging Figure 1 - Household energy flows 4/14

5 If additional framework conditions such as time-dependent energy prices, variable reserves of emergency power, or power limits are to be taken into account, it makes sense to apply additional battery settings. This document explains which settings are possible and which applications are covered. Without additional battery parameters, the device is optimised for maximum self-consumption. The user must decide how important self-consumption, costs, and convenience are to them depending on the application, as self-consumption tends to drop when battery parameters are defined. 2 BATTERY CONTROL PARAMETERS It is possible to set various time-dependent battery parameters relating to charging and discharging power for each day of the week. This restricts the operating range of the battery. The battery is influenced by a few external factors, including calibration charging, permitting charging via AC, power limitation of the inverter, or control parameters sent via Modbus. The time-controlled battery parameters have the lowest priority here and may not be met due to other parameters. 2.1 Battery power limits without parameters If no value is entered for a time period, the power is only restricted by the inverter and battery during this period. Example of the discharging power for the Fronius Energy Package: Max. AC output for Fronius Symo Hybrid 3.0-S => 3,000W Max. AC output for Fronius Symo Hybrid 5-0-S => 5,000W Max. charging and discharging power Fronius Solar Battery 7.5 => 4,000W When combining the Fronius Symo Hybrid 3.0-S and Fronius Solar Battery 7.5, the battery can be discharged with a maximum power of 3,000 W. When combining the Fronius Symo Hybrid 5.0-S and Solar Battery 7.5, the battery can be discharged with a maximum power of 4,000 W. In this case, it is always the lower of the two power figures that is key. When charging the battery, note that it is possible to perform charging using energy from the PV system and additional generators at the same time. In this case, the charging power may be greater than the maximum AC output of the inverter. For further details, see white paper entitled Multiflow Technology. 2.2 Permitted battery restrictions 5/14

6 The following battery restrictions can be applied: Maximum charging power Minimum charging power Maximum discharging power Minimum discharging power A parameter always consists of one of the four restrictions above and the times for which the restriction applies. One or max. two compatible restrictions may be active at any one point in time. Note: defining time ranges that extend past midnight is not permitted. If, for example, a parameter is required from 22:00 to 6:00, one parameter must be specified for 22:00 to 24:00 and a second for 0:00 to 6:00. The permitted operating range can be pictured as a slide rule with two sliders, with the discharging range on the left, neither discharging nor charging in the middle, and the charging range on the right. The operating point of the battery can be found between the two indicators. There are five permitted configurations of two battery restrictions: Maximum charging and discharging limits The max. charging and max. discharging power can be configured at the same time. Figure 2 - Maximum charging and discharging power 6/14

7 Figure 3 - Screenshot, maximum charging and discharging power Specifying the charging range It is possible to define a charging range using a min. and max. charging limit. In this case, discharging of the battery is not possible. Figure 4 - Specifying the charging range Figure 5 - Screenshot, specifying the charging range Specifying the discharging range 7/14

8 It is possible to define a discharging range using a min. and max. discharging limit. In this case, charging of the battery is not possible. Figure 6 - Specifying the discharging range Figure 7 - Screenshot, specifying the discharging range Specifying a defined charging power A defined charging power can be specified by setting the min. and max. charging power to the same value. Figure 8 - Defined charging power 8/14

9 Figure 9 - Screenshot, defined charging power Specifying a defined discharging power A defined discharging power can be specified by setting the min. and max. discharging power to the same value. Figure 10 - Defined discharging power Figure 11 - Screenshot, defined discharging power 2.3 PV power reduction 9/14

10 These battery control parameters have been developed to ensure the energy produced can be consumed by the user as efficiently as possible. However, situations can arise where PV energy cannot be used due to the battery parameters. One such example would be the following: a Fronius Symo Hybrid 3.0-S is configured with a Fronius Solar Battery 7.5 with a defined discharging power of 3,000 W. At the same time, 1,000 W of PV power is being produced. In this case, the inverter must reduce the PV output to 0 W, as the output power of the Fronius Symo Hybrid 3.0-S is 3,000 W and the device is already at maximum capacity due to the discharging power. Since wasting PV power is not in the interest of the user, the power limitation for the battery control parameters is automatically adjusted so that no PV power is wasted. In the example above, this means that the battery is only charged with 2,000 W, so that the 1,000 W PV power can be used. Note: when controlling the battery via Modbus, these parameters are strictly adhered to even if PV energy is being lost. 3 APPLICATIONS 3.1 Time-dependent electricity tariffs Battery configurations in the face of time-dependent electricity tariffs where there is only around a 10% difference between the high and low tariff are not profitable, as the difference is simply too small. One example of major differences in tariff rates is in western Australia, where a difference of $ 0.50 in the high tariff and $ 0.09 in the low tariff is normal Locking the battery during low-tariff times For extremely low tariffs, it makes sense not to discharge the battery at night. The following screenshot shows the setting that prevents discharging between 22:00 and 6:00: Figure 12 - Locking the battery during low-tariff times 10/14

11 3.1.2 Limiting the discharging power in the low tariff If the low tariff rate is half that of the high tariff, for example, it often makes sense to use the stored energy at night. However, it is preferable to still have capacity available in the morning, so that self-generated energy can be used during the high-tariff period until enough PV can be generated to cover the self-consumption requirement again. For these scenarios, the discharging power can be limited during the night. The system in the example has a Fronius Solar Battery 7.5 with 6 kwh of usable energy. It is assumed that the low tariff begins at 19:00 and that the battery is full at this time. At 7:00 the low tariff ends, and 20% residual capacity should still be available. This means that 1.2 kwh must be available at 7:00 and 4.8 kwh can be used in the 12 hours overnight, resulting in a maximum discharging power of 400 W. Figure 13 - Limiting the discharging power during the low-tariff period Charging the battery during the low-tariff period for use during the high-tariff period (3 tariff zones) If there are huge differences between the low and high tariff, an AC-coupled battery can be used without a PV system for charging during the low-tariff period, so that the energy can be used during the high-tariff period. To do so, it must be ensured that discharging does not occur during the medium-tariff period. The following tariffs serve as an example: Low tariff: 22:00-7:00 Medium tariff: from 7:00 14:00 and 20:00 to 22:00 High tariff: 14:00 to 20:00 A 6-kWh battery is used in the example, which is charged in the last two hours of the low-tariff period. 11/14

12 Figure 14 - Charging the battery during the low-tariff period for use during the high-tariff period Fully charging the battery during the medium-tariff period (3 tariff zones) If a PV system is present and the high tariff applies in the afternoon, then the battery is normally already charged with surplus PV power. During bad weather, it may make sense to charge the battery at the end of the medium-tariff period so that it is full for the start of the high-tariff period. In the example, the same tariff and battery type is used as in Figure 15 - Fully charging the battery during the medium-tariff period 3.2 Capacity reservation for power limitation There are markets in which the power fed in to the grid must be reduced to a defined percentage of the system output. Here, it may be the case that PV energy cannot be used during the afternoon. If sufficient battery capacity is available in the afternoon to store the energy not fed into the grid, PV energy does not need to be wasted. In order to ensure that enough capacity is available at midday and in the afternoon, the battery must not be charged without limit in the morning. The ideal setting depends on the consumption pattern, system size and other similar factors. 3.3 Time-dependent capacity reservation for emergency power It is possible to configure a capacity reserve for emergency power mode. However, this surplus capacity is then also held in reserve when there is nobody at home. Individual adjustments can be made using the battery parameters, so for a household where nobody is home during weekdays, the following parameters can be defined: the battery should always be full in the evening, and during the day self-consumption should be optimised. This means that the battery will be charged before 12/14

13 the owners come home in the evening. In this case, it would also be possible to leave the battery to only discharge slowly until midnight, so that capacity is available if emergency power is required. Furthermore, at weekends, discharging could be restricted during the day. 4 SUMMARY This white paper clearly shows that using battery control parameters for a PV system with a storage unit provides a great deal of added value. Using the correct parameters allows the storage solution to adapt to the system owner's individual requirements, eliminating unnecessary costs for additional energy from the grid. 5 LIST OF FIGURES Figure 1 - Household energy flows... 4 Figure 2 - Maximum charging and discharging power... 6 Figure 3 - Screenshot, maximum charging and discharging power... 6 Figure 4 - Specifying the charging range... 7 Figure 5 - Screenshot, specifying the charging range /14

14 Figure 6 - Specifying the discharging range... 7 Figure 7 - Screenshot, specifying the discharging range... 8 Figure 8 - Defined charging power... 8 Figure 9 - Screenshot, defined charging power... 8 Figure 10 - Defined discharging power... 9 Figure 11 - Screenshot, defined discharging power... 9 Figure 12 - Locking the battery during low-tariff times Figure 13 - Limiting the discharging power during the low-tariff period Figure 14 - Charging the battery during the low-tariff period for use during the high-tariff period Figure 15 - Fully charging the battery during the medium-tariff period /14