Preventing Grid Sell-Back When AC Coupling

Transcription

1 Preventing Grid Sell-Back When AC Coupling Overview Some utility connection agreements don t allow for the sell-back of photovoltaic (PV) production back to the utility grid. This can be problematic when battery-less grid-tied inverters are AC coupled with batterybased inverters, as the battery-based inverter is essentially a copper connection between the grid and the grid-tied inverter when the grid is active. While this basic operating characteristic can be a problem for some battery-based inverters, most OutBack Power inverters have the hardware and built-in functionality to overcome the prevention of sell-back to the grid when AC coupled. Scope This application note will discuss how to setup the OutBack Power FR and Radian class inverters that are AC coupled to batteryless grid tied inverters for self-consumption without pushing power back to the grid. A typical AC coupled system configuration is shown below in Figure 1. The particular setup discussed below is unique to OutBack inverters that use the Radian GSLC AC coupling load center with remote operated circuit breaker (ROCB), or an FR inverter with the ROCB kit. The following instructions assume a basic understanding of how to AC couple with OutBack inverters. Those unfamiliar with the topic can find more detailed information on the OutBack Power website in the application note titled, AC Coupling Grid Tie Inverters With OutBack Battery-Based Inverters. Figure 1 - Typical AC Coupled System 2016 OutBack Power Technologies, Arlington, WA 983 RF-MM-6/30/2016 Page 1 of 7

2 Solution Regardless of the input mode selected for the Radian and FR inverters, when grid connected to a live grid, they will always be in a pass through mode of operation whereby the internal transfer switch is closed between the AC input and output. This creates a conductive path for the grid tie inverter coupled at the OutBack inverter s AC output to the AC input which is connected to the grid. In many cases this is a desired condition if the utility connection allows the sell-back of renewable energy (RE) to the grid, but some connection agreements either don t allow this, or the economics of the agreement are more beneficial to fully consume the available RE. The input mode called Mini Grid is designed for RE self-consumption in that its normal state is disconnected from the grid, i.e. the transfer switch between the AC input and output is open circuit. This allows the load panel connected to the AC output to consume all available RE, plus some of the battery energy when the sun goes down as determined by the Mini Grid s battery setting for connection to the grid. Once the low battery setting is reached, a connection to the grid is made to power the loads and stop using battery power to conserve the rest of the battery s energy in case of a power outage, or to prevent deep discharging of the battery which will extend its life. Presumably, the discharging of the battery down to its grid connection setting would happen at night after the sun has gone down, but it s always possible due to high cloud cover, the lack of RE would cause the battery to discharge to its grid connection voltage during the day. In this case, if the sun came back out, then the grid tie inverter could now sell back to the grid because the AC input and output transfer switch is closed to power the loads until the battery is charged back up to its grid disconnect voltage. However, the OutBack AC coupling solution can use the generator lockout relay and Source Status Aux trigger in combination with the Mini Grid mode to prevent the grid tie inverter from coming back on during the connect to grid period, that would otherwise allow the grid tie inverter to sell back. Figure 2 below shows the wiring diagram for the ROCB and the two control relays including the landing points for the grid tie inverter connections designated with a circled x. The ROCB is normally used for two purposes, 1) to open the grid tie inverter connection to the AC output buss, so it doesn t backfeed the batteries with an unregulated charge when RE production exceeds load demand during a grid outage, and 2) to disconnect, or lockout the grid tie inverter when the battery runs down and a generator is called to turn on and charge the batteries and power the critical loads. The V relay in the diagram opens the ROCB and is turned on by the MATE3 AC coupling function. The 48V relay also opens the ROCB, but also locks out the V relay in the event the AC coupling function tries to turn the ROCB back on, in which case the generator could backfeed and damage the grid tie inverter. So instead of setting the Radian inverter s Aux function to start the generator using the Advanced Generator Start (AGS), the Radian Aux can be set to trigger on Source Status which triggers when the inverter is connected to a qualified AC source on its AC input. This keeps the grid tie inverter offline when grid connected, but keeps the loads powered and allows the batteries to charge from the grid if desired, or the inverter s charger can be turned off so the RE can do the charging on the next sunny day. This same capability is available with the FR inverters but requires a second inverter and a second V relay in place of the 48V relay shown in Figure 2. This is due to the Radian inverter having two auxiliary (Aux) ports, one with V output and the other a dry contact output which is used to trigger the 48V relay, versus the FR inverter which has a single V Aux port. The second FR s Aux port would be used to turn on/off the second V relay that replaces the 48V relay used in the Radian configuration. The following procedures outline the solutions for both Radian and FR class inverters OutBack Power Technologies, Arlington, WA 983 RF-MM-6/30/2016 Page 2 of 7

3 V- AU V+ AU AU RELAY AU RELAY NEUTRAL AC GEN L1 AC GEN L2 AC GRID L2 AC GRID L1 AC OUT L2 AC OUT L1 Application Note GROUND W16 To GS8048 GROUND BUS W8 CB1/2 W2 W1 W23 W W25 W26 W W4 W W5 W15 W W7 MECHANICAL INTERLOCK CB3/4 W3 W10 CB5/6 CB7/8 W W17 W6 W13 W19 W18 W9 AC OUT LEG 1 AC OUT LEG 2 AC GRID IN LEG 2 AC GRID IN LEG 1 AC NEUTRAL BUS AC GEN IN LEG 2 AC GEN IN LEG 1 GRID TIE INV L1 GRID TIE INV. L2 ROCB W WAGO 788-3, VDC RELAY Vdc W WAGO VDC RELAY 48Vdc D B A M C 48 Vdc - 48 Vdc + Figure 2 AC Coupling ROCB and relay wiring diagram for the Radian GSLC load center. Hardware Connections Radian GSLC AC Coupling Load Center (GSLC175-AC-0/0) 1. Connect the grid tie inverter L1, L2, N & G wires to the terminal bus bars in the load center designated with a circled x as show in Figure Connect the green/green & white twisted pair that is coiled in the load center to the V Aux port terminals as shown in the GSLC Quick Start Guide OutBack Power Technologies, Arlington, WA 983 RF-MM-6/30/2016 Page 3 of 7

4 V- AU V+ AU NEUTRAL AC GEN L1 AC GEN L2 AC GRID L2 AC GRID L1 AC OUT L2 AC OUT L1 Application Note V+ AU V- AU 3. Connect the orange/orange & white twisted pair that is coiled in the load center to the Aux terminals as shown in the GSLC Quick Start Guide. 4. Make all other AC input/ouput and DC connections as instructed in the GSLC Quick Start Guide. GROUND W16 To FR Inverters GROUND BUS W8 CB1/2 W2 W1 W23 W W26 W25 W W4 W W5 W15 W W7 MECHANICAL INTERLOCK CB3/4 W3 W10 CB5/6 CB7/8 W W17 W6 W13 W19 W18 W9 AC OUT LEG 1 AC OUT LEG 2 AC GRID IN LEG 2 AC GRID IN LEG 1 AC NEUTRAL BUS AC GEN IN LEG 2 AC GEN IN LEG 1 GRID TIE INV L1 GRID TIE INV. L2 ROCB W WAGO 788-3, VDC RELAY Vdc W27 48Vdc OBR-16-DIN B A M D C 48 Vdc - 48 Vdc + Figure 3 - AC Coupling ROCB and relay wiring diagram for the FR FW500-AC load center OutBack Power Technologies, Arlington, WA 983 RF-MM-6/30/2016 Page 4 of 7

5 FLEpower 2 Load Center (FW500-AC) 1. Connect the grid tie inverter L1, L2, N & G wires to the terminal bus bars in the load center designated with a circled x as show in Figure Install the ROCB from the ROCB kit into the AC load panel using three spare breaker slots. See Figure Mount the included DIN rail in the ROCB kit to the inside of the FW500-AC panel, then mount the V relay and the separately ordered OBR-16-DIN which is the same as the V relay that comes in the ROCB kit. See Figure Make the wiring connections between the relays and the ROCB as show in Figure Make all other AC input/ouput and DC connections as instructed in the FP2 Quick Start Guide. Figure 4 - ROCB and relay installation into FM500-AC. System Configuration Programming the MATE3 1. Press the Lock key and enter the 1 password. 2. Select Settings, then Inverter, then AC Coupling. 3. Highlight the Yes/No field and select Y(es). 4. Press the Up key to the Inverter menu and select the Grid AC Input Mode and Limits menu. 5. Change Input Mode to Mini Grid. Change the Connect to Grid setting as desired (too low of a setting may not provide enough battery capacity for backup power in the event of AC power loss). Set Connect Delay time long enough to avoid connecting to grid on short power surges. Disconnect from the grid will be achieved after completion of the next Float cycle. 6. Press the Up key to the Inverter menu and select Auxiliary. 7. Select Aux Mode and change to Source Status OutBack Power Technologies, Arlington, WA 983 RF-MM-6/30/2016 Page 5 of 7

6 8. Press the Up key to the Inverter menu and select Grid-Tie Sell. Select Offset Enable and set to Y(es). Set the Sell Voltage to equal the Float voltage to prevent the ROCB from opening unnecessarily at the end of a Float charge cycle. Exceptions or Precautions It is highly recommended to review the more complete AC Coupling application note titled, AC Coupling Grid It Inverters With OutBack Battery Based Inverters that has more detailed background and covers system sizing guidelines as well OutBack Power Technologies, Arlington, WA 983 RF-MM-6/30/2016 Page 6 of 7

7 About OutBack Power Technologies OutBack Power Technologies is a leader in advanced energy conversion technology. OutBack products include true sine wave inverter/chargers, maximum power point tracking charge controllers, and system communication components, as well as circuit breakers, batteries, accessories, and assembled systems. Grid/Hybrid As a leader in off-grid energy systems designed around energy storage, OutBack Power is an innovator in Grid/Hybrid system technology, providing the best of both worlds: grid-tied system savings during normal or daylight operation, and off-grid independence during peak energy times or in the event of a power outage or an emergency. Grid/Hybrid systems have the intelligence, agility and interoperability to operate in multiple energy modes quickly, efficiently, and seamlessly, in order to deliver clean, continuous and reliable power to residential and commercial users while maintaining grid stability. Contact Information Address: Corporate Headquarters th Avenue N.E. Suite B Arlington, WA 983 USA European Office Hansastrasse 8 D-916 Schwabach, Germany Telephone: (Technical Support) (Fax) (Fax) Website: Support@outbackpower.com Disclaimer UNLESS SPECIFICALLY AGREED TO IN WRITING, OUTBACK POWER TECHLOGIES: (a) MAKES WARRANTY AS TO THE ACCURACY, SUFFICIEY OR SUITABILITY OF ANY TECHNICAL OR OTHER INFORMATION PROVIDED IN ITS MANUALS OR OTHER DOCUMENTATION. (b) ASSUMES RESPONSIBILITY OR LIABILITY FOR LOSS OR DAMAGE, WHETHER DIRECT, INDIRECT, CONSEQUENTIAL OR IIDENTAL, WHICH MIGHT ARISE OUT OF THE USE OF SUCH INFORMATION. THE USE OF ANY SUCH INFORMATION WILL BE ENTIRELY AT THE USER S RISK. OutBack Power Technologies cannot be responsible for system failure, damages, or injury resulting from improper installation of their products. Information included in this manual is subject to change without notice. Notice of Copyright Application Note 2015 by OutBack Power Technologies. All Rights Reserved. Trademarks OutBack Power, the OutBack Power logo, FLEpower ONE, Grid/Hybrid, and OPTICS RE are trademarks owned and used by OutBack Power Technologies, Inc. The ALPHA logo and the phrase member of the Alpha Group are trademarks owned and used by Alpha Technologies Inc. These trademarks may be registered in the United States and other countries OutBack Power Technologies, Arlington, WA 983 RF-MM-6/30/2016 Page 7 of 7