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So called “a.c. coupling” is one of the easiest ways to add a battery storage system, with or without additional solar panels to an existing solar installation. In Figure 1 above, the “Battery Inverter” has been added to “couple” the stored energy in a battery to the switchboard (Load Centre) of the installation. The key component though is the “Energy Meter” upstream of the loads and existing solar generation. This meter allows the battery inverter to “see” the flow of energy into or out of the installation and choose whether to export battery energy to match the energy being consumed by the loads (but not meet fully by the existing solar system).
Put simply, the loads are supplied first by the existing solar inverter and any extra is then supplied by the battery inverter. If both of these is insufficient the the difference is sourced from the grid.
This all happens seamlessly, thanks to the magic of Kirchoff’s circuit laws and to the information that the energy meter supplies to the battery inverter.
DC coupling of batteries to solar PV system
If installing a new solar and battery storage system then d.c. coupling is one of the most popular options as the equipment manages both the battery and the solar generation within the one unit. So called “hybrid” inverters are those that can have both solar PV connected and battery storage.
The advantage of d.c. coupling is that the inverter is only used to converter d.c. to a.c. to supply the loads at the installation – internally the solar is directly charging the battery via a d.c. to d.c. path at very high conversion efficiency.
In Australia and New Zealand where the grid-connection standard AS/NZS 4777.1 applies – total Inverter Energy System (IES) capacity for a single phase installation must be <5kVA and thus limits the number of inverters connected to a total of 5kVA (approx. 5kW). This can be augmented by the local electricity network supply authority (typically with export limiting) but does make adding more a.c. coupled battery storage somewhat limited by total IES capacity of the site.
In Figure 3 above the d.c. coupled hybrid system has no backup circuit. This is not an uncommon arrangement and best suits those customers who merely want to shift energy between solar, storage and their loads.
Backup functionality adds cost and complexity and is not aways available with all hybrid battery storage products.
When sizing a battery storage system for a hybrid solar system it is important to consider to objective. If supplying all the energy to the installation by a combination of solar PV and stored battery energy then the customer’s load profile needs to be carefully considered.
In Figure 4 above you will see that the battery’s State of Charge (SOC) reaches 100% just after midday. This would indicate that the battery capacity is too small to avoid “spilling” solar energy out to the grid and thus loosing the potential savings it might offer.
Also, the energy supplied from the battery to the loads in the evening is capped at 3kW due to the inverter’s limited battery power and thus considerable grid sourced energy is being drawn in during the peak early evening period to make up the difference.
So both battery capacity and inverter power ratings need to be matched to the customer’s load profile.
Smart Energy Lab Students Install New HV LG Chem Battery
The “Dream Team” is our test configuration for adding extra storage capacity using lithium ion battery storage to an existing lead-acid off-grid system.
The configuration consists of a Schneider XW+ with both Conext 600/80 MPPT and 3kW RL charging a 600Ah Neuton Power VRLA (sealed) lead-acid battery bank. This system is a.c. coupled to a SolarEdge SE5000 with Backup Unit attached to the new LG Chem RESU9.8H (400V) battery.
The key to making this work is the SolarEdge supplied Wattnode energy meter installed in the main switchboard. The configuration of the SE5000 is to maximise self-consumption and thus the meter tries to preference the use of SE5000 connected solar (4kW with SolarEdge Optimisers) and the 9.3kWh (usable storage) of the LG Chem battery.
When either power or energy is insufficient to meet the load requirements then the XW+ supports the loads.
Note: SP Pro has been substituted for XW+ in this installation.
The main benefit of this “Dream Team” configuration is that it allows adding additional storage capacity to an existing lead-acid system. The new lithium battery does most of the daily cycling and thus extending the life of the lead-acid battery.
AS/NZS 5033:2014 has an exemption to the requirement to have a switch-disconnector between the PV array and the PCE (inverter, charge controller or load) for DC Conditioning Units.
… (c) Each input is limited to 350 W maximum PV power at STC and a maximum input voltage no greater than ELV.”
However, back in 2014 maximum module size was around 250W and this 350W limit seemed to allow any single module to be connected to a DCU such as those made by SolarEdge, Tigo etc… now, just three years later modules are heading over 300W and some nudging the 350W limit already.Interestingly, module manufacturers such as those listed below, already required covering of the module with an opaque material to limit any current before connecting or disconnecting the plug and sockets of a PV module. This manufacturer’s requirement provides a safe way to attach modules >350W @STC to a DCU and still ensure that the power in the cables is kept below 350W.
Covering with an opaque material also allows a safe (and no plug/socket damaging method) to disconnect a PV module from a faulty DCU (has gone short circuit internally).
I would argue that since the intent of the standard is to limit the power supplying the DCU to <350W, if following manufacturer’s installation instructions and covering the modules before disconnecting plugs and sockets, then modules larger than 350W@STC can be connected to a DCU and still meet the “no switch-disconnector on PV to PCE” exemption of clause 2.1.5.
List of module manufacturer’s who’s installation instructions require covering of the module with an opaque material:
- Ben Q
- Mitsubishi Electric
- Schuco mounting system
- SolTech Power
- First Solar
- SolarTech Micro Inverters
- International Energy Agency Photovoltaics in buildings
- AUO Photovoltaic Modules
- Sharp USA and UK
- Eging PV
- SunPower Modules & Inverters
- Suntech UL Install guide, Global install guide,
- Hareon Solar
- Grape Solar
- Perlight Solar
- Open Renewables
- ET Solar
- Fluitecnik Sun Energy
- Canadian Solar
- Shan Solar
- Cooper Crouse-Hinds Solar Recombiner, Array Fuse, Disconnect Box
- Mage Solar
- Solectria Renewables
- Solahart Australia
- Outback Power
- Advance Power
- SolarGain APS Micro Inverters
- Jinko Solar
- Moser Baer Solar
- Enhance Photovoltaics
- JA Solar
- Kyocera Solar
- DPSun Photovoltaic Modules
- Schutten Solar
- Soli Tek
- SunGrow inverters
- BOSCH solar modules
- Trina Solar
- Xantrex GT AU inverters
- Panasonic PV modules
- Samil Power Micro’s
- Phono Solar
- UPT Solar
- Shell Solar
*If you search the word “opaque” within these documents you will find the procedure to be universally applicable and acceptable.
Some of the exciting new systems at the Smart Energy Lab
Raj showing Mark how to commission the NicestESS 5kW AC coupled battery inverter. This unit can be used to add energy storage to any existing PV inverter system. The NicestESS unit is wired between the existing PV inverter and the switchboard to which it connects. The unit takes 48V Pylontech US2000B batteries.
Shaun and Steve discuss the Victron Energy system being installed into the new IP54 enclosure from Power Plus Solutions. The inverter is the new AS/NZS 4777.2:2015 compliant Multigrid 3kW hybrid inverter. The battery system is a GenZ pack of up to 6 x 3kWh units in the cabinet below.
Midwinter training courses at the Smart Energy Lab
Chula from Sungrow shows the students how to program the SH5K+ hybrid inverter.
New 5kW hybrid from Goodwe, the “EM” model. Same power rating (5kW) as it’s big brother (ES) but with a reduced 50A maximum battery charge/discharge current.
Upgrading an existing Outback system by adding another FM60, Hub and Mate3.
Configuring Suntrix’s myWatt inverter monitor.
Swapping over the GiantPower IPS4000 under harsh weather conditions.
Using the Solar Pathfinder to assess the solar window of a site.
Rachel doing a BMS hardware swap-over on the older Pylontech US2000A batteries.
Installing the new Imeon Energy 9.12kW hybrid inverter.
Duncan MacGregor from Enphase explaining how the Enphase system works.
Stage one of installing the EasyWarm “HotPV” system.
Networking at the end of the day on a cold winter’s night.
Mark configuring the EasyWarm system for both VOV and GT mode.
New products (above) for my students to install on the next course (30 May – 2 June). On every course, suppliers generously donate equipment for my students to train on. Next week we have: Goodwe EM hybrid inverter, NicestESS 5kW AC battery system, Gen2 Pylontech LFP 2.4kWh batteries, Victron 250/100 MPPT, EasyWarm HotPV system, Outback FM60 MPPT, myWatt energy monitor, Sungrow SH5K+ hybrid inverter and backup box plus lots more.
Our new Enphase training system
Enphase “Toolkit” App up on the big screen
Beau explains how he configured the Envoy-S
Beau checking the system performance
Brodie and Ralph working on the Goodwe BP and SolaX Hybrid system that they just installed.
Cameron explaining the configuration of the SolarEdge with Optimisers that they just installed.
Ben shows how to configure the SMA Sunny Island for off-grid installation.
Fotakis installing the Enphase Envoy-S in large switchboard.
John demonstrating the FIAMM molten salt battery
Bradley introducing the GenZ LiFePO4 battery.
Alan installing two Victron BMV700 battery monitors.
Mark showing students how to commission an Enphase system.
Aydin checking out the Envoy-S App.
Duncan & Mark showing how to mount Enphase micros on an indoor demo rail (panels are outside).
December 2016 Solar + Storage Course
The emphasis on our four day course is to blend theory and practice on a daily basis. The program starts with theory in the morning followed by practical sessions to reinforce and expand on the theory, returning to the classroom in the afternoon to explore the problems and solutions.
Many of the systems installed by students on this course are “real” systems. Above is a 1.5kWh/day system for the “Tiny House” located near the training centre. The house is a relocatable home for one person and has been designed from the ground up for minimal energy consumption. The solar panels the students installed were Solimpeks PVT (photovolatic and thermal) collectors. These unique panels combine water heating with electricity generation. Ideal for small roof areas such at this (7m x 2.5m).
“Beer o’clock” and system install review session! These “reviews” are part of the shared learning approach. Each team works on their own projects and come together at the end to present their experiences, likes and dislikes and problems.
Manfred explains how the Studer-Innotec d.c. coupled system works with Sonnenschein VRLA batteries.
Phil from Victron Energy shows the students how to program the 3kW Multiplus with 150/30 MPPT and ColorController.
“Capt. Col” working on the “Dream Team” – SP Pro + SolarEdge + LG Chem + Neuton Power VRLA. The concept of the “Dream Team” is to combine the high efficiency lithium battery with the low cost and depth of discharge capabilities of lead-acid batteries. The SolarEdge inverter meets the daily loads first from the LG Chem battery and only when depth of discharge limit is reached or the load power is greater than the power delivery limits of the lithium battery, is the lead-acid battery “called upon” via the Selectronic SP Pro to support the loads.
Ray carefully tensions battery terminals. Always use insulated tools when working on batteries with exposed terminals.
Ray & Adrian installing Studer XTM4000 and VarioTrack 150/80 MPPT. This d.c. coupled system gives high reliability and “battery centric” solar charging. D.C. coupling is a more reliable way of charging batteries and avoid the “black start” problem of a.c. coupled systems.
The “Tiny House” gets a power system.
David with GiantPower IPS4000 (dual MPPT/UPS inverter-charger)
Kevin, Col and Armin preparing the SolarEdge SE5000 with backup unit.
Ray connecting the Studer MPPT.
Jerry and Matt checking the Solar Analytics remote metering on GiantPower system.