.. Track APT – Energy Planning and Appropriate Power Technology at The 2007 ngNOG Workshop on Network Technology, Power and Policy at Bayero University, Kano on November 18 – 22, 2007 by Rev. Ukaegbu Ogwo (MD/CE, Solartime Electric Ltd.)

DAY 3  ngNOG APT Track 4 –  Back-up Power

INVERTERS  You may have all the energy from your solar array, wind generator and/or micro- hydro systems sitting in your battery bank without being able to even turn on one small bulb.  The inverter is the magic box that converts all that DC power in your battery bank into AC power, the state where it can be useful in powering most of the household and other appliances. Some inverters perform this function better than others.

Low & High Frequency Inverters

Sine Waves and Inverters  Renewable energy usually in DC form, can be stored unlike AC power used as it is generated.  easier and more economical to transport AC power through power lines than DC power.  inverters are a must for RE’s

.  AC delivered in the form of a sine wave.  In Nigeria AC current runs at 50 hertz, i.e. 50 positive to negative cycles per second.

.  An inverter takes low voltage direct current (DC) and converts it into high voltage alternating current (AC).  The heart of the inverter is the transformer.  Transformers work on the principle of inductance.

H-Bridge  The magic is the H-Bridge.  Each of the two legs of the H has a transistor switch near each end – four switches in all – and the legs are joined by the transformer in the middle.  The two bottom switches control the flow of the negative current from the batteries, while the upper switches control the flow back to the batteries.

H-Bridge

.  By electronically timing the opening and closing of the switches, inductance is thus made to occur.

Modified Sine Wave  This basic configuration can be used to create modified sine wave, such as those produced in the Xantrex DR series inverters.  To produce a much better approximation of a sine wave (less than 5% harmonic distortion), a series of H-Bridges, and transformers of varying voltages, are used, creating in essence a series of inverters whose outputs are mixed in ratios determined by the battery voltage.

Sine, Square and Modified Sine wave

Sine Wave Inverters  State-of-the-art sine wave inverters produce a current as clean as the utility grid power.  Every load will run smoothly and efficiently on the current they produce.  Expensive tech.

Outback Sine wave Inverter

Modified Sine Wave Inverters  For a lot less money, you can purchase a modified sine wave inverter, such as one of the Xantrex DR-series or any of a number of inexpensive, lightweight inverters.  If you can afford a sine wave inverter, I would advise against a modified output inverter.  They produce a stepped waveform that tries to approximate a sine wave.

Modified sine wave Inverter

Choosy Supplier  For lights, toasters and vacuum cleaners, it may be good enough. But for certain other appliances, problems may arise.  At the back of the manual for the DR-series inverter, Xantrex has compiled a list of devices that may experience problems running from a modified sine wave inverter.  These include microwave ovens, electric clocks, ceiling fans, dimmer switches, and rechargeable devices.

.  If you let your rechargeable batteries sit in the charger, powered by a modified sine wave inverter, for a long time after they are charged, the batteries would begin to overheat.  If you are installing inverter in a house with all the modern conveniences of today’s home, a sine wave inverter is the only right way to go.

Inverter Functions A good sine wave inverter will have more features than you will ever use. Below are some of the basic features found in inverters.

Functions of the Inverter  High and low voltage shut-off  Battery Charging  Generator and grid tie-ins (for systems with batteries)  Search function

Stackable Inverters  However big your inverter may be, be sure it can be “stacked” with another, identical inverter.  If you discover one day that the inverter you bought has become too small for your growing need, you should have the ability to increase your power generating capacity without necessarily discarding your old inverter.

24KVA STACKED OUTBACK INVERTER POWER SYSTEM

MATE  Outback Power Systems, taking a new approach, now manufactures FX or VFX3000E inverter series that are stackable up to 10 units to give 30kVA block power.  Three of them can also be connected in 3-phase to give 9kVA 3-phase output.  All the stacked inverters can be run from a single remote system controller, the Mate.

Outback MATE

HUB  This small unit can simultaneously run their MX60 charge controller while serving a number of other useful functions.  The HUB is the console that coordinates all of these activities as everything is wired into it.  One of the inverters serves as the master while the others are slaves.  You can add modules in stacking, as you need them, without having to replicate expensive programming electronics.

Outback HUB

Computer Interface  Most high-end inverters can be monitored and programmed via computer, as long as you have the interface and the software to run it.  These are available for Xantrex SW & XW (sine wave) series and also the Outback series inverters.

Essential Accessories  Every inverter installation should have a way to disconnect the inverter from the battery (other than pulling the cable off the battery)  and should also have over-current protection. "Over-current protection" means a device such as a breaker or fuse that will disconnect the line if too much current (amperage) tries to pass down it.

Xantrex DC Disconnect

.  This will protect your inverter in case your batteries should have a fault (short circuit) and vice versa.  You can accomplish this with a DC breaker/disconnect installed in the positive cable from battery to inverter.  Remember to tape those cable together, as well. This reduces impedance and improves efficiency of your power transfer.

.  Also remember to connect an earth/ground cable to every component of your system (ie: inverter box, disconnect, controller, etc.) and to bond it with your AC ground & DC negative at only one point in the system.  You may also want to consider a battery temperature sensor which will connect to your Xantrex or Outback inverter/charger and regulate the battery charge rate to keep your batteries from overheating.

Xantrex Temperature Sensor

.  This is particularly important if your batteries will be installed in a hot place or if you will be charging at a high rate.  A battery capacity meter of some sort will also help your clients to better manage their energy use by showing the amp hours left in their battery bank.

Monitoring Meters

Load Management Exercise  Generally, the types of lamps recommended have a minimum lamp life of 15 years if used for 3-5 hours per day.  As energy saving lamps, the light lumens of these lamps when compared with their power ratings are almost unbelievable.  For example, the typical conventional 40 watts bulb produces about 425 lumens (compare 15watts Energy-saving lamp – 425 lumens). But the 35 watts energy saving lamp produces 4800 lumens.

LED Light

.  This is more than 10 times the illumination of the equivalent conventional bulb.  The reason is that energy saving lamps convert almost all the supplied electrical energy into lighting.  There is little or no heating, compared to the conventional lamps that convert only about 20% of the available electrical energy into lighting - wasting about 80% of the electrical energy in heat that is not required in this environment, thus resulting in shorter lamp life.

.  eliminating time spent monitoring batteries and inverter loads. It does this by continuously monitoring  the battery voltage, state-of-charge, or the inverter charge mode, starting and stopping the generator  when the battery needs additional charging. The XW AGS will also start the generator to assist the  system’s inverter/charger(s) when output power demands are high.

System Monitoring  The Xantrex XW Auto Generator Start (XW AGS) will automatically activate a generator to provide  an XW Series Hybrid Inverter/Charger with power to recharge a depleted battery bank or provideadditional power for heavy loads.  The XW AGS adds intelligence to generator management.

Xantrex Auto-Gen-Start (AGS)

.  The XW AGS can be customized to suit each user’s preferences. The user can define whether the generator should be activated by low-battery voltage, state-of- charge, thermostat operation, or load on the inverter(s).  A quiet-time setting prevents the generator from starting at inconvenient times.  LED lights display the status of the XW AGS, while all user-defined settings are programmed through the XW system control panel (XW SCP).

Xantrex System Control Panel (SCP)

Operational Features  Compatibility – the XW AGS connects to other Xanbus™-enabled XW System devices without requiring additional hubs, control cards, or other device-specific control panels.  Works with AC or DC generators with either two-wire or three-wire start controls  Configurability – comprehensive customizable triggers based on low-battery voltage, change in charging state, high inverter load, thermostat signals, planned exercise periods, max run-time, and quiet- time settings.

.  Non-volatile memory – preserves XW AGS settings even if the network power is interrupted or network communication is disrupted.  Note: The XW AGS requires an XW System Control Panel (XW SCP) for configuration and monitoring.

.  Features:  LED display showing at-a-glance status  20-contact generator connector and three built-in relays support 13 preset generator configurations  Built-in emergency shutdown  Xanbus™-enabled  Interfaces with:  XW Hybrid Inverter/Chargers, XW Solar Charge Controllers, and XW System Control Panel

System Diagram

.  Tech Notes. pdf

The End  Thank You.