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Glossary of Alternative Energy Terms
Download the Glossary of Alternative Energy Terms
What is a Power Inverter?
An Inverter is able to convert battery voltage (DC) to alternating current (AC) e.g. 220V AC/50Hz. This may be achieved in several ways. This may be achieved in several ways depending on the available technology and the intentions of the designer. Basically we have three major types of power inverters, namely: Square wave, Modified Square Wave and Sine Wave
What is a Square Wave Inverters:?
The output of these inverters is a square voltage of 220V AC/50Hz. The regulation of the output voltage is often very inaccurate and directly depending on the input voltage and on the output load. Square Wave Inverters may have very high efficiency for purely resistive loads ( cos phi = 1, e.g. heaters). Switch mode power supplies like he types in computers (as load) may also give good results if the EMI regulations are met by the inverter.
Loads that have problems when used with square wave inverters:
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- Any loads with cos-phi other than 1 ( inductive or capacitive loads, eg fans, refrigerators, and Fluorescent lights with chokes)
- Energy saving lamps and other loads with capacitive voltage dividers. Current peaks caused by very steep voltage slopes cause massive reduction of their life time.
- Interference (white stripes etc.) and audio noise in Hi-Fi, video or TV units.
- Loads with phase control, sensitive electronics.
- Electric motors, there are two major problems: Motors running very hot due to current peaks caused by square wave, motor bearings wear out quickly due to torque variations.
What is a PWM Inverters, Modified Square Wave Inverters, Adapted Sine Wave Inverters?
All of these inverters have in common the sharp voltage slopes of the square wave inverters. The word “sine” is only introduced by marketing people. The only advantage of these inverters is the regulation of the output voltage independently of input voltage and load.
What is a Pure Sine Wave Inverters?
This technology is state of the art for several years now. There is no reason for any other inverter technology except price. The pure sine wave is a “natural” waveform as created by any power station available at your home wall socket.
ANY MAINS LOAD AVAILABLE WAS CREATED FOR USE WITH SINE WAVE ELECTRICITY!
Sine wave inverters are more complicated to build thus resulting in increased manufacturing costs. The sine wave shape is synthesized by an additional PWM filter at the output of the inverter. Idle consumption is slightly higher than square wave inverters. The biggest advantage is found in the high efficiency and hassle free operation of almost any load.
More technical details (Overview):
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- 50/60Hz technology: Isolation and voltage step between DC and AC side is achieved by iron transformers. Very high safety standard. Increased lifetime due to reduction of semiconductors. Battery acts as storage for reactive currents. The only disadvantage is the high weight of iron transformers.
- High frequency technology: These units utilize a HF transformer for the isolation/voltage step. Reduction of weight but increased number of electronic parts. Efficiency is similar to 50/60 Hz technology with resistive loads but there is no chance to use the battery as storage for inductive currents. Loads with low cos phi can cause problems.
- High frequency inverters without isolation between DC/AC: Only used in cheap products. Not recommended for safety reasons, no up to date technology.
What is a Inverter / Solar Battery?
Inverter or Solar battery like any other battery is a piece of device for storage of energy for use when needed. To this end an inverter battery or solar battery must have the ability to charge and retain charge very fast. I will also be able to deliver the charge as needed during usage.
Types of Batteries:
There are several types of batteries, but we can only explain the major types based on our topic here. There are basically two types: Deep cycle and shallow cycle.
What is a Deep Cycle batteries?
Deep Cycle batteries have fewer and thicker cells. This ability gives it the resistance to deliver charge to the inverter to a larger extent, up to 60% or 80% dept of discharge without a defect on the plates or the cells.
What is a Shallow cycle batteries?
Shallow cycle batteries or traction batteries have high numbers of thin plates or cells with the ability to discharge with high current for a short time. A prolonged discharge will normally cause the cells to damage. The shallow cycle batteries are best for car starting.
How to choose the right batteries?
Batteries for inverter or solar energy usage are best rated from 100ah.
Inverters should be operated on batteries of appropriate size. The battery should be cycle proof. Generally, for lead acid batteries: the shorter the discharge time, the lower the energy usage. E.g.: If a battery can deliver 10 Amps for 10 hours, it will deliver 100 Amps only for 20-30 minutes. You should choose the battery size for an operation time of several hours with your estimated load. Additionally, you should only allow for a discharge down to 60 to 70% of full capacity in order to increase battery lifetime. E.g: The lifetime of a battery may be 5000 discharge cycle with 20% discharge per cycle. The same battery will only live for approximately 2000 discharge cycles if every cycle is 40% discharge.
What does a Battery Fuses do?
Battery fuses should be placed as close as possible to the batteries in order to protect the whole battery cable. In case of cable short, fire might occur! It must be rated 25% above the expected maximum energy draw from the battery bank. DC rated fuses are the best for inverters.
How to choose the right Battery Cables?
DC current in battery cables causes voltage drop according to Ohms law V=R*1. As general guidance: 1m of cable 25mm2 has approximately resistance of 0.001 Ohm. This value multiplied by battery current results in voltage drop. Example: PRC 3000/24 with nominal load, DC current approximately 125Amps, 1.5m distance from batteries, V=2*1.5*125*.001=0.38 volts, heat dissipation in Cables 60Watts approximately! This application should have 35mm2 or even 50mm2. Place the inverter as close to the battery as possible. Use inverters with higher input voltage if possible. The higher the input DC value the less the current loss from the cable as the efficiency is increased.
What is a Cos Phi?
With heavy inductive loads, the product V*1 (VA on the AC side) is much larger than the actual watts delivered. E.g. Inductive motors, fluorescent lamps, etc. This means some of the energy is stored in the inductivity of the load and then flows back to the battery. These inductive currents cause heat dissipation in the power semiconductors and in the cables as well. As the capacity is used up for reactive currents, there is “no room” for active currents.
WHY DOES MY 600VA INVERTER NOT WORK ON A LOAD DECLARED 600W?
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- With inductive loads the VA value is bigger than the Watts value. E.g. 600W load, cos phi 0.6 results in 1000VA!
- With motors often the mechanical output is declared so the VA rating is even higher.
- Another cause for malfunction is inrush currents (5 to 10 times nominal current with motors).
How can inverter bw conneted in a parallel?
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- Stand alone inverters: Paralleling is only possible on the DC side; AC sides always have to be isolated. Never connect your mains to the inverter output or connect the out puts of two stand-alone inverters together, immediate destruction will result.
- Grid feeding inverters: Paralleling is possible on the AC side. DC Paralleling is not POSSIBLE since MPP optimization has to be performed by every single inverter on its solar field.
- Some inverters are however designed to be connected in parallel with some special connection meant for frequency synchronization and power out put interconnections.
- Check out for some models of Xantrex, ASP, and Victron inverters for more information.
Is there a need for series diodes on a solar field?
No! Fuses for each string of solar modules are sufficient. Use twice the string current for fuse. Series diodes are only heat dissipaters. By the way, parallel diodes are built into the junction boxes of most solar modules.
Why does a grid connected inverter need earth connection with heavy (25mm2) cable?
The main function of the earth connection cable is lightning protection and interference suppression. The solar panel field acts as an antenna that may transmit interference caused by switching slopes in the inverter. The inbuilt filter circuitry is only active with an appropriate earth connection.
Why does the automatic load sense circuitry not sense some load?
There are some limits to the load sensing circuitry. Since the internal measuring circuits are used for several different purposes, the sensing of very small loads can cause a problem for the inverter. Drifts of the sense circuitry over temperature and voltage may also cause drift.
Some of the energy saving lamps have a very bad cos phi.
Some loads are detected correctly but turn off after 10 seconds because the operating current is lower than the inrush current.
Often the problem is solved by using a different brand of lamps. We will improve load sensing with the next generation of inverters.
What is a Converter:
A piece of electronic device meant for DC/DC conversion e.g 12VDC 10Amps/24VDC 5Amps.
What is a Voltage Transformer:
Transforms or steps AC voltage values from one level to another using transformer e.g. stepdown transformer: 220VAC to 24VAC. Step-up is simply the reverse.
What is a Voltage Adapter / Rectifier:
Changes AC voltage to DC voltage e.g. 220VAC/24VDC. The input value may be the same as output in terms of voltage level.
