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Solar Inverters

Grid tie solar inverters convert the DC voltage from the solar panels directly into standard AC voltage and feed into your house power, without the use of batteries. "Utility Interactive solar Inverters” use batteries and can also tie to the grid to feed back any extra power, or as backup power. While off grid solar inverters basically convert solar DC into standard AC voltage and feed into your house power while also charging the batteries or charges the battery and convert battery DC to house usable AC voltage.

Inverters
inverters are electrical or electro-mechanical device, it does not generate power but rather converts direct current which could be solar -from the sun or stored energy in battery current (DC) to alternating current /Nepa (AC); the resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.
Static inverters have no moving parts and are used in a wide range of applications, from small switching power supplies in computers, to large electric utility high-voltage direct current applications that transport bulk power.
Electrical inverters are high-power electronic oscillator. It is so named because early mechanical AC to DC converters were made to work in reverse, and thus were "inverted", to convert DC to AC. Inverters performs the opposite function of rectifiers. Solar inverters therfore are inverters that makes use of sunlight in generating DC current that is converted to AC.

Definitions

Watts
Watt is basically a measure of how much power a device uses when turned on, or can supply. There is no such thing as "watts per hour", or "watts per day". If a device uses or supply 100 watts, that is simply the voltage times the amps. If it pulls/supply 10 amps at 12 volts, or 1 amp at 120 volts, it is still 120 watts. A watt is defined as a bunch of Joules per second, so saying watts per hour is like saying "miles per hour per day".
Watt-hours
A watt-hour (or kilowatt hour, KWH) is simply how many watts times how many hours that is used for. This is what most people mean when they say "watts per day". If a light uses 100 watts, and it is on for 9 hours, that is 900 watt-hours. If a microwave uses 1500 watts, and runs for 10 minutes, that is 1/6th of an hour x 1500, or 250 WH. When you buy power from your friendly utility (look at your last bill), they sell it to you at so much per KWH. A kwh is a "kilowatt hour", or 1000 watts for one hour (or 1 watt for 1000 hours).
Amps
An amp is the SI unit of electric current intensity. Electric current is measured using an ammeter (Amps do not come in "amps per hour" that will be saying rate of current flow per second per hour or "amps per day" either). Amps are important because it determines what wire size you need, especially on the DC (low voltage) side of inverters. All wire has resistance, and current flowing through a wire generates heat. If your wire is too small for the amps, you get hot wires. You can also get voltage drops in the wire if it is too small. This is not usually a good thing. (An amp is defined as so many electrons per second).
Amp-Hours
Amp-hours (usually abbreviated as AH) are what most people mean when they say "amps per hour" etc. Amps x time = AH. AH are very important, as it is the main measure of battery capacity. Since most inverters run from batteries, the AH capacity determines how long you can run.
Peak Power vs Typical or Average
Inverters needs to supply two needs - Peak, or surge power, and the typical or usual power.

  • Surge is the maximum power that inverters can supply, usually for only a short time - a few seconds up to 15 minutes or so. Some appliances, particularly those with electric motors, need a much higher startup surge than they do when running. Pumps are the most common example - another common one is refrigerators (compressors).
  • Typical is what inverters has to supply on a steady basis. This is the continuous rating. This is usually much lower than the surge. For example, this would be what a refrigerator pulls after the first few seconds it takes for the motor to start up, or what it takes to run the microwave - or what all loads combined will total up to. (see our note about appliance power and/or name tag ratings at the end of this section).
  • Average power would usually be much less than typical or surge, and is not usually a factor in choosing inverters. If you run a pump for 20 minutes and a small TV for 20 minutes during a one hour period, the average might be only 300 watts, even though the pump requires 2000. Average power is only useful in estimating battery capacity needed. Inverters must be sized for the maximum peak load, and for the typical continuous load.

Power Ratings of inverters
Inverters come in size ratings all the way from 50 watts up to 50,000 watts, although units larger than 11,000 watts are very seldom used in household or other PV systems. The first thing you have to know about inverters is what will be the maximum surge, and for how long. (More about 230 volts pumps etc later).

  • Surge: All inverters have a continuous rating and a surge rating. The surge rating is usually specified at so many watts for so many seconds. This means that inverters will handle an overload of that many watts for a short period of time. This surge capacity will vary considerably between inverters, and different types of inverters, and even within the same brand. It may range from as little as 20% to as much s 300%. Generally, a 3 to 15 second surge rating is enough to cover 99% of all appliances - the motor in a pump may actually surge for only 1/2 second or so.