Why Would an Inverter Be Strictly Photovoltaic?

A good answer.

I think that in Solar source Batteries are used to store energy and Inverter runs on batteries; which is considered a constant voltage source.

PWM has a lot of protocols.

Pay in what way? Efficiency losses or just through the nose? I'm already finding I'm at $100,000 USD just for starters...

Thanks for the very informative and understandable answer!

You are mistaken about the ability of modern inverters.

they often produce "higher" AC output voltage than DC input voltage.

They can reduce amperage to increase voltage, and vice versa

Voted GA for you JRaef, that was a great explanation. You are correct, the inverter would not only be photovoltaic, my Xantrx does search for the most efficient power signal needed through the inverter at a point in time. If my panel array (and wind turbine) DC feed in is kicking in more than what is needed, then it does not tap into in my battery bank it uses the DC straight from the panels/turbine. If that isn't enough DC input to invert to AC (or pulse in a wave form as you wrote), then the Xantrex goes to the battery bank.

I am curious though, there are some units available that state "true sine wave" and I have never asked this question before - are those units transforming a near perfect wave with on/off blasts, or are the components really making an AC sine wave?

Matt

Hi Matt,

There are some units available that state "true sine wave"

An inverter that produces a "True Sinewave" does so by using a DC inverter to produce negative and positive DC supplies for a sine wave oscillator controlled linear amplifier to produce a low distortion noise free sine wave output at the desired amplitude and frequency.

I used true sine wave Frequency Converters in my work.

Input from 120 Vac 60Hz line converted 115Vac 400Hz (or whatever the Oscillator unit wants to do) Lots of big transistors on two big heatsinks that use negative and positive supplies of a couple hundred volts each to produce a low distortion noise free sine wave.

One of the oscillator modules available was variable frequency.

I probably could have fed music through it like you can with most most linear amplifiers.

Jon

Jon,

Thanks for explanation - so that's why they cost so much more than ones that don't say true sine wave! GA Jon.

Matt

Yes, that is what the Xantrex lady said, that the "best" they might have to work with our device would be something that actually puts the DC into a battery pack, then used them to feed the inverter for grid supply.

Ok, firstly do you realize how much power 100 kW is?

Would you like to outline say how many houses or factories your project might power? Work on 1 house needs about 2kW to be power neutral - so 50 houses?

Secondly I don't think what you are hearing/relating is what they are saying.

Nearest to what they are saying (at a guess) is in the low or high array output state the inverter tries to stay on-line (outputting AC to the grid), by altering it's current by altering its voltage. It shuts off it it can't. This 'ride thru' is about a cloud masking part or all of the array for a short time.

The most likely reason for the "disclaimer" is backup generator output is not suitable as a DC input without a battery bank of massive capacitors to smooth out frequencies or spikes that would/could upset MOSFETs triggering. If this happens the output goes out of phase with the grid and MASSIVE currents develop - frying everything.

If indeed you are thinking 100kW⁺ I seriously recommend you purchase an expert.

Your array output is more than enough to fry you. Probably 500 volts nominal by 200 amps. This is not a "12 volt" system.

GA, I think you've got it right. It's about the smoothness of the supply.

Well, for what we are seeking to do our unit will have a continous power rating at 454kW AC, nominal DC power rating 470kW DC, nominal voltage 480 Vac 3-phase, nominal AC Freq. 50/60hz, maximum line current 946 amps AC, max open circuit voltage 500Vac -- these are preliminary specs extrapolated from our test unit -- we expect less than 1% fluctuation in power output because we are solid-state thermoelectric

Obviously the circuit doesn't know where it's power is derived (one electon looks much the same as another) however maybe there is something about the characteristics of photovoltaic sources which is less prone to problems than say a bank of lead acid batteries which has a very low internal impedance.
E.G the circuit may have been designed to match a photovoltaic source.

Maybe it's the voltage range and variation which is the key?...I dunno I jus' a Cat.
Del

"something about the characteristics of photovoltaic sources" - yep

A nominal 12 volt panel open circuit voltage may be 160 volts, so if you are 'switching' the array output - it can get interesting.

Out of batteries is much easier circuitry, but 100kW at 500V is a lot of AA cells.

I'd say some cocky decided to hook up the old clunker Genny and blew the crap of the thoroughbred circuit - hence .... Can't blame em, it's cleaver stuff, just not 'fool proof'.

^{Sorry Cat - I tried to resist but am just too weak}

Apparently you can buy this one off one; http://whois.domaintools.com/electon.com ER Rules!

The reason for the "Disclaimer" is very simple. No rocket science required. Photovoltaic sources are high impedance sources.

The standard method of voltage regulation for PV is to short out the panel, the impedance (resistance in this case) is so high that the output voltage is easily controlled.

The high impedance allows for use of cheap components, as the inrush is limited by the impedance. The importance of this feature is that the grid which you are typically generating into is a low impedance sink, basically a dead short. If the grid voltage falls even slightly and the source, (say a motor driven alternator) is also low impedance then a large current fill flow from source to sink attempting to maintain voltage. If the grid voltage falls to zero, then the low impedance source will try its guts out to hold up a mountain and get killed for its effort.

OK, so where does this leave you if you have a battery backed or wind or motor driven (low impedance) system?

Strategies.

1. Seperate the batteries from the grid connected system and give the batteries priority. Or stay off the grid entirely.

2. Use smaller redundant inverters to supply specific load. Modify the load so the inverter is only running when needed. For instance use extra low voltage controls to activate the inverter and avoid quescent current losses.

3. Utilise specific PV circuits for dedicated purposes with excess power dumped to the main system.

4. Use native extra low voltage devices where possible eg Danfoss refrigeration compressors, LED lighting, ELV pump motors. A very powerful (domestic) refrigeration system can be built using staged BD50 Danfoss compressors at 24vdc.

5. Use only just enough power to get the job done.

6. For a stand alone situation keep a low impedance source, eg a 5 kva Honda set, in reserve for adnormal situations.

7. In grid connected situations elect to take over supply to functions such as water pumping from the grid rather than signing up for the package. If the supplied inverters fail to harvest as promised, you would hardly notice it when supplying the grid as the grid will automatically make up any shortfall. Only the bill will remind you.

Grid connection of PV is being marketted and attractively financed at improved margin due to the ability to delete on site storage and consequential cheap inverters.

Comrade Col. Clamrod,

I was just messing with my spare UPS and just connecting a 20 amp current meter between the battery and the UPS upsets it The UPS with its load draws 8 amps.

So, as was mentioned in an earlier post, the UPS for a Photovoltaic source is designed to operate from a "soft" power source.

Even with the right amount of Voltage and current a Battery type UPS would have to have input circuitry to fool it into thinking it had a very low impedence source.

Kuduk