Solar Energy

Inverter should not be a problem, as it is a matter of adding more MOSFETs,and bigger size transformer, Input voltage rating of inverter should be high for 30KW power rating for better energy efficiency,

Infarct you can make it transformerless and get 110 volts AC direct with a push pull type oscillator, only thing you need to do is get a center tap from PV panel, this will make panels as positive and negative power supply.

You can google for PV panal details I think its about 100watt/sq meter of area.

Let me rephrase the question. A client needs to use a renewable (solar) energy system capable of delivering 30kws of power. I do know i need solar panels, charge controllers, inverters, batteries and the rest of other items. My question is how much would such a system cost and what is the best configuration in term's of inverters and system operating DC voltage.

I'm not sure about the cost but a neighbor just received a quote of, I think, about $44,000 (without battery backup) for a 9kw system. My 6 kw system installed 2 years ago, with battery backup, cost $64,000. My system operates on 48 volts.

I strongly suggest that you do more research on the micro inverters which reportedly operate more effeciently and partial shade does not have a system-wide effect on the array, as seems to be the case with the master inverter system. Get a couple of solar installation companies out to give you an estimate which, quite often, is free.

Thanks alot for your response. I will continue with my research. But the challange is most of these companies do not respond atimes. This system is intended for use in Africa-Nigeria to be specific.

Hi,

first,I think that you ought to re-rephrase the question.

Have the PV system need to deliver 30kW AC or DC power?

How long for?An hour,two or ten?

This will give you the kWh per day energy needs,which is the question.

Once you know how many kWh of energy your client needs and the days of autonomy,then I can work out for you the rest.

Cheers

Hi, thanks for you interest. Actually we need an off-grid solar energy system capable of delivering 30kws power. This system should have an autonomy of 3days. By my calculation, i do know we need solar panel's. I also do know i need inverters that convert this DC to AC. The solar panels will operate at 24volts, 280watts and we need about 140 units. The inverter's would be rated each at 24volts 8000watts and the quantiy would be four(4). Do not forget the charge controllers. What is left is to include the cables needed and the batteries to give a 3 day autonomy. All i need is for someone to give a detailed cost of the above mentioned items, if i've missed any points, please include. Will the choice of enphase inverters increase or lower the final cost of thie project.

Hi,

I still need to know how many hours a day you'll need them 30kW ?

Cheers

Hi, we will need the 3okws for atleast twelve (12)hrs each day. Regards

Hello,

I've calculated your system,but I think it's going to be big challenge and very expensive to be built.

1. Your total power needs per day is: 30 000W x 12h = 360 000Wh = 360 kWh.

2. Having 3 days autonomy ,gives you : 360 kWh x 3 = 1 080 kWh = 1.08 MWh !!!

3.To insure enough energy, in 24V arrangement ( which in my opinion is completely not sufficient ,as the lower the voltage - the higher the current , therefore bigger power loses and bigger cables needed.

To avoid this,the best option is to have higher voltage,say 96V , thus reducing the currents.

In your case, a 24V battery arrangement has to have a minimum capacity of 49 827Ah - the arrangement should be 2 batteries in series by 250 packs in parallel ,giving a total number of 500 ( 12V/200Ah) units!That itself weights about 32.5 tons.

4. To charge the batteries , you'll need a minimum of 100 kWp of PV power.Thus is 358 pieces of 280Wp/30V PV modules - all in parallel.

5.Dont know if you still need me to work out your controllers,but if you do,let me know.

About the microinverters, the problem there is,that they cant work off-grid,as they are implemented in the module itself,and the output is 110/230V AC .So you have no way to charge your batteries during the day.

Take care

Dear Amigo,

Sincerely, i must thank you for the insight you have given me. I am most grateful. Well what i had in mind was to use four 8000watts inverters operating at 48volts or five 6000watts inverters operating at 48volts. For these i would stack them to obtain the required 30kws.This is because i imagined that using a single 30kws inverter would be a bit difficult to handle. The solar panels would be used to charge the batteries in the day time or still power the load. We have good sunshine here being in the tropics, West Africa, while in the night the load will run off the batteries. I am supposed to make a presentation by next week, but with your explanation this would be a very expensive project to undertake. Can i have your take on this.

Regards

Hello Chike,

You can use any good inverter of your choice.Most off-grid inverters can work in parallel ,so reaching the output power needed should not be a problem.

I dont think you'll find single off-grid inverter as big as 30kW on the market.But even if you do,they will most probably be 3 phase for sure.

When working off-grid, just remember, that the only job of the PV array is to charge the batteries. All you need to worry about is to insure, that your charge current is always greater than your discharge current! That is the basic rule with the battery powered systems.

The other important thing when sizing the battery pack ,apart from using AGM type maintenance-free batteries, is to insure long and healthy pack life,you should NEVER discharge more than 30% of the full charged state of each battery! 25% or 20% is even better.

The rule is : Deeper the discharge - shorter the battery's life.

Hope that will help you with your presentation.

Cheers

Enphase Inverters are great ... I must be honest ,,we are installers and use only Enphase ... but only on Grid Tied Systems !

These Type of Inverters are GRID INTERACTIVE which means they need the line voltage and frequency of the grid to function ...

If you are off grid ..they do not work ... their are ways around it though ...:)

The Enphase Approach or Topology is an inverter per panel ..this allows for individual MPPT Maximum Power Point Tracking of each panel ... in simple terms .. this means that each panel can operate up to it's maximum potential without the effects of the other panels in the string ... the other panels may not be electrically the same when it comes to their output ... the analogy here is a stagecoach being pulled by 6 horses ..the stagecoach can only go as fast as the slowest horse ... so if any of the panels in a string array ( where the panels are connected in a series arrangement ) goes low due to shading or debris or snow ( not in Nigeria I suspect) it will affect the output of the string ... Enphase has a number of papers on their web site that explain it much better than I can ..

The topology of individual Inverters or MPPT devices at each panel will be the future in my opinion .as a matter of fact there are compnaies now manufacturing AC Panels here in Canada ... direct AC from the panel....

The future is bright for Solar

Hi ceeg052351,

may I ask,in your practice, now many microinverters can you connect in parallel maximum?

I've heard that the number is between 15 and 20.

In other words,what is the largest PV plant that can be built with Enphase microinverters?

Cheers

Amigo : I suppose I should start by suggesting that the way Enphase units are "strung " together is in what they call "Branch Circuits" I suppose they want to stay away from the Central Inverter Terminologies !

You see that in the Central Inverter arrangement all panels are wired in parallel with the output voltages from the panels adding up to a maximum of around 600 volts DC for an input to the large central inverter. This is a wiring nightmare at times as you can imagine.

Since the Enphase Inverters "INVERT" at the panel the output is .... say 240 volts AC ....(I picked that one as they have a 208 version also that you would use for a multi phase connection to the grid since in the US and Canada its 208 VAC between phases) ...The 240 Volts AC produced by each inverter is then connected in parallel with the next inverter and so on ... think of it as a 240 VAC BUSS BAR ... the maximum number of inverters is 15 ( for the 208 volt AC units its 21).... you then take each branch circuit and parallel them through the appropriate fusible disconnect ... this then connects in effect ..to the grid ...

Now to complicate things ...Enphase have come out with a dual M190 ..they call the D380 ...it's just a double M190 in one case ... they have a slightly different wiring setup for these but in the end it's the same thing ..

When contemplating a large system one should look at doing it in 3 phase if you are connecting to the grid ... remember you must balance each phase which means the total number of panels/inverters must be divisible by 3 ...

So to answer your question ... there is NO LIMIT

Thanks for your answer ceeg052351 .

Just to correct you, by saying that " all panels are wired in parallel with the output voltages adding up..." you've probably meant, that the panels are wired in series,until the voltage reaches 600V DC and thus forming a string,and then all strings are connected together in parallel via combiner boxes and fed to the inverter?!

Whatever,I know what you were saying.

Its a big pain in the neck to work out all loses,cable sizes,protections and string configurations to insure maximum power output at minimum costs.

A big advantage with the microinverters is that there is no DC part to worry about.Also as you've said, each inverter works at its own MPP - which is a hard work for the central or string inverters.

As a downside I see their higher prices per Wp ( I have no doubt that Enphase work hard to change that!)

What is the maximum power dis-balance allowed between the phases in Canada? In Europe it is 4.6kW to 5kW.

Thanks

Dear Amigo,

It's been a wonderful experience having this chat with you. Hope to have another season with you soonest.

Regards.

No problem.

I'd be glad to help if I can.

Take care