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Modelling of roof top solar photovoltaic plant in eQUEST

asked 2014-09-16 05:07:27 -0500

Ashok Dhayal's avatar

updated 2015-07-11 14:50:13 -0500

I have modelled 157.5 kWp roof top SPV plant in eQUEST with three electric generators of 52.5 kWp and three inverters of 93% efficiency. Each electric generator of 52.5 kWp is having 210 modules (1 module=250 Wp ) connected in series and parallel combination, i.e. 15 in series and 14 in parallel.

After simulation, In .SIM file, I found that the ratio of inverter output(AC kWh) to inverter input (DC kWh) lies between 60%-75% despite of 93% inverter efficiency.

  1. Would you please answer why 25%-40% loss is shown through inverter?
  2. Is there any option for battery in eQUEST for SPV plant modelling?

Inverter Specifications:

Capacity per inverter : 50 kVA; Efficiency: 93%; Inverter control : Run when needed; Minimum ratio: 0.02; Maximum ratio: 1.0752

Here are the relevant sections of the inp file here.

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@Ashok Dhayal please update your question to show what are the characteristics of the inverters... I've never modeled PV in eQuest but an obvious reason for your problem would be that the inverters are too small compared to your array, which limits the output. This is often called the Actual DC to AC Ratio = Total nameplate Array capacity in DC kWp / Total Nameplate Inverter Capacity in DC kW. A fairly typical value would be around 1.2 or so.

Julien Marrec's avatar Julien Marrec  ( 2014-09-16 07:24:36 -0500 )edit

Inverter specifications:

Capacity per inverter : 50 kVA Efficiency: 93% Inverter control : Run when needed Minimum ratio: 0.02 Maximum ratio: 1.0752

Ashok Dhayal's avatar Ashok Dhayal  ( 2014-09-17 01:38:37 -0500 )edit

Can you share the full .inp section in question? It'll help finding what's wrong. Could be that your inverters Min/Max tracking volts are wrong for your arrays

Julien Marrec's avatar Julien Marrec  ( 2014-09-17 09:05:42 -0500 )edit

I am using default EIR=f(PLR) curve. Please write me how to update this curve if required. Since karma is less than 10, I could not upload .INP section. Would you please write me your email address ?

Ashok Dhayal's avatar Ashok Dhayal  ( 2014-09-18 00:45:06 -0500 )edit

There you go, karma at 11. But you can just include the code (the text) itself in your question. If too long, put a link to a pastebin for example.

Julien Marrec's avatar Julien Marrec  ( 2014-09-18 02:43:57 -0500 )edit

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answered 2014-09-18 04:46:47 -0500

updated 2014-09-18 04:50:46 -0500

The problem right now is on the electric meter. By default, eQuest will put the COGEN-TRACK-MODE on "Track Electric Load".

In your case, and provided you can feed electricity to the grid (net metering, feed-in tariff) or to approach the effect of battery storage (to my knowledge you cannot explicitly model battery storage), you want COGEN-TRACK-MODE = MAX-OUTPUT (Run at maximum), which will allow your generator to produce more power than your building demand. You probably will want to get that straight for your specific needs, and also assign the proper utility rate configuration, including BUY/SELL-MODE.

Doing this will increase your ratio of inverter output(AC kWh) to inverter input (DC kWh) from 76% to 88% on generator 1 for example.

You're not seeing 93% and that's perfectly normal. There are two explanations:

  • Inverter clipping: which is when your inverter is saturated. This won't be the case for you because your Actual DC to AC ratio is basically 1. The industry tends to use 1.2, meaning there could be times where this happens.
  • Array producing a too low voltage which will derate the inverter's efficiency, or so low it will even shut-down.

In eQuest you want to look at the operating limits and conditions:

MIN-OPER-VOLT specifies the minimim input voltage below which the inverter will shut down.

MIN-TRACK-VOLT specifies the minimum input tracking voltage at which the inverter can operate efficiently. Below this value, the inverter can still operate, however its efficiency will drop linearly as a function of the actual input voltage

MAX-TRACK-VOLTS specifies the maximum input tracking voltage at which the inverter can operate efficiently. Any input voltage above this value will be limited to this value in the power conversion calculations.

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hey Julien, Many thanks for your reply, i will apply changes in model and let you know results for dicussion as soon as possible.

Ashok Dhayal's avatar Ashok Dhayal  ( 2014-09-18 06:53:29 -0500 )edit

@Ashok Dhayal: any news?

Julien Marrec's avatar Julien Marrec  ( 2014-09-23 02:55:53 -0500 )edit

thanks Julien, I got generation as per your claim.

Ashok Dhayal's avatar Ashok Dhayal  ( 2014-09-26 07:40:03 -0500 )edit

what percentage of battery loss and other losses are counted in eQUEST for modelling of SPV plant ? (please reply with source)

Ashok Dhayal's avatar Ashok Dhayal  ( 2014-11-15 03:37:31 -0500 )edit

@Ashok Dhayal: I think it'll be better to open a new question for this...

Julien Marrec's avatar Julien Marrec  ( 2014-11-17 01:44:01 -0500 )edit

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Asked: 2014-09-16 05:07:27 -0500

Seen: 1,130 times

Last updated: Sep 18 '14