Are Retscreen and PVWatts Accurate???

[aradsma]

I am investigating a large PV project in Ontario, Canada. I am trying to evaluate the revenue that I can expect various systems to produce, but I get different results from PVWatts and Retscreen. For example, Retscreen says a 250kw system will produce revenue of approximately $240k per year (inputting the numbers provided by those quoting on systems) and PVWatts, using the standard 0.77 derate factor tells me it will generate $190k in revenue. Is there really an accurate way to determine what the system will produce? Are either of these models accurate (if you put in the right information)? What are some good values to enter in Retscreen to make sure it is somewhat accurate?

Does anyone have a comparison of estimated values from a program with actual results from the field?

[Mike90250]

I only know about PV watts, and that they have input weather data into their months, it's not just straight sun angles vs site. What they cannot do is adjust for installed conditions, like un-vented panels flat on a roof, or trees. They use the weather data from about 10 years of reporting, and add your site angle and elevations, and caculate your power.

[lile001]

I am investigating a large PV project in Ontario, Canada. I am trying to evaluate the revenue that I can expect various systems to produce, but I get different results from PVWatts and Retscreen. For example, Retscreen says a 250kw system will produce revenue of approximately $240k per year (inputting the numbers provided by those quoting on systems) and PVWatts, using the standard 0.77 derate factor tells me it will generate $190k in revenue. Is there really an accurate way to determine what the system will produce? Are either of these models accurate (if you put in the right information)? What are some good values to enter in Retscreen to make sure it is somewhat accurate?

Does anyone have a comparison of estimated values from a program with actual results from the field?

My local power company has a 5000 watt grid tied array

http://www.gocolumbiamo.com/WaterandLight/Electric/SolarOne.php

Last year's production agrees with PVWATTS amazingly well.

Note that $240 * 0.77 = 184, or about what PVWATTs is reporting. For a large system like that, you should probably be able to get efficiency numbers for the inverter manufacturers.

For a system of this size, do you have a Professional Engineer involved? If I was registered in Ontario, I'd offer my services.

Lawrence Lile, PE

[aradsma]

Retscreen is a program put out by the Canadian government for assessing all types of renewable energy projects. It also takes into account historical weather data and different derate factors such as panel efficiency, lines losses, inverter losses, etc.

For example (see attached PDF):

Solar panel efficiency (Sanyo Mono-si 210) 16.7%
Nominal operating cell temperature

[Sunking]

77% is an average efficiency for a grid tied system, the actual percentage will be determined by the actual selection of components, shading, distances, wire length runs etc. Only the engineer in charge will be able to give you the actual number which will be between 70 and 80%.

[sr20bet]

[QUOTE=aradsma;7965]Retscreen is a program put out by the Canadian government for assessing all types of renewable energy projects. It also takes into account historical weather data and different derate factors such as panel efficiency, lines losses, inverter losses, etc.

For example (see attached PDF):

Solar panel efficiency (Sanyo Mono-si 210) 16.7%
Nominal operating cell temperature

[russ]

With PV Watts the great majority of the derate factor is the adjustment for panel output under standard conditions (1000 watts/m2) and real conditions (maybe 800 watts/m2) I believe.

You rarely see 1000 watts per m2 and then only for a few minutes at the peak period.

PV Watts outputs seem to parallel NASA historical data.

Russ

[TAB Mech]

System Analysis

Presently my firm uses two pieces of software to do design for the systems that we install here in Ontario. First a shading analysis is performed at site using the Solmetric Suneye. The data collected with this device than can be downloaded to the Solmetric design software for systems up to 15 KW. The majority of the time, we use the Polysun software package which also accepts the shading input file. We have used the Polysun software on designs from 1 KW to 10 MW. Presently we have been confirming the results of the software against th actual installations an are happy with the results.
We generally only use the RETscreen or as we refer to it RETscream!! when required by the client. Basically speaking free software gives you outputs reflecting how much you paid for the software in my opinion.