[Bldg-sim] Real-time pv yield as a surrogate for irradiance

[David Reddy]

Yes, interesting idea and glad to see it discussed here.

This idea also occurred to us when evaluating PV systems on a number of 
buildings in Hawaii.  In that project, we were fortunate enough to have 
a solar monitoring site <http://www.nrel.gov/midc/nelha/> right down the 
street, and he had 15min and 1hour PV  energy generation for every panel 
(micro-invertors) on 15 different buildings, each oriented in the same 
direction.  However, some other issues, besides the one's Joe described, 
came to mind in trying to develop a model that linked the two:

  * In addition to temperature, PV panels energy production also
    degrades as the panels get dirty.  That seemed like the variable
    that is toughest to compensate for.
  * Data connection between the inverters to the cloud was pretty good,
    but we did find gaps a number of gaps; sometimes for up to a month
    or two.

Still yes, an interesting idea, and sounds like a good research project...
David


On 7/20/2015 4:07 PM, Joe Huang wrote:
> This is an intriguing idea (using PV output as a surrogate for 
> irradiance), but there are a number of complications that need to be 
> investigated:
> 1. PV efficiency degrades with temperature; therefore, you have to 
> have some way to adjust the output by the temperature of the PV (not 
> the air temperature)
> 2. you also need to adjust for the tilt and azimuth of the PV panels 
> to derive the equivalent global horizontal radiation.
> 3. you also need to split the global horizontal into direct and 
> diffuse radiation, which could be done using a number of 
> direct/diffuse split models, which is what's done for 99% of the 
> weather files anyway because I've yet to find any measured direct 
> normal radiation outside of strictly research applications.
>
> When I look at this list, all three could be done using a building 
> energy simulation program,  provided that you know the absorptivity of 
> the PV and its conversion efficiency as a function of temperature,  
> but at this point it's getting more hairy than calculating the solar 
> radiation from standard weather station data or, beginning in Sept 
> 2015 for US locations, downloading the solar radiation from NREL.
>
> I'm not being critical, and actually I am quite intrigued by this 
> technique, and would be happy to help evaluate how well it works.
>
> Joe
>
> Joe Huang 	
> White Box Technologies, Inc.
> 346 Rheem Blvd., Suite 205A
> Moraga CA 94556
> yjhuang at whiteboxtechnologies.com
> http://weather.whiteboxtechnologies.com  for simulation-ready weather data
> http://www.whiteboxtechnologies.com
> (o) (925)388-0265
> (c) (510)928-2683
> "building energy simulations at your fingertips"
> On 7/21/2015 2:21 AM, Justin Spencer wrote:
>> You can use anything you want as a surrogate, as long as you have 
>> some way of proving it works. In this case, if you could somehow get 
>> real time PV data for a set of sites that also had actual insolation 
>> and then looked at your results, I think you could derive a typical 
>> relationship that wouldn't lead you too far astray. The problem will 
>> come when there are passing clouds and the PV system is "hunting" all 
>> the time trying to catch up with the changing insolation. I bet you 
>> could find those and apply a bias correction that could then be used 
>> in multiple sites with real time PV data.
>>
>> On Mon, Jul 20, 2015 at 10:55 AM, Chris Yates 
>> <chris.malcolm.yates at gmail.com 
>> <mailto:chris.malcolm.yates at gmail.com>> wrote:
>>
>>     Ok, so there's no substitute for doing weather data right.
>>
>>     However, in the absence of such data, could real-time pv yield be
>>     used as a surrogate?
>>
>>     Chris
>>
>>     Sent from my Android device. Please excuse typos, etc.
>>
>>
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