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

[Joe Huang]

Another note I forgot to mention:  how easy is it to get the hourly 
output from the PV panels?  If the need for the solar radiation data is 
to evaluate actual building DSM, then the PV output data would have to 
have been collected at the same time as the utility billing data.

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 7:07 AM, 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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