[RE-wrenches] Sola-ark cold morning

Sun Dec 4 06:59:39 PST 2022

Dual - Discoverer LI battery bank not sure on battery mode setting (written down but cannot locate at the moment) & no backup generator. Very conservative & minimalist client.  I over designed past his energy load evaluation request on purpose as he did not want to have to use a generator. 

He has built the entire house off of 2 - small 12 volt PV systems & battery charging cordless tools. Living on site in the garage…

I am very impressed with his commitment to low impact & not a wackadoodle or survivalist either. Excellent classical, bluegrass, & jazz cellist.

Dana Orzel -  E - dana at solarwork.com -  C - 208.721.7003     

From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> On Behalf Of Mac Lewis via RE-wrenches
Sent: Sunday, December 4, 2022 7:41 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: Mac Lewis <maclewis1 at gmail.com>
Subject: Re: [RE-wrenches] Sola-ark cold morning

Hi Dana,

What type of batteries?  What battery mode?

If you have Lithium batteries with communication enabled, there are certain modes that the BMS is running the charging show.  I've seen the Sol-Ark throttle back charge as instructed by the BMS under these circumstances.  

A quick check of this would be to start the generator and see if it's on the battery management side or PV only side. 

It seems like you are way below the MPPT upper limit if Im looking at the correct QCell spec sheet.

As far as the temperature theory.  You can have temps on surfaces below ambient.  This can happen in two ways that I am aware of: radiation and evaporation.  The radiation effect occurs because the cold night sky (very cold) is exchanging heat with a surface.  This is why you can get ice on lakes above 32F.  It's very complex to model this but I doubt you could come close to lowering the temperature far enough to drive the Voc out of the MPP range.

Also, there will be competing heat exchange trying to drive that temperature back to ambient.  For example if you had a lot of wind in a clear cold night, the convection heat exchange from the wind would actually warm up the surface.

Evaporation (or any phase change) can drop an object's temperature below ambient as well.  It will pull latent thermal energy from objects in order to change the phase of the molecules.  This actually has a stabilizing effect on temperature typically because it takes a lot of energy to change phase.  This is why people use large water barrels in greenhouses to release latent energy to prevent freezing.

Please let us know what you find out.

Thanks!

On Sun, Dec 4, 2022 at 6:22 AM Dana Orzel via RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org> > wrote:

Hey Now All Wise ones!

An of gird client emailed yesterday that his Solark had been accepting only 350 watts of a 4KW input from the array. The modules are Q-cell 325 watt 2 strings of 7 modules.

Sunrise, full sun, no clouds so no edge of cloud effect, negative temps @ -6˚F, he waited all day with no improvement or change in the charge rate consistent 350watts input & then same thing next morning. Negative temps & full sun & 350watts solar input.

He turned the Solark off for 10 minutes & then turned it back on & 4KW charge input returned. The Solark did not turn off or deliver any alarm or warning.

My initial thought was over-voltage spike, we designed for a -25˚F scenario & 110 PSF snow load. Beefy! 

I did not ask if it was windy additionally. Could this contribute to a colder array temp? I have always been of the impression that wind chill did not affect metal or glass that it has to do with moisture being driven off.

Thoughts & suggestions?

Dana Orzel                              Great Solar Works, Inc. 

C - 208.721.7003                       dana at solarwork.com <mailto:dana at solarwork.com> 

Idaho Contractor - # 028765         Idaho PV # 028374

www.greatsolarworks.com <http://www.greatsolarworks.com/>             www.solarwor.com <http://www.solarwor.com>  

"Responsible Technologies for Responsible People since 1988"  

P Please consider the environment before printing this email.

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-- 

Mac Lewis

"Yo solo sé que no sé nada." -Sócrates

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