Re: [TRNSYS-users] Question about H2 electrolyzer Type 160

Thanks, David.

I have got some reply from other researchers that the Faraday loss is mainly resulting from the unwanted chemical byproduct during the electrolysis process, and thus they are not accounted as heat generation in the electrolyzer (Although some unwanted chemical reactions indeed release some heat).

This is the reason that the heat generation in the electrolyzer model Type160 is calculated as "Pely*(1-eta_e)" rather than "Pely*(1-eta_tot)".

Kind Regards,
Sunliang Cao

Date: Thu, 20 Nov 2014 14:54:07 -0600
From: d.bradley@tess-inc.com
To: trnsys-users@lists.onebuilding.org; caosunliang@msn.com
Subject: Re: [TRNSYS-users] Question about H2 electrolyzer Type 160

Sunliang,
In the Type160 code, the equation for the heat generated by the electrolyzer is qGen = nCells*Iely*(Vcell-Vtn)

where Iely is the electrolyzer current, Vcell is the cell voltage and Vtn is the thermoneutral cell voltage. The Faraday efficiency is computed from:

eta_f = idensity**2/(a1+idensity**2)*a2

where idensity is the current density of the cells (Iely/Acell)

I think that both the Faraday efficiency and the heat generated are a result of the computation of the cell voltage and the stack current. Therefore I think that the heat generation is correctly computed and that the confusion may be in the definition of the energy efficiency and the total energy efficiency.
Kind regards,
David

On 11/20/2014 07:36, SUNLIANG CAO wrote:

Dear all,

I have a question about the H2 electrolyzer model Type160. Shortly: Will the Faraday loss of the electrolyzer be converted into heat in the electrolyzer?

In the electrolyzer model (Type 160 written by Ulleberg) [1], there are three efficiencies: eta_e, eta_F, and eta_tot:

“eta_e” is the energy efficiency of electrolyzer without considering any Faraday loss, i.e. the maximum theoretical proportion of the electricity which can be covered to the hydrogen energy content.

“eta_F” is the Faraday efficiency: it is the ratio of the real final produced H2 energy content to the theoretical maximum produced H2 energy content.

“eta_tot” is the total efficiency of the electrolyzer: it is equal to “eta_e*eta_F”, and thus is the ratio of the final produced H2 energy content to the electricity consumed in the electrolyzer.

In Ullerberg’s model [1] (TRNSYS Type 160), the heating generated by the electrolyzer is calculated by the P_ely*(1-eta_e), which hasn’t taken the Faraday loss into account. However, according to the energy balance, the Faraday loss must be somewhere, which mostly in the form of heat, so I doubt why the Faraday loss hasn’t been taken into account in the thermal part of the electrolyzer model.

Reference [1]: Øystein Ulleberg, Modeling of advanced alkaline electrolyzers: a system simulation approach, International Journal of Hydrogen Energy, Volume 28, Issue 1, January 2003, Pages 21-33. http://www.sciencedirect.com/science/article/pii/S0360319902000332#

Thank you very much.

Kind Regards,

Sunliang Cao
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