Can the the stratified TES's capacity be charged/discharged in one hour (c_rate = 1)?

[MaGering]

Have you checked whether the whole capacity actually can be charged/discharged during one cycle? Is one cycle in our case 1 hour?

Originally posted by @SabineHaas in #148 (comment)

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That is a good question. I must confess I haven't dealt so far with the c_rate factor. In oemof.solph it's the parameters invest_relation_input_capacity and invest_relation_output_capacity.

In the data sheet of the storage, that I consider,

• charge and discharge efficiencies are 100 %
• energy storage capacity per unit (storage) is 3 kWh and
• input and output capacity for one unit (storage) are 20 kW.

Can I get the c_rate from these parameters?

Originally posted by @MaGering in #148 (comment)

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hmm I really don't know. I would expect either a factor [0,1] or the amount of energy you can get from or add to the storage within one hour. 20 kW would be too much for one hour if the capacity is only 3 kWh..

Originally posted by @SabineHaas in #148 (comment)

[MaGering]

I've validated the c_rate of 1 as an assumption. For the storage which has been taking as prototype for the parameterization (TPSL 1000 of Schindler+Hofmann GmbH & Co. KG) and our operating temperatures the nominal capacity is:

(Calculated using pvcompare simulation with fixed height and its value according to manufacturer data)

As a guideline value for maintaining stratification, a maximum flow velocity (w) in the storage of 0.0017m/s to 0.0028m/s is given in Planungshandbuch Fernwärme.

If we assume (modelling with a time step of one hour) that charging and discharging capacity (c-rate) is equal to the nominal capacity (QN) (maximum capacity of storage in one hour) the value of the flow rate needs to be smaller than the one from the guideline.

Charging and discharging capacity can be calculated as follows:

with mass flow (ṁ), heat capacity (cp), density (ρ), temperature difference of high and low temperature of stratification (ΔT) and area (A) of the storage with its diameter d:

.

Rearranging the equation to w leads to:

which is smaller than the guideline's value.