Carnot heat engine available work

In the synthesis of sucrose, 23,000 J of the 29,300 J available from the hydrolysis of ATP are used for synthetic work. If we call 23,000/29,300 the efficiency of this pair of reactions carried out at 37°C, and if we consider 37°C equivalent to the temperamre of the high-temperature reservoir of a heat engine, what would the temperature of the low-temperature reservoir have to be to attain a comparable efficiency for a reversible Carnot engine ... 

Now, this heat energy could be converted into work, and hence electrical energy, using a heat engine and generator. However, even in a reversible system this conversion would be subject to the Carnot limit . The upper temperature is Tp, the temperature of the fuel cell, as this is the temperature at which the gases leave the cell. The lower temperature is the ambient temperature Ta. So, the extra electrical energy that could be available in a reversible system is... 

Clearly, to obtain the maximum useful work all pro-ce.sses should occur reversibly, and all heat transferred to the surroundings should leave the system at Tp. since heat available at any other temperature could be used with a Carnot or similar engine to obtain additional work. For a similar reason, the feed and exit streams in an open process should also be at the ambient conditions. 

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