Question: [![enter image description here](https://i.stack.imgur.com/UBFqR.png)](https://i.stack.imgur.com/UBFqR.png)
The supply voltage is 15 V and RL is 100 kΩ. Find the voltage across each diode and RL.

Is = 0.1 μA, η = 2, and VT = 25 mV.

How can I calculate the net current through RL? I have three unknowns: the net current and the voltages across the diodes.

Answer: 
Assuming the circuit is properly drawn and it is assembled with good parts you will not get any current flow through the circuit except for a small leakage current through the D2. D2 will have the supply dropping across it - the Vf of the first diode. There should be no voltage drop across RL other then what is caused by the leakage of D2.
You simply solve a system with 3 uknowns.

$$
I = I\_{S}\cdot\left(e^{\frac{V\_{D1}}{\eta V\_{T}}}-1\right),\ 
I = I\_{S}\cdot\left(e^{\frac{V\_{D2}}{\eta V\_{T}}}-1\right),\ 
I = \frac{V\_{s}-V\_{D1}-V\_{D2}}{R\_{L}}
$$

Be careful of the sign of the voltages \$V\_{D1}\$ and \$V\_{D2}\$

Hint: one is <0 the other is >0.