How many Peltier will be connected to obtain 18V and 1 amps?
The specification of the Peltier element list what it can handle when you use it to displace heat by applying electrical power to the element.
If sufficient measures have been taken to remove the heat (so that the element does not get too hot, it stays below 138°C) then the element can use up to 92 W of electrical power to displace the heat.
These specifications do not in any way tell you anything about the Peltier element's capabilities of turning a temperature difference into electricity! Those numbers do no tell you anything at all!!!
Using a Peltier element for cooling is quite inefficient, only around 10% - 15% of the electrical energy is actually used for heat displacement (compared with 40–60% achieved by conventional compression-cycle systems). Source: Wikipedia.
If the temperature difference to electrical energy conversion would be equally (in)efficient then the maximum power you could generate with one element would be 15 % of 92 W = 14 W.
This is if that is the case and I expect that this is not the case and that above 14 W is complete nonsense. I expect that the temperature difference to electrical energy conversion is even less efficient than 10% - 15%.
Have a look at others experimenting with Peltier elements and see how much power they are able to extract. I warn you: it is not a lot. You want 18 W, my guess is that it will be very expensive to make a setup that can generate that amount of power. If you would use a solar panel you would get much more power for much less money.
This is a good video by Dave of the EEVBlog explaining Peltier TEG Energy harvesting.