FORECAST and TREND not returning good results

Hi, thanks in advance for your help.

I am trying to predict the future savings of a growing solar photovoltaic panel installation, taking into account the rising cost of electricity based on several past years of rates, and lowering cost of solar pv per kW, based on a conservative 3% annual cost reduction. (I am starting with 20 theoretical $1M systems, then taking 85% of their combined electrical savings to reinvest in MORE solar panels, and continually reinvesting, as electricity gets more expensive and solar PV gets cheaper.)

However, when I try to use TREND or FORECAST to predict future PV or electricity costs they both return numbers that shrink or expand much too rapidly, and what is worse, if I try to forecast/trend for a known year, the numbers are wrong there too.

So I tried to graph it and use the trendline formula to get an equation, but I must be making some sort of syntax error because my returned "y" for my input "x's" are all the same, no matter what data I look at.

To illustrate: for solar panel cost, my returned exponential trendline formula is y = 3E+07e^-8E-05x. I used Wolfram Alpha to convert that into y=(375000000000e-x)/12500, which I "excel converted" to =(((375000000000*EXP(1)-C2))/12500) with C being my column of new dates. But the number returned is 81548455, no matter what is in the C column.

There is potentially another problem, in that when I am searching for a price prediction for a specific day, while my inputs are only years, but I assumed excel could "prorate" the increase.

What am I doing wrong? And as you can't tell, I'm a total noob, so apologies all around. Thanks for taking a look at this. I have attached the relevant worksheet.