ExcelBanter - Need help with finding a function

Hello there,
I have been working on a google sheet in which I compare different bitcoin (cloud) mining offerings. In the sheet I try to make use of compound growth rates to make estimations of an expected yield in the future. I have been looking for a formula/function that automates this process but I have been unable to do it for a very long time :( I have 25 usd in cryptocurrencies available for the person that helps me with the function.

The comparisons can be found in this google sheet: http://bit.ly/cryptosheet

To give a bit of context information: When you buy a bitcoin mining contract, you essentially buy mining power which is expressed in Hashrate per second. If you open the sheet and go to "cloudmining advanced" you find that the price of 1 Terrahash per second (1TH/S) is 80 usd which is 0.017 bitcoin(G10) at the time of writing. The current daily returns for this 1TH/S is about 0.00002 btc per day (G11) which gives you a break even point of 539 days (G12).

The problem is that this 0.00002 btc per day will decrease with an x percentage per day. I calculated/estimated this daily compound growth rate, which can be found in cell B21. From row 32 downwards you can find my calculations of future daily incomes using this percentage with a compound growth rate calculation (=G$11*(1+'Diff vs Price'!$D$7)^$B32).

I used these numbers again to calculate the total profit after 365 (G23) and 730 (G24) days. As you can see, currently non of the cloudmining companies will ever give you a break even point according to my calculations.

However at some point when btc price goes up they will give you a break even point (they did until around February). Currently, to find the break even point I would fill in a total amount of days using a sum if function, and keep changing this amount of days until the total profit after this amount of days is higher than the investment (Cell g20). However this requires me to manually do this for all the different contracts. As the prices and difficulty keeps changing, this would be a lot of work.

There must be a function that automates this process. I know it has probably something to do with the SIGMA sign. However I am no pro in maths nor know how to use the sigma sign in google sheets. If anybody knows the function I am looking for or knows how to solve this problem (perhaps I don't even need the tables below the calculations) you would help me a lot! I also have 25 usd available for the person that helps me, send in cryptocurrency of choice haha.
If anything is unclear please ask so i can further explain.

Thanks alot!
Best,
Rafael