Fourteen-year-old Ishaan Thakur and his sister, 9-year-old Aanya, spent their summer building a lucrative business mining cryptocurrency.

"We started because we wanted to learn something new about technology – and also make some money along the way," Ishaan tells CNBC Make It.

And they have.

Each month, the siblings make over $30,000 mining three digital coins: Bitcoin, the largest cryptocurrency by market value; ether, the second-largest; and ravencoin, an altcoin amid the top 100, Ishaan says.

To do this, Ishaan and Aanya, who are based in Frisco, Texas, had to learn how to mine, which is no simple feat. When mining to earn cryptocurrencies like bitcoin and ether, complex computers are programmed to compete to solve difficult puzzles in order to validate transactions.

"Crypto mining is just like mining for gold or diamonds," Ishaan says. "Instead of using shovels, you mine with computers. Instead of finding a piece of gold or a diamond in the mine, you find a cryptocurrency."

After watching videos on YouTube and searching the internet, Ishaan converted his Alienware, a popular kind of gaming computer, into an ether mining rig in April. (He did this by using the graphics card, which can perform a high volume of calculations for mining.)

His parents were supportive: "We could have spent the entire summer playing video games, but instead we used our spare time to learn about technology," Ishaan says.

The siblings began with ether, because mining bitcoin can be especially difficult. With its limited supply and surging demand, the competition when mining bitcoin can be more intense.

On their first day, "I made $3," Ishaan says.

To make business official, Ishaan and Aanya created their own mining company, Flifer Technologies, with the help of their father, Manish Raj, on April 30.

"We liked it so much that we started to add more processors [or chips], and made $1,000 in our first month" of May, Ishaan says.

The siblings' income continued to rise, and by late July, they could afford to buy equipment, like Antminers and Nvidia RTX 3080-Ti graphics cards, to start mining bitcoin and ravencoin, too. When deciding which to mine, they chose ravencoin because the equipment they had was "optimal" for mining it, Raj says.

In total, they expect to earn around $36,000 in September based on the equipment currently on order, Raj says.

"We can process a little over 10 billion Ethereum algorithms per second" alone, Ishaan says.

Although Ishaan and Aanya have had success, the process is far from easy.

In addition to being very complicated, mining is certainly not cheap, as it requires expensive equipment, a lot of energy and computer power.

Ishaan and Aanya, for example, have over 97 processors, which their father Raj, a former investment banker, helped fund by taking out a loan.

Raj declined to disclose the exact loan amount. But, the worldwide shortage of computer chips made finding equipment much more difficult and set prices at a premium.

Ishaan and Aanya mostly use Nvidia RTX 3090 graphics cards, Ishaan says, and each card alone can cost around $2,500 to $3,000 to buy.

Though at home, the siblings say they use "100% renewable energy for our mining," because "we want to be environmentally friendly," they also rent a data center in Dallas, Texas. In total, for both their home and the data center, the electric bill costs just below $3,000 per month, Ishaan says.

"We moved from my desk to the garage, since the house was getting too much heat and noise. [W]e outgrew the garage, since heat and noise was too much for the garage too," Ishaan says. "We now use the garage only for building and testing mining rigs. When they are ready, we move them to a professional, air-conditioned data center in downtown Dallas."

Ishaan and Aanya were able to "scale up" their operation during their school's summer break, but, looking ahead, they hope to continue to grow their business and balance it with school.

When her friends ask, "I just tell them we're just mining in the garage," Aanya says.

With their profits, they plan to reinvest in their business. But, "hopefully profits from our mining business will [also] pay for our college fees," Ishaan says.

Ishaan hopes to attend the University of Pennsylvania, he says. There, he'd like to study medicine and become a doctor. Aanya also wants to study medicine, but instead, would like to attend New York University.

However, they have a few years left to save – after all, Ishaan is just a freshman in high school, and Aanya is a fourth grader in elementary school.

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