Hich sentence from the article shows the sweat-powered device's MAIN problem? Sweat is "one of the few available energy resources on skin," notes Seokheun Choi. Sweat is "one of the few available energy resources on skin," notes Seokheun Choi. Using sweat, he points out, lets people harness energy that usually goes to waste. Using sweat, he points out, lets people harness energy that usually goes to waste. The power these devices produce is quite low. The power these devices produce is quite low.