Solution: (1) The control experiment is also called univariate experiment, and there is only one experiment with different quantities, and the other quantities are the same. To determine which contains more energy, peanut kernel or walnut kernel, the variable is the amount of energy, so the other amounts must be the same. Therefore, the quality of peanut kernel and walnut kernel must be the same, for example, both are1g. In the experiment, the quality of a peanut kernel and half a walnut kernel may be different.

(2) What Xiao Wei did was to determine how much energy the peanut kernel contained, but Xiao Wei found that the data he measured was less than the standard data, probably because of the lack of heat preservation device and the small heating area of the test tube, which caused the peanut to lose more heat when burning; Inaccurate measurement; Calculation errors, etc.

So the answer is:

(1) is not accurate; Because the variables in the experiment are not well controlled, the quality of a peanut kernel and half a walnut kernel may be different;

(2) Peanut loses more heat when burning.