The projected efficiency of such a plant would be about 30 %, but this fairly low efficiency must be balanced against the facts that energy from the sun costs nothing .

• 译文:这种电厂明显的效率约为30%25；但这么低的效率可以起到平衡作用；(针对这样的事实；)太阳能不花什么成本.；(注:括号内为“减词”