The phrase "essential complement" is correct and usable in written English.
It can be used in contexts where you want to describe something that is a necessary addition or component to complete a whole.
Example: "In this recipe, the spices are an essential complement to the main ingredients, enhancing the overall flavor."
Alternatives: "necessary addition" or "crucial component."
The batteries are costly and their use at such a big scale has not been demonstrated, but they may be an essential complement to renewable power, experts say.
But a qualitative approach is an essential complement to a quantitative one.Another big challenge for risk managers lies in the treatment of innovative products.
A Liberal member of the House of Commons from 1861 until his death, he began in 1866 to demand universal education as an essential complement of parliamentary reform.
Radio 3's weekly audience reach is modest at just over 2 million and apparently incapable of growing, but its sometimes challenging music, drama and arts output provides an essential complement to Classic FM.
But Europe has clearly decided to create the embryo of an army because it has determined that this is in its interest, because it believes that this is the only way to convince skeptical electorates of the need to increase defense spending, and because it views the development as an essential complement to economic and political integration.
The debate about the essential complement to the supervisor a single authority to close down or restructure banks (with access to pooled funds and joint deposit guarantees)—has barely started.The televised exchanges at a meeting of EU finance ministers on December 4th made the divisions plain for all to see.
Insurance and credit instruments for smallholders may need to be seen as essential complements rather than substitutes for risk-reducing and profitable technological innovations.
Key economic and cultural aims are usually oriented around pastoralism, but other economic activities are often essential complements to the livestock economy and these may impact on degrees of mobility and sedentism over time, over space and within families and households.
Sexual behaviours are essential complements to biological evidence in understanding STI/HIV epidemiology.
In addition to the essential functions that define life, an endosymbiont must provide its host all essential complements to its nutritionally deficient diet.
When such guidelines have been further developed into assessment standards, they will provide essential complements to pattern languages in the development of health and safety promotion websites.
