Hybrid renewable fossil fueled power systems

Instead of using a single power source, some designs combine a renewable system (wind, solar or hydro) with a fossil-fueled component. These hybrid systems can avoid the power supply shortages associated with adverse natural conditions – low wind speeds, clouded weather, low water stream conditions.

The wind-Solar hybrid system

A design that combines two (or more) generation renewable sources - wind and solar PV, typically - offers advantages over a system with a single source.

Wind speeds are often low in some parts of the year (or the day) while the sun is brightest. Or the inverse... And that makes hybrid wind-solar systems more likely to deliver clean power when we need it.

But even such hybrid renewable systems are prone to power shortages. Only in the grid-connected design the problem is solved.

Grid-connected systems

Only grid-connected systems can surpass the periods of low or short electricity generation of renewable systems.

In a grid-connected system, if the natural conditions are adverse, the home receives power from the grid, while in other periods the system feed the surplus into the electric grid.

A renewable power system with a fossil fuel component

Hybrid systems with batteries and/or a component powered by fossil fuels are an alternative to grid-connected systems. They may also solve the problem of power shortages, associated with adverse natural conditions and insufficient power generation.

In this type of system, whenever the batteries run low, the engine-generator is programmed to run and to charge the batteries that will be used whenever the renewable system isn't producing enough power.

The back-up system

Hybrid renewable-fossil fuel systems demand a set of batteries and other back-up elements, typically sized for 1 to 3 days of function. The idea is to get a storage capability big enough to supply electrical needs throughout adverse non-charging periods, which depends on the natural conditions in the site.

The backup system includes not only the batteries, but also battery charge controllers, inverters, safety disconnects, outlets, wires, grounding circuits, and several other components – some of them specific to the type of renewable system.

See:
Batteries and back-up systems for Wind, Pv Solar and Hydro Power

the Importance of the components of the hybrid system

There is a common and typical rule in which the renewable system provides around 80% of the power and the fossil fuel system provides the residual 20%.

That «sizing» responds to many situations, but the exact importance of the each part of a hybrid renewable-fossil system will always depend on the patterns of the wind, sun or water in your site.