grid connected vs off-grid power systems

Why connect small solar, wind or hydro power generating systems to the national grid? Is it advantageous?

What’s more advantageous?

A grid connected system is often advantageous over stand-alone systems: it’s cheaper (in most cases), more flexible and excess power generation can be sold (in some cases).

But there are situations that can make stand-alone systems preferable.

Advantages of small stand-alone power systems

Small solar, wind, or hydro power systems can be designed to be connected to the national electricity grid (grid-connected systems), receiving electricity when the renewable system can't provide it, and feeding electricity in the grid, during favorable periods. But they can also be designed to function alone (grid-off systems or stand-alone systems.)

Powering a home using a small stand-alone renewable system makes economic sense in remote locations where the connection to the grid is expensive.

Extending a power line to the electricity grid will cost you at least $15,000 per mile (in some cases the double or the triple), and that is surely a good reason to prefer off-grid systems.

Other advantages or reasons to prefer stand alone systems include the wish to be independent from the utility and the commitment to clean energy sources.

However, in many cases, that desire of independence can have a big cost or even a negative environmental impact, since it may demand an often expensive backup system, and also a fossil-fuel power component to prevent power shortages in periods when the wind, the sun or the stream of water is insufficient to produce enough power.

See: Hybrid Renewable Fossil Fueled Power Systems

The advantages of grid-connected systems

A grid-connected system allows you to power your home with energy even during the periods when renewable system can't produce enough power (when the sun isn’t shining, the water isn’t running or the wind isn’t blowing). During such periods you will be supplied by the grid.

In a grid-connected system, if you use more electricity than that you feed into the grid during a given period you will only pay for the difference between your consumption and your production.

Besides, your excess electricity can be sold to the utility, that is, you may negotiate with the electricity provider the possibility of being compensated for possible net surplus of electricity (something some utilities may refuse to assume).

The other advantage of grid-connected systems is the elimination of the storage devices (batteries and other related hardware), something that can make the initial investment in green electricity production significantly lower.

See: Storage and back-up elements for renewable power systems