Reliable Energy

With regular power interruptions in Nicaragua today, this has become a serious topic. It seems like a good time to talk about the reliability aspects with regard to alternative sources.

While most of the current reliability problems come from a shortage of generation capacity, that is not the whole picture. Depending on the grid means depending on a connection to a central source. While there are multiple feed routes to most consumption centers in the US there isn't to all and there is much less redundancy here in Nicaragua.

Even if there is central redundancy--for example, if there were (which there is not) a backup link between Managua and Estelí, those that find themselves at the end of a rural connection are likely to experience many power outages due to adverse weather conditions. Thus, small-scale distributed production can actually offer reliability advantages.

The usual arguments are "wind doesn't work when there is no wind", "solar doesn't work when the sun isn't shining" and "hydro doesn't work when there is no water". All three are true but the solution is storage. Storage combined with multiple sources is going to be the most reliable.

Nuclear power is actually one of the hardest sources to manage and I am not talking about the dangers side of the issue. Nuclear plants must be brought "on-line" through a lengthly startup sequence and then run at a constant output. Thus, they are fine for handling constant loads but are useless to handle loads that vary significantly during the day or connected to an unreliable grid.

Contrast this with hydroelectric. The storage is the water behind the dam. Hydro plants can "follow" the load requirements. Any system that can handle a variable load must store energy in some way. Water behind a dam is one method. The cable car system in San Francisco uses huge flywheels. Photovoltaic panels typically use batteries.

Designing a reliable energy system thus means two things:

1. Making sure you have sufficient capacity on average to handle the load
2. Making sure you have sufficient storage capacity to cover low input, high demand cycles

One common method at storage is to use what is called a "grid tie" system. This is where you have an inverter that sends your excess generation capacity back into the power grid. The assumption is that the grid will have the necessary storage capacity. You then draw from the grid when you are not producing enough to meet your current needs.

There are two problems with the grid-tie system. The first is the assumption that there is storage capacity on the grid. What this almost always means is that there is some generating system (such as hydroelectric) that can be "slowed down". If grid-time systems became very popular this would likely prove problematic.

The second issue is the grid itself. If the grid is not reliable, every time your grid connection fails you will have little or no storage capacity. Thus, even if you are considering grid-tie, you need to make sure you can cover your local needs.

While you have lots of choices of what to store (you could store heat, for example) the two most practical storage systems are chemical (batteries) and kinetic energy (water behind a dam). With the first, wind-electric generators and photovoltaic panels easily fit in. With the second a water pumping windmill as well as running electric pumps from wind and photovoltaic sources are possible options.