House: Control Systems

What sort of control systems do I want to apply to my off-grid house?

Introduction

There are a lot of controllers available on the market which deal with individual parts of a household energy system: battery charge controllers, solar thermal pump controllers, and so on plus all of the controllers built into individual devices such as refrigerators. However, these tend not to take a very "holistic" view of the situation; the operation of the fridge does not depend on the state of charge of the batteries, output of the PV panels or the amount of wind forecast for the following night.

In particular, management of the the thermal store requires careful consideration of the expected weather over the next few days. Putting extra heat into it during a hot spell in summer does not make sense as it will only make the house uncomfortably warm whereas any energy available needs to be jealously guarded in winter.

Principles

As hinted above, there are two general principles I intend to follow which are somewhat different from those of most installations:

System Architecture

There are a number of problems which could be presented by a centralized control system:

The primary means of dealing with all these will be to use a generic and general purpose controller which is easy to replace or upgrade: a low-power off-the-shelf computer running a standard, easy to manage and easily-available operating system (some flavour of Linux or the like, presumably).

It's fairly key that the central controller be powerful enough that the control software can be written in a straight-forward manner, not needing any special tricks or awkward languages, etc, to fit it in. This way the natural growth in complexity as the system evolves can be kept under control.

From the technology-lock-in point of view it's also worth not getting too obsessed with any one of the various communications technologies available (e.g., 1-Wire, X10, Modbus) but to use whatever is suitable for a particular application with the flexibility to mix-and-match as required and to evolve the system as new technologies become appropriate.

Rest of control

At least part of my thinking here is that there might be an interesting consulting business to be built around the use of open source software and hardware for more sophisticated energy management systems for off-grid and similar houses.