pdjr-skplugin-solarhotwater

Controller for solar powered hot water generation.

Background

My ship has a solar panel array which is used to charge the ship's domestic battery bank. Quite often the battery bank becomes fully charged and most of the continuing output of the solar panel array goes unused.

This plugin was developed so that surplus energy from the solar panel array could be used to heat the ship's thermal store by operating an immersion heater.

Of course, running an electric water heater usually consumes more power than the solar array can supply so top-up from the ship's battery is necessary. Playing off water heating against battery recharge makes a reasonable strategy that allows the battery bank to remain almost fully charged and the water in the thermal store to be successfully heated.

Although pdjr-skplugin-solarhotwater addresses a particular issue, the plugin implements a simple generic algorithm which raises a binary control signal dependent upon the output of some power source and a connected battery's state of charge. This behaviour can be used to control an arbitrary target device and have broader application than just water heating.

Configuration

The plugin recognises the following configuration properties.

Property	Description	Default value
enablepath	Signal K path which indicates whether or not the plugin should operate (value = 1 says 'yes', value = '0' says 'no')	'control.solarhotwater.enabled'
outputpath	Signal K path which will have its value set to 1 when water heating should be ON and 0 when heating should be OFF.	'control.solarhotwater.output'
batterysocpath	The Signal K path which reports battery SOC.	''
batterysocstartthreshold	The SOC at which the controller should start heating (if other conditions are met).	1.0
batterysocstopthreshold	The SOC at which the controller should stop heating.	0.95
powerpath	The Signal K path which reports the output of the power source Watts.	''
powerthreshold	The power source output in Watts above which heating should be allowed.	400

Operation

1. outputpath is set to OFF (0) on startup.

2. Whilst enablepath is (1), the plugin checks the value on batterysocpath to see if it is above batterysocstartthreshold and if so, operation of the plugin is allowed and will remain allowed until the value of batterysocpath falls below battersocstopthreshold.

3. If operation is allowed and enablebath is (1) then the value of solarpowerpath is checked to see if it is greater than solarpowerthreshold, and, if so, outputpath is set to (1), otherwise to (0).

Author

Paul Reeve <preeve_at_pdjr_dot_eu>