The Random Thoughts of a Geek heading for Banbury
The Random Thoughts of a Geek heading for Banbury

Solar Power on Boats

Solar Panel Production at Optimum Angle

A while ago I looked at Solar Panels (Photo Voltaic) and did some research, (including reading a very hippy book [Electro smog1 anyone??])

Tom of nbWaiour wrote this post about nbDestiny’s solar panel mounting system, which he says appears to be “electrically controlled and ‘self-seeking’”.

Solar Trackers are not unusual in commercial PV installations, however they are quite unusual on narrow boats, but not a bad idea; in my solar panel post you will have seen the following heat map:

Solar Panel Production at Optimum Angle

Using Swindon as an example we can get data about the Suns path by visiting this site, however what it still does not give us is the optimum angle for PV array to be pointed at, this is worked out using some fun maths.

First we need to know the location of Swindon (Grabed by typing “what is the latitude of Swindon” into google.), which is 51.5642° N, 1.7708° W, we only need the Latitude,

A quick and easy way to work out the angle the panels should be angled at is:

  • In the winter months, when there’s less sun, take your latitude, multiply it by 0.9, and then add 29 degrees.
  • In summer take your latitude, multiply it by 0.9, and subtract 23.5 degrees.
  • And in Spring & Autumn, take your latitude and subtract 2.5 degrees.

While in a house this may be fairly hard; on a narrowboat the panels should be easy to point at the right angle to the sky, the other general rule is that the panel should point south, however if you can Sun track you will get more power out of your panels:

Solar Tracker Vs Non Tracking

This graph is only for tracking East to West, with the panel at the optimum angle. With tracking in both directions the amount of power from the cells should be increased as well, far beyond the amount of power used to move the panels.

nbSteven currently has two PV cells mounted on the roof, they are neither very large, or very powerful, but they were on the boat when b0atg1rl and I bought her:nbSteven PV

They feed into the boats electrics via a EPIP20 PWM Solar charge controller (does any one have the manual for this?)

EPIP20 PWM Solar charge controller

I know we would get more power out of my panels if I was to use a MPPT solar controller (Maximum Power Point Tracker) rather than the PWM (Pulse Width Modulated) solar controller2, however this is what Steven came with.

After this we have this dandy little box to tell us how much power we have, and the condition of our batteries

Sterling Power - Power Management Panel

The Sterling Power, Power Management Panel sites there telling us the amount of power being fed into, or pulled out of the batteries, unfortunately for us at the moment we are using an electric fridge so we are using more power than our PV panels put back in.

Once we have the rest of the boat up to speed, I will look at making a Solar Tracker for our boat, until then Tamarisk is writing her blog at, soon she will be up to speed with where we are.

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