Wednesday, 11 April 2018

Energy Matters

But first……. Jan became quite excited this morning when she woke to find a blog comment from reader Caroline informing us they had recently seen Waiouru on the Ashby Canal.  It was good to read Waiouru is out and about.  Even more interesting was Caroline & Martin have a narrowboat, Sonia Louise and a blog.  Of course the link can now be found on our Blog List.

Readers might recall I fitted an electrical consumption monitor to the house shortly after we moved in.  The monitor is capable of recording electrical usage by the second and also has the ability to produce various reports.  Today I created monthly reports of our hourly usage for the period Jul 17 to March 18.  The system allows users to download these in CSV (comma separated value) format.  This information can then be inserted into an Excel spreadsheet.

If I’m going to analyse the data then it’s easier to look at it graphically; which is what I did.

The first step was to average the data by month, day of week and hour of day.  Next I produced graphs for average monthly usage by day of week into daylight and night (day 0700-1800) (night 1800-0700).  The logic behind this was to identify our usage so I could establish the size of a proposed future solar panel array and also the size of a battery for use when there’s no sun.


The first thing I noticed was how much lower our consumption was between July and October 2017.  It jumped significantly from November onwards.


This situation is replicated during daylight.


The same during the night

So I had a look at the data for July 2017 by day of week and hour of day.


Except for the time around breakfast (kettle, toaster, etc) were averaging less than 0.5kW per hour.

There was a dramatic change in November which has continued.


You’ll notice the three major spikes between 6 – 7am.  Also, the consumption has risen between midday and 6pm.  After thinking about it I realised those three large spikes were on Sunday, Wednesday and Friday.  This is the electric water pump running the bore water reticulation system for the lawns and gardens.  Also, it was getting hot in November, which is when we started using the air conditioning unit.

With this information I could start calculating the required size of a solar array and battery.  One of a size to enable us to be self-sufficient.

The resulting table looks like this.  If you are interested you should be able to double click on it to see the original size


First column is obviously the month and the second is the average daily hours of sunlight from the government website.  My variables are the size of the solar array (proposed 5kW) and the battery capacity (5kWh with 4.8kWh’s usable)

I’ve assumed the solar panels are 80% efficient.  I’ve also assumed the solar panels have to add an additional 30% to the battery capacity to fully recharge it.

Surplus kWh’s are sold back to the power company at $0.07.  The daily utility company service charge for the privilege of being connected to the electrical grid is $0.9498753. 

The figures that matter are in the last column.  If in red that’s the money the electrical company will owe us.  If it’s black then we owe them. 

Based on this monthly average data we would actually produce more electricity than we require.  However if we wanted the security of being connected to the national grid then we would have to pay during the winter months.

I now need to do a cost comparison of the solar array and battery –vs- paying the full cost of remaining on the grid. 


Hayling Islander said...

Waiouru is now kept in the new Dunchurch Pools Marina on the North Oxford. In fact she is only 3 boats away from us! The new owners seem to be away quite often so we haven't met them yet

Tom and Jan said...

That's interesting. We do hope they get to enjoy her as much as we did!