new solar PV and battery charging strategy

We have solar PV and a battery.  If sunny, we can use the PV during the day and export any excess.  We can charge the battery overnight on cheap rate (6.4p/kWh) for use during cloudy days and in the evenings, when power is more expensive (24.2p/kWh).  We can also charge the battery off any excess production during the day.  And we have an electric car, which we can charge off excess production, or off the grid.

Up until now, we have been trying to balance things so that we minimise our import from the grid.  This means charging the battery as much as possible off excess generation during the day, only topping it up overnight if needed, and even using it all through the night if it has enough charge.  In the winter, this means we have been charging it overnight, but in the summer we have been using it all through the night, and charging it off excess during the day, therby having essentially no grid import at all.

This is all well and good, but there are two issues.  First, and most complicated, is that we need to know how much sunshine there will be tomorrow in order to know whether to charge overnight or not.  We have been making this decision manually, because the automatic system is not very good at predicting the weather. This is better than the automatic system, but it doesn't always work, and in early March this year we didn't charge one night when the weather forecast promised sun the next day, but the sun never appeared.  This meant the battery went flat mid evening and we had to import from the grid at the expensive rate.  This cost us about £1, so, more irritating than anything else.  

The second, and more economic point, is that overnight grid power on our current tarrif costs 6.4p/kWh, whereas we are paid 15p/kWh for export.  This means that it makes financial sense to charge the battery (and the car) on cheap overnight electricity, and export all the excess during the day.  That feels wrong, somehow, because we are using more grid electricity than we need to.  But, presumably, the electricity company prefers to provide us electricity at night, and use ours during the day.  We can timeshift, at a profit.

So we have started a new PV/EV strategy.  From late March we have started charging the battery and car, and using grid power, overnight, then exporting all surplus generation during the day now that we are no longer charging the battery off the PV.  We'll try that for the rest of the year, and have a look at the various bills to see if it makes any significant financial difference.  It is certainly easier to "program": we just set and forget.

reMarkable new toy

I've been thinking about getting a device that allows me to input using handwriting for a while now, as I like to take notes while I am reading non-fiction, and a laptop or other keypoard device is too clumsly for this use in places like on a train.  I've tried stylus-on-tablet a few times, and never liked the feel.  Also, they too are a bit big.

A collegue of mine used a reMarkable notepad, and liked it very much, and said the writing feel was good.  But those are also a bit big: fine for meeting, but not so much for casual note-taking.  Then I came across the reMarkable Paper Pro Move, with a much smaller footprint.  I dithered for a while, then decided to give it a try, as it has a 50 day trial period.

Here it is, against a mass market paperback book for scale:

I haven't gone for the cover (as the point is to have something I can use easily), or the fancy marker with an "eraser" on the end.

I'm off to Eastercon in a couple of days.  I'll use that to try out how well it works.  Review to come!

sequestering carbon, several books at a time CLVIII

 The latest batch:

21 today

We've had a friend visiting for the weekend, and she's into birds, so today we went to RSPB Minsmere.  It's a lovely place, many different habitats, well marked out routes around the site, and numerous hides to stop and watch all the many species of birds (and some other wildlife).  I saw 21 different species (mostly identified for me by my friend, including several I had never even heard of before):

• near the start around the shop and restaurant:
• robin 
• wood pigeon
• pheasant 
• large birds on the water: 
• greylag goose 
• mute swan 
• black headed gull (millions of them!)
• smaller birds on the water (mainly ducks, often in pairs)
• shoveler duck 
• teal 
• shelduck 
• garganey 
• gadwall 
• mallard 
• coot 
• waders
• avocet (about 10 of them standing in a neat row)
• oyster catcher 
• redshank 
• turnstone
• in the reed beds 
• little egret 
• heron 
• bittern 
• circling lazily above the reed beds
• marsh harrier (several of them)

50 years on

Today was Commem, and my year group's 50th anniversay of matriculation.  A group of us went along to to meet up, and see all the changes.

It was great to see old friends (with maybe not too much emphasis on the "old"), and how the buildings have changed, and not changed, over the years.  I was amused to find that my first year room has since been converted into ... a student kitchen.  (The student in the kitchen at the time was somewhat bemused to be descended upon by a group of old ladies :-)  

This specific change is somewhat ironic, given the amount of cooking I did at the time (zero).

round and round and round it goes

I saw a strange bent cloud out the window, and when I looked closer, it looked even stranger:

Strange that is, unless you've spotted the aeroplanes flying in circles in the sky around here, which is a common sight (even more common recently, for some reason...)  

I've never seen them leave circular con trails before, however.

seeing Uranus move

Last Wednesday, as well as getting a SeeStar photo of the Crab Nebula, we also took a picture of Uranus.

5 minute exposure : can you spot Uranus?

The problem is, Uranus looks like a star at the resolution of this telescope.  But, planets wander; it's there in the name.  So, we took another picture on Saturday, when we were also looking at the Orion Nebula.  Putting the two images side by side makes it clear which spot is the wandering planet, and which spots are the fixed stars.

 18 March, 5 minute exposure                                     21 March, 2 minute exposure

Blinking between the two images shows the movement well (but also shows that one image is very slightly rotated with respect to the other).

So how far across the sky does Uranus move in 3 days?  Well, its orbital period is 30,688.5 days, during which time it travels once round the sky, through 360 × 60 arc minutes.  In 3 days, it will therefore travel about one ten thousandth of this, or just over 2 arc minutes, or about 1/15th of the angular diameter of the moon.  So definitely enough to be visible.