The Highs and Lows of a year of Solar

Yesterday (20th April 2013) we surpassed all expectations and managed the best solar day since we had them installed, so it got me wondering about which days were good and bad. Having done the maths, I thought I'd put a table up:

Month	Expected       daily amount	Best day amount	Date	Worst day amount	Date
Mar-12	6.3	15.85	27/3	4.23	31/3	part month
Apr-12	8.7	16.05	1/4	1.21	29/4
May-12	9.8	18.75	25/5	1.73	1/5
Jun-12	9.8	16.95	19/6	2.21	11/6
Jul-12	10.0	18.56	23/7	4.17	13/7
Aug-12	9.1	16.10	9/8	4.63	15/8
Sep-12	7.5	15.59	7/9	0.86	24/9
Oct-12	5.5	12.09	6/10	0.73	23/10
Nov-12	3.4	8.61	11/11	0.03	21/11
Dec-12	2.0	6.86	2/12	0.07	14/12
Jan-13	2.9	7.45	27/1	0	14/1, 19/1-25/1	snow!
Feb-13	4.6	10.91	17/2	0.63	11/2
Mar-13	6.3	11.24	30/3	0.61	8/3
Apr-13	8.7	19.16	20/4	3.63	11/4	part month

And while we are at it, my last post did not account for the FIT payment so this is what we got from March 2012-March 2013 (about 5 days more than the year) = £609.50 total for 4 quarters for a total 2650 units generated. 

The first year of Solar

We have today arrived at our solar panels' anniversary. so here are the figures:

2605.87 kWh (as read on the sunny beam yesterday) although Mike would like me to add half of the 22nd of this year as we got the meter turned on at lunchtime on 22nd last year! This makes the absolute total for the year 2607.14 kWh. Our meter for sending readings to the electricity board is only reading 2591 kWh, I am therefore going to round to 2600 anyway for all the rest of the calculations.

The original estimated generation figure given to us by Hereward Solar was 2190 kWh for the year so we have far surpassed that :) Mike then used an estimating site to generate some monthly amounts - he thinks it was the European Commission Joint Research Centre of the Institute for Environmental Sustainability, Renewable Energies Unit so we then plugged these into pvoutput.org and are using these to see if we are running to target.

Month	Estimate	Actual	Above or Below estimate
April ’12	261	255	below
May	305	328	above
June	295	301	above
July	311	336	above
August	284	326	above
September	226	278	above
October	171	181	above
November	101	104	above
December	63	75	above
January '13	89	68	below
February	129	123	below
March	195	93 in 2012	above total for both part months
		116 in 2013	likely to be below for rest of March
Total	2430	2607

so we have surpassed their estimates as well :)

The more techie toys and monitoring ability Mike gets for me, the more OCD I get about looking at trends, and we started using pvoutput.org to graph our usage as well as our generation in December. So I worked out what we use as a baseline amount over the day. There is an interesting waggle approximately every hour which seems to be the freezer or fridge turning on and off, but basically our low point now is approx 150watts of always on stuff, most of which can be accounted for by the always-on server and hub, router, and WiFi points.

There is an interesting note from one of the points in the office which if you plug a 4-way with a light on it in and leave it on, it seems to use about 30 watts of electricity! - we have turned this off now.
I will put 2 graphs up for the hours from midnight to 6am to show this. The first is from 29/12/12 giving a total usage for 6 hours of 1.73kWh, with a low point of 189W and a high point of 490W:

and the second is from 23/03/13 giving a total usage for 6 hours of 1.46kWh with a low point of 153W and a high point of 450W:

so using a calculation of 1.5kWh for 6 hours, this makes 6kWh for 24 hours or the whole day, assuming we are not in and therefore no kettles, washing machines or televisions are being used.

Given a reasonable sunny day in March - well we did have ONE this year ;) - we can get levels above 400W from 8am till 5pm or 9 hours saving us 2.25kWh during daylight. If I can also arrange for washing machines and tumble driers to be matched up with the really sunny times then I can reasonably ensure free electricity for these items as well, but it does take guesswork and sometimes I am not so good at that, or the weatherman is not specific enough. Now a simple money note is that 1 watt always on is £1 per year and 1kWh costs 12.5p to buy so we were spending 75p per day on baseline or £275 per year, now we have saved 28p per day that it is sunny enough - say 300 days per year or £85 just on having sunshine. 

We appear to have used 3864 units of electricity in 1 year to today. and the year before we used 5708 so all our (my) OCD turning off of unnecessary power/lights etc PLUS the solar has saved us 1415 units or £177 assuming direct translation from units read on the meter into kWh charged on our bill. 

How much power does your house use?

Average usage per day in KWh

Another interesting question for you all, in response to Anne's last post, and my general advocacy of monitoring.

How much power do you think your house uses when you think you've turned everything off you can? So, that's leaving fridges, freezers, computers you never turn off (I have an excuse, dear!), etc etc.

You don't know? You might be very surprised when you find out.

Our average daily usage in 2010 (as per the graph opposite) was around 18KWh, of which a sizeable amount was being contributed by stuff that was always on - old computers with inefficient power supplies can chew a couple of hundred watts, which is getting on for 5KWh over a day.

Stop for a moment, and think about that.

Scary, isn't it. One computer, probably 60p a day. Over £200 a year.

A very handy rule of thumb at
present: if you pay 12p a KWh,
it's accurate to within 5%.
Also: 1 KWh/day for a year = £40

Early in 2011, I finally decommissioned the last of the old servers (I'm an IT professional - I host several web sites and other things for friends, just to keep my hand in as a sysadmin) and replaced it all with a MiniITX box from the rather excellent LinITX.com, that eats, relatively speaking, next to nothing. Somewhere about then is when we started monitoring, and I think our quiescent usage is around about the 300W mark - or about £300 a year.

You'll notice our 2011 average is down to about 13KWh/day. Pretty much, just from doing that.

Our 2012 average is down to about 8.5KWh a day. Why? Actually, most of that's a no-brainer. Solar PV. As soon as the solar panels kick in, they start powering the house. Quite literally: once the sun gets out enough that the watts the PV is kicking out pass the magic 'things that are always on' point, we're running the basic functions of the house for free.

On top of that, our washer and dryer now have timers, so we can run them when the sun's out. And we have a new fridge to replace the 10+ year old one, that only uses about 150KWh a year (that's about 17W!).

Don't do the laundry on the Eco setting...

...or, yet another case for monitoring.

We have a new, shiny, Bosch Advantixx 7 washing machine. Bought, not least, because of it being a Which? Best Buy, its excellent A rating on energy consumption, and a nice button marked "Eco Program".

We also now have one of Current Cost's Individual Appliance Monitors, which allows us to plug any device we like in through it, and (by dint of some handy software of my own devising and a free installation of Splunk) draw graphs of its power consumption over time.

Anne normally uses the 40ºC cottons programme for our general washes, with the Eco button pushed in, 'cause, well, you know, it's Eco, so it must save energy, right? So we thought it would be interesting to graph[1] the power usage of the machine. And here we go:

 
Things to note:

• there's about a 15 minute wide peak at 2.1kW while it heats the cold water fill.
• there's a peak at the end for the spin cycle, and two smaller ones where water gets pumped in and out
• the 'tail' after the water heats up, while the machine's just turning the drum and, you know, doing the laundry, averages around 100-130W
• total power consumption for the roughly 3 1/4 hours is 0.9 kWh.

So. Let's try that with the Eco button off.


Interesting. Key points to note:

• the water takes almost exactly the same time/amount of power to heat - there's a dip which might suggest there's a thermostat there, but several test cycles on different days suggested the incoming water temperature didn't make much difference;
• there's an extra pump cycle;
• the tail averages about 90-100W, rather than 100-130W;
• total power consumption for the roughly 2 1/4 hours is... wait for it... 0.73 kWh

Yup. That's right. The Eco programme at 40ºC takes longer and uses more power. (And before anyone asks, yes we ran this several more times last week on both settings).

Now, of course, what I'd like to do is run another CurrentCost monitor to track the water flow, and see which uses less water, but that'll have to wait until they make one!

Points to take away from this:

• Don't just assume the Eco setting will do what you think it does;
• Cold-fill washing machines use most of their energy (about 0.5kWh) heating the water. I really miss our old hot- and cold-fill one, especially since my hot water is free! Manufacturers, if you're listening....
• Having said that, the water heating peak usage is less than the peak output of our solar PV panels.

Next time? We graphed the tumble dryer!

[1] These graphs will require a modern browser with decent HTML5 support - apologies if you can't view them. Also, apologies that they're not quite the same scale!