Ticking Along Nicely

Not much to add, other than I didn't get the logger running until gone 1.30pm. Now logging at 15 minute intervals and saving in CSV format. I've left it running and I'll have a decent plot come Tuesday.

Minor Tweaks

I've just finished tweaking the Datalogger. I changed the logging interval to 15 minutes regardless of time of day so that the graph is now completely linear.

I also changed the format of the logging file from column delimited text to CSV (Comma Separated Values) which just makes importing into a spreadsheet a little bit simpler.

I have been tinkering with a couple of op-amps to make a 'prescaler' for the temperature sensors. A voltage reference of about 2.6v-2.8v (adjustable) is subtracted from the Kelvin value voltages from the sensors to give an output that is closer to Celcius values. Gain of the differential amplifier is also set at x5 so 10-90 Celcius gives almost a full 5v swing to the input of the digitiser.

In order to get a better accuracy (smaller steps) I have also decided to invest in a different board to try as part of the Datalogger package. The new board is the Tronisoft DACIO 300. 8 Analogue inputs and two 8 bit digital IO ports, all connected to the computer via RS232. I have used this board before in another project so I'm comfortable with it.

The downside is that it needs a COM port, so I'll need to use a USB>RS232 dongle on the laptop. This slight disadvantage is more than made up for by the extra capability and resolution of the new board.

Possible expansion of the logger may include indoor and outdoor temperature sensors, monitoring of the solar panel and battery voltages and some other monitoring functions.

Sun Glorious Sun

And Centigrade Glorious Centigrade! I left the logger on for 48 hours...the data was pretty impressive!

I perhaps need to tweak the maths or the sampling interval time in order to linearise the plot. Between 9am and 5pm, the sampling interval is ten minutes. Outside those hours, it's 20 minutes so there is a nonlinearity in the graph. Alternatively, I could interpolate the missing 10 minute intervals or discard alternate readings during the shorter sampling period.

This is what the graph looks like with the 10 minute intervals removed:

I think that does the job. I'm going to compromise and rewrite the logger so it just logs data at identical 15 minute intervals over the whole 24 hour period. It takes a little 'steppiness' out of the graph, too. Until I tweak the hardware, the accuracy of the temperature measurements is +/- 1 step on the digitiser which equates to roughly 1.9 Celcius. Closer tolerance and equal intervals will mean a more readable graph. Even so, as things stand, the performance of the system can be monitored. Even at almost midnight, the tank was holding up at around 42 Celcius. I really don't need hot water then, but it does show that from when the sun comes up, the system doesn't have to lift the water temperature from a very low starting point if there has been good input on a sunny day.

Disappointing July

I don't know...perhaps August may be better, but I would have expected July to produce some decent performance on the solar thermal. Having said that, I'm not at all disheartened because all I'm using the hot water for is washing up and handwash, and for the volume of water in the calorifier, I can't moan too much. Anything above 40C is good in my book, and temperatures on a variable day like today were pushing 60C. I really ought to leave the logger on long-term and see what the performance is like over a few days. Today in moderately overcast weather, the tank got hot enough for me.

New Logger

Nothing much to report other than I have tidied up my logging app and made it look a bit more pretty.

Rain Stopped Play

The heavens really opened today. I got to the office just after 10 and although the morning had been rather bright up to that point, as I drove down to the Goat Field the clouds let rip with the most torrential rain I can recall for a long time.

Good news - the water tank started filling nicely.

Bad news - I found some leaks and rain was coming in heavily.

Good news - I think I managed to sort the leaks.

Bad news - data wasn't great today.

There was obviously some sun first thing as the tank temperature was up and the pump had obviously been running. With the VM110N modified to accept digital inputs as a 12v signal rather than a switch to ground, I can now monitor the pump control relay. Before I could do any logging, I made a few minor upgrades to the electrics.

The system simply did nothing at all between me getting the logger running just after noon and the rain drying up and the sun trying it's hardest at about 2.30 or so. Well past noon, so only at an angle to the panel, but managed to pump about 10C extra into the tank.

Real-World Logging

I couldn't have chosen a worse day! There was a lightning strike very close to the house up at The Manor yesterday, and it appears my router has gone on the fritz. As I'd emailed myself the software for the logger to download and install on the laptop, this was not an auspicious start to my day. By the time I'd switched over to the fallback internet connection and checked the van for electrical damage, the clouds had come over and the heavens opened. It was pushing 11am by this time and the panel had seen a little sun, but no action until gone 4pm. Rain for most of the day.

I have real data! It's just not very impressive-looking.

Tank temperature barely exceeded 40C, thanks to a bit of early morning sun and then hovered around the 29-31C mark for most of the day, picking up a little diffuse energy around 4.30pm when the sun had come out again...on the wrong end of the box!

What matters is the data though, not how fantastic it looks. The graph is what counts...the fact that the data is logged automatically and can generate the output required.