Clever way of calculating energy output from a solar panel - spa pool

[mark.duyvesteyn]

Hi everyone,

I've got a spa pool hooked up to a 30 tube vacuum solar panel. I have a one wire sensor in the panel, and another in the pool for controlling the small 12v circulation pump.

the basis of the code is pretty simple;

If temperature in the pool is less than 37 degrees, and the solar panel is warmer than the pool, then run the pump, if not then go back to the start. I have a serial LCD display showing the temperatures and whether or not the pump is on. If the pool is above 37 degree then energy is stored in the solar panel until the pool temp decreases then the pump starts.

What i'm wanting to do is calculate the energy gained of the system during the day, and energy lost of the system during the night. The calculation for current energy in the system is (pool volume * temperature + solar Volume * temperature) * 4.19 (constant). What I'm struggling with is how to reset minimums and maximums in a clever way at the start or end of each day, just using the temperature gradients from the sensors.

Any ideas?


thanks heaps

 

[Captain Haddock]

How about add a clock (ds1307 or similar) to give exact timings and just use 'let starttemp = temp' & 'let endtemp = temp' at the appropriate times, maybe add an eeprom while you're at it and borrow some of the code from a datalogger (axe110?) so you can download the data for a week at a time to your pc.
I use these two lines for checking the maximum a tank of water has been up to and resetting at a set time, variable is stored on the ds1307 as the ram is battery backed.

if tanktemp > tempmax then let tempmax = tanktemp:writei2c 08, (tempmax) ;Save tank max temp to rtc ram
	endif

if day = 7 and hours = 11 and mins = 0 then let tempmax = 0:writei2c 08, (tempmax):endif

 

[mark.duyvesteyn]

Hi Captain Haddock

Ideally i will get away with out and more sensors, or inputs. I had thought of using a timer like you mention and could just reset it at midnight. Another option could be using an LDR and capture when it gets dark at night, and light in the morning and use that for the basis for resetting the mins and maxes. I still think it should be possible with a calculation of the energy in the system though!

 

[Captain Haddock]

No doubt someone will be along soon with a much more elegant solution than I will ever come up with, but there may be a 'hangover sudsidence' delay.
Out of interest how hot does that collector get without the pump running? There was a thread about solar collectors a while back and disagreements about just how hot they can get.

 

[mark.duyvesteyn]

the collector holds around 130l of water, and it will boil the water with out circulation in full sun. I blocked the inlet and put on a kettle whistle on the output and when it got really sunny late in the afternoon the whistle was whistling! You could hear the water bubbling away - amazingly efficient devices. I have had the probe attached for the last few days and so far the the highest temp reached 92 degrees, this is in Raglan, New Zealand in the middle of the summer.

 

[SAborn]

In many ways your data is only as good as the time base you record it by, or basic time slicing of data, so Captain Haddock is correct in my view to use a RTC, and rather clever to store data to the RTC, albeit a little limited in volume of data.

I have logged data for years from various sources, and it comes down to if its not consistant data, than its almost useless data to view over a larger period, yeh perhaps it can be ok on a daily viewing, but if you want to plot the data over a broarder period then the detail gets lost fast.

 

[techElder]

Seems to me that just like a solar panel for electricity, you need to add a "dump" function that either dissipates the surplus heat into the environment or stores it separately from the spa pool. That should also be considered in your collection of data.

the collector holds around 130l of water, and it will boil the water with out circulation in full sun. I blocked the inlet and put on a kettle whistle on the output and when it got really sunny late in the afternoon the whistle was whistling! You could hear the water bubbling away - amazingly efficient devices.

 

[bluejets]

How about a chart recorder. Chart driven by a stepper and pen driven by a servo. Both driven by the picaxe.Take temp increase (or decrease) over a period and use you calc. volume /time etc. It would not however allow for any atmospheric variations.

Your idea on the probe in the tank and probe in the pool is how the remote tank solar units operate the pumps here in Aus. They are small diaphragm pumps. Maybe a holding tank would be a good idea also as it takes no time at all for the panel to make steam out of what is in the collector. Seen it happen here on a fairly moderate day here at 10.00am. Plumber had trouble getting the system to bleed the air out.

 

[eclectic]

Seen it happen here on a fairly moderate day here at 10.00am.

On recent days here at 10 ish,
we see vague daylight through the rain or mist.

:-(

 

[SAborn]

On recent days here at 10 ish,
we see vague daylight through the rain or mist.

Well that happens when you give the good country to the criminals.

 

[inglewoodpete]

Well that happens when you give the good country to the criminals.

"Criminals"? That's Australian Royalty. My wife has decended from Royalty.

Sorry, Mark. We're getting a bit off topic. Raglan is a beautiful spot in summer. Do you live there or is it a bach?

 

[mark.duyvesteyn]

We have a place in Hamilton as well, but we are finding we spend more and more time out here in raglan, it is a great place for kitesurfing and general relaxing and projects!

Thanks for the tips so far.

 

[SAborn]

"Criminals"? That's Australian Royalty. My wife has decended from Royalty.

I notice the UK members have gone quite on this OT, perhaps its their poor weather that makes them quite with a silent wish of............[if only my great grandfather had stolen that loaf of bread, i could now be living in sunshine now.]

To me its one part of history that the English got wrong, putting the criminals in the promised land, but hell i aint complaining though.
The sacrifice is, no white Christmas.
Its such a shame we have to suffer hot Christmas days due to a poor judgement call out fore fathers made.

 

[geoff07]

At least we won't run out of water here in the UK.

My solar water panel here in the UK (non vacuum type) never gets above 70 but that is with the pump running. Next time it gets up there I will see what happens with the pump disconnected. That may be some years away if this summer is any guide.