Meter for my solar panel

[JonathanAnon]

Hi guys,

acquired this recently and got it out for a test today.. We had two days of sun in Ireland today, so I thought I'd try it out..

http://videobam.com/wYjOP

I have a fan as well for more stereotypically Irish weather, but I want to work out what sort of power I'm generating before seeing if it's worthwhile utilising.. I have a multimeter so I could check the voltage / current, but I need some for measuring milliwatt/hours or something like that... Should I just look up my wholesaler for a millwatt/hour meter or is there anything else I need to know?

thanks..

[redwire]

Re: Meter for my solar panel

At work here, we use load resistors across solar panels and measure voltage, to compare power output. If you want to measure energy generated, then a watt-hr meter would be used, assuming your load (fan?) works on cloudy days. I gather data over days and different solar panels using a USB data-acquisition board (~$100) and a junk PC. eBay has some DC energy meters...but they require power to run...
http://www.mccdaq.com/solutions/USB-...quisition.aspx
http://labjack.com/

If you look at a typical 6V panel, they put out 10.8VDC in full sun. On a cloudy day if the panel is putting out 4V, will your load (fan) work? It's still generating energy, but of no use to the load, do you want to count this?

I find the weather matters the most. Mild cloud and a panel puts out like 5-25% of full power! In Alberta here (latitude 53°N), winter can have weeks of full cloud cover and short days so solar systems run totally on battery and aren't always useful. The weather office can give typical sunlight hours for your locale.

A DC-DC converter might help match the panel to the load voltage.

[JonathanAnon]

Re: Meter for my solar panel

If you look at a typical 6V panel, they put out 10.8VDC in full sun. On a cloudy day if the panel is putting out 4V, will your load (fan) work? It's still generating energy, but of no use to the load, do you want to count this?

Okay I did a "snapshot" calculation there at the midday sun, on probably what is the best day of the year possible here in Ireland.... It's generally dull ~90% of the time. There was 16.8v across the fan, and I put my MM in series to measure a current of 170mA.

16.8v x 170mA = 2.856 Watts of power

So, if I get that for an hour then it's 2856 milliwatt hours then right...


I understand what you're saying about the lack of regulation on the circuit.. I was kind of assuming that there would have been some sort of regulation built in to the panel, but I guess it makes more sense that there isnt..

[redwire]

Re: Meter for my solar panel

That looks right - to calculate energy, you measure power and accumulate that over time.
Today it's cloudy and I'm getting only 10% power.

[JonathanAnon]

Re: Meter for my solar panel

Okay so how about this... If I set up a voltage regulator, and wire an ammeter in series with the line in, I can then just multiply what I see on the ammeter by the (now constant) voltage and I can work out what power I am generating..

I've been looking at these cheap ones online
http://radionics.rs-online.com/web/p...eters/0313716/

It would be a lot easier if there was a watt meter that I could leave on for a full day so that I could get more accurate power estimations over longer periods of time rather than the snapshots that an ammeter would give me? Is there nothing like those Kill A Watt meters (normally used for working out the usage of appliances) for calculating the power generated?

I found this one on youtube http://www.youtube.com/watch?v=kfs4Bs3H7gw , but my supplier doesnt seem to have anything similar.

[retiredcaps]

Re: Meter for my solar panel

Martin's channel has some reviews on panel meters.

http://www.youtube.com/watch?v=Lxv9Rozs774

If you like GT one, Franky at

http://www.ebay.ca/itm/200907749348

sells them.

He is well known over at eevblog and provides excellent service and communication. I have no financial affiliation with either Martin or Franky. I have purchased things from Franky in the past.

[JonathanAnon]

Re: Meter for my solar panel

That GT Power seems to do the job alright.. Did you see in the video where he crossed the probes (at 20:53) ..

He says that the digital counter at the bottom left is the accumulative meter.. that it does Vmax, Amax, Wmax and Whours ... I assume that this is the average Watt hours? This is what would be of use to me for what I'm working with.

[retiredcaps]

Re: Meter for my solar panel

That GT Power seems to do the job alright.. Did you see in the video where he crossed the probes (at 20:53) ..

Yes, I recall that. If I remember correctly, he did talk it in a followup T4D video?

He says that the digital counter at the bottom left is the accumulative meter.. that it does Vmax, Amax, Wmax and Whours ... I assume that this is the average Watt hours? This is what would be of use to me for what I'm working with.

I have no interest in panel meters (which is odd because I love learning more about multimeters right now) so I don't know the answer to your question.

You can ask Martin or Franky. Neither are members here so you will have to join Martin's forum or get a hold of Franky via ebay messaging system.

[JonathanAnon]

Re: Meter for my solar panel

Yes, I recall that. If I remember correctly, he did talk it in a followup T4D video?

Havent seen that.. I mailed the company asking them if they had a reseller in Ireland and havent got a response.. Gonna contact them again today..

It seems like it will do the job.. At only £25 STR, you cant go wrong really.. I'm gonna buy two of them.

[retiredcaps]

Re: Meter for my solar panel

Havent seen that.

Follow up here

http://www.youtube.com/watch?v=CXibZ0HEwWk

I don't know what he is saying in it because my speakers are off line right now.

[JonathanAnon]

Re: Meter for my solar panel

That company in the UK still hasnt got back to me about the power meter so I'm gonna have to ring them...

But I've got my hands on a 12v/44aH car battery just to make a start on getting a basic system of solar panel | charge controller | battery system up and running..



There's a limit of 17v/350mA on the small solar panel that I have so it's safe to use with the LM317T (which is good up to 1.5Amps). I have a 10K pot as R2 in the configuration, and if I tune this to 9.3K this will give me ~ 12.9v on my battery. I spose I should probably add a diode to make sure the current always flows in the one direction..

[kc8adu]

Re: Meter for my solar panel

set it for 13.8-14.2 or your battery will never fully charge and then will sulphate and die.

[JonathanAnon]

Re: Meter for my solar panel

set it for 13.8-14.2 or your battery will never fully charge and then will sulphate and die.

When the battery was in my VW Golf, I ran the multimeter across it with the car running it and it was being charged to 13.8v, but I wasnt sure what to set this to.. I think the battery is fully charged at 12.8v, is there not a possibility of OVER charging it?

[redwire]

Re: Meter for my solar panel

You need a blocking diode on the output of your charger. At night-time or in shade, you will get backfeed into the Vreg and the solar panel from the battery. The leakage is maybe 10mA, but also the LM317 can get damaged. In the datasheet there are also two protection diodes, so I'd put those in too. That's three more diodes.

Car batteries need more than their resting voltage (12.2-12.8V) in order to charge. The exact voltage depends on temperature, but 13.8V at 20°C is typical.

Your charger can't really overcharge... take 17V from the solar panel, subtract the 2V lost in the LM317 and output diode 0.7V, and well 14.3V is about the max. output I think you will see from your charger. Car batteries don't mind this at all.

[JonathanAnon]

Re: Meter for my solar panel

I left out the decoupling caps, and the protection diodes for the moment... But I did put in the diode between the LM317T output and the battery to stop the reverse current.. And I put in an LED on it as well.. Here's a quick pick.

http://omg.wthax.org/6CBhUx.jpg

The battery charges to 12.66v, and seems to lost charge very quickly, but I think this is due to the fact that the battery is past it's best... I will see if I can get my hands on a good battery... But I have a basic charging system up and running...

I'm gonna look in to practical ways of using it in the house now... Fans maybe, small lights... boiling a kettle would be handy, but I'm not buying an inverter at this stage, and I've read that those 12V kettles are a nightmare..

[budm]

Re: Meter for my solar panel

Do you know how much the charging current is so you can figure out how long it will take to fully charge your battery?

[JonathanAnon]

Re: Meter for my solar panel

Do you know how much the charging current is so you can figure out how long it will take to fully charge your battery?

The battery is 44Ah at 12v = 528Wh

But the panel is very hard to measure... It's meant to be max 17v 350mA = 5.95 Watts.. So if you got consistent sunlight for the period of an hour then you would get 5.95 Wh.. But then you have to take in to account the losses through the little voltage regulator circuit. I have put an ammeter between the voltage regulator circuit and the battery, but it varies hugely.. I will work out the watts coming out of it with varying sunlight.

See, given that it is Ireland and I'm using a solar panel, I was already conscious of the fact that the sunlight would not be consistent.. I was hoping I could use it in the same way that rainwater would fill up a barrel, slowly but surely..

[redwire]

Re: Meter for my solar panel

In full sun the panel puts out 6W and with a regulator loss of 1W, you have 5W available at best; 84% charger efficiency is my estimate. I have a 6W panel on my kitchen table and it's pretty finicky for angle of the sun and cloud to get 6W out of it. Shadow from one lousy tree leaf is enough for it to have low output.

Note that car battery self-discharge is about 4% per week (~10mA). It's worse if you've ever added tap water or it's hot out. I calculate you need 5hrs/wk of full sun just to keep the battery topped up, which is reasonable for Ireland?
Also, the battery capacity is 44Ah but charging it you have to put more in. Batteries are not 100% efficient in "charge efficiency or acceptance" and lead-acid is 50-92% efficient overall according to Tesla Motors. It looks like discharging the battery below 80% capacity is when they get inefficient.

Just me rambling here- I think it will work for you, although the panel is a bit small. I usually use 30W to 85W panels, depending on the load and that is here in Canada where it gets cloudy for weeks in January and pretty cold at -20°C or worse.

[JonathanAnon]

Re: Meter for my solar panel

That's all very useful information, redwire, thanks.. My plan is to just work with what I have at the moment and upgrade it bit by bit and hopefully make it practical so that it can save money, rather than just being a science project.. I'll just work it in blocks...

energy source -> charge controller -> battery -> 12VDC load/inverter

Wind energy is more feasible as an energy source with the climate here, so I'm more looking towards that option... though that does usually involve applying for planning permission from the Government authorities.. Using the solar as just a quick means of getting the rest of the system working and testing it.

With regard to the battery, I've seen another guy online who was fully off the grid, and with the way that he had his system set up, he could fully power everything in his house with only 50% discharge of his batteries... He had charts from the battery supplier which showed that if you discharge 100% of the battery (to 12.2%), then the battery is only good for 500 cycles.. Whereas if he discharge the battery only 10%, then the battery would be good for 6000 cycles.

[kc8adu]

Re: Meter for my solar panel

does not stretch out the life in years though.that just means grid corrosion is what does them in rather than paste fallout.
i find that 50% is a good compromise.
even an occasional near 100% actually helps.
i have a 1 year old mk/deka 8d gel someone had me replace in an rv.
had a wasted one in the basement i used as the core and kept this one to play with.turns out the rv owners never cycled it at all in that year and didnt get the expected runtime.it was out of warrenty like they were really entitled to one anyway.sure enough it returned about 80% of its rating.
3 hard deep cycles later its 10% over rated capacity.
love it when i get free $500 batteries that are perfectly fine!

He had charts from the battery supplier which showed that if you discharge 100% of the battery (to 12.2%), then the battery is only good for 500 cycles.. Whereas if he discharge the battery only 10%, then the battery would be good for 6000 cycles.