Build a solar pv system to power this little lot??

Pete_M · Post by **Pete_M** » 26 Apr 2007, 21:06

240 W panels - Id no idea they were available with that output. How big (dimensions and weight) are they? To be honest Im finding it hard work wall mounting two of my 175W units.

The correct answer to the question "Can you supply me with wall mounting brackets for my 175W 19Kg panels" is NO - they are too big, not, we will see if the supplier can make some for you.

Still 15 10mm brick bolts and three brackets per panel seems to be doing the job. Never the less I wouldnt advise wall mounting panels of this size.

Pete M

Post by **mikepepler** » 27 Apr 2007, 09:49

poisondwarf wrote:Andy,

Have a look at this, I think that it may help you

To test a used solar panel, set your voltmeter to DC volts, and measure across the + and - terminals of the panel. This is called the "open-circuit voltage." A 12 volt panel should show about 21 volts in full sun. Panels designed to be connected in sets of 4 (4 panels in series) will show 4 to 5 volts. If your meter can measure DC amperes, set it for this (on a high enough range so your meter won't go up in smoke) and connect it between the + and - terminals in full sun. This measurement is called the short circuit current, and is how much current you can expect from the panels. For a 12 volt panel, multiply your current by 17 volts to get watts. (17 volts is the rated voltage of most 12 volt panels

Spot on. The technical abbreviations for what'd being measured are Voc for "open circuit voltage", and Isc for "short circuit current". You may well have a label on the back of the solar panel giving figures for Voc and Isc. Be careful not to damage your multimeter measuring Isc - even my little 10W panel is rated at 0.65A

The other thing that may be on the label (or spec sheet, etc.) is Vmp and Imp. These are the voltage and current at the "maximum power point", know as Pmax. The reason such a point exists can be seen in this graph:

source: http://www.soton.ac.uk/~solar/intro/tech6.htm

So, as well as checking Voc and Isc, you could also measure the voltage and current with the panel charging the batteries, to make sure they are close to Vmp and Imp.

poisondwarf · Post by **poisondwarf** » 28 Apr 2007, 12:40

Hi Andy

Have you tested them yet? Today would be a good day as there is plenty of sun about

Cheers

Andy Hunt · Post by **Andy Hunt** » 28 Apr 2007, 20:15

Don't have a multimeter yet.

I'm really not sure that my system is working properly. There is hardly anything connected to the mains at the minute, today was mega-sunny, yet the PV panels don't seem to have charged the batteries at all.

This morning the batteries were showing 24.2V. During the day, with the sun on the panels, the IOC was showing up to 24.8V. But now the day is drawing to a close, the charge is showing 24.2 again.

Admittedly the solar hot water pump has been running all day, and there are a few bits and pieces plugged in, but I would have thought it would have charged the batteries a bit more.

Can anyone help me here? Does this sound right? I might call Powermaster next week, who make the inverter, and ask their advice.

Kentucky Fried Panda · Post by **Kentucky Fried Panda** » 28 Apr 2007, 23:11

Multimeters are pretty cheap, Maplins sell quite a few models that will measure DC output from your panels and AC from the invertor.
Is the output true RMS or modified sine wave?

Post by **kenneal - lagger** » 29 Apr 2007, 04:22

Andy, are your batteries holding the charge. If you've discharged them to over 50% Depth of Discharge (DOD) regularly, their life will be severely shortened. Do you know at what level the input low voltage protection and the low battery alarm are set to on the inverter? If it is set above 50%, which it could be, the batteries will not last as long.

At 50% DOD Sealed Gel Deep Cycle batteries should last just under 5 years (4.9yrs - 1800 cycles). At 60% they will last just over 4 years(4.1yrs - 1500 cycles)

poisondwarf · Post by **poisondwarf** » 29 Apr 2007, 10:10

Andy, are your batteries holding the charge.

Just what I was thinking......are the batteries ok?

If you've discharged them to over 50% Depth of Discharge (DOD) regularly, their life will be severely shortened. Do you know at what level the input low voltage protection and the low battery alarm are set to on the inverter? If it is set above 50%, which it could be, the batteries will not last as long.

I wasn't thinking any of that I'm afraid

At 50% DOD Sealed Gel Deep Cycle batteries should last just under 5 years (4.9yrs - 1800 cycles). At 60% they will last just over 4 years(4.1yrs - 1500 cycles)

In view of the above, how long should they last at 30% or indeed 40%?

Andy, I can't remember wether you said that you had Sealed gel batteries, and if indeed you do have this type, then I have no idea how to test them to find out what they are up to.

If you have the lead acid type, then they are quite easy to check, and I can run you through a couple of very simple tests.

One more thing, I was wondering wether someone on our 'world famous' Bury market sells multi meters. If they do you can bet your life that they are cheaper than Maplins. Check ebay as well for prices, maybe even Argos.

Cheers

Andy Hunt · Post by **Andy Hunt** » 29 Apr 2007, 11:18

Going to nip down to B&Q today for a multimeter.

The batteries are all set up correctly, their maximum discharge is set to 23.8V for extra long life, they are pretty much brand new so I don't think that's the problem.

I am wondering whether the operating voltage of the panels is too low somehow - it would be somewhat bizarre if it was, as they are fairly standard 24V Schuco panels, but the multimeter should give some indication. If that is the problem, I'm not sure what I can do about it though. Speak to Powermaster probably!

There is definitely something not right about the setup, I don't think it is the panels or the batteries, just something not 'tweaked' right somewhere. But then, experimentation is what it's all about eh?!

Andy Hunt · Post by **Andy Hunt** » 29 Apr 2007, 15:13

Well my panels are currently giving out 27V.

Maybe this means they are mis-matched with the built-in solar controller in the inverter/charger.

I suppose I could always get a dedicated solar controller to do the job. Can anyone tell me if I could just hook it up to the opposite ends of the battery bank from the inverter?

Post by **kenneal - lagger** » 30 Apr 2007, 01:32

The regulator is connected to the battery and the inverter is probably connected to the regulator as well because it, the regulator, will probably control the load as well as the charging. It does this to prevent the batteries being over discharged.

Maybe this means they are mis-matched with the built-in solar controller in the inverter/charger.

27V is not an excessive voltage Andy, but there should be a booklet that came with the inverter to give all this information. To fully charge your batteries you would need 30V. A fully charged cell should have a specific gravity of 1.28. According to my tables a 27V charge should give a sg of 1.20 to 1.21 which equates to 40 to 50% charge. Can you test the sg of the battery? You can get an hydrometer from Halfords or most car spares stores for a few quid. If your inverter/solar controller can't knock the voltage up to 30V, you may have to top up the charge from the mains

The batteries are all set up correctly, their maximum discharge is set to 23.8V for extra long life, they are pretty much brand new so I don't think that's the problem.

This equates to a 20% DOD which should give a 7.7 year life. The most economic life, i.e. the most energy stored over its lifetime, is when the DOD is 50 or 60 %. Its best to set it at 50%, then in an emergency you can always squeeze another 10% out of the battery. (20% DOD - almost full, 100% DOD completely empty)

By the way, are they deep cycle/leisure/solar batteries or car/lorry type batteries, Andy?

Andy Hunt · Post by **Andy Hunt** » 30 Apr 2007, 10:56

Hi Ken,

Thanks for the advice, all this is really helping me to understand my system!

The batteries are sealed gel deep-cycle batteries, so I have no way of testing specific gravity etc.

I have spoken to Powermaster who make the inverter, and they were very helpful actually.

Yesterday I measured 27V coming out of the panels - they are 24V panels and their maximum circuit voltage is 30.4V, so they should have been producing roughly half their maximum output, which would have been about 165W.

During the day there was a load on the batteries of my solar hot water system, which was running for most of the day, and a few other bits and pieces such as a clock radio, wireless network hub, cable modem, and maybe the odd thing on standby (don't worry, I'm working on that!!). The system successfully fed everything during the day, and last night lost less than 0.2V overnight, despite use of laptops, stereo etc.

So maybe it is working OK for this time of year. It's another sunny day today, so I will see what has happened when I get home tonight.

I've decided to see how it performs over the summer, and maybe add an extra monocrystalline panel into the system in the autumn to give it a bit of a boost.

One good suggestion they came up with is for me to measure the battery charge directly with a voltmeter on the batteries, rather than using the indication of charge on the inverter display.

Got some of these remote control plug sockets yesterday too, I wasn't going to get them but my other half is a bit of a techno-geek, so she bought them. They are quite handy actually, we can switch off all sockets in the house which have them from the remote control, and also program table lamps etc to switch themselves off at a certain time. Then we can switch them all back on at the same time from the remote.

Interesting that these remote control sockets were being sold as 'customise your home' rather than 'save energy'. Having a techno-home is a bit more 'sexy' than saving energy I suppose, although they achieve the same thing!!

Our place is getting pretty slick now, energy efficiency-wise. We have 'intelliplugs' for the two desktop computers too, which only feed power to printers etc when the actual PC is switched on. Very handy!

The best part of yesterday was soaking up the solar radiation in the back garden though, with a cup of tea!

poisondwarf · Post by **poisondwarf** » 01 May 2007, 18:47

Hi Andy,

Well, we have had a good many sunny days now around our area, and it looks like a good many more to come before the end of the week.

How is your system performing?

One more thing, I have never heard of remote controlled sockets whereby you can control all of your sockets. Where did you get them from?

Cheers

Andy Hunt · Post by **Andy Hunt** » 02 May 2007, 10:35

poisondwarf wrote:Hi Andy,

Well, we have had a good many sunny days now around our area, and it looks like a good many more to come before the end of the week.

How is your system performing?

One more thing, I have never heard of remote controlled sockets whereby you can control all of your sockets. Where did you get them from?

Cheers

The system is performing OK, it seems to be basically holding its charge despite running our solar hot water system and a load of other fairly low-power bits and pieces.

Still might get another panel though

Remote control sockets from B&Q, about ?30 for 4 plus remote control.

Erik · Post by **Erik** » 02 May 2007, 12:16

Andy Hunt wrote:The system is performing OK, it seems to be basically holding its charge despite running our solar hot water system and a load of other fairly low-power bits and pieces.

What are you running in the solar hot water system - just a pump or something else? How much power does it take?

Andy Hunt · Post by **Andy Hunt** » 02 May 2007, 12:43

Erik wrote:
Andy Hunt wrote:The system is performing OK, it seems to be basically holding its charge despite running our solar hot water system and a load of other fairly low-power bits and pieces.
What are you running in the solar hot water system - just a pump or something else? How much power does it take?

Just a pump and solar controller. Don't know how much power it takes - I don't think very much. The pump is running pretty much all day at the minute though.