Adding a big panel - beginner questions

JFKinYK · July 2013

Hi Everyone-

I've been lurking on this board for a few weeks. We recently moved to an off grid houseboat with an existing 12 volt solar system:

3 - Sharp 80 watt panels. Vpmax = 17.1
2 - 6 volt 4000 series Rolls batteries
1 - Trace inverter DR Series - DR2412
1 - Morningstar MPPT 45 charge controller

The system works well in summer as we live in Yellowknife, and receive 20+ hours of sun. Since we've only lived on the boat since May, we assume (and have heard from our neighbors) that the systems start to lag in fall and winter as we approach 4 hours of low angle sun. A Yamaha generator provides extra juice at that point.

I'd like to reduce our generator time as much as possible. There are solar panels for sale in town, one is a Kyocera 245 watt with a Vpmax of around 30 volts.

Right now, all three Sharp panels come together on the roof at one point, and then one large set of pos/neg cables run down inside to the charge controller.

Can I just throw up this Kyocera panel and wire it into the system on the roof so I have 4 panels coming together? That seems too easy! The system would still be below the max for the charge controller of 150 solar dc volts.

Thanks for any advice. This forum is an amazing resource.

Cariboocoot · July 2013

Re: Adding a big panel - beginner questions

Welcome to the forum.

Yellowknife? In Winter? Brrrrrrrrrrrrrrr!

What you have now is probably all three of those 80 Watt panels wired in parallel. This means the array Vmp is the same as the individual panels: 17.1 Volts. This is basically incompatible with the higher Wattage panels which have Vmp around 30. If you add one of these in as it is now you will be "throwing away" about half the power potential of the panel.

Moreover, since it is not a "true 24 Volt" panel you can't rewire the others (of which you have three; another logistic problem) in series and match Vmp's that way. Although two in series would be 34.2, which is much closer to 30 and would work better. Having an MPPT type controller solves the Voltage difference between array and batteries. But then you have one panel left over.

You can't put them all in series because you could have Voc above the 150 Volt limit in Winter, and the Imp rating of the panels is different (about 4.6 for the small panels, about 8 for the large one) which would limit the current to the lower number, again wasting power potential of the large panel.

There's no way around this without getting another controller, panel, or just plain redoing everything. Sorry.

JFKinYK · July 2013

Re: Adding a big panel - beginner questions

Brutally honest, I like it.

Thanks for the info, I'm glad I asked before buying the new panel. This also explains why I keep getting around 20 volts on my multimeter at every single spot on my system, from each individual panel on the roof, down to the large cables down inside by the controller. I kept thinking it should be around 50 (17 x 3) but as you said, they are not wired in series.

I see two potential paths forward:

1. I buy a Kyocera 135 watt panel that is listed at 17.7 volts. Could I wire that up in parallel with the others?
2. I wire 2 of my 80 W in series, getting to around 34 volts, and then use the 245 watt listed around 30 V in parallel with them (and try to sell my extra 80 watt panel to a buddy)

Yes, brrrr, but we hit the 90s last week with 22 hrs of sun, so it sort of makes up for it. Almost.

icarus · July 2013

Re: Adding a big panel - beginner questions

You could simply add the panel, but you would then want to add an additional MPPT controller in paralell so you whorls in essence have two side by side systems. Not the greatest solution, but it would work. I would also note that your battery bank is far too small for the amount of PV, if I am guessing on the battery AH size. Probably works fine for 20 hours of sun...not so well after/before equinox.

The trade of course is balancing a very big (and expensive) system for your wild variation in insolation. A plethora in the the summer, a dearth in the winter. If you triple or quadruple the sytem for the winter, you will be " wasting" vast potential in the summer, and may still not have enough in the winter. (winter loading is also likely to be significantly higher). Hence, the need for the genny and more (expensive) fuel.

Tony

Cariboocoot · July 2013

Re: Adding a big panel - beginner questions

JFKinYK wrote: »

1. I buy a Kyocera 135 watt panel that is listed at 17.7 volts. Could I wire that up in parallel with the others?

Yes; the Vmp is close enough that it would function without a hitch. This would give you 375 Watts. Around 24 Amps peak charging current (without cold temp factor).

2. I wire 2 of my 80 W in series, getting to around 34 volts, and then use the 245 watt listed around 30 V in parallel with them (and try to sell my extra 80 watt panel to a buddy)

Yes; this would give you about 405 Watts. I'm not sure what the Amp hour rating of your batteries is. Possibly 350? Anyway, you should get around 26 Amps peak from this (not including cold temps upping the Voltage and increasing the current further). It would probably be the better choice. You could also do this and add the third 80 Watt panel back in on a small PWM controller (like this: http://www.solar-electric.com/sg-4.html ).

Yes, brrrr, but we hit the 90s last week with 22 hrs of sun, so it sort of makes up for it. Almost.

Well we hit 36C here yesterday, but our days only get to 16 hours. Mind you they seem longer when you're boiling in your own skin.

JFKinYK · July 2013

Re: Adding a big panel - beginner questions

The 20 hour rate on our batteries is 450 AH.

Agreed, the variables in our weather are a challenge, not just for a solar system!

I don't mind throwing a few hundred dollars at our solar system to beef it up. I just assumed the best way to do that was with another panel. We are extremely conservative with our power (propane fridge, no kids) so it seems that the two batteries will work, if we can keep them charged. I know we will still need the generator during our long, dark winters. My goal is to know we've done our best to limit it, within our means of knowledge, money, and preference for simplicity.

I'm impressed with getting responses already. Thanks again for the help. Happy July 4th from a fellow American living up North!

JFKinYK · July 2013

Re: Adding a big panel - beginner questions

Wait, I now see you both are in Canada too! Nice. The forum saying Arizona had me thinking south...makes more sense to be getting replies on July 4th.

Anyway, thanks for the detailed response Cariboo. I'll think through how much I want to tackle and go from there. The 135 watt would certainly be easier, but the price difference in getting the 245 watt is barely anything.

Cariboocoot · July 2013

Re: Adding a big panel - beginner questions

At 450 Amp hours we'd typically want to see 45 Amps of charge current which would mean 700 Watts of array.

Now, some things can play in your favour. High elevation, for example. Cold temps, for certain. In Winter that 405 Watt array could behave like 525 Watts for example. But that's still a bit low.

Maybe you want to see about replacing all the small panels?

BTW, Tony and I are both Canadians living in Canada. (If we were members of the Senate we'd of course be living in Mexico.

)

JFKinYK · July 2013

Re: Adding a big panel - beginner questions

Wow, 700 watts. That is quite the upgrade. I'll be speaking with my partner about this tonight. She is still trying to decide what new woodstove we want!

And that much still just for two batteries? Would I still need to equalize as often, or would a 45 amp system help delay equalization too?

Elevation isn't a factor here, but yes, the cold will help, we can always count on the cold! Don't melt down there. At least you don't have crazy wildfires yet. We had 120 going at last count.

icarus · July 2013

Re: Adding a big panel - beginner questions

Your issue is going to be the short days/long nights in the winter. Doing a real world load calc for your winter loads is probably a good idea. I'm guessing they will be double what they'd re in the summer.

T

Cariboocoot · July 2013

Re: Adding a big panel - beginner questions

Well I have 700 Watts on 232 Amp hours @ 24 Volts, which is about the same amount of battery power as your 450 @ 12 Volts (multiplied out its 5,568 Watt hours vs. 5,400 Watt hours).

The whole thing here is trying to get the batteries charged up in the limited amount of daylight hours. The deeper in to Winter, the more limited the daylight. If I were designing a permanent system for year-round up there I'd go with 20% peak current rating - and know that the generator would still need to be run.

Yes, improving the panel charging will decrease the need for corrective equalization.

We've escaped wildfires so far this year because it basically rained all of May and June. Last year we weren't so "lucky". And now it is drying up.

BTW, the forum host is Northern Arizona Wind and Sun; we moderators are volunteers and have no business connection with the host company. It works out well because it keeps business out of the forum and the forum out of the business.

westbranch · July 2013

Re: Adding a big panel - beginner questions

IMHO, being just a tad , 60 miles , North of 'Coot, I would seriously re-think the controller issue. With the low prices of panels nowadays, you can buy a matched set of new panels, ~$1/W, and an up-to-date MPPT charge controller and still run the old system in parallel on the battery bank. This could cut back on the EQ's you do ans give you better battery life...

JFKinYK · July 2013

Re: Adding a big panel - beginner questions

Interesting idea westbranch.

Our panels are a bit more than $1/W here. The Kyocera 245w is $415 after GST. Although we can get a 30% rebate on that from the territorial government, if they accept our application, which would bring it darn close to $1/W.

I think we need to spend a winter with the system, see how it works, and go from there. The advice given here has been very useful. I'll try to keep everyone posted. Right now, we are going to get the 245 watt panel, and run it in parallel with 2 80W in series. That will almost double our panel wattage.

The old system has been in place for over 10 years, so likely can use a total upgrade, but it also worked just fine for those 10 years, although I'm sure the generator time can become an issue. Without an electric fridge or TV, our biggest draw is our wireless internet, and charging up some devices - ipad, cordless drill, etc, and of course our lights in the winter (all LED with some compact flouro). Our batteries are only a couple of years old, so that helps too.

Again, thanks for all the help from those up North, who know about the unique challenges that come with the territory (pun intended).

westbranch · July 2013

Re: Adding a big panel - beginner questions

the other thing to evaluate is a switch to 24 V.

I see you have an inverter that is quite long in the tooth, it may be ready to go out on you...

Adding a big panel - beginner questions

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