Considering upgrading 5 year old offgrid system

We installed 3.9 kW of panels on our off grid cabin 5 and a half years ago. Since then we've added on to the cabin, installed a bigger air conditioner unit and built a guest cottage (with it's own A/C unit).  During the late summer and early fall we could really use an energy generation boost.

Here is my existing array (taken August 10 at 10:30 am):

Existing 3.9 kilowatt array at 10:30 AM August 10th

At first I was thinking of adding another string. The existing modules are in the best position as the western side of the roof is shaded in mid to late afternoon. I would also have to get some racking and move the combiner box.

After looking at the module available now I'm considering just replacing my 320 watt modules with 450 watt bifacial ones. That way I could use my existing racking system and my generation would be 5.4 - 6.5 kW.

In the picture above you can see that the lowest row of modules is still partially shaded at 10:30 am. So, I also was thinking about ditching my inverter, charge controller, and the combiner box for an inverter with a built in charge controller and dual mppt so the performance of the partially shaded panels doesn't drag down the rest of the system. Seems like I could get all of this for $4000 not including the federal tax credit if I install it before the end of the year. Then I could use my still good quality existing components on a project down the road.

Any downsides with taking this route (other than probably convincing myself that I need a new a battery bank as well)?

Your spot looks peaceful, so glad you can enjoy natural surroundings like that.
My experience with living off grid prompts me to ask

Are trees too near the house for safety's sake? When I had shaded panels and entertained your suggestion to boost power, I stopped to take a long look at all trees close to my  house. Spending a long weekend with a chainsaw also improved my sunlight, so I hit repeat for the following short weekend.  While on this vendetta I found some surprise interior rot , typical red oak, darn good idea I cut before the next big storm.  A year later a midsized pine was snapped in a storm and hit my house, just replaced shingles that time.

So please consider a low priced solution first, if possible,  I would deem this sweat/ effort equity to invest in your house.  Of course it depends on slope, soil, hardwood vs conifer, weather, ad infinitum

Hi
I just  helped with a similar upgrade at latitude 46.
Where are you?
We left the existing roof panels,
and added a ground mount array at a steeper angle for season extension and snow shedding.
Your roof pitch looks quite shallow for anything except summer; unless you are equatorial.
Bifacials will not give much extra benefit on a roof; little light from below.
We used an EG4 12kpv all in one, with 2 mppt.
Each mppt can accept 2 identical input strings.  The 2 mppt do not have to be balanced.
We needed the EG4 12kpv for cold weather; there are other options for above freezing.

I also agree that tree trimming is a place to start.
cheers Doug

Rico Loma wrote:
Are trees too near the house for safety's sake? When I had shaded panels and entertained your suggestion to boost power, I stopped to take a long look at all trees close to my  house. Spending a long weekend with a chainsaw also improved my sunlight, so I hit repeat for the following short weekend.  While on this vendetta I found some surprise interior rot , typical red oak, darn good idea I cut before the next big storm.  A year later a midsized pine was snapped in a storm and hit my house, just replaced shingles that time.

Tree trimming is in the plans as well. I cut the trees back before building seven years ago but they've grown back in and this time it's going to take some rope work which I'm practicing now. The one shading the lowest row of modules is about 30 feet from the cabin and probably 50 feet tall. If I get really comfortable in a harness, I might climb up there and try to thin the canopy some. The one in the picture on the western side is a live oak which is only about 30 feet tall and has some limbs that have grown over the porch roof. I'll cut that one back in the winter.

Douglas Campbell wrote:
I just  helped with a similar upgrade at latitude 46.
Where are you?
We left the existing roof panels,
and added a ground mount array at a steeper angle for season extension and snow shedding.
Your roof pitch looks quite shallow for anything except summer; unless you are equatorial.
Bifacials will not give much extra benefit on a roof; little light from below.
We used an EG4 12kpv all in one, with 2 mppt.
Each mppt can accept 2 identical input strings.  The 2 mppt do not have to be balanced.
We needed the EG4 12kpv for cold weather; there are other options for above freezing.

We're in central Texas latitude 30. The roof is pitched at 18° so the modules could be pitched up some for optimum performance although our primary energy need is during the summer and shoulder seasons. I'd much prefer to do a ground mount array but it would require some pretty significant clearing to create a good location. I haven used bifacials before. That's good to know about their limited benefit on roof mounted systems. Dual mppt sounds great. It seems like I got my current system right on the cusp of a great advancement in consumer solar equipment. My 5-6 year old solar modules, charger controller, combiner box and flooded lead acid battery bank feel extremely antiquated.  

I salute your efforts. Good luck on your trimming. True, getting some hours in with rope, saw, harness will pay handsome dividends down the road. Start small and nibble away at the problem areas, it seems most of your trees will be easier winter or early spring, im always surprised how heavy leaves will be.

Gotcha on equipment 5years old being almost outdated.    My first off grid setup was in 1995 and those prices were, hmm, burdensome at the time. My wallet started to hide from my eager hand at one point....

Aaron Yarbrough wrote:We installed

After looking at the module available now I'm considering just replacing my 320 watt modules with 450 watt bifacial ones. That way I could use my existing racking system and my generation would be 5.4 - 6.5 kW.

In the picture above you can see that the lowest row of modules is still partially shaded at 10:30 am. So, I also was thinking about ditching my inverter, charge controller, and the combiner box for an inverter with a built in charge controller and dual mppt so the performance of the partially shaded panels doesn't drag down the rest of the system. Seems like I could get all of this for $4000 not including the federal tax credit if I install it before the end of the year. Then I could use my still good quality existing components on a project down the road.

Any downsides with taking this route (other than probably convincing myself that I need a new a battery bank as well)?

I would suggest neither replacing you panels, or your inverter/charge controller is a good idea.  You can simply upgrade your system by adding additional strings in another location.

First, before diving in, please explain in detail your inverter and charge controller settings, what the voltage/amperage limits of each?  Those numbers are critical to proper design.  What voltages and amperages are you running through your wiring right now?

I could suggest a couple of things, based on my own personal experience with my own system upgrades.  It looks like you have your panels wired 4S3P, is that correct?  I guestimate that your strings are running at ~150VDC?  Is that correct?  What is the Voc of those panels?  How low are your winter lows?  I would guess the Voc of your strings might exceed 200V around freezing or so?

One easy way to add capacity is through what is referred to as "virtual tracking", that is positioning additional strings of panels in directions other than South.  For my own system, my primary arrays also face South, but I have additional arrays designed to face East, and West.  I say "designed" because they are all on single-pole rotating ground mounts.  You could do exactly the same.  You could place a ground mount facing due East to catch morning sun, or a West-facing mount for the late afternoon.  Besides my 4500W of South-facing panels (but can be rotated), I have 1000W facing East, and another 2000W facing West.  I'm planning on adding another 1000W on to the West-facing array (3000W total) because I typically need a lot more at 5pm, instead of 8am.

It's important that string voltage be within 5% of each other, but amperage may vary from string to string.  That means you do NOT have to have exactly the same panels, just match the voltages.  Any string putting out between 143-157V is going to work just fine.

Another option is you simply add a second charge controller to the system.  You will need to match up the charging parameters so they are exactly the same, and it will work best if you use a brand that is designed to be paralleled and can communicate with each other.  But, with the second controller, you have total freedom as to your string voltages and amperages, independent of your existing strings.

With ground mounts, and string voltages in the 150V range, you can run at least 150' from the charge controller with zero voltage drop.  Right now, I'm running 120VDC for ~130' through 10 gauge copper, and I can't measure any voltage drop at all.

We're in central Texas latitude 30. The roof is pitched at 18° so the modules could be pitched up some for optimum performance although our primary energy need is during the summer and shoulder seasons. I'd much prefer to do a ground mount array but it would require some pretty significant clearing to create a good location. I haven used bifacials before. That's good to know about their limited benefit on roof mounted systems. Dual mppt sounds great. It seems like I got my current system right on the cusp of a great advancement in consumer solar equipment. My 5-6 year old solar modules, charger controller, combiner box and flooded lead acid battery bank feel extremely antiquated.  

I would say you hit the nail on the head. The new generation of all in one inverters have taken over from the more traditional transformer based units. Along with multi charge controllers for different producing strings you also get code approved 2 way communication with the new lithium battery packs. Lithium is a game changer as well as you can get full array production since they have low resistance to charging unlike lead and you don't waste time at the high voltage low amperage low production absorb stage. It has forced solar designers to change their ways as we now maximize panel numbers due to low panel costs as our first priority. On the down side you are usually best to repanel completely so you can maximize your strings and the all in one inverters are terrible at lead acid charging as they lack a proper 3 stage charging profile. The EG 4 mentioned above is a rebadged lux inverter, LUX being  my prefered inverter these days. Solark is another name to check out. Being in Ontario I am forced to comply with UL9540 which is rules around 2 way communication between battery and inverter so not all brands of batteries will qualify. These days I am installing Pytes batteries.  Its a brave new world. I fully agree that your first step should be aggressive trimming. Also mentioned was bifacial panels... They would be of no real benefit to you on a roof as they can catch no reflection on the back side.
Cheers,  David

I forgot to add:
Try different chainsaws as you work on tree trimming, please. I am no expert, but  I keep learning as i go.  Also over time I have learned more about balance and accuracy while cutting at 20-40 ft elevation. Certainly recommend electric  14 inch and 6 inch saws if possible,  the lack of power is counterbalanced by great results,  

My 14 inch saw is mid or low range 40v Skil model. Low price for my first model. A minimum saw, I think, but if you keep it very sharp the benefit (light weight and no worrying about idling, exhaust) is amazing. Probably the big names have better products , try a couple.

Lastly, I prefer one of these saws for wrist sized limbs or smaller.  Six inch bar seems like a toy until you get going for an hour, caution, they all have no safety features so please keep your wits about you.  Seems like 4 or 5 brands  that I have worked with were essentially the same saw. Please keep it oiled and tight, and rest assured it will last only a year or so.  CAVEAT:  it saves you money in the long run, if you use it judiciously, by difficult sawing near soil , stone, et al.    Just my 2 wood chips

So sorry everyone,  Mea Culpa, my comment about the smallest chainsaws is the antithesis of Permies culture. Disposable tools ARE a sinister plot, I agree, and should be avoided.   But to be honest, the 30 to 40 dollars spent on a tiny saw could save a life if you are working in a tall tree.  Please try one, I think you'll understand my belief

My 49$ saw

Michael Qulek wrote:
I would suggest neither replacing you panels, or your inverter/charge controller is a good idea.  You can simply upgrade your system by adding additional strings in another location.

First, before diving in, please explain in detail your inverter and charge controller settings, what the voltage/amperage limits of each?  Those numbers are critical to proper design.  What voltages and amperages are you running through your wiring right now?

I could suggest a couple of things, based on my own personal experience with my own system upgrades.  It looks like you have your panels wired 4S3P, is that correct?  I guestimate that your strings are running at ~150VDC?  Is that correct?  What is the Voc of those panels?  How low are your winter lows?  I would guess the Voc of your strings might exceed 200V around freezing or so?

You're right on with your estimates. Charge controller has an operating range of 72V to 187V. 4 panels with 34.2 Vmp in series so ~136 VDC per string. Voc of the panels are 40.8. We rarely get below freezing.    

Michael Qulek wrote:
One easy way to add capacity is through what is referred to as "virtual tracking", that is positioning additional strings of panels in directions other than South.  For my own system, my primary arrays also face South, but I have additional arrays designed to face East, and West.  I say "designed" because they are all on single-pole rotating ground mounts.  You could do exactly the same.  You could place a ground mount facing due East to catch morning sun, or a West-facing mount for the late afternoon.  Besides my 4500W of South-facing panels (but can be rotated), I have 1000W facing East, and another 2000W facing West.  I'm planning on adding another 1000W on to the West-facing array (3000W total) because I typically need a lot more at 5pm, instead of 8am.

I like the idea of a western facing array. That array would need a separate charge controller then the south facing array though wouldn't it?

Michael Qulek wrote:
It's important that string voltage be within 5% of each other, but amperage may vary from string to string.  That means you do NOT have to have exactly the same panels, just match the voltages.  Any string putting out between 143-157V is going to work just fine.

Thanks, that was my biggest question concerning adding a string.

Michael Qulek wrote:
With ground mounts, and string voltages in the 150V range, you can run at least 150' from the charge controller with zero voltage drop.  Right now, I'm running 120VDC for ~130' through 10 gauge copper, and I can't measure any voltage drop at all.

That's good to know. When I first built my current system I was so concerned with voltage drop that I put the combiner box on the roof. Silly me.

David Baillie wrote:
I would say you hit the nail on the head. The new generation of all in one inverters have taken over from the more traditional transformer based units. Along with multi charge controllers for different producing strings you also get code approved 2 way communication with the new lithium battery packs. Lithium is a game changer as well as you can get full array production since they have low resistance to charging unlike lead and you don't waste time at the high voltage low amperage low production absorb stage. It has forced solar designers to change their ways as we now maximize panel numbers due to low panel costs as our first priority. On the down side you are usually best to repanel completely so you can maximize your strings and the all in one inverters are terrible at lead acid charging as they lack a proper 3 stage charging profile. The EG 4 mentioned above is a rebadged lux inverter, LUX being  my prefered inverter these days. Solark is another name to check out. Being in Ontario I am forced to comply with UL9540 which is rules around 2 way communication between battery and inverter so not all brands of batteries will qualify. These days I am installing Pytes batteries.  Its a brave new world. I fully agree that your first step should be aggressive trimming. Also mentioned was bifacial panels... They would be of no real benefit to you on a roof as they can catch no reflection on the back side.
Cheers,  David

When I built my system I got a quote for lithium batteries and it 4 times that of FLA battery bank I ended up with. Now, I could get a bigger lithium battery for less than my batteries cost.

Rico Loma wrote:I forgot to add:
Try different chainsaws as you work on tree trimming, please. I am no expert, but  I keep learning as i go.  Also over time I have learned more about balance and accuracy while cutting at 20-40 ft elevation. Certainly recommend electric  14 inch and 6 inch saws if possible,  the lack of power is counterbalanced by great results,  

I have a 12 inch green works saw that is pretty light but I might pick up a six inch saw as well.

So, I found an aerial shot of my property and I guess I could do with some tree trimming....

Winter 2022 Aerial Image of Solar Panels

Granted, it looks like this picture was taken late afternoon in the winter.