Solar Sizing | I thing I done goofed.

[Over9000]

Hello All,

My current equipment is (9) SunGoldPower 460W Panels + (1) TP6048 Inverter + (4) Ecoworthy 12V 280Ah LFP + (6) Renogy 48V 50Ah LFP.

My net demand is approximately 26kWh per day.

When sizing my system, I had the following calculations:

• Power Generation = 460W x 9 panels x 6.5 hours per day = 26.9kWh
• Actual Avg. Power Generation = 3.4kWh per day
  • Min = 0.96kWh, Max = 10.0kWh (Measured over 20 days)

I am way off where I need to be. when I run the calculations, I'm operating at about 16% efficiency and in 20-years, I'll be at 13% efficiency.

Now it's clear that I done goofed, but I can't put 96 more panels in to bridge the demand gap if I'm only making 60W/h instead of 460W/h.

Any thoughts?

PS: Pic not related, but I know where the power's coming from because I backtraced it.

 

[Mattb4]

6.5 hour average is unrealistic for most locations even in Summer. However your actual amount seems very low for your location and this being Winter almost. Either you have a shading issue or your Weather has been poor for many days.

I would expect on a sunny day that you should get in excess of 10kWh.

 

[Over9000]

6.5 hour average is unrealistic for most locations even in Summer. However your actual amount seems very low for your location and this being Winter almost. Either you have a shading issue or your Weather has been poor for many days.

I would expect on a sunny day that you should get in excess of 10kWh.

Our weather has been pretty crappy & overcast, normal for Michigan this time of year. I definitely do not have a shading issue. Panels are at about 36~38 degree angles relative to the sun - not quite 47% - but it shouldn't cause this big of a gap.

What calculations should I use?

 

[MisterSandals]

What calculations should I use?

Solar Irradiance Calculator

www.solarelectricityhandbook.com

Reducing energy needs thru efficiency is always cheaper and usually easier than more production.

 

[Over9000]

Solar Irradiance Calculator

www.solarelectricityhandbook.com

Reducing energy needs thru efficiency is always cheaper and usually easier than more production.

Per your link, see the image & definition below:

• You can multiply this irradiance figure by the wattage of your photovoltaic panels to give you an average daily amount of energy you can expect to generate with your system, measured in watt-hours.

What it isn't clear about is which power rating on the panel to consider. If I consider the STC value (at year 0) = 460W x 9 panels x 2.44 (December) = 10,101Wh. As shown in my numbers above, I hit 10kWh exactly one time in the previous 20 days (November), with a mean generation of 3.4kWh.

If I use a "general" NMOT factor I've found of 75%, I'd downgrade my output to (460 x 0.75 x 9 x 2.44) = 7576Wh which is still more than double my mean generation.

So I'm not sure exactly how this link / info helps. Thoughts?

 

[400bird]

All those calculations assume the sun is out.
Clouds kill production and there isn't much you can do about it.

Either be happy with what you have and wait until the sun is out, put up 100 times more panels, move, build a nuclear generator, increase efficiency, lower thermostat temp, etc.

What do you summer numbers look like? Will the system meet you needs when the weather cooperates?

 

[Over9000]

All those calculations assume the sun is out.
Clouds kill production and there isn't much you can do about it.

Either be happy with what you have and wait until the sun is out, put up 100 times more panels, move, build a nuclear generator, increase efficiency, lower thermostat temp, etc.

What do you summer numbers look like? Will the system meet you needs when the weather cooperates?

I don't know what the summer looks like yet, but I'm really not sure what that one link helps me with.

The reality is that my production is ass (3.4kWh yield vs. 27kWh needs). I have no room for 9x as many panels.

If I scale things way the hell back in terms of usage, my worst month is 20kWh. So still, 6x as many panels. Might as well put up a wind turbine.

What if I add more batteries that can charge up during the summer and leech off of it during the winter?

 

[Mattb4]

Per your link, see the image & definition below:
View attachment 259934

What it isn't clear about is which power rating on the panel to consider. If I consider the STC value (at year 0) = 460W x 9 panels x 2.44 (December) = 10,101Wh. As shown in my numbers above, I hit 10kWh exactly one time in the previous 20 days (November), with a mean generation of 3.4kWh.

If I use a "general" NMOT factor I've found of 75%, I'd downgrade my output to (460 x 0.75 x 9 x 2.44) = 7576Wh which is still more than double my mean generation.

So I'm not sure exactly how this link / info helps. Thoughts?

Averages can help you figure what you might expect. That does not mean you will get the average. But yes you us the STC number times the insolation average for your area.

One other factor however should be considered if your array is producing much less than expected with a good sunny day is if there is a connection or panel fault going on.

Solar panels need sun. Rainy, foggy days are production killers.

 

[Supervstech]

I don't know what the summer looks like yet, but I'm really not sure what that one link helps me with.

The reality is that my production is ass (3.4kWh yield vs. 27kWh needs). I have no room for 9x as many panels.

If I scale things way the hell back in terms of usage, my worst month is 20kWh. So still, 6x as many panels. Might as well put up a wind turbine.

What if I add more batteries that can charge up during the summer and leech off of it during the winter?

You either hav bad wiring or defective panels with that low production.
You need to go over all strings output, and find the issue.

 

[Over9000]

You either hav bad wiring or defective panels with that low production.
You need to go over all strings output, and find the issue.

You think even though I've hit 10kW on one day that I have a defect somewhere? If so, that's going to suck trying to figure out. I guess I'd go panel by panel and plug it into the TP6048 and see what it reads and look for any gross anomalies.

 

[Texas-Mark]

When sizing my system, I had the following calculations:

• Power Generation = 460W x 9 panels x 6.5 hours per day = 26.9kWh

Right off the bat, I would guesstimate you would in real life see about half of that.

What if I add more batteries that can charge up during the summer and leech off of it during the winter?

You would need a LOT of batteries.

 

[GXMnow]

I live in "Sunny Southern California" but near the winter solstice as we are now (Solstice occurs on Dec. 19th) production is going to be low. My 4.8 KW STC rated system produces over 30 KWHs a day in May, but only made 3 KWHs a few days ago when we had clouds and drizzle. Th few good sunny winter days still only make 12 to 15 KWHs this time of year. After Dec 19, the numbers will start going back up as the days get longer again.

Since you did hit 10 KWHs, there is a chance, your low production is just from clouds. If you are not seeing good shadows cast on the ground from the sun, power will be greatly reduced. Overcast skies block a lot of sunlight. Human vision does an amazing job of adjusting, so you don't realize how much dimmer the sunlight really is.

How are you panels wired? Are they all in a single series string? If so, check your string voltage and current. The voltage should be close to the VMP voltage of the panels multiplied by the number of panels. I think I found the right data sheet on Amazon. It lists the VMP as 34.5 volts. Even with clouds, the MPPT should still hunt for the maximum power, so the voltage will stay close. With 9 in series, I would expect to see about 300 volts at the input of the inverter. If it is less, you probably have panels that are shaded. Even a tiny shadow on a panel can drop that panel's voltage by 1/3, or even 2/3 or completely if it crosses the different regions. Most large panels are in 3 zones with bypass diodes in case of shade. The current is strictly a measure of the sun intensity on the worst panel in the series string. The STC rated power is almost never reached. That is a lab test with 1,000 watts of light energy hitting each square meter of panel area while the panel is at only 25C (77F). To get that much light, the panel needs to be perfectly flat to the sun, at high noon, on a perfectly clear day. And that usually will heat the panel up quite a bit. The solar irradiance tables take that into account by listing "Sun Hours". Even if perfect conditions, it typically takes well over an hour to get a real full "Sun Hour" on the panels. My peak power today only hit 3,000 watts from my 4,800 watt array. That is just 62.5% of rated power. And that was clear sky, full sun, and pretty cool air. My panels are angled a bit better for spring to summer, so the sun is a bit lower than the panel angle right now.

Storing summer energy for winter is not going to happen. Let's say you just want to store 10 KWHs per day for one month. That is 300 KWHs. OUCH. And batteries all self discharge some over a 6 month span.

 

[Supervstech]

You think even though I've hit 10kW on one day that I have a defect somewhere? If so, that's going to suck trying to figure out. I guess I'd go panel by panel and plug it into the TP6048 and see what it reads and look for any gross anomalies.

Yes, because likely the 10kWh production was on a longer day.

 

[42OhmsPA]

I guess I'd go panel by panel and plug it into the TP6048 and see what it reads and look for any gross anomalies.

Don't waste your time, it will need a minimum of 3 panels in series to wake the MPPT up.

Have you figured out your battery issues in your other thread?

Listen to what every else is telling you, you need more panels, more batteries or less loads to survive without the grid or generator. You picked a discouraging time of year to start your journey.

Share a photo of how your panels are mounted currently.

Attached is what 14.5KW of panels looks like, 8.88 of them angled appropriately. Notice the drop in winter.
I just angled my ground mounts steeper today.

 

[Over9000]

How are you panels wired? Are they all in a single series string? If so, check your string voltage and current. The voltage should be close to the VMP voltage of the panels multiplied by the number of panels. I think I found the right data sheet on Amazon. It lists the VMP as 34.5 volts. Even with clouds, the MPPT should still hunt for the maximum power, so the voltage will stay close. With 9 in series, I would expect to see about 300 volts at the input of the inverter. If it is less, you probably have panels that are shaded. Even a tiny shadow on a panel can drop that panel's voltage by 1/3, or even 2/3 or completely if it crosses the different regions. Most large panels are in 3 zones with bypass diodes in case of shade. The current is strictly a measure of the sun intensity on the worst panel in the series string. The STC rated power is almost never reached. That is a lab test with 1,000 watts of light energy hitting each square meter of panel area while the panel is at only 25C (77F). To get that much light, the panel needs to be perfectly flat to the sun, at high noon, on a perfectly clear day. And that usually will heat the panel up quite a bit. The solar irradiance tables take that into account by listing "Sun Hours". Even if perfect conditions, it typically takes well over an hour to get a real full "Sun Hour" on the panels. My peak power today only hit 3,000 watts from my 4,800 watt array. That is just 62.5% of rated power. And that was clear sky, full sun, and pretty cool air. My panels are angled a bit better for spring to summer, so the sun is a bit lower than the panel angle right now.

Storing summer energy for winter is not going to happen. Let's say you just want to store 10 KWHs per day for one month. That is 300 KWHs. OUCH. And batteries all self discharge some over a 6 month span.

Everything is wired in a single series and my voltage is ALWAYS > 300V. There is no overhead shade at all. It's a wide open area.

If the voltage is > 300V always, is it fair to say that the panels are likely fine (they're band new anyways) and that Michigan just isn't very favorable to this kind of setup given the loads I have?

Regarding batteries, tomorrow is a good day for buying them (so it would seem) in case I wanted to increase my supply. I had the following options in mind:

• Chins 12.8V 280Ah @ $391 per battery x 8 = $3128 and would increase my total bank to 3.19 days
• Chins 12.8V 290Ah @ $486 per battery x 8 = $3888 and would increase my total bank to 3.24 days.
• LiTime 12.8V 230Ah @ $411 per battery x 8 = $3285, 2.96 days.
• EcoWorthy 12.8V 280Ah @ $480 per battery x 8 = $3840, 3.19 days.
  

Any tips? Is this a complete waste of time to boost this capacity? Prices okay? Other options I should consider?

 

[Texas-Mark]

• Chins 12.8V 280Ah @ $391 per battery x 8 = $3128 and would increase my total bank to 3.19 days
• Chins 12.8V 290Ah @ $486 per battery x 8 = $3888 and would increase my total bank to 3.24 days.

I would not pay an extra $90 for just 10Ah more unless that second one has BT that the first one doesn't. I have a few Chins batteries with BT and like them.

Oh, and why are you using 12V batteries anyway?

 

[42OhmsPA]

Any tips?

Stop buying 12V batteries and putting them in series.

I'm pretty we covered this in your other thread but can't remember. How are the panels angled?

 

[Over9000]

Oh, and why are you using 12V batteries anyway?

It seems like the best bang for my buck.

Stop buying 12V batteries and putting them in series.

What's wrong with it? If I use 48V Batteries, here's my best option:

Chins 51.2V 100Ah x 5 @ $743 each = $3715 and 3.06 days. Link

 

[42OhmsPA]

What's wrong with it?

48V Batteries: 49.02, 48.92, 48.98, 49.03, 48.96, 49.04

12V Batteries: 12.47, 12.12, 12.01, 12.31

 

[Over9000]

Right, but couldn't that be fixed with a balancer?

 

[42OhmsPA]

Right, but couldn't that be fixed with a balancer?

They sell 48V balancers for 12V packs in series, I don't remember what they are called; even using one you'll still have issues with the 12V packs cells losing balance if you don't regularly charge to at least 3.45V / cell.

Here's the first 1 I found on Amazon, no idea if it's any good. I've never used one and have no plant to; I build my packs to the system voltage.

https://a.co/d/eKvk8pN

 

[GXMnow]

I have to agree here, use 48 volt batteries with a proper BMS running all the cells as one battery. Running 12 volt units in series is not great. The cells can drift out of balance with nothing to pull them back in. While it does work, it is not ideal and you can run into problems with a single battery shutting off due to balance issues. They do sell 4 x 12 volt balancers that can help, but again, it is a bandaid on a bigger problem.

Here is one of those units.

https://www.amazon.com/Battery-Equalizer-Balancer-Supports-Trolling/dp/B0CLTZ2XQX/ref=sr_1_1_sspa?crid=1XS9LBYKK8TW6&dib=eyJ2IjoiMSJ9.Xf2uQsFzjviI-NxMK8YsYDR7jpvss4f4CQLpc9hQqS5W_JeYW9wuzX2jyQWFo_b4c_ku8Dx18Ft7459KhTTrMvyEQIcO9pHMG0j17wefYCqDUTG4BrVUJX-t6b8GTyB06djAti-8MzfD9Ebw_aNRngOSvx-rHo5SNApqYpyN_OBuXB8_6KGldiwp7jTHqiMZcmqvSyR6SQxycEhUPWju4HOXkFcmKN1d5C4zIQUTzmk.n0P0GpYlHphRi8SstAOrMv3VoBzl1SB5Nu2TxaBC-ds&dib_tag=se&keywords=12+volt+battery+balancer&qid=1733097411&sprefix=12+volt+battery+balance%2Caps%2C201&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

While more battery is a good thing, you also do need a bit more PV solar panel to charge them all up. The only way to gain net charge is to produce more energy than you used. As long as you are using more than you are producing, you will end up having to pull some from the grid. After Dec. 19th, it will slowly get better, but I doubt you will ever get much more than 21 KWHs a day even in perfect conditions in Michigan. It looks like 5 Sun Hours is about what you can expect even in Summer, unless you adjust the panel angle. My system makes more than I need for 8 months of the year, The 9th month, I am just about dead even, fell behind this year. Then 2 or 3 months, I have to buy some grid power to kep everything running.

Since you are seeing the 300 volts, that is good, all of the 9 panels are producing close to VMP voltage, at least at low current, so they are all working. There is still a small possibility of a bad connection but unlikely with seeing full voltage unless the current is extremely low from a connection issue. Again, since you did see 10 KWHs a few days ago, it is likely just the clouds that are killing the power. Here is an example from my system.

November 26 looked like this.

It was a cloudy day with a little rain. But then just 2 days later, we had a fairly clear sky with just a few cloud patches and the system did this.

The dip in the curve after 1 pm is due to a palm tree casting a shadow on a few panels. But the production went from just 3 KWHs on the 26th to 16.8 KWHs on the 28th. That is over 5 times the energy from cloudy to clear.

 

[Over9000]

Do you guys think I should add those 48V Chins batteries I linked?

FYI - I have no grid connection to this building.

 

[42OhmsPA]

Do you guys think I should add those 48V Chins batteries I linked?

FYI - I have no grid connection to this building.

What's the point if you can't charge them?
I'd buy a generator and power rectifier (or chargeverter for simplicity)

 

[rogerheflin]

If you are going to do batteries then build your own batteries. Buy raw Eve 304ah cells and cases. It comes to about $2000-$2200/15.7kwh. Cells are about $1500 delivered from a US supplier. At best you will be able to buffer a few days, and will need enough panels that on a sunny day you can produce all of your power and charge the batteries.

Having a bunch of different 12v batteries is really tricky to manage. Each battery has its own balancer(that you may need to check every so often) and then you have to balance across the multiple 12v batteries in the string. A few large batteries ends up being simpler.