PV upgrade decision

[jayw900]

Right to the point: should I upgrade to a bigger panel or to an mppt controller?

More info for those that take the time to read:

I have a 100 watt, 21 ish volt panel and a pwm controller right now. I'd like to get a 345 watt, 39ish volt panel and mppt controller but they can't happen at the same time. Would it be better to go with the bigger panel knowing I'll lose out on some power right now or get an mppt controller to try and squeeze any extra out of my current 100 watt?

Right now I'm thinking the larger panel would be better even with the losses but want to make sure I'm not missing anything.

[Almot]

westend wrote:
FWIW, I have a single 235 W module, using an MPPT controller. The panel is rated to 8 amps or so, IIRC. The voltage is 36V. I've seen days where batteries are low and output approaches 15 amps.

Good. Then 3*235W would be a match to TS MPPT 45. If he has enough space on the roof.

[KD4UPL]

2oldman wrote:

KD4UPL wrote:
Did you look at the specs on the Sun Power panel? It's well over a 50v input and it's no where near the 9.5A you mention.

The one in the link the OP made? I see 9a.

Missed that. I was looking at the first one that pianotuna posted a link too. It sure does make a big difference on the specs. It would be nice if when people post a question they list specifically what they're talking about right away.

[westend]

MPPT is not going to make a big difference in harvest with a 100W panel, maybe 10-15 percent in the most favorable conditions. MPPT will be necessary when using 24V nominal or greater voltages. Otherwise, you will be missing a lot of amps that could be harvested.

FWIW, I have a single 235 W module, using an MPPT controller. The panel is rated to 8 amps or so, IIRC. The voltage is 36V. I've seen days where batteries are low and output approaches 15 amps.

[Almot]

KD4UPL wrote:

Did you look at the specs on the Sun Power panel? It's well over a 50v input and it's no where near the 9.5A you mention.

KD, his intended panel was by Solar World, 9A. With all these sun/solar names it can get confusing indeed.

It's interesting that SMK didn't chime in saying that with TS MPPT 45 they might as well get 3*235W from Solar Blvd, $150 a piece ;)...

I believe in old mantra "There is no such thing as too much solar". If controller harvested enough by noon with "too big" solar, it will happily take an afternoon nap. But when it's dark and wet, it will still make enough to keep juices flowing, while a smaller solar would mean starting a generator.

To further complicate the matter, - there is more than one way to skin a cat. 700W is just a hair over the limit for 45A MPPT, still doable. MPPT are tolerant to a little excess of input watts.
Similarly, 450-500W is doable with 30A MPPT. And here the Bogart 30A PWM combo comes to mind, with 4 or 5*100W panels in parallel - it's different from all other PWM because it can handle excess watts, clipping them off. You can get 100W for $100 from Home Depot, free shipping or pick it up.

2*250W in series with MPPT is easier though.

[2oldman]

KD4UPL wrote:
Did you look at the specs on the Sun Power panel? It's well over a 50v input and it's no where near the 9.5A you mention.

The one in the link the OP made? I see 9a.

[KD4UPL]

MrWizard wrote:

Sunpower used to require their panels be positive grounded. If I'm reading the spec. sheet right this one does not require that. However, I'd verify for sure because it would probably be really hard to have a positive ground solar system in a negative ground RV.

there are quite a few controllers that are 'common positive' and 'control the negative' side of charge circuit

i don't remember seeing anything about 'grounding' the positive of the panels

common and ground are NOT always the same thing, in electrical circuits
grounding in a vehicle is the chassis, which by USA standards is negative
grounding in buildings is earth ground for AC power

Common in DC circuits is the common power or common return, the part NOT controlled
in a vehicle this is the Negative aka chassis

IF Sun recommends Grounding the positive of the panels
this would be in a commercial install and would be an earth bond for the positive side of the panels before connecting to a grid tie inverter,
this is lighting protection
the earth is Positive with respect to the Clouds

and has nothing to do with the actual electrical operation of the panel OR with mounting it on an RV

I'm well aware of the difference between common and ground. Older Sun Power panels did indeed require the positive wire to be grounded. This worked fine with grid tie inverters that used an isolating transformer. It would NOT work if you were trying to charge a battery that had it's negative connected to ground like in an RV.
As I mentioned however, it appears that with these new Sun Power panels they have dropped the positive ground requirement, thankfully. But, I would verify with Sun Power before purchasing.

[KD4UPL]

Almot wrote:

jayw900 wrote:

it does sound like I should just wait till I can do both

I would say - go ahead, if your old PWM has at least 50V input and current rating at least 12A.

9.5A - until you get MPPT - is a lot more than 5.5A of your 100W panel.

H4 connectors of this panel are compatible with more commonly used MC4. The only drawback is that monocrystalline panels are slightly less efficient than polycrystalline.

$1 per watt is not terribly high, but you can do better than that. A pair of these will give you 500W for less money. No minimum purchase. Solarworld is a better brand though. Shipping costs can be high in either scenario.

Did you look at the specs on the Sun Power panel? It's well over a 50v input and it's no where near the 9.5A you mention.

[Almot]

Either one of these 250W panels - Tyn or Ameri - have voltage below 40, so your controller will handle ONE of them. It "could" work with 2*250W, but the total current will be dangerously close to the limit. With one panel you will still see a notable increase in amps, compared to 100W.

For MPPT you need to decide whether to wire 2*250 in series or parallel series. Will work either way but the cable should be different.

If you shop around, you will find 280W panels of the same size and weight as 250W. Won't make a difference in controllers choice, you'll probably have to buy TS MPPT 45 anyway.

[jayw900]

Almot wrote:

jayw900 wrote:

it does sound like I should just wait till I can do both

I would say - go ahead, if your old PWM has at least 50V input and current rating at least 12A.

9.5A - until you get MPPT - is a lot more than 5.5A of your 100W panel.

H4 connectors of this panel are compatible with more commonly used MC4. The only drawback is that monocrystalline panels are slightly less efficient than polycrystalline.

$1 per watt is not terribly high, but you can do better than that. A pair of these will give you 500W for less money. No minimum purchase. Solarworld is a better brand though. Shipping costs can be high in either scenario.

That's a very nice price, thanks for that link. I just double checked and my controller is 20 amps with a 50v max

[Almot]

Must be a conspiracy between Tyn and Amerisol, - identical price and wattage 🙂

[MrWizard]

Sunpower used to require their panels be positive grounded. If I'm reading the spec. sheet right this one does not require that. However, I'd verify for sure because it would probably be really hard to have a positive ground solar system in a negative ground RV.

there are quite a few controllers that are 'common positive' and 'control the negative' side of charge circuit

i don't remember seeing anything about 'grounding' the positive of the panels

common and ground are NOT always the same thing, in electrical circuits
grounding in a vehicle is the chassis, which by USA standards is negative
grounding in buildings is earth ground for AC power

Common in DC circuits is the common power or common return, the part NOT controlled
in a vehicle this is the Negative aka chassis

IF Sun recommends Grounding the positive of the panels
this would be in a commercial install and would be an earth bond for the positive side of the panels before connecting to a grid tie inverter,
this is lighting protection
the earth is Positive with respect to the Clouds

and has nothing to do with the actual electrical operation of the panel OR with mounting it on an RV

[time2roll]

jayw900 wrote:
For those that are interested

Panel

It caught my eye because a few others I've seen have a minimum purchase.

For that price you can have 500 watts in SoCal.
https://www.solarblvd.com/product_info.php?cPath=1_270&products_id=3070

Shipping is a big issue on these oversize panels so buy local if you can.

[Almot]

jayw900 wrote:

it does sound like I should just wait till I can do both

I would say - go ahead, if your old PWM has at least 50V input and current rating at least 12A.

9.5A - until you get MPPT - is a lot more than 5.5A of your 100W panel.

H4 connectors of this panel are compatible with more commonly used MC4. The only drawback is that monocrystalline panels are slightly less efficient than polycrystalline.

$1 per watt is not terribly high, but you can do better than that. A pair of these will give you 500W for less money. No minimum purchase. Solarworld is a better brand though. Shipping costs can be high in either scenario.

[jayw900]

For those that are interested

Panel

It caught my eye because a few others I've seen have a minimum purchase.