Adding Panels to existing system

[bjspdx]

We've had our system for about 4 years now and want to add additional panels to increase production. Our inverter is a Sunny Boy 6000US and the existing panels are Sanyo HIP-200BA3 and we currently have 21 and want to go to 35. The panels are 200w at 42v. My understanding is the panels may be difficult to find so I'm trying to understand my options for adding panels.

Can we add panels of different watts/volts? Do we go lower or higher? This is all very disappointing to me since we bought a larger inverter just so we could do this.

Thanks for any help.

[andrewc]

It sounds like you currently have 3 strings of 7 and you are wishing to add an additional 2 strings of 7. To get optimal results, you need to match voltage. Look for a panel with an exact (or slightly higher) voltage. Also, keep in mind that voltage increases when panels are connected in series. So, assuming the 42v figure you gave (the spec sheet I just looked up for the HIP-200BA3 gives a different figure) if you have 7 in series, you should have around 294 volts per string. You could look for a panel that gives you a close multiple to that when strung together, for example, a 37v panel (and in that case you'd put them in strings of 8 to get 296v per string). That principal gives you a bit more flexibility when it comes to panel selection if you can't source the same panel you currently have. The lowest string voltage in your entire system is what gets used. If you size your new panels below that, it will bring your whole system down. And if you size your new panels too large, then all the extra voltage gets unused/wasted.

[bjspdx]

Now I'm confused

First, thanks for responding. I am confused about the voltage...what voltage did you find for the panels? I found on the spec sheets the voltage at maximum power as 55.8 but everywhere else they were listed as 42v.

I don't think I have room for 16 panels on my roof. Can I use higher voltage panels with fewer of them? I haven't seen panels listed by voltage, only watts. Most of the panels I can find are much lower voltages.

[Naptown]

It appears that Wholesale solar in Calif has some (That's where I found the specs)
Now you could add another string of 7 to what you have.

[andrewc]

I should say this. The manufacturer does not recommend mixing different panels in the same inverter. Therefore, going for as close to a panel as you already have is for the better. It appears the xxxBA20 panels by Sanyo currently listed on their website have identical electrical specifications (size is slightly different). Going with those panels in strings of 7 should mesh well with your existing array, assuming you can find a place to get them in the quantity you desire.

As for voltages, you can look at the display on your inverter and see what the system voltage is (though it will change based on ambient temperature). Divide that by 7 and you can figure out how close you are to 42v or 55v (and you can use temperature coefficient figures with an cell temperature reading to be even more precise). On paper, your peak power voltage is 390.6v per string. Your best bet is to aim for that or a little higher when sizing your new strings. Those Sanyo panels will do the trick.

Another thing to think about. How are you strings currently going into your inverter? Do you have an independent combiner box, or are you using an SMA disconnect? As the latter usually only has 4 terminals. So with 5 strings, you'll need an outside combiner box.

[Naptown]

I should say this. The manufacturer does not recommend mixing different panels in the same inverter. Therefore, going for as close to a panel as you already have is for the better. It appears the xxxBA20 panels by Sanyo currently listed on their website have identical electrical specifications (size is slightly different). Going with those panels in strings of 7 should mesh well with your existing array, assuming you can find a place to get them in the quantity you desire.

As for voltages, you can look at the display on your inverter and see what the system voltage is (though it will change based on ambient temperature). Divide that by 7 and you can figure out how close you are to 42v or 55v (and you can use temperature coefficient figures with an cell temperature reading to be even more precise). On paper, your peak power voltage is 390.6v per string. Your best bet is to aim for that or a little higher when sizing your new strings. Those Sanyo panels will do the trick.

Another thing to think about. How are you strings currently going into your inverter? Do you have an independent combiner box, or are you using an SMA disconnect? As the latter usually only has 4 terminals. So with 5 strings, you'll need an outside combiner box.

I think he said he doesn't have room for 16 more If he would tell us how much room he has it would be easier.

[andrewc]

In the first post, the user said they wanted to go 21 to 35, which makes me think there is room for 14 more panels, so going with a similarly speced Sanyo panel would still be an option (but trying to use a panel with less voltage with a larger string size would be if there isn't room for more than 14).

[Naptown]

Just ran sunny design today for a location of Los Angles He could add 14 more in two strings of 7 for a total of 5 strings of 7. This falls within the SMA compatible array size.

[Mike90250]

You HAVE to go with PV Watts and size your array properly. I'd installed a 4.5KW array, with a 3.8 GT inverter, and with proper planning, only maxed out the inverter a couple times a year, either on cold windy clear days, or the week of summer solstice when cool and clear. Array angle and orientation input is critical to properly forecast harvest, and I don't know of a better database then PV Watts for USA based systems.
Pay attention to the cold weather voltages, exceeding that is fatal to the inverter. You can rely on the inverter for occasional "thermal or power" throttling back for self protection, but hanging an array with an expected 6KW harvest, on a 4KW inverter, hoping to have maximum harvest for 3 hours a day, is asking for a short inverter lifetime.
(charts and photo of my 4.5KW west oriented GT array)

[russ]

You HAVE to go with PV Watts and size your array properly.

PV Watts is based on 20 year NASA data - about as good of a data base as you can find for most anywhere in the world.

If you hear (or read) 'my output is exactly on with PV Watts' You know it is either sheer chance or someone spreading BS. Over time (years) it will be right - on a given day no.

[Renova]

As indicated in some of the answers, your inverter should be able to take on an additional 14 modules of the Sanyo 200ba3. Also you may want to consider your conduit; the DC conduit will have to be rated for the additional 4 wires along with the A.C conduit wires from the inverter to Main panel, the wires will have to be able to carry 36 amps safely, and the breaker has got to be at least a 40amp breaker.


Mod note links are not allowed except in some occasions by older trusted members.

[Solarpod]

Adding a panel in parallel with a shaded one

In an array of 9 panels, what happens if one is in complete shade? Is there a reverse diode across the individual panels so that the remaining 8 would continue to put out current?
That shaded panel is on one side of a chimney. Could another panel on the opposite side of the chimney be paralleled with its brother panel to ensure that at least one of the panels is in sunlight the entire day?
Thanks

[Naptown]

Best to move the panel to an unshaded spot. Is this a string or micro inverters?

[Mike90250]

In an array of 9 panels, what happens if one is in complete shade? Is there a reverse diode across the individual panels so that the remaining 8 would continue

Bypass diodes embedded in the panels are only rated to handle being invoked occasionally. A daily shade source will eventually BBQ the diodes in the shaded panel.

[Solarpod]

tight space

Best to move the panel to an unshaded spot. Is this a string or micro inverters?

String inverter. The roof is pretty tight. The city does not allow installation at the top of the e-w ridge for fire marshall reasons.