seeking advice re buying inverter with future considerations

bcguy

Hi all, thanks in advance for the free advice...

I have been experimenting with solar for a while, and I want to get more serious, but make the purchases in logical steps. I now have 20 unisolar PVL124 flexable panels, 10 on the roof, and 10 in reserve. The 10 are wired in parallel to a 20 amp charge controller, and a bank of 8 old car batteries in parallel (I know, not ideal but it works for now). Running off the batteries was a xantrex prowatt 1500 inverter. I had been running the shop lights, charging e-bike batteries, etc, until the inverter quit when I shut the lights off the other day.

I have significant shading issues, with the panels only getting good sun for 8 months of the year. This makes me think that long string type panel arrays are not the best solution, but individual charge controllers for each panel. There dose not seem to be a solution for grid tie with battery back up like this.

Eventually I want to have a grid tie system with battery back up, and I want to be able to use components that I buy now in that system later if possible.

For the first step I would like to get an inverter that will act as an emergency back up for our well pump (3/4 hp 230V) and 1/2 hp jet pump plus the fridge and freezer and a few lights. So is there a hot recommendation for this? Should I look at getting all the parts from the same manufacturer so that they work together as a system? Next would be a better charge controller, or controllers.

Best Regards

Cariboocoot

Re: seeking advice re buying inverter with future considerations

Welcome to the forum.

You've got a few problems there. One being the need to power water pumps and refrigeration. Both have hefty demands for start-up current. The pumps may not run so long, but the 'frige is bound to use a fair amount of power per day.

A 12 Volt system would not be desirable here. The combination of high current demands and significant Watt hours use means a 24 or even 48 Volt system will perform much better. I'm not sure of the specs on those panels, but you're really looking at starting over to achieve your goals.

You can in fact have a grid tie system with battery back-up and panels facing every which-way. It just means each array set has to have its own controller to optimize output to the batteries. How efficient would this be? That depends on how much panel you cn have facing in any given direction. If you can't get enough insolation at any time to provide full DC power there isn't going to be anything surplus to sell back to the grid. But it just might be possible to putter along with low number all day rather than a high output peak midday.

As for integrating components, that becomes desirable when you have either multiple controllers or multiple inverters or both. That way they share data necessary to their particular function and improve efficiency somewhat. If it is only one controller and one inverter it is really not necessary for them to be the same. There are many companies that make only one or the other component, and they can be work together fine.

bcguy

Re: seeking advice re buying inverter with future considerations

Thanks that helps.

The panels are NOCT rated at Pmax 3.42A @ 28V This seems about right as I have seen about 100W per panel on a good day. They have bypass diodes on every cell.

I suppose that makes them a little low in voltage for a 24V system, so I would have to use two in series. I assume that parallel is better than series if shading is a problem giver adequate voltage?

The two inverters I have been looking at are:

Apollo Solar Inverter Charger TSW3224 $1595 3200 Watts, 24V in, Internal transfer relay, 100 amp charger, true sine 120/240V

Xantrex Grid-Tie/Off-Grid Inverter/Charger 4000 Watts 24 Volts XW4024 $2498.00 Configurable for stand alone or grid tie 240V

So the Xantrex has grid tie as well, but is more that I had hoped to pay. Could the Apollo be used in a grid tie with additional components for about the difference in price, or should I be saving for the Xantrex?

Thanks for the help, I am already understanding things a bit more clearly.

Cariboocoot

Re: seeking advice re buying inverter with future considerations

No, the Apollo can not be turned in to a GT inverter. There's too much that would have to be changed. If it were possible the extra components would probably add up to the $1000 difference.

Paralleling panels is preferable for reducing shading effect, but it's more a matter of where the shade will fall; if you can keep both of the panels in a string of two free of shade there's no problem. You are correct that the 28 Vmp isn't suitable for directly charging a 24 Volt system. They probably don't have a bypass diode on every cell; there isn't much point in doing that. Usually there is a bypass diode on each cell string, because an individual cell is only about half a Volt. So typically several cells in series have one bypass diode across in case of shading.

At some point you're going to have to decide which way to go. Remember that grid-tie systems need to be done with plans and permits and permission. Since the process is the same regardless of size, a larger system is more worthwhile.

As for back-up power, you need to evaluate how often and how long outages are to see if it's worth investing in battery back-up (pretty expensive) or a good generator (less money for the power delivered).

bcguy

Re: seeking advice re buying inverter with future considerations

OK thats what I figured about the inverters...If I get the Xantrex, then I can use it for now as a back up, and later get all the permits and permissions for grid tie without re buying.
The panels are strange beasts, 15' long, and about 15" wide. They are meant to be stuck down to a metal roof. Here's the basic specs.

Dimensions: Length: 5007 mm (197.1"), Width: 394 mm (15.5"), Depth: 4 mm (0.2"),
16 mm (0.6") including potted terminal housing assembly
Weight: 7.0 kg (15.5 lbs)
Output Cables: 4 mm2
(12 AWG) cable with weatherproof DC rated quick-connect terminals*
560mm (22“) length.
By-pass Diodes: Connected across every solar cell
Encapsulation: Durable ETFE high light-transmissive polymer
Adhesive: Ethylene propylene copolymer adhesive-sealant with microbial inhibitor
Cell Type: 20 triple junction amorphous silicon solar cells 356 mm x 239 mm
(14" x 9.4") connected in series

Unisolar has gone out of business, but Sun Electronics and many other vendors still have them, some at less than $1.00/watt (they were about $600.00 when they first came out)

Thanks for the help