Most people shop for solar panels by two numbers: watts and price. For a home battery that is the wrong place to start. The battery's solar input decides which panels will work well, which will waste part of what you paid for, and which can damage the unit. Read the input specs first, then go looking for panels that fit them.
I run a 6.38 kW ground mount into two EcoFlow inverters at my house in Charleston: ten ZnShine 440 W panels and six Silfab 330 W panels, wired as four strings into four solar inputs. Two panel models, two directions and four inputs with different limits is exactly the situation where the specs matter. The layout is further down. First, the order I would do it in.
A solar input has three limits
The watt rating is the one on the product page. The other two are in the manual, and they are the ones that decide which panels fit.
| DELTA Pro Ultra | DELTA Pro Ultra X | |
|---|---|---|
| Solar inputs | 2: one high-voltage, one low-voltage | 2: both high-voltage |
| Voltage window | 80–450 V (high), 30–150 V (low) | 80–500 V on each |
| Current limit | 15 A on each | 15 A on each |
| Power limit | 4,000 W (high) + 1,600 W (low) | 5,000 W on each |
| Total solar | 5.6 kW | 10 kW |
Figures are EcoFlow's published specifications for the DELTA Pro Ultra and the DELTA Pro Ultra X, checked November 2026. Other brands publish the same three limits for their own inputs. If you can't find all three, keep looking before you order anything.
The panel's label has the matching numbers
Every panel has a datasheet and a label on the back. Four lines on it matter here:
- Voc, open-circuit voltage. The highest voltage the panel produces. This is the number you check against the top of the input's window.
- Vmp, operating voltage. What the panel runs at while producing. This is the number you check against the bottom of the window.
- Isc and Imp, short-circuit and operating current. These are checked against the input's amp limit.
- Temperature coefficient of Voc. How much the voltage rises as the panel gets colder, usually around 0.25% to 0.30% per degree Celsius.
Series or parallel: what each does to the numbers
There are two ways to wire panels together, and they push the numbers in opposite directions.
In series, the positive lead of one panel plugs into the negative lead of the next, end to end. The result is called a string. In parallel, all the positive leads are joined together and all the negative leads are joined together.
| Series | Parallel | |
|---|---|---|
| Voltage | adds up | stays at one panel's |
| Current | stays at one panel's | adds up |
| Check it against | the input's maximum voltage, on a cold morning | the input's amp limit |
| One shaded panel | drags on the whole string | affects only itself |
| Mixed panel models | the weakest current sets the string | the lowest voltage sets the group |
Take four 440 W panels, each rated 39 V and 14 A. In series they make 156 V at 14 A, which sits inside a high-voltage input's window and under its amp limit. The same four in parallel make 39 V at 56 A. That is below the 80 V the input needs to start, and nearly four times its 15 A limit.
That example is why home battery inputs are wired in series. Their windows run up to 450 or 500 V and their amp limits are low, so a long string is what they are built for. EcoFlow advises against paralleling panels on these inputs at all. Series has a second advantage on a ground mount: lower current loses less power in a long cable run back to the house.
Parallel has its place on inputs with a low voltage ceiling and a higher amp limit, the kind found on small portable power stations and 12 V charge controllers. On the inputs in the table above there is little room for it.
Volts: count panels for the coldest morning
A series string's voltage is the sum of its panels: ten at 39 V make a 390 V string. That total has to stay under the input's maximum, because voltage above the maximum can damage the input.
Here is the part that catches people. The voltage on the label is measured at 77°F. Panels produce more voltage as they get colder, and the highest voltage of the year arrives on a clear winter morning, when the sun hits a cold panel.
Take a 440 W panel whose label reads 39.0 V open-circuit with a coefficient of 0.25% per degree Celsius. On a 20°F morning, about as cold as a typical Charleston winter gets, that panel is about 32°C colder than its label conditions and produces about 8% more voltage: 42.1 V.
| Panels in the string | Label voltage | On a 20°F morning | DELTA Pro Ultra (450 V) | Ultra X (500 V) |
|---|---|---|---|---|
| 10 | 390 V | 421 V | fits | fits |
| 11 | 429 V | 463 V | over | fits |
| 12 | 468 V | 505 V | over | over |
Eleven of these panels look fine on a DELTA Pro Ultra if you only multiply the label voltage. On a cold morning the same string is 13 V over the limit. Twelve look fine on an Ultra X and end up 5 V over. The right count is the one that fits on your coldest morning, with some room left for a colder one.
The low-voltage input on the DELTA Pro Ultra works the same way with a much lower ceiling. Three of these panels reach 126 V on that cold morning and fit under 150 V. Four are over the limit straight off the label.
Too few panels is also a problem
The window has a bottom. A high-voltage input needs 80 V before it starts taking in power. Two of the panels above make 78 V with nothing connected, so a two-panel string on that input produces nothing at all.
Operating voltage is lower than open-circuit voltage, and it drops further when the panels are hot, so check the floor against the operating figure. Three of these panels run near 98 V, which clears 80 V with room for a summer afternoon. Three is the shortest string that works on a high-voltage input with a panel like this one.
Amps: what gets left on the table
A series string carries the current of one panel, and the inputs above take in up to 15 A.
A 440 W panel of the common residential size is rated around 14 A, which fits. Some of the large-format panels sold at 550 W and up are rated at 17 or 18 A on their own. An input limited to 15 A takes in 15 A, and the rest of what that panel could deliver goes unused. A bigger panel can be the worse buy for a given input.
The watt limit works the same way. Ten 440 W panels are 4.4 kW into the DELTA Pro Ultra's 4 kW high-voltage input. The top of a clear summer midday gets trimmed, and the extra panel area earns its keep on cloudy days and in winter. I covered that trade in how much solar a home battery can use.
Why mixing panels costs output
Every panel in a series string carries the same current, and that current is set by the weakest panel in the string.
Put a 440 W panel that runs at 13.5 A in line with a 330 W panel that runs at 9.9 A. The string settles near 9.9 A, and the 440 W panel delivers about three quarters of its rating. You paid for 440 W and you are getting roughly 330 W, on every panel of the larger model, every sunny hour.
Mixing in parallel has its own version of the problem: the panels are held to a shared voltage, and the higher-voltage ones give up output to match the lowest.
The rule that comes out of this is short. One panel model per string. Different models are fine on the same battery as long as each has its own input. That is how my two models live together: the six Silfabs are a string of their own on one input, and the ZnShines fill the other three.
One direction per string
The same logic applies to where the panels point. A panel in weaker light produces less current, and it holds the rest of its string down with it. A string with half its panels facing southeast and half facing west underperforms all day.
Splitting directions between strings is a different matter, and a useful one. On each of my inverters, one string faces southeast for the morning and another faces west for the afternoon. Production spreads across the day, and each string has all of its panels in the same light.
How my own array is wired
Four strings, four inputs:
| Input | Panels in the string | Faces | String size | Input's power limit |
|---|---|---|---|---|
| Ultra X, input 1 | 6 × Silfab 330 W | West | 1.98 kW | 5 kW |
| Ultra X, input 2 | 3 × ZnShine 440 W | Southeast | 1.32 kW | 5 kW |
| DELTA Pro Ultra, high-voltage | 4 × ZnShine 440 W | Southeast | 1.76 kW | 4 kW |
| DELTA Pro Ultra, low-voltage | 3 × ZnShine 440 W | West | 1.32 kW | 1.6 kW |
Every string is one panel model facing one direction. No string is wired in parallel with another, so each input sees the current of a single panel. The low-voltage input, with its 150 V ceiling, carries a three-panel string.
That adds up to 6.38 kW against 15.6 kW of total input across the two inverters, so about 9 kW is still open for more panels. When I add them, the string math above decides where they go.
Before you buy
- Write down your battery's voltage window, amp limit and watt limit for each solar input.
- From the panel's datasheet, take the open-circuit voltage, the short-circuit current and the temperature coefficient.
- Work out the panel's voltage on your coldest morning, and count how many fit under the input's maximum.
- Check that the string clears the input's minimum voltage with room to spare.
- Check the panel's current against the input's amp limit.
- Plan one panel model and one direction per string.
Then shop. The solar simulator lets you set the panel wattage and the number of panels and see what that array delivers to each battery system across a day, including what the input limit turns away. When a panel at one of the retailers I list looks right, pull its datasheet and run steps 2 through 5 before it goes in the cart. Ordering has its own steps, covered in buying solar panels online.
Choosing the panels is your decision, and it is worth an hour with two spec sheets. The mounting and the DC wiring are work for an electrician.