Gulf Island Off-Grid System - Part 4

David and Laura
David and Laura Solar Expert Posts: 139 ✭
in Off Grid Solar & Battery Systems #1
The system at our cabin (see Part 1, Part 2) has remained pretty much unchanged (we finally put a protective box around the batteries), but we've been making significant progress on our second solar system for our guest house/shop (See Part 3 for our initial design concepts).

Solar Array Under Construction

After much searching, we were able to find the best compromise between proximity to the building, solar exposure and minimizing the number of trees that we'll have to cut down. We sure do envy our neighbours, who have this beautiful south-facing bluff that is just perfect for solar!

So, here's the progress on the array so far:

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We opted to use concrete filled sonotubes and heavy aluminium "L" bars to reduce the amount of concrete while still providing a good foundation for the array, as we can get some fairly significant snow loading (local climactic data says that the combined snow and rain load, with wet snow representing the worst-case loading, can approach 46 pounds per square foot!). The site is a solid rock outcropping, so that also helps.

Here's a closer look at the west side of the array:

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We have 24 Sharp ND-H235Q2 panels that we'll be mounting in a 3x8 configuration. Electrically, they will be cabled into two strings, with each string connected to a SMA Sunny Boy 3000TL-US inverters (we originally were going to be using two Sunny Boy 2500HF-US inverters, but SMA recalled them for off-grid use).

The string calculations all seem to work out with lots of headroom:

For worst case voltage, we take the panel Voc (37.2v), multiply it by 12, then by 1.2 for overvoltage. That gives us 535.7 volts, which is well below the maximum rated voltage of 600 volts. So, we're good there.

For max power, we take the rated power Pmax (235w) and multiply it by 12. That gives us 2820 watts. The max power rating for the 3000TL-US is 3200 watts, so we're good there too.

As an aside, we typically _really_ poor sun conditions, and we've never seen anything close to the rated panel power from our existing panels (we're lucky if we get 60% of the rated power on the best, most sunny day given our location). During very cold weather, we might get a higher then 100% current rating, but that is also the time of the year when we get the weakest sun due to it being very low to the horizon.

For max amperage, we take the maximum power amperage Imp (7.81a), and with only a single string, that is well below the 15 amp rating.

And, finally, for minimum voltage, we take the maximum power voltage Vpm (30.1) and multiply that by 12. That gives us 361.2 volts, which is well above the 150 v rating of the inverter.

Power Container Progress

The shipping container arrives today, and the SMA Sunny Islands and Smartformer already arrived a few weeks back. The welder is ready to start making the required modifications to the container, so we should start seeing some substantial progress on this front too.

Inverters on the ferry:

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We're certainly looking forward to seeing more progress, and working towards getting everything up and running in time for the summer!

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House: 2x SMA SI 6048 w 24x 2V DEKA Unigy II; 2x SMA SB 3000TL-US w 24x Sharp ND-H235Q2
Cabin: 1x Magnum MS4024 w 24x 2V DEKA Unigy II; 1x Morningstar TS-MPPT-60 w 6x Sharp ND-H235Q2; 1x 200 Watt Harris microhydro
Intertie: 1x SMA WB 3800; 1x Lambda GEN-600 DC Supply; 2x PSL pQube
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