3kW Grid Support Solar System

Here is an overview of my Grid-Support Solar setup. It blends the benefits of an off-grid and an on-grid setup. I designed and installed this system myself on my house in Tegucigalpa, Honduras.

Main System Components

  • 4x Trojan SAGM 12v 105Ah AGM Batteries
  • 9x Peimar SG340P Panels (3 in series, 3 in parallel)
    • Nominal output: 340W - 38.3V & 8.88A
    • VOC: 46.73V
    • ISC: 9.51A
  • Growatt 24v SPF 3000TL LVM 3kW All-in-one Inverter
    • Inverter output: 3000W output @ 120 VAC
    • 2000W max solar input
    • 150VDC max VOC
    • Can be upgraded to 240V or more input & output by buying more units and connecting them in parallel
  • Lots and lots of cable. See details on cable sizes in the diagram below.
  • DIY combiner box with inline auto/marine fuses
  • Large disconnect cables with L5-30 connectors to allow for easy system bypass or connection to a generator
  • Concrete blocks to support solar panels (the panels are also tied to the blocks with galvanized wire)
I'm still learning!
This has very much been a learning process for me. If you have comments or questions on my system, please let me know!
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My System Design

Click on the diagram to pan or zoom. Click the camera icons for photos of that part of the system.

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  • I selected 7 breakers that had high during-the-day usage to move to the sub panel that is fed by the inverter.
  • I oversized my solar array by 1000W to get better performance in the early morning. It often rains in the afternoon but the mornings are almost always clear.
  • The L5-30 connectors on input and output of the inverter give a lot of control. You can easily bypass the inverter or connect a generator to the inverter input (or directly to the sub panel input and bypass the inverter entirely)
  • Ground and Neutral are bonded at the output of the inverter in the L5-30 connector.
  • My main load center also bonds G-N. I was concerned about double bonding, but Ian at Watts 24/7 helped confirm there is no issue with this double bond as long as nothing else is connected to the ground wire in the cable between the main load center and the input of the inverter. Curiously, a Growatt representative told me that bonding on the output could damage the inverter, but even their manual talks about bonding the output.
  • My batteries are connected in series, then parallel for double the Ah and double the voltage. If you look closely, you'll see I connect the inverter + and - to opposite ends of the parallel stack so that they charge/discharge evenly. I could probably get away with 2 more batteries in parallel, but beyond that, I should upgrade to a 48V system
  • I would ideally drive a ground rod into the ground for the solar panel ground, but I don't have easy access to do that and my house does not have a ground rod (the ground comes from the center tap transformer on the street).
  • Except for the Growatt Inverter, my equipment choices were limited on what I could find avaliable in Tegucigalpa, Honduras

Want an interactive diagram like this?

I had fun putting this interactive design together. If you would like me to build a model like this for your system, just let me know!

What Is Grid-Support

Off-Grid Grid-Support On-Grid
How it works Your panels connect to your inverter and batteries. You have no connection to a grid. You do not need an electricity meter. You select part (or all) of your house to be fed by a solar system. Generally, you include a transfer switch so that if the inverter cannot supply power, you will fall back to the grid power. You do not need a special meter as you will not feed power back to the grid. With a special meter, you can sell your excess power back to the grid. It is possible to completely offset your consumption by selling this power. Special permits and equipment will always be needed.
When do you have power? As long as the sun is up or your batteries are full enough to power your inverter. As long as the sun is up, your batteries are full, or the grid has power. Almost always. As long as the grid has power. If there is a power outage and you have no batteries, generally your system will disengage to prevent backfeeding to the grid
Storage You generally need to size your batteries for how many consecutively cloudy days you experience. Could be 4 or more days. Batteries can be quite small, or large if you want to survive power outages. You get to decide the balance. Generally no storage. When the power goes out, you lose power too.
Money Savings Every kWh of power you use is free With smaller batteries, you will really only offset the power you use during the day. If you run appliances or AC at night, this will still be power you buy from the grid. You cannot sell power back to the grid, so you should only generate what you need. Probably the most cost effective option. You can vastly oversize your panels because you can sell energy back to the grid.