This is my Solar Grid Tie and Off Grid Hybrid solar power system using 2 system with relays to automatically switch from grid tie to off grid system. This is a low cost system since most hybrid system is really expensive, the inverter alone costs as my whole system expense. The system works as Grid Tie primarily, Solar power is pumped to the Grid Tie inverter and the grid tie convert it to AC power and injects it in your utility outlet, reducing your electricity bill, unfortunately during power outage, the Grid Tie stops and your solar power would be idle, this is due to anti-islanding protection of the grid tie inverter to prevent utility personnel fixing something near your area and getting electrocuted. So during a power outage, my system will automatically switch to the Off Grid system to power your needs and back when power normalizes. Now what is my needs, basically its just internet routers/switches, DC fan, emergency lights, USB chargers, things that could still make me comfortable during power outages, these needs is connected to an exclusive 12v utility line. Some solar hybrid is connected to your AC utility line and can power your utility line during outages, like ref and tv and everything, but that system is very very expensive and not really necessary as power outages happens rarely and just be done in a few hours. My system has a separate 12v DC line to power only crucial 12v devices. It uses components similar to Car/RV with lighter plugs so it would be easier to use car accessories with it.
Why don't I just use an Off Grid system? well for me Off Grid is not economical if there is an accessible utility power available, its only good in the provinces with hard to no accessible electric utility provider or if it's just your Hobby. If not then its not economical. The reason is the battery technology. Battery is expensive, yes there are cheaper ones like lead acid batteries but those things would just die out after 2-3 years, leaving you in the dark while waiting for replacement, the more reliable/durable battery you buy, the more expensive it is. Your savings in Off Grid free energy would end up buying for battery replacements every couple of year or so, your panels, inverters, controllers would last years and years but not the batteries. Another downside of an off grid system is its hard to efficiently use it. Either the weather is good and the solar controller is cutting off too much power on the solar panel, or the weather is bad that it will lack power to fully charge your batteries. Unlike the Grid Tie system which just pump solar power to your Grid(reduce electric bill) what ever it can give and does not rely on problematic batteries that will leave you in the dark if one day it dies out and it will.
In an off grid system, you will use larger batteries that can supply your Needs in a day for about 12 to 14 hours supply daily, charge it and discharge it cycle everyday thus its life is reduced compared to standby batteries. On my system, you use half of the battery capacity as its only on standby and will only be used during power outages probably 6 to 8 hours usage and happens rarely. The problem with standby batteries is sometimes it gets neglected for months self discharged and dies out if it stays like that for long uncharged, that is why I place a battery voltage monitor to solve that. One of my panel is wired separately with a relay and voltage monitor cut-off, so if the battery voltage an example went too low like 12.3v that's like 70% capacity, the voltage monitor will cut off signal to one of the relay and one of the solar panels would switch automatically to the solar controller, charging the battery until a certain point, maybe set to 14.4v at full state, if the battery voltage monitor detected that, it would signal the relay and the panel connection goes back to the grid tie inverter. The voltage cut off can be set on specific voltage of your choice, you don't want to end up with an under charged battery like 50% when you need it most on a power outage.
This is the diagram of my solar hybrid system.
I have separate wires for every solar panel rather than use a combiner, I did that for experimental purposes, so I can do/change stuff without going into the roof, you don't need to do this but a least for one of the panel for charging battery backup.
I used a 12volts Grid Tie inverter to match my 12v solar controller/12v battery/utility line so it won't have problems interchanging by the relay due to mismatch voltage. If you have an MPPT solar controller that is capable of 24volts solar voltage and 12v battery, then having a 24v version of the grid tie inverter is better for efficiency, also configure your solar panel into a 24v system. I prefer the 24v version than the 12v in the solar voltage side. But when it comes to battery and utility line, I prefer to stick with the lower 12v, as most common devices are on 12v and its safer, you might also need a step-down buck module to reduce a 24v to 12v every time if you use a 24v utility system. Using 12v as default utility voltage may suffer from voltage loss compared to 24v. Voltage loss is when you run a long wire from the solar controller then to your room, the longer the wire is, the higher it suffers from voltage drop, like your solar controller would be like at 12.5volts, but when it reaches your room, it would be like 11.9volts. To fix this is to use thicker gauge wires, the farther your room is, the thicker gauge wire you use to reduce voltage drop, this would add expense of course, but for me its still cheaper and safer to get the thicker wires than put a step-down 24v to 12v buck converter on every end outlet, maintenance wise and safety, the wires are passive and will last for a long time than a step-down module and would consume a little watts on its circuit and led indicator whether you use it or not.
This is the battery voltage cut off monitor, it makes sure your battery backup won't be undercharged for long periods of time. You can specify the ranges of voltage for connect and disconnect, it cuts connection to the relay thus one of the solar panel connects to the solar controller and charge it, then reconnect when the battery is full, the solar panel switch back to the grid tie system after that.
This is what my Relay/Transfer switch looks like, I use an 8-pin relay so both system's positive/negative line is isolated. Its a 12v DC version. This is what controls the solar panels connection from switching going to the grid tie inverter or to the solar controller. 12v DC version is just the coil trigger, there are other variants like 24v or AC version, but I use the 12v DC version because I connected the coil to the 12v power supply. The coil is the one that automatically switch the connection, you power the coil, it connects to Line2(called NO or normally open), you remove the power of the coil, the line goes back to Line1(called NC or normally closed). So in Line2 where there is power to the coil, the solar panel is connected to the grid tie inverter, when there is power outage, the 12v power supply wont supply power to the relay coil, so the relay will switch back to Line1 where it is connected to the solar controller thus switching your system into Off grid. Typically, you use 3 relay. One for your main Solar panels 30amps, another for battery monitor charging 10amps and the last is for Load Output 20amps, the one that goes to the 12v Utility Line. Its better to use Larger Ampere rated capacity than the one you uses, like example, my 100watts solar for the battery monitor is about 5.5amps, I used a relay with 10amp capacity, this is to make sure ampere current won't bottleneck in the relay, it seems the relay wire inside it thin and maybe substandard as these are cheap relay so getting a larger ampere capacity is on the safe side, you don't want your relay to act as a fuse. It depends on your requirements on what amps you are going to use.
This is my 12v 30amp power supply, during normal days, this is the one that powers my 12v Utility Line, also this is where the relay's coil are connected. Despite my 12v Utility line is only rated at 10amps, I got a 30amps power supply to be on the safe side and room for an upgrade, I maybe planning to increase my 12v utility line into a 20amp after i replace my solar controller. Its a CCTV power supply, but as long as your usage on ampere capacity fits it, it will be ok, CCTV power supply is designed to run 24/7, with fan that automatically activates if it runs too hot. It also has a voltage adjust knob, so you can increase the voltage a little to help with the voltage loss. The power supply gets power in the grid. But it feeds on in the grid tie first during the day. When power outage occurs, everything switch to offgrid, your solar controller powering your exclusive 12v utility line and not the power supply. If you feel you want to go off grid, you can easily unplug the power supply and your system will go offgrid, of course you will need a larger battery for your needs.
This is a larger 8pin relay for the Load output, this is connected to the exclusive 12v utility line. This relay will select which is the source of power of the 12v utility line, normally the source of power is the 12v powersupply, but in an event of power outage, the coil which is also connected to the power supply loses power, thus switching it solar controller. The solar controller will now the source of power for the 12v utility line, turning your system into an off grid solar power system. Your 12v utility line will now be reliant on battery and solar power during those event. I get a higher 30A relay to be more robust, the relay also heats up, unbearable to the touch, good thing it has a metal back plate, I could attach a heatsink behind it to reduce heat. You can get heat sink in busted motherboards, videocards and power supply.
Here is a video to understand how 8pin Relay works.
This is my exclusive 12v Utility Line. I use lighter plug similar to what you would see on cars. These are easier to use, safer(fused) and compatible with car accessories you can buy. Very handy for plugging DC fan, emergency lights, USB chargers. It is also more efficient to use DC devices than doing an AC to DC conversion with inverters.
Just some switches, this manually cut off connections for the relay coil, so conviniently manually you can connect the solar panel to the controller if you plan to charge something like a car battery and you need the solar panel's power to the solar controller without removing screws and wirings.
My Grid Tie inverter and 12v Power supply share an outlet before passing into this sub-meter, and is then connected to the Grid outlet. Just to monitor how many watts the Grid Tie inverter is feeding the 12v power supply and the rest giving back to the Grid outlet.
