All-In-One versus separate SCC and Inverter?

I'm designing an off-grid solar generator for the lighting of a building,
so (after reading many FIY threads) I have two main questions in mind:

1. I cannot decide between getting an All-In-One solar generator system versus getting a separate SCC and Inverter?

I'm considering getting a "SCC only" because I want to be off grid and I don't want to have the risk to send back any energy to the grid.

However, with a "SCC only" I wonder how to determine when the battery is discharged (so I could disconnect my load and connect it to the grid)?



2. I would like to dump any solar excess into a diversion load, during the summer.

Some devices, such as the Midnite SCC have a load diversion control feature,
but I am puzzle about the batteries micro cycling issue, after watching this video:



I wonder how to trigger a relay to activate a dump load inverter if the SCC don't have a load diversion feature?


To be able to connect a dump load diversion is also something that I am considering for my choice of
getting an All-In-One solar generator system versus getting a separate SCC and Inverter:


Conclusion:
I would like to make progress in my project and to find the AIO or the separate solar devices that I will need.
Any additional comments would be very helpful, as I feel being in front of a wall.

Why do you want a "dump load"? Do you have an actual use or are you of the misunderstanding that somehow the "excess production" needs to be disposed of? It doesn't work that way.

Good inverters also have built in automatic transfer switches and chargers. My inverter can be programmed to run everything off the grid and only use solar power if the grid goes down, or it can run everything off solar and switch to grid if the solar power gets too low, and it switches in less than one cycle of electricity (1/60th of a second here).

I have Midnite Solar classics feeding a battery bank, which feeds Samlex Evo inverters, a 4kw and a 2.2kw. The 4kw feeds my house, the 2.2 my shop. The house has a transfer switch by the main power panel where I can switch up to 6 circuits from grid to solar, that's done manually and prevent backfeeding of the grid. The shop is run entirely off solar, the 2.2kw Samlex charger runs my 2HP lathe, mill and table saw just fine (one at a time).

Mostly AIO systems could be configured to not send power to the grid and can be configured to do most of what you need.

For a quasi-DIY approach that requires some electric knowledge, my few small ideas below:

About the lights, you can use an SCC with a dry contact output that closes when:
- battery voltage is higher than VELB + a certain value
- the voltage from the PV array is lower than a certain parameter, which tells the charger that it is night
Those SCCs are mainly used for public streets illumination. They will charge the battery and provide power to the load only during the night or a user defined period.
The dry contact output of the SCC can be used to tell an inverter to leave stand-by mode and consequently power on the external lights. In case of an SCC with a direct load output, you can get the same result by using an external relay.

About switching between grid and inverter output, you can wire the same SCC contact output to a two-way relay or to a double relay with interlock.
If you plan to power on all the lights together, take power surges into account when choosing the inverter size. Also, whether the fans will be spinning or not it will depend on the internal inverter temperature, which is more or less a byproduct of the inverter load and efficiency. When picking an inverter you could check the efficiency curve to understand which would be better at your costant power output.

About using any excess PV power when battery is charged, you could use a battery BMS with a dry charge/discharge output to control an external relay to provide power to any other load during the day when battery voltage is only at some range near VEoC, to prioritize most of the energy usage for the night. Note that the load during the day could be connected and disconnected many times, based on the weather and the actual power usage, if the day usage policy will be too strict, hence the voltage range from N to VEoC for powering the load will be set too narrow.
This will be depending on how you will be sizing everything.

About "micro cycling" I don't see the big problem that is usually advertised. If at the EoC the battery is connected to an external load that draws current, the battery voltage will normally drop, but the current that goes into the external load and that is lowering the voltage is almost immediately compensated by the solar charger and what you take from the battery is just a small initial current.
Voltage and battery capacity are never to be considered linearly proportional, especially under load.
If the load is continuously connected and disconnected enough to create the "micro cycling" problem, that means the load that takes the excessive solar power is oversized compared to the overall solar system. An oversized load that takes the excessive solar power will naturally discharge the battery so that it will be disconnected and connected again in a continuous loop.
But that is just my general opinion on the matter and I could not be taking into account many factors and system setups.

Please correct me if I'm confused by original posting. Always thought "dump" pertained to wind generators. There are devices that choose inverter or grid Will: automatic transfer switch Separate components do have $$ advantage if repairs are needed. Just replace broken components, not the whole thing. My cheap 2000w inverter has a thermostat controlling the fan. Fan is on periodically only when loads are higher.

再生可能 エネルギー said:

would like to make progress in my project and to find the AIO or the separate solar devices that I will need.
Any additional comments would be very helpful, as I feel being in front of a wall.

Click to expand...

Way overthinking things, and reading wonky stuff.

You don’t need a dump load.

What we need is the wattage and duty cycle of said load? Then we can see what you need to handle and advise. A 1000W load like you mentioned is potential handled several different ways.

Post what stated 1000W load is and it’s duty cycle. Then folks can provide advice regarding the system needed to support your use

Bvillebob said:

Why do you want a "dump load"? Do you have an actual use or are you of the misunderstanding that somehow the "excess production" needs to be disposed of? It doesn't work that way.

Click to expand...

Well, to reduce (in half) some electricity bills, I'd like to get at least 15kWh of solar electricity
a day in winter, which means about 20kWh of solar energy, considering all the conversion losses.

It happens that I can easily install between 18 and 24 large PVs of 400W 72 Cells type.
Doing some irradiance calculation, I estimate that those PVs, with different orientations,
will produce about 20 kWh in winter and more than 35 kWh during the summer.

So yes, I will have some excess solar energy that I plan to use to run a heat pump to get some hot water.
Currently there are two water heater using natural gas with a consumptionof about 300 Therms a month.

I plan to keep the natural gas heater to get instant hot water and to use a heat pup to pre-heat the water
and reduce the gas consumption. The heat pump could be running only few hours a day on solar energy,
or maybe thereafter using the grid, but I need to do some experimentation.

The hot water system has a recirculation pump, so I plan to install the heap pump as part
of the recirculation circuit to keep the overall temperature of the water tanks uniform.

Bvillebob said:

Good inverters also have built in automatic transfer switches and chargers. My inverter can be programmed to run everything off the grid and only use solar power if the grid goes down, or it can run everything off solar and switch to grid if the solar power gets too low, and it switches in less than one cycle of electricity (1/60th of a second here).

Click to expand...

I looked at various All-In-One inverters users manuals, and noticed that you can select some settings
to only charge the battery using solar energy. But I am afraid that someone migh play with the settings
and by mistake will send solar energy back to the grid.

Or also, my electrical company might force me to have a subscription to smart metering because
I have an AIO Inverter capable to send energy back to the grid even if I don't plan to do it.

Bvillebob said:

I have Midnite Solar classics feeding a battery bank, which feeds Samlex Evo inverters, a 4kw and a 2.2kw. The 4kw feeds my house, the 2.2 my shop.

Click to expand...

I looked at the Samplex web site, and all the devices seems very sturdy.

Bvillebob said:

The house has a transfer switch by the main power panel where I can switch up to 6 circuits from grid to solar, that's done manually and prevent backfeeding of the grid. The shop is run entirely off solar, the 2.2kw Samlex charger runs my 2HP lathe, mill and table saw just fine (one at a time).

Click to expand...

I need to have an automatic transfer switch, to switch between the grid or the battery inverter based on the batteries Soc.

circus said:

Please correct me if I'm confused by original posting. Always thought "dump" pertained to wind generators.

Click to expand...

Good point, wind generators are not like solar panels. You cannot disconnect them,
otherwise there could be a risk of overvoltage.

So resistors have been used to absorb some surplus of energy.
Those resistors could be used to heat water or to simply heat a room.

Does the "Diversion" load could be more appropriate to use
to describe transferring solar surplus to an external load?

circus said:

There are devices that choose inverter or grid Will: automatic transfer switch Separate components do have $$ advantage if repairs are needed. Just replace broken components, not the whole thing. My cheap 2000w inverter has a thermostat controlling the fan. Fan is on periodically only when loads are higher.

Click to expand...

I was looking at such transfer switch, based on battery voltage, but I was considering to build one myself.

However, considering that some other person that myself could play with the solar system settings,
it seems preferable to have a system already validated,
and honestly I could not build a system as practical and as sturdy.

I would have to use it not directly but to control my own transfer switch as I need to use
the solar energy like an UPS to keep the light on in the case of power grid failure.

Also, I plan to have a second Inverter used to run a Heat Pump. So in this case.
I would need to install some delays, I think like 3 minutes, when transferring power source,
because the phase could not be guaranteed.

Noday said:

Mostly AIO systems could be configured to not send power to the grid and can be configured to do most of what you need.

Click to expand...

I am just afraid that someone might change my setting and send solar energy to the grid.

Noday said:

For a quasi-DIY approach that requires some electric knowledge, my few small ideas below:

About the lights, you can use an SCC with a dry contact output that closes when:
- battery voltage is higher than VELB + a certain value
- the voltage from the PV array is lower than a certain parameter, which tells the charger that it is night
Those SCCs are mainly used for public streets illumination. They will charge the battery and provide power to the load only during the night or a user defined period.
The dry contact output of the SCC can be used to tell an inverter to leave stand-by mode and consequently power on the external lights. In case of an SCC with a direct load output, you can get the same result by using an external relay.

Click to expand...

I am considering using the 'dry' generator connection to start an Inverter and run a load.

However, to detect possible cloudy weather, with low solar power, I was thinking to add '
a DC probe connected to the wires comming from the PV array tro avoid discharging the
battery in case of bad weather, and to use the Grid instead.

Noday said:

Also, whether the fans will be spinning or not it will depend on the internal inverter temperature, which is more or less a byproduct of the inverter load and efficiency.

Click to expand...

I plan to run a larger Inverter to run an Heat Pump,
so I could send the cold air output to the Inverter to avoid having the fan getting activated.

Noday said:

When picking an inverter you could check the efficiency curve to understand which would be better at your costant power output.

About using any excess PV power when battery is charged, you could use a battery BMS with a dry charge/discharge output to control an external relay to provide power to any other load during the day when battery voltage is only at some range near VEoC, to prioritize most of the energy usage for the night.

Click to expand...

Is it what is discribed in this video: Difference between Common Port & Separate Port Battery Management System (BMS)

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