Solar, HWC, Shelly… Oh my!

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MadEngineer

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#319197 1-Apr-2025 12:09

timmmay:

Stu1:

looking foward to the pics

Here's a few pics.

The SigEnergy 6kw inverter on the wall. It gets reasonably warm, 55c today when it was putting out around 6kw.

Switchboard with modules 1) Underfloor heating switch and timer 2) Siemens contactor 3) SigEnergy switchboard module 4) ShellyPro EM-50 controlling hot water and providing power usage for hot water and ducted heating.

You get a lovely big green stick on your meter board.

Solar panels look like solar panels. These are the 9 west facing, we have another 13 north facing that I can't really photograph but they look like solar panels on a roof. Total panels 9.2kw.

The electrician didn't use the ABB 40A switchboard switch which is a bypass to the Shelly, he supplied a Siemens switch because he said it makes it look better if they're all the same brand. So I have an ABB 40A switchboard switch plus a heavy duty Vemer digital timer that used to be in the switchboard sitting in my office until I work out what to do with them. I'll probably sell them when I get around to it.

As someone requested, taking this out of the main thread.

@timmmay can you share what the Shelly setup for that looks like? Have just ordered an EM-50 and a contactor.

You're not on Atlantis anymore, Duncan Idaho.

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#3359478 1-Apr-2025 13:19

@MadEngineer happy to help, what exactly would you like to know about the setup? In the switchboard it looks like the Shelly, a bypass switch, and the controller side by side, the electrician set it up and I don't know much about the details. The EM50 I integrated with Home Assistant but the Shelly itself can do basic timers and such, not much to tell you about there. I have a spare bypass switch because the electrician used his own.

MadEngineer

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#3359500 1-Apr-2025 14:44

I'm curious about the configuration on the Shelly side. I'm thinking to start with I'll simply have a timer function on it but may look later to implement cycling it based on solar output.

The obviously perfect scenario would be to have the tank only heated with solar but you also have to account for keeping the water sanitary which means providing it with enough on-time regardless of generation, but never for example powering it on during morning showers until the sun rises. Bonus points if you could "boost" the hot water say to an extra 10degC during periods of excess generation.

Hopefully I can get away with using the inverter's own monitoring (and its own additional CT input module) without adding another Shelly to monitor solar.

Are you running a HA server?

I'll just throw this into the mix too: Save on Electricity Bills with CATCH Power | Solar Energy Management anyone tried that? Preferring to go with Shelly however as it's more available.

You're not on Atlantis anymore, Duncan Idaho.

eonsim

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#3359509 1-Apr-2025 15:32

MadEngineer:

I'm curious about the configuration on the Shelly side. I'm thinking to start with I'll simply have a timer function on it but may look later to implement cycling it based on solar output.

...

I'll just throw this into the mix too: Save on Electricity Bills with CATCH Power | Solar Energy Management anyone tried that? Preferring to go with Shelly however as it's more available.

There are two different ways to use solar to reduce your hotwater bills:

Solar diverter - Catch Power, Paladin, Eddy etc

Hotwater timer - Standard timer, Shelly etc

The diverters work by shaping the power flow so the hotwater cylinder is only heated using spare solar power that would otherwise be exported (by default they do not allow any grid use and shape the power to make sure it heats the cylinder). They do this by monitoring the exported power and redirecting it to the hotwater cylinder, they will also have systems to keep track of power demand from the hotwater cylinder and make sure it fully heats at least XX hours to prevent bacterial growth etc. Tend to cost ~$1,000 with install, and will switch to grid power if you solar system stops working etc.

The basic timers are a cheaper cruder system which simply turns the hotwater cylinder on at times of day when you are likely to have plenty of solar power, or at night when power is cheap or free. If there isn't enough solar power when the timer is turned on the cylinder will draw a mix of Solar and Grid power. A shelly is a more sophisticated version of a timer, in that you can control it digitally via your phone or home-assistant and program it to respond to the solar power, that allows you to set rules like, 'turn on between 10am and 5pm if there is >3kW being exported'.

So for example with a 5kW system with a 3kW cylinder on a typical day:

Solar diverter, as soon as there is spare power being exported the diverter will shift it to the hotwater cylinder so if there is 1kW spare at 8am it'll get sent to the cylinder, constantly matching the power sent to the cylinder to what excess is being generated. Approximately zero grid power will be used, even if at 11am a cloud covered the sun reducing generation to 0.
Basic timer - Hotwater cylinder will turn on and pull it's full 3kW at the specified time, regardless of amount of generation. So if at 10am it turns on and there is 2.5kW being exported it will grab that and an extra 500W from the grid to make it up to the 3kW it needs. At 11am when the solar drops to zero the cylinder will draw all 3kW from the grid. This substantially reduces the amount of grid power used to heat hotwater (assuming you set the time correctly) but does not eliminate it and depending on the day and weather could use alot of grid power.
Shelly with Power rules - Shelly is only set to turn on when there is at least 3kW of exported power. At 10am the shelly checks the generation and stays off as there is only 2.5kW spare, at 10:15 it turns on when export passes 3kW. At 11am it would turn off as the generation is now less than 3kW, and would turn on when the generation recovers back to 3kW. This works much the same as the basic timer, plus what ever smart rules you add around spare power. Requires a custom solution and depending on how it's programmed will use less grid power than a basic timer, but more than a diverter.

timmmay

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#3359513 1-Apr-2025 15:43

Given power costs us 21c and we get paid 19c for it I'm not too bothered about using our own power vs exporting. I'll make some basic efforts to use the solar ourselves, but I'm not going to install a $1000 diverter or automate too much. It'll probably take a few weeks to get the export meter installed, so I'm doing the odd thing manually until then, if it's looks really sunny I turn the HWC on.

I basically have Home Assistant monitoring excess solar, if there's 3kw available for 10 mins it turns the cylinder on. If solar drops, oh well, I leave it on. If the big heat pump comes on and there's not enough solar I might turn the HWC heating off. I also have a time based trigger that monitors total time the HWC has been switched on for the day, if at around 2pm it hasn't been on for at least 3 hours today it turns it back on.

Here's a quick dashboard I created in HA with Power Flow Plus. I started using Home Assistant a few years back, I have most things connected to it - three heat pumps, hot water now, blinds, a bit of lighting, probably other bits and pieces.

MadEngineer

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#3359571 1-Apr-2025 19:35

^ Out of interest, is there a 2A breaker protecting the EM-50 in your switchboard?

You're not on Atlantis anymore, Duncan Idaho.

timmmay

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#3359573 1-Apr-2025 19:41

I have a switch labelled 6A "timer, coil, meter power" so maybe, not sure. I figure electrical work like this if subject to regulations and the electrical will do whatever is required.

thewabbit

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#3359623 2-Apr-2025 07:32

I've setup my HWC to come on an hour before peak solar and to stay on for 3 hours. This is done in HASS using the solar production graph and an automation. I have also setup a button on my dashboard that allows you to 'boost' the HWC for a period of time

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prob

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#3361341 6-Apr-2025 16:19

Greetings. So we can compare, can you please share the cost of the system, your normal usage and your electricity plan?

MadEngineer

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#3363305 12-Apr-2025 19:40

24 panels. My power bill is ~$250/month and the number of panels will be overkill but when I'm getting it at a good rate it'd be silly not to.

You're not on Atlantis anymore, Duncan Idaho.

prob

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#3363398 12-Apr-2025 21:34

I have similar power needs, went for 18 panels and now regret not getting more...

MadEngineer

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#3363550 13-Apr-2025 11:54

As we were loading up the roof with our panels the sparky was arranging them so that we could expand if required. We could add another four or so. The panels themselves are a relatively cheap component of the whole system. When you buy them they are pre-wired with connectors and just plug in to each other. I'd need to extend the rails however which means buying more of the mounting hardware.

One more day is required to complete my installation. The weather last week caused a bit of a delay. Looking forward to watching the numbers and setting up the Shelly.

You're not on Atlantis anymore, Duncan Idaho.

MadEngineer

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#3364513 15-Apr-2025 22:09

One more day and the install is done, then have to wait for the 3x certificates to be fired off to the power co to get our meter set for export. This can take over a month I hear.

Can't wait to have this not burning power after dark: