PV Diverters alternative

[JohnMo]

My second PV diverter has now given up. Coming to the conclusion the multiple switching isn't good for their health and they are cheap rubbish. Not willing to part anymore cash on them.

 

So looking to go basic but smart enabled.

 

Control scheme will be something like x kW being generated, battery state of charge is higher than x%, run full 3kW into immersion for 30 min recheck and run again etc

 

Can do the control via Shelly and home assistant - have both already.

 

But need a relay that is happy switching 3kW reliably - anyone got a recommendation? Not sure I would trust a Shelly do that directly

 

Does the control sound feasibly?

 

 

[Alan Ambrose]

Probably just the relay - you can probably change it easy enough if you can do basic electrical soldering. It'll be marked with it's part number.

[ProDave]

Open up the failed ones and post pictures inside.  I bet they can be repaired and improved.  I fixed one for a friend where the wiring uses was totally inadequate, rewired it with thicker wire etc and it has lasted years since.

 

Likewise a cheap Chinese inverter failed due to insufficient heatsink compound.  2 new transistors properly mounted with enough compound and that is still working years later.

[JohnMo]

Opened up the box, and found the fuse blown.

 

So first job replaced fuse and check over the wiring to the box. Other than that without desoldering it cannot be taken apart easily.

 

Big heat sink and fan at the top 

 

[JohnMo]

[joth]

I'm using a Carlo Gavazzi SSR with phase angle switching (0-10v comtrol) driven by Loxone. Runs cool and no issues so far 4 years in.

I see they even do versions with modbusTCP control which would be even easier integration to home assistant 

Edited October 26 by joth

[dpmiller]

so what's it doing/ not doing?

[JohnMo]

49 minutes ago, dpmiller said:

so what's it doing/ not doing?

Powered it's self off.

 

I have just bought a Sonoff POWR3. So now just need to put automation(s) in home assistant.

 

Something like 

 

PV output above 1500W and battery above 98%, run immersion. Need to put a cut off in there, so if battery charge drops below say 95% the immersion switches off - repeat

[SteamyTea]

8 hours ago, JohnMo said:

battery charge drops below say 95%

Is that the best way to charge a battery, the last 15% or so takes a long time and can possible shorted the battery life.

 

[JohnMo]

1 hour ago, SteamyTea said:

Is that the best way to charge a battery, the last 15% or so takes a long time and can possible shorted the battery life.

 

That's something I am sure of. I want PV to charge the battery, I don't want to export. There are two options I will implement, first run heat pump at a higher flow temp and buffer heat into floor. The other is to put heat in hot water cylinder via immersion.

 

The heat pump automation is between run rise and sun set, battery above 95% SoC and generating more than 1500W, run heat pump for one hour - this is repeating action. So if SoC stays above 95% and PV keeps generating more than 1500W the timer keeps getting reset. I may need to add another bit in there to make it seasonal.

 

So looking to do similar for the immersion, but instead of matching export to immersion power, looking to put the full 3kW to the immersion. So it may be better setting the automation similar to the heat pump, but set SoC to above 99% and then power immersion for say 10 mins (500Wh) with a repeat action. How does that sound?

Edited October 27 by JohnMo

[SteamyTea]

20 minutes ago, JohnMo said:

How does that sound

Would it not be easier to add some extra battery storage and just charge then to 80% before diverting.

A lot of it does depend on how much you discharge the battery.  If you usually only use 20% of the capacity, then no need to, but if you often run it down to 20% of capacity, then a charging routine is needed.

[JohnMo]

36 minutes ago, SteamyTea said:

Would it not be easier to add some extra battery storage and just charge then to 80% before diverting.

A lot of it does depend on how much you discharge the battery.  If you usually only use 20% of the capacity, then no need to, but if you often run it down to 20% of capacity, then a charging routine is needed.

Adding battery isn't cheap.

 

This time of year battery gets fully charged at night on E7. Have found the expected solar generation can be a bit hit or miss, we seem to have our own micro climate. Then depending on outside temp, heat pump can run in the evening. Last night (midnight) the battery was down to about 30%. The day before with very little solar was depleted by midnight.

 

So my base case, now clocks have changed, by 0830 battery is fully charged. 0030 timer set to get battery fully recharged overnight. DHW cylinder gets heated at 0030 on E7 electric via heat pump to 50 deg, heat pump then does heating until 0730, can run on either of two settings, standard WC or and elevated WC (3 degs hotter) based on thermostat settings and actual house temperature. At 0730 heating is mostly off, but standard WC setting runs in background, but due the charging floor overnight, and a lower thermostat setting, is generally just circulating water.

 

Then if excess solar being generated have automation to set heat pump to elevated WC, so heat pump runs and buffers heat to floor, but heat pump is likely to cycle.

 

So really about making best use of excess solar. Heat pump running will mop up 800 to 900W, but could be generating in excess of 4kW.

[JohnMo]

Well that was all pretty simple

 

Sonoff POWR3, £30 from Amazon 

An indication 20A switch for immersion heaters, a small JB and surface mount 1G box and 2 packs of glands £15 from Screwfix. So £45 all materials.

 

1 hour research on adding Sonoff to Home Assistant - Added Sonoff app to phone for pairing, same app added in Home Assistant plus SonoffLAN.

 

Simple automation, trigger - PV generation above 500W, condition battery above 98%,  run immersion for 10 mins, restart automation if condition remains true. Sends me a notification. Also records energy usage so added that to home screen.

 

Wired in parallel, so switch can trigger the immersion manually. Indication light on switch comes on when relay is triggered.

[ProDave]

7 minutes ago, JohnMo said:

Simple automation, trigger - PV generation above 500W, condition battery above 98%,  run immersion for 10 mins, restart automation if condition remains true.

That is vastly different to a "normal" PV diverter.

 

Your example appears to be turning on the immersion with a relay and leaving it on for a time and re evaluating.

 

A "normal" PV diverter measures PV generation and house consumption (in my case every half second) and adjusts the power being sent to the immersion by burst firing the immersion using a solid state relay.

 

I guess in your case you are using the immersion as a "excess power dump load" so it only needs to be a coarse on or off, with the battery controller soaking up the rest and doing the detailed work.  

[JohnMo]

4 minutes ago, ProDave said:

That is vastly different to a "normal" PV diverter.

 

Your example appears to be turning on the immersion with a relay and leaving it on for a time and re evaluating.

 

A "normal" PV diverter measures PV generation and house consumption (in my case every half second) and adjusts the power being sent to the immersion by burst firing the immersion using a solid state relay.

 

I guess in your case you are using the immersion as a "excess power dump load" so it only needs to be a coarse on or off, with the battery controller soaking up the rest and doing the detailed work.  

Advantage of the battery in the system is use case becomes simple. Took me a while for that realisation, keep it simple. Think the "normal" diverter and battery control may fight each other a little and you certainly get electric slipping past to the grid.

[JohnMo]

Update

Have now got the system fully automated, after a few iterations of home assistant automation.

 

2 diversions have been set, have a higher flow temp setup on ASHP which is selected via a shelly relay. So that clicks on if forecast temp minimum is below 9 deg, battery is above 96% and generating more than 500W, it runs for 20 minutes minimum and after stopped if battery is below 94%.

 

And immersion similar to above but without weather forecast temperature requirements. Immersion gets the full 3kW instead of small amounts, so seems to get the water hot in no time. It has no time limits set just switches off when battery drops below 94%.

 

So the way it runs, battery charged overnight, keeps house in energy until PV starts up, PV recharges battery to 97%, once there we start to use immersion or ASHP, if generation is enough it keeps going for as long as needed, or clicks of when battery hits 94% - repeat.

 

Getting way less energy slipping past, making its way to the grid. Original PV diverter would only step in, once batteries fully charged and exporting above a set number of watts.

 

Battery fully charged on E7 overnight.

At 1pm we have generated 8.3kWh PV.

8kWh of heat added to floor via ASHP.

3.7kWh added to DHW - cylinder at 65 degs.

Have had a cooked lunch

And battery is sitting at 95%

PV is generating 3.5kW.

 

If you have a battery, a commercial PV diverter is not needed and isn't really that good at optimization of battery usage if you don't paid for export.

 

Charging the floor doesn't seem to overheat the house, it does push back ASHP normally restarting on WC for many hours.

 

DHW hasn't needed to be heated for a couple of days now, it's all being done via the immersion, which didn't happen very often before.

[Andehh]

That is very, that level of electrical capability is a skill I wish I knew more about. Alas life gets in the way.

[JohnMo]

58 minutes ago, Andehh said:

That is very, that level of electrical capability is a skill I wish I knew more about. Alas life gets in the way.

Taken a long time to get head around it, didn't come that easy. A breakdown forced my hand.

 

Next job is sort more diverted electric dumps, thinking about towel rads next.

 

Ended up with a cylinder up to 73 degs, couldn't get it any hotter, and 14.5kWh in the floor.

[sgt_woulds]

Are those single-insulated tails?  (Blue and Brown cables)  If so, they need additional mechanical protection to comply with wiring regs.  

 

Diverters are prone to failure after a few years - they are normally fitted in airing cupboards without airflow - heat soaking of components is probably a factor in the failure rates.  The most robust units we fitted were the Solic 200 (Designed by an ex-MOD engineer - bulletproof) without bells and whistles or 'smart stuff' going on.  

 

From your description, once the battery tops up, and the underfloor is up to temperature, the immersion kicks in at full whack.  If PV is not producing enough to supply the full rated power of the immersion, (and other loads in the house) the battery kicks in to supply the rest?

 

If this situation continues for a period of time then battery drops below 95%, immersion switches off and goes back to charging the battery.

 

In this scenario, the battery is discharging and recharging a lot at the top end of its capacity.  Have you discussed this with the manufacturer and are they happy to maintain the warranty in this scenario?  The last 20% of charging on Lithium cells creates heat and internal resistance - depending on the chemistry this will put a lot of stress on the cells and shorten the life expectancy.

 

When we were running a fleet of 4 Nissan E-NV 200,  half the vehicles were charged to 100% regularly but then discharged, (driven!) until at least 20% before a full recharge cycle.  After 2 years battery health was very good, with no loss of range (140 miles indicated on the GoM but 100 miles max in RW use with load - 80 miles average per day with at least 400 kg in the back).

 

The other vans never dropped below 75% SOC and were constantly topped back up to 95-100%, (short infrequent road trips with same loading).  After 2 years the range had reduced in RW use to 80 miles max.

 

I realise the chemistry, scenario and stress is different for a vehicle compared to a static battery but I'd be surprised if you'll achieve maximum life expectancy with this regime - which could cost a lot more in the long run than replacing diverters.  

 

Please keep us updated - it would be useful to know how this works after a couple of years as it is an interesting setup.

[JohnMo]

40 minutes ago, sgt_woulds said:

The most robust units we fitted were the Solic 200 (Designed by an ex-MOD engineer - bulletproof) without bells and whistles or 'smart stuff' going on.  

Been there that failed also

 

41 minutes ago, sgt_woulds said:

the battery kicks in to supply the rest

Correct 

42 minutes ago, sgt_woulds said:

 

In this scenario, the battery is discharging and recharging a lot at the top end of its capacity.  Have you discussed this with the manufacturer and are they happy to maintain the warranty in this scenario?  The last 20% of charging on Lithium cells creates heat and internal resistance - depending on the chemistry this will put a lot of stress on the cells and shorten the life expectancy

So are you saying people shouldn't put the oven or kettle on either? The general situation is especially in winter is the battery is generally depleted over the evening from the 95%

[sgt_woulds]

In a normal situation with BSS kettles, ovens, immersions, etc would run off the solar and battery with grid backup if there is too much demand and the battery would be depleted well below 95%.  It also wouldn't immediately recharge to 95% after use.  Thus it would be in a more depleted state towards the evening with normal use case and charging profile.

 

Perhaps I'm not understanding your setup correctly, but it sounds like you are not letting the battery drop below 95% during sun hours or overnight when it charges on E7?

 

How many hours in a day will it deplete below 50% or complete a full cycle from 20-80%?