DIY solution for charging with excess solar without Zappi/Hypervolt

[vanhtu1987]

I recently acquired a Shelly EM Shelly EM + 120A Clamp | Shelly Store UK | Smart Home Automation to make use of our excess solar, as it's that time of the year again.

Using the data I got from it with the help from Home Assistant Home Assistant . I used a TP-Link Tapo P110 smart socket to turn on our electric heater whenever there's excess solar, which worked pretty well with low-latency. The only misgiving is that the heater does not manage to use all the excess solar, since it has a few fixed heat settings thus it usually has to turn off completely or not manage to make full use of the excess. All in all, it was a good proof-of-concept.

Today I set up Home Assistant to integrate with the car to start charging when there's a certain amount of minimum excess solar, and vary the charging amps so that it can use all of the excess, with fine granularity of up to 250W (~1A, since it's the unit of charging that the car lets us set). I managed to get 10% over 4 hour of charging:

The blue line is the charge amperage which mirrors solar output. Not a bad result for basically a lunch out and a couple of hours! . This will tide us over nicely until we get our storage battery system.

I can share my automation configuration in HA if anyone is interested.

 

[djtaylor]

I recently acquired a Shelly EM Shelly EM + 120A Clamp | Shelly Store UK | Smart Home Automation to make use of our excess solar, as it's that time of the year again.

Using the data I got from it with the help from Home Assistant Home Assistant . I used a TP-Link Tapo P110 smart socket to turn on our electric heater whenever there's excess solar, which worked pretty well with low-latency. The only misgiving is that the heater does not manage to use all the excess solar, since it has a few fixed heat settings thus it usually has to turn off completely or not manage to make full use of the excess. All in all, it was a good proof-of-concept.

Today I set up Home Assistant to integrate with the car to start charging when there's a certain amount of minimum excess solar, and vary the charging amps so that it can use all of the excess, with fine granularity of up to 250W (~1A, since it's the unit of charging that the car lets us set). I managed to get 10% over 4 hour of charging:

View attachment 926049

The blue line is the charge amperage which mirrors solar output. Not a bad result for basically a lunch out and a couple of hours! . This will tide us over nicely until

I can share my automation configuration in HA if anyone is interested.

I'd be interested in taking a look. I don't run HA but use emonPi and have been fiddling about with a python script to call Tessie API's to the same effect.

 

[vanhtu1987]

I'd be interested in taking a look. I don't run HA but use emonPi and have been fiddling about with a python script to call Tessie API's to the same effect.

The nice thing about HA is that it already has the necessary integration for these devices, so what's left is mostly the programming.

Here are some potentially relevant information for the automations I set up for the car.

This monitors the excess power to start charging the car at a minimum of 5A when the car is is home, plugged in and not charging:

Adjusting the car's charge amperage is a little bit more involved. This runs every 5 seconds when the car is being charged at home at < 16A (since if I force it to charge then it'd always be at 32A):

then still in the same automation, the actions are:
- Check if we're drawing from the grid:
+ If so, check if we're charging at 5A:
* If so, stop the charging
* If not, drop the charge amp by 1
- If not, check if we are generating at least 250W:
+ If so, increase the charge amp by 1

Both of these automations in effect mean that:
- The car will start charging if the system is generating at least 5A for a minimum of 15 minutes
- When charging, the charge amp will vary by 1A at a time every 5-15 seconds (the period is 5 seconds but there are additional delays due to communication with the car)
+ It also means that if there is cloud cover that stops the generation, the charging is allowed to happen (at gradually decreasing charge amp) for 1-2 minutes before the charging is stopped. This provides a nice hysteresis at the cost of a small amount of power being draw from the grid.

The JSON config would be clearer, I'm happy to share if you'll find it useful.

 

[NewbieT]

Why not cut out the Tessie API and communicate straight with Tesla? API is fairly straight forward once you have a token.

 

[WannabeOwner]

the charging is allowed to happen (at gradually decreasing charge amp) for 1-2 minutes before the charging is stopped

I assume your home battery will help you there - allow the charging to continue for longer / improved hysteresis, depleting house battery somewhat, rather than stopping car charging (as I understand it reducing stop/start of car charge would prevent undue wear on the contactor).

In that vein I dunno what Zappi does - it adjusts the AMPs, but once it gets down to 5AMPs I presume it will stop if a cloud comes over.

With house battery my additional sophistication would be to add a "Sundown" time and the moment it falls below 5AMPs then stop - otherwise using battery with no hope of it climbing/much above 5AMPs again that day.

That depends on what tolerance you have wrt house battery size I suppose. I use 7%/hour over night, so every-little-helps

The JSON config would be clearer, I'm happy to share if you'll find it useful.

Yes please Thanks

Dunno what else you are doing with TP-Link Tapo?

We recently rewired the house and took opportunity to put in an HA system for the lights, so I have no interest in 3rd party for that, but I am interested in other areas (I saw a Dr Jake YouTube yesterday of SwitchBot which had a device to push/retract a physical light switch! - and a curtain closer/opener ...)

- but apart from using my TP-Links (Kasa in my case 'coz I thought I might want ITTT) to log consumption of devices, I haven't got around to trying to think of excess-consumption sources in Summer (and things to turn off at night). We have a portable Air Con unit, but basically if its hot we turn that on regardless. We are also having a borehole installed, so the pump for that could be intermittent when sunny, and maybe additional air pumps for the fish pond ... beyond that unless the sunny days coincide with when I have driven somewhere and need to recharge I'm exporting. Interseasonal store would be good ... I haven't seen anything at a "Domestic" scale

 

[djtaylor]

Why not cut out the Tessie API and communicate straight with Tesla? API is fairly straight forward once you have a token.

Yes I may do that. I got as far as Tessie simply because I was playing with the API on the "try it now" webpage one night in bed.

 

[djtaylor]

The nice thing about HA is that it already has the necessary integration for these devices, so what's left is mostly the programming.

Yes that would be nice. The integration and conditionals would certainly make it easier.
I may crack out another Pi or maybe install it on the one I'm using for TessieMate.

 

[vanhtu1987]

I assume your home battery will help you there - allow the charging to continue for longer / improved hysteresis, depleting house battery somewhat, rather than stopping car charging (as I understand it reducing stop/start of car charge would prevent undue wear on the contactor).

Yes, we haven't had one installed yet but this would work well enough to absorb the excess once the battery is fully charged. The gradual ramping down of charge amp before it's stopped completely will cost perhaps 40W, which should be easy to recoup.

In that vein I dunno what Zappi does - it adjusts the AMPs, but once it gets down to 5AMPs I presume it will stop if a cloud comes over.

As far as I understand, the Zappi has 2 modes for this:
- Eco: which charges at a minimum of 1.4kW regardless of whether there is solar generation.
- Eco+: which after a delay (configurable by up to 4 minutes), charges the car on excess solar only and stop the charge as soon as generation stops.
+ It has a slider called "Minimum Green Level" that allows partial imports from the grid in case there's not at least 1.4kW of surplus power, but it doesn't seem to have a setting for 'maximum draw before charging must be stopped' like this custom solution.

I don't have first-hand experience with the Zappi, but it seems that partly cloudly day might be a bit of an issue with frequent charge starts/stops, particularly considering that with storage battery system it would be preferable to actually draw a bit of energy from the battery.

With house battery my additional sophistication would be to add a "Sundown" time and the moment it falls below 5AMPs then stop - otherwise using battery with no hope of it climbing/much above 5AMPs again that day.

That depends on what tolerance you have wrt house battery size I suppose. I use 7%/hour over night, so every-little-helps

The car is only instructed to start charging if there's a minimum of 1.25kW export for 15 minutes so I'd expect the charging to stop for good during sundown, or if it starts raining .

Yes please Thanks

Please have a look at the attached.

Dunno what else you are doing with TP-Link Tapo?

With Intelligent Octopus our monthly electricity cost (which includes charging the car, of course) is ~100 quid. There doesn't seem to be much rooms for improvement without a battery system. All of our appliances at home run on electricity including power shower and stove. At least with the power shower we optimise by trying to use it when the car is charging.

The other major cost is central heating, which is still on natural gas and averages 150 quid/month. During last December it was over 200 . I still need to work on optimising that (already have a Google Nest which does a good job of halving our gas usage since installed).

The TP-Link Tapo is currently set up to turn on an electric heater whenever there's surplus solar. Since the boiler is turned off for most of the day, the house could use extra heat at any time.

I had a look at portable heat pumps but the installation is not convenient enough (it needs hoses to the outside, which only works with sliding windows), so I've settled with normal electric heater for now.

Air source heat pump system's ROI still doesn't make sense for us. Disregarding the installation cost: it might still cost us more to run compared to gas, unfortunately. I think it might work well enough for households with large solar panels. Ours can produce only about 3kW during peak times and we can't change it due to FiT.

 

[chwe]

Yes, we haven't had one installed yet but this would work well enough to absorb the excess once the battery is fully charged. The gradual ramping down of charge amp before it's stopped completely will cost perhaps 40W, which should be easy to recoup.



As far as I understand, the Zappi has 2 modes for this:
- Eco: which charges at a minimum of 1.4kW regardless of whether there is solar generation.
- Eco+: which after a delay (configurable by up to 4 minutes), charges the car on excess solar only and stop the charge as soon as generation stops.
+ It has a slider called "Minimum Green Level" that allows partial imports from the grid in case there's not at least 1.4kW of surplus power, but it doesn't seem to have a setting for 'maximum draw before charging must be stopped' like this custom solution.

I don't have first-hand experience with the Zappi, but it seems that partly cloudly day might be a bit of an issue with frequent charge starts/stops, particularly considering that with storage battery system it would be preferable to actually draw a bit of energy from the battery.


The car is only instructed to start charging if there's a minimum of 1.25kW export for 15 minutes so I'd expect the charging to stop for good during sundown, or if it starts raining .


Please have a look at the attached.



With Intelligent Octopus our monthly electricity cost (which includes charging the car, of course) is ~100 quid. There doesn't seem to be much rooms for improvement without a battery system. All of our appliances at home run on electricity including power shower and stove. At least with the power shower we optimise by trying to use it when the car is charging.

The other major cost is central heating, which is still on natural gas and averages 150 quid/month. During last December it was over 200 . I still need to work on optimising that (already have a Google Nest which does a good job of halving our gas usage since installed).

The TP-Link Tapo is currently set up to turn on an electric heater whenever there's surplus solar. Since the boiler is turned off for most of the day, the house could use extra heat at any time.

I had a look at portable heat pumps but the installation is not convenient enough (it needs hoses to the outside, which only works with sliding windows), so I've settled with normal electric heater for now.

Air source heat pump system's ROI still doesn't make sense for us. Disregarding the installation cost: it might still cost us more to run compared to gas, unfortunately. I think it might work well enough for households with large solar panels. Ours can produce only about 3kW during peak times and we can't change it due to FiT.

Your situation sounds almost precisely like mine! Although I use dehumidifiers as well to use up excess solar.

I've rigged up a similar car 'charging ramp' script in Domoticz to make use of our relatively small PV array (2.7kW) but am currently transitioning to home assistant. I haven't got any of my automations running in HA yet though, so have them both running side by side.

I'm also waiting for a GivEnergy battery install and will therefore likely wait until that's set up before tinkering. If you could share your script with me via DM though that would be great!

 

[vanhtu1987]

Your situation sounds almost precisely like mine! Although I use dehumidifiers as well to use up excess solar.

I've rigged up a similar car 'charging ramp' script in Domoticz to make use of our relatively small PV array (2.7kW) but am currently transitioning to home assistant. I haven't got any of my automations running in HA yet though, so have them both running side by side.

I'm also waiting for a GivEnergy battery install and will therefore likely wait until that's set up before tinkering. If you could share your script with me via DM though that would be great!

I've attached the YAML files for HA in my previous post .

One of my colleagues has a GivEnergy battery system installed and whilst it works, it does not respond quickly enough to sudden changes in the flow of energy between the household and the grid. For many smart heaters that power on and off quickly for precise temperature regulation: it means that he ends up drawing from the grid for the brief 2-5 seconds before the inverter wakes up and connects the battery. It is an issue the other way around too: when the appliance turns off briefly, excess solar would end up being exported rather than going back to the battery.

I'm waiting for more information from my installer for a SolaX AC inverter which outputs at 7.5kW and has a respond time of < 10ms, assuming that is trust-worthy. In theory the excess solar and energy drawn from the grid in these cases would be minimal.

 

[chwe]

I've attached the YAML files for HA in my previous post .

One of my colleagues has a GivEnergy battery system installed and whilst it works, it does not respond quickly enough to sudden changes in the flow of energy between the household and the grid. For many smart heaters that power on and off quickly for precise temperature regulation: it means that he ends up drawing from the grid for the brief 2-5 seconds before the inverter wakes up and connects the battery. It is an issue the other way around too: when the appliance turns off briefly, excess solar would end up being exported rather than going back to the battery.

I'm waiting for more information from my installer for a SolaX AC inverter which outputs at 7.5kW and has a respond time of < 10ms, assuming that is trust-worthy. In theory the excess solar and energy drawn from the grid in these cases would be minimal.

Ah thanks. Missed those!

Good to know on the GivEnergy response times, although in reality I'll not be looking to avoid all import/export so I figure it will be fine for us.

 

[WannabeOwner]

The TP-Link Tapo is currently set up to turn on an electric heater whenever there's surplus solar
...
the house could use extra heat at any time

Presumably a winter (and shoulder month) solution? Any PV I get in mid winter is "tiny" and just offsets what the house is using. In the shoulder-months my house is well insulated so not really needing that sort of solution (very little heating during 2nd half of March, and rarely used now we are in April), and cars normally are wanting some charging for the sunny days we do get ... but its a good point, thanks, I could use TP-Link to turn on a heater if there is export and in the months when additional heat would be helpful (ditto for Air Con in Summer) - house being well insulated means its not going to escape

I had a look at portable heat pumps but the installation is not convenient enough (it needs hoses to the outside, which only works with sliding windows), so I've settled with normal electric heater for now.

We have sash windows. I got some dense-ish foam, cut it in half and made a cutout for the "exhaust nozzle", and I just pinch the foam by lowering the sash window onto it. Duno if that would suit other types of windows (because house is well insulated and has MVHR that one unit, in effect, cools the whole house

Air source heat pump system's ROI still doesn't make sense for us. Disregarding the installation cost: it might still cost us more to run compared to gas, unfortunately. I think it might work well enough for households with large solar panels

I am doubtful that at UK latitudes we get enough Winter sun to make any contribution to Winter heating (e.g. using heat pump)

26-Dec we had wall-to-wall sun. I have 48 panels, we got 16.8 kWh total, but all of that in the interval from 9:30-ish to 14:00-ish. My background usage, daytime in winter, is around 2kW so it covered all of that plus an additional 4 hours battery top up - no contribution (in my case) to central heating. Can probably count the number of days we get that much Winter sun on the fingers of one hand!!

By comparison a wall-to-wall sun day on 10-Jul was 97.6 kWh, spread between 06:00 and 19:00 - I can easily survive the night, 19:00 - 06:00, on a full battery, and for 4 months in the Summer, in addition to household usage and battery, I get about 1,000 miles / month into the cars

Any more panels (e.g. to get more Winter kWh) is going be diminishing returns

GivEnergy battery system installed and whilst it works, it does not respond quickly enough to sudden changes in the flow of energy between the household and the grid

Interesting to know, thanks (and for the scripts )

 

[vanhtu1987]

Presumably a winter (and shoulder month) solution? Any PV I get in mid winter is "tiny" and just offsets what the house is using. In the shoulder-months my house is well insulated so not really needing that sort of solution (very little heating during 2nd half of March, and rarely used now we are in April), and cars normally are wanting some charging for the sunny days we do get ... but its a good point, thanks, I could use TP-Link to turn on a heater if there is export and in the months when additional heat would be helpful (ditto for Air Con in Summer) - house being well insulated means its not going to escape


We have sash windows. I got some dense-ish foam, cut it in half and made a cutout for the "exhaust nozzle", and I just pinch the foam by lowering the sash window onto it. Duno if that would suit other types of windows (because house is well insulated and has MVHR that one unit, in effect, cools the whole house

Yes, I think the portable heat pumps work perfectly for that type of windows. Ours open outwards so there's no easy way to keep it open without a lot of air leakage.

I am doubtful that at UK latitudes we get enough Winter sun to make any contribution to Winter heating (e.g. using heat pump)

26-Dec we had wall-to-wall sun. I have 48 panels, we got 16.8 kWh total, but all of that in the interval from 9:30-ish to 14:00-ish. My background usage, daytime in winter, is around 2kW so it covered all of that plus an additional 4 hours battery top up - no contribution (in my case) to central heating. Can probably count the number of days we get that much Winter sun on the fingers of one hand!!

48 panels and MVHR?. I'm, like, not jealous at all

Agreed, I think until V2H becomes more commonplace or 50kWh storage battery system is affordable, it seems rather tricky to make heat pump's running cost as cheap as gas boiler. As far as I've read, a heat pump can consume 7kW on peak usage and is ~1.5-2kW on average. In the middle of winter, assuming one is on IO with 6 hours of off-peak rates (40p peak/10p off-peak), the daily running cost for a heat pump could be: (0.4 * 18 + 0.1 * 6) * 2 = £15, or £450/month without the offsets from solar panels/battery.

If you have a ASHP then has that matched your experience?. Last December we paid ~£250 for gas, which was among the highest. But even that pales in comparison with what a heat pump system would cost to run.

 

[WannabeOwner]

I think until V2H becomes more commonplace or 50kWh storage battery system is affordable, it seems rather tricky to make heat pump's running cost as cheap as gas boiler

Well ... you could insulate the house and then only run heat pump during Off Peak (i.e. house wouldn't lose that heat during the rest of the day). My house loses about 0.5C per day if we go away mid winter and turn everything off ...

.... but if you have old housing stock it will cost a small fortune to fix, so you'd only be doing it because you want the improvement (for comfort / health, or planet - rather than for your wallet).

If you have a ASHP then has that matched your experience?

I have bio-mass boiler. Old part of house thermal efficiency has been upgraded best-as-we-can/afford. Fortuitously it [the method of construction] was relatively easy to do. We added an extension which is Passive Haus. New part included MVHR, we liked that so much that we retro fitted MVHR to old part too (once it was sufficiently air tight), and that [and a few other mods] has fixed all winter window condensation and any mould spores etc. - a dramatic improvement to air quality and comfort. I'm in rolled up shirt sleeves all year round (house also gains heat slowly during hot Summer weather)

We have UFH in new part (given we already had a boiler). Extension increased the foot print 50% and (coupled with thermal improvements to old part) our heating fuel has gone down 50% compared to "before"

 

[kfly212]

May install Home Assistant to automate EV charging on 20 amp outlet with excess Solar.
Want to do:
if server battery rack at >95% charge and Solar is producing > 2K, start charging EV with 20 amp outlet.
Question:
Has anyone done something like this? Does anyone know of a zwave 20 amp outlet that is able to do 20amp continuous? Would rather do a Zwave outlet than a dry contact.
Thx

 

[GRiLLA]

May install Home Assistant to automate EV charging on 20 amp outlet with excess Solar.
Want to do:
if server battery rack at >95% charge and Solar is producing > 2K, start charging EV with 20 amp outlet.
Question:
Has anyone done something like this? Does anyone know of a zwave 20 amp outlet that is able to do 20amp continuous? Would rather do a Zwave outlet than a dry contact.
Thx

This is the UK forum, we don't really have 20A outlets.

As is mentioned above this approach doesn't really work unless you can react quickly enough to detection changes in outgoing electricity flow, I tried to do this using my solar and 32A charger but both had about a minutes delay and the result was just that it flattened my house battery as the charge rate didn't come down quickly enough.

 

[G4WFT]

I've been thinking about the issue of using excess solar to charge the car but at the moment my Octopus Go tariff let's me charge for four hours overnight at 9p/kWh whereas I can get 12p/kWh for exported power, through Scottish Power. So, unless I'm mistaken I'm better off financially to export rather than charge?

 

[GRiLLA]

I've been thinking about the issue of using excess solar to charge the car but at the moment my Octopus Go tariff let's me charge for four hours overnight at 9p/kWh whereas I can get 12p/kWh for exported power, through Scottish Power. So, unless I'm mistaken I'm better off financially to export rather than charge?

Yup.

Why don't you use Intelligent Go though? 7.5p buy, 15p sell, billed monthly for both by Octopus.

 

[G4WFT]

Yup.

Why don't you use Intelligent Go though? 7.5p buy, 15p sell, billed monthly for both by Octopus.

I didn't realise that you got the 15p export rate on the Go tariffs? Sounds a no-brainer!

 

[GRiLLA]

I didn't realise that you got the 15p export rate on the Go tariffs? Sounds a no-brainer!

Yeah, it changed last month.