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Generations of my solar charger

I just came across some of the pictures from last year of different iterations as I was developing my solar powered car charger.


The left picture shows my first attempt using a Mode 2 charger (i.e. one that plugs into a standard socket outlet). The design attempted to turn the car on and off by the equivalent of pushing the latch button on the vehicle connector. That approach stopped charging effectively, but starting charging was subject to long delays so that wasn’t a practical solution.

The middle picture show the second attempt using a commercial Mode 3 charger (i.e. one that’s hardwired into the fixed wiring). In this iteration the commercial charger was gutted so that, although it retained the original external appearance, inside was all different content including a protocol controller and a radio receiver. This was an effective on/off solution.

The right picture shows the third iteration which addd a programmable logic controller to generate a variable charge rate for the electric car i.e. more than just simple on/off. The hardware to achieve this is too bulky for the case of the commercial charger, and so it was repackaged in consumer unit case. A consumer unit case is cost-effective solution for a bigger box to house the DIN rail mounting components, but is of course only suitable for indoor use as it’s not waterproof to the required standard for outdoor use.

Oops no heat

No heat this morning (not that its absence is a major issues as the weather is fairly mild). Initial analysis via the Apple Home App is that some of the radiator valves can’t be reached, and thus I assume that the rules that enable the gas boiler can’t be satisfied.

As a short term fix I could have turned on the boiler manually via the app or using the central timer which is normally set to off for space heating (but not hot water) when using the smart controls, but I didn’t need to do that as I quickly found the root cause.

I initially thought that there was some corruption in the configuration of individual valves, so I was planning to delete them from the App and then re-pair them, but then I spotted that as I moved around the house I was losing different valves, so I turned my attention to the hub i.e. the Apple TV box.

Turning on the box it appears that it downloaded a software update overnight. As soon as I acknowledged a screen describing the changes then all the valves became reachable, the control rules were satisfied, and the gas boiler was enabled.

It would be more robust if you could specify a default value in a rule to be used if the actual value was unavailable from the device.  The actual value being unavailable would also happen with a flat device battery for example.

Here’s a little Tonik..


Today my energy supplier Tonik wrote to me inviting me to consider solar panels, a car charger, or a storage battery – all of which I already have.  However on their website I found a wider vision of the future home which they thought could halve energy consumption. I thought it would be interesting to compare their vision with my status.

As you can see from the table below the content is quite similar, although I have more ambitious use of solar and more sophisticated smart heating management.

Tonik's VisionMy status
Switch to Tonik for lowest cost renewable electricity.Done.
Smart meterWaiting on Tonik
Connected thermostat (whole of house device)Connected thermostats (individual room temperatures and schedules)
LED bulbsDone.
Smart tariffWithout a smart meter on nearest equivalent (Economy 7)
Solar PV Done.
Battery storage.Done.
-Surplus solar electricity diverted to charge electric car.
-Surplus solar electricity diverted to heat water.

Using an Apple TV box as a home hub


When I first set up the smart home system I used my iPad as a hub.  You don’t need a hub at all for the individual smart radiator valves to follow their daily schedules, but the use of a hub is required for devices to interact with each other (such as a valve calling for the boiler to come on) or indeed to identify which days are working days and which are non-working days (since this is taken from a calendar). However of course this doesn’t work when the iPad is removed from the home.

The solution is to configure an Apple TV box as a home hub – enabling devices to communicate via the TV box.  This also enables remote control so a user with an iPad can operate the system when away from the home – such as disabling the vacation settings while still on vacation to allow the house to warm up.

Of course the Apple TV box can also be used to watch TV which my daughter uses to watch CBeebies or YouTube kids TV via the appropriate apps.

To date we have 7 smart devices – 6 radiator valves divided between 4 rooms, and a socket which is used to enable the boiler when any smart valve demands heat.

Contents of my solar car charger

My electric car charger is built into a case more normally used for household consumer units.  From left to right its contents are:

  1. 2 slots – Double pole on/off switch to isolate the incoming mains supply entering from below.
  2. 4 slots – Programmable Logic Controller (PLC) which takes 2 inputs (remote on/off via radio link and contactor status – see item #4) and generates 1 of 4 outputs (corresponding to off, 6 Amps, 10 Amps or 16 Amps).  Beneath the PLC (and not visible inside the case) sits a circuit board with an array of resistors corresponding to the required current settings.
  3. 2 slots – Protocol controller which handles the Mode 3 handshake with the car and switches between current settings based on the selected resistor.
  4. 1 slot – Contactor which turns the power to the vehicle on/off based on the output from the protocol controller.  Cable to car exits below.
  5. 1 slot – unused.

The dedicated charger circuit is fed from a RCBO in a small consumer unit on the other side of the garage which combines overcurrent protection (20 Amps) and Type A residual current detection (30 mA).

 

 

 

A mixed August day of charging


Today I was at home working on a DIY project while the car was on charge for much of the day, a day which was fairly mixed in weather terms.  I thought it would be appropriate for an update on the car charger which has been in operation for around a year.

You may recall that the car generally remains plugged into the charger whenever it is at home, but doesn’t generally charge until there’s sufficient surplus on the solar panels, unless timed charging has been enabled for when the weather isn’t so sunny.

The picture shows the charger itself built into a case intended for a consumer unit.  Alongside the charger sits the receiver for the Mainslink system which provides for a radio signal from the house turning on the charger in the garage.  The smaller black unit is the holster for the vehicle connector so that it doesn’t lie on the floor when not in use.

The screenshot to the left shows the electricity consumption of the house including the car charger (the purple line) tracking the output of the solar panels (the green area).  Any failure to fully use all the electricity available causes the remaining electrical surplus to be diverted via a proportional control to the immersion heater to make hot water (the blue line).

Over the course of the day although we’ve used 17.1 kWh of electricity directly, and another 2.8 kWh of electricity for water heating (making 19.9 kWh used in total); but we’ve bought only 3.1 kWh of electricity.

Solar output – 2017 Jan – Jun

2017 H1

Now that we’re half way through 2017 it seemed appropriate to have a look at energy usage from the solar panels – especially as those six months reflect the first six months with the battery storage system.

The graph is taken from my ImmerSUN smart controller which automatically diverts surplus solar electricity to the car charger or immersion heater.  The battery storage system has independent controls but its benefits can be seen via the ImmerSUN.

The purple line shows the consumption of electricity (excluding the immersion heater) and is relatively stable month by month.  Consumption is relatively large due to my electric car and cooking with electricity.

The green line shows the generation of electricity from my solar panels.  Not surprisingly output is lower in the winter, but from April we generate more electricity than we use despite our relatively high consumption.  In principle we could be electricity independent during those months but for the time of consumption not matching the time of generation.

The red line complements the green line as it shows the import or purchase of electricity from the grid, and thus reduces as the generation rises.

The blue line shows the diversion  of electricity to heat water via the immersion heater when neither the battery storage system nor the car charger can absorb the available electricity.

Finally on the graph the turquoise line shows export of electricity to the grid when all smart capability within the house to use electricity is exhausted i.e. battery storage system at maximum power or full, electric car battery full or absent, and water in cylinder is hot.

Among the numbers:

‘Savings” at £80 refer only to the value of the water heating achieved from solar electricity versus buying electricity (although our backup is mains gas).

“Self consumption” at 86% refers to the proportion of solar panel output used i.e. not exported to the grid.

“Green contribution” at 59% refers to the proportion of total electricity consumption (excluding water heating) derived from the panels rather than from the grid.

 

Battery storage – the first 6 months

I’ve now completed 6 calendar months with the battery storage system.  Those six months cover January – June so might be considered representative of the year as a whole.  I have real-time monitoring of solar panel output and house consumption / export so I have clear visibility that the battery is working and storing energy, and then discharging energy through the evening as I see the house with near zero electricity consumption sometimes through into the early hours of the morning (less if we’ve cooked our evening meal on electricity).  So, environmentally it’s doing its stuff, but what is it saving financially?

There are at least three ways to assess that, so let’s see how they look.

Firstly, from the capacity of the battery (4 kWh), and assuming that it’s filled daily one can calculate a benefit.  That benefit would tend to overestimate benefit in winter when there may not be enough energy to fill the battery, but equally could understate saving some days when the battery goes through repeated periods of charging and discharging during the day.  One could imagine the heating cycle of the dishwasher, for example, perhaps causing some discharge of the battery during the day if the washing machine load isn’t met from the solar panels, but then then re-charging before the evening and thus its daily throughput being higher than it’s capacity as some of that capacity is used more than once per day.

So, if the battery stores 4 kWh and there are 365 days in a year where each kWh not bought is worth 11.5 p/kWh then the saving might be 4 kWh/day x 365 days/year x 11.5 p/kWh =  £167.90.

Secondly, let’s look at electricity savings.   If I compare the first 6 months of 2017 (with a battery) to the first 6 months of 2016 (without a battery) then electricity purchase has reduced by 824 kWh (38%).  Thus the saving could be 824 kWh/six-months x 2 six-months/year x 11.5 p/kWh =  £189.52.

Of course, as my chart shows, there are other changes that potentially impact electricity use between those 2 time periods, so that might be an overestimate.

The third and final way that I’ve analysed this is to look at the data about how the output of the solar panels has been used.  In 2016 I used 44% of the output of the panels to replace bought electricity, and a further 28% of output to replace gas consumption.  In the first half of 2017 however I used 63% of the output of the panel to replace bought electricity, but only 24% of output to replace gas consumption.  The reduction in use for water heating reflects the prioritisation of the battery over water heating as a kWh of electricity purchase avoided is much more valuable than a kWh of gas purchase avoided.  Against 2016’s full year generation of 4,192 kWh that gives a saving of only £87.84 which is much the lowest of the 3 figures.  However this only accounts for more efficient use of the solar panel output, and not winter savings from shifting energy purchase from day to night time when it’s cheaper.

Whether any of these figures represents a saving over the life of the storage system entirely depends on the lifetime of the system, the life of the batteries inside it, and the replacement costs of those batteries

Adding smart boiler control

In my previous post I described replacing conventional thermostatic radiator valves (TRVs) with smart valves (sometimes called eTRVs).  The smart valves include both temperature set points and a schedule which allows me to operate shorter on times in rooms not used so much – such as the playroom heating turning off after my daughter’s bedtime.

My latest update is to link the valves to the boiler so that heat demand from a smart valve fires up the boiler, regardless of the settings of the older central timer and hall thermostat.  That would mean, for example, that if my wife want to watch a late film then commanding heat in the lounge would restart the boiler even if outside normal heating hours.

The effect of this change can be seen in the attached image which shows three days of valve position information for the two radiators in the lounge: two days where the boiler was enabled by the conventional timer and central thermostat, and the third day with smart boiler control.

For the first two days you can see the valve open wide for an extended period during some of which time the boiler won’t be pumping hot water as the hall is up to temperature.  However on the third day, with the link to the boiler, the valve closes very quickly from its initial position and then modulates to maintain the temperature since the boiler is running all the time when any valve is open.

The system is controlled by two rules through Apple Home:

  1. If any valve moves off closed (triggers)  then enable boiler.
  2. If any valve moves to closed (triggers), and all valves are closed (conditions), then disable boiler.

The picture shows the actual mechanism to turn the boiler on or off via the Elgato Eve Energy (which is a switchable mains outlet and energy meter) in the right side socket outlet.  I use the Eve Energy to operate a mains relay (in the black box) which in turn closes a contact between two terminals of the heating wiring box, which bypasses the heating timer and hall thermostat, sending a mains control signal to the dual port valve for the heating thus opening the valve thereby enabling the boiler through the existing controls.

The first evening’s operation showed two issues:

  1. Room temperature was reported as overshooting in some rooms, but not in one room with a newly installed valve. It may thus be that the older valves have self-tuned their controls and need to re-tune to the new more dynamic system characteristics.
  2. I needed to manually turn down the radiator in the hall which was getting too hot.  If that persists then I may need to add a TRV or smart valve to the hall.