Author Archives: Greening Me

Mid-year thoughts

Summer is definitely upon us now as we enjoy the glorious summer weather.  Disappointing weather earlier in 2018 has given way to two record months in May and June which yielded the highest monthly outputs for their respective months since the system was installed back in 2015.  Some days we buy no measurable electricity or gas  (given that the electricity meter has a resolution of 1 kWh) depending on what the need to charge the car.  If the car is at home then I can fully charge it from the solar panels, whereas if the car is at away from home during the day then I may need to give it some charge overnight.  When charging overnight I have been tending to charge for the minimum number of hours up to 7:30 AM when I typically leave home on a weekday – that pattern provides for mostly Economy 7 Energy from the grid less whatever comes off the solar panels from the rising sun less whatever might be left in the PowerVault from the previous day as illustrated below:
The green ‘hill’ from around 3:30 to 7:30 AM is created by car charging.  Normally this would be seen as a rectangular block as the car charger effectively runs at a constant 10 Amps (2.3 kW) through the operating period.  However in the illustration the charging event (at least in terms of power drawn from the grid) seems rounded at both the beginning and the end.  At the beginning of the car charging period the mustard ‘Device Power Out’ curve shows the last remaining stored energy from yesterday being drawn from the PowerVault, while at the end of the charging period the ramp down is a result of increasing output from the solar panels reducing the need for power from the grid.  Hence at the moment the car charging ends there’s a sudden switch to charging the PowerVault at full power (the blue line) and some surplus power not used by the PowerVault (the purple line) – suggesting that something around 1 kW is suddenly available.  Although the purple line is described as ‘Grid Power Out’ that’s not strictly true here as much of that surplus is being diverted to make hot water (although this is invisible to the PowerVault).

After that digression, my actual purpose in making this post was to reflect upon relative energy costs and the best use of my solar power to reduce energy cost.

Energy usagePetrolDaytime ElectricityNighttime ElectricityGasSolar Electricity
Battery Storagen/an/a - no economic case to charge battery from grid during dayOptional - need to consider value of saved energy versus cost of 1 cycle of battery cycle-lifen/aSelf-use Priority #1 via PowerVault (daytime electricity -> solar)
Car ChargingManual 3rd backup (typically only used for long journeys when charging en-route becomes impractical) Manual 2nd back-upAutomated 1st backupn/aSelf-use Priority #2 via ImmerSUN (nighttime electricity -> solar)
Water Heatingn/aManual 3rd backup (never used in 3 years)Manual 2nd backup (never used in 3 years)Automated 1st backup for dull daysSelf-use Priority #3 via ImmerSUN (gas to solar)
Space Heatingn/aManual backupManual backupDefaultn/a - a summer solar surplus is a poor match to winter heating demand but could be Priority #4

 
The table above shows columns of energy sources ordered by reverse energy cost versus the major energy consumers in the house: battery storage, car charging, space heating and water heating. Energy consumers are ranked according to the value of displacing the the alternative energy course if not solar:

  1. Battery storage – I currently only charge the battery storage from solar, although there would be a seasonal economic argument to charge from cheap rate electricity if the differential between day and night rates was higher.
  2. Car charging – I generally charge on cheap night-rate electricity when I don’t have enough solar. In summer I program my car charger via the ImmerSUN’s 7-day timer to deliver sufficient charge for the day ahead, but sufficient headroom to make use of any available solar.
  3. Water heating – water heating is my 3rd priority for solar self-use and is automatically based up by the gas boiler which runs for an hour making hot water in the early evening if the tank isn’t already hot from diverted solar power during the day. The gas thermostat is also set slightly colder than the immersion heater – still very usable for a bath or shower from gas but giving some ability to delay water heating from a dull day to a following sunny day.
  4. Space heating – my space heating is generally gas. It would be possible to run a heater (or heaters) such as storage radiators via the ImmerSUN’s third output, but I consider that the cost of the heater(s) and installation is unlikely to be recouped given the major mismatch between surplus solar generally being in summer and heat demand being in winter.

Clamp orientation for ImmerSUN and PowerVault

In the last few days I’ve been assisting a reader of this blog who also has an ImmerSUN immersion heater controller plus PowerVault storage battery combination.  Like me, he had the immerSUN first and later added a PowerVault, but had immediately disabled the ImmerSUN to get the PowerVault to work.  Left to their own devices, the ImmerSUN will normally take the surplus power first before the PowerVault has chance to respond since it has a more dynamic control system, however economically it makes more sense to prioritise the PowerVault.

I previously posted on this topic in Prioritising smart loads for self-consumption but wanted to provide more clarity on the orientation of the clamps.

Both ImmerSUN and PowerVault rely on current clamps to get their control signal. Such clamps fit around an electrical cable and measure the flow of electricity through that cable.  Normally clamps for both these devices alone would be around the live in the incoming mains cable, but do that with both and the ImmerSUN will always take the available power first which is undesireable.

The illustration shows my solution, as per the prior post, where the PowerVault clamp surrounds both the incoming live and the live output to the immersion heater.  If the clamps are correctly orientated, this allows the PowerVault storage battery to be prioritised over the ImmerSUN immersion heater controller.  When the PowerVault clamp surrounds the two cables, it is important that outgoing power to the grid and outgoing power to the immersion heater from the consumer unit pass through the clamp in the same direction.  This solution should work for clamp-driven solutions too.

The PowerVault clamp is directional – it has an arrow which should point towards the consumer unit.  That means, if you pair the two cables as I described, so outgoing power flows in the same direction in both cables through the clamp, then the arrow should point in the opposite direction i.e. towards the consumer unit.

Fundamentally it doesn’t matter which way the ImmerSUN clamp faces, as during commissioning the ImmerSUN will work it out by cycling the power several times, but you shouldn’t change it after commissioning.

Daytime charging as quickly as possible

On Wednesday an unusual pattern of vehicle use occurred (at least for me) which showed another way the charger could be used. I needed to take my daughter on a round trip in the morning (dad’s taxi), return home, and then repeat the trip later in the afternoon. Each round trip pretty much exhausted the range of my electric car, so I needed to recharge in between. My normal home charge routine would have prioritised the home storage battery, but that would have left me completing the second round trip partially on petrol which isn’t the optimum solution.

To fully recharge the vehicle to complete the second round trip (and thus avoid using petrol) I disabled the programmable logic controller (PLC) on the car charger using a push button which suspends the program causing the charger to operate at full power. It was a sunny day (at least for March) so the solar panels were producing a similar amount of power to that required to charge the car and, with the fixed battery partially charged during the period I was making the first round trip, the fixed battery was able to manage the difference between power generated by the panels and that required by the home (including car charging) for much of the period.

The result was an almost fully charged car for the second round trip (sufficient to avoid using petrol) for only around 1kWh of grid energy.

Electricity use 2017

The image above shows my solar electricity generation and usage in 2017 by calendar month.

  • The purple line shows the use of electricity (excluding gas replacement) by month. It’s relatively stable through the year, although it does rise in the autumn as my daughter started school and so my electric car mileage increased.
  • The green line shows the output from the solar panels.  From April to August (5 months) solar panel output exceeded usage giving the potential not to buy electricity with sufficient smart capability – be that electricity storage or alignment of consumption with availability.
  • The red line shows import of electricity from the mains.  It tends to be the reverse of the solar panel output.  It’s never zero indicating potential (at cost) to improve smart usage.  Solar power is a more significant energy source than imported power from March to September (7 months).
  • The blue line shows diversion of surplus electricity to water heating as gas replacement.
  • The turquoise line shows export of electricity to the grid.  This occurs when there is insufficient energy smart resource available to store or self-use the surplus power.  Export amounts to about 12% of total solar panel output.  While this potentially free energy, the economics of storage or smart controls make using this remainder increasingly costly from an investment perspective.  In my case this surplus occurs on particularly sunny summer days when the electric car is not at home or is already fully charged – which might be vacation periods when the house is unoccupied for example.

Solar PV Installation – 2 years on

The end of 2017 sees 2 full calendar years of output completed (plus a few months at the end of the prior year) so it seemed like a good time to assess performance and return.  Return comprises two parts – firstly the payments received for electricity generation (and export) the so-called feed-in tariff or FiT and secondly the savings obtained from using that free energy myself instead of buying it from the grid.  In my case I can use and store my solar electricity directly, or use it to heat water via the immersion heater thus replacing gas.

I’ve summarised the status in the following table:

 Nominal20162017 
Generated366840564033kWh
FIT£629.36£639.61
Electricity self-use50%41%64%of Generated
183416632596kWh
£159.65£251.12
Gas replacement27%23%of Generated
1095941kWh
£41.20£27.66
Export50%32%12%of Generated
Return in calendar year£830.46£918.40
13.6%15.1%of PV cost
Return cumulative£830.46£1748.86
13.6%28.7%of PV cost

Summary:

  • Output from the panels was slightly reduced in 2017 versus 2016, but still significantly above the performance projected in the quotation.  I put the slight reduction down to year-to-year differences in the weather.  Over time I would expect panel output to decline, but I think it’s too soon to attribute any decline to this.
  • Income from FIT was slightly higher as inflation on the price / kWh has overcome the slight output reduction.
  • Electricity self-use is up considerably from 41% to 64% due to my 4 kWh storage battery.  The costs of that battery are not reflected in the table.  Return would have been 8.8% in 2017 (rather than 15.1%) if the cost of the battery was included.
  • Gas replacement is down from 27 to 23% versus 2016 as more of the electricity from the panels is used for high value activities like charging the storage battery or my electric car, and less is left over for water heating.  The low price of gas per kWh makes gas replacement my lowest priority for self-use.
  • Exported electricity (i.e. what’s left-over that I cannot use myself) is considerably reduced from 32 to 12% largely as a result of increased electricity self-use.
  • Financial return in calendar year 2017 is improved from 13.6 to 15.1% neglecting the costs of the battery, or reduced from 15.1 to 8.8% taking into account capital costs of the battery.
  • It will take approximately 7 years (i.e. 2 past + 5 future years) for the combination of the solar panels and battery storage to pay for the solar panels (neglecting the battery costs), and a further 2 years of system savings to pay for the storage battery.

Save energy — 19 free energy saving tips

Today I received the following 19 free energy-saving tips (click image for original article).

I quote the article here with my own observations.

Saving energy isn’t just about helping you to save electricity or be more energy efficient — it’s also a great way to save money.

We all know we could do more around the home to save energy, but where to start? While some of the biggest energy savers require time and money there are still plenty of lifestyle changes you can make that will save energy, and money.

With just a few simple changes to your lifestyle and your home, you could be saving hundreds of pounds on your heating, gas and electricity bills.

So, if you’re looking for ways to cut down on your spending, try these 19 free energy saving tips.

How to save money on heating

  1. Stay warm, cut costs. Turning your thermostat down by 1°C can save you as much as £60 per year. Also, keeping your heating on constantly on a low heat could potentially save you more money than switching it on and off for big blasts of heat. This is where getting to know and understand the timer settings on your thermostat will really pay off.

That I can see both ways. On the one hand not stressing a condensing boiler too much can keep it in condensing mode, and thus increase its efficiency. However keeping the home unnecessarily hot will increase the heat loss to the outside world (which is proportionate to the temperature difference between inside and outside) so an unoccupied house at an elevated temperature will increase heat loss, but might make heat more efficiently.

Also for many people, timers and thermostats are two different components and the use of the timer turns the heating on and off – not between two alternative temperature set points.

Our own smart heating does in fact switch between a high and low temperature (not on and off) but at 10C the low temperature is such that room temperatures don’t generally fall to the low temperature before high temperature is demanded again.

  1. Get cosy. Wearing more jumpers, socks and slippers around the house, and putting an extra blanket on the bed means you won’t be tempted to turn the heating up.
  2. Turn the pressure down on the power shower. A high-pressure power shower is a great luxury to have but you’d be surprised how much water they use – sometimes even more than a bath.

Be efficient with cooking

  1. Save time and stock up. If you’re going to use the oven, bake a few meals at a time to get the most out of having your oven on. After all, oven’s don’t allow us to heat one shelf at a time so why waste your heat?
  2. Heat your home with cooking. Leave the oven door open after cooking to let the heat warm your kitchen. The oven might give off enough heat for you to adjust your thermostat, a far more efficient use of that stored heat than throwing it out of your home with an extractor fan.

Heat from the oven after cooking certainly does heat the kitchen, but personally I would wouldn’t leave the oven door open which provides too much of a heat rush – I prefer to leave the door closed and allow the same heat to move into the room more slowly.

I wouldn’t adjust the thermostat – it’s goal is to control to a comfortable temperature. Does the comfortable temperature change when you’re cooking? If you’re too hot when cooking the thermostat (potentially a TRV in the kitchen) will already have turned the heating off.

As to extractor fans, their purpose is to remove steam from boiling pans and save energy by significantly reducing condensation. Turning off the extractor fan while generating steam is a false economy.

  1. Let the dishwasher do the dirty work . Avoid pre-rinsing the dishes in hot water. Save water and energy by just scraping the dishes before they go in.
  2. Make things easy for your fridge and freezer. Keeping them full means they don’t have to work as hard and therefore they use less energy. Empty space in your fridge or freezer wastes not only space but energy too.

Again not so sure about this one. In general the energy to run a fridge or freezer will be a function of the temperature difference between inside the freezer and the room in which it is found. I can have assume that this point relates to the frequency at which the door is opened where an empty upright fridge or freezer will rapidly dump cold air into the room, whereas a full fridge or freezer has less cold air to dump.

  1. Use the right ring for the right thing. If your cooker has a small ring, use a small pan. You might only be heating up a small meal, and doing so in a big pan wastes a lot of energy. Conversely if you try and heat a large pan on the small ring you’re more likely to end up heating for longer than saving any money or energy.

Be efficient with washing.

  1. Shrink your bills, not your clothes. 90% of a washing machine’s energy expenditure is spent on heating the water, so if you wash your clothes at 30-40 °C you’re saving significant amounts of money.
  2. Hang up your laundry. Air-dry your laundry rather than tumble drying it, particularly if there’s warm or windy weather. What’s more nothing smells better than air-dried clothes.
  3. Save yourself ironing time. Take your clothes out of the dryer before they’re completely dry – they’ll iron much quicker and you’ll use less energy on your drier.

Energy efficiency and electricity saving tips for your appliances

  1. Switch it off and save. Unplug all the appliances that you aren’t using regularly – even chargers continue to use electricity when they aren’t charging. Also, make sure you’re not leaving appliances on standby: it may be easier but it’s also a guaranteed way to waster energy compared to turning things off at the socket.
  2. Get the kids involved. Play energy-saving games with your kids. Get them to spot the areas in the home where energy is being wasted and where lights, switches or appliances have been left on.
  3. Let the sunshine in. On a sunny day, opening your curtains will let warmth into your house, but when it’s colder or the sun goes down don’t forget to close them to keep that heat in.

Be efficient with your whole home

  1. Get free cavity wall insulation. There are now government-backed full and partial grants available to help you pay for insulation if your home has cavity walls. Getting this done could save you around 15% on your fuel bills, so you could be saving on average £98 a year. Even if you don’t receive money from the government insulation is still worth it in the long run.
  2. Get free loft insulation. Because heat rises, as much as 25% of the heat in your house could be disappearing into your loft space. What’s more, even older properties that already have insulation in place may not have the recommended levels, particularly if it was installed in the 1970s or 1980s. If you apply for a loft insulation grant, you could save about 19% on your fuel bills – which works out at an average of £128 per year.
  3. Get free solar panels. Having solar panels installed on your house could save you as much as a third on your electricity bills. What’s more, thanks to the government’s Feed-in Tariff scheme solar panel installers get paid for the energy generated, so they may install them for free.

Indeed they might install them for free, but they do so because they get a good return on their investment via the feed-in tariff. If you have the capital available pay for it yourself, get the feed-in tariffs for yourself, and avoid any legal issues with rent-a-roof if you choose to sell your home in future.

  1. Apply for an energy-saving grant. There are plenty of energy-saving grants available to help with the cost of home improvements.

Don’t overpay for the energy you’re using

  1. Compare gas and electricity prices with to make sure you’re on the cheapest tariff for you. It only takes a few minutes.

Energy Smart in action

Here we have the system in action earlier today.  With 1542 Watts coming from the solar panels, the house (including the PowerVault storage battery) is running at a maximum of 1097 Watts, with the balance of the available power controlled by the ImmerSUN- 410 Watts to water heating and at the point of this snapshot 35 Watts into the grid.  At this moment that’s 97% of generation used as such self-consumption and 100% of energy being consumed coming from the solar panels.

if the ImmerSUN had priority then it would have taken all the available power leaving nothing for the PowerVault storage battery.

Zappi?

It’s now over a year since I built my solar-powered car charger which is enabled automatically by surplus electricity output from my solar panels, but can also be run on a timer when required to use cheap night-time power too.

However since then a new product has come to market from myenergi (a new company led by some of the team responsible for developing the ImmerSUN) which provides the same sorts of capabilities although in a professionally-produced solution. I don’t own one, I’ve never used one, but I think that this is a solution which I’d be seriously considering if I hadn’t already made something similar.

The only downside that I can see is that it’s available in either Type 1 or Type 2 forms with tethered leads only, so if you have a mixture of EVs then a single Zappi may not be compatible with all your vehicles; whereas a charger with a Type 2 socket outlet would be.

You can learn more about Zappi here

An attack of the clamps

In a prior post I described the use of current clamps to prioritise smart loads that are enabled by surplus solar power to maximise self-use of this ‘free’ electricity.  That’s free in the sense that a deemed export tariff doesn’t pay any more for an extra kWh exported, or pay any less for an extra kWh used, and so the marginal cost of using that (and every other) kWh is zero.  In that post three current clamps were visible in the picture – though I described only the function of the right-most.

In fact my home currently has 6 current clamps which is probably more current measurement than the substation that supplies my area.  The six clamps are as follows:

 ImmerSUN PowerVaultData Logger
Solar panel outputReport (1)-Report (4)
Immersion heaterControlMeasure sum (3)-
Import / ExportMeasure (2)Report (5)
Battery In / Out-ControlReport (6)

I’ve tried to distinguish between their functions as follows:

  1. Control – is an output current actively controlled by a device so there’s generally no need to measure it with a clamp.
  2. Measure – a clamp whose output is analysed automatically to create a control action such as divert more or less power to some device.
  3. Report – it’s just reporting something for the purposes of understanding, but it’s not used to directly control anything.

So the 6 clamps are:

  1. The optional ImmerSUN monitoring package adds a clamp to measure the output of the solar panels which then enables the charts and self-use calculations that I’ve used before to illustrate system behaviour.
  2. The ImmerSUN fundamentally operates by measuring export via this clamp and then responding to minimise that export.
  3. The operation of the PowerVault uses this clamp.  In most installations that’s simply around the live of the incoming supply, but for me it’s also around the live feed to the immersion heater to set priorities.
  4. I also have 3 data loggers at my home to provide a year’s data for UKPN around self-usage so that they can assess the impact on the grid from large scale battery adoption.  Each logger measures one of the fundamentals for battery behaviour: output from the solar panels, ..
  5. .. import to / export from my home, ..
  6. .. and current to / from the PowerVault.  From those three you can infer what is being used by my home in its entirety, but not how power is divided between (for example) car charging and water heating.

 

 

Prioritising smart loads for self-consumption

This week I was discussing how to maximise the benefit of self-consumption with an installer.  The issue here is, where one has multiple independent systems (such as a battery and a water heater) each looking to use any surplus self-generated electricity, how does one set the priorities of the devices or is it just a lottery which gets the surplus power first?  In my own case, for example, I recognise that the surplus invested in my battery storage  is better value than investing that surplus in hot water as electricity is considerably more expensive than gas.

I have previously written on this subject Prioritising the battery, but the installer was unaware of my solution and recommended an alternative which I consider flawed. The solution recommended by the installer is to enter the maximum charging power of the battery as the export threshold in the ImmerSUN controller. This does indeed create headroom for the battery to charge, but I believe does not use the ImmerSUN to best advantage. Let me use a table to contrast what might happen at 3kW generation with both the installer’s and my own solutions:

 Installer's solutionMy solution
Total load / total generation3.0 kW3.0 kW
Baseload of house0.2 kW0.2 kW
ImmerSUN Export threshold0.8 kW-
Battery charging0.8 kW0.8 kW
Balance for water heating1.2 kW2.0 kW

The installer’s solution will potentially always waste an amount of power equal to the maximum battery charge power / ImmerSUN export threshold. My solution doesn’t do this, although there is an aspect of immersion heater operation that may or may not concern you.

In my scheme I modify use of the current clamp for the priority device – the battery for me. Such current clamps have the property of summing the current in all the cables which they surround and, as you’ll see from the pictures, my control clamp for the battery surrounds both the incoming power cable from the grid and the outgoing cable to the immersion heater.

The effect of this arrangement leaves the ImmerSUN acting normally – it sees any export and diverts it to hot water.

The current clamp for battery however sees the sum of the export current and the current diverted to the immersion heater, so it doesn’t matter how much the ImmerSUN diverts (and thus reduces the export) – the battery ‘sees’ what would have been exported without the ImmerSUN and responds according.

The ImmerSUN clamp then ‘sees’  the export current drop as the battery charge current increases and  thus reduces its own current proportionately.

To gain access to both the incoming live mains supply cable and the outgoing live feed to the immersion heater, my current clamp is located within the consumer unit.  It’s the blue clamp on the right around the larger incoming cable and the smaller brown cable for the immersion heater.  You need to be a competent person to work inside a consumer unit.  (There are two further blue clamps to the left but their function isn’t relevant to this post.)

The aspect of this that may concern you (but doesn’t bother me) occurs if you want to run the immersion heater from stored electricity rather than just using surplus from the solar panels immediately.  If you turn on the immersion heater using the Immersun (known as ‘boosting’ in ImmerSUN vocabulary) then the current from the consumer unit to the immersion heater is equal and opposite to the current from the grid to the consumer unit, which is summed by the battery’s current clamp to zero and thus the battery neither ‘sees’ that current nor discharges to meet that load.  To me this isn’t an issue as I consider transferring energy stored in one device (a battery) to another storage device (a hot water cylinder) is poor practice; and in any case the battery doesn’t have enough power capability (maximum 1.2 kW) to run the immersion heater at full load (3 kW) so you’d always be importing at least 1.8 kW to run the immersion heater.

As a final note – it is critical to orientate the two cables in the battery’s current clamp correctly for the system to work as intended.  Current from the consumer unit to the grid, and from the consumer unit to the immersion heater, must flow in the same direction through the battery’s clamp.