TSHE: Solar Panels + 1 year review

Too many of these really messes with your solar panel figures! (credit)

The year 2019 is over and I have received the official numbers on the scoreboard for the first year of The Solar House Experiment (TSHE). Just in case you haven’t read the previous overview post, I installed a 3.6 kW solar array on my house in November 2018. There were then a few additions to the system over the year:

  • April 2019 – I installed a solar diverter that takes excess solar energy and dumps this into our hot water tank, providing ‘free’ hot water
  • September 2019 – I bought an electric car after my poor old Ford Fiesta died rather spectacularly after 9 years of reliable service
  • Late November 2019 – a shiny new 7.7 kW EV charger was installed which has the ability to dump excess solar power into the car, or charge the car rapidly overnight

The total cost for my installed solar panels was £7,566. This included parts and labour, but I went and fished out the original invoice to show how much exactly the panels, inverters and monitoring software individually cost and what the labour charge was. Please free feel to use this as a comparison if you decide to get your own panels installed in the future!

Solar panel choices and micro-inverters

Solar Panel choice: Panasonic 330W HIT N330
Price per Panel: ~£225 (including 5% VAT)
Total for 11 Panels: £2,478

Due to space constraints on our house, I went for the Panasonic 330W panels. At the time of purchase they were one of the highest wattage panels in the ‘normal’ panel size. With a claimed efficiency of >19% they were also some of the most efficient, though I imagine the panel technology has gotten even better since 2018. For reference, your ‘average’ mass produced panel was closer to 265W and 15% efficiency.


Micro-Inverter choice: Enphase IQ 7+ Micro Inverter
Cost per Micro-Inverter: £105 (including 5% VAT)
Total for 11 Micro-Inverters: £1,155

There are generally two types of inverters used with solar panels: string and micro. String inverters can connect multiple panels at once and are thus cheaper, however, their drawback is that they can only convert power equal to the worst performing panel in the string. If one of your, say, eight panels has a shading issue, then the rest of the panels in the array could only output the same amount of power as that shaded panel.
Micro-inverters are attached in a 1:1 ratio (one inverter per panel). This allows each panel to produce the absolute maximum possible and feed it into your home/the grid. I had additional reasons to get these as I have 11 panels and some of them are at different angles on the roofs, meaning I’d get sub-par performance otherwise. An additional benefit is I can see the production of solar on a per-panel basis with the monitoring software!


Monitoring Software: Enphase Envoy Enlighten
Cost: £300

This little box sits near your electric fuse box and has a couple of CT clamps attached to it that measure the energy following in from the panels and the input/output of power from and to the grid. The software works very well with the micro-inverters (same company) and provides insights and useful statistical data, some of which I’ll be discussing later in this post! At £300 it’s not cheap but does make sure everything is running smoothly in your system and allows for remote troubleshooting if necessary (which you can disable if you wish / have privacy concerns).


The remaining costs were for some mounting kits to the roof (~£400), an additional fuse box and wiring for my garage (~£200) and labour/setup costs of about £2,800. The company who did my installation weren’t the cheapest but they were the friendliest and answered every question I had with detailed replies – which was a great learning experience for me!

The solar year in review

First let’s look at the yearly graph to see how much solar was generated and consumed:

A summary of solar panel production and house energy consumption for 2019. Blue is production and orange is overall household energy consumption.

There’s quite a bit to unpack from this screenshot and there’s a couple of errors I need to point out as some of the values are slightly off:

  • May 2019 – the CT clamp measuring the power flowing in/out of the house was switched accidentally by my Dad and myself when we were installing the solar diverter and we didn’t catch it till the end of May. My energy bills from May are not much different from April or June, so ignore this.
  • June 2019 – my panels were producing so much solar power, they kept shutting themselves off during peak periods due to overheating. The company who installed the panels very graciously upgraded all the micro-inverters for free and didn’t charge for parts or labour. As you can see in July, they fixed the issue! This does mean my panels didn’t generate about an additional ~200 kW by my reckoning though.
  • September 2019 – The power consumption spikes up massively because I bought an electric car and, on a day I charge it, it easily adds on 30 kW to our daily consumption.

Solar Stats Breakdown

MonthSolar Gen.
(kWh)
House Usage
(kWh)
Exported
(kWh)
Used Solar
(kWh)
Solar Used
(%)
JAN82.6789.3173.239.4411.42
FEB161.4277.81131.2630.1618.68
MAR195.1789.49147.2447.9324.56
APR250.9573.16169.5881.3732.42
MAY277.9490.00*150.00*202.3446.03
JUN248.8073.6791.05157.7563.40
JUL459.4451.65238.81220.6348.02
AUG423.6858.75235.97187.7144.30
SEP322.3091.36136.51185.7957.65
OCT162.61139.3862.8499.7761.36
NOV91.55226.1516.4775.0882.01
DEC79.02345.968.0271.0089.85
Total:2,755.551,406.691,460.981,294.5746.98
Monthly usage stats from the solar panels and house consumption.
* denotes estimated values.

So as you can see above, the panels produced 2.75 MEGA Watts (2,755 kW) of carbon-free power to the house and national grid as a whole. Not bad for a first year! With the kinks ironed out now, I think it’s possible they’ll do 3 Mega Watts in 2020! In terms of saving us money on our electricity bills, we’ll get to that in a minute. First let’s compare our 2018 and 2019 usage (removing the electric car for the moment).

House Usage 2018 (kWh)House Usage 2019 (kWh)Electricity Usage DIFF. (kWh)Electricity Usage DIFF. (%)
1586965*62139.2%
House electricity consumption years compared.
* denotes that the 2019 figures are excluding the electric car charging, which is quite substantial!

To put that another way, on our normal day to day energy usage, we are using nearly 40% less electricity to power our home a year. Though interestingly, we are only making use of about ~22.5% of the solar power produced to do this. How was the other ~24% of solar power consumed then?

The solar diverter to the rescue

Photo from 9th January 2020 – last year’s total was (682 – 9) = 673 kWh of solar power used!

As you can see from the above photo, the solar diverter (MyEnergi Eddi) device helped drastically boost the solar usage from the house by using 673 kW of solar power. By taking excess energy from the panels when there’s no other electrical loads in the house, we get to enjoy ‘free’ hot water, especially during the summer months. We were able to turn the gas boiler off completely for a while!

As the solar diverter was not installed until late April, there is a chance we might be able to get to 1 Mega Watt (1,000 kW) of hot water heated next year! Last year’s 673 kW of solar energy currently equates to 136.6 kg of co2 not released due to burning natural gas! Fantastic!

Thoughts on solar consumption

I was very unsure how much of the solar power produced we would be able to use on a day to day basis. Our main problem is that when the solar panels are at their most powerful, in the middle of the day, my wife and I are generally at work so we can’t make the best use of the power. The incredibly obvious solution is to get a solar battery but these are very very expensive and currently the payback period is way too long to justify one. At just under £400, the MyEnergi Eddi is an excellent addition to The Solar House Experiment as it allows for the power to be used regardless of who is in the house or what is happening in it. It is completely fit and forget.

That isn’t to say we didn’t make efforts to do things such as use the washing machine, dish washer and oven during peak solar periods where possible but this is not always practical. It was interesting to note that when working from home that the panels, even in winter, would generally power all the computers and equipment I use for my work which was cool!

With the addition of the electric car and its huge battery and my new EV charger (MyEnergi Zappi) I will hopefully be able to increase that solar usage number even further, especially during the summer months. The best solar generation was in July when the panels produced 22 kW of power in one day(!) Our house uses about 3-4 kW on an average day so that is frankly an insane amount of power to use up! That amount would let me add nearly 90 miles of driving range a day to my car, for free!

The money side of things

Finally, let’s discuss what has been the payback on the panels and solar diverter and how long will it take for them to pay for themselves. First, note that the solar diverter is replacing much cheaper natural gas with solar generated electricity, so it’s cost savings are less than they might first appear. For comparison, my unit rates for each are:

Price Per kWh (GAS)Price per kWh (Electricity)
3.51p*
*(4.13p assuming 85% efficient gas boiler)
13.80p
Current rates for electricity and gas on my tariff

So with no further ado, let’s breakdown the returns from the panels:

Solar ComponentCalculationMoney Earned/Savedco2 Saved (KG)
Feed In Tariffs2755 kW x 6.68p£184.04851.30
Solar Consumption
(House)
621 kW (E) x 14.80p£85.70191.89*
Solar Consumption
(Hot Water)
673 kW (G) x 4.13p£27.80136.60*
Total:£297.54851.30
Breaking down the money saved via the solar panels and solar diverter.
* We cannot double count the generation and consumption, but I’ve provided them as separate numbers

With a total install price of £7,931 (panels + solar diverter), this is equivalent to a yearly return of 3.75%.

This is a little on the low side of what I expected. I was aiming for about a 4.5% return. The missing June solar generation would have been an additional ~£13 of Feed In Tariff payments and I’ve only had the solar diverter installed for two-thirds of the year, so those numbers will definitely improve in 2020. At the current rate of return, I am therefore on track to breaking even in Year 19. I will be doing everything in my power to bring that down to Year 12!

The major difference in 2020 will be that I’m fuelling my electric car with solar power! As you saw above, over half of my solar power is being exported out to the grid at the moment – with the car battery able to soak up loads more of this electricity, I should be able to raise the solar consumption much higher and boost the returns as well. If I’m able to get to a 6% return each year then it will only take the 12 years I want for the payback period.

God I wish solar batteries were cheaper though, it would make everything so much easier!

In summary

I hope this has been an insightful look into installing your own solar array on your house and what the possible payback will look like. The ‘problem’, if you like, with our house is that it is already super efficient and we were already using well below the average electricity usage for a typical household of our size (roughly 120m squared). Like I said previously, on an average day we use between 3-4 kWh, whereas I believe the UK average is closer to 4,800 kWh(!).

People with larger houses (and therefore roofs) can install more panels than we can and can use the much cheaper, if slightly less efficient, versions and make their money back quicker. But we didn’t install all this purely for the financial side of things – we are choosing to use our money to reduce the carbon impact of our home as much as we can. I actually have an upcoming post on how even a small number of panels and a small 2-3 kW battery could drastically reduce your carbon impact, so stay tuned for that.

And with that, we’re done! Please feel free to share with anyone who has questions about getting their own solar panels installed!


2 thoughts on “TSHE: Solar Panels + 1 year review

    • Well, funny story… my wife quit her job and has started up her own company and works from home ~50% of the time now. She keeps saying she’s choosing to be FI (and me explaining that’s not how it works lol). My own travel costs are covered by the company I work for, so I actually make money on my commute – especially now I have an electric car but they still reimburse me at 45p/mile(!).

      Liked by 1 person

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