The Joy of Solar 4: A Second Installation

8 of the 16 Panels in Place – Including One on Dormer (Image: T. Larkum)
8 of the 16 Panels in Place – Including One on the Dormer (Image: T. Larkum)

Today is a big day as we’ve having a second solar array installed – this should provide sufficient electricity to cover the remaining usage for the house, plus enough left over to charge the ZOE.  The rear roof of the house is completely covered by the existing system so this one has to go on the front. That means it will be north facing so I’m prepared to have a lower than average yield. However, the predictions I’ve seen imply that it will still be economic, it will just take a little longer to pay off – perhaps 10-11 years rather than 8-10.

Rewiring Around Consumer Unit (Image: T. Larkum)
Rewiring Around Consumer Unit (Image: T. Larkum)

Last night after the scaffolding went up I cleaned the moss off the roof tiles – not necessary, but the only opportunity I’ll get to do it. I finished that this morning just before the installers (Greenday Renewables) turned up. It’s now the afternoon and so far most of the panels are up on the roof, and the inverter is in the loft, and currently all the connections into the consumer unit/fuse box are being made.

Two Hours Later – 15 Panels in Place (Image: T. Larkum)
Two Hours Later – 15 Panels in Place (Image: T. Larkum)

Update: It’s now the evening, the installers have gone, and I’ve finished tidying up. The weather was foul for most of the day, with almost non-stop rain from late morning, which made things harder (and a bit messier) than usual. Nonetheless the system is complete and working, although the amount of energy being generated at the end of a day when the sky is overcast is relatively small, making it harder to confirm that it is wired and operating correctly.

Inverter and Isolators in Loft (Image: T. Larkum)
Inverter and Isolators in Loft (Image: T. Larkum)

The inverter in the loft is fixed to a wooden upright as the prime location (the end wall nearest the consumer unit) has the inverter for the existing solar array. I made up a wooden board and that went across the upright to mount the isolators.

View Along Roof Ridge – New System (North-Facing) on Left and Old System (South-Facing) on Right (Image: T. Larkum)
View Along Roof Ridge – New System (North-Facing) on Left and Old System (South-Facing) on Right (Image: T. Larkum)

This time around the system includes the addition of a Wattson Solar Plus Energy Monitor. It displays total solar generation less usage, so you know how much ‘free’ electricity there is to spare (which might prompt you to switch on the dishwasher, etc.). More on Wattson in a later post – suffice to say for the next few days I’ll be switching things on and off to see the real-time effect on our usage and so work out where in particular our energy (and therefore money) is currently going.

Bouygues Gets a ZOE

Ghosn gives ZOE keys to Bouygues (Image: Renault)
Ghosn gives ZOE keys to Bouygues (Image: Renault)

Renault ZE made an announcement today on Twitter:

“Today, Renault CEO C. Ghosn gave Renault ZOE keys to CEO M. Bouygues. Congratulations to him for being an EV driver!”

Martin Bouygues leads the Bouygues industrial group, a conglomerate with interests in construction, telecoms, energy and transportation.

Grid Electricity Usage

Domestic Electricity Imported from the Grid (Image: T. Larkum)
Domestic Electricity Imported from the Grid (Image: T. Larkum)

Looking at how much electricity our solar array has generated prompted me to look at how much electricity we’ve been using over the last few years. I was able to dig out most of my energy bills back five years and used those in a similar process to graph our usage – see the chart above.

One of the first things that is obvious is that there is only data for the four quarterly bills in a year, there is no data per month never mind per week. This general point highlights how poor are the systems in place for tracking energy usage. I didn’t realise it before this exercise but our meters are only read about twice per year (typically in May and November) so there’s no real indication of how much energy you are using at any time, and the bills in between these readings are just based on estimates.

Of course the government has plans for everyone to get smart meters installed to give better tracking of energy usage. However, the start of the rollout was planned for next year and has just been delayed by a year. They won’t be fully in place before 2020 which is a long time to wait. In the meantime to address the issue of a lack of detailed information on energy usage I have started to manually record the electricity (and gas) meter readings once per week.

Anyway, back to the chart. Given the lack of data, and its questionable accuracy (since it includes estimated readings) it is dangerous to deduce too much from it. It fairly clearly and as expected shows higher electricity usage in winter months compared to the summer – presumably from more use of lighting, and perhaps more time spent indoors watching television, etc.

I would also like to conclude from it that our usage of electricity from the grid has reduced since installing solar, i.e. that the values for 2011 and 2012 are lower than previous years. However, that is not obvious, and in particular the usage for Jan/Feb 2011 is particularly high. It would probably be wishful thinking anyway, since we are often out (and hence electricity usage is low) when the sun is shining brightest. So what can be done to get more benefit from solar?

There are three key income elements to the government’s solar feed-in-tariff system:

  1. You get paid a generation amount for each unit of electricity generated.
  2. You get paid for each unit exported to the grid. However, since there are no smart meters in place yet this is done notionally: you get paid an export amount for exactly half of what you generate as though you exported it.
  3. Given that the export isn’t metered, you can use the electricity you generate for whatever you want for free.

This means that there is a clear economic benefit to using as much of the electricity you generate as it is being generated, since it deemed to be exported but is actually available to use. This ignores, of course, the complex moral question of whether you should just export it anyway so as to reduce your neighbours’ carbon footprints regardless of the economic cost to yourself, and I may return to this question in a future post.

Anyway, assuming for now the aim is to get the best economic benefit from the solar array, I have been considering some ideas on how to achieve it:

  1. We need to defer our electricity usage to the times when most electricity is being generated. This means, for example, operating the dishwasher and washing machine during the day rather than in the evening (and so using their timer functions if we are out during the day).
  2. Use some electricity storage such as batteries. However I believe such systems are still too expensive to be economically justifiable.
  3. Heating our water electrically to save on gas usage, i.e. operate our electrical immersion heater from solar during the day. There are some technically advanced systems for doing this such as Immersun but they are expensive and so payback would take a long time. I am currently looking into simply running the immersion heater from a timer during the summer months so it operates during daylight hours.

As well as economic benefits I am determined to reduce our family’s carbon footprint – getting the solar array and the ZOE are the key elements to this. There are also other approaches and lifestyle changes that I will be investigating; others are further along this road than I am and I recommend anyone interested to research further. I have put some starting links on the Links page, for example the excellent Earth Notes site.

The Joy of Solar 3: Making Electricity

Solar Array – South Facing (Image: T. Larkum)
Solar Array – South Facing (Image: T. Larkum)

I previously described the installation and setup of the solar system on the back (south facing) roof of our house. It was installed by Greenday Renewables who I highly recommend – we have had no trouble with it and it works very well.

The most important information, however, is of course how successful it has been at generating electricity. The system is a 3.7 kWp array, consisting of 10 panels each of 185 Wp (plus an inverter in the loft), where Wp indicates ‘Watts peak’. What this means is that in an ideal (‘peak’) situation the 185 Wp panels could each produce 185 Watts of electrical power, so all ten together could generate 3.7 kilowatts. Of course, they are never used in perfect conditions so an estimate is generally provided of the likely total amount of power generated for a particular system arranged at a given angle, direction and latitude. For our system this was 3333 kWh per year, where 1 kWh of energy is a kilowatt of power provided for one hour.

The size of the system was determined by the roof space – it was the largest system that could fit. It is eligible for the government feed in tariff (FIT) which applies to any domestic system up to 4 kWp. We would have gone for the full 4 kWp if there had been the space.

The system was installed in September 2010 so we now have two full calendar years of data on electricity generation, covering 2011 and 2012. Up until the start of 2012 I recorded the meter reading virtually every day but since then I’ve been doing it once per week. The data is recorded manually and then transcribed into an Excel spread sheet (soon I hope to replace that process with an automated system, but more of that in a later post). From the spread sheet I have been able to graphically chart the data – see below (and click to enlarge).

Electricity Generated by Solar Array in 2011 and 2012 (Image: T. Larkum)
Electricity Generated by Our Solar Array in 2011 and 2012 (Image: T. Larkum)

Considered in broad terms the chart shows pretty much what you would expect – low generation in the early part of each year, building up through the summer and dropping again as winter returns. However, looking in more detail it is perhaps surprising just how much the rate of generation varies week by week as well as year by year. It is possible for one week to generate twice as much energy as another week in the same month. Similarly each year can have very different weather, so for example 2011 had generation peaks in April and May, while 2012 had peaks in May, August and September. In fact 2012 was significantly more variable than 2011.

Fortunately over a whole year the peaks and troughs average out pretty well, and the system has performed well. It generated 3650 kWh (3.65 megawatt hours) in 2011 and 3500 kWh (3.5 MWh) in 2012, and these numbers compare very favourably with the 3333 kWh that was predicted. Over these two years it was eligible for FIT payments of £3130 which is about one-fifth of its installation cost (£15750) so it is on course to pay for itself in about 10 years without even counting the cost of the electricity saved.

After it’s paid off the benefits don’t stop, of course – it is eligible to get FIT payments for a further 15 years – index linked – and after that we will have free electricity for life.

Overall it has been a great investment, so much so that we are looking to add another system on the front of the house with a view to using it to power our ZOE – more to follow on that in a future post.

[The Joy of Solar 4: A Second Installation]

[See also Grid Electricity Usage]

ZOE Wins 25 Hour Energy Saving Race

ZOE at the ‘25 Ore di Magione’ (Image:
ZOE at the ‘25 Ore di Magione’ (Image:

Last weekend the Renault ZOE took part in the Italian ‘25 Ore di Magione Energy Saving Race’ (25 Hour Magione Energy Saving Race) and won both categories in which it competed: ‘utility’ and ‘electric powered vehicle’. The race began at the Autodrome di Magione in Umbria with the first part following the road around Lake Trasimeno, while the night section took place within the autodrome.

The total distance covered was 236km, which the ZOE achieved with two uses of its fast Chameleon charger. It won on criteria that considered the vehicle weight, average speed and distance travelled per kWh, at one point achieving 193.4km on a charge at an average speed of 45km/h.