5 months of domestic battery data

We’ve now had our Wattstor 6 kW battery (‘Bert’) for 5 months. The first chart shows our daily kWh averages and how they are changing as summer tails off into autumn.  Our daily average demand (red) has remained relatively consistent at 7.5-8 kWh a day other than June when we had 2 weeks away.


The PV generation (yellow) is dropping sharply with the shorter days and lower sun in the sky which (in our case) disappears behind two trees in the adjacent field in the afternoon. The average surplus kWh we have exported to the grid each day (green) is falling and the average we have had to import from the grid (black) is now rising sharply. September was the first month we have taken more from the grid than we exported to it.

For many happy days in high summer, the PV panels and Bert met all our demand and we imported nothing from the grid at all. But in September, the daily import needed from the grid rose sharply once we were cooking supper after dark and Bert could no longer reach 100% capacity from the day’s sun.

The second chart shows the proportion of our daily electricity demand which came from each source and how that is changing month to month.


The grid provided only 4% of our electricity in June and July but in September was up to 33%. The proportion of energy we take from the solar panels directly versus from the solar via the battery is also changing. In the last two months we have taken a higher proportion from the battery than directly from the sun. Again, we think this is because our consumption peaks in early evening (like most of the population!) when we are cooking (mainly on electric) after the sun has set.

Thierry Twizy above Usk Reservoir

Thierry Twizy above Usk Reservoir

On the days we need to charge our Renault Twizy, the solar PV (4kW) is rarely able to consistently provide all of the power required (2kW) for a few hours so the rest is taken either from Bert-the-battery (if he’s full enough) or the grid.

Fortunately, our Twizy only has a small battery 6kWh (same capacity as Bert) and operates at very low energy (140 Wh/mile). In this country, you’d need a huge South facing property with maybe 8-12 kW of PV panels to be able to charge a full-sized electric vehicle every day and still have surplus Wh to fill a domestic battery. And, as discussed previously, we now think it would be horribly complex to double one’s electric vehicle battery as domestic storage. The two usage patterns are too often in direct conflict.




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ETN member wins AA Award

Angel signCongratulations to our ETN member, The Angel Hotel in Abergavenny, who have won the AA Hotel of the Year in Wales -well deserved and we are delighted for them.

Of course, we’d like to think that Talia, their Twizy, won the award single handedly for them but I doubt that to be the case given the excellence of their food and accommodation! But Talia does put in a rather fine guest appearance at the end of their short award video.

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May to July with Bert-the-Battery

We’ve analysed the performance of our Wattstor battery (‘Bert’ to his friends) for the 3 months May 1st-July 31st (92 days).

During that time, we consumed 666 kWh (7.2 kWh/day).

Our 4kW solar PV generated 1,225 kWh (13.3 kWh/day) and we exported 504 kWh to the grid for others to use.

The pie chart below shows the percentage of our home electricity consumption which came from each source.

Bert pie

Source of domestic electricity May-July 2016

Comp Carm vansWe are still experimenting with the best time of day to charge our Twizy  which also has a 6kWh battery. The aim is to ensure that any excess solar (which Bert can’t absorb fast enough) gets used to charge the Twizy rather than exported to the grid. When there is no excess solar (or even enough to charge Bert), then we are trying to ensure that the Twizy doesn’t completely drain Bert. The two 6kWh batteries are definitely in direct competition – one to store solar energy for our domestic use later in the day and the other to store solar energy to take us places. It leaves us bemused as to how the model of using one’s electric vehicle battery as a back up domestic store would work. That would certainly give rise to conflicts – either cook supper here or have enough juice in your vehicle battery to drive for supper elsewhere!

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First 54 days of Bert-the-Battery

It’s now been 54 days since our 6 kWh Wattstor battery was installed enabling us to make much more use of the solar which our 4kW PV panels generate.

The resident data hound has just been at work and here are some headline figures (obviously we are currently at the optimal time of year):-

Solar generation: 760 kWh (14 kWh/day)

Our demand: 392 kWh (7.2 kWh/day) – this includes one thirsty Twizy!

Imported from the Grid: 30 kWh (0.5 kWh/day)

Exported to the Grid: 335 kWh (6.2 kWh/day)

Battery charge 225 kWh (4.1 kWh/day)

Battery discharge 180 kWh (3.3 kWh/day)





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Boma-friendly routes in Brecon Beacons

Not surprisingly, we occasionally get asked by Boma owners if we can recommend Boma-friendly routes in the Brecon Beacons National Park. We find this quite hard to do and are uncomfortable making strong recommendations without having recently checked for locked gates, stiles, fallen trees or other Boma-unfriendly impediments (which can appear unannounced) and also without knowing how well equipped for rough terrain and hilltop weather people are.

Local walking/cycling guide, Rob of Exploring Mid-Wales is happy to accompany Boswell (or any visiting Boma) on a guided day or 1/2 day walk.

If you want to go it alone, then here are a couple of suggestions (with no guarantees attached!). In the Brecon Beacons,  always carry warm and waterproof clothing and check the local weather weather conditions which can change rapidly. Remember, also, that mobile phone signals can be unreliable here.

Myndd Illtyd Common just South of Brecon. OS X (Eastings)  297732
OS Y (Northings) 226275, Nearest Post Code   LD3 8ER. You can park at the National Park Visitor Centre where there are disabled toilets and a cafe. There are lots of grassy paths across the common all with views of Pen-y-fan and the option of a circular 5 mile walk.

LongShot myndd Illtyd

The Begwyns – North of Glasbury on minor roads. OS X (Eastings) 316138 OS Y (Northings) 244068, Nearest Post Code LD2 3JN . The Begwyns is another area of high common land with great views and small peaks where you can wander along open grassy tracks in pretty much any direction you like. Apparently, there is room to park on the verge.

comp Begwyns

Usk Reservoir – West of Sennybridge OS X (Eastings) 283378 OS Y (Northings)  28662,
Nearest Post Code  LD3 8YF. There is a car park and an easy level-ish cycle track around the reservoir (5.5 miles) with glorious views. Unfortunately, there is a barrier across the dam at the start so a Boma has to take a short detour around by a small lane.

IMG_0018 usk map

Our Boma, Boswell, has been up Pen-y-fan once (video here) but we don’t recommend it because of the many deep drainage ditches across the path some of which are wide and deep enough to catch the Boma wheels. It is also necessary to contact the National Trust (Tel. 01874 625515) to arrange for them to open the gate to access the path in a Boma.

There are also a number of traffic free cycle trails in the National Park (the Usk Reservoir circuit being one of them). You can find a list of them here.  In principle, these should all be Boma-able. We know, for example, that the Mon & Brec canal path between Brecon and Talybont-on-Usk is as is the Taff Trail between Talybont village and the Talybont Reservoir (albeit quite bumpy). It is possible though that there might be impediments on some of them, e.g. a car barrier across the path with only room for a bicycle (not a Boma) to pass either side of it.

If you do successfully try any of these routes (or any others) in your Boma, please let us know and we will add them to this page.

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Early experiences with domestic energy storage

Comp Carm vans

We’ve written up our early thoughts and experiences of juggling solar PV input for our newly installed Wattstor battery with charging Thierry Twizy. Both hold 6Kwh – one to use for travel and the other for covering our household energy needs once the sun goes down. Working out how to optimise the solar input is proving interesting!


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Boswell-the-Boma in Ten Tors Challenge

Last w/e, our Boswell-the-Boma 7 was hired by Able Sharp of Totnes to enable him to take part in the Jubilee Ten Tors Challenge on Dartmoor. A great time was had by all and here are some photos of Able and Boswell receiving their well-deserved medal at the end of the challenge.


Able receiving his medal from the Army


Well done Able and Boswell-the-Boma


Dry run before the challenge

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