Tesla Power Walls in the UK?

[Fran Smitherman]

Hi Nickfromwales!  If the northfacing slope is part of an equilateral triangle (0.5metre base, 0.5 metre vertically to apex) I suppose the pitch on the north face is 60 degrees.  The southfacing slope is the hypoteneuse of a triangle with 1.5 metres base and 0.5 metre vertically to apex.  Does 'how many m2' refer to the area of the southfacing slope?: that would be 5 metres wide and 1.57 metres from top to bottom of the slope.

 

My next query is: does an inverter need its own power source to do its job?  If so, I think I'll probably go for powering my underfloor heating from the mains (there's a charging point for Mum's mobility scooter about 3 metres from the proposed new summerhouse - I expect we can extend from there to power the summerhouse) rather than  paying for a complicated roof, solar panels, inverter (and power source?), battery pack etc.

 

So now I'm thinking in terms of a flat roof (5 metres by 3 metres), resting on the double skin breezeblock walls (with 4.5 metre run of patio doors facing south).  What are the options for roofing materials?  Perhaps I need to move into a different thread on this site to discuss roofing.  

 

I'm logging off in the library for today.  When I visit the library again (probably next Wednesday) I'll check in this thread to see what further posts there have been, and look for a new thread.

 

Fran

[ProDave]

I would look at roofing the whole thing in a monopitch roof to get the maximum area south facing.  The small triangles you describe are too small for much in the way of panels.The "flat" bit is more promising but would be better if is sloped to the south rather than being flat.

 

The way a normal system works is you have a consumer unit in your building. That will have a light and socket circuit for the normal stuff.  You then have another circuit for the inverter.  A Grid tied inverter generates power synchronised to the mains frequency.  Such power generated will power anything in your home and so reduce your electrcity bill.  Even if your heating in the summerhouse is not on, something somewhere in the house will probably use it.

 

If reduced running costs is your objective, is looking at the summerhouse roof tacking it the wrong way?  Would you be better putting a larger bank of panels on the house roof?

[Fran Smitherman]

Thanks ProDave!  The house roof faces east and west so possibly wouldn't be conveniently oriented to the sun for harvesting sun's rays.  

 

You may have noticed that, when I posted yesterday, I mistakenly gave the pitch on the north-facing part of the summerhouse roof as 60 degrees when I should have typed 45 degrees.

 

No matter!  The consensus of opinion among my siblings is to power the underfloor heating direct from the mains and, having decided again solar panels, to put a flat roof on the summerhouse.  

 

I'll probably be back in the library on Thursday and will look then for a new thread to discuss roofing materials eg toughened glass as in a conservatory (obviating the need for windows in the walls facing east and west) as against a well-insulated roof to retain heat rising from the underfloor heating.

 

Fran

 

 

[Ed Davies]

Don't knock east/west panels too much. Each panel will obviously produce less than a similar one facing south but if you're limited by roof space E/W can produce more over the whole year because you can probably fit twice as many panels producing about 3/4 of the energy each. They'll also tend to produce for a longer period of the day getting into the morning and evening peaks for the better half of the year which can help with self-consumption. The downside of E/W is that they're even more biased towards the summer months than south facing.

[ProDave]

4 minutes ago, Ed Davies said:

Don't knock east/west panels too much. Each panel will obviously produce less than a similar one facing south but if you're limited by roof space E/W can produce more over the whole year because you can probably fit twice as many panels producing about 3/4 of the energy each. They'll also tend to produce for a longer period of the day getting into the morning and evening peaks for the better half of the year which can help with self-consumption. The downside of E/W is that they're even more biased towards the summer months than south facing.

I have dome mine E/W for that reason, to try and make a longer, but lower generation period each day to better the chances of self usage.

[Jeremy Harris]

If maximising self-generation is the aim then I think an East/West set up may well be better, even if the total generation is a bit lower.  Our demand tends to have two peaks, first thing in the morning then again late afternoon/early evening.  For much of the year an East/West system would be a better match, especially if at a fairly steep angle so that it makes better use of low angle sun.

[scottishjohn]

has there been any proper survey on advantage of sun tracking panels -presuming ground is suitable

with a ground array it could be quite easy i to have a swing from se through south to sw 

Edited February 18, 2019 by scottishjohn

[EverHopefull]

I have had West facing only for the last 8 years. They produce a similar total to another system in the family that is purely South facing but as is suggested at different times of the day.

The survey prior to install did warn of less production and the non ideal facing but I can produce longer and higher into the evening which would benefit some.

On the new house I will go for East facing exclusively as the peak demand is first thing in the morning and so I can feed my Solar Boost before lunchtime. This is purely a personal decision and would not suit all.

 

*The most surreal situation is when I have been wondering the house at night and found that the moon is reflecting enough sun to power the house in slumber! Unless i had seen it I would not have believed it possible.

[Miek]

4 hours ago, scottishjohn said:

has there been any proper survey on advantage of sun tracking panels -presuming ground is suitable

with a ground array it could be quite easy i to have a swing from se through south to sw 

A full azimuth tracker could give around 30% more energy in the UK, but generally the cost of the tracker is too high to justify it. Better to spend the extra money on more PV point it south and have no moving parts. I've never seen a commercial setup using trackers. They all use fixed frames for a good reason I think. 

[Big Neil]

Two sprockets from a pedal bike (one from the front and another from the rear) connected to a motor which itself had a speed controller programmed with the sun timings for that day. How would that work as a DIY system?

 

Or a motorised bottle jack instead of the chain and sprocket system, but with broadly the same idea relating to control

[Jeremy Harris]

If looking to build a tracker, then it's probably easiest to use an electric motor driven linear actuator, as these are available at a reasonable price for use on things like electric gates.  The control system needs something to reset the array at night, ready for the next morning, plus something like a 4 quadrant optical sensor to drive the array to point directly at the sun (something like the crude sensors used on early heat-seeking missiles).  Not that hard to come up with a tracking control system, I think, but the engineering involved in making a strong enough mount for the array might be a bit challenging. 

[Big Neil]

26 minutes ago, JSHarris said:

the engineering involved in making a strong enough mount for the array might be a bit challenging. 

 

whats the average panel weight for a PV panel  - something like 20kg if I recall (variable i know, but roughly speaking). So ten panels at lets say 22kg including mounting brackets etc. I wonder if it might be achievable with a modification of existing static mounts plus some automotive parts such as wheel bearings at each end and at a couple of intermediate points for support, running along the middle

[ProDave]

The issue is not the panel weight, but the wind loading.  A 4KW array is something like 25 square metres of "sail".  A 2 axis tracker must take that and support it at a single point, and be strong enough that it does not break when that 25 metres of sail is subject to say 60mph gales.

 

A bit easier is a single axis tracker where the elevation is fixed and only the azimuth adjusts throughout the day.

 

You also need more space for a tracker than you do a fixed array, I am pretty certain I would not have room to fit a tracking array, I only just had enough room for a fixed array.

[Jeremy Harris]

As a very rough indicator of the wind loading, a 25m² array, flat on to the wind, would have a wind loading imposed on it in a 60mph wind of around 13,200 N, or about 1,346 kgf (1.346 tonnes force).  The wind loading could be at least as high as this in an upward or downward direction if the array was inclined at a shallow angle, too, due to the lift forces act on it.

 

The small efficiency improvement would have to be justified by the higher cost, and maintenance needs, for a tracker mounted array.  Could take a long time to recover the extra cost.

[Big Neil]

32 minutes ago, JSHarris said:

As a very rough indicator of the wind loading, a 25m² array, flat on to the wind, would have a wind loading imposed on it in a 60mph wind of around 13,200 N, or about 1,346 kgf (1.346 tonnes force).  The wind loading could be at least as high as this in an upward or downward direction if the array was inclined at a shallow angle, too, due to the lift forces act on it.

 

The small efficiency improvement would have to be justified by the higher cost, and maintenance needs, for a tracker mounted array.  Could take a long time to recover the extra cost.

 

bloody loving the data - thanks...

[Ed Davies]

Also, a tracker gives the greatest improvement in summer because in winter the sun's only in one direction, really. Summer is when the extra energy harvested is least valuable.