Very basic questions about solar, starting now if you don't mind.

[saveasteading]

I read all the discussions here on solar. Sometimes they are far beyond my understanding but it's all very useful.

I think I have noticed a big change in  recommendations over 3 years, and it's because of battery technology improving perhaps.

 

Context. Converting a barn. 19m x 19m. plus a garage 14 x9.

We think that panels on the SW face of the garage roof is perhaps sufficient.  70m2 of roof, say 60m2 of panels?

No shading.

A gable faces SE but vertical panels seem to be out of fashion again.

On the garage will mean it is all easy to access for installation, inspection  and cleaning.

Heating will be air source: 2 units attached to the house.

We have 3 phase supply if that is relevant.

All the switchgear will be in the garage, then it's 15m to the house.

The garage can remain unheated.

Have had an initial consultation from a supplier.

 

Question one. Battery principles.

In principle I assume we want to catch all possible rays on the bright days, to use on the following darker days.

Thus don't undersize the battery.*

So will it be very big? The guy said it's about 0.5 x 0.5 and height is stackable, about 1m if 'oversized'. That felt small.

And is it a fire risk? The video we were directed to last week says one in a million batteries goes on fire.

I had assumed that we would build a block or plasterboard enclosure for it, but the guy said it is enclosed against fire, and weatherproof ? is this so? Keep it in the garage or outside?

 

* my analogy is rainwater harvesting. I did it once, and I doubled the tank size that everyone else suggested (from 5m23 to 10m3.) and collected every drop from the roof. This proved correct as when it rained heavily it didn't run past to the pond, but was all collected, and never ran dry. But the investment was just for a bigger plastic tank. A battery is on a different price level.

 

I'm interested in experiences and informed hunches as well as scientific fact.

 

 

 

 

[JohnMo]

 

 

The way (for me) to size battery is ignore solar (for now) calculate the electricity demand on your coldest day or close to that.

 

So now you need to get a battery that deliver that electric without have to use peak electricity.

 

Octopus Cosy gives you three cheap periods, think the longest period between cheap periods is 7 hrs. And there are 8 hours of cheap electric, so you can just draw from grid in this periods and recharge battery.

 

So battery only needs to be able to last 7 hrs at highest demand. So in simple terms xkWh, divide by 24, then multiply by 7. Example 40kWh/24, is 1.6kWh, them multiple by 7, so just under 12kWh. With conversion losses (DC to AC) you need to add another 10% so now you are at 13.2kWh. So really an actual capacity closer to 15kWh. Or a GivEnergy AIO, with an available capacity of 13.4kWh, which is what I chose.

[JohnMo]

3 hours ago, saveasteading said:

garage can remain unheated

You will get a battery capacity hit as it will self heat using it's own capacity or just give less capacity.

 

3 hours ago, saveasteading said:

assume we want to catch all possible rays on the bright days, to use on the following darker days.

Maybe better filling a reasonable sized battery and export. Cosy is 12.7p to buy and they will pay 15p to export. Keep what is cost effective to keep, sell the rest.

 

Fires - battery chemistry is pretty safe in house batteries. Mine is in loft/plant room, fully insulated space. 

 

Other thing to look at is inverter size so you can have multiple things drawing electric without sucking in mains electricity, 6kW works well for us.

 

Plus look what happens in a power cut, some systems shutdown most except an emergency circuit, so rest of house goes black. Good thing with AC coupled (GivEnergy AIO) house just runs as normal with no interruption.

[Kelvin]

We have a Sigenergy system. 12kWh inverter and 24kWh of batteries and gateway (for power cuts) 19 panels mounted East/West on garage with a plan to add more ground mounted. Our peak load with everything on can hit 9kW. Background load is 600W.  We consume around 18kWh of electricity per day right now. Those last two figures will obviously increase in the winter months. I’ve set some limits on our battery SoC so we have 20kWh available. The gateway provides wholehome backup as an uninterruptible power supply and it works seamlessly and the inverted can peak to more than 12kW for 10 secs on switchover. 
 

Mounting the PV panels on your garage roof is a good decision. I wouldn’t fit the batteries outside. While some of these systems can be mounted outside I’m unconvinced over the long term unless they are sheltered in some way. Some batteries have heaters built in (not all and not all within the same range so make sure you ask) The Sigenergy batteries have a fairly comprehensive physical safety system that they market as 5 layers of safety. They also need to have free space around them rather than mounted inside something. A lot of the newer systems are modular and are actually quite compact. Ours is 84cm wide by 124cm high and sits 33cm off the wall (batteries and inverter)

 

We’re on Octopus Intelligent Go and their Outgoing tariff so we get paid when we export. 

 

 

[SteamyTea]

I am going to have to ponder all this in depth.

 

As a start, model your roof in PVGIS.

Model just 1 kW_p of solar, then you can easily multiply to a sensible size.

Remember that they will be average figures, so a sensible standard deviation (limiting to say 65% of the figures) needs to be included).

 

Can you model your usage? I know you want to use a spreadsheet more.

 

You can also store energy thermally, which is cheap and safe if you have the design right.

[Kelvin]

As far as which system to go for it’s a bit of a minefield and depends on what you want from it, cost, and what the local installers to you typically fit. I got 6 quotes for five different systems. I did originally want the GivEnergy AiO that @JohnMo has but I couldn’t get a local installer to quote as they have all pulled out of installing them citing too many issues, poor support and a difficult commissioning process. The company we went with said they’ve removed two GivEnergy systems and replaced with something else. 
 

I got quotes for: 

 

SolarEdge - very dear and would have taken up a lot of space for half the battery storage but the 3 phase system is modular and better designed imo. Supports whole or partial backup. Very good PV optimiser solution. 
 

Givenergy AiO - Couldn’t get a local installer to quote. Contacted Giv and they put me onto a Manchester based company so that was a non-starter. Was the cheapest quote by far. Expandability of the AiO system didn’t seem possible but I didn’t investigate it further. They do stackable batteries and 3 phase inverters. Very good warranty. 
 

Tesla Powerwall 3 - Much better than the PW2. Safer too as it uses different battery chemistry. The inverter size can be changed in software so no need to replace the inverter  if you got a bigger export limit from your DNO for example. It supports 3 phase but can only backup a single phase. You’d have to buy a PW3 for each phase if you wanted wholehome backup. It also doesn’t switch over instantaneously during a power cut. Was very good value for money. I was expecting it to be dear but it wasn’t. 

 

 

Fox - The dearest quote I got by almost £2000 after haggling. This was for their EP11 battery system which took up a lot of space. The home backup option was a bit confusing as I couldn’t get a straight answer from the installer. I also found the Fox website hard to navigate. 

 

 

Sigenergy - I got two quotes for this system and they were within a few hundred pounds of each other and priced quite competitively at very slightly dearer than Tesla (this was for a 16kWh battery system) I eventually went with this option and added an extra battery which was still cheaper than both the Fox and SolarEdge quotes with twice the storage and a home backup gateway. However Sigenergy are very new to the market (2022) and their kit has consequently less real World field testing so there’s some risk there. The installers love it because it’s very easy and quick to install and commissioning is literally minutes rather than hours with the other systems. They have a comprehensive range of options for single and 3 phase. The battery safety systems seem quite comprehensive which was a big plus for me. They do have a warranty requirement where it needs to be connected to their cloud service and if it isn’t for 90 days then it automatically goes into a safe operating mode whatever that is. It is very popular at the moment and some of the kit is in short supply. 
 

All of these systems need to be connected to the internet if you want to use their app to communicate with the system so you’ll need to provision a connection in the garage if there isn’t one WiFi or ethernet and ethernet is likely better. You also need to ask the installers to be clear on exactly the cabling each system needs and how that translates to your situation especially if the system equipment is split between the garage and house as mine is (inverter and batteries in the garage, gateway in the house) The Sigenergy system seemed to be the easiest to cable. 

[SteamyTea]

@Kelvin

 

You have highlighted nicely the problems with early adoption of technology.

The first practical cars were electric, then ethanol, then diesel and gasoline.

Taken 100 years to get back to electric, not for lack of trying.

My feeling about buying into an energy storage technology/system is like the French Revolution, 'it is still to early to say if it has worked'.

 

(There were steam, LNG, hydrigen powered vehicles as well)

Edited August 27 by SteamyTea

[Kelvin]

The principle is sound, the economics marginal although with our system we were able to get it financed through Home Energy Scotland so for us the economics are fine. The longevity who knows. 10 year warranties are great but 10 years is a long time both for the technology and for the energy market. 

[saveasteading]

That's all great info. thanks. I will digest this and respond in due course.

The PVGIS site isn't working properly so I will try that tomorrow.

[Gus Potter]

8 hours ago, saveasteading said:

I read all the discussions here on solar. Sometimes they are far beyond my understanding but it's all very useful.

I think I have noticed a big change in  recommendations over 3 years, and it's because of battery technology improving perhaps.

 

Context. Converting a barn. 19m x 19m. plus a garage 14 x9.

We think that panels on the SW face of the garage roof is perhaps sufficient.  70m2 of roof, say 60m2 of panels?

No shading.

A gable faces SE but vertical panels seem to be out of fashion again.

On the garage will mean it is all easy to access for installation, inspection  and cleaning.

Heating will be air source: 2 units attached to the house.

We have 3 phase supply if that is relevant.

All the switchgear will be in the garage, then it's 15m to the house.

The garage can remain unheated.

Have had an initial consultation from a supplier.

 

Question one. Battery principles.

In principle I assume we want to catch all possible rays on the bright days, to use on the following darker days.

Thus don't undersize the battery.*

So will it be very big? The guy said it's about 0.5 x 0.5 and height is stackable, about 1m if 'oversized'. That felt small.

And is it a fire risk? The video we were directed to last week says one in a million batteries goes on fire.

I had assumed that we would build a block or plasterboard enclosure for it, but the guy said it is enclosed against fire, and weatherproof ? is this so? Keep it in the garage or outside?

 

* my analogy is rainwater harvesting. I did it once, and I doubled the tank size that everyone else suggested (from 5m23 to 10m3.) and collected every drop from the roof. This proved correct as when it rained heavily it didn't run past to the pond, but was all collected, and never ran dry. But the investment was just for a bigger plastic tank. A battery is on a different price level.

 

I'm interested in experiences and informed hunches as well as scientific fact.

Ok let's say you have a big plot and in that case I would say if you want to get there, don't start from here! 

 

Consider a ground mounted system even if to rule out.

 

There are significant advantages of ground mounted. You can optimise the orientation of the panels. In the years to come as they start to fail you can replace easily in stages from ground level. If you need a soakaway for say your sewage plant then put that under the solar field if possible as the panels will restrict plant growth that could clog the soak away.  Every time you add something to a roof it requires flashings and details.. all that is extra maintenence and cost. Think forever home and resale value if you need to move out.

 

8 hours ago, saveasteading said:

And is it a fire risk?

Well from my experience they used to be. When I worked as a designer for a cold formed steel shed business ( the biggest by far in the UK, we did at least 700 to 800 sheds a year) the feed in tarrif was exceptional. The company I worked for sold a deal to farmers whereby their shed came free but they had to agree to put a 40kW solar system on the roof. During that time they were responsible for maintenance and after 25 years they got to keep the lot. It was a great deal but the folk that were supplying the invertors were cowboys and two buildings went on fire and one from memory killed valuable animals inside.. the word got about on say the Farming Forum and the game was a bogey. So yes, there is still a fire risk but why take any risk if you don't need to?  Best to keep the invertor and so on outwith the building envelope if you can. 

 

For all on BH if you have ground available then use it for a solar field. Think maintenance. Say you have a two story house and someone needs to go up and clear the drainage around the roof and panels and give the panels a wash. Two men half a day = £400 quid plus a cherry picker.. call it £ 800 -1000.00 a visit. But if ground mounted you can give you solar panels a quick wash when you are mowing the grass.  Even if you do a quick sum you can see that long term the maintenence is a key issue. 

 

If you split the difference you can then maybe buy the best performing panels and best quality currently on the market and still be quids in on ground mounted once you consider the maintenance cost. 

 

 

8 hours ago, saveasteading said:

But the investment was just for a bigger plastic tank.

Like this analogy. @saveasteading I've made some points. Good design is often about ruling things out rather than in as this allows you to focus on the things that you really are going to build. 

 

This is where Build Hub excels as it let's members float and discuss their ideas at a really basic concept design stage without any real pressure or getting slagged off and dismissed. 

 

 

 

 

[Gus Potter]

To add a bit. The framework for ground mounted solar panels is often galvanised steel cee sections, similar to what you seen on motorway barriers. These are designed to last about 25 years, if in the country you just need a local fencing contractor to knock these into the ground for you. They are used to getting fences straight so not a challenge in this respect. 

Edited August 27 by Gus Potter

[Gus Potter]

5 hours ago, Kelvin said:

Fox - The dearest quote I got by almost £2000 after haggling.

In the grand scheme of things a difference of 2.0k is neither here nor there when you consider maintenance, replacement cost with a system that might not be compatible with your roof makeup and the fundamental design choice of ground or roof mounted. The way we mount solar panles on roof has changes a lot just in the last few years so expect this to continue. 

 

There is discussion around net zero and we can see good farmland getting build over. Ask, why are we not covering industrial buildings in PV right next to the point of demand.. it's down to cost and ongoing maintenance. So for self builders if you have space then just follow the ground mounted route. 

Edited August 27 by Gus Potter

[Kelvin]

I tried really hard to ground mount ours but while we have a reasonable amount of space none of it is ideal for ground mounting. I even had a go in the digger and created a level flat area on top of the cliff and built up the bank to hide it. Put down gravel and dropped off three bags of ballast for the console tubs. Other half adamant they mustn’t spoil the view. However, our cliff is soft sandstone that is always moving a bit with bits falling off it. Therefore running cables down it and across the burn then 80m back to the garage  isn’t the best idea. I’m thinking of putting some bee hives there instead.  I have since cleared the top corner of the plot which is much closer to the garage and an easier run back to it and I reckon I can get 10 panels in there south facing and maybe a few more at the front. But I’m with Gus if you can avoid them on the house roof and keep the batteries out of the house then do that. We have friends whose new self build went on fire due to a cabling fault with their PV panels. Had to rebuild the house and then couldn’t live in it. 

[Kelvin]

9 minutes ago, Gus Potter said:

In the grand scheme of things a difference of 2.0k is neither here nor there when you consider maintenance, replacement cost with a system that might not be compatible with your roof makeup and the fundamental design choice of ground or roof mounted. The way we mount solar panles on roof has changes a lot just in the last few years so expect this to continue. 

 

There is discussion around net zero and we can see good farmland getting build over. Ask, why are we not covering industrial buildings in PV right next to the point of demand.. it's down to cost and ongoing maintenance. So for self builders if you have space then just follow the ground mounted route. 

The extra £2k was just for the battery system. Roughly the cost of a whole other battery module for the system we went with. The PV quotes were all very similar. 

[Gus Potter]

Just now, Kelvin said:

The PV quotes were all very similar. 

Missunderstood so appologise. 

 

4 minutes ago, Kelvin said:

I tried really hard to ground mount ours but while we have a reasonable amount of space none of it is ideal for ground mounting. I even had a go in the digger and created a level flat area on top of the cliff and built up the bank to hide it. Put down gravel and dropped off three bags of ballast for the console tubs. Other half adamant they mustn’t spoil the view. However, our cliff is soft sandstone that is always moving a bit with bits falling off it. Therefore running cables down it and across the burn then 80m back to the garage  isn’t the best idea. I’m thinking of putting some bee hives there instead.  I have since cleared the top corner of the plot which is much closer to the garage and an easier run back to it and I reckon I can get 10 panels in there south facing and maybe a few more at the front. But I’m with Gus if you can avoid them on the house roof and keep the batteries out of the house then do that. We have friends whose new self build went on fire due to a cabling fault with their PV panels. Had to rebuild the house and then couldn’t live in it. 

I think @saveasteading has a generous plot but if building on a quarter of an acre you can't go ground mounted. 

 

8 minutes ago, Kelvin said:

I’m thinking of putting some bee hives there instead

 

My Mum kept bees in Perthshire, hive orientation is one key aspect. Is your cliff not north east facing? The bees will freeze in the winter? Likewise if the hive get too much direct summer sun then the bees struggle to keep the hive cool.

 

12 minutes ago, Kelvin said:

But I’m with Gus

Ta. As a desinger I have to consider fire. In the old days we would have a petrol or diesel car in an intergal garage and we would design for that going on fire. But now we have EV's that are a different risk in that the development of a fire is different. A big solar battery contains lots of energy but is maybe not subject to the same level of safety scrutiny as a car. So why have that in your house if you can avoid it. 

 

18 minutes ago, Kelvin said:

I reckon I can get 10 panels in there south

Sometimes we can tailor the landscaping to compliment the modern solar panel. In Scotland on a banking we will select heather plants that change colour and flower at different times of the year. You can contrast this with the stark canvas of solar panels, you are not trying to hide the panels rather, you state.. here is a mix of old and modern. 

[Kelvin]

No the top of the cliff faces south. Best orientation for bee hives is south east or south to catch the morning sun and get them active. 
 

On the PV. My current East/West array is doing better than I expected. It’s generated 1.15MWh since 15 July. 

[Gus Potter]

On 28/08/2025 at 00:29, Kelvin said:

On the PV. My current East/West array is doing better than I expected.

Nice to get a surprise like that when something performs better than you expect. Well done!

[SteamyTea]

9 minutes ago, Gus Potter said:

On 28/08/2025 at 00:29, Kelvin said:

On the PV. My current East/West array is doing better than I expected.

Nice to get a surprise like that when something performs better than you expect

Is it the system performing better, or the weather is different?

 

Having studied solar energy for over 2 decades now, something has just occured to me.

I have never seen a systems performance compared to that systems normalised performance.

It's a bit like a cars performance figures, there are standard tests (which are highly criticised) and real world performance (which are highly individual). 

Then there is weather.

 

[Gus Potter]

24 minutes ago, SteamyTea said:

I have never seen a systems performance compared to that systems normalised performance.

 

On 28/08/2025 at 00:29, Kelvin said:

On the PV. My current East/West array is doing better than I expected. It’s generated 1.15MWh since 15 July. 

It's interesting. I hope I'm not identifying Kelvin's site but I've been there. About a mile or so down the road is a farm that I have a family connection to. This used to be a highly productive soft fruit farm and if you wander about you can still see the bases of the prefabs that armies of berry pickers would come to every year. 

 

The key thing is that this farm sits in the rain shaddow of the mountains but also the geography then further splits the weather and that doesn't get picked up even in the local weather forcasts. Go five miles further up the road and I think you would get a different output from your PV. 

[Kelvin]

It’s certainly weather related. But we get a lot of weather here. Admittedly it’s been incredibly dry for a while (getting on for a year of well below the mean rainfall*) but it can still be very overcast.    We also can get a lot of morning mist so I was expecting to miss the morning sun on a lot of days. However it’s generating enough to power the house and charge the batteries most days. In fact yesterday was the first day I had to charge the batteries from the grid in the cheap window for the next day since it was installed. 
 

* Off topic (but weather related) I fret a bit about water as we’re on a borehole. It’s generally assumed that boreholes are a more predictable and reliable source of water. This depends on the geology of course. I was chatting with someone recently who is converting an old hall. His builder lives on the south coast. He’s been on a 120m borehole as his primary potable water source for 10

years.  It’s run dry. Chap I was chatting with didn’t know any of the specifics about the borehole so it might be in poor location or always had a poor yield or was badly drilled  etc but nevertheless boreholes don’t often  dry up. One swallow does not a summer make and all that of course. 

Edited August 29 by Kelvin

[Gus Potter]

On 29/08/2025 at 23:22, Kelvin said:

It’s certainly weather related. But we get a lot of weather here.

Local topography can vary a lot. On my self build, Qouthquan, near Biggar we had Tinto hill and the upper part of the clyde valley that would move the "local" weather about. Yes, you will get a lot of different weather, four seasons in one day. You will no doubt be appreciating how dynamic the weather is at your house, but one thing... it's not boring!

 

On 29/08/2025 at 23:22, Kelvin said:

 It’s run dry.

Parts of the south do seem to be suffering from a long term decline in the main aquire level. That said it could just be that the performance of the borehole has dropped off, got clogged. Some boreholes don't last forever and that I suppose has to be factored into the long term (maintenence) cost when buying a house with a borehole. 

[saveasteading]

On 27/08/2025 at 15:07, JohnMo said:

calculate the electricity demand on your coldest day or close to that.

 

I have information.

The steading phase 1 (3 bedrooms ) has been in use for a year or so. A self contained unit of 107m2 gross internal. Ufh to the ground floor and radiators 1st floor, all from an ashp. All electric,  No solar or battery. 

 

The power used has been rigorously recorded from monthly bills.

 

Nov to March inclusive we will consider to be winter.

0.19kWh /m2 /day average

Cost £200 / month use winter 

Summer £20/month.

 

The insulation is good but to conversion standards, not new. Also the surface area is very high compared to floor area.

 

And it is Highlands. 

So for a chunky building in SE England it should be much less.

 

So I think I may simply forecast the barn conversion   use as kW/m2 x our floor area. 0.19 may be extreme as an average but a decent guide as worst case.

 

Any thoughts or your own numbers?

[JohnMo]

19 minutes ago, saveasteading said:

0.19kWh /m2 /day average

Suspect a cold day would be about 50% higher than the average. So if your 200m² (add your own area) that's about 50kWh to cover all consumption on the coldest day on cheap rate - let's assume Cosy tariff for now.

 

50kWh a day is around 2kWh per hour. Cosy gives 8 hrs of cheap rate, so that's 16kWh (2x8) and needs battery for 34kWh. 34kWh/3 needs just over 11kWh battery to cover all electrical demand on cheap rate on the coldest day, if charged three times.

 

The shortest cheap tariff period is 2 hrs, so you would need a 6kW inverter to comfortably to charge.

 

Just add your building size.

 

 

[renovator123]

TL;DR

Got ours installed last month.

Obsessed with the details now.

 

Energy Savings Trust PV calculator is excellent although we went for double the size. 

 

I think you are overestimating the number of panels that will fit. They are big and don't come in that many different sizes or shapes.

 

Similarly crap solar PV forecast in my location, but it cut our usage by 50% in Oct-Nov. Ours is the SE roof only, 45 sq m in 22 panels giving 9.8kwh peak, house footprint is 75 sq m, generated 6.5kwh last month with a large battery.

 

Info dump to follow.

 

Scroll to pics.

 

Estimated solar PV needs

We started off with the Energy Savings Trust PV calculator, super helpful but it wouldn't do calculations for our size of system and limited our annual electric use to 6,000kwh when it is double that (yours will be on your bill). 

 

Solar PV depends on location - not just roof direction - west coast UK being the worst area (dark clouds and thick clouds)- put it in a calculator to find out, but it also depends far more on time of year.

It can vary a lot between days - batteries will smooth this out - but what you will notice more is exporting excess to the grid most days in summer, and rarely being self-sufficient in winter (depending on your calcs).

 

Several apps will do a daily solar PV estimate if you enter your longitude and latitude, expected system size, and the angle ("azimuth") which is usually degrees from South. Typical roof pitch is 35 degrees. PV Caculator and SolXpress are free ones. You can monitor the predication charts this winter, compared to average daily usage (from your bill).

 

Heat pump cylinder

Some of solar PV compatible and some aren't. I have no idea what this means since that's next year's job!

 

Batteries are big

They can go outside (under a shade canopy), in garages and I think probably in lofts. Might fit in a garage loft if it has a sloped ceiling. It CANNOT be fully boxed in because ventilation is needed but this can be at the top, sides, and underneath if wall hung. If you put it outside the garage you can hide it with planting on trellis or similar. We can't get them outdoors here due to limited space.

 

Our house layout is extremely complicated with no garage, and internal thick stone walls. We have a 13.5kwh Givenergy All in One battery unit and it fits in a typical "alcove" - its at the side of our disused chimney breast where you might fit a bookcase and takes up almost the full depth and width of the alcove. It is about 1.2m high x 0.65 x 0.65 (I think), above it are 2 small string inverters (Solis ones about 0.30-0.35m deep) and 3 isolation switches plus the cabling between them so basically nearly up to ceiling (which is quite low) and about 0.20m off floor. It actually works well with something similarly sized in the other alcove. It is similar to a 250L heat pump cylinder but boxier, and has string inverters above it (they are not much bigger than A4 paper but shouldn't be right next to each other). You can probably get much smaller batteries but ours is a modular system we can easily add to. It does hum, the smaller string inverters are much quieter. It is a large capacity battery given the size of our panels, although your home is much bigger I think (assuming you have 2 floors) so you might want similar battery size. It is in the office/study and I plan to cover the front of it with (removable, painted) ply sheet with top and underneath gaps for ventilation - luckily we have a MVHR supply valve right above it that gives continuous ventilation moving heat away from it. I wouldn't be able to tolerate working with the hum but it is fine for my other half. LAN cables needed for us (dodgy wifi) go up to ceiling and under upstairs hallway down to router.

 

I think I remember that the battery should be near the string inverters and panels, ours is directly below the middle of the panels. Further away works but you can lose some power I think.

You can fit to outside of house under opaque canopy, or in an unheated porch (it will warm the porch a little). They should have shutdown safety features, fire risk didn't come up when were seeing installers but they can get hot especially boxed in. Ours briefly got to 31C in October indoors which is fine (we are in a stone house that doesn't overheat). I wouldn't put one in direct sunlight though. And don't put it in the lounge or a bedroom lol because of the bright LEDs and hum. Wide hallway would be fine, under the stairs if not enclosed by a cupboard. Kitchen or utility would be ok but I would raise it a bit off the floor in case of flood from washing machine.

 

You don't have to have batteries but if you do then you will be able to get the bonus export prices during high demand, and it will pay for itself quicker, and in winter yoy can charge batteries from the grid at night for us in peak hours on gloomy days eg 5-7pm when it is dark.

 

Calculations example

43sq m of panels (22 panels), all SE facing, 9.79kwh peak, 13.5kwh storage, West of UK (poorer solar irridiance), no shade, typical usage 13kwh/day.

Installed last month (mid Oct), first electric bill since showed 50% less electricity usage.

 

Our typical electric bill is £120-150/month, in summer we except export amount may cover the £13 standing charge and zero usage. 13kwh/month going up to 15kwh in spring, autumn and winter once we get a ASHP and EV.

 

For us at the moment (mid Nov which is the 3rd worst solar month, we are in the west coast, by hills), today Sun is forecast 18.6kwh, Mon 21.5kwh, Tue 3.8kwh but last 2 days were less (storm and power cuts). Our usage is 13kwh/day (no heat pump yet but an electric immersion heater runs the hot water, induction hobs and electric oven).

Our batteries are 13.5kwh so these few sunny days this week will be self-sufficient and charge our pretty flat batteries enough for an extra day (75 sq m footprint, 9.8kwh system only on the SE roof so not ideal setup. BTW we have A LOT of battery given the number of panels, and the fact we only use 13kwh/day.

 

Exactly 1 month after getting solar PV our electric bill was halved (and that's for October!). We haven't yet got income for exporting and the standing charge came to £15.

 

We are expecting close to 100% electric met by solar in summer because there won't be a heat pump on. It will be a 8kwh heat pump with SCOP approx 4.2 so should run at about 2kwh when it's on, given it is an old house it will need more heating than many. We don't know how not having an immersion heater will reduce the bills. We can decide after a few years on whether we should do the NW roof, since adding to the system is cheaper than the initial install and we won't increase battery capacity. It is a modular system so adding or upgrading the string inverter plus the new panels is all that is needed, but pv panels may have improved efficiency by then.

 

We went for extra batteries to smooth out the times when there are several darker days in a row particularly in spring and autumn.

 

Payback time

In general UK solar PV payback time should be 7-10 years usually (it is better if you have some batteries), occasionally up to 15 years payback but it can be up to 20 years for direct North facing. (This is assuming that you are getting hot water from electrics.)

 

For us having off-grid generation and battery use during power cuts was about 2.5 years extra payback time.

 

Electricity standing charge currently approx £0.50/day (£15/month) but this can be offset by money from exporting.

 

MCS certified installers will do very helpful calculations for you including estimated kwh, price savings and payback time. Some energy companies will give you a much higher export rate if you get them to do the install as well. Export rates (SEG tarrif) can be anywhere from 1p/kwh to 21p/kwh and you need a smart meter (with a working half-hourly signal) for this

 

Power cuts

If you want to generate or use your solar for the ASHP during powercuts you need extras eg a gateway (often there is a single plug EPS that can work from batteries but solar PV generation disconnects for safety during power cuts. We had 3 brief power cuts during the storm Fri/Sat but being November and dark already the battery was empty (we plan to tweak the settings to reverse some battery for the next power cuts, we had 30 last year!)

 

Heat pump size has a big effect here, and that is based on insulation (especially wall insulation vs uninsulated solid walls and windows) - assuming here that loft insulation is topped up as needed for the heat pump BUS grant. So 8kwh heat pump vs 15kwh heat pump dramatically alters what electricity you need from autumn to spring.

 

The gateway for off grid needed to be near our consumer unit, which is actually in the lounge, we have the gateway outside directly through the wall to the consumer unit, it is I think 30-35cm deep, not that big and wall mounted under a canopy (rainfall is heavy here, and we get wind driven rain from that side, it is IP 65 or 66 rated.

 

Panel choice

Vertical panels aren't as good because they don't get as much light as roof panels.

 

Integrated solar (that looks like roof tiles) generates maybe 10-15% less than "on roof" but are far better in strong winds and there is easier cleaning and maintenance with no need for netting to keep birds from nesting up there.

 

I think your roof surface area calc are most likely too high because it depends on the panels and what sizes are available plus manufacturer clearances from the edge and working around any chimney. If you want to work it out, we just had Viridian Clearline Fusion panels and the sizes and specs are online.

 

Wifi
If inverters or batteries are in garage or outdoors then check the wifi signal because although you can do fit it and forget it being able to monitor it and checking when it is at peak so you can run washing machine, dish washer etc will save you from drawing from the grid when out of battery.

If you don't have wifi you need to run LAN cables to your router, and possibly between consumer unit and batteries, and have a system allowing a LAN connection. Our installer was crap with commissioning (I was literally reading him the manual) and tried to convince us to "just try wifi" so we had to insist on LAN.

 

EV charger

Worth getting at the same time if you don't have one yet.

 

Photos 

1. SolXpect forecast graph for week of Nov 16, 9.8kwh system on SE roof in west.

 

2. Electric bill from mid Oct - mid Nov compared to last year shows 50% less usage, it does not including export to grid but unless we want to pay ££££ we can only export 3.6kwh at once (40% of what we could generate).

Edited 8 hours ago by renovator123
summary needed for this dissertation