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 Wednesday at 18:03 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 Wednesday at 22:31 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 Wednesday at 22:42 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.