Should I fit solar panels

[Ballynoes]

I believe there is an option to charge batteries, and through an inverter reuse the power that way.

 

Has anyone come across this option, and is it viable for domestic use.

[Big Neil]

@Ballynoes - on the cost question - do you know the roof covering  you're having? I can't think of a reason why for example you couldn't tell your main contractor what to get, where to get it from and then have him factor the installation into the job as a whole. You could have the best of both worlds then, i.e. panels and mounting kits you have paid for yourself, fitted by a competent installer. I reckon we can get that 6 grand down for you by tons. First pass just clicking on the midsummer system builder is £2959.96 on materials alone....

 

There must be an installer here - i know there is just can't remember who - who could put a fag packet to the connection cost?

[Jeremy Harris]

Several here are looking at installing battery storage, but the economic justification is pretty slim, unless you're able to to both generate and self-consume a fair bit of energy.  The lower your overall electricity usage the harder it is to make the economic case stack up.  For example, I looked initially at fitting a Tesla PowerWall 2, but worked out that the repayment on capital was likely to take longer than the usable lifetime of the batteries.  There are other, more cost effective options, though, but it's still pretty tight in terms of whether or not a system would recover the capital investment within its lifetime.  I'm going to be fitting a battery system before long, as I think I can just about get it to almost cover the initial cost, but part of my motivation is because we have fairly regular power cuts and being able to use the (separate) uninterruptible supply from the battery system during a power cut seems a very useful capability to have.

[Ballynoes]

Hi

13 minutes ago, Big Neil said:

@Ballynoes - on the cost question - do you know the roof covering  you're having? I can't think of a reason why for example you couldn't tell your main contractor what to get, where to get it from and then have him factor the installation into the job as a whole. You could have the best of both worlds then, i.e. panels and mounting kits you have paid for yourself, fitted by a competent installer. I reckon we can get that 6 grand down for you by tons. First pass just clicking on the midsummer system builder is £2959.96 on materials alone....

 

There must be an installer here - i know there is just can't remember who - who could put a fag packet to the connection cost?

 

This is possibly a good solution, as I intend to purchase items like the kitchen and bathrooms of our choice and get the contractor to fit them.

 

So asking them to fit a solar system will not be that much more different, esp if it is specified in the contract terms.

 

Hadn't thought of that way.

 

I would imagine I will be "forced" by planning to install slates of some description as all the other properties around have slate roofs, probably Spanish slates.

 

Thanks.

[Alex C]

I have a 5.5kw system and even though I work from home and put on appliances during the day I would say there is no way we consume as much as 50% even with the excess dumped into the hot water. on recent clear days we have been generating 20kwh and during the summer that is well over 30kwh. I think the turning point for me will be either cheap batteries or an electric car. As I am at home most of the day a car could charge for free for at least 7 months of the year. When doing your sums just make sure you are realistic on what you will actually be able to consume from whats generated.

[Big Neil]

Just a cursory look of spanish roof slates at £1.09 inc VAT says approximately 20 per square meter just for the slates so allow maybe what, 10% for margin including wasteage X 24m2 makes £575.52 in slate alone. So take that off the figure above, and you're down to about £2500. That by itself is only 16 years, and the cleverer members of the forum here will i'm sure figure out ways to justify around some of the rest

[Ed Davies]

A big part of the cost of a retrofit install is the scaffolding. For a new build the scaffolding is there anyway…

[Lorraine Griffiths]

6 hours ago, Alex C said:

I have a 5.5kw system and even though I work from home and put on appliances during the day I would say there is no way we consume as much as 50% even with the excess dumped into the hot water. on recent clear days we have been generating 20kwh and during the summer that is well over 30kwh. I think the turning point for me will be either cheap batteries or an electric car. As I am at home most of the day a car could charge for free for at least 7 months of the year. When doing your sums just make sure you are realistic on what you will actually be able to consume from whats generated.

 

Silly question time......

 

So, if you've installed a 5.5kw system & you're only consuming approximately 50% does this mean that you've effectively installed too large a system? So, if you'd installed say a 3.5kw system (if there is such a thing) would it have been sufficient or am I looking at this too simplistically?

 

Also, is there a website of some kind that allows you to work out how much electricity you would potentially be using? It's no good basing it on our current usage as we live in the most electricity unfriendly house on the planet!

 

I'm finding all the responses really interesting so thanks for everyone's help  

[ProDave]

The trouble with solar PV is the amount it generates is dependant on how much the sin shines, and that varies from day to day and season to season.

 

A system that produces "just enough" on a bright sunny day, will produce a lot less on a dull day.  So you might want to just install as much as you have room for or can afford, so on the dull days it can produce a useful amount.

 

Any surplus between what is generated and what is used, gets exported to the grid.  That is not bad if you are getting paid for it, but feels "wrong" if you are not.

 

The normal thing to soak up excess generation is a device to send excess power to an immersion heater. you can buy them ready made or do as I have just done, and build your own for a fraction of the cost.

[Jeremy Harris]

1 hour ago, ProDave said:

The trouble with solar PV is the amount it generates is dependant on how much the sin shines, and that varies from day to day and season to season.

 

 

We must have been dreadful sinners during February, as we seem to have generated loads more than we did this time last year.  Not sure if it's me or SWMBO that's the sinner though; I shall make some enquiries...

[Triassic]

Are prices for kit falling, what with the end of the feed in tariff?

 

My local supplier has stopped stocking PV kit as he says the future is too uncertain.

 

Just looked at a Wagner quote for 4kw all black panel system to fit in a slate roof, sent to me in October, their price was £4633.

 

 

Edited March 6, 2019 by Triassic

[BMcN]

16 hours ago, Big Neil said:

Just a cursory look of spanish roof slates at £1.09 inc VAT says approximately 20 per square meter just for the slates so allow maybe what, 10% for margin including wasteage X 24m2 makes £575.52 in slate alone. So take that off the figure above, and you're down to about £2500. That by itself is only 16 years, and the cleverer members of the forum here will i'm sure figure out ways to justify around some of the rest

I just fitted 12x 300w panels  using gse mounts. 

 

For the panels, mounts and all the other bits and bobs needed, cost 2.5k Inc vat and delivery. 

 

The mounts saved approx 26m2 slates.  Think it was 28 slates p/m at 0.75ea.  So approx £550 slates. So I'm looking at around £1500-1600 all in once we get the vat back. 

 

I have not included labour as we did the panels ourselves with the help of the roofer, so I think this would have been similar to the cost of him slating it. 

[Alex C]

12 hours ago, Lorraine Griffiths said:

 

Silly question time......

 

So, if you've installed a 5.5kw system & you're only consuming approximately 50% does this mean that you've effectively installed too large a system? So, if you'd installed say a 3.5kw system (if there is such a thing) would it have been sufficient or am I looking at this too simplistically?

 

Also, is there a website of some kind that allows you to work out how much electricity you would potentially be using? It's no good basing it on our current usage as we live in the most electricity unfriendly house on the planet!

 

I'm finding all the responses really interesting so thanks for everyone's help  

Its not a silly question. The answer is yes maybe. I installed 5.5 kw mainly as I was doing some game playing to score 100 for my SAP so I could use a particular lender. The extra cost of the pv was more than offset by the cheaper fee and lack of broker fee by going with my lender. I decided I would much rather spend the cash on something tangiable like pv than on someones fee. Also 5.5 kw fits well on my roof and 4kw would have proportionally looked a bit odd. For most days 4kw would have been more than enough for my needs, but as has been mentioned on a more cloudy day I still produce more with 5.5kw than I would with 4kw. If I could plug in an electric car it would be a complete game changer in terms of using what I produce, and I think for a lot of people that isnt too far away.

[Jeremy Harris]

11 minutes ago, Alex C said:

 If I could plug in an electric car it would be a complete game changer in terms of using what I produce, and I think for a lot of people that isnt too far away.

 

My car has now charged up from excess PV generation twice in the past couple of weeks.  I suspect that over the course of a year more than 50% of my car energy requirement will be at no cost.  It definitely increases the "smug factor" when you're driving around for zero fuel cost.

[Oz07]

22 hours ago, Big Neil said:

 

 

I'm sure you had considered this anyway, but as it's a new build you could justifiably offset the panel cost against the roofing material cost, as others have suggested elsewhere in the past I believe. NOw I don't know what your roofing material is planned to be, but there's a cost to be offset either way. 4kwp is something like 15 panels i would think depending on the maximum power, and panels are often around the 1X1.6m size so circa 22.5m2 roof plus flashings etc.

 

I don't know what rate your roofer will lay whatever the rest of the covering is, but I don't imagine it's as fast as a competent installer doing the PV panels, so there's a justifiable cost saving there as well.

 

You think that your going to get 22m2 of panels fitted cheaper than the equivalent amount of roofing. With all the fiddly flashing?!

[Triassic]

Burlington blue/grey best grade slates @ £1,335/tonne, coverage 18.4m²/tonne.

[epsilonGreedy]

40 minutes ago, Triassic said:

Burlington blue/grey best grade slates @ £1,335/tonne, coverage 18.4m²/tonne.

 

 

= £72 per m2.

 

This link (2015) suggests a much lower £27 m2 for Spanish slate.

https://www.homebuilding.co.uk/how-much-does-it-cost-to-tile-a-roof/

 

When I looked at in-roof PV mounting panels they came out at nearly £30 m2 plus the per meter squared cost of the actual PV.

 

I wish it was true that in-roof PV mounting would be subsidized by the saving of an expensive roof cover but I am not seeing it in the figures.

[Big Neil]

2 hours ago, Oz07 said:

You think that your going to get 22m2 of panels fitted cheaper than the equivalent amount of roofing. With all the fiddly flashing?!

 

Not quite what I meant. I'm just talking about offsetting costs there. Raw materials seem to be something like 5 X more I'm that particular example 

[BMcN]

4 hours ago, Big Neil said:

 

Not quite what I meant. I'm just talking about offsetting costs there. Raw materials seem to be something like 5 X more I'm that particular example 

Using my above example, by not buying slates it reduced the cost of the PV install by approx 25%.

[Big Neil]

ahh- i was close - jiggling around on the bus.

 

I think there's a reasonable case to be made IF:

 

You put tons of it on your roof

Have battery backup

consider it as like a standard roof covering like tiles (so replace one if it gets broken)

Have an electric car

ride an electric bike

don't have gas fitted yto your house at al

Divert to a hot water cylinder etc etc

 

PLus if the house is one you ight consider selling, it could have that halo effect. Bare oak stairs don't change the functionm they just add to the actual and perceived quality i think. There was a maybach covered in Swarovski crystals some years pack. Totally pointless but certainly helped the value even if there wasn't a practical benefit.

[jfb]

Quick question for the unenlightened - I'm sure I have seen stuff about it before but can't remember where - what is the maximum size of install in KW allowed before it becomes difficult to DIY (is there a threshold at which it needs greater cooperation with electric companies)?

[ProDave]

10 minutes ago, jfb said:

Quick question for the unenlightened - I'm sure I have seen stuff about it before but can't remember where - what is the maximum size of install in KW allowed before it becomes difficult to DIY (is there a threshold at which it needs greater cooperation with electric companies)?

Above 3.68Kw you need prior permission from the DNO BEFORE you connect it. they may or may not give permission and they may or may not make a charge if they have to upgrade the network to accommodate the size of the generation.

 

I don't think from the DNO's point of view there is any difference who fits it.

[Jeremy Harris]

4 minutes ago, jfb said:

Quick question for the unenlightened - I'm sure I have seen stuff about it before but can't remember where - what is the maximum size of install in KW allowed before it becomes difficult to DIY (is there a threshold at which it needs greater cooperation with electric companies)?

 

You can DIY any practical domestic scale installation, but if planning to export more than 16 A per phase to the grid then you need approval from the DNO, who will set an export limit.  In our case I wasn't sure what size array would be allowed, so just asked the DNO for the maximum they would allow and they set the limit at 12 kWp.  Our system is only 6.25 kWp, so I can increase the size at any time, up to the 12 kWp limit.

 

In terms of hardware, then there's no real difference, as the price pretty much scales with the power generation capacity.  As far as installing the system goes, then it's the same for either a < 16 A per phase as it is for a >16 A per phase system.  In England and Wales that means that the electrical installation and testing must be undertaken by a Part P accredited competent person and the installation certificate must be lodged on the database by them.  If you don't intend to claim any payments, and are under the 16 A per phase limit, then the only other thing to do is notify the DNO after completing the installation.  If the system is over 16 A per phase then that notification would have been done before you do the install, as part of the process of getting DNO consent.

 

In Scotland (not sure about NI) then any competent person can do the electrical installation and testing, and the EIC only needs to be given to the house folder, it doesn't have to be notified to building control or put on a database.

[ProDave]

37 minutes ago, Big Neil said:

PLus if the house is one you ight consider selling, it could have that halo effect. Bare oak stairs don't change the functionm they just add to the actual and perceived quality i think. There was a maybach covered in Swarovski crystals some years pack. Totally pointless but certainly helped the value even if there wasn't a practical benefit.

I am not convinced solar PV actually makes a house more attractive to the average buyer.  In fact I know of one sale where the buyer (against my advice) pulled out of the purchase because of the solar PV.

 

When we were trying to sell the old house those viewing were completely disinterested in the fact it had solar PV and was paying the FIT for another 20 years.  So no hope of a buyer being at all interested if there is not even the FIT to entice them with.  But then again the average buyer is not the least bit interested in the EPC rating and the annual fuel bills.

[Ed Davies]

2 hours ago, ProDave said:

Above 3.68Kw you need prior permission from the DNO BEFORE you connect it.

 

2 hours ago, JSHarris said:

but if planning to export more than 16 A per phase to the grid then you need approval from the DNO,

 

The legal limit is 16 amps per phase which works out as 3.68 kW at 230 volts. In practice, DNOs accept the power limit even though it'll technically be putting in a bit more than 16 amps when the mains voltage is below 230 volts. However, that's the output to the DNO's network; there's no legal limit on the size of the PV itself [¹] so it would be quite reasonable to have a few more panels, say 4 or 5 kW's worth, as most of the time they'll be generating less than 100% of their nameplate power. When they are generating more than 3.68 kW the inverter will just not draw that power from them and it'll be dissipated as heat on the roof (in just the same way that waste heat is dissipated when the sun shines on any dark-coloured thing).

 

It's also possible to generate more power out of the inverter then use a divertor to limit the power or current fed into the network. The rules vary between DNOs on this; AIUI only a few will allow this and only with specific approved diverters but my information on this is possibly a bit out of date.

 

Once upon a time the FiT scheme had a separate break-point at 4 kW where the payment dropped down. That was determined by the panels, not the inverter. That big difference has long gone from the FiT scheme and the FiT scheme itself will be gone before anybody just contemplating it now could get in so that limit is now very moot.

 

[¹] Permitted development rules are typically phrased as being for “microgeneration” but that's defined as up to 50 kW so not likely to be a consideration for domestic PV.