How much does DNO approval cost / is it worth it for my system

Oh_No

Been quoted 8.5k for 

6.4kW of panels over a couple of roof elevations
solaredge 3.68kW inverter 
solar immersion heater thingy
bird barrier

Now I know that the panels are overspecced but believe this is due to two things, they are on different facing roofs and will degrade over time . But I was wondering if its worth upgrading the inverter and going for DNO approval (G99).

Anyone know what it costs to go for G99 compared to G98? Is it worth it

Was going to give battery a miss as its a lot of extra money up front and I am not convinced they pay for themselves

ABrass

That's a silly level of overprovision. Degradation is negligible. In 30 years you'll still be producing 5.2kW at maximum performance. Or 157% of what your inverter can manage.

I'm not convinced by the solar immersion heaters, they've always seemed to have pretty awful payback periods.

G99 costs vary by DNO, I think mine does them for free, but there's effort in doing the paperwork. Apparently they're typically 300-500.

Martyn1981

I think you need to go for a bigger export limit.

Our 5.58kW system is across two roofs with a 180d difference, but still can hold 4.2kW in ideal conditions, and peak and hold close to 5kW for short periods (minute or less). It wouldn't be the end of the World if ours operated across a 3.68kW cap, but still a bit wasteful.

So, using that as a baseline, I think 6.4kWp would be far too capped at 3.68kW.

BTW, after 11yrs, I can't detect any noticeable degradation in annual generation, despite originally expecting about 1%pa. Weather differences make direct comparisons YoY tricky, but I suspect any loss we do have, must be less than 5%, perhaps 2 or 3 percent at most.

ed110220

Degradation is the least important reason to have as much wattage of panels as possible, as degradation is very slow and most info indicates it is considerably slower than the maximum allowed under the panel's guarantee.

 Much more important is that the more wattage you have, the more you'll be able to cover your consumption on overcast days and especially in the darker part of the year. 

For example with 4.8 kWp, I'm generating two or three times more than I use (~10 kWh) on sunny or partially sunny days in summer, but only barely covering consumption or even dropping slightly below on the most overcast days. 

In December I'm only expecting to generate about 3.5 kWh per day on average, less on very overcast days, so little more than a third of my consumption. 

If I had more panels I could cover more of my winter consumption, but unfortunately I don't have any more suitable roof!

So ideally you want to squeeze as much panel wattage in as possible I think, especially as our electricity demand is probably going to increase as we switch from using gas to heat pumps for heating. Though there doesn't seem to be an easy rule for working out exactly how much is economically ideal. Ie going so large as to cover the most overcast days in late December is probably not economic, but most people would run into space limitations well before then anyway.

ispookie666

Probably around 250. It's a bit of faff. The G98 is only export limitation. These are the options 
1. G99 
2. Reduce the array size to 4KWpwith a view to add additional panels and battery at a later stage along with DNO approval. 
3. Get a bigger size inverter and limit to 3.68KWp export. 

Spies

I think the 2nd option that @ispookie666 suggests will be best.

ccbrowning

Is there a range? I spoke to an installer who told me to speak to the DNO first and it could be up to £9k, to go over 3.68kW. I have an existing 3.4kW system and want to expand and add a battery.

Can you just get an inverter that limits export?
https://www.enwl.co.uk/get-connected/apply-for-a-new-connection/generation-and-storage/micro-generation-and-storage-connections/

Integrated micro-generation and storage

Working in partnership with the ENA, a relaxation was written into G99. This relaxation has primarily been developed where a customer is wishing to combine a G83/G98 generator with an Energy Storage Device.

To qualify, the following conditions must be met:

• Total generation capacity installed should not exceed 7.36KW (including battery storage)

• All generators should be connected via a Type approved G83/G98 protection device

• The maximum export should be limited to 3.68KW per phase utilising a Type approved EREC G100 device

• The system should not generate during a power-cut (island mode) 

Hexane

I would definitely seek DNO approval. They might agree with a small fee, they might agree without a fee, they might flat out say no, they might quote you a fee of thousands for approval. My DNO initially asked for a £1500 fee, then later agreed to our proposal without a fee.

It really doesn't seem worth limiting your generation (or even your export) by so much, if there's a way round it.

ccbrowning

Hexane said:

I would definitely seek DNO approval. They might agree with a small fee, they might agree without a fee, they might flat out say no, they might quote you a fee of thousands for approval. My DNO initially asked for a £1500 fee, then later agreed to our proposal without a fee.

It really doesn't seem worth limiting your generation (or even your export) by so much, if there's a way round it.

I see - well that is one installer who is out of the picture, since they wanted me to find out first? One out of Yorkshire.

ABrass

ccbrowning said:

Is there a range? I spoke to an installer who told me to speak to the DNO first and it could be up to £9k, to go over 3.68kW. I have an existing 3.4kW system and want to expand and add a battery.

Can you just get an inverter that limits export?
https://www.enwl.co.uk/get-connected/apply-for-a-new-connection/generation-and-storage/micro-generation-and-storage-connections/

Integrated micro-generation and storage

Working in partnership with the ENA, a relaxation was written into G99. This relaxation has primarily been developed where a customer is wishing to combine a G83/G98 generator with an Energy Storage Device.

To qualify, the following conditions must be met:

• Total generation capacity installed should not exceed 7.36KW (including battery storage)

• All generators should be connected via a Type approved G83/G98 protection device

• The maximum export should be limited to 3.68KW per phase utilising a Type approved EREC G100 device

• The system should not generate during a power-cut (island mode) 

The only reason it might cost £9k is if you need to install 3 phase power. And that seems like an expensive quote for that.

Many modern inverters can cap export, it's a common feature now.

ispookie666

@ccbrowning Export limitation becomes a G100, your DNO can play hard ball and would want to do a site visit to check if the export limit is met.  For a few inverters, export limitation is just a software mod/profile.  
The cost for DNo approval would depend on a lot of things - your total house current input, high ampere devices, local grid capacity, age of the supply lines etc. 
You could always call the DNO and check.  I did contact my DNO a few years ago for a Inverter battery install(DIY self install). They were very accomodating and mentioned to get inverter which were already certified/tested so that site visit was not needed.