Solar Panel Quote

Coastalwatch

frozen_wastes said:

Very interesting to note.  Out of interest what part of the country do you live in, and how much shading are you contending with?
I'm up in Aberdeenshire, so I'm expecting solar insolation over the course of the year to be maybe 20% lower than examples in the south of england.

Same east coast on the Suffolk Essex border so approx 370 miles south.

Using the pvgis calculator, I placed our array at your location which suggests an output of 7335 kWh's annually. Don't know how your aspect and pitch/slope compares to ours. We have some minor shading in the earlier part of the day due to a neighbours silver birch.

Interested to read the figures you've uncovered on inverter efficiencies, which Mart advised us of when researching our installation.

Prior to this the max SE inverter for single phase was 6k, although larger capacities were available for three phase. Wasn't previously aware of your supply so didn't feel worth mentioning.

I suspect your installer may split the panel array into two strings each with it's own inverter of say 3.5 or 4 kWh! As suggested previously you should be offered the opportunity of increasing the warranty period to match that of the panels for a moderate sum. We were quoted £150/ inverter.

Exiled_Tyke

A few further thoughts: 

1. The elephant in the room is of course the price difference - a couple of hundred quid? Which even at higher outputs with slightly better effeciency is probably not worth paying.
2. Maximising efficiency at the dullest time of year should be a priority for almost all of us. In the best months we don't need the extra fraction of a percentage improvement because we won't be using all of the electricity (and the difference in the export value will hardly be noticed). But in winter even a system of this size is unlikely to meet all your needs. So I'd rather have those few hours of producing 200W over nothing please (rather than having the extra in summer)
3. I can't see the point of using two inverters. From what I can see two 3.5kW  inverters works out a lot more expensive than on 8kW.  

frozen_wastes

So, latest situation:
Local council has confirmed that neither planning permission or building warrants are required for an in-roof system.  So I've asked my installer to adjust the quote a little (hot water controller) and start the G99 application process.  In other words I'm going ahead with the quote, subject to G99 approval.

Here's the bad part about G99, installer reckons it could be upto 6 six weeks to get a reply from the DNO.  I'm hoping it'll be faster though.  There are various application forms for differing installations.  For single phase installations less than 17kw, using Type Approved equipment,  it's a simple form (Form A1-1).  So, we're looking at October potentially before installation can proceed.
https://www.energynetworks.org/electricity/engineering/distributed-generation/engineering-recommendation-g99.html

I asked the installer about the 10kW inverter.  His response was that that was what the solaredge design software recommended.  He said the difference between the 8kw and 10kw price was so small, that you may as well get the larger 10kW inverter.

I've done some further calculations, plugging in info from the quote, as well as my electricity bill.  I've examined six scenarios:
- Worst Case (all generated electricty exported), results in a 17 year payback, assuming 6% energy price inflation for both import and export prices
- Existing case results in 15 year payback
- Optimisation of existing case (time shifting heavy consumers) results in 14 year payback
- Solar hot water results in very little improvement (saving in propane is offset by loss of export income).  This was very illuminating.
- Adding an electric car results in an 11 year payback (this considers savings going from grid  --> solar electric, not diesel --> grid electric)
- Adding a suitable sized battery, that results in a 90% reduction in grid consumption will reduce payback by 2 years, but you need to have a suitably large battery (at least 7kWH) costing less than £2000 fully installed.  Such a battery does not exist --- yet!

The big assumption with all these figures is the rate of inflation.  I've taken 6% from my quote, but truth of the matter is that it's been rather volatile when you look at historical prices.  I don't have energy bills from 10 years ago to check.  But if the rate of inflation is low, then payback will certainly take longer.  But with the figures given, for a solar panel enthusiast, I think the economic case for solar panels is favourable, and that's without subsidies.  However for an uninterested member of the public, it's a harder sell for our climate right now.

The other assumption is generation.  The quote is very conservative compared to other generators in my village (figures suggest 0.86MWH/kWp).  So I could well be generating more than the figures below, which in turn favours a smaller payback time.

ASavvyBuyer

frozen_wastes said:

 assuming 6% energy price inflation for both import and export prices

Using 6% inflation (compounded?) for your assessment appears to be on the high side compared with the actual trend for prices to stay within normal inflation rates of about 2%/year.

Also, if you switch to a time of use tariff, like Octopus Agile, or even Octopus Go, we have found that the average rate for all imported electric is less than 8p/kWh. In fact since being on Agile, our average rate has been about 6p/kWh.

Exiled_Tyke

ASavvyBuyer said:

frozen_wastes said:

 assuming 6% energy price inflation for both import and export prices

Using 6% inflation (compounded?) for your assessment appears to be on the high side compared with the actual trend for prices to stay within normal inflation rates of about 2%/year.

Also, if you switch to a time of use tariff, like Octopus Agile, or even Octopus Go, we have found that the average rate for all imported electric is less than 8p/kWh. In fact since being on Agile, our average rate has been about 6p/kWh.

If as ASavvyBuyer says, energy inflation is roughly in line with general price inflation then you can pretty much ignore it.   As any accountant will tell you, payback is not a valid way to calculate the benefit of an investment, although these figures show that there is no chance of a real return on investment 
I think the only way to get a solar scheme to pay these days is to pay in the region of £1k per kW of production capacity and definitely not to have a battery.   That said there are plenty of us on here who have made solar investment decision knowing that the numbers don't stack up, but that's not the only reason for going down this route. 

Don't you really need a battery or be able to completely stay away from peak time (early evening) consumption to benefit from Octopus Agile?

Martyn1981

I would 'third' the argument about real inflation rates and ignoring them from the calculations.
I recall us using a figure of 12p-13p for leccy costs 10yrs ago on here, and now we use ~15p. So let's say 3p rise on 12p, or 25% which is just over 2% compounded.
I think that can be written off against panel degradation and the cost of capital (lost interest on the monies spent), making the overall calculation a tad easier by removing three variables.

Edit - I don't think its cheating to simplify the calculation (given the long warranty on the inverter) down to cost divided by annual income (savings + export earning) = years for return.
[Note, this isn't because I think we should typically ignore all the other factors, it's just that with PV they are almost negligible, or, as above, can be cancelled out against each other.]

ASavvyBuyer

Exiled_Tyke said:

Don't you really need a battery or be able to completely stay away from peak time (early evening) consumption to benefit from Octopus Agile?

As we are retired, we don't have any problem with avoiding the 4pm-7pm peak electricity prices on Agile.

Also, our Solar panels are West facing, so quite often they are generating during that peak time, easily covering base load (and more).

If Agile rates increase too much during the winter, we shall just switch back to GO.

This new guide to Octopus Tariffs has some useful info

stone248

Type your comFirst post so go easy...….hopefully having solar installed and going for a 6.8kw system with tesla powerwall. We have an old house which requires a complete overahaul from an old single pipe gas central heating new boiler etc etc cost £7000. we were just wondering if anyone has installed the above system and gone completely gas free (apart from cooking, im not losing the gas for that) so the house will be heated and run via the solar PV system and the grid.  Also any other comments that might be relevant are always welcomedment

frozen_wastes

My story so far.  I accepted my quote from the electrician around the 25th August.  At this point the G99 application was sent off to the DNO for an 8.9kW solar array coupled to a 10kW inverter.

Fast forward to the end of last week (2nd October).  The feedback from the DNO was that it would cost £7k + VAT to reinforce the supply to my house for the spec provided.  I didn't get the details as to what was involved in that cost, but I understand that the transformer tappings need to be upgraded rather than the cable to my house.

So after some discussions between the electrician and the DNO, they provisionally suggested that the spec should be changed to an 8kw inverter, with a 5kW export limit in order to avoid costs associated with reinforcing the supply to my house.  I've accepted that suggestion, so a revised G99 application has been submitted to the DNO by the electrician. 

I'm happy with an 8kW inverter.  I've got plans to make sure as little electricity is curtailed as possible, utilising the hot water immersion heater as well as other heavy consumers during the peak spring/summer days.  So I'm happy that the 5kw export limit isn't going to be too limiting.

DNO has indicated that we shouldn't have to wait another 5 weeks for a decision, the revised application is tagged onto the original application.

frozen_wastes

The story so far:
In summary, nearly installed.  Final install + Commissioning tomorrow!  Getting Excited.
Long Story:
DNO Confirmed that an 8KW inverter with 5KW export limit is permitted to be connected to the grid for no extra charge!  They confirmed this end of October.  So I went ahead and paid my deposit.  By the beginning of November I had all the equipment delivered to my driveway.  
Last Thursday the crew started work on the roof installation, and by Friday evening they were all done with the roof work.
Next job is wiring, inverter installation and ancillary equipment.  Follow finally by commissioning and energisation.
I made a youtube video about my analysis and choice of solar panels, as well as a background introduction to all the other previous energy saving measures applied to my house.  This goes into some economic analysis, pre-installation process, installation work and a brief tour outside of the panels.
https://www.youtube.com/watch?v=lCko6ipmX6g