Electricity Use With Solar Panels

In principle it's a bit of both - I get 40-odd pence per kWh generated (regardless of where it goes) plus a few pence per kWh exported.


But because the value of the export is so low, for most domestic installations it's not worth installing an extra meter to measure it - so the system "deems" export to be 50% of generation. So mostly in practice it amounts to being based all on the total generation readings but at a slightly higher rate (i.e FIT p/kWh + 50% of  export p/kWh). That might change when they get smart meters sorted out properly so they can record both import and export.


   - Andy.

Andy,

So am I correct in thinking that the kWh generated is from a seperate meter measuring the output of the inverter?  And for export, if a deemed figure was NOT used, then there would be another meter looking at the kWH flowing into the external network after any home usage?  Would that be the same as the main supply meter in effect running backwards, so that unused power at home gives a refund?


The person who has asked me is thinking of installing panels on the roof of a building - which has its own supply meter  - where there is normally very little daytime electricity usage, thus most of the time 100% or near would be exported.


Thanks

Clive

Bear in mind that the rules have changed.  If you install solar panels now, then there is no feed in tariff any more; the scheme is closed to new applicants.  You may be able to find an electricity supplier who is willing to pay you something for your exported electricity, provided that you have a smart meter that is capable of measuring export.  Otherwise, you get paid nothing for any excess electricity you export.  It just subsidises the losses in the national grid.


The end result is that it for many people, there is no business case for installing a small number of solar panels any more.  It's only worth it if you can use almost all the electricity you generate.


Older installs were quite different.  There was a generation meter on the output of the inverter, which measures all electricity generated, regardless of whether it is exported or used by the householder.  The owner of the installation was paid a feed in tariff based on that generation.  For anybody who is already signed up, the scheme runs for a fixed period of 20 years, after which the payments stop.

Oh it is a mess.

Rules and rates have changed like the wind in the last 12 years - some people are on very good rates, other far less so.

9p /kwhr was typical pre FIT which kicked off slowly in in 2008.


The rates for small photovoltaic installations started at  43.3p/kWh generated, regardless of exported or local use,  then as demand outstripped the budget these were reduced to 21 pence/kWh. in 2011. However folk with the higher paying  25 year agreement retain the higher level.

On top of this 4-5 p per unit is paid for electricity exported. The 25 year period was then reduced to 20.

At the same time the maximum number of registrations per month was capped, so there has been a backlog of systems installed months previous  waiting to register ever since.

Although it is closed to new systems, anything that has been waiting to be registered and was installed before last May can still try and register for FIT before April.

Then there are other rates for non-domestic systems.


The practical upshot - some folk who put panels in before 2008 have never had a feed in tarrif, just lower bills due to home consumption, others about 9p /unit  some who installed 2008-2010 have already paid back their investment many times,  (or actually in a lot of cases the 'we rent your roof, and in 20 years the clapped out solar panels are free' mob have been paid many times, the householder just gets reduced bills due to using less )


Those put in since 2012 have been doing less well, and if you are considering installing now, you are on your own completely, there is no more govt subsidy to be had, you need to ask and  see if your supplier will pay you for export. Probably that 4p or 5p per unit ?

Perhaps unsurprisingly rate of new installs have dropped, and some of the more lightweight 'free' solar companies that relied on the tarrif to keep them afloat have ceased trading or merged.

As I have suspected for some time, I missed the boat long ago.


Cost of a 4 kW array seems to be about £6000 fitted. However, most generation will be in the summer when you may not be able to use it all. If you buy at 15 p per unit and sell at 5 p, that doesn't work very well.


Material on line suggests a return of perhaps 5% over 20 years, but what is the life of a panel?


New premises yes, old ones no!

Very true Alan. There is also the geographical position to consider. Right in the South of England is probably OK. Going North rapidly decreases the amount of solar radiation, and Latitude gives the Cos of the sun angle as you will be familiar. The irradiation is essentially zero at the poles and 100% on the equator. Here in the UK the cosine rapidly becomes quite small, and those with solar panels in Scotland are quite disappointed! You also need to consider the cloud cover which is considerable in places like Northern Ireland. Probably a better investment is available than panels which are also not maintenance free and this seems to be ignored. Solar is not bad on the equator, but one has then to move!

Well, all 'govt' money is a tax on some other activity of course, just in this case the connection was direct.


As an aside, the amount you may get for exporting surplus production varies over 3 orders of magnitude with different suppliers.

I cannot see Shell Energy keeping many customers with solar panels (scroll to the comparison table)  I detect an element of 'contractual obligation' rather than keenness

Chris Pearson:

Material on line suggests a return of perhaps 5% over 20 years, but what is the life of a panel?

The panels should last a good 20 years, if properly installed, so they don't blow away in a storm.  You should even be able to get ones guaranteed for that long.  25 years is reasonable, with a gradually diminishing output as the UV degrades the panels.


The inverter may not last so long.  Early ones were rubbish - my first one was guaranteed for 5½ years and died after 6.  The new ones should last at least 10 years.  So it's probably worth assuming one inverter replacement during the life of the installation.


If you are looking for a return on investment, you need to consider how you're going to use the electricity.  A "diverter" can send spare electricity to an immersion heater to give you free hot water.  A battery is nice to have, but adds considerably to the cost, and the payback period may be longer than the life of the battery.  But these days, it makes more sense for livestock farms or industrial situations where there is a significant constant load during the day.

---

The government completely bungled the feed in tariff system.  It was supposed to kick-start a sustainable UK solar industry.  But they kept the FIT too high for too long.  The installers made big profits over-pricing the installations, and the customers kept signing up as the FIT was so profitable.


Eventually the government saw how fast the money was running out and made a big cut to the FIT.  Installations dried up until the cost of the panels came down.  But every time solar became cost-effective again, the pot of money allocated for FITs started running out, and the government cut the FIT again.  The end result was a series of booms and busts, and many (most?) installers went out of business.


Now the FIT is zero, so small-scale rooftop installs make little sense to new buyers.  Instead of every house with a suitable roof being covered in solar panels, nobody is bothering any more.

Simon Barker:

Now the FIT is zero, so small-scale rooftop installs make little sense to new buyers.  Instead of every house with a suitable roof being covered in solar panels, nobody is bothering any more.

 

Although to be fair, the cost is also now pretty low as an initial capital cost.


I'm planning a modest new build and using PV with a decent heat pump, thermal store for low temperature UFH and DHWS (with immersion top up) and a vehicle charge point shows some economic value regardless of the FIT payment


I can get a 3kW "in roof system" with a 20 year guarantee on panels and invertor for about £4K fitted (and no need for MCS mark up on certification). By the time I account for the saving in roof covering and cost in for more integrated controls it will pay back well within the guarantee period. Not bothered by battery storage - just a big tank of warm water to do the same job


Not sure it will save the planet - but it does provide a hedge against fuel cost escalation in the next 20 years.


Regards


OMS