Wind Power vs. Solar

Reed_Richards

Mickey666 said:

Assuming a grid cost of 15p/kWh that 430Whr is worth about 6.5p x24 x365 makes about £565 per year.

Since I just squeezed into FIT payments it has been worth £242.45 per year plus the value of whatever PV electricity I can actually use.  The first FIT payment worked out at 6.48p per kWh generated, my last payment was 6.62p per generated kWh.

If I could actually use all the electricity I generate than your calculated £565 would come on top of that.  But I can't for two reasons:

1. The rate at which I can charge my battery is limited to something like 2.6 kW compared to a maximum output from the panels of 4.8 kW.
2. On a sunny day from mid March to mid September I can fully charge my battery and heat my hot water tank to around 70 C by early afternoon and then I run out of things to do with the solar electricity.     

Martyn1981

Reed_Richards said:

1. On a sunny day from mid March to mid September I can fully charge my battery and heat my hot water tank to around 70 C by early afternoon and then I run out of things to do with the solar electricity.     

Just a thought, but do you have a BEV, or are thinking about getting one, because if you can charge at home during the day, then depending on mileage, you may be able to drive on sunshine for all of that period. Average UK mileage is about 22 miles per day (7,900pa), so if you are around that, then that might be a perfect way to increase your own consumption by 1,000-1,500kWh pa.

I'm almost managing to do this, but without a battery, then on days when the sun is averaging about 2.5kW, but fluctuating, I will be drawing some grid leccy, whereas your battery buffer would guarantee you 100% solar, so long as you charge on the sunny days.
I'm not convinced by the economics of domestic batteries, but the idea/principle of better managing leccy demand, now that we have a BEV, is getting much more compelling.

Reed_Richards

I bought a "self-charging hybrid" in 2013, although they just called it a "hybrid" in those days.  I'm in no hurry to replace this but my next car will most likely be a BEV.  But I would have to give some consideration to what I would do in winter when I would want to both run my ASHP and charge my BEV without exceeding the 80 Amp capacity of my mains supply.

Reed_Richards

Looking at other people's quotes I can see that it cost me a lot more 26 months ago than an equivalent set-up would do now, even without the benefit of the now-abolished FIT.  This is the projection that came with the sales literature, based on electricity at 16p per unit going up by 5% each year.  This is for 16x 295 W panels and a battery with a 6.5 kWh capacity.   

Martyn1981

Reed_Richards said:

I bought a "self-charging hybrid" in 2013, although they just called it a "hybrid" in those days.  I'm in no hurry to replace this but my next car will most likely be a BEV.  But I would have to give some consideration to what I would do in winter when I would want to both run my ASHP and charge my BEV without exceeding the 80 Amp capacity of my mains supply.

Even a fast charger is only 7kW, so about 30A's, though of course you could use a granny charger 3x more often, and only draw around 10A's. That would leave more than enough for the ASHP if it's having to run hard, assuming you have something around 12-16kW, so drawing around 5kW's/20A's?

We've got two small HP's of 3.5kW's each, so they can draw about 1.5kW's if neither has warmed a room yet. And you could also ask the DNO to upgrade your supply to 100A, especially if the 'fuse' isn't too old, as there would be a good chance that it's 100A capable, but they tend to not like giving 100A unless really needed. Ours was changed just over a year ago from 60A, on the request of the V2G trial we were to do, but couldn't in the end. They fitted a 100A housing, but explained that only an 80A 'fuse' could be justified. But yes, lots to consider.

ABrass

Reed_Richards said:

I bought a "self-charging hybrid" in 2013, although they just called it a "hybrid" in those days.  I'm in no hurry to replace this but my next car will most likely be a BEV.  But I would have to give some consideration to what I would do in winter when I would want to both run my ASHP and charge my BEV without exceeding the 80 Amp capacity of my mains supply.

I think you should be able to upgrade to 100A without too much cost if needed. If I remember right the fuse is something UKPN are responsible for, but the rest of the system is your responsibility (i.e. meter tails and consumer unit). I got lucky and when I got my smart meter installed I asked nicely and they upgraded my tails to 25mm for free, which meant it was a zero cost activity for me.

Going from the older 30/60 A systems (as I did) to 80/100 is pretty commonplace, going from 80>100 seems to be less common but once you explain your setup (when you go BEV) I'd expect they'd agree.

QrizB

Reed_Richards said:

This is the projection that came with the sales literature, based on electricity at 16p per unit going up by 5% each year.  This is for 16x 295 W panels and a battery with a 6.5 kWh capacity.  

I know very little about your situation so what follows is inevitably a guess.

You have a nominal 4.72kWp system but are (probably) limited by a 3.68kW inverter. You've previously said your annual generation averages 430 watts, ie around 3800kWh per year, and I'll assume you're on deemed export not metered. Your FIT rate is something like 3.9p per kW generated plus 5.5p for the half you export. Your FIT will earn (3800x3.9p+1900x5.5p) £253 per year (not far off the number you quoted above). That's the red bar at the bottom of the chart.

You will use some of the power you generate. Unfortunately most people use most in winter and generate most in summer, but (ignoring batteries for the moment) let's say you use a third of the power you generate, 1267 kWh per year. At 16p/kWh that's a saving of £203 per year, the yellow bar in the middle of the chart.

Your DC-coupled battery will let you use some of the surplus power you generate in the daytime, in the evening. It may also allow you to smooth out your daytime peaks and troughs. In order to do this you need to have some surplus power in the first place, so let's say that you make use of 6kWh of capacity (as generous "battery full") for 200 days of the year. That's an extra 1200kWh that you can use, rather than export, and at 16p per kWh that's an additional saving of £182, the orange bar at the top of the chart.

I'm going to ignore inflation in the next paragraphs, because I'm not a solar panel salesman. Your FIT payments rise with inflation and the price of energy is one of the factors used when calculating inflation.

A 4.72kWp system without batteries will cost around £5000 installed (give or take a bit). Without batteries you would be earning £253 a year and saving £203 a year, a total annual benefit of £456, and the system would pay for itself in 11 years.

A 6.5kW battery would add about £3000 to the system. It provides a benefit of £182 per year and pays for itself in 16.5 years. (This assumes it lasts that long, which is a bit of an unknown.)

Reed_Richards

QrizB said:

I know very little about your situation so what follows is inevitably a guess.

You have a nominal 4.72kWp system but are (probably) limited by a 3.68kW inverter. 

No, the inverter is not limited (the export is limited in software).  And (although it's a trivial difference) I actually ended up with 300 W panels, not the 295 W panels quoted.

QrizB said;
I'll assume you're on deemed export not metered. Your FIT rate is something like 3.9p per kW generated plus 5.5p for the half you export. Your FIT will earn (3800x3.9p+1900x5.5p) £253 per year (not far off the number you quoted above). That's the red bar at the bottom of the chart.

My FIT rate (which is indeed based on deemed export) is currently 6.62p per generated kWh (that's 3.87 + 5.5/2).  I did not read the generation meter after exactly two years so the figure of a 430 W average is a bit approximate.

Sadly I paid about 20% more for both panels and battery than the prices you suggest.  Prices fell as soon as the FIT was discontinued.  I rushed to get in before that happened and only had time to get two quotes; the other installer seemed way too optimistic about energy savings for me to trust them.


 

Reed_Richards

I just "upgraded" my mains fuse from 60 A to 80 A except when the the cover labelled 60 A was removed it turned out I already had an 80 A fuse!  80 A was the most they would give me without charge.

QrizB

Reed_Richards said:

[T]he inverter is not limited (the export is limited in software).  And (although it's a trivial difference) I actually ended up with 300 W panels, not the 295 W panels quoted.

My FIT rate (which is indeed based on deemed export) is currently 6.62p per generated kWh (that's 3.87 + 5.5/2).  I did not read the generation meter after exactly two years so the figure of a 430 W average is a bit approximate.
Sadly I paid about 20% more for both panels and battery than the prices you suggest.  Prices fell as soon as the FIT was discontinued.  I rushed to get in before that happened and only had time to get two quotes; the other installer seemed way too optimistic about energy savings for me to trust them.

The software-limited inverter and marginally larger panels both work in your favour. My inverter is old(er) and dumb(er), so my export will always be reduced by my self-consumption to be less than the DNO-notified value. In your case self-consumption is additional to the export limit (and your DC-coupled batteries are helpful here too). Alas these bonuses are already factored into the calculations.

Paying 20% more to get the FIT benefit will pay off in time, the FIT is almost 40% of your payback.