Solar PV quote Good or bad?

[SteamyTea]

6 minutes ago, G and J said:

And that I think is my base case against which other scenarios are compared.  

It is what I always do.

[JohnMo]

18 minutes ago, G and J said:

May I ask what the electricity unit rate you are using in that calculation ? (And PS I’m sorry if I’ve given you a headache lol)

 

At 6 years payback I’d be tempted.  
 

Also, am I correct in thinking that one has to have an MCS approved installer to get a FIT?

Fit doesn't exist any more, you get paid per kWh of actual export. But I don't get paid, so haven't used anything for that.

 

So standard tariff I used 25p

E7 I used 14p and 30p

[Gone West]

There seems to be a large variation between peak and off-peak prices for different suppliers. Table below is taken from an email Money Saving Expert sent me.

 

The two tables below show the difference in average rates between providers' standard Economy 7 tariff and their standard normal, single-rate electricity tariff. Assuming 42% of electricity is used at night – the national average – an Economy 7 tariff could typically save you around £50 a year, compared to the Price Cap rates that most non-Economy 7 customers are paying right now.

Average rates compared under the April to June 2024 Price Cap: Economy 7 vs electricity Price Cap rate paying by direct debit

ENERGY PROVIDER	AVERAGE PEAK (DAY) RATE	AVERAGE OFF-PEAK (NIGHT) RATE	AVERAGE STANDING CHARGE	AVERAGE COST (1)
British Gas	29.38p/kWh	14.64/kWh	60.33p/day	£1,125/year
EDF	30.06p/kWh	13.71p/kWh	60.34p/day	£1,125/year
E.on	32.06p/kWh	10.95p/kWh	60.33p/day	£1,125/year
Fuse	29.44p/kWh	12.28p/kWh	57.59p/day	£1,077/year
Octopus	30.41p/kWh	13.22p/kWh	58.27p/day	£1,117/year
Ovo	27.60p/kWh	17.10p/kWh	60.33p/day	£1,125/year
Scottish Power	29.89p/kWh	13.94p/kWh	60.33p/day	£1,125/year
Utility Warehouse	33.88p/kWh	8.43p/kWh	60.20p/day	£1,124/year
Price Cap (single rate)	24.50p/kWh	24.50p/kWh	60.10p/day	£1,175/year
Last updated: April 2024. Rates are averages, actual prices vary by region. (1) Based on regulator Ofgem's average usage figure for Economy 7 of 3,900 kilowatt hours (kWh) of electricity a year, paying by direct debit. Economy 7 assumes 42% off-peak usage.   Off-peak rates usually run from midnight to 7am, with a peak rate throughout the rest of the day (though precise times vary by supplier).

Note. The figures above are based on what Ofgem considers "typical use" for a household on Economy 7 (currently 3,900kWh a year). We think this is low for electric-only homes, so it's likely you'll pay more than this over a year, but it should give you an idea of how prices compare. 

[trialuser]

Would 18 panels at about 40v max put the inverter over the maximin input voltage, or if connected series/parallel, put it over its max input current?

I understand you can over power them in wattage but thought the max volts was absolute?

 

[sharpener]

14 hours ago, G and J said:

Also, am I correct in thinking that one has to have an MCS approved installer to get a FIT?

 

In the sense that you will require it to register for an export tariff under Smart Export Guarantee which IIRC is what the replacement for the FIT scheme is now called.

 

Intelligent Octopus Go and maybe some of their other tariffs pay 15p/kWh, there was an experimental way you could get this without MCS but you had to pay £250 and produce a structural survey of your roof, don't know if this is still available.

 

See also this thread.

 

Edited May 21 by sharpener

[sharpener]

18 minutes ago, trialuser said:

Would 18 panels at about 40v max put the inverter over the maximin input voltage, or if connected series/parallel, put it over its max input current?

I understand you can over power them in wattage but thought the max volts was absolute?

 

How long is a piece of string? What do you mean by "the inverter"?

 

Few inverters will take 720V though IIRC there is a big new Victron one that does. You also need to be careful the open circuit voltage at minimum expected air temperature does not exceed inverter rating.

 

18 panels if of the current typical ~400W output will be 7.2 kW. Overpanelling up to 20% is reckoned to be the max sensible amount so that would imply you need a 6kW inverter as a minimum. That would probably have two MPPT inputs so 2 strings rated at 360V 10A, sounds about right.

[SteamyTea]

3 hours ago, Gone West said:

Note. The figures above are based on what Ofgem considers "typical use" for a household on Economy 7 (currently 3,900kWh a year). We think this is low for electric-only homes, so it's likely you'll pay more than this over a year, but it should give you an idea of how prices compare

E7 places tend to be small, and often very small flats.

[G and J]

1 hour ago, sharpener said:

 Overpanelling up to 20% is reckoned to be the max sensible amount so that would imply you need a 6kW inverter as a minimum. That would probably have two MPPT inputs so 2 strings rated at 360V 10A, sounds about right.

Is that to save money on inverter sizing/purchase cost and thus accepting some lost Solar power on the sunniest of days?

[Alexphd1]

I think it's more to do with maxin out grid connection. Solax inverters max input is 150% of inverter size so technically you could have 5.5kw of panels on a 3.68kw connection. Tbh not much jump in inverter cost going up a size.

Edited May 21 by Alexphd1

[Gone West]

56 minutes ago, SteamyTea said:

E7 places tend to be small, and often very small flats.

I'm surprised that Ovo has a price differential of around 10p/kWh and Utility Warehouse around 25p/kWh. If I was using mostly E7 then I would be buying from Utility Warehouse. Might even be worth it to have a battery and charge at E7, if you could guarantee the price differential staying the same.

Edited May 21 by Gone West

[sharpener]

1 hour ago, SteamyTea said:

E7 places tend to be small, and often very small flats.

 

Not sure of yr basis for this. Perhaps a legacy from flats having storage heaters, we once owned one, son's flat was also converted from that to gas ch hence some very bizarre wiring.

 

50 minutes ago, G and J said:

Is that to save money on inverter sizing/purchase cost and thus accepting some lost Solar power on the sunniest of days?

 

Not sure which way round the thinking is. My 2nd array has 8 x 405W panels with a 48V 60A Victron MPPT bc the 70A was a lot more expensive, was an older design and had less flexibility.

 

But equally if you are limited to a 3.68kW inverter it is better to have more panels than that as you get more output in the shoulders of the day and the seasons, for this 20% is thought to be the sweet spot between capital cost and revenue.

[G and J]

20 minutes ago, Alexphd1 said:

I think it's more to do with maxin out grid connection. Solax inverters max input is 150% of inverter size so technically you could have 5.5kw of panels on a 3.68kw connection. Tbh not much jump in inverter cost going up a size.

So if my DNO allowed only 4kW and thus I had a 3.6kW inverter I could still have 5kW of panels?

[sharpener]

Yes almost certainly, but (as above) anything over about 4.5kW is probably not worth the extra expense. However there are practical considerations like the shape of your roof and what your chosen installer prefers to fit.

 

I had a quote for 10 x 400W panels, but the day before he was due to install he pulled out (and nearly left me with a bill for a scaffold tower). New ppl couldn't supply the particular long thin panels that fitted best so I had to settle for 8 and a bit of shading in late afternoon.

 

They told me they would bring their own tower but in fact the crew turned up with just a ladder and carried the 25kg panels up that single handed. Which was almost certainly in breach of HaSaW Act, and scary to watch.

 

 

 

Edited May 21 by sharpener

[Alexphd1]

When we installed a few years ago the dno went by inverter size and if we kept it below 3.68kw there was no problem with grid connection. We had a 3.68 with 4.4kw of panels done by a registered installer. I presume still the same now. I am planning on beefing up system

[trialuser]

I hadn't realised the max 550-600v was per string

[sharpener]

22 minutes ago, Alexphd1 said:

I am planning on beefing up system

 

We couldn't get more than 3.68kW so our 4.4kVA inverter has to be restricted. Is the DNO now allowing you a beefier connection or is it a case of adding the extra power on the battery side like we did so you avoid this?

 

2 minutes ago, trialuser said:

I hadn't realised the max 550-600v was per string

 

Yes. Dividing the array into two parallel strings will halve the voltage and double the total current.

 

[SteamyTea]

1 hour ago, sharpener said:

Not sure of yr basis for this.

I looked into it a few years ago and found some government figures that showed local area usage and tariff details.

Then cross referenced it against a similar housing database.

Also, at ~4 MWh/year usage is low, compared to the national average of ~20 MWh, of which 2.5 MWh/year is just electricity.

[Dillsue]

4 hours ago, G and J said:

So if my DNO allowed only 4kW and thus I had a 3.6kW inverter I could still have 5kW of panels?

You can have significantly more than that. If you stick within the G98 limit of 3,68kw inverter rating, then you can get inverters that allow 200% oversizing on the DC input so you can have 7.3kw of panels. If your panels are facing differing directions then you can have more still subject to sticking within the inverters max input limits. Panels are cheap and maxing your array gives useful generation year round.