Help with solar pv

[Mike_scotland]

5 minutes ago, BMcN said:

When I did it you pay a huge premium for the MSC sign off.  Far better to do it yourself.  

 

I put in 3.6kw integrated.  The whole kit cost approx £2000 ex VAT including the GSE in roof mounts.  Using the same sort of figures as you have it will pay itself off in half the time as the MSC one.  Also you can factor in the square meterage of slate saved (I would guess around £700 worth of slate saved).

 

yeah 100% something to look out for, the msc seems a rip off lol 5p for a unit of electricity who cares..

[SteamyTea]

40 minutes ago, Mike_scotland said:

50% sell to grid for a measly but still something 0.05p per kw (3600 x 0.05p = £120) 

Is that really right, or is it £0.05, 5p/kWh?

https://www.solarpanelprices.co.uk/articles/solar-panels/best-smart-export-guarantee-tariffs/

 

Will your DNO (that is the people that own the grid) allow you to install 8 kW_p without an expensive upgrade?

[AliG]

The trouble is the batteries are expensive and have a much shorter lifespan than the PV panels (10 vs 25 years), whilst only optimising the use of your system. Thus they don't have a great return.

 

I did put some numbers not the Tesla Energy Plan calculator at Octopus and it suggests that you would save around £1500 a year with a Powerwall (I guessed 7000kWh of net electricity consumption).

 

It looks like I would save £2000 a year, this is the first time that a Powerwall has looked interesting to me (There is a problem in that I think I use too much electricity during the day to qualify for one at the moment)

 

The recent rise in electricity prices is actually making this kind of thing more viable, but I am not sure how they are making the calculations. They assume that you import electricity to the battery during the night and sell it during the day. I would not be assuming that current prices persist for the next 10 years.

[AliG]

41 minutes ago, SteamyTea said:

Will your DNO (that is the people that own the grid) allow you to install 8 kW_p without an expensive upgrade?

Good point. You need DNO permission for over 4kw, unless you have three phase then the limit is 4kw per phase.

[Mike_scotland]

41 minutes ago, SteamyTea said:

Is that really right, or is it £0.05, 5p/kWh?

https://www.solarpanelprices.co.uk/articles/solar-panels/best-smart-export-guarantee-tariffs/

 

Will your DNO (that is the people that own the grid) allow you to install 8 kW_p without an expensive upgrade?

From what im led to believe the seg ranges from 1.5p to 11p depending on who you chose to export to so on average they say 5p per kwh.

[Nickfromwales]

2 hours ago, AliG said:

Good point. You need DNO permission for over 4kw, unless you have three phase then the limit is 4kw per phase.

We've done 5 - 8kWp installs on single phase by utilising an export limitation device. DNO's were happy with that. Some did, and some did not want to come and witness them in 'person'.

[Nickfromwales]

3 hours ago, Mike_scotland said:

sounds great doesnt it in the summer banking 10kwh or energy during the day for nighttime cooking etc is all free

First it's not "free", it is at the expense of the cells in the batteries vs how 'hard' you cycle the battery system to get your desired "pound of flesh". Hammer the batteries and you may get as little as 8 years useful life vs the assumed 10+ years. Manufacturers will offer warranties, choose wisely, and read the small print ( especially if choosing a Powerwall, as it's a huge battery for a regular domestic install with not huge amounts of solar revenue  ).

Next is your perception of how quickly you can suck the power out of your intended battery. That analogy is thus; take a full pint glass and chug it down as fast as you can. Now, add a battery inverter ( in this case a drinking straw ) and now you'll take a heck of a lot longer to empty the same glass. So, if cooking, and the cooker ( and hob ) takes say 10kW combined, then at any one time the battery system is likely to give 3.6 to 5.0 kWh of energy throughput at any one given time, ergo cooking will pull 5 from the grid and 5 from the battery.

Maintaining a healthy state of charge in a battery all winter ( an A/C coupled battery will be like having a baby in the house, and will feed on demand from grid electricity if it has not had it's 'fill' off 'free' PV that day ) will cost you. It's only the Solarwatt D/C batteries that are warrantied to hibernate for ( IIRC ) up to 3 months of the year, whereas A/C systems will need constant connection to the grid to keep themselves in check. You can strategize that off E7/E10 etc but burning through a battery system to harvest cheap electricity to consume at a later time is not cost effective in the current stated lifespan of a domestic battery. Then factor in its disposal when it finally snuffs it.   

[joth]

10 hours ago, Nickfromwales said:

So, if cooking, and the cooker ( and hob ) takes say 10kW combined, then at any one time the battery system is likely to give 3.6 to 5.0 kWh of energy throughput at any one given time

"Energy throughput" is called Power and is measured in Watts or kW, not kWh. (Just saying, as someone was bound to)

 

I think of it as the battery is like a water butt with a very small constrained outlet tap. If you get impatient filling a bucket from it, and fill it from the (expensive) mains-fed hose at the same time as from the ("free") water butt, then it will use less volume from the butt and thus not get as much usage from it as anticipated

 

[SteamyTea]

32 minutes ago, joth said:

Energy throughput" is called Power and is measured in Watts or kW, not kWh. (Just saying, as someone was bound to)

A unit of energy is the joule [J].  A watt [W] is a joule per second [J/s or Js^-1].

The joule is often changed into the more confusing unit the Wh, or kWh.  There are 3,600,000 J in a kWh.  This is because k [kilo] is 1000 and there are 3600 s [seconds] in an hour.

 

Just to make it really hard, the joule is a derived SI unit, so is made up from the base units of the kilogram, the metre and time. kg.m².s^-2.

This allows it to me used for all forms of energy.

 

J = kg.m²/s² = N.m = Ps.m³ = W.s = C.V = Ω.A².s

 

To put it into simpler terms, if a 2 kg mass is moving at 1 m/s, the kinetic energy is 1 J.

So about 4.4 lb moving at 2.2 MPH (you can see why we use SI units).  1 J = 0.0009478171 BTU (how horrible is that)

 

To convert joule to Wh, multiply by 0.0002777778 which is just 1/3600

 

Just for a laugh, and I cannot be bothered to get up out the chair this morning, the letters used in SI units are important.

 

J is used for joule, which is named after the man Joule, only use Joule when referring to the man, or at the beginning of a sentence, the same is true for W, watt, named after Watt, though it should really be named after Trevithick, but we use T for temperature, t for time, which is usually s for seconds.

3600 seconds is an hour, h and k is 1000, K is kelvin, named after Kelvin, and is a temperature scale, with 0 K being the point where motion stops.

So if you see KWH that is actually a temperature times a watt times an inductance KelvinWattHenry. Which I think is a totally nonsense unit.

Edited September 28, 2021 by SteamyTea

[Mike_scotland]

i get the idea, likely solar power at 4kw is ok idea but anything above is going to need more permissions and a battery is 100% no go! 

i think im going to go with a 4kw system 8 if i can get permission and leave the battery to another time when there more efficient or better priced etc.

[SteamyTea]

1 hour ago, Mike_scotland said:

think im going to go with a 4kw system 8 if i can get permission and leave the battery to another time when there more efficient or better priced etc.

Just design your DHW system so that you can divert excess PV power to it.

Diverters are not, in the scheme of things, that expensive.

[joth]

On 27/09/2021 at 18:50, Mike_scotland said:

From what im led to believe the seg ranges from 1.5p to 11p depending on who you chose to export to so on average they say 5p per kwh.

Octopus have just increased their fixed rate SEG export price to 7.5p/kWh which moves the needle a little bit in making battery even less economically justified for me, and also flips the self consumption incentive: it's better for me to minimise my PV self consumption and maximize export at 7.5p and then buy it back at the overnight 5p rate.

 

 

"We’re increasing your export prices from 5.5p / kWh to 7.5p / kWh, a total increase of 36%."