Anyone gone down the max self consumption route?

[Alan Ambrose]

By which I mean large overcapacity of panels. Object being to provide almost all power in the summer & shoulder seasons - only using imported power in the winter?

 

[mistake_not]

Yes, have a 7.5kw generation capacity - could do with more in winter. Have space to get some more panels on the garage so might do that. 

 

However with hindsight the thing that actually has quickest payback is battery and night charge in winter at cheap rate.

[G and J]

59 minutes ago, Alan Ambrose said:

By which I mean large overcapacity of panels. Object being to provide almost all power in the summer & shoulder seasons - only using imported power in the winter?

 

Yes.  Ish.  I’d not call it overcapacity, even though we can’t export quite all we generate, even after we've refilled the battery.  The numbers made it an easy win.

[JohnMo]

57 minutes ago, Alan Ambrose said:

only using imported power in the winter?

Not sure only importing in winter is practical, rainy days generation is pants any time if the year. We import all year, but export more than we import most of the summer.

 

1 hour ago, Alan Ambrose said:

By which I mean large overcapacity of panels

Yes we have lots more panel capacity compared to inverter capacity. The inverters rarely run at max capacity anyway. But we have tried to optimise for winter rather summer as summer you over produce anyway.

 

But with big arrays you really need to export and import most the year - we do in NE Scotland, maybe different 500/600 miles further south.

[G and J]

Boils my brain to try and get a feel for it, but I think there may be a 5D graph possible showing payback period vs panel capacity, orientation, inverter capacity and battery capacity.   
 

For us and I assume many, maxing the panels on one face of the roof was a no brainer as it saved slate (I’m not a fan of surface mount panels).  
 

From that our installer used a sort of rule of thumb/wet finger analysis to give us an inverter/battery pair he’d used loads of times on our sort of size if installation and which was well priced.  So the 5D graph and all the AI advanced modelling wasn’t needed.  
 

So no deep thinking needed.   Simples. 

[RobLe]

Yes, 14kWp of panels, 4+4kWp inverters, 16kWh battery.

We started with 4 ages ago, and as the price has dropped we extended; it’s not about cost, but rather the warm glow generating more than we use gives:-)

In winter we want every drop, in summer there’s too much to just export as we get it.  We have ‘Solar Assistant’  to manage this - software that lives on a raspberry pi - it’s a bit like home assistant but more specific and easier to use.  If it’s predicted to be sunny the battery is flattened in the morning, so that there’s enough space for mid day sun in it. 

[SteamyTea]

First thing to look at is your time series usage.

Then you know what you can easily shift (temporally), store and finally, but most importantly, change behaviour.

 

As for PV v Batteries payback, this is a difficult way to look at it and very easy to introduce bias into the calculations.

 

And it is kW and kWh, not kw or kwh.

Edited Thursday at 09:13 by SteamyTea

[-rick-]

37 minutes ago, SteamyTea said:

And it is kW and kWh, not kw or kwh.

 

Ah it's been a while! Not sure if it's the forum being quieter or you've been slacking

 

[SteamyTea]

31 minutes ago, -rick- said:

you've been slacking

Been busy at work, it had been a strange year 

[Bramco]

16 hours ago, mistake_not said:

Yes, have a 7.5kw generation capacity - could do with more in winter. Have space to get some more panels on the garage so might do that. 

 

However with hindsight the thing that actually has quickest payback is battery and night charge in winter at cheap rate.

 

Yes quick payback is battery and cheap rate charge. We have 6.5kWp of solar and batteries.  This allows us to only import at the cheap rate overnight, so no standard rate, or very, very little. The only time we import at standard rate is if the family are home during the winter and we haven't enough battery, or solar to cover the hot water usage, cooking etc.  Our Octopus bill last year was £150 for the whole year, that's for everything, heating, DHW, cooking etc. That's for a 250m2 all electric house with ASHP, MVHR etc.

[JohnMo]

3 hours ago, Bramco said:

Octopus bill last year was £150 for the whole year

Oh to have the solar output, we have 11+kW of panels, but lots of trees and up in Scotland. We almost never import expensive rates always cheap, but our bills are still way higher than yours. But still very low in reality. Considering we cool most the summer months and shoulder months as well as well.

 

3 hours ago, Bramco said:

Yes quick payback is battery

But yes even so the battery is allowing all our current electricity to come in at 10p instead of 27p(?). We seem to consume around 10,000kWh, so even without any export or PV we save £1700 a year. So battery is about 2.5 years payback. 

[Bramco]

46 minutes ago, JohnMo said:

Considering we cool most the summer months and shoulder months as well as well.

You must have some serious south facing glass to have to cool for that long. We have overhangs on south facing glass as well as external blinds - this keeps the heat out.  The great thing about the blinds is from the shoulder season through winter, they let in the heat.  I think we've used our cooling for less than 10 days this year - and we are east midlands, so we've had every heat wave, although not as bad as further south.

[Dillsue]

20 hours ago, Alan Ambrose said:

By which I mean large overcapacity of panels. Object being to provide almost all power in the summer & shoulder seasons - only using imported power in the winter?

 

When we added a second set of PV a few years ago the plan was to have generation all day long by spreading the panels from SE to NW as we didn't have a battery. The NW array does virtually nothing in the winter but does keep the generation going to cook tea for maybe 6 months of the year.

 

Now we have a battery charged off cheap overnight eleccy we let all the PV run to the grid and grab the Octopus export payments.

 

Without a battery you'd need quite a sizeable array correctly orientated to power you through early morning and evening without drawing much from the grid, even in summer. PVGIS gives your hourly generation forecasts so you can have a play and model the panels you could install versus the house load through the day. Or get a battery.

[JohnMo]

Our lounge is all glass on one wall but to make things worse it comes out to a peak to form a bay window 6m tall. So we get Westerly sun which circumvents the roof overhang. Fine mid afternoon.

 

But on the upside we have only used 144kWh of electric doing cooling this year, getting SCoP of 6+. All of that supplied direct from PV. So missed out on £17 of export.

Edited Thursday at 17:16 by JohnMo

[Alan Ambrose]

Is there ever a problem where you would like to have more panels but your DNO-agreed inverter size and the max oversize of panel capacity for your mppts limits your shoulder seasons generation?

[Dillsue]

Whatever export limit the DNO sets you can always have a much bigger inverter and array and just export limit via G99+G100.

[JohnMo]

1 hour ago, Alan Ambrose said:

Is there ever a problem where you would like to have more panels but your DNO-agreed inverter size and the max oversize of panel capacity for your mppts limits your shoulder seasons generation?

You need to make sure you stay inside the max voltage and amp limits of the inverter. We have a 3.6kW inverter with 6.5kW of panels. But these are also vertical and we are NE Scotland, so output is capped somewhat anyway.

 

The science of PV is peak power is only momentary or short lived, nearly all the time the panels run in a derated state, sun angle, sun heat, cloud etc all affect the panel performance.

[Alan Ambrose]

So, am I right in thinking that the old way of looking at the problem was to optimise for max summer output i.e. S facing and make the most of the panels you’ve got. And the max self consumption route is: panels are cheap, spread panels east-west for long output during the day; have max panels for usable output in the shoulder seasons; and then a bit of battery to cope with occasional dull days and to keep the heat pump running overnight. Almost ‘off grid’ for 3 seasons, with a bit of backup help from the grid in winter?

[JohnMo]

18 minutes ago, Alan Ambrose said:

, am I right in thinking that the old way of looking at the problem was to optimise for max summer output i.e. S facing and make the most of the panels you’ve got.

Really depends on export limit - for us zero point fully optimise i could generate 11kW now, but can't export that much, so no point. Most of the time would get very serious clipping.

21 minutes ago, Alan Ambrose said:

And the max self consumption route is: panels are cheap, spread panels east-west for long output during the day; have max panels for usable output in the shoulder seasons

Angle also makes a huge difference, vertical are rubbish in summer compared to 37 to 45 degs, but still produce well enough. The same vertical panels produce well in winter, although day is shorter.

 

23 minutes ago, Alan Ambrose said:

and then a bit of battery to cope with occasiona dull days and to keep the heat pump running overnight.

Winter running an ASHP and solar are very different things. ASHP will use way more than your winter production will ever cover. Your real energy bills come in the winter, PV export is very low. So size your battery to eliminate almost all normal or peak rate usage so you only use low rate, would be my advise.

 

28 minutes ago, Alan Ambrose said:

and to keep the heat pump running overnight

Your CoP is generally worse at night because it's colder outside. I would size you heat pump correctly. I have now had an oversized and correctly sized heat pump, I dumped the oversized one because general perform and CoP wasn't anywhere near as good as it could be. A well insulated house at 7 degs needs vert little heat, a correct sized heat pump will run long and slow giving excellent performance and oversized one will cycle killing CoP in real life. On your cold days you correctly sized heat pump will mostly run all day.

[Beelbeebub]

I went the max panel and inverter route.

 

Size of inverter was partly determined by desire to cover peaks without drawing from grid i.e. kettle, toaster, air fryer all on at same time.

 

This allowed for a large number of panels (24).

 

This was dictated strongly by my (carport) roof size.  I wanted to get it looking neat so fewer panels would look stupid. 24 panels filled the roof really nicely.

 

It also compensated for sub optimal angle and orientation (12 degrees and South West).

 

It also allowed reasonable generation (enough to cover daily demand) in the shoulder months as the panels are badly shaded by trees and the house.

 

All in all we have zero import for 6 months and produce about 25% of demand in deep winter.

 

The array easily saturates my export limit (a measly 3.6kw) so we have alot of potential excess in the summer.

 

One advantage of the big array and inverter in the winter is the charge rate can be really high so you can take advantage of the 2 or 3 hours of sun during an otherwise dull day.  3 hours of good sun is about all I need to top up.

[Dillsue]

6 hours ago, Alan Ambrose said:

So, am I right in thinking that the old way of looking at the problem was to optimise for max summer output i.e. S facing and make the most of the panels you’ve got. And the max self consumption route is: panels are cheap, spread panels east-west for long output during the day; have max panels for usable output in the shoulder seasons; and then a bit of battery to cope with occasional dull days and to keep the heat pump running overnight. Almost ‘off grid’ for 3 seasons, with a bit of backup help from the grid in winter?

Adding a battery potentially changes the dynamics. In the winter panels spread through 180 degrees from E-W will likely generate less than the same panels all facing south and pumping the peak generation into a battery. Run the figures through PVGIS and see how it pans out ie 2kw East + 2kw West versus 4 kw facing south

[Beelbeebub]

10 hours ago, Dillsue said:

Adding a battery potentially changes the dynamics. In the winter panels spread through 180 degrees from E-W will likely generate less than the same panels all facing south and pumping the peak generation into a battery. Run the figures through PVGIS and see how it pans out ie 2kw East + 2kw West versus 4 kw facing south

Yes with a suitable battery and inverter you don't need to spread the generation via different orientation. 

 

On a slight tangent, my 24 panels system occupies the 12 degree mono pitch of a roughly 7x7m footprint carport.

 

That's 50m2ish. Or about the footprint of modern 3bed house (about 100m2 over both floors).

 

It strikes me that you could provide any house with 24 panels if you use a low mono pitch.

 

Sure some would be sub optimal in terms of orientation or shading but even shaded or on an overcast days they put out 500w or so - enough for base load.

 

It was about £3k in panels and mounting hardware (inverter and batteries were another 7-8k) and very easy to install (low pitch, metal roof). Hardly breaking the bank for a new build. And that house would be low electricity consumption in the winter and zero in the summer. If the occupants had an electric car it would do a good deal of their "fuel" over the summer, an immersion heater or heat pump and free hot water as well.  That would do very nicely against the cost of living.

[Bramco]

17 hours ago, JohnMo said:

Angle also makes a huge difference, vertical are rubbish in summer compared to 37 to 45 degs, but still produce well enough. The same vertical panels produce well in winter, although day is shorter.

 

We've covered this before but if you have a ground mounted array, the angle is up to you. So start with PVGIS and try out different angles. From memory, it gives you the angle which generates the highest output in mid summer - but if you vary the angle, you can find a point where the total yearly output is the same but the highest output is less and output is pushed more into the shoulder months.

So if your inverter would normally be clipping at the highest output, you'll get more out of the installation by finding that angle - for us it's about 45deg rather then the ~33deg (from memory) that gives highest level of output.

We have 6.5kWp of solar and an 5kW inverter - yesterday at the peak we were generating 5.4kW from the solar, so only losing a bit due to the inverter clipping. From here on in, this will get closer and sometime in September we'll be generating much more than we would have been doing at 33deg and we'll be able to use all of it.

 

So it's worth doing a bit of analysis to work out what the best orientation and angle will be over the full year.

[scottishjohn]

tricky question 

 

If I had been 20years younger I would have done it all myself 

 

but trying to work on a roof with one leg that hardly works and gives way at any time was not on 

 

 so mine was professionally fitted with extra costs involved

 

26 panels --11kw invertor and  a stack of 5 batteries  17kw capacity

 

 

 it became clear to me from the start that the tariff you pick will decide what the installation should be 

 

I picked battery make so i could go  octopus intelligent flux 

 

 which at this time your import and export rates are identical for same time periods

 

eg most of day +night it it 20.6p per unit

 

good time is 16.00  to 20,00 then it is 27.6p for export --but also import is same

 

there is no night cheap rate as such 

 

they have total control of when it chargers and discharges the battery --sounds bad -- but in practise it works fairly well

 

-my panels all face s/w on the roof of house

 

house is shieled by a hill behind  so no major production happens till it gets high enough to get at   the far side of roof

 

the house is all electric ASHP  

 

 

 so this morning as an example  --battery been sucked  down to 20% in peak time last night 

 

 so this morning it is dry and i,m importing a small amount ( 500w) and it is also charging the battery a little  as the panels are only making 800w  at 07.30

 

this continued to 08.30 when the panels started to make more than usage -- so now the battery is still low but gradually charging 

 

I expect that it will start taking small amount of import  if sun does not come out properly till round about 12.00

 

and usually  battery -is full by 13.00-- so then it starts to export back to grid at same price i paid this morning-- so actually no cost to me to fill battery 

 

and in the afternoon when its doing well --11kW  -it will keep sending it back at the 20.6  till the peak time when it will most likely still be full -then it will be 27.6 p a unit when they start to take it back 

 

It is supposed to only go down to 20% --but quite often they will suck it down to  5% --I am guessing it is something to do with grid balancing and they get more money for it then 

 

 if they do suck it dry then they will start to recharge it at some point at the lower rate

 

so all it all I find it a simple and fair system 

 

I have also joined AXLE energy  for their grid events  where they will pay you £1 per unit when they want it  events last one to two hours and can be any time of day 

they will pay you £10 a month even if you send nothing back- but fi you do the first £10 is from what you send  

 

If any body is interested mail me and we can both get some money for me passing your details on 

 

what would I change if doing it again --smaller battery stack -as cost of extra batteries will never be got back --and as the pay you for export when batteries are full    no point in having too many batteries

 

to completely cover consumption of  a 16kw ASHP  with battery  storage    in should months would be prohibitive

 

 

Edited 3 hours ago by scottishjohn

[scottishjohn]

14 minutes ago, Bramco said:

So if your inverter would normally be clipping at the highest output, you'll get more out of the installation by finding that angle - for us it's about 45deg rather then the ~33deg (from memory) that gives highest level of output.

I went through this when I fitted solar thermal  20+years ago on old house 

 unless its different for solar -- then the angle should be same as your  latitude  approx 53-54 for me 

but in winter they worked better when hung at an even steeper angle due to height of sun 

in my case I opted to go an even higher angle as in summer they produced too much and boiled by 300 litre tank  - unregulated panels--  but in winter when my underfloor was wanting heat they did help  as long as it was clear skies

 

it was always my intention to go full solar if i was building a new house -- but costs of 60000 litre insulated storage tank under the house might have been prohibitive-- basically  a very wet cellar

 

 but where  I ended up on this quarry site rebuilding an old house  which is built on live rock   --made that a non starter 

 

maybe just as well as price of solar thermal panels have not dropped at all -best output for a £2400 solar panel would be 4kw--where PV panels have and thats only 8 solar panels at £120  each ?

providing you have the space 

 

 

 

Edited 3 hours ago by scottishjohn