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