Pete UK
Member
Wow. Thanks for the fast reply. Probably like 5-10 mins per pageHero! 103 pages / 7 days = 97 minutes per page. Comprehension should be good
Winter heating? You will get diddly-squat from PV in winter (Dec/Jan will be 10% of mid Summer peak). Oct-mid-Nov and Mid-Feb onwards you will get some - but weather has to co-operate by being sunny on cold [central heating] days ...
I suggest you need useful logged data for consumption. You need to know hour-by-hour what you use in various scenarios:
(Hour-by-hour because you need to know what is during Off Peak (you can price that buying from Grid), whether likely to have some PV at that time, and for the rest "Price from grid")
Winter, artic outside, heating on full blast. Both "house occupied" and "away for weekend"
Normal average Summer day consumption. Maybe a party-day as well as an ordinary at home day - and a weekday / weekend day. Baking / Washing / tumble drying days (if you have those high-consumption days) vs. normal days
Smart Meter (got one of those?) might give you that data, or a plug in gadget such as Owl
Then, if you are up for it, you need to crunch those numbers. I think the calcs you need are for:
Winter days - assuming you will charge the battery 100% on Off Peak (in Spring/Autumn that will be partially-charged on some/majority of nights - depending on prediction of tomorrow's sun [Tesla and Givenergy will do that, or you can roll-your-own using e.g. Solcast])
What is the consumption from end-of-off-peak to start-of-off-peak following night? Your ideal would be a battery that can cover that. I guess 80:20 would do - so what size battery would cover 80% of the days usage.
However, you probably don't actually want to try to achieve that in Dec/Jan. By mid Feb you will get some useful sun PV (when it isn't raining - if it rains then same sum-game as Dec/Jan). Use figures for likely Monthly generation which you can put in the mix. My battery does about 1/3rd of a winters daily Peak tariff, but by mid Feb I have days where I use zero Peak tariff, and only charge battery to 50% on Off Peak - enough to run until Sun Up, and then Sun will charge to 100%-ish, and then that will run down from 14:00 - 15:00 (Feb PV-SunDown) onwards ... up until Off Peak starts.
In Summer the tables turn. You want the battery to go from "PV SunDown" (the moment at which the PV is generating less than the house is using) until PV-SunUp. If you have East and West arrays that will probably be 2 hours better than a South-only array. Of course that includes the night time, which will be your lowest consumption, which helps eek the battery out. My battery will last me a bit over 12 hours (over night) at Summer Consumption, at which time my PV-SunDown to SunUp is about 7PM to 7AM.
On top of that no point installing panels if you cannot use their output - bigger battery, or a car (parked at home during nice sunny summer days, Natch!), or a summer usage - Air Con, Hot Tub, Immersions etc.
Yeah, me too
Not sure the North are going to contribute enough (on top of the others) to make them worthwhile.
Multiple elevations may require multiple inverters, or some other fancy "balancing" stuff. (Not something I know about, but might mean that North benefit is offset by having to buy "more stuff" like inverters, wiring, scaffolding, etc.)
Ask them what their lead-time is. If it is 12 months (might well be ...) then you might want something else
If you are going to plug-and-forget that won't matter, You could install e.g. a Zappi charger and let it just divert excess PV to Car (if it is at home and plugged in) and use Eddie (IIRC??) to divert excess power to Immersion and so on.
If you want to tinker then I think it it definitely helps. I can go into Tesla APP, see that the battery is almost full, PV has several hours peak to go, and I can start one/both cars charging (and choose low AMPs if I only want to divert a bit). I don't think I'd do that as often if I had to go in and out of several APPs. All that can be "automated" with Tesla API. Again, harder if there are several different APIs to make connections to - and X-times more hassle whenever anything changes in any/one of them.
I don't think that figure is useful. You need a) household consumption in various scenarios (as described above) and then match that with likely PV production (month by month). I suggest you have a go with PVWatts - that will let you figure out (for your exact location) what roof area you have (for each elevation) and [at that Lat/Long] what your likely generation will be month-by-month
Make separate calcs, for each of your orientations. Then copy/paste the month-by-month production figures to a spreadsheet - and then see when producing more than house will use, and when not enough. That can influence battery size (or whether you need car to be at home any day in Summer when sun is shining! or also buy an Air Con system for the house! and also clarify that you aren't going to get any benefit for winter heating in Dec / Jan at least)
I have a loop system like that. We have a pump (special hot water pump - I think that is referred to as "bronze") which comes on to pump the ciruit, on a 5 minute timer and overridden if thermostat sees that the return temperature is "hot"). We have bedside / bathroom switches (on home automation system) to "trigger" that. The plumbing is configured so that there is a non-return valve when pump is running, and when not the hot water can flow both ways round the loop - which provides benefit of more hot water "flow" than only a single circuit.
Before we put the pump in the water cylinder was cold within about 4 hours.
We also have towel radiators on the hot water circuit (special towel rails, stainless maybe?, sorry about that ...). Run the pump (and/or run a bath/shower) and the flow of hot water heats the towel rail, which coincides with use of course. Or just turn the pump on if you want the towels heated at any other time.
If you are doing it you want to put up as many panels as you will ever need - there is a fixed cost for scaffolding and "getting installer on site", and quite possibly "one inverter", so incremental cost of a few more panels is small.
If you are sizing to have a reasonably decent amount in Spring / Autumn you will definitely have excess in Summer.
Adding Air Con, in Summer, would use up some excess ... even a plug in one with a snorkel-pipe out-the-window would do. Or some other heavy summer time usage.
but it was a mission I needed to complete !Yeah, I’m aware generation is gonna be almost zero for a good few winter months. Thanks for the reality check though, (Maybe 10% ish - cover the base load). Hence the need for largish battery charging requirements off-peak. (I did mention I’d just read the whole thread, didn’t I?
). I’m not even sure I’d make it through a full spring day TBH ! - Not without something changing. Maybe though. 
I’m aware I need to attack the top power offenders. Getting the data is not gonna be easy just now. Going that way, I need to get some power monitors/ loggers and go around each power drain.
BUT I’m pretty sure - initially anyway, I’ve identified the top 2 culprits already. And if I’m maxing out the roof space, what else can I do? - Can’t add any more. So that bit is sorted. It’s just about how much battery I need from end of off peak to start of off peak again really now, minimising the hungry loads and being able to pre-schedule/ program the battery for the year. (ie Allow the car to charge in the IO schedule, charge the batteries to 100% overnight 3 months in winter, say, 95% in Feb, 90% in Mach, then 50 % in April, 10% in May? etc, or whatever….). Gonna need to experiment a bit on that. And suck up any over ambitious errors as a learning experience. Excess battery capacity will help cushion that there though hopefully.
Lots to think about. I’ll have a go on the PVwatts thingy.
I did have lots of data, but the supplier (SSE) got taken over by OVO and the data didn’t follow (only the massive bills) our smart meters also be stopped communicating in Dec apparently, although I can still see the daily and “real-time” Consumption on the smart display. I think the supplier is probably guessing our usage at the moment as every day is almost the same in the app’s “daily usage”. Not ideal.
I was sceptical about the north facing panels TBH. But from the modelling estimates, they are obviously showing much less than south facing but ‘some’ useful yearly output. Especially on cloudy days. Researching it a fair bit, looks like about 50% of what the South facing ones will give. But I am looking at it like this; I can only fit 5 on the south face anyway. Estimated to get me about “2015” kW per year. 8 on the north face they estimate will get me “1929” kW per year. Ok, so that’s 58% of the max, assume it’s less, say 50%, that’s 1,600 kW. So having 8 on the north should generate about the same as having 4 extra on the South side. So for the price of 4 extra panels (£800? Plus a bit for ancillaries) it should be worth the small extra cost while they are on site for 1,600kW extra a year - which could be 50p a kW by the time it’s installed - or…. about £800 !
Also I’m thinking if a south or east facing panel goes kaput, it’s a readily available spare not doing much to swap over in case they don’t make them anymore. Keeping the string balanced.
Let’s see what price they come back with. I’m liking the idea of being able to pre-program and fine tune the pre-programming of the off peak SE battery charge though and the IO 6 hour window decreases the survival time on the battery during peak rate as well.
What are the physical devices you’ve got for your set up of the water recirculation loop? I’ve just got a timer at the moment (like a hard wired mechanical plug with dip switches for the times you want it on or off) but I’m pretty sure the water is kept hot all the time. Yeah the water tank cools I guess but that heat escapes into the bathroom as heat, so it warms the room anyway, so the energy isn’t really lost I suppose.
Anyone got any feedback on the Solar Edge ecosystem? I’m trying to eke out all the extra performance I can. Any %age wasted on unnecessary conversions or inverter losses equates to less kW bough in and less time the rest is on peak. Even 6% of 7,000 (420kW) at 45p is an £190 extra a year.
Cheers all !
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