scdoubleu
Member
Both charge and discharge are limited. Bloody annoying, but better than not having the PW at all.
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Solar Panels UK - is it worth it?
- Thread starter jdwuk
- Start date
PITA
Model 3 Performance
We have one Tesla Ev linked to Intelligent Octopus which needs to use the IO Schedule at least once a month.
The other Skoda Ev and two Powerwalls and house demand are a 'free for all' during the 11:30 to 05:30 hours.
During the day, we export excess solar into the cars.
I can understand the charge limitation, but if you're not exporting to the grid I don't understand why the DNO should have a say on what you do with your electricity once it's beyond the meter and how quickly the PW can discharge into your consumer unit. Bloody cheek of it!
Is there any reason you wouldn't export the excess solar via SEG? We're basically doing mostly the same as you, but exporting the solar at 12p, living off the PWs for day-time use, and charging the car with the overnight 7.5p.
In the winter we'll keep all the solar (however much that will be) as we'll need as much as possible for daytime usage (ASHP) and more than the PWs will be able to provide.
Drew57
Active ember
Same here apparently - yesterday the DNO have asked my installer to fit a limiter to the smaller 2.5kWh inverter to restrict PV to 5kWh max export (I have three inverters, two at 3.6kWh & one at 2.5kWh). They are concerned that I may decide to discharge batteries at 3.6kWh on a sunny day at the same time as high PV export (yesterday/today exporting at 5.8kWh for part of the day). Restricting the smaller inverter would not guarantee that of course but that's what they want!
It is of no consequence as I can only receive FIT payments (18 years remaining) from the main 5kW PV system so any additional export has no benefit to me (but could for the grid). I never discharge batteries to grid either.
Just going back to this quickly if that's ok? I've finally had some decent quotes from a local fitter with a good reputation. I have a choice of the Viessmann 050 or for £305 more, the 100. Not sure if the 100 is worth the extra? It seems to be slightly more efficient at 94% vs 92% and has some slightly better internals, better display, etc. Did you consider both?
I also need to decide between a 30kw or 35kw (for either model). A 35kw may or may not require an upgraded gas supply from the meter at an additional cost of £436. If that is required I'm not sure its worth it for the extra flow rate. However if the existing gas supply is sufficient there is only a £80 difference between the two so the 35kw might be worth it in that case.
I'm thinking of going for the weather compensator for an extra £87. Apparently opentherm won't work with the weather compensator, but as I already have Hive that isn't opentherm compatible, I may as well let the compensator do the modulating.
Drew57
Active ember
My deemed export at 50% of generation from the 5kW is a lot more than my actual export & I will continue to receive the increase in £/kWh via FIT for another 18 years. It is worth more than SEG and guaranteed to rise every 12 months.
Last edited:
I did look at it and can’t remember why I stuck with the 50. Probably cost. I think the 100 maybe has better modulation ratio too? that was one critical reason for the 050 it had a 1:8 ratio so 30kw can drop to around 4kw for heating. still too high in mild weather but not as bad as many. Bear in mind 35kw will mean higher minimum heat output for central heating whihc likely won’t be needed (have you done heat loss estimate?) so unless you run mulitple hot showers at the same time I’d imagine 30 is fine?
definitely get some form of load compensation. If Hive is on/off then weather compensation is a good shout. you can experiment with the curves to get the response you need and it’ll run much cooler and use less gas.
Thanks. Yes I'm wondering if 35kw is overkill. The 30kw is described as suitable for "homes with 2-4 bedrooms, 1-2 bathrooms and up to 15 radiators" which easily covers our situation.
The 100 has a modulation of 1:10 so slightly better than the 050. Not sure if its £300 worth of "better" though!
I haven't done a heat loss estimate but should do. Any recommendations for online calculators or iphone apps or are they all much the same?
*edit* the fitter has just come back to me to explain that because we have a very high flow rate (18lpm) it's better to have a higher kw boiler. Although saying that, the outgoing boiler is only 23kw so even the 30kw is a big improvement.
Last edited:
WannabeOwner
Well-Known Member
That's your answer I reckon. Personally I would also want to figure into it what insulation you have / could have. Insulation will save on fuel, of course, but I think more important is the benefit to "comfort" from running a more even temperature. When the boiler cuts out the rate at which the room temperature falls is slower and once the low thermostat setting brings the boiler back on the temperature the room has fallen to before rads start to raise it, so the rooms stay within a narrower band.
You'd also need to get rid of any gaps around doors and windows where you can see daylight!
I live in a Passive Haus, so the only buzzword I know is "PHPP". Its basically just a monster spreadsheet, but I don't know if it is available without purchase etc. or if, for a layperson, the vast amount of information (about materials used for construction of the house etc.) is viable. With PHPP (and presumably? the APPs that are available) its then possible to do What-If - swapping windows for triple glazed, adding insulation, and so on. That would help with what benefit you could get from "improvments"
I have a thermal store (although mine is a big system, and not a combi); mine includes solar thermal to heat the thermal store (and, prior to that, the DHW tank until it is at temperature). In the summer we don't use anything else, immersion is set to come on during Off Peak to make sure we wake up with hot water, but its rare that it actually fires during Summer). My boiler is large (big house) and using the thermal store as a buffer, means it cycles less, we use considerably less fuel than the original boiler manufacture's calculations (and we could have had a smaller boiler, but I elected for larger boiler, faster ability to heat the thermal store / house, because thermal store means it won't be cycling inefficiently ... either it is on, for a decent length of time, or it is off - also for a decent length of time!)
Just a thought.... reading all these stories about charging over night or at other off peak times etc.
How on earth does the network know what is essential real time demand vs highly discretionary / opportunistic battery charging? I wonder if they can be sure that one customer's battery / PV isn't being used to supply someone else's battery charging?
Without careful control, that sometimes happens within my own system!
How on earth does the network know what is essential real time demand vs highly discretionary / opportunistic battery charging? I wonder if they can be sure that one customer's battery / PV isn't being used to supply someone else's battery charging?
Without careful control, that sometimes happens within my own system!
Pink Duck
Active Member
With multiple time-of-use tariff rates it is pretty unlikely to happen. Most peak periods are similar, typically 16:00–19:00, and so are priced highest for import. Any sensible battery storage solution wouldn’t be charging from grid (even if generated in part from someone’s nearby excess solar) then.
Chimpy McChimp
Member
Day 2 of my install today. Battery went in yesterday. Solar panels today. Fingers crossed, by the end of the day I will be generating some of my own electricity!!
Pete UK
Member
Chimpy McChimp
Member
5.2kW Solar Array (13 x 400w Trina Vertex S Panels),
GivEnergy 5.0kW Hybrid Inverter, Associated Switch Gear,
Circuit Protection,
Standard Bird Protection.
GivEnergy 9.5kWh LiFePO4 battery Storage System
Nearly only ended up with 11 panels as somewhere they miscalculated when I was quoted and they then discovered 2 panels wouldn't fit on the house. But I asked them to fit on the garage which they did. Shame it gets shaded earlier than if it had been up on the house roof but, hey ho. I'd rather have the 2 panels there than not at all.
Still trying to get my head round the information being provided in the GivEnergy app and also need to figure out an export tariff (suggestions welcomed!) I have a fixed tariff for electricity and gas that doesn't expire until next year and is silly cheap (comparatively)so don't want to change that at moment.
My situation is a little simpler as my tariff doesn't have any off or on peak stuff so I'm not having to think about different times of the day.
Chimpy McChimp
Member
Now I've had time to think (overthink???) Does it make sense for the battery to charge from grid then charge house as I have a flat rate. Seems like unnecessary charge/discharge cycles on the battery.
phil4
Member
You're spot on with your rethink... the reason you'd charge the battery from the grid is to store cheap electricity to use later when the price is higher. If you have a flat tariff there's no point at all charging the battery from the grid.
At the moment all is not lost though, you can store the sun and use that to save, and the battery will help smooth the use vs generation, so you use all of it.
