Hi Jackis69
2. 14 Longi HiMo5 405W, SolaX X1 G4 6.0D hybrid inverter, and SolaX Triple 5.8kWh battery
3. 14 Trina 425W Solar, GIV-HY5.0 GiveEnery inverter, and Giv-Bat5.2 battery
Out of curiosity I plugged a couple of these into easy-pv, assumed a 30deg roof pitch and a nominal postcode area and ran the numbers. Take the comparisons exact numbers with a pinch of salt, just look at the main trends.
I think easy-pv is using an average household consumption profile curve through the day, and a set of yearly solar irradiance data, so it works out an example electricity demand and PV production through the day, and adds it up over the year.
You can compare with PVGIS, they seemed pretty close.
Numbers below are all in kWh, per annum
2. Solax inverter system
2a. PV Generation 5404, Self consumption 2837 61%, battery contributes 28%, Import 1858 Export 2430
2b. PV Generation 5404, Self consumption 3062 65%, battery contributes 31%, Import 1632 Export 2182 kWh ( has 2x battery.)
3. I used a Gen 3 Giv 5kW inverter with a 5.2kWh battery as couldn't get data for Gen2 inverter quickly. I used the trina vertex S not the S+ version.
3a. PV Generation 5670, Self consumption 2716 58%, battery contributes 24%, Import 1978 Export 2763
3b. PV Generation 5670, Self consumption 3054 65%, battery contributes 31%, Import 1640 Export 2369 (has one 9.5kWh Giv battery)
The panel generation is more for 3a but the self-consumption is less and elec import is more, in other words the elec bills will be slightly higher for 3 vs 2. (about 120kWh p.a. more, which ain't much, at 30p/kWh that's only £40 p.a., but it all adds up)
Why is 3a not reducing the elec bill more than 2a ?
Possible factors:
- Slightly smaller battery for 3a
- The discharge rate from the battery through the inverter has a limit, so at peak usage in the evening you may be importing from the grid, despite still having energy in the battery. This discharge rate limit may be lower for 3a than 2a.
- At peak generation some of the panels energy is 'wasted' as 3a has a 5kW inverter (AC output) and it's got up to 5.67 kWp going onto it, 2a has a 6kW inverter so doesn't have this problem
- the inverter startup voltage may be a factor, the lower this is then the earlier in the day the inverter can process the PV generation, and the better the system capability when its less sunny
There's about 330kWh more export for 3a, at 5p/kWh export that's a princely £16.50 p.a.
More battery improves self consumption as you can see. About 340 kWh for 3b vs 3a, so saves £110 p.a. which will escalate with inflation. Not much payback on the extra up-front purchase price though.
The real difference more battery can make though is in wintertime, when PV generation is much lower, in that you can store nighttime cheaper electric to use during the daytime. 5kWh of battery looks quite low for this, winter household electric use is 10-15kWh typically. Would be worth considering adding battery capacity.
Regarding panels, the less percentage degradation per annum the better, the higher the efficiency the better, the max kWp on the roof the better, its about getting the maximum generation density up there.
For me panel choice currently feels like a toss-up between
a) choosing cheaper panels with more degradation p.a. which might get upgraded in 10-20yrs time as technology improves efficiency and
b) choosing better quality panels now which will supposedly last 25-30yrs but are 50-70% more pricey than the cheaper ones. Scouting around, the difference is maybe £130 vs £210 so £80 a panel at wholesale purchase, so about £1100 difference now vs less savings later due to less PV generation. Where's the value for money point?
A degradation of 0.5% p.a. seems pretty common, so you're down to approx. 80% generation in 20yrs time. 14x 400W is 5600 kWp, so reducing to 4480 kWp in 20yrs, so there a reducing saving on elec. cost and a reducing SEG payback over time to bear in mind. Best panel degradation I've seen results in about 90% in 30yrs time IIRC, so you can do the sums for that.
You have the fixed cost of scaffolding now either way, and from what I've read on forums, replacing panels in 10yrs time may not be straightforward due to corrosion of the mountings. So which way to go? My head is telling me go quality, my pocket is telling me go cheaper, the head needs some more detailed sums to convince the pocket!
OK, warning, cynical mode active now...
How does a manufacturer test for 25yr panel degradation anyway? Is it worth the paper it's written on?
As for warranty, who knows if that company will be around in 10yrs time to honour the claim, or if the retailer, importer or installer will have gone bust. And does that problem panel or inverter or battery get a new for old replacement under the warranty anyway? Even if it should, is that item still made in 5yrs time? Is it compatible with your existing kit? Probably not. In which case are you up the infamous creek without a paddle?
There's also the eastern concept of 'face' in play potentially. According to one utubers reported experience a particular 48V LiFePO4 battery company was instructing new batteries with faults to be returned to retailer, repaired and returned to customer, not being replaced under warranty with a new one.
... cynical mode over.
Point is, does the manufacturer have an active UK-based support function and are they well-established?
Apologies, this has become quite a long post, and might have diverged with too much opinion, but hopefully there's something helpful in there for you!
