PhilT

I think you are spot on and it's a very interesting observation on the motivations driving the battery consumer market

That seems to be a fairly common approach towards the cost/benefit of battery ownership.

It probably does but I wouldn't get too carried away with the apparent benefit. On Flux, every solar kWh you use to charge your battery before 16:00 costs you 24p, plus say 10% charging loss = 26p. If you then export it at the 16:00-19:00 peak rate 36p/kWh you only make 10p/kWh.

Did this happen suddenly just now? What are you reading from? Are you able to corroborate app data with solar generation meter and a rough idea from whatever mains/export meter setup you have? I had a glitch once due to a CT clamp being knocked out of position

I can't get anywhere near those outputs using PVGIS, what's your secret - are you in south Spain?

Not shingle, they are JA Solar 410W with optimisers fitted to all panels, two strings of 8 each going via an SE3000H non hybrid inverter (the one with the LCD display and 4 buttons), which are selling on eBay for not a lot of money. The winter months were interesting - I got nearly 600kWh in Jan+Feb, which seems like a good result given my roof surfaces have so many shading issues. The data monitoring by panel is a nice feature.

so at the time of this photo here is the snapshot from the playback data. In this graphic the right string of 8 is actually horizontal on my extension roof so top right panel in this graphic (39.22W) is actually top left in the photo and panel showing 166.9W is bottom left landscape in photo

My supplier quoted for one 6kW inverter but actually fitted two 3kW, so I could have split my roof and extension (the one in the photo) into 4 separate strings and therefore probably not needed optimisers. Hey ho hindsight

Was it worthwhile getting optimisers? Not sure. In this photo, taken yesterday late afternoon, the left panels where the vertical shade line is have dropped from 320W to 40W. Am I right in thinking that all 8 panels would fall to 40W without optimisers? If so, from the data playback function I worked out that this would have been worth c. 4kWh yesterday.

https://www.weather.gov/abr/frost_fall2012#:~:text=Because cold air sinks relative,the 2-meter thermometer height. "Because cold air sinks relative to warm air, and because the ground radiates heat very efficiently during calm, clear nights, the temperature at or near ground level can often be several degrees cooler than the temperature at the 2-meter thermometer height"

Is there anywhere on rear or side wall area where you could hang it up high like an air con unit. I nearly did this with a Vaillant offering (which I didn't go for in the end), as it would have been the only way to get around the minimum fire reg distances from doors, windows and drain covers, but I know for sure from that supplier that he installed a few in this way. This also has an advantage on very cold still winter nights when the air above 1m from the ground is a few degrees warmer - improved COP etc.

Absolutely right to be cautious about this, same for batteries, however some say the outlook for energy prices to be at least double the 5 year pre 2021 average until 2030 https://www.cornwall-insight.com/press/energy-prices-to-remain-significantly-above-average-up-to-2030-and-beyond/

PV great but do you really need batteries? Have you worked out the cost/benefit? If you are able to get any decent rate for export, a battery may not be fiancially viable. I know mine isn't and with hindsight I wouldn't have bought it

Not sure what you are disagreeing with. My battery works great too but with export rates so high, it currently makes no financial return on a commercial price of around £3k for a 3kWh battery and inverter, but if you can get one for a lot less then well done and good luck, and it could all change of course.

Largely agreed. Keep the decision about the battery entirely separate from the PVs and don't just accept it because it's part a commercial supplier quote because it's unlikely to be financially justifiable. Even "by far the best return" 21.6p/kWh comes nowhere near. With interest rates so high, perhaps a better use for one's hard earned cash would be a 10 year fixed term savings deposit. Unlike heat pumps and solar panels, batteries have little altruistic value except perhaps, as you say, grid load shift support.

🤢wish I was one of them. The only upside now is the possibility of keeping two fridge freezers and one chest freezer full of food from going off, and some lights on, in a (hopefully unlikely) power cut

I have this too. It happens with radiator systems. So we only run our hot water during the early afternoon, as it gives the best possible CoP, controlled entirely by the timer, so temp drop isn't relevant for us. 45degC is plenty but there are only 2 of us. Also we have the heating switched off between 11 and 6 at night, again mainly due to the background hum issue

If you go down the MCS/Export route think carefully about whether or not solar battery storage makes sense. Solar storage is not "renewable" or "green", being a net consumer of energy, not to mention the materials and energy used in the making. I have a 3kWh battery, which I could justify with the Cosy tariff, but no longer now I'm on the Flux tariff. I get 23p standard rate for every kWh exported. That means it's costing me 23p/kWh to charge my battery, plus 10% charging loss = 25p/kWh, so I only make (33-25 = ) 8p/kWh saving by using "free" solar energy. Now work out the payback on the cost of your battery...

One advantage of in-roof is no doves crawling underneath. I have this problem and it's a losing battle - may have to bite the bullett and get some protective mesh at some point.

One issue is the relative efficiency - most sources say in-roof panels are 5-10% less efficient because on-roof panels have a gap between the panel and roof tiles which allows air to circulate, keeping the panels at a lower temperature

What, that oversizing is a major problem? My experience is quite the opposite. Billt's video rule of thumb suggests a 5.6 but I have an 11.2 and so far (2yrs) it's performed way better than design. I think modern scroll comp R32 or R290 heat pumps are so much more efficient at low output than they used to be. Looking at my graphs for early May there wasn't much comp cycling. Most of the"cycling" is simply the pump running for shorter periods and the room stat switching the pump off for longer periods when target room temp is met.

Sorry if I missed this in your other posts but what system and spec did you go for, and how is it performing vs design etc?

So the 50p per 1.5kWh mentioned by ProDave above would actually be 38p, making it even less viable. And by the way the best standard export rate you can get currently is 24p per kWh which, if sustainable, makes batteries, generally, non viable. And I say this even though I have a battery.

What rate are you getting for export?

Varies enormously - time of year, time of day, peak startup or continuous, heating or hot water. My 11.2 draws anything from 1 to 7kW. More to the point, why the concern about the relatively small amount of draw from the grid in excess of battery power during the short start up times?