The Solar Thread

Also any idea how many kwh it takes to make a difference to hot water, we have a 300 L tank with 2 x 3 kwh immersions of which one is wired via the iboost, 0.83 kwh went to heating hot water yesterday (after fully charging batteries) which I’m guessing would have diddly squat impact on a tank that size?

Same set up here, 300l tank, 2 heaters.  We use about 1/2 tank a day (2 showers, a  bath and general handwashing). A daily input of 6 to 8kW is enough to serve our needs and not have the boiler fire up for hot water. The bottom half the tank maximises energy capture of sunny days, at least surplus from today does a bit of preheating for tomorrow. A maxed out tank will do 2 days even if tomorrow is dark heavy rainy day. I’ve seen the tank take over 20kWh from mostly cold state on a good summers day.

YMMV

@Surfer – that’s pretty much what I was considering as there’s not much in the way of alternatives.

The specific heat of water is 4184 Joules per kg per degree C. So a 300L tank is 300kg, to heat it by 1ºC requires 300×4184 = 1255200 Joules. A Joule is one Watt for 1 second, so 1kWh is 3600,000 Joules. Which means 1kWh will raise the temp of the tank by just under 2.9º, and 0.83kWh by about 2.4ºC.

THIS is why SI units should ALWAYS be used.

Also any idea how many kwh it takes to make a difference to hot water

@Witterings

My most helpful spreadsheet!

https://docs.google.com/spreadsheets/d/1SxnVJvlijlLh-v197njAT-U_5tF8v-Ymo6TeO5pHCKA/edit?usp=drivesdk

Hit a milestone last night – first 24 hours without taking anything from the grid (system went went in last December). Previously the best we’d managed was about 10pm…

Battery dropped to 20% before we started charging again and should achieve similar tonight.

1st 24 Hours Battery by Ben Freeman[/url], on Flickr

Another sunny day forecast for tomorrow.

We’ve done the last 3 days and that included charging the car for a few hours!  Average gain for the last 3 days has been over 17.5kWh a day and we’re still only generating a max of 3.6kW at any given point from a 5.4kWp array.  It’s like magic!

Any body have recommendations of companies who install around Worcester ?

It’s like magic!

Haha us to. Had a few sporadic days end of Jan when we lasted all day into the next charge period off a full charge during Eco7, then enough solar to get the battery at 100% by sunset. All depends on us using the oven or not or if we are out for tea or at the cinema during the evening. Still paying about £2 per day to fully charge the battery so it should be interesting during the longer days when we may not even have to do that and yesterday I fed back almost 5kW so I actually generated more than I used during that 24hr period which is a landmark for us. Being a net contributor at certain times of the year looks achievable.

@mmcd

I recommended the company I used on here a little while back and although they are based in the North West I was happy with the whole thing, including the price. I wont put the name on here but DM me if you want it. No idea if they will travel that far but worth asking, they can only say no.

Moving my question as suggested..

I’ve a lux 5k hybrid inverter.
it takes 8kw input but the output is 5kw. My panels are 6kw.

so on a sunny day producing 6kw what happens? Do I lose 1kw?

https://www.infinityinnovations.co.uk/wp-content/uploads/2021/01/Lux-Hybrid-Datasheet-3-5K.pdf

so on a sunny day producing 6kw what happens? Do I lose 1kw?

Yes.  You can have the biggest array in the world (kinda) but you will only get the maximum the inverter is set to output *

That said, your panels will not be producing the maximum that often so you’re better off (within reason) having more potential production than the inverter can output.

[Another person with an inverter that will output significantly more than the standard allowed!]

* unless a hybrid inverter can simultaneously send a max of 3kw to the grid and the rest to the battery …… I’m not well educated on hybrid inverters.

I’ve a lux 5k hybrid inverter.
it takes 8kw input but the output is 5kw. My panels are 6kw.

so on a sunny day producing 6kw what happens? Do I lose 1kw?

If you don’t have a battery, or if the battery is full, yes; if you do have a battery though, even if the inverter is producing 5kw AC it could still put 3kw above that straight into a battery.

In the UK a 6kwp system will likely not get much above 5kw so it’s probably a moot point, mind.

unless a hybrid inverter can simultaneously send a max of 3kw to the grid and the rest to the battery …… I’m not well educated on hybrid inverters.

Yes they can; we have a 5kw hybrid inverter on an 8kwp array but I’ve seen it accept 6.2kw, so I guess the battery was charging at full tilt and the rest was being used or exported…

Doesn’t the array usually run at full chat in summer?

Not sure I understand the point about the standard. If we run the kettle or hob and the fridge and a few pcs then the draw will easily be 5kw or more.

If I want to make the system work in a power outage will an isolator switch enable this or does it still depend on the inverter, I’ve no idea how I tell what mine will permit.

Doesn’t the array usually run at full chat in summer?

Not really, clouds, sun angle, losses within the system all conspire to lower production a bit.  There will be times when all the stars align and you’re maxed out, but it’s unlikely to be [# of panels] x [advertised panel generation].

Not sure I understand the point about the standard.

It’s more to do with what the grid infrastructure around you can handle coming in.

If I want to make the system work in a power outage will an isolator switch enable this or does it still depend on the inverter, I’ve no idea how I tell what mine will permit.

It’s not that simple.  Most inverters are grid tied – if they do not see a connection to the grid then they will not work.  It’s a safety thing.

Your system will have an isolator switch between the inverter and the consumer unit – switch it off (to simulate a power cut) and see what happens.

[Hint – the inverter is going to shut down!]

Quite excited. Getting ours installed in 10 days time by a company recommended on STW.

18x 405w panels (half east/half west) should give 7.2kw capacity or about 5250kw per annum on the model.

Also twin Lux Squirrel Pod invertors to give 7kw max draw (this is important to us) and 12.8kw of Greenlinx battery storage.

All links in dynamically to Octopus Agile for low cost charging from grid as needed.

Will report back after its up and running.

Nice!

I’ve been cursing my E/W array recently – they’re good in the ‘6’ summer months but fairly crap during the winter.

Hence why I want to add a further south facing 2-3kw ground mounted – that would be a great combo as the extended generation times of an E/W array is really good in the summer.

@chb that sounds pretty gold standard. I assume you need two inverters for just the reason I’ve noticed?

Apparently the lux hybrid inverter has seamless switching in 0.1s for UPS. No idea what that means in practice?

Hybrid inverters normally have an “EPS” Emergency Power Supply output that will stay active running on battery power in a power cut. Normally it’s connected to the mains like everything else, but in a power cut it will, after some delay, be isolated from the mains and connected to the battery instead.

Installers often connect a socket to this; theoretically you can have house circuits moved to it permanently or using a changeover switch but it’s a faff, expensive, there will be complications with earthing (you can’t rely on the mains earth in a power cut) and probably not worth the effort. During a power cut you can still power things from this if the battery is not empty, and the inverter can still charge the battery from solar. It just won’t export anything or run the normal house circuits.

The rating of the panels in “kwp” assumes perfect conditions such as sun shining square on the panel (which it won’t be very often or at all) while the panel is cold (which it won’t be if it’s that sunny). I think the actual peak is normally about 80% or so of the nameplate rating.

any recommendations south of london? need to get some panels put on as part of an extension

Is the expense the change over switch and earthing?

Does the earthing need not apply to the standalone socket too?

Does the earthing need not apply to the standalone socket too?

Yes but it’s considerably easier than a change over switch to implement correctly .

Mine is AC Coupled, so has three inverters. One for the panels and a dual/twin (think its two separate boxes but not sure) for the batteries. Each Lux Squirrel Pod can output 3.5kW so there are two of them (each with two 3.2kW Greenlinx batteries).

It does mean that to charge the batteries the you go from DC-AC- DC so marginal losses, but it means panels and batteries can run independently and top up from grid to batteries is automatically scheduled.

Hi, can someone please just put up link of 250-300L unvented water tank that can be used for future, if solar panels are added? So many tanks out there my mind goes blank!

I have to upgrade whole heating/hot water system, Currently combi but seems a tank would be better for future if we want solar. Also house will have 3 bathrooms fairly soon. Ta jon

I think you just need a cylinder with a direct means of heating (immersion) either as the only means or if you want to use the boiler as well then you need an indirect cylinder with an immersion which I think is almost all of them. Having two immersions one top and one bottom will enable a smaller amount of water to be heated, whether this is helpful or not depends how you use the 300l I think.

If you plan to have a thermo solar panel rather than one that generates electricity (pv) then you will need a twin coil cylinder.

Mains water pressure cylinders are referred to as unvented.

Thanks James, I think will be one that just allows 2 immersions? No need for thermal (I believe thats not really a thing now). Still would love a link as so confusing? Ta

the battery instructions for my solar batteries note that the voltage difference must be less than 100ma. Whilst this might be the case on day 1 presumably this might not be the case in the future..

So we’re up and running now.

I wondered though, is there any way to sense check whether everything is working as it should do and for example one of the panels isn’t duff? I’ve gone for optimisers so I’m guessing one or two having a problem won’t bring the whole lot down.

I have more questions..

my battery is apparently 47pct soc (so I assume around 2kwh as there are two batteries with 2.2kwh usable capacity each). But I am importing a few hundred watts from the grid. Why might this be?

But I am importing a few hundred watts from the grid

Unless you are exporting then all systems use a small amount of grid power but it should be around 40w per hour. A few hundred seems excessive.

I wondered though, is there any way to sense check whether everything is working as it should do

depends on your manufacturer and the software they provide. I have a Foxess system and the supplied software isnt particularly sophisticated so I installed Home assistant which provides very detailed data.

Hi, can someone please just put up link of 250-300L unvented water tank that can be used for future, if solar panels are added? So many tanks out there my mind goes blank!

I am upgrading my tank (vented) and I have an iBoost solar diverter which will support 2 immersion heaters. I also have a gas boiler which we use for heating water in the winter. 250-300L seems very large. I am looking about 150L.

Try these Gledhill

Is home assistant an app? Do you have a linky?

I’m not sure if the solar set up is using 400w I think it is just the gubbins in the house like fridge, pc, stuff on standby. It was more why hasn’t the battery dropped to something like 10 or 20 pct before calling on the grid. They are 90pct depth discharge I think so would have thought they would approach 10 pct?

depending on the invertor sometimes it will “balance out” a little and show it pulling from the grid. Also i have a luxpower and they say just use it as a guide. The data is meant to be viewed historically an sometimes when you looking at the instantaneous bit it can show some strange figures. 99% of the time though its right.

Andy. Do you have an app other than the lux one?

@muddyjames

There is a minimum SOC that you can set within your battery config. I suspect you BMS will set that at around 10-20% to protect the battery and wont let you go lower than 10%.

I run Home Assistant on a Raspberry Pi and its easy to download HA and and set it up using an image. Have a root around here for the one thats right for you Home Assistant

I connected my inverter to my network using an Ethernet cable (bit of fiddling around on my Mesh network) and the Pi was able to connect directly. running the cable from my garage was the hard part. HA is a good bit of software and I am particularly keen on estimating my payback. HA allows me to do that very accurately. For example (with a bit of spreadsheet work) in February alone, so far, I estimate my electricity savings to be £105. With the lengthening days that is increasing day on day. So far very pleased with the outlay.

@5lab I’m not sure where you are south of London but we used Home Smart Energy based in Burgess Hill for a 3.6kWh 10 panel, inverter and battery installation last year.

Muddy@ out of interest how big is your battery and what sort of cost was that?

@muddy@rseguy thanks, we’re just round the corner in Hassocks, I’ve been on a few muddyarse rides in my time as well (back in the day)

There is a minimum SOC that you can set within your battery config. I suspect you BMS will set that at around 10-20% to protect the battery and wont let you go lower than 10%.

Ours is set at 5% by default, but you don’t actually know what that is 5% of as in what the minimum cut off voltage it, so it could still have plenty of margin or be very close to cells being exhausted…

Huawei system.