New Solar & Battery Install

swanny65

We are fortunate to have had a small cash windfall. Having discussed solar/batteries with a sell builder/house renovator friend we trust, we have decided now is the time to install solar panels and batteries as; we use approx 4500kWh electricity a year (we have a hot tub we use April/May-Sept/Oct); our gas boiler is 13 yrs old (will replace with a Heat Pump later / when it dies); our pressurised cylinder is 25 yrs old (again will replace with the boiler / when it dies); our next car will use batteries (we current have a petrol car). We have underfloor heating - if I am correct a Heat Pump will satisfy our heating demand. Thats my thinking…..

Our friend and several other properties in their village have used a local company, to be honest if they are good enough for him they are good enough for us. They are MCS certified.

We had an initial fully installed quote of £8500 for 12 × 475W AIKO Solar Neostar panels on our garage roof; 11kWh SolaX Power Batteries and a 5kW SolaX Power X1 inverter.

However after a site visit yesterday we need to install the panels on a second roof as the garage can only take 9 panels. This is good in that the second roof is south facing and will take extra 6 panels (15 in total). I was told will need a second inverter. I also wanted to increase our battery storage and 14.5kWh was agreed. All this will be connected wirelessly to my meter - I dont want to dig up my garden and patio to connect to the meter which is 30-40m from the inverters/batteries.

A few questions:

1. Power cuts - forgot to ask about auto switch over to batteries. Is this a nice to have or an essential? Any idea of the approx additional cost?
2. On costs - how does the initial quote look ? What ball park figure should I aim for after the site visit……
3. Tariff's - confused ! Currently I am tied in with OVO on an extended fix that started 31/05/2025 and ends 31/08/2026.
   1. Can I feed back generated solar electricity to OVO on this tariff ?
   2. I pay a £75 electricty exit penalty and move to a different provider. Our friend is with Octopus and gets 15p per kWh. OVO link https://www.ovoenergy.com/seg here indicates I would get 12p per kWh. So in the short term stick with OVO
4. Apps - is there a go to app. I know I will need one but the thought of setting up an app is daunting, might need my friends help !
5. Anything else……..

Apologies for the long ramble, downloading everything in my head ! and thanks in advance for taking the time to read.

Screwdriva

Sorry to share, I believe your installer is misleading you. You do not need two inverters - you need a single 7kW inverter with 2 string inputs.

For perspective, installers I use now offer 15 X Eurener 515W bifacial panels (vastly superior to the Aiko you have been quoted) paired to a Tesla PW3 for just under £12K installed. Don't forget the Tesla rebate on offer for another few weeks (£375),

That's a larger 7.5kWp system with 13.5kW of usable storage, offering whole house backup, superior software, aftersales support and best in class reliability and cold weather performance. I would cast a wider net if I were you.

Martyn1981

Hi. Not suggesting anything wrong with your plans, but several things you mentioned all made me wonder if a Tesla Powerwall 3 battery might be a good/better choice for you.

Combined with a Tesla Gateway device this can shift the house over to batts (and solar) during a power cut, and as it has multiple MPPT's (maximum power point trackers) it can handle several arrays that have differing orientations, and sizes, without the need for any additional inverter. In effect, all the panels, from several arrays/roofs, can all feed directly into the same PW3.

Sorry, I know you didn't ask about this, but you could consider longer term going 'heat pump light', with the install of A2A units (air to air HP's, think air con units). There's also a HW tank with built in HP, that can also run a small underfloor heating circuit. Put these all together, and it may suit you well, or not, just mentioning it, as I now heat my house using two A2A units. Recently a £2.5k grant was introduced for the A2A approach.

The combination of PV, batts, HP's, electric car and cheap rate leccy, can work as a nice package, all leaning on each other to improve the whole (greater than the sum of the parts). Our annual leccy bill now looks to be about £600pa (2 people, 3 bed semi), with PV export income of about £600, so approx zero energy bill for everything (normal leccy, DHW (domestic hot water), cooking, heating and two BEV's (approx 12,000 miles pa)).

swanny65

https://forums.moneysavingexpert.com/discussion/comment/81878551#Comment_81878551

Thanks, really helpful. Happy for you to name here or PM me a recommended installer(s).

Please correct me if wrong. The two roofs are about 10m apart and on buildings on different levels. I think joining the two sets of panels will still entail digging up some of the garden / patio / retaining wall / steps to connect the two sets of panels to one inverter in the garage - hence two inverters. The armoured electric cable supply to the garage was laid from the other building, next to the footing of the retaining wall and through the garages concrete floor. Apologies could have been clearer earlier.

Thanks again

swanny65

Thats what i am targetting 😁 We have UFH throughout our property - cant recall the total pipe length but there is a minimum 9 x 100m loops.

Thinking my properties layout, as mentioned in the reply above, makes the one inverter problematical……

Screwdriva

It is remarkably common for different roof aspects to be on different elevations and/ or face different directions with distance in between them. The Powerwall 3 has 3 String inputs and can be connected to 3 different roof surfaces with little difficulty while remaining situated in your garage.

Having 2 inverters means twice the failure points (not to mention Solax is vastly inferior) compared to the PW3. Feel free to DM me and I'll do what I can to help!

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/81878703#Comment_81878703

Hiya. Ineresting points. Always got to be careful about commenting on something from just a brief description, v's the full knowledge of the person concerned, but I'm not sure I'm seeing the same problem.

So, first off, if you have two separate arrays connected to two separate inverters, they will still need to run their AC side cables back to the consumer unit (a single point).

So I'm not clear how that differs to running the cables from the PV, to a single point, such as one inverter with an attached battery, or a Tesla PW3 (battery and inverter in one)?

Whatever the route the AC cabling will take, can't the DC cables from the PV take the same route? I suspect there's a good reason(?), just one that you know that needs a bit more explaining.

However, DC cabling from panels is actually very small cabling, and can be easily housed in 'discreet' plastic tubing. I have a small ground array, and the cables travel ~12m from panels to inverter across/around the garden. So it might be possible for you to pick the preferred location for the inverter/battery, favouring one of the arrays, and then bring the DC cables from the other, to that location. [I'm guessing that you are concerned that one of the arrays would have to travel all the way (not half the way to a mid point) back to the 'better' location (the garage)?]

Don't worry, we aren't arguing with you for fun, or trying to be critical, just thinking through the options, in order to find the best solution for you. One inverter makes life easier, cheaper, and probably more efficient. Also, may complicate approval from the DNO (district network operator), as they will want to add the two inverter sizes together, whereas a shared single inverter, especially one like the PW3 that can be limited in export terms, may be lower, and easier to get approval. But if it's not possible, that's fine. Just don't worry too much, yet! 😉

Ohh, another thought, if you really catch the PV bug, like me with 4 distinct arrays, then the PW3 with 6 (I believe) MPPT's, would also allow for further expansion, and not require DNO approval/notification if the output isn't changed, regardless of how the input (kWp of panels) does. Maybe some wall mounted panels on the garage …….

Qyburn

https://forums.moneysavingexpert.com/discussion/comment/81878866#Comment_81878866

So, first off, if you have two separate arrays connected to two separate inverters, they will still need to run their AC side cables back to the consumer unit (a single point).

OP mentioned existing SWA to the garage. IIf the garage has its own DB and the SWA is suitably rated, the inverter can connect locally in the garage with no new AC cable needed. That's the arrangement that we have.

If installing a battery in the garage there will need to be some form of signal cable back to the incoming supply so the battery or its controller can sense import/export. Again that's what we have.

NedS

Longer runs of DC cable will require thinker cabling to counteract any voltage drop (which slightly increases the cost), but your solar installer should be aware of this. I see no issue with 10-20m runs of solar DC cabling from array to inverter.

Ohh, another thought, if you really catch the PV bug, like me with 4 distinct arrays, then the PW3 with 6 (I believe) MPPT's, would also allow for further expansion, and not require DNO approval/notification if the output isn't changed, regardless of how the input (kWp of panels) does. Maybe some wall mounted panels on the garage

Slight correction to the above - whilst the PW3 does indeed have 6 MPPT's, the UK specification only has 3 available as they are paralleled into pairs (3 pairs) in the UK model, allowing more panels per MPPT string.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/81878891#Comment_81878891

I think I'm following that idea, but do you mean the leccy from the other inverter has to come in as AC via the household main CU? So an AC side battery picking up the excess from the two arrays, rather than a DC side battery? That might explain what I was missing, as i was trying to get the two DC supplies to the same common point.

@NedS. Thanks, didn't know that, and I suppose makes sense, after all, what sort of idiot what have more than 3 distinct PV arrays …… (where's the whistling emoji when you need one?)

NedS

@NedS . Thanks, didn't know that, and I suppose makes sense, after all, what sort of idiot what have more than 3 distinct PV arrays …… (where's the whistling emoji when you need one?)

I think it is partially related to the fact that roofs in the US can be more complex (more aspects) than roofs in the UK (where 3 MPPTs was deemed sufficient for most homes), but also to do with the peak current output of modern solar panels - by paralleling two MPPTs, they can handle higher current panels.

A single MPPT can handle 13A max, or 26A max where two MPPTs are configured in parallel as with the UK spec PW3. I note my JA 450W solar panels can produce 13.7A, exceeding the 13A limit of a single MPPT.