Other Any solar pv/battery ninjas in here?

Hey all,

I'm seriously considering having a solar installation with battery storage but it's a minefield out there. I've had what I *think* is a good quote financially, but I'm unsure on the spec of the system.

They've quoted 14x 440W panels (90% efficient) ~ 5500W, with a battery storage of 8.7kWh or a cheaper option of 5.6kWh battery for £9 less pcm.

Now unless I'm getting confused, it surely must be more beneficial to store as much as you can and use without drawing from the grid at all, right?

I've read that for a 6kWp array, it should have a battery of at least 12kWh. Does anyone know any better or can help me get my head around this and the reasoning?

Thanks in advance. Don't want to waste money spec'ing the wrong system and be stuck with it for 20 years.

 

How long is a piece of string........ it's entirely dependent on your usage.

Yes for not importing from the grid, but you may want to export, depend on your tariff.

For example, my "Intelligent Octopus Go" tariff gives me 7p/kWh overnight allows me to sign up to Octopus Outgoing export tariff which pays 15p/kWh for export. Meaning it is beneficial to only use the battery to not import, time-shift import to the cheap 7p/kWh but export without going through battery system and suffer conversion losses
https://octopus.energy/help-and-faq...t-tariff-can-i-combine-with-my-import-tariff/

With solar and battery, it's totally worth considering a time-of-use tariff. So you can charge up whilst cheap and not import anything when price is expensive. Using solar and a psudo-battery (using EV as home battery via V2H bi-directional charger, but unlike home battery, it's not connected 24/7) I am averaging 8 p/kWh when tariff cheapest price is 7 p/kWh.


Generally, the bigger your solar output, the bigger your battery need to be. I have a tiny 2.9 kWp system, so I only export 34%. But assuming same household usage with bigger solar output capacity, almost everything generated on top will need to go into the battery or the grid.

How much does your house typically use during the evenings in winter? The battery need to carry you mostly through a wintery day with just 2 kWh generated. BUT don't size for extremes, if it happens less than 10 days a year, it's not worth the up front cost.

Essentially, I'm saying size your battery for your household usage that covers 90-95% of the days throughout the year with solar generation taken into account.


Then there's question if your system allows you to plug in another battery in the future? Battery price is always falling.

Another key spec is inverter power. Assuming you are going for hybrid inverter, you'd need to look at typical house max power draw and size that accordingly.

In your very enviable situation, with such a big roof, I'd go for the smaller battery first provided there's option to plug more in later on. Sign up to time of use tariff with high export payment. Then gauge your needs from there.
But having said that, I'm currently considering GivEnergy AIO or Tesla Powerwall 3 as addition to my 9 years old solar system, it makes sense now that retrofit batteries is also 0% VAT from Feb this year. They are both 13.5 kWh, waaaay too big for my needs. But it's the cheapest way to get whole house backup power.

 

Thanks very much for the detailed reply. I missed out quite a few key details in my confusion/haste to get help!

House is very nearly south facing at the rear: 210deg. Roof is pitched and faces same heading. 48 degree pitch on the roof, no shade at all from any obstacles. They've spec'd as above - 14x 440W panels ~5500W

We don't own any EVs yet - no immediate plans either due to ownership and lease deals ongoing, but never say never hence battery considerations.

The energy plan we'll be switched onto is Intelligent Octopus Flux - we're already with Octopus but it's who the solar company recommend anyway so that's an easy change.

Our annual consumption is between 4500-5000kWh - partner works from home, small child = laundry, gaming, aircon etc...
House is heated with gas. Brand new high efficiency boiler went in back in Feb at the point of sale.

The solar kit we've been spec'd is:

14x Trina Solar 440W Vertex S+ Glass Bifacials
FoxESS H1 Hybrid Inverter 5kW
Fox ECS2900-H3 or H4 (8.6kWh or 11.52kWh)

We could stack another battery onto the H3 at a later date, as you suggest. Modules seem readily available, but would be at cost and not covered by the deal with SunSave (i.e. financed)

Deal comes in at £94 per month, nothing up front, for 20 years. Comes with 20 year guarantee on every part of the installation too.

Of note, that's less than our current monthly elec bill, hence why we're giving it serious consideration - particularly when energy prices are only going to go up from here, not down. It'd mean we pay a flat rate per month for 20 years, with the exception of low solar gen days for a few winter months.

Change anything from your advice?

 

So just to put it in context:

• 94*12*20= £22,560
• 14 x Trina Solar 440W Vertex S+ Glass Bifacials = £1148+ mounts
• Fox ESS H1 Hybrid Inverter 5kW = £762
• Fox ECS2900-H3 8.6kWh = £2,726.40
• Total £4,637
  
• Labour and other misc parts £17,923 (plus interest on the loan)

So firstly, I'd look at how much of that payment is interest and try to take a shorter term, as that seems like a steep price to pay!

Oh top of that, I wouldn't trust any of the aftercare or support, these solar companies have a habit of disappearing after a few years. The inverter and the battery have 5 and 12 year warranties, so that could be another £6,923.4 to buy new ones over the 20 years if they die out of warranty.

As I showed above, the parts cost is fairly minimal, so maybe right around some reputable electricians as a lot of them do solar installs too these days and see what they'll quote. Far more likely to be going over the life of the kit and you'll have a local person to go to for support when it inevitably goes wrong! Your mileage will vary with electricians, but worth exploring with this level of kit.

Also, from watching electrician youtubers (artisan electrics is great for all this) a lot of installs don't allow export, they'll usually only be for your premise, so its worth checking if this allows for export and if it doesn't scale accordingly.

In terms of the tech, the panels are fine, fairly mid/low cost ones. Ain't no LG Black's thats for sure! The inverter is an odd one as I thought the industry was moving towards micro inverters and AC systems for the efficiency gains. If memory serves, in chained panels like these will likely be set up, failure or degradation of one panel will affect the whole array. On the older panel tech even a shadow on a few cells can cause a power drop, so its weird you're not getting micro inverters. I'm guessing this one is cheaper. Battery is LiFePO4 so safe and good, will have tens of thousands of cycles.

 

Thanks for the info Pete. Yeah, it's not the cheapest option but it does reduce our bills from month 1, unlike taking a shorter loan which would give us higher bills for a few years before we're in the green.

This setup does indeed allow exports and it's set up for exactly that.

Not ideal but with us locked into a higher mortgage rate as we moved in Feb this year, it was a consideration for sure.

Will think on.

 

Totally, my west-west-north facing panel has shade in winter, expect almost nothing after 3pm around the shortest time of the year.

Excellent analysis by Pete.
That's quite a huge chunk of money, is there no interest free option?

My 2.9 kWp 10 panel 2-string system on 2 sides costed me £7000, should be cheaper now. I'm planning to spend another £7000 to install GivEnergy AIO 13.5 kWh with gateway for whole house backup. Solar I've got payback around last year to now. Batteries I expect payback in 10-11 years.

Try Heatable.co.uk. I'm planning to do 3 year interest free with them for the battery retrofit. Now is good time for interest free options for things already buying.

In your system, the hybrid inverter is key. If/when it fails, you'd loose both solar and battery. These are said to last around 10 years. My string inverter (not hybrid, don't do battery) is still okay at 9 years old but I'm expecting it to fail at any moment.

+1 on solar companies going under. My one went under about a year after FIT went away.

Remember there's still the ever increasing standing charge. Expect low but not zero electricity charge because it is a grid-tied inverter, and it will most likely react to load changes by looking at CT clamp. This means there will still be some constant small power draw, depending on how good the inverter is.

For Intelligent Octopus Flux tariff, the input rate is not as advantageous as Intelligent Go.
On one hand, this one only has a short expensive peak, so I would think a smaller battery able to last through it would be enough. Saving a bit on battery purchase.
On the other hand, you can do some maths for Go tariff at much cheaper overnight rate, see if you can have large enough battery to last all day.

 

I would echo the above that you're paying an extraordinary amount to reduce the initial outgoings, shop around.

 

Thanks folks, for all of the advice above. I've thinned them out and am now shopping around. Turns out even Octopus do a package with the same number of panels, a larger 10kW battery and micro inverters for £11k... I've no idea where the other £9k was going....

Still getting quotes at present but I may come back with a few more questions!! I appreciate the help, thanks again.

 

I'll be very interested to see how you get on, we have a south-facing roof which is gasping for some solar panels I think

 

I've looked at solar / battery etc. a few times but it always comes back to being a worse ROI than overpaying my mortgage

 

Well, we've decided to pause for now. Funding the panels through a standard loan wouldn't yield any return for quite a few years so we've decided to wait and see what Labour do for 'green funding'. Probably nothing, in which case we're no worse off and we've had a year or two to save considerably towards the cost and reduce the monthlies.

 

My advice given the current costs. Don’t.

I would look at GivEnergy, I’d look at their all one one hybrid inverter battery and then panels to boot. The kit is around £6.5-7k, the labour and scaffold rental will bring the price up to around £12.5k.

This is for a typical 12/14 panel arrangement with a built in 9.5kwh battery.

Even if you factor in a loan at around 7% apr you will still need to borrow over around 10 years to making manageable at which point nothing has a warranty and the battery/inverter is probably going to be on its last legs.

I have solar, EVs, battery storage, sell to the grid and everything in between.

I wouldn’t do it again now given the new electricity costs. You would be better off buying a battery and seeing if you can tie it in somehow and just charge it at night on a cheap rate ignoring everything else that you can get away with ignoring.

Food for thought.

 

Thanks for the extra input, appreciated!

We're looking at kicking it down the road 18-24mnths minimum, so maybe something will change. We live in hope...

 

I can show you how to wire the electrics so you don't pay anything..

In the spirit of modding, of course.

 

I've been saying this since the energy price hike. Get a battery to time-shift all consumption to off-peak price is most straightforward and works for everyone. ROI 5-10 years depending on cost of system, with 10 years battery warranty, I believe battery will continue to work many years after warranty expires.

ROI for solar depends on the roof, install cost varies hugely. But sounds like OP have the perfect roof for a nice return. I think key is financing in such a way so that it wouldn't become a debt burden.

 

and this is exactly the predicament. Our electricity bills aren't exactly horrendous. ~£100-120 per month, which when considering we have a child and a ton of laundry and my OH works from home 99% of the time... There's little benefit (at present...) to increasing our monthly outgoings for the next 5-8 years. Maybe I'll just hang on for my pension lump sum in a few years and pay for it outright.