Tessa Power Wall

Alan_Brown

One for Martyn I guess, as he has experience of multiple orientation solar arrays....

I was looking at expanding our solar installation by adding panels to a couple of buildings in the garden. I estimate that I could get 1.8kw on one building and maybe 0.5kw on another. They face in different orientations and have different power outputs, so I'd need maybe 2 inverters.

I already have an east/west 4kw array. I was wondering if all of these could feed into a bank of power wall type batteries and then feed into the inverter as a single feed?

I understand there is an issue with the feed in tariff, but as I have had zero this first year due to a problem with my meter, I'm actually quite happy to just focus on going off grid than any income from the panels.

There is also a possibility of fitting a ground based solar array in the garden that could also supply the batteries, if this is all feasible.

Is it feasible?

Martyn1981

Boy! I read that and my mind spun to about 5 pages before I could hit reply.

So let's start slowly, and remember this is just my ponderings, mostly based on info and advice I've read from others.

First thought, extensions don't qualify for FiT anymore, going to have to burst the bubble .... but you covered that at the end, before I had to break the bad news. So, so long as you are aware of this, keep going.

Multiple arrays and ground mounts, could all be linked via a SolarEdge system, assuming they aren't too far apart. Or, as you say garden buildings, maybe micro-inverters if access is easy, bringing several AC cables together into a junction (perhaps a small consumer unit) before wiring the single output to your main consumer unit. Or, go with multiple inverters, the prices of some of the cheaper, smaller units, with 10yr (I think) warranties are quite low, then, again bring them together into a small CU.

Shame the Swithenbanks site has closed, that was such a great source of multiple information on inverters etc.

Next batteries. Presumably you could feed all the new systems directly into a battery bank as DC, but you'll need good advice on that, and presumably they'll have to go through a charge controller.

If they can all connect to a single SolarEdge inverter, then that would work well, as generation in excess of your demand would be diverted to the Powerwall as DC, so it only goes through the inverter (suffering losses) once.

But, if you have lots of multiple feeds then it might be better to have an AC side battery. This will operate a bit like the Immersun's etc, diverting export AC into the battery. This does mean the leccy goes DC - inverter - AC - CU - inverter - DC - battery - inverter - AC, but you'd have a single system linked to all of your PV and excess.

Moving on to off-grid. I'm going to assume you mean minimising import, rather than full off-grid. To go full off-grid you'd need PV and batts to deal with poor periods, rather than average periods, and a back up gennie.

In an ideal world an average amount of PV and batts would work, but you'd have to scale up just in case. Also, I assume this would impact your current FiT, plus your existing inverter wouldn't work as it's a grid-tied model.

Going off-grid may make sense if the cost of connecting to the grid is high, or not possible, but as you are on-grid, you won't benefit from the savings. However, you can go 'off-grid light' by switching to a no standing charge account. That way you only pay for the leccy you buy (at a higher price admittedly) but don't have to over scale your system.

Problems - DNO - will you get permission for potential export based on the sum of the inverters output?

Possible solutions - you can't really move yet, as the battery prices are very high, but that gives you a few years to watch, wait and learn. If the DNO give you permission, and you're happy to add an AC batt system later, then you can still go with the PV, and reduce your import.

Whilst waiting for the battery prices to come down, start researching some of the export capping (NOT generation capping) technologies that exist. I think the industrial models are called something like EMMA GVS, but SolarEdge or SMA might be developing something themselves.

What these do is cap export to within an agreed limit, so let's say you can't exceed 3.68kW, rather than cap the inverters (generation) at 3.68kW, it'll take into account on-site consumption. So, imagine you are consuming 1kW and diverting 2kW into a battery, then the inverters would start capping at 6.68kW, when export has reached 3.68kW.

This tech does exist, and some DNO's already allow it, but on a domestic scale it's still early days, but worth reading up on, or contacting your DNO directly to ask for info, thoughts etc. be warned though, some DNO staff may not know what the bod on the other side of the desk knows, as things are still changing/developing so do some homework first.

[Edit - ground mount may require planning permission if more than 9m2. M.]

Best stop there. Happy to elaborate, though you may need someone on a higher pay grade to go further!

Mart.

Alan_Brown

Brilliant info as always, thanks Mart. I'll have a good read and do some googling to look at the various options. I'd assumed that the panels go into the power wall as I looked at this image, but it's obv. not as simple as that.



I know it doesn't all add up financially, but we're so incensed with the governments decision to go ahead with Hinkley Point and fracking in Lancashire that we just want to get off grid so we're not part of this madness. :mad:

Martyn1981

Hi. The SolarEdge inverter decides if it wants the PV generation for inversion, and if not, redirects it to the battery, as DC. So it's pretty clever.

To go off-grid it gets a hell of a lot more complicated, and you need an off-grid inverter.

Hard to go off-grid in the UK without some wind or hydro input. But they come with their own problems, and most sites (like mine) aren't wind friendly due to turbulence from other buildings, structures, trees etc.

If you really want to go off-grid, then join some forums and chat. Lead acid batts are cheaper, but you'll need to learn where to buy a big bank, as individual prices are high. Lithium is more expensive but you can buy less as they can be discharged deeper without damaging them, so let's say 25kWh of Li-ion giving you 20kWh useable at 80% DoD (depth of discharge), v's 40kWh of LA's giving you 20kWh at 50% DoD.

Counter argument is that the LA's would give you 32kWh for the occasional 80% DoD in extreme situations.

So loads to think about and learn, and I suspect different off-gridders will argue for the battery technology and type that they use.


I salute your motives, but consider a counter argument. As you are already on grid, if you over produce, then your excess helps to reduce demand on the grid (almost certainly gas generation). So you can be part of the solution, simply by being a net exporter of leccy. Here, Wifey and I generate around 4,200 - 4,600kWh pa, but consume about 3,000kWh, so we are a net exporter of leccy.

You can also invest, via Abundance or similar, in PV, hydro, wind schemes, possibly matching almost all of your consumption, to some generation somewhere at the same time(ish).

This is a big issue, but if you are willing to wait and watch till 2020, then the options and prices should improve massively. Hope this doesn't confuse (it sort of makes sense in my head) but whilst I'm willing to jump into the battery world a bit early (but not yet) and perhaps lose a bit of money across the lifetime, I'm wary that the system losses will mean a net reduction in export/offset. So I lose a bit of money, and the UK grid loses a bit of leccy.

However, it gets more complex, because if the batts help to shift some of my daytime export to reduced evening import, that might be ok, as the average CO2 levels of UK generation rise with demand as more FF back up comes on line. But counter counter-argument the peak is coming down ..... Nothing simple here, but fascinating .... to me.

Mart.

zeupater

Alan_Brown wrote: »

... I know it doesn't all add up financially, but we're so incensed with the governments decision to go ahead with Hinkley Point and fracking in Lancashire that we just want to get off grid so we're not part of this madness. :mad:

Hi

No matter what the idealogical position on nuclear power is, Hinckley-C is a ridiculous waste of money and an unnecessary diversion of both focus and resource which can result in little more than more expensive energy being forced on the consumer .... the deal should have been renegotiated or cancelled.

As for fracking, well the negative issues are certainly being overhyped by many at the moment. Basically it's simply employing the same technology as water-supply boreholes which you can find all around the country, just accessing far, far deeper deposits of gas. If there are worries on toxic chemicals, well, what are they and how toxic are they ? ... input from a previous discussion thread ... http://forums.moneysavingexpert.com/showpost.php?p=63333679&postcount=30 ... so then there's decarbonisation of energy - well, yes we need to do that, but ..... an example, with the fracking decision being on the news yesterday one of the 'usual suspects' (Caroline Lucas) was giving a sermon on fracking, nuclear, wind, solar, generation decarbonisation and how apocalyptic the gas decision was, however this completely and conveniently missed the obvious elephant in the room, yet no-one else seemed to notice ....

So what is this elephant that is being so conveniently ignored? The average household in the UK uses gas for heating and buys around 4x more energy (kWh) in the form of gas than the do electricity per year, so don't worry about so-called 'experts' and ideologists on TV concentrating on and moaning about the climatic impact of utilising gas for generating electricity it's simply a case that with currently installed heating technologies, 'no gas' means 'no heating' ... why do I mention this?, well it looked like the sermon was being made over a video-link from the dining-room of a domestic property which, looking to be pretty cosy, almost certainly, would have GCH (anyone else see a degree of hypocrisy here ?).... furthermore, what's the climatic and economic benefit of shipping LNG half way around the world when it's on our own doorstep - trade deficit anyone? - every pound sent overseas is a pound less (+multiplier effect) invested into the UK economy ...

As is normal on many cases involving energy, the NIMBYism and mainly unfounded ideological positions of a very vocal minority can certainly hurt the pockets of the majority they claim to represent the view of, often also being counter-productive to what they claim to want to achieve.

Logical myopia needn't be contagious !

HTH
Z

Ectophile

Your biggest problem going off-grid with nothing but solar power is that you'll be left sitting in the dark in the depths of winter.

As the days get shorter and the nights get longer, you may find it only takes a couple of grey gloomy days before the batteries are flat and you have no electricity.

You need some plan as to what to do when that happens. A petrol generator may be the answer, but it's not very green.