Grid tie inverter with limiting for UK use?

[megatron-uk]

Hi folks,

Starting to dip my toes in the water of building a DIY solar system to offset some of the base electrical load of our property.

At the moment I have a liberal spread of power monitoring sockets (Tasmota based, from mylocalbytes) around the house at some of the hot-spots to identify what is using power, as well as an Efergy Elite monitor clamped to the main meter. I'm capturing both sets of data (the Tasmota sockets over wifi, the Efergy meter and some legacy Energenie devices over 433MHz radio) using a Pi, logging 5 minute averages and graphing results on a regular basis.

As a result, I have a fairly good understanding of what my average base load is throughout the week, for the morning, day and evening. I mainly work from home, with the odd day in the office, my wife is the opposite of that.

I'm looking at an average, daytime base load of around 350-400w. That comprises my workstation and network equipment, fridge/freezer, two small fish tanks, battery chargers in the garage trickle charging a car, and other assorted electronics going (radio, speakers, phone chargers etc).

I'd like to be able to offset as much of that daytime 'chunk' of load as possible with solar. I am not interested in trying to sell back additional capacity, nor am I (at this time) looking to have battery storage. I want to maximise the impact on my daytime use as cheaply as possible.

I was considering a small pv setup of perhaps four second hand 220-250w panels, along with a small inverter/controller of between 1-2kW.

Initially I was interested in the SUN GTIL-1000/2000 because of the grid limiting functionality, and the ease of installation.... but I understand that these are not compliant with UK legislation, since they do not meet any of the recent specs.

Is there a cheap option in the 1-2kW range, with MPTT, grid-tie features, with export limitation that meets UK specs? Ideally, to keep things simple, I don't want to have to worry about feeding anything back into the external grid.

Realistically, I want to do this all DIY, and including all equipment, don't really want to spend over £1000.

 

[eXodus]

First - it's amazing that you have such a good understanding what your usage is. Most don't

If you don't want to have anything feeding in, you almost need a Battery system.

With any grid-tie inverter even with limiting features you risk exporting to the grid. So depends if you want to do this under the radar or if you want to pull permits and do everything according to specs.
The utilities know when you install a grid tie inverter behind a smart meter. Even with Zero export, they maybe choosing not to do anything about it. But they certainly know from the data.

You got some conflicting requirements here, if you want to offset your load without troubling with the utilities - you need a Hybrid Inverter with batteries which can also charge from the grid. The utility side would be - you plug it into an outlet and always only consume power - never send back.

You can build a small battery system under 1000 - which could run maybe your fridge and few other things. Since you got all the data - pick a few devices which draw most of your baseload and connect those to directly to the battery solar system. Configure it in a way that it only recharges from the grid to a certain point in the morning - so that you can take advantage of solar for most of the day.

 

[megatron-uk]

Thanks for the info - if I had the opportunity to do so, I think I would seriously consider a stand-alone battery system and save all of the (potential) headaches associated with feeding back into the grid. We recently (~2 years ago) had our house and garage extended, and in hindsight, that would have been the ideal opportunity to do something like this; dedicated 'battery' circuit sockets, and things like that. As it was, we really didn't pay any attention to it, as our power bills were not huge at the time... times have changed so quickly!

At the moment our house is still on an old-fashioned rotational meter - we've resisted having it replaced for a number of years.

Realistically, without a significant amount of rewiring within the house, I don't think a dedicated set of battery-circuit sockets is going to be an option.

I believe the UK regs state that I need a G98 grid-tie system, but these only (as standard) offer a means to set a fixed upper limit of power you feed back into the grid, so they don't use the current clamp to dynamically adjust the amount of power fed into your home circuit based on load/pv generation. The latter appears to be a fairly rare option, at least on budget, UK-regs-meeting devices :-(

 

[SeaGal]

I believe the UK regs state that I need a G98 grid-tie system, but these only (as standard) offer a means to set a fixed upper limit of power you feed back into the grid, so they don't use the current clamp to dynamically adjust the amount of power fed into your home circuit based on load/pv generation. The latter appears to be a fairly rare option, at least on budget, UK-regs-meeting devices :-(

Good to see other UK DIY installs. You _will_ need a G98 compliant inverter for connection to your house system. These grid-tied inverters (mine is a Solis) will automatically supply your house load up to the maximum solar power being generated, before they export any to the grid. So, if your base load is 400W, then if the solar output is 400W or above, all your house load will be 'free'. Any excess above that will simply be exported to the grid (unless, of course, you have a hybrid inverter which will charge batteries with any 'spare' power). You don't _need_ to restrict any export to the grid, as under G98 regulations you are allowed to export up to 3680W (16A). Your DNO will need to be notified, but this is a simple process done within 28 days after commissioning - i.e. shouldn't have any "headaches associated with feeding back into the grid".

If you can stretch to a hybrid inverter and batteries, that would be better, but you're looking at several 1000 GBP for such a solution.

A cheaper option (if it suits your lifestyle) would be to have an immersion diverter installed that can use any spare that would otherwise have been exported to heat up a hot water tank if you have one.

Bear in mind though, that you'll only get around 10 - 15% of your panel's kWp rating on a cloudy day, so if you can afford a few more panels, that would be good.

 

[SeaGal]

P.S. Just to add, something like a basic Solis would sound idea for your setup. And IMHO there is no point trying to restrict excess export to the grid unless there are technical reasons why you need to. In fact, I'd say it is better to not restrict... If you have an export limit running then, when your house demands more load (e.g. when you put a kettle on, or a fridge switches on) it takes the inverter a few seconds 'notice' the change and increase its draw from the PV panels, so you loose a few seconds of self generated power. If, on the otherhand, the inverter is running at the max possible all the time, then any extra load will automatically be used immediately (as the voltage from the inverter will already be higher than the local grid voltage). Hope that makes sense.

 

[megatron-uk]

That sounds more promising - I wasn't aware that the regulations permitted the export to the grid as long as you had a G98 complying device. I was assuming that any export at all would need agreement with electrical supplier etc. I'd rather not have that complication.

I have read about diverting unused pv power to an immersion heater and it would make a lot of sense to put that unused power somewhere... but we don't have one; no upstairs tank and all hot water is from the gas combi boiler.

My mounting surface is likely to be the rear of our garage - it points south west and we get sunlight from around 11.00am through to early evening. I did consider the possibility of mounting 4 (for example) panels on the rear of the garage roof, with 2 on the front for early morning capture... but I'm not sure the (admittedly minimal) cost of a couple of panels on the front and the gains from them would offset the cost of a potentially more expensive twin-string controller/inverter.

Looking at Solis, they appear to have G98 rated mini controllers in the 1-1.5kW range for £350-£450 range. With approximately the same again on perhaps half a dozen older generation panels, that could potentially bring me to around £1000 with a controller and perhaps half a dozen panels.

 

[SeaGal]

... I was assuming that any export at all would need agreement with electrical supplier etc. I'd rather not have that complication.

No, but you won't get paid for it... think of it as your donation to the greater good

You will need to comply with IET Wiring Regulations and Building Regs, Part-P for physical connection of your system to the consumer unit / grid. This _may_ involve getting a sparky to do the final connection, but that depends on whether your house's particular wiring. The DNO only need to be told about it afterwards, but you will need to provide them with a schematic of the installation to show it has met the necessary requirements. These include having a lockable isolation switch and suitable labelling etc.

More G98 info can be found here..https://www.energynetworks.org/operating-the-networks/connecting-to-the-networks/connecting-generation-to-the-electricity-networks and the inverter will need to be on the type register.

 

[megatron-uk]

Great stuff. That is really helpful. My installation plans involve having the inverter installed within our extended garage, which was all rewired and subject to sign off as part of the recent building work - so hopefully any additional work for this would be minimal, and as you say, could potentially just be a sign-off of the final connection to the consumer unit/grid. I think I am reasonably technically savvy and am willing to pretty much do all of it myself and just get someone to sign it off.

 

[eXodus]

You could just make everything legal, tell the utility what you do and you should be fine without battery.

Its a optimization problem, you can either invest into batteries and rewiring the house or into permits and a licensed electrician to hookup a grid tied inverter It depends on your specific situation what is best.

Do what you are doing here - ask lots of questions and try different ways.
European Energy prices are going to go bananas in the next few months, I would consider investing a bit more.

 

[megatron-uk]

I agree - I don't think the energy market is going to settle any time soon...

 

[megatron-uk]

Found quite a few Solis inverters on ebay, either new in box, or used, and the newest ones with G98+ compliance appear fairly cheap (£200-£400 for 1.5-3.5kW).

The question I've now got is whether to spend a little more on the (non mini) S6 Solis range, and get a dual MPPT controller, or stick with the more basic (mini) S6 series with just a single MPPT controller. Both ranges appear to have remote monitoring/metric functions, both are UK regs compliant, and both are available cheaply second hand at a variety of power ratings from 1kW up to 3.6Kw.

I guess I need to figure out if I have any potential advantage to two runs of panels - but there isn't really an option to have them arranged with much difference between them. The main roof our our house is a 4-sided hip roof, so the opportunity to mount any panels there is almost non-existant.
The only options I have are the north-east facing garage roof (which only gets sun for an hour or two early morning), or the rear facing garage roof and roof of the ground-floor extension, all of which face the same south-west aspect.

The only real difference that I can make on the rear mounting option is how high up the garage roof the panels are fitted (I can get two rows of probably 3-4 standard sized panels), and whether to extend a small number of panels along the narrower ground floor extension (likely 2-3 panels maximum, as I have to avoid a skylight and two roof vents above the kitchen).

The rear aspect of the house looks like this, from left to right, and gets sun from approx mid-day onwards (obviously varying depending on time of year):




The front mounting options are clearly a non starter due to the facing: