The Solar Thread

I’ve not done it…but why do you think you need to

Your changing capacity – not your ability to feed into the grid – that’s controlled by your inverter.

When we were installing our array, SSEN wanted to know the type and size of the battery and the array being installed as they used sum total potential discharge (12.5kW) to determine the ability of the grid to handle the load. They didn’t accept the max limit on the inverter as an actual limit.

When we were installing our array, SSEN wanted to know the type and size of the battery and the array being installed as they used sum total potential discharge (12.5kW) to determine the ability of the grid to handle the load.

And yet they take the limit as gospel when you do a g98……. Even though you could stick nearly 8kw of panels on a 3.6kw inverter without exceeding string voltage.

They forced me into a G99 as the inverter was a physical 5kW unit with a software lock at 3.7kW. Delayed the whole thing for months. They also charged £700 to determine that “no modifications to the grid were required” to deal with their forced recognition of the 5kW limit and the 12.5kW potential discharge limit. PITA company to deal with.

My panels were installed in November 2022 but it wasn’t until early this month that I got around to setting up Home assistant on my Raspberry Pi properly. I wont have a full month of numbers until the end of Feb as I missed the first 5 days of Jan but I am keen to estimate my payback period (£12k outlay)

Obviously many factors can change and the amount and way that we use electricity is key to these savings however what I am pleased about is how closely our monthly usage appears to align with the PVGIS Solar model. (PVGIS) which estimated around 160kW for January. If I take even a conservative average to compensate for the early days missed (they were shorter days) then I am slightly above this which is encouraging.
At this rate our payback will be 6.6 years which is impressive.

Surfer, how much effort was setting all of that up on Home Assistant? It’s loosely on my list of things to look at for keeping an eye on energy consumption.

Is it talking to a smart meter to monitor power in from the grid?

I know many of you are neck deep in the detail, but please can I go back to a basic ‘what if?’ question.

I have a SSW facing, low angle roof on two different storeys.
The higher roof gets sun most of the year, with a about a month where the shadow of the hill behind cuts across the roof mid-winter. The upper roof is only 6m wide and 3m deep.
The lower roof is shaded from sun for about 16 weeks of the year, due to the hillside. 10m wide and 2m deep.

This gives you an idea of the roofs and the slope we face. The back of the house is exactly SSW.
Garden by Matt[/url], on Flickr

We are pricing up all sorts of renovation and improvement – we have no underfloor insulation, replace internal ‘dot and dab’ drafty plasterboard with proper plaster, remove and replace cavity wall insulation, re-plumb the heating system, new bathroom and kitchen. As part of this, solar seems another ‘ought to do’.

I really don’t want to spend huge sums and either not add enough value (and I know energy efficiency doesn’t payback in the house selling market) or enough return on reduced bills.

Is the best thing to do to get a local company to do a survey and cost? I am planning same with our builder for other costs..

low hanging insulate first.

Sort the plumbing – Fit a tank not a combi.

solar later

Expensive / hard/ problematic insulating after

Anyway it seems that the suns back – our 4kw system is peaking over 3kw for prolonged periods for the first time this year. – its 11.30am and we have got 5kWh yield already – North east scotland

hasnt been past 1.5kw since about mid november – which isnt unusual.

remove and replace cavity wall insulation

How on earth do you do this without hacking lumps out of your walls? Is there some non-intrusive way of doing it?

Like trailrat says insulate first if practicable and fit a tank. Make sure heating pipework is at least 15mm so you have the option of fitting a heat pump later. In fact it might be worthwhile doing some homework on a heat pump anyway if you are replacing a boiler. Get a solar installer to do a survey. Wont cost you anything as they use Google Maps but make sure they know about and take into account your topography.

Anyway it seems that the suns back – our 4kw system is peaking over 3kw for prolonged periods for the first time this year. – its 11.30am and we have got 5kWh yield already – North east scotland

hasnt been past 1.5kw since about mid november – which isnt unusual.

only getting 500w on average bout 2kw a day

I’m just having my solar fitted today, not a pro by any stretch but have just been through the process for my situation.

A 6m x 3m roof is quite small compared to some of the systems discussed on here, i expect you’d get 5 or 6 panels on
top giving 2.7kwp, assuming 450w / panel. If motivated by financial savings the question will be how much of your generation you can get from your roof sizes given the shading issues. And whether its worth adding panels to the lower shaded pitches.

I’d first educate yourself a bit in the basics so you know what to ask for. I went in blind, was baffled, so spent some time researching. If you let suppliers dictate the solution you might just get what they want to sell. It’s the easiest way so if you just want a quick look it might be fine for you – i was disappointed with the quality of the replies I got, they didnt tell me what i needed, so I think work it out for yourself first.

Find your average electricity consumption (average is around 10-12 kwh per day i think). See how much generation you could fit on your roof (start with 2.7kwh for just the top) and put that into an online tool like PVGIS. This will give you a figure for average generation you can expect for a given system size on your home (your azimuth and roof pitch). It doesn’t estimate shading so you might have to add a fudge factor. When you factor in your electricity costs it’ll quickly show you how much you might save on the bills. Then I’d start asking for quotes. Likely you’ll want battery storage if your load patterns are average, probably quite small if you only put panels on the top roof, maybe 5-6kwh of storage. Too big and you might not charge it, unless you want to start charging during off peak rates (another kettle of fish).

How on earth do you do this without hacking lumps out of your walls? Is there some non-intrusive way of doing it?

Remove a few bricks from the bottom and the tops of the windows, place a length of flexible plastic/rubber into the end of a drill and slowly work the drill/plastic up from the bottom and down from the top. It’ll mulch what’s in there and allow it to be extracted at the bottom with a vacuum cleaner. The you block the lower holes and refill from the top ones with new stuff and block the holes.

It’s time consuming compared to a first fill, but not overly difficult.

@surfer

You’re in Wirral aren’t you?
I’m in Higher Bebington with a big South facing roof so your figures are pretty encouraging. I’m at home all day so could maximise usage.

@swanny853

It was pretty straightforward. Ethernet cable into the Inverter back to my home router then set up an Raspberry Pi that I already had. Hardest part was getting the cable through an outer wall (garage and house) and finding a USB keyboard…. After that it was straightforward and there are lots of Youtube videos outlining the steps and you can just download the HA image for your Pi. The inverter does all the clever stuff and you can then choose the entitie’s that you want to monitor. It doesn’t touch the smart meter but its easy to calculate the savings once you have accurate PV data.

@colp Yes, I would use the PVGIS site to calculate your estimated PV as I said I have found it accurate. Fortunate that we dont have any shading.

low hanging insulate first.

That’s a given. The issue being, and why we’ve not done it so far, is that it is so intrusive and involves new kitchens etc

Cavity wall – part of the house is timber frame so can’t be insulated. Part of the house is narrow cavity and cannot be insulated. The part that can be insulated has basically a few mm’s of dusty, degraded foam. A quick hoover out from the bottom will be all it takes. But that means less than a third of the house can be cavity wall insulated.

Sort the plumbing – Fit a tank not a combi.

Sadly we’ve a 5 year old combi that I’m not replacing, but I will consider what we can do to make a tank easier when it does die.

It’s a proper ‘hard to treat’ house insulation wise. It sits out of sun in the deep freeze for 12 weeks a year – meaning our winter heating is 30% more than friends with similar house in the sun.

I’m so tempted to sell and move…

@surfer

Cheers, sadly I don’t have an inverter to plug it into as battery and solar is probably not on the list for this house. I was thinking about getting something set up so I’d had a bit of practice in monitoring useage when it did come to sizing a solar/battery system.

My figures are in for January (lets ignore tomorrow which is set to be a very sunny day and take it as given it will cover all my energy needs). Until this evening the panels have generated 191 KWh for the month (I fully expect another 12 KWh minimum tomorrow). In reality it has meant I have been completely disconnected from the grid for 20 days out of 30. Not bad for January. As production of solar ramps up we will be connecting in my brothers house next door to use the excess and if that doesn’t use it all we will be fitting an immersion heater and turning off the oil-fired Rayburn that heats our hot water for a few months I hope.

I did some sums earlier today. I have used £116 worth of electric this month if I was buying it on my current contract. Because of the solar I will only have to pay £14.40

How many panels do you have strapped to the sheep though @welshfarmer? To give you that sort of production – 10kw?

lol. I have 12x400W panels on my house and 3 375W panels on the workshop. So just shy of 6KW total

I’m having 15 400w panels installed tomorrow. I hope to get as good production as you do! Probably not at optimally aligned as yours though. Only 5kw battery though so will need to try and use the power as generated.

Still haven’t worked out if the inverter they are fitting will enable an EPS or other form of grid disconnection.

188kWh for us with 94.5% self use. Not bad given that at this time of the year almost half our array is in shade until just before midday.

We still used almost another 300kWh from the grid, though I did try to charge the battery during the greenest periods.

@matt_outandabout

The darkest 4 months of the year produce about 10% of my annual output, so it’s not a killer if they are shaded. You might consider micro-inverters, ie, each panel has a separate inverter so that it can be optimised individually when part of the array is shaded. If you have string inverters (ie, serving a string of panels) and one panel is even partly shaded, the inverter has to reduce the output from all of them.

That’s not entirely true with modern panels. Most modern panels have multiple diodes that allow partial suspension of a panel with affecting the whole string.

On ours in the early morning 2/3rds of 6 of the 7 panels that make up the lower string are in shade from the neighbouring roof. That string produces less power, but not nothing. It’ll be something like 1500W for the unshaded string and maybe 450-500W for the string with one clear panel and 6 panels which’re 2/3 shaded.

@muddyjames so long as your panels are orientated roughly south-SW at around 35-40 degree pitch you should be able to outdo me as we are in a fairly narrow valley between 2000 foot hills. In Dec-Jan the direct sunlight doesn’t hit the panels until 10 am and then is gone again by 4 pm. In fact there were 2 days during the snow when the panels shut down due to the batteries being full and we had no other way to use the energy. Based on the previous sunnny days we missed out on another 10 KWh of solar there. However, I think we have been lucky this year with it being a particularly bright January. In comparison, during December we only produced 111 KW in total, though I didn’t fit the 3 extra panels until the middle of the month.

Hang on. I seem to recall I know who Muddyjames is so you know exactly where I live and what the topography is like! 😉

I didn’t realise that shading isn’t such a problem for modern panels sounds like I have wasted some money on the optimisers.

I don’t know about wasted. In theory the optimisers should be more efficient at load balancing than the diodes as the diodes have a discrete capability where the optimisers are continuous, so you should still get more. It’s just less of a clear case than when panels were without or with only a single diode.

If you have string inverters (ie, serving a string of panels) and one panel is even partly shaded, the inverter has to reduce the output from all of them

Not exactly true. We have a dual MPPT inverter with an input of each of our E/W strings – this way the east facing string does not pull down the generation when the sun is in the west.

I didn’t realise that shading isn’t such a problem for modern panels sounds like I have wasted some money on the optimisers.

I don’t think you have. The issue I have with micro-inverters/optimisers is that if one fails you need to get back on the roof (so scaffolding cost), find out which one has failed and replace it. Or just leave the panel dead.

I don’t know how reliable they are but you’ve certainly got many (?) more points of failure compared to a single inverter that is easily accessed!

My roof is split about 50/50 sw/se so semi optimal.

Myeddi – diverter of choice? Easy diy install?

@matt_outandabout I have a solar calculator I built for my project you can have, it’s an excel spreadsheet that just needs angles for the panels inputting, you can then overlay the top of the hill (pretty sure I built that in) and see what kind of operating envelope you have. If trail rat’s figures are anything to go by it’s accurate enough.

That might be worth a look at – can you PM me?

Myeddi – diverter of choice? Easy diy install?

Cant comment on the Myeddi but I have an iBoost which was fitted as part of my overall install and I would have done it myself in a few minutes.

Does anyone have a recommendation for tidying up the wires of an external pair of batteries, connectors, coupler, inverter?

I was thinking of galvanised conduit, but the cables are pretty thick 20mm and I’m not sure they’re go round corners very easily and even when they do, they’ll terminate near the various boxes and just sort of pop out near them.

Any suggestions?  At the moment it’s only 3 cables from the battery to the inverter, but it’ll soon be 9 cables in a mix of black red and orange.

Wouldnt it be easier to just trim and crimp them to the right and matching length and colour and leave them exposed. I hate untidy cables (I worked in IT infrastructure for years) but sometimes if the colours are coded correctly, straight and parallel lengths and neatly installed they can look better than some conduit or containment. If they are not pristine then you could look at something like this, flexible conduit from the top of the stack of batteries then a wide conduit on the wall with the same conduit breaking out.

Does gas & electric kwh produce the same amount of heat for water, trying to work out if it’s worth switching off the iboost?

Just using round figures, if you can sell excess electricity for 15p per kwh and only pay 10p per kwh for gas, surely you’re better off switching off the iboost and taking the 5p difference … unless for some reason a kwh of gas isn’t as efficient at heating water?

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?

Electric water heating is close to 100% efficient, gas boilers around 94% + losses from pipes between the boiler and the tank. I think gas heating the tank should come out ahead if the pipe run is well enough insulated. On top of that, add in the pump at 1 kW electric…

“Just using round figures, if you can sell excess electricity for 15p per kwh and only pay 10p per kwh for gas, surely you’re better off switching off the iboost and taking the 5p difference”

Your assuming that they use the same amount of kW for each to deliver the same amount of hot water. My boiler is ancient so efficiency is not great but I suspect all boilers use comparably more gas per hot water heated.

I only use my iBoost for free solar not as our main way of heating water. We use gas heating at the moment and hot water is a by product.

Edit: what has happened to the quote feature…

Your assuming that they use the same amount of kW for each to deliver the same amount of hot water.

I wasn’t assuming at all it’s the whole reason I posted it as a question and the post starts off …. “Does gas & electric kwh produce the same amount of heat for water”

As Murray says, electricity is more efficient however it is also more expensive.