West facing array

[Eric12]

Hi I have just joined this forum to hopefully find some answers to my questions regarding a proposed solar array at my house. My annual electricity consumption is quite low @ around 1300 KW, and I'm considering fitting a 2KW system (5 x 400w panels) on my roof. My house and roof is in a terraced road in Kent, all with North/South facing gable roofs The south facing portion of my roof is flanked either side by loft extensions, so not ideal to install here due to shading. However there is a portion of the roof (which projects out at a right angle from the main roof) facing West and I'm considering installing a 2kw system here. Would a 2KW, West facing system of 5 x 400w panels be sufficient to generate 25KW per week (1300/52 = 25KW) ??. The portion of the west facing roof (with a slope of about 35 degrees) can catch a good deal of sunlight during the afternoon, however being a terrace the house next door will prevent total exposure during late evening; would this be a problem though as the sun gets lower during late evening anyway ??. I have looked on the PVGIS website and my locality with a west (90 degree azimuth) looks promising (1465 KW per annum on a 2KW system with 20% system losses) but hoping for some real world feedback from anyone who has a 2KW system on a west facing roof, and how much it generates. I'm toying with the idea of putting some kind of sensor on the roof that can tell me what sort of radiance (is that the right word) I can expect up there before going ahead with a full install. Thanks for any advice

[Countrypaul]

You don't give any indication of what use you will make of the power generated, but unless you also plan to use batteries of some kind the power will need to be used when it is produced. In this country, the vast majority if the power from PV is generated in the late spring/summer/early autumn with relatively little in the colder period.

When I refer to batteries, I am including storage of energy in any form, so electrical, or heat such as hot water tank or storage heater via a device such as an Eddi.

Putting up additional panels during initial installation works out much more cost effective than adding more later. You may find that different panels (possibly smaller) can fit producing more energy overall. There are also optimisers such ad Tigo that can be used with panels that suffer shading to oost overall output. One panel being shaded by something as simple as an aerial can have a significant impact on the whole installation performance otherwise.

[Eric12]

Thanks for the reply Country Paul, my power needs are quite minimal considering its a 2 bed house. I want the system to be grid tied, not totally off grid !!

I guess the most demanding items are a washing machine (maybe twice a week), and a fridge freezer (24/7); other items include a TV, laptop, router (24/7), lighting, and other intermittent small power (iron, kitchen blender). A combi boiler takes care of central heating (which is to stay), and hot water; oven is gas (which is to stay)

Yes I will likely use batteries for storage, and utilise a myenergi eddi to divert any surplus power to my immersion tank (as it also runs on an electric if I want it to).
So as you can see my electric demand is minimal (Avg 1300KW per annum); what I really need to determine is if a west facing roof with 2KW of panels will produce enough to charge batteries and/or use direct to cover me for most days. My daily power needs average 25KW per week, probably 3KW per day for 5 days and 5 KW per day for 2 days of the week on average. There is no shading on the west facing roof, but I guess any panels there will only produce from noon onwards till just before sunset, but given my demand is not too high will a west facing roof suffice ??

[Mr Gus]

What is the max you estimate as winter production on that amount via your calculations? a year is 4 very different seasons production, presumably this is when your needs are greatest & if you wish to even it out over the course of a year or is your aim simply to be "on paper at least" seen to be cancelling itself out.

With energy squeezed & "peak demand" likely to result in increased tariffs in coming months / years due to all the recent chaos, it is wise to max out your roof space regardless (its not so much the cost of panels these days so much as labour, H&S, scaffold hire etc so more installed in the first instance is likely to give you a better result overall, especially in prep for storage at a later date.

Can you reach them to give them an annual clean? ..simple things like access will affect output once installed, grot builds up & the kWh's harvest drop off, especially if the sizing is tight & you are relying on it to cancel out, thus headroom, if you have access to anyones records for your area who has logged over say a 5 year period then you will have more confidence in your sizing based on close proximity estimates.

Any local doors with solar you can knock on to ask for a nearby comparison based on orientation & size for some fag packet math to achieve a localised result?

What have you calculated your losses to be within your panel sizing & cable runs from the cable you've specced? (presumably standard pv 4mm core)
All the above is relevant to hazard an answer based on the positioning (but you take what you can get, thus oversizing to help compensate for a bad solar year)

[Eric12]

Mr Gus thanks for the reply. During the winter months I dont expect my electricity consumption to increase too much, maybe a bit for lighting as the lighting will be on for longer. Gas consumption will increase for winter for sure due to heating ! So yeah I suppose im looking at the project as getting free electricity only and so reducing the electricity bill. Theres not much I can do about the gas as my old mum will not allow any tinkering with the heating system full stop. So yeah im looking at this project as a way to (greatly) reduce my electricity consumption from the grid and maybe taking the edge off the hot water system via an eddi.
Your likely correct that feed in Tarrifs may increase from the meagre 4-5p per KWh offered today, in the future, especially at peak times like in the afternoon; and so a west facing array may be beneficial in this instance, as will maxxing out the amount of panels I can physically fit too make an extra buck or ten. However it all boils down to how well a west facing array will fare, with the space that i have, which is something im not atall sure of ?? and wish to determine as part of a design process (to a certain extent at least).

Access to my roof without scaffolding will be with a ladder, so cleaning any panels with a brush & hosepipe will not be a great challenge, however fitting them will require scaffolding ! What I really need is some way of determining how efficient any panels will be in their proposed locations; that will give me a datum value, which I would like to have, so I know what to aim for. I could get up to 10 regular sized panels on the roof space I expect.

I have not yet calculated losses from cabling (panel to inverter and so forth), but I can fit all the equipment in the loft space so runs of cable can be kept to a minimum. I can increase cable CC (diameter) to minimise losses can I not ? At this point in time I just need to know in a nutshell if I place panels on a west facing roof (as opposed to a south facing roof) will they generate enough for my needs ?? Once I know that then I can design the layout of the system, and I do have enough physical space in the loft to place the equipment, as well as a clear run from the loft to the consumer unit !

[Bugtownboy]

Hi Eric12, we’re just a bit east of you on the Somerset ‘lowlands’.

Interested to see your RE journey

[Oldgreybeard]

I think there is a lot to be said in support of East or West facing arrays, TBH. They won't give as much peak output, but we have a 6kW array facing SSW and although the peak output is fairly high, it is really at the wrong time of day. Our output peaks at around 14:00, when ideally I'd prefer to get more power first thing in the morning and also more later in the afternoon.

I'm in the process of adding another 2.4kW of panels to the ESE side of our house, mainly to get more early morning generation. We have a battery storage system and getting more power into that first thing in the morning will help to recharge it from the overnight energy that has been used. There's also local weather patterns to consider. It's fairly common here to have pretty clear, bright and cold early morning sun in winter. With luck that may give us more output at that time of the year than the PVGIS model predicts.

[Eric12]

Ive just measured my west facing roof (it is directly facing west btw !) and its roughly 3m x 3m with a bit extra at one edge where it meets the main south facing roof (not in the pic), but the south facing roof is shaded by loft conversions either side. So I could fit 6-7 3ft x 5ft panels on this roof !




The roof opposite this is similar but does not appear to cast any shadow until the sun is out of sight anyway, see below




So this is my canvas, do you think it will work ??

[MoSTiE]

West array 6 x 410w panels (still 2 to be added) fitted mid April 22, generated 1049kWh as of today.

[Mr Gus]

Everything is subjective to kit, losses & weather, & is H.L.I.A.P.O. String theory, thus the questions for folk to get a closer accuracy estimate, we know you want a specific answer, give it time, let people read your post detail & someone with a similar set up will get closer to a realistic number when passing through.

(Like mostie just did, whilst I was typing)

The devil really is in the detail.