Off-Grid Solar PV Setup

[chrrris]

Partly for reasons of giving myself an interesting project, partly for research/self-education purposes, and partly for reasons of having a means of looking after myself and the Mrs in the event of any forthcoming zombie apocalypse, I decided to set myself up with a home built off-grid solar PV solution. Thought I'd document it here in case anyone else is interested in toying around with such things, and to give anyone who actually knows what they're doing an opportunity to rip the p**s out my attempt...

I started by building a weatherproof cabinet to house the gubbins (technical term...) in my back garden. The top is double-skinned -- a plywood interior, heavily sealed to protect against water ingress, with featheredge boards over that to keep the worst of the weather from getting anywhere near the inside layer:-

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The cabinet is (hopefully, time will tell...) weatherproof but not airtight as some ventilation is required in the event the battery produces hydrogen during charging. Although I believe the only tends to happen if it's overcharging, which the charge controller should ensure never happens:-

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Into this cabinet went the magical electronic giblets, consisting of an EPEver MPPT Solar Charge Controller, a 120Ah marine/leisure deep-cycle battery, a 1.5kW pure sine wave inverter, an earth block, and - not shown in this photo - I also added a RS485 to WiFi dongle so I can monitor everything from inside the house:-

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The battery's negative terminal is earthed, and all the metallic gubbins in the cabinet is grounded, via an 8ft copper rod knocked into the ground just outside the box.

Next, I hoiked a big 7' by 3'6" monocrystalline PV panel up onto the (single-story) extension roof. This panel can produce 360W of the good stuff, but obviously that is in full sun and under ideal conditions. No doubt the reality will be somewhat lower. To avoid breaching my lovely EPDM roof, I fixed battens to the fascia board of the extension to mount the panel on:-

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The panel is mounted at approximately 45deg which I decided was a fair compromise for all-year-round performance (in the summer a flatter angle is optimal, in the winter a mere 13deg from vertical is optimal). This setup slightly favours winter current generation over summer. The mounting brackets are fully adjustable, but I can't imagine I'll be going up on the roof to adjust it very often.

And finally, inside the house I have the remote control for the inverter (showing the battery charge level and an on/off switch for the inverter). At the moment, I just have this one double-socket with USB ports. Assuming the panel generates as much electricity as I'm expecting it to as winter sets in, then I'll be moving the house lighting circuit (all LED, totalling about 150W if I have every light in the house switched on at the same time) over to it. I may also add a second battery and a second 360W panel so I can get the fridge/freezer (approx. 880Wh/day) on there too.

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Of course, there is also nothing to stop me charging the battery(s) overnight from the on-grid mains, to ensure they're topped up in the event of a power cut, but I'm not looking to get into that at the moment.

I literally only just switched this on and tested it today, so I have absolutely no idea how well it will perform in reality.
I'm not an electrician. I'm not a solar PV specialist. I'm doing this mainly for experimentation purposes. Any constructive criticism is welcome.

[Someone-Else]

It sounds an interesting project, I hope you have more success than I did when I tried it (On this forum) nearly 3 years ago Click Here

I have a few points to note about your project.

You do realise what you are doing with the USB socket? You are changing 12v (Solar) to 240v (inverter) back down to 5v (USB socket)
A fridge / freezer has a motor to operate the compressor, when the motor starts it draws a very large current, this could fry your inverter. (It only draws a lot of current for a second or two, but it still does it)

I do not see a fuse on the battery, if you get a fault, there is nothing to stop it shorting out and catching fire.

If you want it to light the house you should install independent lights. The reason is so there is no possibility of back feeding into the grid. I shall expand on that. If you have solar panels and an inverter professionally installed and connected to the mains (Like folk do when they have solar panels put on the roof) you would have thought that if there is a power cut they will be ok as they have solar. What actually happens is the inverter detects no incoming mains and switches off, the reason it does this is so that it does not put 240v on the incoming cables, that may not sound too bad, BUT if you send 240 ac down your mains cable in a powercut, it will also put 240v into the transformer that supplies your house, this transformer probably has an incoming side of 11000v, which means if you put 240 in the output side you get 11000v out on the input side, yes the current will be tiny, but at that voltage it doesn't need to be big to kill some poor worker trying to restore your supply.

By all means carry on with your project, just keep it independent of your house wiring.

If you read my project, the solar pump is still connected, but only works in really bright sunshine. Over all, my project was interesting to try, but viable? no.

[Rorschach]

I'll second the advice about keeping everything separate from your house wiring. Personally I would look at using it to power a single appliance such as the fridge you mention or even better, a chest freezer. Reason for this is not only is it a constant low load but that load is lower in the winter when you are producing less and higher in the summer when you are producing more. A chest freezer is also perfectly capable of going without power for several hours, possibly even days in the winter so if you ran out of power overnight it wouldn't be a big issue and you cold switch to mains in the morning when you do your daily check (or set an alarm device).

I will also second the point on the USB chargers, run a 12v line directly from the battery to a 12v-5v USB plug as used on a vehicle, much more efficient transfer of energy.

[chrrris]

The inverter is indeed fused and also provides a bunch of additional protection - over and undervoltage, short-circuit protection, battery temperature monitoring, and it shuts down cleanly to prevent full discharge of the battery. It does have a USB output built-in which could be extended into the house but I'm currently minimising the sockets and cables running about the place for reasons of matrimonial harmony.

The tech has really moved on a lot in recent years. Monocrystalline panels work fairly well in overcast conditions and the MPPT controllers are reputed to be around 25-30% more efficient than the older PWM type. Again, this is particularly beneficial in less than perfect conditions. The charge controller also does battery temp monitoring to optimise the charge current and voltage. Very clever stuff. The prices have been coming down for a couple of years, but I notice them going back up again at the moment. Presumably due to increased demand.

[mikew1972]

Have you considered not using a battery or any electronics?

[Rorschach]

Have you considered not using a battery or any electronics?

[youtube]<span class="skimlinks-unlinked">https://www.youtube.com/watch?v=r7g-27AXFEg</span>[/youtube]

This is a great way to store energy if your circumstances allow it. A channel I watch (Maximus Ironthumper) uses this method. Once his batteries are fully charged the solar power is switched over to heating water, he is totally off grid so needs to maximise efficiency.

[kellys_eye]

My tuppence-worth...

The featherboarding on the top - laid the wrong direction? I'd have considered a redundant external electricity meter box for the electronics, separate box for the battery(ies).

More batteries. 12V @: 120Ahr is a theoretical 1440 watt-hours but, in the real world, maybe 800. OK for lighting and potentially entertainment too but won't last long doing 'real' work (fridge etc) so doubling or quadrupling up would be a good idea.

But as a comparison I offer my own current sit rep....

1. Two off (one for spare) 750W inverter gensets. These feed an outside socket which is wired (going in as we speak) to a separate circuit that comprises 8-off 13A (red in colour) sockets, strategically placed around the property for lighting (table lamps), tablet chargers, router and TV plus a spur off to our gas water boiler (for the igintion). I'm also planning on fittin auto-change-over for the house main lighting circuit so all ceiling lights work too. Sufficient lighting, powering the tablets and router plus running a (small) TV set consumes 150W max - barely 'tickover' for the IG sets and 8-hours runtime on a 4.5litre tank full. They cost me £175 each.
2. A 'whole house' genset (7.5kW) with dual fuel capability (delivered three days ago) running petrol or LPG and four off 47kg bottles to run it (does 1kg/hour at 3kW load so an effective 6-day (140+hours) non-stop capability but, with limited usage I expect 3 months at least), with 100litres of de-ethanol-ed petrol as backup. Genset cost ~£900. This is being wired to a change-over switch on the c.u. I'm aware of the issues re back-feeding etc so all precautions are being taken.
3. I'm contemplating getting a diesel setup for business reasons - not to mention you can legally use red diesel (or heating oil) in them and store pretty much as much as you want on-site. These aren't that much more expensive than the duel-fuel setup I've already got, say £1500 for a semi-decent one.

I plan to fit solar but where I live too but I don't expect a lot from it due to a mainly overcast outlook but will still fit 300W of panels and the appropriate electronics/batteries as per your effort Chris purely as a 'last resort'. We could live on such a setup (after retirement) as our main power needs are currently business-based but the house needs 'nothing' in comparison as all heating is via woodstove. And we live in a forest.

As much as they're trying to scandalise fossil fuels there will (soon) come a time when reality hits and they acknowledge that they will be here for a long time yet - particularly LPG (which I believe would be the answer to powering vehicles too) so I'm confident of maintaining supplies as long as I might need them.

Strangely ('not' as the case turns out) I'm not the only one around my parts doing this kind of thing - 'everyone' seems to be doing it (we had offers to loan a genset when we had the last power cut as the locals all know of our business needs - kind of them but we were already covered) and it was surprising how many offers came along. It's as if every other house has one! I now have a 3kW genset 'redundant' that I'm giving away to a neighbour - just finished rebuilding it so good for another few decades.

[kellys_eye]

This is a great way to store energy if your circumstances allow it.

I'm often jealous of those that have an abundance of solar input. Solar is great for some parts of the world but northern latitudes? We need to have alternative backup as it can't be relied upon - pretty much as unreliable as wind power too.

[mikew1972]

A channel I watch (Maximus Ironthumper) uses this method.

Yes, Another good channel. I've been watching, enjoying and learning from his videos for a few years.

[ayjay]

My tuppence-worth...

The featherboarding on the top - laid the wrong direction?

That's what stood out for me.

I don't understand the rest of it anyway.

[chrrris]

This is a great way to store energy if your circumstances allow it. A channel I watch (Maximus Ironthumper) uses this method. Once his batteries are fully charged the solar power is switched over to heating water, he is totally off grid so needs to maximise efficiency.

Yes, I've been watching that channel too when I was planning out how to do all of this stuff. He's very informative. I wonder if anyone uses the grid suppliers' technique of pumping water up to the top of a hill using excess generated energy, then using hydroelecric dams? Probably only cost effective on a massive scale I imagine.

The featherboarding on the top - laid the wrong direction? I'd have considered a redundant external electricity meter box for the electronics, separate box for the battery(ies).

Heheh... I don't think so -- the top of the cabinet slopes down about 1.5" towards the front. If I laid the featheredge across the width, water would pool at the joints, no? This way round, it runs off the front. That was my thinking, anyway. I appreciate it looks less aesthetic though.

A lot of this little project is governed by matrimonial requirements. That's the whole reason for the wood and the featheredge -- "It'll blend in with the garden, love. You won't even know it's there..." White UPVC meter box would have been overruled, as was having a separate box for the batteries. I was not popular when she realised that the panel was mounted at 45deg rather than being flat on the roof as she expected. Got to break her in gently!

I plan to see how much juice I can get from this over the next few weeks before investing in a second panel and another marine battery. The existing charge set up will work as it stands (more efficiently...) at 24V rather than 12V. And I've oversized the cables to allow for possible future expansion. Unless it turns out to be crap, of course, at which point I guess I'll be rubbing sticks together. It's currently clouded-over here and I'm only getting 7W from the panel which is less than ideal:-

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[chrrris]

Heheh... I don't think so -- the top of the cabinet slopes down about 1.5" towards the front. If I laid the featheredge across the width, water would pool at the joints, no? This way round, it runs off the front. That was my thinking, anyway. I appreciate it looks less aesthetic though.

Oh, hang on. I see what you mean now; running the boards up from the bottom to the top. I'm a div! Might have to change that at some point.

Unless it turns out to be crap, of course, at which point I guess I'll be rubbing sticks together. It's currently clouded-over here and I'm only getting 7W from the panel which is less than ideal:-

Hmmm... scrap that. I didn't realise how the charge controller works. I thought the 7W was the max available from the panel, but it turns out that was being drawn to replace the 7W drain on the battery at the time to keep it from discharging. I plugged the fridge and me Henry in and did some hoovering -- and the panel jumped up to 330W in full sun and 170W in hazy/partially cloudy conditions. It's sunny now and the panel is generating 90W to run the Fridge and the battery is full. This might just work!

[Neelix]

We’ve got solar and the divertor to send excess lecky to the immersion

I doubt there are many days per year that we could sensibly store much extra lecky … and as we have a lecky cooker, that would empty batteries super fast

[kellys_eye]

This might just work!

Not that cost is a particular issue these days but what are the figures for the stuff you've fitted?

[chrrris]

This might just work!

Not that cost is a particular issue these days but what are the figures for the stuff you've fitted?

360W Panel = £299.99
120AH Battery = £109.99
1.5KW Inverter = £170.99
12/24V MPPT Charge Controller = £97.98
WiFi Monitoring/Logging Thingy = £23.99
Aluminium Brackets for Panel = £39.99
Misc Solar Cables and Connectors = £50 ish
Timber and screws for cabinet = £60 ish
Sockets/pattress/Conduit/Cable/Sealant = £70 ish

So a shade over £920 or thereabouts. Obviously that buys a fair amount of electricity, even at today's prices, but it 's more about catering for outages and being self-sufficient for me. A lot of people (not people on here necessarily, but the public in general...) probably miss the fact that if there's a power-cut they'll lose their gas/oil CH and hot water for the duration too -- I like the idea of being able to power our combi boiler by solar in that situation.

We'll see how it progresses as winter sets in. I'm fairly happy so far but it's very early days. Cost of adding another 360W panel and battery would be £600 quid as I'd need to replace the inverter with a 24VDC one. I'm slightly worried about the cheap Chinese-made inverters and how reliable they'll prove to be...