Off-grid solar PV upgrade

Sorry there's been no posts for a while, but as you can see I've had a lot going on!

With the help of my friend Rich, I've upgraded our off-grid solar PV system, removing some of the panels we installed a couple of years ago and replacing them with some much larger models. Here's a video summarising what's been done:

And if you want more detail, here's a video of the installation of the new controller that's needed to handle the increased power - it's a Morningstar TriStar MPPT 60A.

And for those who are into technical stuff and software, here's a video showing what the software Morningstar provide can do to gather and display data on the controller's operation (best watched full screen in HD so you can see everything):

Here's the photos (some of which are in the first video above).

First, here's the original system. The reason for the upgrade is simply that prices of solar panels have dropped a lot, and doing an upgrade now meant that the same roof-mounting kit was still available to buy (just!) so I could extend the rails easily. I'm finding good homes for the old panels...

First we removed the old panels, which was easily done from a ladder:

After that we set up the scaffolding that Rich had brought:

Then we removed the top mounting rail, shifting it up a bit, and extended both rails to the right, using the extra kit I managed to source from Midsummer Energy - thanks for the help guys! We'd also got some advice from Midsummer Energy on installation, so we removed the tiles we'd lightly ground using an angle grinder last time, and made some more aggressive cuts into them to fit round the mounting brackets:

This enabled the tiles to fit much more neatly - some of the ones we did last time had broken since installation, probably due to the wind making the array flex and press on them.

We also put into practice some advice on adding a bit of felt just to ensure waterproofing, although in practice this area is under the panels so gets less wet anyway in the rain.

I'd also uncovered the manual for the mounting system on the internet, from Grace Solar in China. This included useful tips like how to slot in the connectors that the clamps screw into, without sliding them all the way along the rails - very useful to know! (see the video for more info)

The new panels are Suntech 250W monocrystalline, and as they weigh nearly 20kg each we had to come up with a way of keeping them in place while we got the next one ready. The solution was a piece of wood of the same thickness, which the mid-clamps could grip onto allowing the panel to be held while we moved the scaffolding and got the next one in place.

It wasn't long before all three new panels were up, and we've kept one of the old ones to run a small 12V system that's used for phone charging, running a laptop and powering the cockatiels' night light:

Wiring up the electrics was much easier than last time, partly because a lot of the wiring was already in place and could be reused, but also because the new panels came with MC4 connectors, so I was able to prepare cables and then just plug in!

So, the system has been up and running for a week now, the fridge and freezer have been off-grid continuously during that time and we've even done two loads in the washing machine off-grid! The new controller gives me loads of data, and the Mastervolt inverter we've added now is pretty neat too, so I might write another blog post later with some extra technical details...

Mike

Related posts:

• Insulating the cavity walls
• Insulating the loft
• Flat roof insulation
• Insulating the dormer roof
• Sweeping the chimney
• Installing the wood stove
• Plumbing and testing the wood stove
• Installing solar water heating
• Installing off-grid solar PV (part 1)
• Installing off-grid solar PV (part 2)
• Off-grid solar PV upgrade to 1250W

Click here to read the rest of this post.

Parallel lead acid batteries with solar PV

Just a quick update to my previous post about wiring up our off-grid solar PV system. The friend I bought the batteries off has swapped the dead one for one the others he had, so I now have a working pair:

I'd originally been planning to put them in series for a 24V system, but I've reconsidered and am currently going to keep it as 12V, partly for simplicity and partly because that gives me greater redundancy in future if parts should ever fail and prove difficult to replace.

There are several important considerations when wiring batteries in parallel:

• It's best to have them the same make and capacity.
• It's best to have them the same age and condition.
• It's important to wire them so that the load and charging currents are spread equally across them.

I'd already got these first two points sorted. The last point requires making sure that the length of wire the current must travel to a load or from the charge controller is the same for each battery. If you don't do this, the battery that is nearer to the load/charge connection will discharge and charge faster than the other one, potentially resulting in premature failure.

The solution for two batteries in parallel is simply to connect together the positive terminals with a length of wire, connect together the negative terminals with another equal length of wire, and then make sure the positive and negative connections for the load and charge controller DON'T go to the same battery. This way, the current must always flow through one length of wire to reach either battery, so keeping them equally charged. Here's a pic, with the +to+ and -to- links on the right, and load/charge connections coming in from the left:

All I need now is some sunshine, and there's certainly no shortage of that right now!

Mike

Related posts:
Sweeping the chimney
Installing the wood stove
Plumbing and testing the wood stove
Installing solar water heating
Insulating the cavity walls
Insulating the loft
Flat roof insulation
Installing off-grid solar PV (part 1)
Installing off-grid solar PV (part 2)

Click here to read the rest of this post.

Eco-refurbishment - installing off-grid solar PV (part 2)

Our off-grid solar PV is now up and running! Part 1 covered installing the panels on the roof, this post is all about wiring them in. This started with screwing a waterproof junction box to the wall and then fixing a dual busbar inside it:

The next step was to wire in the PV panels. As I was setting this part of the system up at 24V, I wired the panels in pairs, as you can see below, with each PV cable having one wire screwed to the busbar and the other soldered to a wire from the opposite cable. The solder joints are then wrapped in heatshrink and PVC tape, to avoid any accidental short circuits. The wires coming out the right hand side of the junction box take the combined output of all six panels into the house.

Before you ask, yes there are seven panels on the roof, but only six wired into the junction box. That's because one of the panels feeds straight into an existing 12V system I have set up which is used for DC supplies to charge small electronic appliances and also to power a night light for our cockatiels!

Anyway, here's the junction box with all the wires neatly bundled up:

At the other end of the pair of cables heading off to the right, they disappear into an air vent...

only to emerge inside the house, under the stairs. We had this vent put in by the cavity wall insulation installer, in preparation for this use.

Once inside the cables head through a gap in the board on the left, going past the battery:

I had bought two batteries second-hand from a friend, but it turns out one of them is dead, so I'll be running the system on 12V rather than 24V. More on that later... While we're looking at the battery, here's some detail on the wiring. There's a pair of wires going to the charge controller, and another pair going straight to an inverter. The little black pods are fuse holders, the rear one's open and you can see the red fuse inside it:

Round the other side of that board is a neat little display I found, wired up to a switch so that when the switch is set to "1", it displays the battery voltage.

That photo doesn't really do it justice though, as it glows in the dark!

OK, on to the key component in the system - the charge controller, a Morningstar SunSaver MPPT. This performs several key tasks:

• It uses a Maximum Power Point Tracker (MPPT) to allow the solar PV panels to operate at the voltage at which they will deliver the most power, and then converts this to whatever voltage the battery requires. This is done dynamically, as the MPP changes according to light levels. The other advantage of this feature is that it can take an input voltage up to 70V, which is why it didn't matter that I'd wired the panels for 24V operation, but then ended up using a 12V battery. In fact, using a higher voltage reduces current losses in the cables, so this is a good thing to do anyway.
• It can auto switch to 12V or 24V. So, if I do decide to run a 24V system later on, it will work just fine (though I'd have some other bits of wiring to do on the load side of the system).
• It prevents the battery being overcharged, and actually goes through a 4-stage charging process to ensure that the battery is kept in good health.
• It prevents any loads connected to it from running the battery down so low that it is damaged.
• It includes protection against short circuit and excessive voltage on all of its connections.

With all that, you're probably not surprised to hear it cost as much as two of the 40W solar panels on the roof!

The load connections from the charge controller go to a pair of busbars. I'll make a plastic cover for one to prevent short circuits later on, for now it just has some tape over it to prevent accidents. Connected to the busbars is a 12V socket, like you'd find in a car, and plenty of room to add some more. This means anything you can get a car adaptor for, you can plug in here.

For mains appliances I've got a Victron 180W pure sine inverter. Because this can draw more power than the charge controller can handle, it's connected directly to the battery. This isn't a problem, as the inverter also can detect when the battery voltage is too low, and disconnect itself.

I've had this inverter for some time, so it was just a case of screwing it to the wall and plugging it in. I got a pure sine version so it can run all kinds of electronics with no problems. Modified sine inverters are cheap, but won't work with everything... I plan to get a much larger inverter later on, so we can run things like the fridge or freezer for a few days in the event of a power cut.

At the output of the inverter I've plugged in a monitor, to see how many kWh of electricity I've used from the system. My general plan is to use the power when the sun is out, and not when it's dark or cloudy. While this means I'm not getting the maximum amount out of it, it does mean the battery is always full, ready for any power cut that may happen.

Finally, the battery is boxed into a small compartment under the stairs, with the air vent inside it. This is essential, as charging a battery produces hydrogen, and as we saw in Fukushima, hydrogen mixed with air in confined spaces is not a good idea... Keeping it sealed away with a vent should eliminate any explosion risk.

So, what have I learned from all this? Several things:

• How to use a hydrometer to check if all the cells in a battery are working - and to check second hand batteries before buying them, even from a trusted source (as they may not know they're dead).
• How to do the basics of fitting roof tiles - after the PV was done, I went round the other side of the house and replaced a few low down cracked tiles myself.
• That the ancillary components of an off-grid PV system can cost more than the panels themselves!

It certainly would have been easier to pay someone to fit the system, but doing it myself was much more satisfying (and cheaper). It also meant that I was able to make some decisions as I went along, and as I designed and built the system, I know exactly how to fix it if it goes wrong.

So, I'm writing this blog post with my laptop and router running off grid! Very satisfying! :-)

Mike


UPDATE: I've got two batteries now, wired in parallel.

Related posts:

• Insulating the cavity walls
• Insulating the loft
• Flat roof insulation
• Insulating the dormer roof
• Sweeping the chimney
• Installing the wood stove
• Plumbing and testing the wood stove
• Installing solar water heating
• Installing off-grid solar PV (part 1)
• Off-grid solar PV upgrade to 750W
• Off-grid solar PV upgrade to 1250W

Click here to read the rest of this post.

Eco-refubishment - installing off-grid solar PV (part 1)

Yesterday we installed our solar PV panels on the roof!

But let's start at the beginning... Our friend Rich came to help us do the work, as he's had past experience doing roofing work. We did a work swap, I helped him in his wood back in January, in return for his help yesterday. He also brought a lot of useful kit with him, like this scaffold tower:

The process started by removing some tiles to find where the rafters were under the batons, as the brackets needed to screw onto these for strength.

Having located these, we decided to grind a slot in the tiles so that they'd fit neatly round the brackets:

Then the brackets could be screwed down (with a small wooden spacer underneath to help them fit better):

and the tiles slotted back in:

Of course, it wasn't all that simple, as soon as you put any weight on the bracket it put pressure onto the tiles at a single point, and some broke...

To resolve this we used more spacers underneath, bent the brackets slightly and also used the grinder to thin the tile a bit at that point, giving more clearance for the bracket:

Here's the detail of how the rails fix onto the brackets:

And here's an interlocking piece of aluminium to join two rails together (we had two 2m rails). There's a couple of allen key bolts to lock it in place.

Then it was time to clamp down the panels. Here's a clamp with one panel in, and space for the next:

and here's one with both panels in and tightened up:

The first three panels in place:

And here's the finished set, with the solar thermal tubes higher up the roof:

The wires from the panels are zip-tied in place under the panels:

Then they all come down in a bundle to connect into a junction box:

That'll come in Part 2 though, where I'll explain the wiring system.


Mike

Related posts:

• Insulating the cavity walls
• Insulating the loft
• Flat roof insulation
• Insulating the dormer roof
• Sweeping the chimney
• Installing the wood stove
• Plumbing and testing the wood stove
• Installing solar water heating
• Installing off-grid solar PV (part 2)
• Off-grid solar PV upgrade to 750W
• Off-grid solar PV upgrade to 1250W

Click here to read the rest of this post.