West facing solar panels are something of an anathema; most folk whose roofs are oriented east west find the subject very frustrating. The can't easily build a photoelectric farm on their homes.
However, I'm on a jaunt in the Netherlands right now, and I've found that homes there too have taken on east and west facing solar panels. Whilst not as effective as a PV directed to the south in this northern hemisphere city, they produce a far greater than expected output.
So why would you deliberately face your panels in a westerly direction where they only get direct sun for half the day?
There's a simple explanation; you have sufficient power from your panels for most of the day, but not enough in the late afternoon when cooking the evening meal is starting to happen.
For that matter you could also put up a few east facing solar panels to catch the early morning sun. I haven't done that yet; it's worth a consideration in the future.
The first dilemma is whether you have a suitable west facing wall, or part of the roof that's not going to be shaded by a tree or chimney.
Partial shading is actually less of a problem than most folk think but if one panel falls completely in the silhouette of branch, say, none of the PVs in series will function at all.
Remember too that shadows on PV panels will change in summer and winter.
These west facing solar panels on a typical Dutch duplex are their only option, not having a south facing roof. Notice there are two different size panels; this can only be done if you know how diodes work.
These were my initial considerations; but notice the shadows that would stretch across the panels at certain times of the day. I eventually ditched the idea.
So, during the day, we have more than enough energy coming in from Mr Golden Sun to supply the pool pump, the kettle, the oven, the breadmaker, the dishwasher and the electric lawn mower.
But come 4pm when the sun is falling obliquely on the PVs, and the incoming energy falls below 1kW, there's not enough electricity to cook the evening dinner; enter west facing solar panels.
These west facing panels do not need to be oriented at 30 odd degrees, like those that are on the north face of your roof. In fact they can be quite close to vertical. They won't produce much energy at midday, but after 1pm they will start to supply electricity just as the others begin to fade.
There is an alternative. One could add another 48V of batteries to store that electricity coming in during the day; but good quality is very expensive. It would mean another R25,000, or roughly $10,000.
There is another alternative; tie onto the grid, but that's still illegal in South Africa and, I understand, means no power from the sun if the grid goes down.
Grid tied inverter technology is rapidly improving, and that remains an option for the future.
So, having done your homework concerning potential shadows on PV panels, and chosen your west facing wall, the next step is to build a framework to hold them firmly in place at your chosen angle.
Remember it's the same amount of work to erect a large panel as a small one, so my philosophy is to go for as large a panel as you can find.
In this case I chose three 305W panels. An extra 700 to 900 watts for most of the afternoon is exactly what we need. Whilst a modern electric oven draws 2000W, once it's up to your chosen temperature, only small amounts of energy are required.
Making a frame to house your solar panel is actually quite a challenge, so I discovered. I chose to build it out of 50x50x3mm angle iron. The first step is to build a rectangle, braced at the corners that accurately will hold the PV. Allow at least a millimetre, perhaps two or three all round, remembering you have to paint it. The structure needs to be exactly square.
Measure the panel exactly, mitre four lengths using an offcut saw, tack weld on an exactly flat surface, using a large square, and test the panel fits before doing the final welds and the bracing.
One important tip: absolutely no welding inside the frame, unless you're an expert welder. Filing down this raised blob of weld that made the panel sit proud was not easy.
No comments from the peanut gallery about my welding please!
Testing the panel fits snuggly in the frame. Quite right, it's in back to front but no matter; we are only testing the frame for a good fit.
The next step is to cut four feet for each frame. These are 15cm lengths. There's been some debate about how many plugs we need on the wall. I started with thinking four per foot, in case of very strong winds, but I'm told that's overkill for panels that are up against a wall. I ended up drilling one hole in the centre of each toe of the foot. Thus eight coach screws will hold each panel firmly against the wall.
Now cut the legs for the feet. I chose two lengths, 20cm and 30cm to give a slight upward tilt to the panel, but to gain full, direct sun in the late afternoon.
Below you can see the corner of the frame, braced, 20cm leg and foot, with two holes for bolts into the wall.
The other end of the frame is identical, but has a 30cm leg.
Note the black arrow; there should be absolutely no weld in here, otherwise the panel won't sit flush in the frame.
The frame has been primed with red lead oxide.
Here's the completed frame; I think you can see the legs at the top are slightly longer than those in the foreground. Don't be confused by the shadows on the ground.
Now to mount the frames on the wall, install the panels and connect the wiring. That may take a week or two. I'll need help bolting the panels to the wall.
Lateral thinking is always important in life; it's always difficult to reject a half built project, but it's better than sitting with a problem for ever and aye.
Finally I made the decision to put the panels where they should have gone from the beginning; on the roof. Because it was high, and slippery, I was against the idea because I wanted to do it all myself; pride cometh before a fall.
The cost of having a local company fit these west facing solar panels was much less than I expected; and I didn't have to risk my neck.
They are the largest panels I have ever seen; 310W each, providing an extra 930 watts.
The most surprising feature, despite the fact they are west facing, is that by 9am they are already contributing. Under the eves, shadowed by the overhang they would have delivered no power until after lunch.
But the real benefit of over-supply is that every time a cloud passes over the sun, I no longer have to rush inside and turn off appliances. And on a marginal overcast day of we still have more than enough energy for computers, and to fill the batteries for lights at night.
The other major benefit of course is that late in the afternoon, these west facing solar panels are pumping in a lot more power, directly facing the sun.
One other consideration is that it has meant adding an extra MPPT controller. They can only handle 60 amps each, and the new west facing panels exceeded that maximum.
East facing solar panels are something for the future.
You should not use the same MPPT for north, east and west facing solar panels. The voltage of the various strings, oriented differently to the sun, will be quite different, and that will confuse the regulator.
In any case, once you get to adding either east or west facing solar panels, or both, you'll be needing an extra MPPT. You shouldn't have more than two strings on one MPPT apparently, both oriented the same, but I confess I have three and it's working fine. It's probably not the right thing to do.
Ideally I would be thinking of about 4kW of north (or south in the northern hemisphere) facing solar panels, and perhaps 1kW east facing, and 1kw or west facing to provide later afternoon energy.
Smaller 20A MPPTs would be suitable for the east and west facing panels.
I'm considering a mobile array at ground level that can be turned manually to follow the sun instead of one facing east with its own MPPT, and another facing west, also with its own MPPT. I would angle them a say 60 degrees to maximise the early and late radiation.
Our whole solar power energy is derived from 3.2kW of panels on the roof, plus now an extra 930W from the west facing solar panels. This should supply most of our needs; it does as long as the weather is fine.
The extra MPPT allows for the addition of east facing panels in the future to catch the early morning sun when energy is needed for the coffee machine and toasting our low GI bread.
Bernard Preston is something of a backyard permaculture freak. That means working with nature rather than against it; collecting the sun's energy and rainwater, and growing his own fruit and vegetables free of chemicals is just one small part of the whole. West facing solar panels is a late development.
It's to augment the need for more energy in the late afternoon and was something of an experiment, and has been remarkably successful.
A day in the life of solar geek Bernard Preston
» West facing solar panels