Let's have more solar power

On Wednesday we brought home some solar panels and an inverter and we finished installing them on the roof of our garage today.

These panels are aimed to the south to try to pick up the maximum sun that they can over the whole day, but nearby trees will cause some shading.

We bought this set of parts from a local supplier, Cedel, so that we could pick them up. The panels aren't extremely heavy, at about 18 kg each, but they are large at 1.8 m x 1.1 m each and of course they're made of glass so quite delicate. As a result, this turned out to be one of the very rare jobs which couldn't be done by bicycle but luckily our son-in-law volunteered to drive with a trailer to collect the panels. Cedel sells a set of two 400 Wp panels with a Hoymiles HM-800 micro-inverter for €800, including a plug and play cable which can simply be connected to an electrical outlet, but I paid an extra €50 for an HM-1500 which can run four panels so that we can expand this system economically in the future. An expanded system will require wiring directly to the meter cupboard so that's another thing that I'll had to do if we decide to add those extra panels

Due to supply chain issues, standard mounting parts were not available. However, that's not really a difficult job. A quick bit of SohCahToa remembered from school and some literally back of the envelope calculations allowed me to work out dimensions for the substantial impregnated fence posts which I'd decided to use to construct the supports.

It turned out that when I included the 68 mm width of the posts in the calculation I could make the entire support with wooden parts of 1 m in length for all the horizontal parts and 0.4 m in length for all the vertical parts, dimensions which resulted in the minimum of waste from fence posts of a standard 2.4 m length.

Our garden fence consists of 4 m2 panels each of which is held up by two fence posts of the same type shared with the next panel. i.e. there's about one post per 4 m2. This has stayed intact through every kind of storm for at least 20 years, and the only work I've had to do was to re-enforce a few panels  which gone rotten at the base where they're buried in soil. So I think the same type of wood is certainly strong and resilient enough in much shorter lengths when holding a 2 m2 panel at a 22 degree angle from horizontal.

It's recommended that 22 kg of ballast be used for each panel in our location and at the height of our garage roof. These supports much heavier than the commercial systems, already weighing nearly 20 kg for each panel, and I've added quite a lot of tiles from the garden, each of which weighs about 8 kg so in total including the supports we have about 70 kg of ballast per panel. This should be adequate. Note that while that sounds like a heavy thing to put on the roof, I weigh nearly as much as the ballast and panel combined and when I walk on the garage roof all the weight is concentrated in the area of one of my feet. The solar panels mounted in this way spread their similar weight over about 4 times the area that I do when I walk.

This took about two days to do, including all the measuring, lifting, cutting etc. We were also delayed by rain. It's a fairly easy DIY job. And if the panels generate around 800 kWh per year, then at next year's 60 cent per kWh price it'll take less than two years for them to earn back what they cost.

The parts were ordered last Friday and ready for collection on Monday. It then took me two days to arrange collection and today I finished installing this setup on the roof of our garage. It's almost impossible to get anything done quickly by someone else at the moment due to covid related staff shortages, but if you're willing to do some DIY most things can still be done quite quickly.

That's not all

These aren't our first solar panels. Actually, we had 16 235 Wp panels installed on our roof ten years ago which still operate perfectly.

Our original 16 panels oriented south-west and still working as well as when they were first installed 10 years ago.

When the 16 panels were originally installed we expected that they'd fall a little short of covering our annual consumption of electricity, but actually they turned out to produce more than had been estimated and almost exactly the same amount as we used. Over time, our consumption has dropped quite a lot while production of the panels has stayed exactly the same for ten years, so for the last few years we've exported more electricity to the grid than we have taken from it. The only problem we've had with that system in the last ten years is that the inverter failed four years ago, but even though the manufacturer wasn't co-operative at all I fixed it at minimal cost and it's operated perfectly since then.

So you might wonder why we are now installing more panels. The answer of course is that we want to get rid of all our gas appliances. It's been known for many years that fossil fuels are endangering all life on the planet. This has to stop. We can't control everything, but we can control our own consumption. By continuing to buy fossil fuel we empower the companies that produce it and we just can't keep doing that. Insulating our home has already reduced our gas consumption for heating to less than an average small apartment, and we now cook entirely with electricity (the cooker only ever used a fraction of the gas that heating uses). We didn't replace our central heating boiler, which is old and inefficient, because buying a new boiler would lock us in to continued gas usage. Our low consumption is entirely the result of it not having much to do any more because the house is so well insulated. That means we could now economically replace our gas central heating with electrical heating, and that's even more true as of today with the extra pair of solar panels.

Heat pumps which could replace the central heating and heat the entire house in winter are still quite expensive and a bit hard to justify on price grounds, but we could install a small air conditioning unit which can produce heat with about the same efficiency as a heat pump in the living room as that's relatively inexpensive so that may be what we choose. We barely use any heating in the upstairs anyway.

A third smaller, experimental system

We've also been experimenting with smaller scale solar power system. One of our daughters lives in a flat in Assen. Unfortunately we can't fit solar panels anywhere on the outside. The balcony might have been an option but it faces north west so only receives sun just before sun-down which means it's quite a pleasant place to sit on a summer evening, but doesn't make any sense at all for solar panels. The rear windows face south east, but there's no place outside on that side of the building. As there are no really good options I decided to experiment with mounting solar panels inside the double glazed windows. After all, if you don't try it you don't know how well it works.

From the outside it's quite difficult to tell which window is full of solar panels.

They're just the right size to fill this window. Luckily there are other windows in this flat so this doesn't block all light.

The panels for the flat are a flexible type ordered from Aliexpress. I couldn't find them anywhere else. Luckily, one supplier has a depot in Poland which because it's inside the EU meant they were delivered to us promptly and without any unpleasant customs related surprises. These panels are a quarter of the size of the new panels that we've installed on the garage, just 1050 mm long by 550 mm wide. They're also really light in weight. As a result they're much easier to transport, I took both of these panels to the flat packed in their cardboard box by riding my bike with the box wedged under one arm. The inverter in this case is a Hoymiles HM-400, which operates quite well with two of these panels connected in series, though as it's rated for 400 W it's working well under maximum capacity.

These panels are nominally rated at 100 W each. Two of them connected in series and propped up in our garden roughly aimed at the sun on the reasonably sunny day when they arrived together produced 140 W, which seems quite reasonable. In the window of the flat we've not yet seen more than 90 W due to losses caused by the glass and the requirement to mount them vertically. Update later in September: we've now seen over 100 W on several occasions from the panels in the flat window. This might make them more worthwhile.

It's still an experiment. We want to help our daughter with the ever rising energy costs, but will this be worth doing given that the output is quite low ? It seems that mounting the panels inside roughly halves their output. This will vary depending on the glass, of course, and also on the panels due to different panels reacting to different frequencies of light. One smaller 12 V / 20 W panel that I have at home loses only about 20% due to being held inside a double glazed window, but unfortunately these panels are affected to a larger degree.

In total this system cost about €360. Half of the price was for the solar panels and the other half for the inverter. In the first week that they were connected, in September, we saw about 0.25 kWh per day from the panels mounted inside the flat. At the end of the year my daughter's electricity will cost over 60 cents per kWh, so that's worth about 15 cents per day. If we estimate that the average over a year is about half that much the electricity generated by these panels will be worth about €27 a year, which means a payback period of over thirteen years which I think is too long by any way of looking at it.

How about if we add two more panels (connected serial/parallel - making the equivalent of one 400 Wp panel which is still within the specs for the HM-400) ? Obviously this would block another window. It would also increase the cost of the system by 50%, but output would increase by 100%, or perhaps even slightly more if the inverter wakes up earlier due to the increased output of four panels. The result is a would be a payback period of almost exactly ten years, if the electricity price stays at 60 cents per kWh, which is still not great, but it's not far off what I originally expected from the roof-top system. Of course if prices continue to rise then the payback period will become shorter, but they may also drop.

For now I don't desperately need these panels for another purpose so they can stay put for a longer experimental period, or until my daughter says she wants rid of them. They'd perhaps be more effectively deployed on the south west facing wall of our home where they'd pick up the early morning light without their output being reduced by being mounted behind glass, and pay for themselves in about 7 years. I think a set of four of these would make a fairly good easily transportable system for someone who lives in a rented apartment and has a south facing balcony as they'd then pay for themselves in about five years.

Another really small system

I've had a small flexible solar panel on my velomobile for over ten years. In summer it's kept the battery charged so everyday use didn't require plugging in a charger. Unfortunately, the circuit got damaged and I had to replace it. I decided that this time I'd use a much simpler circuit - a shunt regulator with a zener and a single transistor to limit the voltage to about 7 V. Current is limited by the panel itself, the internal resistance of the battery and because once the voltage gets close to the maximum the shunt starts to conduct a bit. This circuit does a reasonable job of keeping a NiMH battery pack topped up and it can't damage that kind of battery. Don't even think about trying this with a lithium battery. I built two of these so that Judy no longer has to charge the battery for her velomobile either:

Velomobiles are the most efficient vehicles on the planet, maximising the potential of human muscle power. Judy's now has a small solar panel, just like that on my velomobile, which keeps the battery used for lighting and indicators topped up.

Of course I've not even tried to work out whether this is economical compared with charging from the mains. I had the parts and it's convenient for us.

Repairing and improving a vacuum cleaner. Samsung SC4580/SC4581 motor replacement and leak fix

 A few days ago our vacuum cleaner stopped working. What actually happened is that it made a rather unpleasant burning electronics smell, accompanied by a significant reduction in suction. I took it apart, and the first thing that was required was a good clean. Clearly the dust which went into this vacuum cleaner did not all end up being collected, but was instead swirling around all the internal parts because there were so many leaks. So the first thing I did was take everything into the garden for a wash.

By connecting the mains electricity directly to the motor instead of running it through the electronic speed controller I could confirm that it was indeed the motor itself which was faulty. The motor is combined with an impeller and put together without any easily removable fasteners. They are not separable or easily maintainable. The bearing seemed to be fine, but it was obvious that the coils had become rather hot and that the insulation on them was no working properly

A direct replacement motor is available from Samsung, but this costs about €90. On the other hand a generic replacement motor with the same dimensions (130 mm diameter, 110 mm height), described as suitable for Samsung / Dyson / AEG and other makes, cost only €30. So that's what I ordered as a replacement. Note that this suggests that all these vacuum cleaners have essentially the same parts inside apart from the plastic mouldings around the motor.

Label on the generic replacement motor. Little information other than diameter, height and wattage.

The generic motor was the same size, but not identical in all ways. In particular, the two holes on the top of the motor must line up with two plastic studs inside the plastic housing which hold in place a piece of rubber which absorbs shock and stops the motor from rotating:

This, of course could be fixed. I cut off the plastic studs, drilled holes in the correct place for the replacement motor and glued some wooden dowels into place with epoxy:

Another small issue was the power connectors were a different place on the replacement motor and the housing didn't provide space for them. I found that they could be bent slightly to fit and then I had to solder wire directly to the terminals instead of using push-on connectors. The parts could then be re-assembled.

While looking for information about these vacuum cleaners I came across an interesting blog from someone who had eliminated the leaks. While re-assembling I followed his suggestions in the hope that this would improve performance.

Result: Our vacuum cleaner now works perfectly again

It's as good as new. Actually it's better than new in three ways:

1. It sucks better than ever
2. It is much quieter than it used to be
3. It uses uses less electricity than before

The replacement motor is rated at 1200 W instead of the 2000 W originally fitted so power consumption is lower (this obviously depends on the power setting), but it's sucking better because sealing the leaks means that less of the effort put in by the motor is wasted. Meanwhile, getting rid of the leaks also means that most of the wind noise that the machine made has now gone away.

Ten years of rooftop solar power - no decline in output can be seen

Today is the tenth anniversary of the installation of our mains connected rooftop solar panels. In total the inverter reports that 33935 kWh of electricity have been generated in ten years, an average of 3394 kWh per year since they were installed.

After ten years we still can't see any decline in output

Output in kWh per year. Note that there's considerable variation depending on the weather. The lowest output was 3126 kWh in 2018-2019 and the highest 3516 kWh in the second year. Last year was also higher than average, within 0.1% of the highest.

A rough calculation before installation suggested that we could expect around 3478 kWh of electricity each year under ideal circumstances, but our supplier suggested that in practice given the angle of our roof we should expect around 3150 kWh per year. The guarantee with the panels said that a decline in performance of 10% over the first 10 years was within normal bounds. This year's 3392 kWh is only slightly under the ten year average, but as it's higher than four of the previous years (including the first year) it's also far from abnormal. I don't see evidence of a decline in output due to aging.

We still produce more electricity than we consume

Blue and red bars show production and consumption per month. The yellow line shows the cumulative difference which we've exported to the grid. We started consuming less electricity five years ago, but over the last year we've consumed slightly more than the previous four years.

I painted our house last year, but I didn't clean
the solar panels. That doesn't seem to matter at all

Over the ten year period we've produced about 10% more electricity than we've consumed, but actually for the first five years our consumption was close to the production (for reasons explained previously) so it's more accurate to say that we've produced about 20% "too much" over the last five years. In other words, our overproduction over five years is roughly the same as the annual consumption of a household like ours.

Cooking with electricity changes the pattern

You'll notice that the graph showing the cumulative difference between our production and consumption has actually leveled off a bit over the last year. The reason for this is that we've switched to cooking with electricity instead of gas, this being one of the ways we've been trying to further reduce the footprint of our already low carbon diet. There's no new kitchen, that'll have to wait for a while. We've been using a small portable electric hob resting on top of the gas appliance as an experiment, which has worked out very well. An induction hob would probably work better. Anyway, it's nice to see that despite this increase in electricity consumption the yellow line is still heading upward at a faster rate than it did on any year before 2016.

Thoughts about home storage

A smart meter was installed four years ago so we now have three full years of smart meter readings. Though we have a single tariff contract so pay the same for electricity any time night or day, the smart meter nevertheless separates out the low and high rates of electricity which roughly correspond to day and night. Overall through the year, 39% of the electricity that we use comes directly from our own panels while 61% comes from the grid and we use 38% of what is generated by our panels while exporting 62%. Obviously a battery comes to mind immediately when looking at these figures, but I'm still not convinced that it's worth the investment. How much could it change these figures ? I think by less than we might hope:

Home storage batteries have capacities of around half of a day to a whole day of typical usage. It's enough to reliably keep your refrigerator going overnight during summer, but not remotely enough to span the seasons.

In the summer months such a battery would fill up in the first couple of days and then it would stay nearly full for weeks. The battery would allow us to consume our own electricity overnight, so that for periods of nice weather all of the electricity we use would be "our" electricity from our panels, which is of course an attractive idea. During that best case scenario we would increase from the average 60% of our electricity that currently comes from our own panels during summer to 100%. For the six best months each year we produce on average between 1.7x and 2.1x as much electricity as we consume so even with a battery working as well as it possibly could we could still only capture some of our own electricity for our usage and doing this would only actually increase the percentage of our own electricity that we consumed from the current still 30-35%% to about 50-60%. Also, this is Northern Europe. There are periods even during the nicest Northern European summers when the solar panels don't produce as much as we'd like, so the battery will run down and we would still have to buy some of our electricity from the grid.

New, huge, windturbine in Drenthe

And then there's winter: In the winter months there's far less sunlight falling on our panels and we possibly produce enough electricity to cover our own usage without annexing our neighbours' roofs. Because there's so little sun in the winter what comes from our panels currently covers only about 10-15% of our consumption and during these dark months that means we are already consuming 70-80% of our own electricity just with normal daytime usage. During the winter a battery would therefore be empty or near empty most of the time. While a battery would mean we would reliably consume all of our "own" electricity during winter it wouldn't win us much because there's not much to store: It would reduce the proportion of our electricity that we buy from the grid from the approximately 90% during winter now to around 85% with a battery.

Financially I don't see the benefit of a battery at all. It's an expensive gadget which will change very little. Let's also remember that the electricity leaving our home is not wasted. It's used elsewhere, reducing demand for other, on average less green, generation. So what exactly is gained by trying to keep our electricity to ourselves ? It seems more likely to benefit the ego than the environment.

So to summarise, I'm still not convinced that there is actually any real point in home storage using batteries. I think we'd possibly get some real benefit from installing a few more panels on the roof as while these could of course not do anything about our nighttime usage they would mean that we'd cover more of our own consumption during the day and if we get around to installing an electrical heat-pump for heating (instead of the old gas boiler) then balancing the resultant greater electricity consumption with more panels would make sense. I also have doubts about how wise it is to encourage people to install large and potentially highly flammable lithium batteries in their homes. They might be fine when new, but what happens in 20 years time when they've not seen maintenance engineers in many years and they're failing in various unexpected ways? I think it is a better idea to install batteries as large scale devices at substations or next to large solar parks or wind turbines.

Our business is also powered by these solar panels. We sell practical bike parts which help people, especially those in other countries where such parts are not so easy to find, to reduce their impact by cycling. Bicycles are the most efficient vehicles on the planet. We don't use motor vehicles so every shipment begins with at least the first few km on my bicycle, using nothing but human power.