Friday, 9 September 2022

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.

Wednesday, 24 August 2022

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.

Tuesday, 5 April 2022

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.

Thursday, 2 December 2021

Modifying a thermostat to make our heating more efficient

It's December 2nd and it snowed today. That was the first time that it snowed this winter, and it reminded me to write about a very cheap modification to our thermostat which made our heating system both more efficient (using less gas) as well as giving us better control of the temperature in our home.

Our central heating system is quite old and inefficient, dating from the 1990s. I've been meaning to replace it since we moved in, but first we did quite a bit of insulating, including the walls, roof, floor and triple glazed windows. All of this dramatically reduced the energy input required to stay warm and as a result we've gone from a home which was expensive to run in winter even while we were still cold to one which is very efficient so the heating doesn't come on very often. Much of our gas usage now is actually due to our even more inefficient and old water heater. We now burn far less gas than average because even though our central heating boiler remains old and inefficient it doesn't come on very often and last December we used less than half the amount of gas that average homes of our size required for heating, less even than an average apartment. Insulation works.

This shows gas usage last December. Our bill for electricity and gas together averages around €45 per month over the year. In part this is because the energy company pays us for our excess solar power.

One of the things that put me off buying newer gas appliances was wanting to get rid of them altogether. Unfortunately, when I first looked into doing this I was getting five figure quotes for heat pumps which made it impossible to justify them on economic grounds. Insulating saved us more money more quickly, and the solar panels were also far easier to justify economically. But the price of heat pumps has come down and I do now want to switch. Unfortunately, the absolutely awful government which this country currently has has ensured that the covid pandemic has already gone on for nearly two years and it'll probably go on for a while yet. I'm not keen on having people come into our home while this disease is spreading so the heat pump will have to wait. However I did think of a way of making our existing system more efficient:

Uneven temperature due to too much insulation and an overenthusiastic central heating system

Our boiler and radiators were designed for a leaky house. The radiators are large and the boiler likes to generate lots of really hot water. I turned down the temperature setting on the boiler a very long while ago and there's no problem with the house heating up (this bodes well for replacing it with a heat pump which will produce cooler warm water) but we still had a problem with excessive heat.

What happens is that thermostat switches on, the radiators heat up and because it takes quite a long time for convection to transport heat from radiator to the thermostat the heating would continue to push out heat for far too long resulting in the temperature overshooting sometimes by 3 C over our selected temperature. Setting the thermostat at a lower temperature doesn't fix this problem because that means that the lower temperature has to be reached before we get any heating at all. We were a victim of our good insulation.

My first thought was to replace the thermostat with an Arduino programmed to turn the heating on only for short bursts and I started working on doing this before I realised I was overthinking it: Couldn't I instead do something to convince the existing thermostat to switch for short bursts ? At first I thought perhaps this could be done by adding something like a 555 timer circuit which would change the state of the relay in the thermostat more often, but then I thought of an even simpler solution:

The solution which costs just a few cents

The thermostat operates by closing a relay contact between two contacts attached to wires from the central heating boiler. Those wires have 24 V AC on them when they're open. When they are shorted that powers something within the central heating boiler which turns on the gas and the pump. I found that a dead short wasn't required. Actually, any low value resistor across the two wires worked just as well as a dead short to make the boiler start up. Trying different values allowed me to calculate that the boiler consumes a constant current of about 80 mA for any low value of resistor across the contacts. A 47 ohm resistor drops about 3.7 V and consumes about a third of a watt itself which is enough to make it slowly warm up. I realised that if I installed this small "heater" inside the thermostat next to the temperature sensor it would give just the desired effect of short bursts of heat from the system before the thermostat thought the room had warmed up and would switch off again.

The temperature sensor is easy to spot. It's mounted such that ambient air can easily influence its temperature.

It was easy to find the temperature sensor inside the thermostat and easy to confirm that that is what it was because holding it between your fingers results in the temperature on the front panel of the thermostat rising quickly.

A 47 ohm resistor wrapped in self-amalgamating tape. This is now installed inside the thermostat next to the temperature sensor in the photo above

I attached a couple of wires to a 5 W 47 ohm resistor from my collection of parts, wrapped it in self-amalgamating tape to ensure that it doesn't cause a short and have installed this next to the temperature sensor in the thermostat. As I didn't need to actually buy anything to make this modification it cost more or less nothing to make it. If I'd had to buy the parts the most expensive thing would have been the roll of tape.

It works !

Now the thermostat can turn on the heating only for a couple of minutes before the resistor has warmed up enough that it thinks the target temperature has been reached. It then switches off again and the thermostat slowly returns to room temperature. If this is still below the target temperature then the heating will switch back on again for a few minutes. It takes a little longer than before to warm from a cold room, but we never overshoot by more than a fraction of a degree. Though the radiators never really get hot any more, there is enough energy in them to heat the room without burning more gas. This results in much more consistent and comfortable temperatures in the room and we hope also to see a lower gas bill due to less gas being burnt.

Next year perhaps we'll look again at replacing our central heating boiler with a heat pump. It's important that we all stop using fossil fuels but for now, with covid raging, the step of using a bit less is still worthwhile.

The result

We consumed 148 m3 of gas in December 2021 vs. 147 m3 in both December 2019 and 2020, the two previous winters with full triple glazing downstairs. Clearly there's no dramatic change there. January, February and March looked a lot better: We consumed 183 m3, 144 m3 and 107 m3 in Jan, Feb and March 2021 vs. 130 m3, 107m3 and 50m3 in 2022. There's still little data and this could be because those months in 2022 were milder. As more time passes there will be more data. But even if this makes no difference to gas consumption it does at least make our home more comfortable.

Our gas consumption in March was really low. Our home is a "2 Onder 1 kap" type so we used under a quarter of the average Dutch home, not only because of the other measures we've taken but also because we turned the thermostat to an even lower temperature than usual in order to avoid funding Putin's war in Ukraine. March was also unusually sunny so the energy company owes us €100 for the electricity that we supplied to the grid in March.

Monday, 5 April 2021

Nine years of solar power. 30 MWh generated.

Today is an anniversary. Our rooftop solar power setup was installed on this day nine years ago. When the system was first installed I had two concerns, about the inverter and about the panels themselves.

Inverter
The biggest concern was about the inverter. I expected that this would have a limited life because an inverter is inevitably a box of power electronics which has to work quite hard. Power supplies, especially in my experience switched mode supplies, can be quite unreliable after a few years. I've fixed quite a few of them in the past, and switched mode supplies can be quite tedious to work on. An inverter is like a large switched mode power supply which works in reverse so I didn't have huge expectations for longevity and sadly the inverter has actually failed twice, first in 2018 and then in 2020. In both cases it was quite simple to fix and because I know which end of a soldering iron to hold onto I did that myself.

Panels
The other concern was the less well known longevity of the solar panels. There are two main ways in which solar panels degrade. The first is due to corrosion should they become damp and the second due to the sun light falling on the panels degrading them. I've had solar panels on homes that I lived in since the mid 1980s, starting with several 30 cm x 30 cm panels which I used to charge batteries. Those panels were not sealed from the weather so they got damp, there was visible corrosion in some places, and their output dropped markedly over time. But around the turn of the century I bought a 12 V sealed panel to replace them. I still have that on my garage roof and it's output is still close to the specification so I hoped that the panels for the roof be similarly long lasting.

The guarantee said that the output of the rooftop panels would still be at 90% of the initial level after 10 years of use. I realised soon after the panels were installed that their peak output was significantly higher than it the specification suggested. The rated peak output for the installation was 3760 W and the installers suggested that we'd probably not see more than about 3600 W because of the angle of our roof. But within a few days I was seeing ~3990 W. I had some concerns at that time that perhaps there had been a little slight of hand on the part of the manufacturer, who perhaps under specified the panels in order to protect themselves from guarantee claims. i.e. Perhaps we'd see the panels degrade by more than 10% over ten years but that they'd still be within 10% of 3760 W or even within 10% of 3600 W in ten years time, meaning that a loss of almost 20% of output would be possible without being able to claim on the guarantee. But this has not turned out to be the case at all. There is no degradation. I can happily report that the observed peaks last summer were still around 3990 W. What's more, we're not quite at ten years yet, but the total output from the system also seems not to have dropped even slightly. After the first three years passed I noted that the system had generated 10200 kWh in total. Six years further on the total is almost exactly three times this, at 30556 kWh. What's more, if not for the inverter glitch in 2018 which costs us about 250 kWh of output, we'd actually be ahead of the first three years by now.

Graph of output over time

The orange line shows our excess production over time. It goes up in summer and down in winter, and by March we just about break even which is why the last part looks flat. When the panels were installed we had teenage children at home and our consumption was similar to our rate of generation. You can tell how long ago our children left home from this graph (some lower power appliances also made a difference). The glitch three summers ago was caused by the inverter failing and my taking a few days to fix it. The second failure was a year ago in February and lost only one day's winter output so that isn't visible on the graph.
Finance
When the panels were installed I estimated that it'd take about ten years for them to pay for themselves. Because electricity prices change, we've changed our electricity meter once and supplier more than once, it's quite difficult to work out exactly where we are now so far as the return on investment is concerned. However it's quite easy to make an approximate calculation so that's what I'll do. I know that we'd generated 30442kWh up to the end of March, and of that we'd consumed 27767 kWh and exported 2589 kWh. Electricity costs us just under 20c per kWh so we've saved about €5300 from our electricity bill. With our current tariff we get pretty much the same for what we export so that's worth about €500. This leaves us with about €5800 of our original €8000 investment returned, and at the same rate the system will have paid for itself in about 13-14 years after installation. This is about the same result as I came to about three years ago. Just four or five more years to wait, then.

Note that in reality over a whole year we use about 40% of our own generation directly from the panels and export the rest of what we produce. The electricity company doesn't bill based on this, though, so for a purely financial calculation we don't need to take that into account.

Conclusion
I'm happy with the system. The inverter fault was disappointing and the manufacturer's response even more so, but I fixed that. The panels are faultless. Solar panels with lower performance were much more expensive when I first started experimenting with them in the 1980s but when we installed this system it was clear that they'd pay back within a reasonable amount of time. They're now not far from half the price that they were then so someone considering installation these days can expect to see their money back very quickly indeed.

Sunday, 5 April 2020

Eight years of solar power. How much of our own generation do we consume ?

As of today our rooftop solar panels are eight years old. Here's the latest graph of electrical generation vs. consumption. You can see the eight years which have passed, the data neatly making sinusoidal shapes due to changing seasons caused by the rotation of our planet around the sun:
The blip in the graph is due to the inverter failing in 2018. It also failed in January but I got my soldering iron out sooner this time and because it was January and not the middle of summer far less was lost. Therefore no visible second blip.
The red bars show our consumption of electricity each month. The blue bars show the generation of electricity from our solar panels each month and the yellow line shows our total generation vs. consumption. Since the beginning we've generated more electricity each year than we used and in the last four years we've reduced our consumption making this difference between generation and use much greater. This led to the yellow line rising steadily higher. If you live in the Netherlands or anywhere in Europe connected to the same grid then it's possible that during the last eight years you've used some of the electricity generated on our roof as what we don't use goes into the grid.

Over the last eight years the system has produced 27039 kWh of electricity. That's 3380 kWh per year, very close to the estimated 3478 kWh per year predicted before they were installed. But this total over eight years was impacted quite severely by the period when the inverter failed two years ago. Over just the last 12 months we generated 3438 kWh, which is remarkably close to the prediction.

But while it's nice to see that we generate much more electricity than we use and the system is working very nicely, the graph also exposes an obvious problem. We never manage to generate even close to enough electricity in the winter, and of course there's never any output from our panels over night, which is exactly when we turn on our light bulbs. The installation of a smart meter a year ago has given me more data to work with and so now I can see how much of the electricity that we use ourselves comes from our panels and how much of our own electricity we use (these are not the same thing...). When we're not using our own electricity we're using what comes from the grid, and the Dutch grid is far from 100% renewable (we have of course signed up to a 100% renewable contract, but the effect of that is mostly only to make the paperwork say its renewable).
Data from the beginning of January 2019 until the end of March 2020.
Blue: our generation vs. consumption. Any month where this is above one we generated more electricity than we consumed.
 Red: the proportion of our consumption which was from our panels, varying between 0.12 in winter and 0.6 in summer.
Yellow: proportion of our generation which we consume, varying between 0.25 in summer and 0.75 in the winter.
This new graph which makes use of the smartmeter data shows a more complicated picture. Though each year we generate far more electricity than we consume (blue bars are often well above 1), our pattern of usage doesn't match the generation very well. We over-produce in summer, under-produce in winter and we keep putting our lights on when it's dark outside rather than in the middle of the day. We come closest to being independent of the grid in the summer when our panels generate more than twice what we consume, and though we don't use much of our own electricity (yellow bars) it does make up nearly 2/3rds of our consumption (red bars). On the other hand, while in the winter we consume most of the electricity that we generate, there is very little of it so it accounts for only about an eight of our consumption, the other 7/8th coming from the grid.

As you can see, having solar panels on the roof, even if they generate far more electricity than we use, does not make us even close to being independent from the grid. What's more, there's no way we could make ourselves so.

Batteries
It is of course possible to buy a relatively small domestic battery which has enough capacity to store about one day's supply. If we had one of those it would allow us to consume exclusively our own electricity for March through to September, pushing the red bars for those months up to 1. However in the winter months it would be nearly idle because we then generate on average only about a quarter of our consumption, falling to a sixth in the worst month, and we are already using a high proportion of our generation (the yellow bars reach as high as 0.9), so the battery could do almost nothing to help in winter.

To be independent from the grid through the winter we'd need to store electricity from June, July, August and September to fill the trough in our production between October and February and there is no possible storage system which could do this. At present we could buy a small unit which we could fit into our garage, costing a not inconsiderable sum, to cover ~24 hours usage but to store enough to go through winter we'd need something about 120 times as large and 120 times as expensive. It's just not a sensible idea on any level.

Quite apart from the cost and I have reservations about the reliability of batteries for home storage. We already know that, as I expected in advance, inverters are not entirely reliable. It's a box of power electronics which works hard and so we should expect less than perfect reliability. A domestic back-up battery adds far more complication and is almost certainly less reliable. Why ? Because such a battery installation would require not only its own inverter circuitry similar to what we already have in association with the solar panels, but also a battery charger and the battery itself. More power electronics means more to go wrong.

Doubling the number of panels on our already full south facing
roof isn't an option. North facing panels won't work so well.
Such a battery would more than double the price of the solar panel system, more than double the embedded carbon cost, more than double the chance of it going wrong and requiring costly maintenance or replacement as a result. None of that is good news for us or for the planet. Even given all those constraints, it seems that the manufacturers' somewhat optimistic assumptions still suggest that a battery could only provide us 100% usage of our own solar power if we also at least doubled the number of solar panels that we have. As our roof is already almost full this would require us to annex our neighbour's roof entirely for our own use. That's not going to happen.

Let us remember that the excess that we generate and do not use is not lost. Investing too much in trying to use our own electricity ourselves is almost certainly counterproductive. A good proportion of our excess is consumed by other electricity users, both domestic and industrial. This leads to those consumers having lower emissions from their electricity consumption.

Reduce consumption!
A domestic battery makes no practical sense and doesn't necessarily make sense for our environment either. The best thing for us to do, and I would suggest for everyone else as well, is to reduce energy consumption as much as possible. We're continuing on that path, making our home more efficient every year. The less we consume, the easier it will be for our grid to operate without fossil fuel input. Any additional loads will keep the fossil fuels burning for longer.

Domestic and commercial
Our domestic solar panel setup is not actually 100% domestic. We operate our business, Dutch Bike Bits, out of our home, so the business is also powered from our solar panels. We try to run our business in the most ethical way we can. Therefore there is no extra energy consumption in another building and we don't use any form of motorized transport so our parcels, all of which contain goods to support people who cycle and are therefore assisting other to also use the most efficient vehicles on the planet, begin their journeys by bicycle.

Monday, 23 March 2020

Low carbon footprint hummus (super fast and economical to make)

Ingredients: Chick peas, garlic, tahini,
lemon juice, salt
Hummus is one of the tastiest things to eat for lunch on bread. It's also super easy to make yourself, even from a store cupboard if you're trying not to go outdoors (the COVID-19 pandemic is a very big problem at the moment in the Netherlands).

So if you're stuck for something tasty to put on bread for lunch, consider making hummus. It takes far less time than going to the shops, it's cheaper than commercial hummus and the result is tastier.

The ingredients required as all easily stored except for the garlic. The only fresh ingredient needed is garlic, though you can use garlic from jars if required.

In this example I used a 400 g tin of chick peas, one table-spoon of olive oil, a couple of tablespoons of tahini and small squirt of lemon juice, four cloves of garlic and a tea-spoon of salt.

Drain the chick peas, but keep the liquid. You'll find you need to add some liquid while liquidizing and this is the best thing to use. Keep any which is left over for use as liquid in other recipes (it'll go off if left too long - I put seal on the tin and use within a day or so).

The exact proportions of ingredients are not important. You can vary them to suit your taste buds and also to suit what you have in stock. Even the main ingredient, chick peas, isn't really necessary. OK, so real hummus may be a chick pea dish, but exactly the same procedure can be followed with any kind of tinned or pre-cooked bean and it you get a similar tasty result. So if you need something to spread on your bread and don't have any chick peas, try some other bean. For instance, black-eyed beans make a great spread as well.
Super simple - just put everything in a liquidizer. No cooking is required. Note that everything is shown "dry" here. It's always necessary to add some of the liquid from the chick pea tin to make it liquidize properly. You can also vary that according to taste - some like their hummus to be more liquid than others. If you don't have a liquidizer you can simply mash all the ingredients together. 


After 30 seconds or so it'll look like this. Stop when you like the consistency. It's immediately ready to serve.
One 400 g tin of chickpeas and the other ingredients together make about enough hummus to fill two average commercial retail hummus containers. We buy these only occasionally and when we do that we keep the containers which can be re-used many times. The red specks are due to an optional extra ingredient - I included a red chilli this time around. Other spices or herbs can be added in the liquidizer at the start.
Lunch. This recipe always makes delicious hummus.

Carbon footprint

As before when I made a pizza, I wanted to calculate the carbon footprint of this meal. It won't be very high for the calories because vegan food never is. And in this case it'll last for a few days of lunches so the cost per day will be low anyway. Unfortunately, I couldn't find accurate figures for the chick peas or tahini, so I warn you in advance that the following figures are to a large extent guess work. Perhaps you can help with this.

The first part is easy. The liquidizer consumes 1000 W but it's required for only a very short time. Less than 30 seconds in total. Therefore the total amount of energy consumed is very small. This works out as about about 8.3 Wh, or 0.0083 kWh. Due to the full sun today the only effect that it really had was to make our electricity meter run backward less quickly but I've calculated here as if we were using the average carbon footprint for electricity across Europe. Even so, the liquidizer doesn't do much harm:

Ingredient Quantity (g) CO2 equivalent (kg/kg) Total CO2 (g) kcal
Electricity 0.0083 kW 500 g/W 4.2
Chick peas 400 0.7 280 468
Tahini302.369170
Olive oil 10 1.5 15 80
Lemon juice 10 0.5 5
Salt100
Total carbon footprint / calories373.2 g718 kcal

As explained before, I cannot claim this time that the figures above are in any way accurate. The carbon intensity of tinned chickpeas and of tahini are both based on figures that I found (here) for similar ingredients. I picked "ready to eat meals" for the chick peas and "Nuts and almonds" for tahini (which is ground up sesame seed). As those two items dominate the total this makes the entire result questionable. However I have picked replacement values which are on the high side so I would be surprised if the carbon footprint of hummus made this way is greater than what is shown above.

I hope that readers can contribute better sources for those ingredients.

How much did it cost to make ?

These cheap chickpeas cost about 60 cents a tin, the small amount of Tahini is worth about 20 cents. The other ingredients perhaps 10 cents at most between them. That makes for a total cost of probably less than 90 cents for an equivalent amount of hummus as is found in two commercially made pre-prepared packs which cost about €2 each.

What about dried chickpeas ?

Dried chickpeas have a lower carbon footprint when sitting on your shelf than does an equivalent quantity of tinned chickpeas. However a lot of energy is required to boil them at home. I therefore would expect a higher carbon footprint for chickpeas that I boil myself than is the case for those bought in a tin where economies of scale will make the process more efficient, almost certainly more energy than is consumed in making the small amount of steel in a can. This seems to be confirmed by various sources.