First two weeks of solar power

Wet solar panels are not the most
productive solar panels

I was going to write this after one week, but time kept passing. We've now had solar panels on our roof for 15 whole days.

April has been extremely variable so far. We've had very bright times and also heavy rain and hail. Temperatures in the morning have been low enough for there to be a fairly heavy frost on some days.

The peak recorded output of the system so far is 3994 W, and most days a figure very near this is reached at some point or another. However, output can dip as low as 100 W during an otherwise sunny afternoon if the weather turns bad. This has happened quite often, and these two weeks have been far from optimal for generating solar electricity.

Over the last 15 days, our system has generated a total of 178 kWh. Our consumption over this period days was just 139 kWh so we've contributed 39 kWh to the grid. However, last year we consumed a total of 4048 kWh. This works out as 11 kWh per day, or 166 kWh over an average 15 day period. When viewed against this average, our excess is far smaller.

A day later, production was at 191 kWh

The figures for last year's consumption were what we used as a target when deciding on the capacity of our system. We benefit from the retail price of electricity (in our case about 18 cents per kWh) for any amount that we generate up to our own usage but can expect a far lower benefit for each excess kWh that we generate.

Our expectation is that in the summer, with consistently better weather, we'll generate more, but in the winter with worse weather we'll generate considerably less.

It's too early yet to say how well the system will work through the entire year, but performance so far does seem to be roughly in line with expectations. If electricity prices do not vary and we generate exactly the same amount of electricity as we consume then the system will pay for itself in just over 11 years. Any increase in the price of electricity makes the payback period shorter, and as soon as the system has paid for itself we're effectively on free of charge electricity for as long as it lasts.

This is part of our pension, and in essence, we have used it to make a bet that energy prices will increase. I'm not normally a betting man, but I like the odds for this.

Read more about our system.

We now have our own solar power

I've had an interest in solar power for many years. There's a cost in both money and environmental damage in building the equipment, but once installed it's clean, green and gives free energy. It has been obvious to me for some time that the sums add up well for PV, and others have also shown that the best alternative to fossil fuels which currently exists is electricity from photovoltaic panels.

For over twenty years I've had small PV systems powering things in the garage and/or garden shed. Since we've lived in the Netherlands, I have had a 12 V panel on the top of the garage which runs a radio and light and little else. This, like previous efforts, is a hobby, not a serious attempt to power anything. However, now that the cost of installation of a serious system has fallen so much, I felt it was now time to get serious.


After a period of subsidies coming and going, and this rather screwing up the market for home PV installations, there are no subsidies available at the moment. However, the price has stabilized at a reasonable figure. We paid just over €8000 our system, and this should pay for itself in about 10 years - even if electricity prices don't increase. Prices are far more likely to increase than decrease, so the pay-back period could well be better than ten years.

The system that we've had installed consists of 16 ET-P660235 235 W panels from ET-Solar connected in two strings of eight each into a Power-One Aurora PVI-4.2 inverter. This gives a rated output of about 3600 W when the sun is shining directly onto the panels on a sunny day. Overcast days will of course produce less electricity. The panels are guaranteed to have over 90% of this output after 10 years and over 80% after 25 years.

We consumed just over 4000 kWh last year. That's quite a lot, but it's explained in part by our working from home and having two teenagers living at home. Our PV system's expected output is a little lower than this, but we could fit not more panels onto our roof. If we are to avoid paying for electricity, then we will have to reduce our consumption to match our generation.

I'll blog further about how successful the system is in reality. At the time of writing, it's been in operation for under 24 hours.

Our system was installed by EnergieWonen in Almere. If you contact them for a quote, tell them that I sent you in their direction.

The first panel being lifted onto the roof

Fitting of the first panel

They're big. Each is about 8x the area of the small panel on the roof of our garage.

Fitting of second panel

All sixteen on the roof.

Read more about our solar power system including a summary of its effectiveness after the first year.