Our photovoltaic solar panels were installed on our roof just over a year ago, in
April 2012. As they've been installed for a whole year now, we can see how effective they've been not only in Summer but also in Winter.
Having kept note of production from the solar panels also meter readings for the last year, it's possible to draw a graph. The graph takes into account 12 months, I've added the first six days of April 2013 to the April 2012 figure in order to show that as a complete month:
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| Note that apparent downward trends in consumption for May/June and July/August/September in 2012 were due to our reading the meter inconsistently in those months so we don't have exact figures. However, total area of the red "actual use" is correct. |
The blue bars show solar energy production each month. Red bars show our consumption. It's quite pleasing to see the blue bars drawing a good approximation of a sine wave, as they were expected to do over a year. It's also interesting to note that our electricity has some similarity to a cosine curve. While we don't use electricity for heating, we use electric lights a lot more in winter than in summer, and perhaps we also bake more in winter.
Successful experiment !
I'm pleased with the result of our first year of solar power. The electricity that we generated from April 2012 to April 2013 totalled 3286 kWh with a value of about €680. The shortfall was 133 kWh, which has a value of about €27. So long as the system remains so effective our electricity bills will remain minute.
The predicted output of our panels in our location was about 3150 kWh, so in the first year we've generated about 5% more than the supplier said we would. No cause for complaint there, especially given that last summer was
one of the wettest on record.
The system cost €8000. It will take just under 12 years for the system to pay for itself if electricity does not go up in price within that period. I predict that it will and therefore I expect the system to pay for itself sooner. Time will tell. In any case, we are effectively immunized from the effect of any electricity price rises.
The panels are guaranteed to have over 90% of their rated output in 10 years time and over 80% after 25 years.
Peaks and troughs
Our peak month was May when we produced 447 kWh. June had the best ratio of production vs. consumption, 392 kWh vs. 223 kWh (production was 175% of consumption). You'll note that the lacklustre summer of 2012 caused June and July to have lower output than May.
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Even when completely covered in frost there is still some
output - 600 W when this photo was taken. |
The worst month was December. In this month we produced just 35.2 kWh but consumed 328 kWh. Our production was just 11% of the consumption. January was also low, but note that production held up quite well in other winter months, in November we produced a third of the electricity we consumed and in February over 40%.
From April when the panels were installed through to January, we had a positive balance in the amount of electricity generated vs. consumption. In February the balance went negative.
What happens at night ?
It costs us roughly €240 per year to be connected to the grid. This gives security of supply and of course for us the grid operates as a "battery".
There is no practical way of storing large amounts of electricity. People often imagine it's as simple as having a car battery in some corner of your home, but actually it requires a huge battery to store enough energy to run an average western home at night time. What's more, as you can see from the sine-wave of production vs. cosine wave of consumption, we don't have just a 24 hour cycle over which our consumption has to be matched to production but a 365 day cycle. To store enough electricity in Summertime to power the homes of people with average Western lifestyles through Winter is in fact impossible. The earth
does not have enough resources to built a battery capable of doing this.
And what is that "battery" in reality ?
My electricity provider, Oxxio, state that the electricity I buy from them is entirely "green". They say that the energy comes almost entirely from water power, but of course there are no hydroelectric power stations in the Netherlands, so what does this mean ?
Oxxio, like other suppliers, buy "green" Guarantee of Origin certificates from Norway. Norway and the Netherlands are linked by
a 700 MW cable, enough to balance the grids a little but only to carry but a fraction of either country's use. The Netherlands as a whole uses a lot more than 700 MW of electricity. Oxxio have
800000 customers. If each of their customers consumes electricity at the same average rate as we do (and we're a little below average) then total consumption of Oxxio customers is about the same as half of the capacity of the link between here and Norway. Oxxio are but the fourth largest electricity supplier in the Netherlands. One of their competitors, Essent, has over 2.3 million customers and many of their customers are signed up to "green" electricity as well.
The figures don't add up and when you look at it, it's obvious why. While companies in the Netherlands and elsewhere are buying
Green Certificates which say that the electricity they sell is "green", nothing requires that the electricity they sell genuinely comes from a "green" source as these certificates are "
traded separately from the energy produced".
I'm pretty sure that Norwegian consumers assume all their electricity is "green" because virtually all (
98%) of their electricity generation is from hydro electric plants. As a result, the "green" electricity is in effect being sold twice. Electricity sold to Norwegians, whether they realise it or not, is now certified as being
over 75% non green even though they are being sold electricity which overwhelmingly comes from that country's hydro electric power stations. The reason is that Norway is selling their Green Certificates. The result is that Norwegians, perhaps unwittingly, buy their hydro-electric power as "not green" at a lower price while those of us in countries like the Netherlands who buy "green" electricity are actually been sold electricity which comes
almost entirely not from renewable sources but with an additional charge to cover the Green Certificates.
And so in reality when we switch on our lights at night time or in winter, our electricity comes almost entirely from non-renewable sources. That we produce and export genuinely green electricity much of the rest of the time doesn't help at night because there is no way to store "our" electricity and return it to us. Similarly, it doesn't help much that we're signed up to a green energy supplier because they have no way of guaranteeing that our electricity genuinely comes from a green source.
I still think it's a good thing to have the panels on our roof, and I still think it's got to help a little to buy from a green supplier. However, this isn't quite the green energy revolution that I'd hoped for. If you know of a solution, please let me know.
One solution, the most important of all, is to consume less. That was the immediate response from a friend of mine. We are working on that too !
