Full disclosure: the Plugwise set with which I monitor our solar panels and which is the subject of this review was given to me for free. Plugwise has imposed no limitation of any kind about what I could or couldn’t write about their products and services. I am not connected to Plugwise in any way, except for being a customer. I have tried not to let the fact that the set was free influence my objectivity – and  I think I managed that quite well. I will let what I did speak for itself: a short while ago I bought another Home Basic set out of my own pocket, that’s how pleased I am with this product. If the Plugwise set hadn’t worked well the second time, I would have just shipped it back of course and certainly not have bought more plugs.

Many people with solar panels don’t monitor the output, which is a shame. The big advantages of solar panels (no moving parts, quiet, no emissions) make it impossible to see at a glance if the installation is working right. Especially in the ‘dark ages’, when the reliability of solar inverters left much to be desired, many people unknowingly had a non-function solar system on their roofs. But even now, in 2010, it’s possible that a plug gets disconnected, corrosion causes a contact to deteriorate or an inverter simply breaks down. All these causes will lead to decreased output, which is obviously something to be avoided.

With this in mind it’s hard to understand why output monitoring is as neglected as it is by both inverter manufacturers, resellers and installers of solar power installations. A monitoring device of some description is seldom a standard option, it has to be requested separately by the customer and is often quite expensive. There are even inverters, usually the smaller ones, which don’t have the option to monitor the output at all. Other inverters offer the possibility to connect to a computer, but require a computer to be running 24/7 for real output monitoring, which is of course undesirable from an energy consumption point of view. Even an energy-efficient laptop computer which consumes 20W would use nearly 200kWh per year, which is equal to the production of one large solar panel.

In our case there is another challenge: because we have expanded our installation several times through the years it consists of six ‘sub-installations’ using three types of inverter. Two of these types (the Soladin 600 and the OK4) are equipped with a data connection but need a computer running 24/7 for monitoring. The third type (Philips PSI300) has no data connection so that can’t be monitored at all.

And yet, I wanted to monitor our installation, not only to keep an eye on the performance but also to generate the statistics for this website so that I can show the public what a solar installation like ours produces. It took me a long time to figure out how I could do this, but I think I found a great solution.

When our installation consisted of only one, and later, two, sub-installations, I monitored the production with a simple analogue kWh-counter, the PM16AR. It worked fine, I just wrote down the meter reading every day after sunset and processed that information in a spreadsheet. When our installation grew to three and later four sub-installations this method quickly became unworkable, and another disadvantage was that I could not monitor production when I wasn’t home.

During my search for a good monitoring product I first came accross the Conrad Energy Logger 3500. Unfortunately that turned out to be a big disappointment () so I quickly shipped that back. Even if the device had worked as advertised much manual labour would have remained because I would have had to periodically read the five memory cards etc.

Further research led me to Plugwise, which looked like a very interesting product because it supported multiple measuring devices which send their data wirelessly to each other and to a computer. A Home Start Pakket () with two measuring plugs costs € 125, but I could make use of a nice discount so I ordered a set to see how it would work. After several frustrating evenings () I unfortunately had no choice but to put the Plugwise set back into its box and ship it back to where it came from. I could not get it to work reliably. The possibilities to monitor our solar system in a user-friendly and affordable way seemed exhausted and I just went back to manually recording the meter readings.

Fortunately the story does not end there: some one from Plugwise saw my article online and called me. Of course they weren’t happy that some one wrote on the internet that their product didn’t work, but they seemd genuinely concerned that I had a negative experience with their product. After e-mailing back and forth a bit they offered me a free (!)  Home Basic set () with nine measuring plugs and a newer software version. That was an offer I could not refuse, and since the beginning of 2010 I monitor the production of our solar installation with Plugwise.

A new start

After unpacking the box, installing the software and USB-stick and placing the measuring plugs in the wall sockets things went much more smoothly than the previous time. All plugs were recognised within a few minutes and I got to work quickly on naming the plugs and installing them at the inverters. I won’t tell much about the installation procedure, it’s all very easy and if you follow the manual there’s little to go wrong.

As mentioned earlier, our solar installation consists of six sub-installations, of which two feed-in their produced power over one wall socket. This means I need five measuring plugs. Three of those five are located in the attic (connected to the  555, 510 and 300Wp installations) and two are on the first floor (connected to the 660 en 100Wp installations). I estimate that the biggest distance between any two plugs is about six metres and the wireless communication between plugs and stick works fine. The plugs use the Zigbee-protocol () to set up a so-called ‘mesh-network’. This means every plug can communicate with all other plugs within its range. If there are one or more plugs which can not be reached directly the network tries to reach those plugs through other paths. This makes the network very robust and measuring data very nearly always reaches the computer. It should be said that this works better with more plugs in the network as there are more potential paths in that situation. I could notice this in use when the plugs in the attic only became available reliably when I installed a plug at the washing machine, at the first floor. Because this is halfway it could apparently cover the gap in coverage. Before that plug was installed I sometimes had to take my laptop to the first floor before the system ‘saw’ all the plugs installed in the attic. Now that almost never happens.

The software is very flexible, plugs can for instance be combined into groups. I created a single group to gather all the subinstallations together, but it would be very easy to create al kind of groups. If, for instance, you have several installations installed on both east and west-facing roofs, you could group the installations together per roof-side. The measuring data can be presented in many different ways, hourly, daily, weekly, monthly and yearly. If the presentation-possibilities of the software are too limited for a certain purpose it’s very easy to export the data to a .csv file which can be read by any spreadsheet software. This allows the data to be processed further for presentation in graphs etc.

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Besides historic data the software can also present current measuring data. Especially on cool, partly cloudy days its great fun to have this screen open. Because the solar panels are cool they can, when the sun peeks from behind a cloud, produce spectacularly high production peaks – sometime even higher then the sticker value of those panels. That lasts for ten, maybe twenty seconds until the panels heat up  and then it drops to more realistic values. Very addictive to watch.

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The plugs themselves use a bit less than 1W per plug. In our situation, with five measuring plugs, that means a total consumption of less than 5W, which means that the system uses approximately 44kWh per year. That’s substantial but much, much less than the more than 200kWh a laptop would use when running 24/7. And besides, we have a substantial electricity surplus anyway and I don’t mind sacrificing a small part of that surplus for a good monitoring system.

On the picture to the right you can see all nine plugs that came with the Home Basic Set on the Conrad Energy Monitor 3000 all at once. It’s nearly ten years old but it still works perfectly.

This brings me to the accuracy of the system. For the first three months of use I used the Plugwise plugs together with my analogue meters. The measured values were nearly always within a few percent of each other. It was only during the dark winter months, which also saw much snow on the solar panels, when the measured values differed markedly, but that was no surprise. I think the accuracy is good enough to reliably monitor a solar electric system.

Disadvantages

No product is perfect and Plugwise is no exception. I haven’t been able to find many disadvantages, except these:

Privacy

When installing the Plugwise software the user is given the option of ticking a box with the text: “I allow my anonymised data to be sent”. When you choose not to give this permission, like I did, the following message is displayed: “Warning: By disabling the anonymised upload, you are not in compliance with the license agreement. You will be excluded from the right to receive any updates and support from Plugwise until you enable it again.” So, when you don’t want Plugwise to have your anonymised measuring data (anonymised according to them) you are excluded from support and automatic updates. For me this has not been a problem as have not needed any support and new software versions van be downloaded manually from the Plugwise website, but still…  I think it feels a bit like ‘teasing the customer’).

Many people don’t understand why I think this is a problem. I find it hard to explain as I’m still discovering what my opinion on privacy () is, exactly. I’m already sure that I just don’t want companies and the government to have access to so much data about what I do, without much control by me. Much can be read from data like this: when and for how long we’re on holiday, how much TV we watch or how often we’re using he computer, how many times the washing machine runs. This kind of data is a gold mine for corporations, but I would like to be in control about who has access to this data. It is comparable to the debate about the so-called ‘smart’ meter (), a device which I don’t want to have for much the same reasons.

A second point that I find troubling is that it seems that the data is only anonymised after it arrives at the Plugwise server. According to some people in a domotica forum () I read the Plugwise software sends very detailed information to the Plugwise servers, including names of the plugs and name/address data. Of course I need to be honest and say that I found this information on a public forum wher everyone can say anything without any check on truthfulness. It’s possible that the information about Plugwise is not correct (anymore), but it seems to me like there are some very smart people there with a thorough technical knowledge.

All this means that I’ll have to trust Plugwise that they’ll anonymise the data after it arrives on their servers – but I have no way to check it. It’s certainly possible that some one breaks into their servers  and gains access to my data, because the anonymising might only be doen just prior to using it for whatever they use it for.

For people who don’t care about their privacy, or people who don’t mind giving up the right to support and automatic updates this disadvantage is not applicable. My opinion is people should care about their privacy, but everyone has to decide that for oneself.

In a German review () of the Plugwise system, which I found on the internet and which was generally positive about the system, one of the four pages is used to describe the privacy aspects of the system.

Measurements are logged only once per hour

The highest resolution in which the Plugwise system can display the measuring data is one hour. If I remember correctly the Conrad Energy Logger 3500 could log data every 30 seconds. I would be happy with a resolution of ten to fifteen minutes, but after a while of use  I don’t mind this limitation as much anymore. I am also realistic enough to realise that if Plugwise logged with a resolution of ten minutes I would be asking for a five or two-minute resolution

Price

The system is not cheap. A Home Start Pakket () with two measuring plugs costs  € 125, and a Home Basic pakket with nine measuring plugs costs € 370. In our situation we need a minimum of five measuring plugs, it would be possible to buy a Home Start Pakket, and add a Home Start Extension Pakket () which contains three measuring plugs. That would set me back a total of € 242 kosten. For comparison: five Conrad Energy Logger 3500′s would cost me € 195, cheaper than the Plugwise system but requiring a lot more manual work juggling the memory cards. Also, Plugwise simply works, which is more than I can say about the Conrad device.

There are often discount actions, like the one from Vereniging Eigen Huis (), which can save up to 20%. I saved 20% when I bought my second Home Basic Set.

Regarding all the systems properties I’d say it’s good value for money.

Reliability

I put this under disadvantages, but actually it is an advantage. Twice the system stopped logging. That was nasty enough because in both cases I lost more than a day of measuring data. This turned out to be a known error which was solved in a newer version. New versions of the software are presented regularly, and you have the option of having those installed automatically if you choose to share your measuring data. Alternatively, if you don’t want to share your data it’s possible to download an install the updates manually. I think the developers at Plugwise really listen to the feedback.

It possible to register as a beta-user, Plugwise will then make betaversions of the software available. These versions usually have solutions for known problems, new functionality but sometimes have reduced reliability.

Conclusion

De conclusion is simple: I’ve been using the system for about six months now to monitor our solar panels and it performs very, very well. Except for two ‘hiccups’ which I described in the previous paragraph the system has proved to be very reliable. The software is very user-friendly and the data can be displayed in several forms. If none of those forms is to your liking, export to any spreadsheet is easy. Purely on its technical merits I can recommend this system to anyone with a complex solar system like us.

The one stumbling block is the way Plugwise treats privacy. I didn’t mind switching the option to share the measuring data off, thereby giving up the right on support and automatic updates so I left that behind me. Some worry strongly worry about this, others don’t care at all. Make up your mind before you buy it and think about it whilst considering a measuring system.

It’s certainly not cheap, but you get what you pay for. The system is versatile and reliable and that cost money. There not many other options for our situation – with five inverters – which are user-friendly and affordable.

All in all I can recommend Plugwise.

Measuring energy consumption

Although measuring solar power works fine Plugwise was designed to measure electricity consumption. This works fine, too, and I’ve been measuring the electricity consumption of several devices in hour home to see how they behave throughout the seasons. This will however have be the subject of another article