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Wattson Solar Plus brings electricity use and generation to life

Posted by Cathy Debenham on 25 June 2012 at 9:36 am

Earlier this year I wrote about how the Wattson* Solar Plus energy monitor helps me make the most of my solar generated electricity by letting me know when I'm generating more electricity than I'm using. I just have to look over, see if it's glowing green, and if so I turn on the washing machine. Read my review of the Wattson here.

The unit also records data on your electricity usage and renewable generation, which you can load  onto your computer and analyse using the Holmes software which comes with the Wattson.

First, let me declare that I'm about as far from being a data nerd as it's possible to get. Give me a spreadsheet full of figures and my eyes go a bit blurry. So I haven't taken full advantage of all the functionality. But those among you who like staring at spreadsheets can download the raw data for further analysis (amount used, and amount generated is logged every 5 minutes). However, I've been surprised by how interesting I found the broad range of graphs that I can look at.

You can view graphs in hours, days or months, for energy use, power use, cost, and carbon dioxide emissions. You can also compare usage with the energy that you are generating.

The top diagram above (click on it to enlarge it) shows 24 hours of electricity use in my house. The blue is the energy use, and the green line is energy generated. You'll notice the big thin spikes which mainly represent boiling the kettle. Using the oven also sends the line soaring.

The other thing that this graph shows is that we use most of our electricity in the evening (cooking, lights, TV) and, not surprisingly, generate most of our electricity in the middle of the day. If only we were charged for our net use, rather than buying at a high rate and selling at 3.2p per kWh!

The second picture shows a week's electricity use. Working at home obviously contributes to higher use, as bars representing the weekend are lower. I was rather surprised that a having one computer on all day, with an external hard disk regularly backing things up, should make as much difference as it does.The amount of solar electricity generated also varies significantly depending on the weather. April was pretty miserable and wet here in Devon, but I've managed to capture the data for a rare sunny weekend.

All in all the data side is much more interesting than I thought it would be. It's easy to get drawn into it, trying to work out what caused different movements on the graph. The only drawback is that the main unit can only store 28 days of data, so you have to remember to plug it in and upload it to your computer every four weeks. It would be good if it could sync automatically through the wireless broadband. Otherwise very interesting.

*This is an affiliate link, which means that we get a small commission if you click through and buy the Wattson Solar Plus.


If you have a question about anything in the above blog, please ask it in the comments section below.

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6 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 2 August 2012 at 8:29 am

Hi Barnbarroch

Yes, you're spot on there. The more of your generated electricity you can use, the more you will benefit from the panels, as you won't have to buy so much. What you pay for imported electricity is 4 - 5 times a much as what they pay you for electricity you export.

The simplest way of doing it is just to look out the window and see whether the sun's out before you put your washing machine or dishwasher on. Also run them one after the other, rather than together.

As you'll see from my reviews, I like the Wattson, as it tells me at a glance whether I'm a net importer or exporter, and I can tell from the figures whether there's enough spare to run the appliance I'm putting on.

If you're out during the day, you can just use a timer plug, and the weather forecast.

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BarnbarrochComment left on: 2 August 2012 at 8:12 am

Cathy, I bet you can clear up one confusion that I suffer from! With solar panels fitted, is it an advantage to me to try to switch my  electricity use to the daytime when it's being generated?

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Cathy Debenham

Cathy DebenhamComment left on: 28 June 2012 at 9:07 am

I did some crowd sourcing on Twitter on this question and came up with the following: 

 Wattson can monitor 2 (or more) PV arrays, just add an additional TX for Wattson and perhaps an Easifit and you're laughing. (This was confirmed by Wattson staff).

Other suggestions that will do the job include: SunnyBeam will do up to 12 if you have SMA inverters (says @StarfishPV); Solar Log is inverter agnostic and will post to the web (@msundog) but expensive for small systems (@RichardAdamsCS)

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THILLComment left on: 26 June 2012 at 8:24 pm

I don't have 2 inverters for my system but I do monitor both my pv generation and my domestic usage using a current cost meter (fitted by simply putting a clamp around the appropriate cables - see

Both generated electricity and usage are recorded by the current cost meter on separate channels, so you could do the same with generation from 2 different inverters.

My meter is also attached to my pc which uploads the data every 5 mins to a fantastic free website ( where I can monitor my live usage (see todays at:

The site is excellent in allowing you to compare generation & usage on daily, monthly etc. as well as compare with other systems nearby. 

Well worth looking into this if you are in anyway interested in monitoring how much you generate & use. 

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Rudge Energy

Rudge EnergyComment left on: 26 June 2012 at 5:26 pm

if both your systems have the same inverter, such as Sunny Boy, Fronius or Power One, then a single wireless display will show the sum of both system outputs.

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DimitriComment left on: 26 June 2012 at 5:03 pm

I have two PV systems, one of 4kWp and another of 6kWp. Neither Wattson or Ecoeye seem able to offer monitoring systems for such an installation. Both terminate in the same consumer unit. Anybody got any ideas?.

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