FREE MONEY FROM THE SKY!
pv solar · 20 comments · 1,350 words · Viewed ~1,885 times.
(With a little upfront investment).
I've blogged before about our Solar Panels and how they're performing. Liz and I have recently moved house, and decided that it made sense to get panels on our new property. Basically, we're so capitalist that we can only enjoy the warm glow of Earth's yellow sun when it is enriching our bank accounts.
We looked at several local installers, before settling on Sims Solar. Paul was able to produce a detailed set of measurements, understood my crazy data-logging requirements, and gave us an excellent price. As a bonus, he went to the same university as me and Liz - UEA!
It took a day to stick up the scaffolding, then a day to physically install the panels and monkey around with the wiring and fuse boxes. Then a couple of hours yesterday to set up the Internet connection to the inverter.
Here's the result:
Yup - that's our ancient electricity meter running backwards! As all that lovely sky juice gets slurped up by the silicon wafers, the photons are crushed and gently fermented into electrons, which are then organically fed back into the mains. Good people of Oxford - charge your phones on me!
This is how we have set everything up...
Solar Panels - made by SunPower - eight of them on the roof.
4kW Inverter - Made by Fronius.
DataCard - allows the whole system to be connected via Ethernet or WiFi (2.4GHz only though) Fronius Datamanager - as well as a nice web front end, there is an API. Made sure it was running the latest Fronius firmware.
And this is what it all looks like when wired up in our utility closet. The solar power AC has its own isolator, meter, and RCD before being split into the house consumer unit and mains electricity meter.
The more observant of you will have noticed the Solar iBoost nestling in that tangle of wire. The iBoost has a sensor which monitors the flow of electricity from the panels. If there is surplus electricity flowing back into the grid (i.e. the house is using less than is being generated) it sends a radio signal out at 868.3 MHz to its companion device near the hot water tank.
The iBoost switches on the electric immersion heater until the desired water temperature has been reached or the electricity load drops.
So, during a typical day, the panels may be generating 1400 Watts. But if the fridge, phone chargers, and computers are drawing less than that - the remainder is used to heat up the water. Rather neatly saving on gas costs as well.
Monitoring and the Internet of Things
As I mentioned, the inverter has Ethernet and WiFi connections. This allows the user to monitor the system via a web interface, hook it up to remote monitoring, and to programmatically get access to the device's API.
The local web interface is basic and functional - but it links up to Solar.web which allows realtime and archive access to your data.
There are also Solar.web apps for iOS, Android, and BlackBerry.
The documentation for the V1 API is sparse and slightly cumbersome (you can't copy & paste from the PDF). But it does work very well - spitting out JSON for just about every conceivable function.
A single API call can get realtime information about what the panels are currently generating - and how much they've generated in total.
/solar_api/v1/GetInverterRealtimeData.cgi?Scope=Device&DeviceID=1&DataCollection=CommonInverterData
Gives
JSON
{
"Head" : {
"RequestArguments" : {
"DataCollection" : "CommonInverterData",
"DeviceClass" : "Inverter",
"DeviceId" : "1",
"Scope" : "Device"
},
"Status" : {
"Code" : 0,
"Reason" : "",
"UserMessage" : ""
},
"Timestamp" : "2013-12-18T09:12:06+00:00"
},
"Body" : {
"Data" : {
"DAY_ENERGY" : {
"Value" : 664,
"Unit" : "Wh"
},
"FAC" : {
"Value" : 50.03,
"Unit" : "Hz"
},
"IAC" : {
"Value" : 1.1,
"Unit" : "A"
},
"IDC" : {
"Value" : 0.83,
"Unit" : "A"
},
"PAC" : {
"Value" : 274,
"Unit" : "W"
},
"TOTAL_ENERGY" : {
"Value" : 4000,
"Unit" : "Wh"
},
"UAC" : {
"Value" : 247,
"Unit" : "V"
},
"UDC" : {
"Value" : 326,
"Unit" : "V"
},
"YEAR_ENERGY" : {
"Value" : 4000,
"Unit" : "Wh"
},
"DeviceStatus" : {
"StatusCode" : 7,
"MgmtTimerRemainingTime" : -1,
"ErrorCode" : 0,
"LEDColor" : 2,
"LEDState" : 0,
"StateToReset" : false
}
}
}
}
So, plenty to play about with. It should be fairly easy to set up something useful to do with the data.
Cost And Payback
The total system cost just shy of £8,000. That's a hefty chunk of money - but I feel it's a wise investment.
The panels - and their associated bits and bobs - are guaranteed for 10-25 years. Although the panels will degrade over their lifetime, it's not by a hugely significant amount.
According to the solar power calculators, the panels should generate an average of 3478kWh per year.
The Government's Feed In Tariff scheme will pay 14.9p per kWh generated and 4.64p per kWh exported back to the grid. They assume a uniform 50% export, meaning a total payment of 17.22p per kWh. That price rises with inflation and is guaranteed for 25 years.
Assuming my maths is correct, we'll be paid around £600 per year for generating solar power. At that rate, it will take 13 years to pay back the cost of the system.
Of course, that doesn't take into account the total savings from generating our own power. Based on our other panels, I'd expect them to generate about 2/3rds of the electricity we use. Now, the sun only shines in the day - and most days I'm out at work. But I still leave my fridge, servers, and security cameras on. I can set the washing machine and tumble dryer to come on around noon to take advantage of the solar output. On the days I work from home, my MacBook and microwave pizza will be sunshine powered.
Let's say that it will knock our electricity bills down by a third.
I'm with Ovo (switch and we both get £20) - at the moment, their electricity price is 12.15p/kWh. So, I reckon that we'll be saving at least £120/year.
Finally, there's the gas savings to consider. Again, with Ovo we pay 4.13p/kWh for gas. I've no idea how much the Solar iBoost will save as it heats up the water tank. Since having the system installed 5 hours ago, it has saved me 1.34kWh.
Assuming that's the same every day - a total of £20 per year. Not a huge amount, but enough for a celebratory gin and tonic every now and again.
That takes the repay time for the panels to about 11 years (£8000 / £10+£120+£600).
All of this assumes that the price for gas and electricity doesn't rise beyond the rate of inflation. If you've been following the UK energy markets, you'll know that most of the providers raised their prices by 10% (not Ovo though!)
I suppose there's two ways of looking at it.
- Best case scenario - there's an energy shortage and the repay period goes down.
- Worst case scenario - cold fusion becomes a reality and electricity becomes too cheap to charge for. In which case, I'm stuck with an interesting historical anomaly on the roof. Oh well!
Onwards!
Expect lots of solar data geekery from this blog :-)
At the moment, my household appliance are fairly dumb. I'd like to see if there's a way I can hook them up to an API which takes into account the current power being generated and the weather forecast to find the optimal time to switch on.
It would also be interesting to see if there's a way to get data out of the Solar iBoost. At the moment, the physical display screen will let me see how much power it has used per day / month / year - but it would be fun to get some more info out of it.
I'm going to start monitoring in earnest from the winter solstice - that's the 21st of December this year. I should be able to chart a steady rise in the amount of free money falling from the sky!
Massive thanks to Sims Solar for such a fast and professional install. If you want panels in the Oxford area, Paul is your man.
Graphing My Solar Panels (Open Source)
2013 - What a year!
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