Sunday, September 30, 2012

Guerilla PV Time

'Guerilla PV' is bodger slang for the connection of unregistered microgenerators to the power grid.

You can't earn any FIT payments for it because it is an unregistered generator and has no MCS certification.  You may get into trouble with the energy supplier and/or network operator, as your import meter may run backwards or may set an anti-tamper fraud alarm built into the meter.

Being unregistered, non-certified, and not installed by a 'qualified'  person (electrician), the network operator would have cause for alarm.  Is this thing safe?  Will lines men working on a failed power line in your area get an unexpected shock - literally?

So why would you want to do such a thing and what of those companies claiming to sell a simple plug in solar panel that anyone can install without professional help?

I decided to find out more, and in true bodging style, "Just bosh one on there and see what happens".

I managed to acquire an example of one of these kits.  They normally sell a whole thing with a PV panel with a micro inverter bolted on the back, a PV mounting kit and a long AC cable that ends in a RCD plug. In my case, I already have a whole load of PV panels, so only needed the micro inverter and AC cable.

The idea is that the kit just plugs into a normal ring main 13A socket somewhere near your garden or wherever the solar panel is.  The cable kit was well made, using fully waterproof connectors.  The micro inverter is 'micro' because it only accepts power from one PV 35V (72 cell) panel of up to 240Wp output.  So for a typical 4kW installation, you'd need about 16 of these things, one for each panel on the roof.

But if you've only got one panel, then it's a pretty neat idea.  Your solar panel literally just plugs into the AC as if it were an appliance.

Now, I don't want to get anyone killed, so I looked at what the kit is composed of.

The micro inverter is one of the well respected Enecsys models that comes with UK G83/1 certification for anti-islanding.  This is the important part, as without this it is illegal to connect to the power grid and may be extremely dangerous.  Beware the cheap Chinese grid tied inverters on eBay with no certifications!

The Enecsys inverter is has full galvanic isolation of the DC side from the AC side, to prevent high voltage AC leakage to the solar panel frame (bearing in mind this panel could be on your lawn).  The DC connections are made by MC4 connectors, so it's waterproof and somewhat foolproof in connecting the panel up.  The inverter has bolt tabs so it would just bolt to the back of the panel.

The issue of the potential for live AC appearing on the AC plug pins is countered by a RCD breaker plug.  This has to be manually reset to 'on' each time you plug the panel into a wall socket.  If the mains power fails or you pull the plug out of the wall socket, the RCD breaker is of the type that immediately clicks off, isolating the AC plug pins from the inverter output.  It can then only be reset to the on position by plugging it back into a socket and pressing the reset button.

So... Seems safe enough to connect to the grid.  It doesn't output enough power to cause a problem for a mains ring circuit (only up to 225W for the 240W input model) and has adequate certifications and disconnect provisions to prevent it being a danger.

But what of the other issues with it being unregistered and not capable of earning FITs (as it's not a MCS qualified install)..?

Without MCS certification (for the installation) or registration on the Ofgem microgenerators register, you can't claim any FIT payments for generation or export of your solar power.  With PV as cheap as it is now and the cost of the Enecsys having come down to under £100, maybe you don't need the FIT payments.  It will take longer for the kit to pay for itself, but it will reduce your electricity bills a bit (remember it only puts out a maximum of 225W of power in daylight hours).  Most people use the bulk of their imported electricity in the evening, so the plug in solar isn't going to help reduce bills there.  But a fridge freezer uses about 0.4kWh during the main daylight hours from 9am to 5pm.  It only has a working load of about 125W, so a single solar panel could do that much.

Then there are the other leeches around the house.  It took a lot of work for me to root out all the little things around the house that use power when you're not looking.  Classics are phone chargers, radio DECT phones, cooker clocks, gas boiler controls... A single 200W solar panel could negate all these leeches during daylight hours as well.  There wouldn't be much left over to export to the grid and a lot of the time it wouldn't cover all of the load, but it would reduce your background consumption bill.

So there's a case for it (maybe a bit shaky on finances but a case for the environment).

Getting into trouble with the energy supplier or network operator is another thing.  When plugged into a home without a registered micro generator, the existing electric meter may do one of a few things...  It could run backwards if it's a mechanical disk type of meter.  This 'unwinding' of imported electricity is illegal and counts a fraud or theft of electricity, same as clocking a car to make it look like it's done less miles than it really has.  You are stealing the energy companies money.  This is because you used the mains at night (winding the clock forward) and then gave them back the energy in the day when you weren't using all of the solar power (winding the clock backwards).  But you still burned their gas, coal, nuclear, or whatever fuel in the evening.

Most meters are being converted to LCD digital ones.  These can't run backwards.  But some do detect illegal reverse flow and will set an alarm that the meter reader will see when he or she visits to read the meters.  They may accuse you of electricity fraud.

Some meters get around the issue by counting up even when the power is going backwards (solar power is being exported).  In that case, they don't care that you have an unregistered generator but you would be paying the electricity supplier for every unit of electricity you gave them!  Your solar generator would actually increase your electricity bill rather than reduce it!

Next time... Connecting up this thingy and testing it on my guinea pig house :D


  1. :) Did you get caught, really bodgering something up with the mains?? Is that why you went MIA?

    1. I'm looking to purchase 1-2 KW of panels and 4KWH worth of LiPOfe Calbs for a tiny off grid cabin/house build I will be doing this summer once free of this seasonal aerial mapping job.

      Your blog is the only one I have found using Lipos for PV systems.

  2. Can you tell us where to buy the microinvertor kits? I have a spare 200W solar panel and I am curious to try it

    1. The guy who was doing them has closed down. Not much call for them as you can't earn any FIT revenue and it's only a little bit of power (200W doesn't get you very far).

  3. his understanding of the anti-islanding features of the micro are lacking.
    RCD plug or not unless the inverter sees the grid for 60s it will not convert DC to AC power.

    RCD plug is there as the house has RCD's, if someone sticks their finger in the power point an RCD will (should) trip.
    a micro inverter has on the other hand no protection against earth leakage faults and hence could easily electrocute you.
    after loss of the grid or a major AC side fault the micro has 1 second to respond, again to re-iterate more than enough to kill.

    Hence the cable laying in your lawn hit by mower= death by electrocution

    1. Enecsys micro-inverters do include an internal GFDI (Ground Fault Detector Interrupter) for that case where there is earth leakage from the generation side. This reacts much faster than the G/83 anti-islanding function in the case of a local wiring fault (as opposed to a grid fault).

      True, the instructions for these micro-inverters only consider permanent installation on roofs and so on with hard-wire connection to the grid.

  4. Any chance you can advise on the wiring colour scheme, i have a unit and want to chop of the tri oval connector and wire in a plug or rcd ? Thanks

    1. Haven't looked inside the plug but assume that it's the usual brown (live), blue (neutral) & green & yellow (earth). You could hard wire it into a fused RCD spur switch, like those used for bathroom wall fans and heaters.