A Grid Tie Revolution

Or the Law of Unexpected Consequences

One of the most clever and potentially game changing pieces of kit to come out of the mad dash to solar PV is the grid tie inverter.

Is this going to be a whimsical tekkie diatribe? Well, partly. But there is a sting in the tail at the end.

The small grid tie inverter is the piece of equipment that has made domestic Solar PV technically viable.

It is very, very clever.

Due to the fact that reference designs by companies like Microchip are freely available, small grid tie inverters rated at about 250-300W are cheap and plentiful. They cost about £70 -£150 on ebay (p.s. you get what you pay for)

So what is it and why is it so special?

Well, a grid tie inverter, like a normal inverter will turn a DC low voltage source into an AC mains voltage source. So your low voltage solar panels end up outputting mains electricity.

But that has been done for years.

The clever part is that the grid tie does this synchronously with the mains feed into the house.

Why is this important?

Because the grid tie is synchronised to the main frequency, you can use the power output of the grid tie to supplement/replace or even output power to the mains. Without this sychonicity all you would end up with is a lot of sparks and smouldering electronics.

The result of this is that you do not need to abandon a normal electricity supply and go off grid. If for example, when you want to use the washing machine that may take 2KW, your grid tie contributes to that value. You do not need to provide the maximum power your washing machine needs. But anything the grid tie does produce will reduce the amount of power you draw from the grid, thus reducing your electricity bill.

The whole of the current FIT subsidy orgy could not take place without cheap and effective small grid ties.

Currently, in order to claim the FIT subsidy, you need an "approved" installer with "approved kit" that are registered with a trade cartel (er.. sorry i mean trade body) and it costs A LOT of money. Of course it costs everyone else even more to pay your FIT, but that's the way it is.

But what if you don't claim the FIT? What if you set up a system that simply offsets your mains usage? You still massively reduce your electricity bill. There is incidentally at least one company on the market already doing this. FIT free (and cheap)

But what about "approvals" "Part P" etc. Well, as I understand it, most of the modern small grid ties are G83 approved and are advertised as "Plug and Play" They literally plug in like an appliance, but they actually drive electricity into your ring main not suck it out. Setting up a couple of solar panels to supplement your electricity supply could not be simpler. You reduce you electricity bills and so don't personally end up paying other peoples FITs, and you system is massively cheaper than an "approved" installer one. As you can appreciate this gets more and more worthwhile the higher electricity prices go.

But here is the sting in the tail.

The current Grid ties almost universally have what is known a MPPT (Maximum power point tracking) front end that is tailored to extract the most energy possible from solar panels.

So what happens when someone comes up with a cheap grid tie that instead of interfacing to solar PV, interfaces to a small generators? Or even more likely when some clever wag designs an interface to fake up an MPPT output  from a petrol generator?

We end up with people backing off the mains with polluting small generators simply because electricity has become so expensive due to the ridiculous ROC and FIT subsidies.

But surely mains electricity is cheaper than equivalent petrol or diesel? Today? Only just. But if you use LPG or Tesco's best sunflower oil, probably not even today.

Remember you do not need to power your maximum requirement you just reduce it, so a small cheap generator is all that is needed.

If electricity prices continue to rise, people will find ways to beat the system and solar PV will only be a small part of it.  We will end up with distributed pollution rather than distributed "renewables".

But worse, the people still paying for the ROCs and the FITs will be the poorest and most vulnerable who don't have the wherewithal to beat the system.