Matching Panels to Suitable Inverter:

I explored various options; you can purchase micro inverters which are linked to each panel on the roof, but these proved way too costly and I was not given suitable assurance that they would grid-tie correctly at 230V 50Hz, our supply voltage. I then investigated other inverters such as Steca, Fronius, SMA and Aurora but these were all too expensive for such a small system, so in the end decided on the Mastervolt Soladin 600 inverter. There are a few reasons for choosing this, namely:

• it can accept 700 watts of solar panels in a string formation (more on this later).
• it is G83 certified (UK certificate)
• it can be plugged directly into the wall socket, and does not require an electrician
• it has inbuilt MPPT (maximum power point tracking) to get the highest watts from the panels

This is an ideal candidate - a picture of the inverter is shown above.. . It gives me the ability to sync to the grid by simply plugging into the wall socket and therefore ticks all the boxes for me. The main requirement for the inverter is that it accepts a voltage range of between 45-130v. My single 12V 100W panel would produce appx 21v in an open circuit configuration. An open circuit configuration simply measures how much voltage is produced when its not connected to anything - this can be determined by placing a meter on the positive and negative wires in the sunshine, and reading the results.

So in order for me to get the inverter working at peak efficiency, I need to feed it higher voltages than 45v, so this is why we change the panel configuration from a parallel system to a series system, thereby creating what's called a a string. So instead of my positive and negative cables going from each panel back to the junction box, in parallel mode, in the garage roof space I now snip the wires from every panel except the first positive and last negative. Then I connect the negative wire from the first panel to the positive wire from the 2nd panel, the negative from the 2nd to the positive of the 3rd, and so on, as shown below.

So this creates a string of over 100V which is ready to feed into the Soladin, using MC4 connectors shown on the right hand side of the previous picture. Because I already used 6mm2 cable size, I don't need to resize the wires. The MC4 connectors are a bit fiddly to put together, but they will accept 6mm2 size cable which was lucky! The other end of the inverter is plugged into the wall socket and presto - it syncs to the grid and once the sync is established it begins to pump the power to the ring main. Its important to ensure that the inverter is the G83 certified UK model, this is the version which can be used in Ireland. Other versions for other territories should not be used as they have different sync voltages. All Soladins have built in islanding protection, meaning that no power is produced if no mains voltage is present at the plug.

Matching The Final Panel:

We have one remaining panel left to hook up - remember the Soladin can only accept 700watts maximum so I started to look for a suitable G83 lower spec inverter which would manage my remaining panel. I could not find any low wattage inverters to do this, but I did come across a G83 version of the Chinese grid-tie wind/solar inverters that can handle up to 300watts. I obtained this from a company called "One Nation Net". It has a sticker on the front of the inverter stating G83 and an associated G3 certificate, an can accept wind or solar inputs, with a voltage range of 14-28V. This voltage range would be ideal for my single 100w panel, so again this is hooked up direct to the remaining panel and plugged into the mains socket.

Again once plugged in this functions the same as the Soladin - it syncs to the grid voltage and then begins to export the power available to the ring main. There was minimal setup involved, all I needed to do was to terminate the solar panel wires in appropriately sized ring connectors and then hook up and switch on. Islanding protection is also built into the inverter.

Lets move on to the issue of connecting up the 12V 400w turbines to the grid next.....