How do I install solar on an block of units / apartment block?

Q. I own a 10-apartment building. I would like some idea of the potential options for the Body Corporate to install a solar system on the roof. The body corporate power bill is around $3500 per year, and residents are around $1000/year. Can you please give me some pointers?

A. There are three configurations you could consider. 

Update: There is a fourth option: Allume Energy SolShare - which is explained in detail here.

Option #1

 Have one solar meter, and sub-meter everyone else.

Pros:

• This configuration will generate the most savings for the apartment as a whole.
• You only have to buy one inverter - not 11.

Cons:

• A lot of work and bureaucracy is involved.
• Although this maximised self consumption of the whole building, the solar will be unevenly distributed. Those who use the most electricity during the day will get the most solar energy and save the most money.
• This is not a regular install, so you'll need to search for a smart installer for the sub-metering. 
• You'll need some software to handle the billing.
• Depending on your local rules, you may need special permission to act as an electricity retailer. So there may be some (or a lot of) bureaucracy to navigate.
• Some companies can do all this for you and handle the billing (they will bill everyone themselves). This is called an 'embedded network'. Unfortunately, this means the embedded network will get a good slice of the solar savings to pay their costs and make a profit.

You'll also need a big roof - enough for at least 30kW with the consumption you describe.

In this configuration, you have one big solar system, and connect all the solar to one solar meter. Then you 'sub-meter' the Body corporate and all residents. This way, the solar will be used first by the building, and any excess will be sent to the grid. It maximises your self consumption of solar, giving you the most savings.

In this diagram, the red boxes are meters, and the blue is solar. You can see that the grid and solar are connected into a single master meter, and all the residents' meters are connected after the output of this master meter. I've only shown 6 units for clarity.

Option #2

Just connect the Body Corporate Meter to the solar.

Pros: 

• Simple install
• No change to residents' billing.
• Smaller system required.

Cons:

• Only the common area gets a reduced bill.

In this configuration you install a smaller solar system - and connect it into the body corporate meter.

The solar will only be used by the common areas, surplus will be exported. The residents share the savings equally through a reduced body corporate bill.

Option #3

Each apartment is connected to solar. So if you had a 120 panel system and 10 units - each unit could get 10 panels connected into their meter, and the body corporate could have 20. You'd probably do this with microinverters.

Pros:

• No change to residents' billing

Cons 

• Lots of extra wiring through the unit - adds to the installation cost.
• One inverter needed per apartment(if using string inverters) or one microinverter comms unit (e.g. Enphase Envoy) per unit. Expensive!
• Does not maximise self-consumption of the building as well as option #1

​I'd recommend looking at Solshare - it adds to the upfront cost - but keeps things simple for the body corporate. They have also done this many, many times - so a better chance of a smooth install and smooth paperwork processing.