A few weeks ago I blogged about my mate who really hates his electricity company. In fact he hates them so much he wanted his new house to have an expensive off grid solar system with battery backup, diesel genset, the works.
I blogged how the cost of going off grid with solar would be over $50,000 compared to about $12,000 for a standard, grid connect 5kW system and that it would be economically barmy to go completely off grid if your home already has a connection to the grid which you can use.
At the end of that blog post I noted that there is a third option for those amongst you who like the idea of off-grid solar (or at least being less dependent on the electricity grid) but who don’t want to drop 50 grand and mess around with diesel generators.
The compromise solution may be to get a grid connected system with battery backup (aka Hybrid Solar).
Hybrid Solar: A cheaper off grid solar alternative
A hybrid solar system (aka “grid-tie with power backup”, “grid failover” or “grid fallback”) is basically a grid connect solar system with batteries and some funky electronics. The electronics continuously monitor the batteries, the solar panels and the grid and decide:
a) when to charge/discharge the batteries.
b) when to connect/disconnect from the grid
This may sound very similar in cost and complexity to an off grid system. But the crucial point to understand is that, because your system is not totally disconnected from the grid, you save an awful lot of money on hardware. The grid is always there if you need an electricity top up. This means that your system needs fewer batteries and no backup power source (i.e. expensive and smelly diesel genset).
4 Reasons You May Choose To Pay More For a Hybrid Solar System
So why are people increasingly considering adding batteries to their grid connect solar system?
Hybrid Solar Reason #1: To keep the lights on (and the beer cold?)
The obvious advantage of batteries is that you can keep the lights on when the grid goes down. A standard solar system will shut itself down when the grid goes down. Why? To protect any lineworkers on the grid. Imagine if your solar powered home kept pumping 240VAC out into the transmission lines after a power cut. Any lineworkers who came to work on the wires in your street would get a nasty, if not lethal, shock!
A bank of batteries, combined with a smart box of electronics can safely disconnect your house from the grid in the event of a power cut, and also create an “island” of electricity within the confines of your home. Your own little mini grid if you like.
(There is also a newish product out there called the PowerRouter which claims it can do this without any batteries. Of course this particular product will only work if the sun is shining, so you would be out of luck if the grid went down at night, but it is a very clever development nonetheless).
Hybrid Solar Reason #2: To overcome solar system “size limits” imposed by your local electricity network.
I’ve had many emails from people (mostly on the end of SWER lines for the techies out there) who have had their grid connection application for their solar system knocked back. Allegedly their local electricity network can’t handle the power.
These guys are usually told that they can only have a max solar system size of between 1 and 3 kW.
One way to get around this is to use one of a new breed of smart inverters in tandem with your battery bank. These smart boxes can decide when to charge your batteries, and when to export to the grid and can be configured to lots of very useful and cool things. A great (Australian Made!) example is the Selectronic SP Pro inverter.
Imagine you are limited to having a 1kW system due to local regulations. With s Selectronic SP Pro, you could still stick 3kW of panels on your roof. Here’s the trick: you can configure the SPPro to have a maximum export rate of 1kW. Any power from your solar panels over 1kW can be used to charge the batteries. If the batteries are full then you simply dump the electricity through resistors (but this dumping would be minimised in a well designed system).
The result: Everyone is happy. You get your big solar system, and your electricity company gets to stay in the 20th century with its arcane regulations.
Hybrid Solar Reason #3: To get around stingy (or non existent) Feed in Tariffs.
If you live in NSW, as well as being ruled by a premier that appears to think renewable energy is the devil’s spawn, you also get a miserable 7c per kWh for any solar energy you export to the grid. Compare this to the 25c per kWh saved if you use the energy in your home.
For a typical household who is not home during the day, that can be half or more of your solar energy that is getting the miserly 7c per kWh:
If you’ve got a smart inverter and a bank of batteries you can tell the inverter to charge up your batteries instead of exporting to the grid between 11am and 4pm. Then come 6pm when the sun has gone down, but everyone is home, you can fulfil a lot of the evening’s electricity demand with all that stored solar energy. Your electricity demand profile then looks like the graph below – no precious solar energy is wasted – woohoo!
Hybrid Solar Reason #4: To Game Your Electricity Tariff.
Time of use electricity tariffs which charge different amounts per kWh depending on the time of day, can vary from about 12c per kWh at night to around 50c per kWh in the afternoon. If you have a bank of batteries and some smart electronics (you don’t even need any solar panels!) then you can buy electricity when it is cheap and sell it when it is expensive. Hmmmm, that’s got you thinking hasn’t it!
Coming Up Next…
In my next post I’ll go through the design and hardware options you have if you are considering going “grid connect with battery backup” and I’ll also walk you through some typical costings compared to a “standard” grid connect solar system.
Read Part 2 on Hybrid Solar Design here….