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Hybrid Solar Systems

solar panel and batteryDo you hate the electricity companies?

Do you marvel at the electricity-generating ability of a decent-sized solar system?

Ever thought "Why can't I get all the electricity I need right from my roof during the day, store it in batteries, and really give the middle finger to those greedy, polluting power companies?"

Pretty natural thought process, right? And modern technology does agree with you – if cost isn’t a factor. For reasons I've outlined in another post it is possible to go completely off-grid with a big old pile of batteries and a boatload of cash.

I've taken some heat for suggesting that going completely off grid may not be a great idea if you have a grid connection at your doorstep.

After all, there’s nothing inherently wrong with the grid. It is an amazing bit of infrastructure that has already been built, works very well 99.9% of the time and allows us to share our excess energy with our neighbours.

The problem lies in the attitudes and policies of the people who own the grid. Because the companies that own the grid are so hated, I've lost count of the times I've been accused of being a clandestine agent of the power companies when I dare to say:

"Think twice before spending $30,000 to $50,000 to go off grid in the city!".

The objective truth is this: Off grid can make sense for you in certain situations (which I outlined in my original off-grid post), but otherwise it is a whole lot of expense for no other reason than a vague desire to "stick it to the power companies".

Luckily for us, there’s a compromise: Hybrid systems!

Hybrid solar power systems are the best of both worlds: You get the guaranteed (well, 99.9% of the time) electricity supply of the grid, with the ability to store your excess solar energy for use when the sun isn't shining.  You can also switch over to your own battery reserves if the grid goes down.

Hybrid systems are also at least half the price of an off-grid system and don't require diesel back up. They're still more expensive than a purely on-grid system, but the benefits of those batteries are persuading an increasing number of people to pay the premium. In fact, the number of hybrid enquiries to this website is doubling every year.

(If you want 3 competitive quotes for a hybrid solar system, from local hybrid specialists you can get them here. Otherwise read on to learn whether a hybrid system is right for you.)

Here are 4 reasons to consider getting a hybrid solar system instead of a regular battery-free system: 

 

1) To keep the electricity flowing if the grid goes down

Standard on-grid solar systems shut down if they detect the failure of the grid. This is to protect any lineworkers making repairs to the wires outside your home. They wouldn't like it very much if your solar system sent a current straight to their fingertips while they're trying to work on the wires in your street.

A properly designed hybrid solar system can safely disconnect your house from the grid in the event of a power outage, and turn your house into a little mini grid. Imagine the smugness as yours is the only house in the street with the lights on, the TV blaring, the fridge humming and the beers cold.

Update May 2015: Tesla's recently announced PowerWall system has introduced a factor that wasn't previously a concern for hybrid solar installations: Backup compatibility. Previously, all hybrid systems provided backup electricity in case the grid went down - but this naturally increased the price you paid for a system due to the cost of specialised equipment. Tesla's PowerWall has made it possible to have a hybrid system without backup capability, meaning that the overall price you pay for the system is a few thousand dollars cheaper, but if you're hit by a blackout you'll be left staring at your big fancy battery pack on the wall and wondering why you can't just switch over to that. I've written a blog post explaining this in far greater detail.

 

2) To overcome solar system 'size limits' imposed by your local electricity network

Some unlucky folks have local electricity networks that are really anal.  They have really tight restrictions on maximum solar system sizes. They claim their poor little grid can't handle the additional electricity that larger solar systems provide (although they'll be happy for you to install a 10kW air conditioner that intermittently pulls massive amounts of power from the same grid!). This often results in homeowners being forced into a solar power system size much smaller than they need to offset their bills.

The way that hybrid systems get around this limitation is by using a smart inverter that works in tandem with your battery bank. These inverters can be configured to have a maximum export rate that's way below what your system can actually produce when the sun is at full whack. So to the grid your 10kW solar system can look like a puny 2kW system. Whilst only 2kW is exported to the grid, the other 8kW or so is diverted to your batteries. 

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.

 

3) To get around stingy feed-in tariffs

Many states have quite low net feed-in tariffs. This means that you're only getting a measly 6-12c per kWh for any excess solar energy that you export.

Using a hybrid system, you can tell your solar inverter to charge your batteries with your excess solar power. Then, when you get home, you can switch on your battery bank and get 'free' electricity instead of paying for it from the grid! Genius.

 

4) To game your electricity tariff

'Time of use' tariffs have been introduced in some states – this means that electricity from the grid costs more during periods of peak demand. If you have a hybrid solar system, you can simply set it so that when prices are high you're drawing power from your batteries or solar panels. And if your batteries need a little top up in winter because you haven't seen the sun for a few days, you can program them to charge using off peak tariffs only.

Hybrid systems can also be used, with the help of some special hardware, to configure the charge/discharge period of your battery banks in a way that can be adjusted in case pricing structures change in the future. You are future proofing your home against any tariff changes the electricity companies dream up to try and protect their profits as solar power becomes more widespread.

I already have a regular solar system - can I add batteries?

Yes, you can - but it may be expensive if upgrades to your system are needed.

To make a standard solar power system compatible with batteries, I'd suggest a system size of at least 5kW so you can generate enough electricity to actually charge your batteries in the winter, and when the weather is overcast.

If you currently have a system that's under 5kW in size, you should consider adding more panels, unless you have a really efficient house and a really small battery pack. If you are adding panels, you may need to increase the size of the inverter to cope.

It is actually fine (and often a very smart move) to oversize your solar panel array to your inverter. More kW won't harm the inverter (as long as the voltage and current specs are maintained - which your installer can confirm).  Your installer can advise on whther your inverter needs to be upsized based on your local climate, your battery size, and your household energy usage.

If you are adding a 'new generation' battery like the Tesla Powerwall that can reuse an existing inverter (sharing it with your panels) then your solar inverter may not need upgrading. Keep in mind that if you are able to reuse your existing inverter, it probably wont have backup functionality (as this is what newer hybrid inverters are designed for).

It all depends if it can talk the same language as the batteries BMS (battery management system). The newer the solar inverter, and the more expensive the brand, the more likely it is to be compatible, possibly with the addition of an interface box.

Old, cheap inverters are unlikely to ever be compatible with the PowerWall. 

If you are adding a conventional style of battery pack, (pre-Tesla) then they usually need their own battery inverter, which generally includes "islanding functionality". This means the batteries can run some appliances in your home even if the grid goes down. 

How much does a hybrid solar system cost?

Now we've reached the million-dollar question: How much extra can you expect to pay for a hybrid solar power system compared to a standard, on-grid system?

It all depends on how many batteries you want. But the short answer is: you'll pay double for a hybrid solar system.

At the time of writing, a good 3kW system costs about $5,000 installed. If you want to add 4kWh of usable storage to this, expect to pay about $10,000 for the complete system. 4kWh of electricity storage will get an efficient house through the night.

The average Aussie home is not that efficient unfortunately - so you may need a bigger system. A 5kW system without batteries will currently cost you about $8,000 installed. If you add 8kWh of usable storage, the total price would be closer to $18,000. This would get an average home through the night.

 

What kind of batteries can you use for a hybrid solar system, and how often will they need to be replaced?

There are two main types of batteries going into hybrid systems:

1) Lead acid (usually sealed lead acid - don't buy unsealed ones unless you like monitoring and topping up the liquid every month or so).  

These will give you 1000-3000 cycles at about 60% depth of discharge. In plain English: You can discharge them 60% 1000-3000 times depending on the quality (price!) of the batteries. So if you are discharging 60% every day, they'll last 3-8 years.

BUT - these figures are usually quoted at a 20 degrees C ambient temperature. If your battery storage area gets hotter than this, the performance will be worse.

2) LiOn / LiFePo AKA Lithium Ion / Lithium Iron Phosphate. These will give you 4,000 - 6,000 cycles at 80% discharge. e.g. 13-18 years. But these are much more expensive than (1). At least double the cost.

Bear in mind that with battery prices dropping, your replacement batteries may be much cheaper than your original ones.

Update May 2015: Tesla Motors have announced their new LiOn battery pack, the Tesla PowerWall. The 7kWh daily discharge PowerWall is priced at roughly $8,000 AUD, which is one of the cheaper LiOn battery packs currently on the market.

Is hybrid solar worth the extra money?

This all depends on how much electricity you use when the sun is not shining.

Take me, as an example. I work from home and have a very efficient house. I recently wrote a blog post explaining how I get a $33 power bill with a standard 6kW grid connect system. If I'm only paying $33 per quarter to the electricity company, it is quite obviously not worth spending thousands of dollars to install batteries and get my bill down to $0 per quarter!

However, I do have a very efficient house and use most of my electricity during daylight hours.

A more typical working household would use more electricity in the evenings and less in the day. For this situation, a well designed hybrid system may be able to pay back faster than a standard grid connect system, despite the extra expense. Especially if it is financed cheaply (e.g. added to your mortgage). And boy, wouldn't it feel good to use your own solar energy instead of selling to the grid for a pittance!

The payback calculations are quite involved, but a good solar installer/salesperson will be able to do them for you, and show you which options give which returns.

If you want 3 competitive quotes for a hybrid solar system, from local hybrid specialists (including payback calculations), you can get them here

 

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