Hybrid solar costs and battery storage | RenewEconomy

Hybrid solar costs and battery storage

With a plethora of battery storage products about to, or already hitting the market – 2015 is surely bringing in the age of hybrid solar.




2015 is surely bringing in the age of hybrid solar. In recent months we have seen the release of Samsung’s ESS systemSMA’s TL Hybrid combo and new models within Schneider Electric’s Conext range. There are also a plethora of other brands about to, or already hitting the market including Bosch, ABB Aurora and BYD.

What is Hybrid Solar and What are its Costs?

Hybrid solar is a typical pv system with the addition of batteries, often used to store excess power so that it can be used to offset peak load or night time use. It is generally not intended to take a household ‘off grid,’ however in many cases it has the capability to do so. To understand this in more detail lets look at some terminology.

Solar PV

Solar PV refers to the panels on your roof which are then ‘tied’ or ‘coupled’ to an inversion system on the ground. A ‘grid tie solar PV’ system is the technical term for your typical domestic or commercial solar system and is commonly made up of panels and a single inverter. These days it is also possible to purchase an AC solar system using micro inverters.

AC Coupled Hybrid

This refers to a standard grid tie system ‘coupled’ to a hybrid inverter, which then charges batteries and outputs to the home and/or grid. We expect this type of system to become extremely popular, as it will be a great way to upgrade from existing PV and it is also extremely cost effective as a new install.

DC Coupled Hybrid

This is where we run the solar PV into a regulator, which also acts as a battery charger. This then connects directly to the batteries, which are then connected to the hybrid inverter. This is your typical structure for a full off grid system.

So now that we’re all on the same page where to from here?

What is the right system for you? Which batteries should you use? Is it cost effective and why install hybrid?

For most people the common scenario is going to be an AC coupled system using a standard inverter, running into a hybrid unit such as the Schneider Conext XW+. A system like this can be selected as an add on, and allows for complete off grid functionality at a later date. There are a number of design considerations to look at when selecting a hybrid system. These can have a dramatic effect on operation so should be considered closely.

1 Peak Draw

This is the highest amount of power one expects to draw at any one point in time usually measured in kW or watts, but sometimes in amps. Since peak is a limiting factor in any hybrid or off grid installation it makes sense to ‘load shift’ devices, so that they’re not all on at once. For example one may tell the hot water system to heat, followed by the swimming pool to clean – all outside of peak (ie cooking hours). It may also be beneficial to change appliances such as stoves to gas, and it will certainly make sense to change lighting to LED. In saying that the latest XW+ can deliver a sustained load of 28A and handle a peak of 50A for up to 60 seconds and 35A for up to 30 minutes. This will handle the average home and for larger installations they can be chained together in bundles of up to 110kW three phase – enough to power a small community!

2 Storage Capacity

It is important to look at storage not just in terms of peak over night use, but also in terms of ‘days of autonomy.’ This refers to the number of days one expects to be without sun and usually varies between 2-4 days. Storage is generally measured in amp hours, but can easily be converted to kWhrs by multiplying amp hours by the battery bank voltage. For example a 200AH battery at 12V gives 2.4kWhrs of storage.

3 Depth of Discharge and Battery Life

There are a lot of battery technologies available on the market with massive differences in performance and price. It is important to consider firstly the application of the system and then also its requirements in terms of discharge and life cycle. If one is designing a backup system which will be rarely used, then ‘number of cycle’s’ becomes less important, as the system is only intended to take infrequent shallow discharges. This may be suitable as a gate opener, or for a holiday home, and is commonly used in telecommunications systems as secondary backup.

For the home or business however, the batteries will be discharged on a daily basis and it therefore becomes important to consider how many times this can occur before the batteries will begin losing capacity, or fail all together. Finally one needs to consider the rate of discharge and any environment factors such as physical space, temperature and weight.

We will write another blog on batteries later, but in short the selection is best left to a very qualified and experienced professional.

What are the costs of Hybrid Solar?

OK lets look at a typical Australian home using 25kWhr per day with roughly 6-8kWhr of that at night. This home has the following features;

1 Electric storage hot water
2 Electric oven
3 Gas hot plates
4 Ceiling fans in every room used often
5 Intermittent AC used only during the day
6 Fully featured AV and computers
7 Swimming pool

The first trick is to ensure that the electric hot water and swimming pool are set to run during the day. This allows us to put up more highly cost effective solar PV, and at the same time reduce our battery capacity. We then use these appliances as a ‘dump load’ for excess PV generation meaning that we dont ‘export,’ as the power is either used, or ‘dumped’ into appliances. This allows us to factor all production against the tariff rate of 30c per kWhr INC GST. Please note that all figures are inclusive of GST as the system price is inclusive of GST. There is no need for night tariff’s as the dump loads are allocated against PV, which has an installed cost of around 7c per kWhr.

The next trick is to maximize PV capacity to ensure that even on cloudy days we are still generating ample amounts of power. For some people this wont be possible due to a lack of roof space, however once all roof faces are considered most homes can fit the required 7-10kW of panels. To ensure that we have enough generation, the minimum is 1kW of panels installed for every 1kWhr of storage. This is a rough guide and depends on day time usage.

Next we shift loads where we can such as the hot water and swimming pools to reduce the peak demand. This minimises the hybrid inverter size and once again reduces costs.

Hybrid Solar Costs – The End Result

The home in our example will run their AC off mains power, which makes this a ‘hybrid’ rather than ‘off grid’ solution. If they wanted to run electric hot plates and AC that would be possible, but it would also incur significant additional costs. The rest of the home will run comfortably off PV and batteries some 360 days of the year with the remaining 5 darkest of days drawing some power from the grid. Once again for full autonomy one could increase the battery size, however this once again significantly increase initial outlay.

Therefore the most cost effective method is to operate hybrid solar, which would give us total system costs of around 30K giving a payback period of 9 years and an ROI of about 9% p.a. It’s important to remember that the life cycle of the system is 10 years, meaning that the purchase is for 10 years worth of electricity resulting in one year for free – when compared against grid costs.

It is also worth remembering that we have assumed electricity prices will remain the same. If electricity prices rise then the final result will be far more beneficial. Furthermore at the 10 year mark the batteries will need to be replaced, however the panels will continue producing for up to 25 years resulting in a second investment cycle with much higher returns.

Hybrid Solar Calculator

The calculation of hybrid solar production values and hybrid costs is extremely complicated and involves both modelling software and very detailed spreadsheets. If you are interested in a hybrid solar calculator specific to your requirements, please contact us and we will model something for your specific situation.

Hybrid and Off Grid systems if configured and or installed incorrectly can have a high fail rate. If you are looking at purchasing a hybrid system a ‘cheap import’ solution will almost certainly result in a bad investment and equipment failure. Ecoelectric provide detailed production estimates guaranteed in writing thereby ensuring that you get what you paid for.

Jeff Wehl is managing director of EcoElectric

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  1. juxx0r 6 years ago

    I find it hard to believe that an air conditioner for cooling can’t run during the daytime if you’re building a 7-10kW system. Then again i find it hard to understand how the average house uses almost 10 times as much electricity as i do.

    • Miles Harding 6 years ago

      Hmmm, that would make you one of the “Energy Aware” set!

      Easily done without moving into a cave, as well. 🙂

      Tom Murphy’s “do the math” blog has a a great discussion on becoming energy aware, although you may know more about it than he does.

    • Jeff Ecoelectric 6 years ago

      In this example the house doesnt really have any limitations during the day. Thats why we shift the hot water and pool to day time use. In regards to AC they would have the production but this home had 5 AC units so if we put them all on the XW+ even with its fantastic peak ratings it wouldnt handle it. So it becomes a maximum demand issue. If they didnt have a pool then we could easily put an AC or maybe 2 on, but for now were monitoring its output.

      ‘Average home’ is a pretty wide ranging term really. Some say its around 18kWhr, but we have quoted homes that use 60kWhr. 25kWhr is around average for a family home.

      • juxx0r 6 years ago

        More than 1 air conditioner per person and we can still call it a home?

        Another concept i’m going to have trouble understanding.

        • Jeff Ecoelectric 6 years ago

          Its fair to say some have a different definition of essential or non essential : )

          • juxx0r 6 years ago

            I don’t mean to poo-poo your good work, i just think we should take a holistic approach to energy.

      • neroden 6 years ago

        Why not (a) insulate the house, and (b) install a single high-COP heat pump system to replace the AC units?

  2. Vincent Selleck 6 years ago

    Good work Jeff! The Schneider XW+ solution is great for robust off-grid power supply. Their SW range is much more affordable but limited to a 24V battery bank until a new 48V version is released later this year.

    The ideal place for hybrid power is sitting inside the Peak power charges where you will get best value for the use of batteries which have a price per KWH for energy stored over the cycle life of the battery. We are getting about 20 cents per KWH from our Gel Acid batteries at the moment, which is certainly better than peak grid charges.

    We tend to leave the pool and hot water on off peak controlled load as it is cheaper to do this than run them off batteries. If we get 80% of peak use covered by the hybrid solar each day this is a good price point and means we do not have to buy heaps of batteries to cover several days use. That is what the grid is for – our back up system! Batteries will fall in price fast, and according to most forecasts as much as 50% in the next three years. Another good reason to spend less now.

    Payback rates are coming down fast as well. We have a new Charge Controller that plugs into any existing grid connect inverter with quality gel acid batteries that installs in 2 hours as a retrofit. At $5888 installed with 9.6kwh of battery storage it makes an excellent add on for instant hybrid upgrade. When we couple this to our new 3KW solar system we get a payback period of 5 years. The batteries have a 5 year battery life warranty and are scheduled for replacement at 8 years.

    We are fortunate to have reseller status with the importer and are offering great incentives for installers in Nth NSW and SE Qld who would like to contract installations and offer this upgrade to their existing customer base.

    We also do full off grid technology mainly using Schneider and Outback inverters and charge controllers now, but these tend to cost more and the payback goes out to 6-7 years. They do provide power when the grid goes down, which is a good advantage, particularly for rural dwellers.

    The real value of hybrid systems is in combating the imposition of network demand charges that is coming soon. Using the battery power to lower your high usage spikes after sunlight hours could make every cent spent on hybrid double its current value now.

    Perhaps the best thing about hybrid systems is that you are one step closer to cutting the wire forever. Quality off grid inverters and chargers can be upgraded with more batteries and solar when the first batteries come to the end of their life, creating a full off-grid lifestyle. Let them keep their gold plated poles and wires. We are taking back our power!

    Contact me at http://www.888solartek.com.au

    • Jeff Ecoelectric 6 years ago

      Thanks Vincent it sounds like youre very handy with the solar calculator too! Were finding a lot of our design methodology is specific only from here to say Cairns. Any further south and the production is too low in winter – any further north and the wet season kills summer. It is as you say essential that dump loads are taken from day time supply only, which means over sizing arrays considerably.

  3. Miles Harding 6 years ago

    Good roundup Jeff!

    One thing missing is the consumer in this. I have noticed that once a consumer becomes energy aware, their consumption usually drops significantly. It is not uncommon to go from 20 units per day to 6, although a pool will make that difficult to achieve. It is fair to say that an energy storage system should move any consumer well along this path, needing much less battery and solar to achieve the same outcome.

    The cover picture ($20K for a schneider storage system) should not put anybody off, as this is considerably more expensive than a storage system needs to be. Last time I checked, 10kWh of LiFePO4 battery is less than $5000 and a reliable chinese-made 10kW low frequency inverter (overkill) is about $4K.

    The LiFePO4 solution should be a 10 year proposition with zero maintenance. LiFePO4 are perfectly happy being discharged 70% each day, so a much smaller battery is needed if reserve capacity isn’t considered.

    I recently probed the pricing on Lead Acid and found that with ‘mail order’ of good quality flooded (Trojan T-105) batteries, the cost has come down a lot, such that a pack suitable to deliver 10kWh on a regular basis (25% depth of discharge, or total capacity of 40kWh) will cost around $7500.00, delivered to most metro areas. With this sort of lead acid, a 10 year working life should be possible, and it will have a lot of reserve capacity for those occasional runs of dark days. Approx. 10% more solar will be needed to allow for the losses in charging and maintaining this battery.
    Likely this is overkill, will be bulky and need periodic maintenance in the form of watering the cells every 4 weeks or so. There are automatic watering systems available.

    • Paul Lemming 6 years ago

      I see lots of discussion here about how cheap you can all get batteries and systems for , but I see a real danger of going down the cheap SOLAR system problems all over again. Which we are only seeing the tip of the iceberg now with.
      This time we don’t have rooftop isolator issues to contend with , I see explosive battery situations.
      Has anyone considered that there are actually standards that apply to all of this.
      Has anyone really looked into this , before blindly rushing in and start selling or designing these things. ??
      I can tell you now NO.
      AS3947 , AS3439 , AS4509.1 , AS2676 , AS4086 , AS3011, Lets not forget AS3000. Lets not also forget the BCA class 1-10 building.
      Quite a few system landing on our shores – BOSCH , BYD don’t meet the requirements , but are already being stocked by distributors /wholesalers , rubbing their hands together waiting for the anticipated boom in this sector. I say that a bit tongue in cheek , but let see how enthusiastic or should I say ethical some of these companies are when they have an Explosive incident , let alone a fatality from one of there systems have a Thermal runaway event on their TOP of the range cheapest sourced Lithium batteries that basically have a nonexistant BMS (battery management system ) Just saying …….
      I’ve already seen a few companies get caught out , by having not met BCA V1 C2.12 – FRL120 rule ,and having to install a BLAST/fire door on the room where the batteries were going at a cost of $5000+
      So My question is really do we what to go down the path of promoting the cheapest batteries, the cheapest inverters , panels , switchgear etc. etc.
      To say the hell with safety and life expectency of systems , only to have the Market lose confidence in these systems all together.
      hate to be the devils advocate here , but I can see another round of companies selling these things for a few years/months , then closing up shop , leaving customers disillusioned all over again.
      Heaven help us if we head down the incentive road again, and watch the system start to get advertised for $1499 with 4 Panels, lucky dip on the inverter and batteries , and the Utilities refusing to connect the hybrid systems.
      In QLD , you need 3-Phase to go above 5kw, you need ZERO Feed also if you connect batteries , which I know is different to other states, but makes me question whether you can neatly package these systems up , and promote them as such a quick fix for everyone. I see lots of development to still happen in the battery storage area , let alone lots of adjustment in the rules and regulations and licensing needed to make this industry truly viable in the short term , let alone the long term.
      Bracing myself for the backlash of course.

      • Jeff Ecoelectric 6 years ago

        No backlash here Paul we completely agree; you’re right – plenty of people are claiming that products will last 10 years when theyve only being on the market for 3 or less.

      • Miles Harding 6 years ago

        No backlash here.

        Battery cost, actually LCOE, is very important, as it determines whether it will be worthwhile storing energy in the battery.

        The EV community has had similar issues using lead acid in vehicle conversions, there are serious isolation issues when installing them within the vehicle body. Fortunately, nobody even considers them these days. Most are LiFePO4 which has been proven to be safe, effective and reliable.


        The currently Tesla make big storage modules in the 400kwh range for
        commercial applications like Walmart stores and the company’s own
        Superchargers. The units are in self-contained outdoor rated skid
        mounted containers, ready to connect.

        They are poised to enter the Home storage market, later this year, which will be interesting. Elon Musk is on a crusade to change the face of energy storage. We can expect Tesla to deliver a big slap to the existing players.

    • Jeff Ecoelectric 6 years ago

      Thanks Miles, were finding lithium with BMS is around $750-$1000 per kWhr for now (usable storage and installed price). So 5kWhr is 5k, but there are plenty of solutions around and yes many are cheaper. There are also plenty that are more expensive. In regards to lead acid we think salt/cotton will have a huge future https://www.ecoelectric.com.au/shop/2kwhr-battery-aquion-s20.html

      • Miles Harding 6 years ago

        I would agree with the system essentials included.

        I have been monitoring Aquion for some time. It’s good to see you are selling their modules. Cheers.

        I am using a re-purposed LiFePO4 traction battery (a car conversion project that morphed into a factory made purchase) for an off-grid home buffer, it allows much of the house to be run, as well as charge an EV at night from stored sunlight when necessary.

        It replaces an VRLA battery that had seen better days.

  4. Paul Bolger 6 years ago

    Very interesting.

    How about EV integration? – An electric car will typically have over 20kwh of batteries on board and could be used both as an outlet for surplus solar power and a secondary battery bank for a home

    I’m also interested what would be required to convert a home to true ‘smart’ consumption, where fridges, ovens, HWS etc could be controlled individually to get the most out of the available (and cheap) power. Presumably you’d need to rewire the home breaker box with relays switched by a power management system. You’d also probably need IR extenders which could tell heat pump/air conditioners when to switch on. Is this sort of stuff here yet?

    • Jeff Ecoelectric 6 years ago

      Hi Paul,

      EV will most certainly be an excellent ‘dump load’ however some homes will have troubles finding enough roof space to get their production high enough. If we look at an EV on top of all the above one would need a 15kW or so system to get through winter. RE: smart homes the tech is here and I will blog on that some time this year, as we’re also KNX integrators, but its fairly expensive and yes very technical. Some promising technologies include the Zigbee protocol, which is KNX compatible, and there is also a whole host of ‘proprietry’ systems hitting the market such as Google’s Nest, Samsung, Miele and LG with ‘internet of things’ systems. On top of that SMA have their home manager system which allows for basic automation and energy management. In any case this is a *very* in depth topic in itself. We have a brief product guide here https://www.ecoelectric.com.au/smart-home-automation/ but this is more aimed at high end homes with large budgets.

      • Paul Bolger 6 years ago

        I’m in NZ so roof space isn’t such a big issue. Panel price is though – they are about double the AU price over here. At AU prices 15kw of panels would be expensive, but not prohibitive. Over here we call ‘air conditioners’ ‘heat pumps’, and they are not considered an indulgence!

        The KNX etc looks interesting, but also like it’d cost a lot more than you would save. I was more getting at just replacing the ‘dumb’ breaker box with one were the individual circuits could be managed by the charger/inverter/controller. At the moment we have a rudimentary form of this in that the HWS is on a night rate circuit (although the power company often forget to turn it on until a few hours into the cheaper tariff period).

      • TechinBris 6 years ago

        The Budget isn’t that large, once you realise with a AU$1K power bill each quarter, it only takes 5 years to pay off a system with a controller to manage a few Inverters, even if it is sans battery.
        We put in a 14.6kWh system (that is what we could fit) and even though it has to wind back its power generation to what we use and what we are allowed to feed into the grid (though it is hardly worth it so we don’t worry much about it), our power usage from the grid has plummeted and costs are next to nothing. Turn something on and up the power production rises to meet the demand.
        But being able to turn on the Air Conditioning on hot sunny days without a care of the possible power bill is such a wonderful bonus. Our old Off-Peak Hot Water systems turns on to heat in the day now, which is better use of our power than bothering with the grid, making it (in a way) an energy battery also.
        So you see, even if they try to rip us off with pathetic feed in tariffs, we can still be the ones that can win because of their own flawed business models that refuse to evolve, thus making them a candidate for extinction.
        We are currently preparing for batteries in the near future, as we can afford it. But we are doing it without credit here, so step at a time. But it is possible to achieve something that seems hard to get to, when you are willing to sacrifice that which you don’t really need to survive, for something you really do need in order to survive the compulsory gouging that is so pervasive from Corporations these days.

  5. Leigh Ryan 6 years ago

    I am looking at Hybrid, but i am only considering it to offset the peak from 4pm to 8pm, one of the big issues not being looked at is our home itself, most Australian homes are inherently energy guzzlers due to poor design and situation, lack of insulation, bad roof design, it’s our builders and architects that need a boot in the behind, if i was building a new home today i think i would find it difficult to find a builder with a spec home that would suit my goals, most likely would have to design the house myself.
    When it comes to saving energy, renewables are great but the real problems start at the concrete pad and our builders and land developers in their desire for profit appear to care too little for the consumer, i think we need to get our young on the ball here and have them demand energy efficient homes even in the pre-fab market.

    • neroden 6 years ago

      Yeah. Super Insulated Houses (or Passivhaus, in German) were perfected back in the 1970s, but they don’t seem to have reached Australia.

      You can retrofit nearly any house to be super-insulated relatively cheaply. The bible for this is old — the “Super Insulated Retrofit Book” from 1981.

  6. Jon 5 years ago

    I already have a 5k system on my roof. How much will it cost me to have the battery backup part of it installed?

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