Deciding to go Off Grid is a big decision, so we wanted to compile some literature to educate and shed some more light on this to potential customers and those existing ones who want a refresh on how the system works. In this guide you will learn why we recommend our batteries, what sets them apart from our competitors and how they will work best for you. We will also introduce the range of inverting equipment that we most recommend and trust.
Our DCS PV series batteries are setting the benchmark in performance and lifespan for off grid storage systems and our 10 year warranty backs what we say. LifePO4 as a cell chemistry has come a long way since it was first pioneered back in 1996, it’s gained significant uptake in the solar industry due to it’s non-toxicity, phenomenal thermal stability, electrochemical performance and safety characteristics. There is a natural abundance of iron one of the main components inside the battery cells and now our latest generation of LiFePO4 chemistry is able to achieve 2500 cycles @ 100% DOD @ 1C but more on that later.
Selectronic Battery Inverting:
The award winning Selectronics SP PRO 7.5kw battery inverters, are what we most trust and recommend. They are a top of the range product designed and manufactured right here in Melbourne, Australia. With an integrated generator controller, AC continuous load power from 5kW to 60kW, ability to be retrofitted on to existing systems, phenomenal surge capability, precision charging control, compatible with single, dual or three phase, and are also backed by a 10 year warranty.
Fronius PV Inverting:
As the technology leader in the photovoltaics industry, time and again Fronius inverters shift the limits of what’s possible and set trends that set the market in the long term. Fronius Primo range of inverters are super impressive with their performance and reliability and provide the perfect platform for managing PV. The Fronius Primo 8.2kW is our inverter of choice. Further integration between the Fronius PV inverters and the Selectronic SP PRO’s consist of a managed directional control link which controls the flow of energy from the solar panels with a fine control down to 0.1% increments.
So how does this system work?
Lets begin with a quick overview of how an off grid system using DCS batteries, Selectronics SP Pro battery inverter and Fronius PV inverter works.
The Sun outputs light energy.
The Solar Panels (Photovoltaic) convert this light energy into DC power (Direct Current).
The Fronius PV Inverter takes this DC power and inverters it into AC Power (Alternating Current).
The Selectronic SP Pro Battery Inverter either sends this AC power directly to the house to manage energy loads OR converts back to DC in order to charge the DCS Batteries.
So we can see that the Selectronics SP Pro, and the DCS batteries work closely together to ensure optimal delivery of power to your home. Just to put this into perspective, this power delivery is so precise and so consistent at least 5 times more stable than that of any major power utility station can ever dream of supplying. This level of consistency means your appliances will last significantly longer. Light globes actually have a chance to provide their full design service life.
Below is an example of a typical off grid system installed inside a garage wall for a newly built small family single story home;
– 2 x DCS PV series 10.0W LFP batteries
– 1 x Selectronic 7.5kw SP PRO
– 1 x Fronius 8.2kw Primo inverter
• 10 ~ 12kw of solar PV panels
• (1 x 5kVa diesel backup generator)
Is this system right for me?
Perhaps not this exact system, but we would definitely have one suitable for your situation after we review your unique requirements. Also because every aspect of the system can be expanded in the future, you can always add to it at a later date should your lifestyle change.
This is hugely beneficial to many of our customers as the road to off grid living is not always a straight forward one.
Many of our customers begin their journey in a converted shed or granny flat whilst their home is being built.
And because our system is expandable it means the only restriction is how much infrastructure you are willing to put in place.
And because your Selectronics SP Pro controls and manages all aspects of energy usage and storage, it’s a completely hassle free experience. For example you could install the system in a shed and expand it to provide power to a number of future dwellings, bore/dam pumps located several hundreds of meters away.
What appliances can I run?
Whatever appliances you have, you can use. With a little consideration into the timing of their use and the demands on the system, you can continue to use your appliances as usual (as if you are connected to the grid) with our Off Grid systems.
Most of the time a well set up system with adequate amounts of solar should mean little if any adjustments to your current lifestyle and power usage habits when grid connected.
However there will be times when the demand on your system is greater than normal. Examples of this might include having house guests, consecutive cloudy days, or a spike in power consumption for some reason (a party or function for example). Ensuring that you have enough solar, installed with optimal positioning for maximum uptake of PV is essential. This may mean having to install additional panels on top of garages, car ports, sheds or possibly ground mounted.
It is well worth paying attention to what appliances you are running at what time of the day also. It is good practice to run things like washing machines, the oven, dishwashers, hot water services etc during daylight hours when power will be supplied directly from the PV panels and not your battery bank. If you have appliances that pull a lot of energy for sustained periods, consider putting these on a timer (pool & bore pumps and HWS) so they come on during sunlight hours.
If you have very old, energy hungry appliances, you should consider replacing these with more energy efficient ones before you move into your new home if you are able to do so.
So how much power do I have to use? What if it’s a cloudy day? Or the middle of winter?
Once your panels are no longer generating power for your home, you will be running off whatever power your DCS batteries have stored. 99% of the time, with your well set up off grid system, your batteries will be fully charged every evening. So using the system example above, you have 2 x 10kWh batteries that are fully charged, so you have 20kWh of energy at your disposal until your panels start producing power again the next day. Now when looking at an off grid system, its important to always have a reserve. We like to work with 20%. So even though we have 20kWh in our batteries, we will work with 80% of that (80%DOD) ensuring we have our 20% reserve in place. So that leaves us with 16kWh of useable energy for night time loads.
80% DOD (Depth of Discharge) sounds absurd when traditionally only 20-30% DOD’s have been permitted by battery manufacturers from the dinosaur ages of lead acid based technologies such as GEL & AGM.
GEL Vs DCS LFP:
For example to provide the same usable storage capacity and cycle life using top shelf German manufactured GEL based (VRLA-GEL) battery cells from a leading well known manufacture would require a 18% DOD according to their Cycles V DOD chart data to achieve a 10,000 cycle service life seen below;
VRLA-GEL Cycle life as a function of DOD.
DCS-LFP Cycle life as a function of DOD.
DCS PV series batteries can achieve a 10,000 cycle life at only a 60% DOD. In our example the customer has 16kWh of usable storage or 16,000W / 48V = 333Ah’s. Doing 60% DOD’s on this 333Ah bank to achieve the 10,000 cycle life means you would need to cycle 60% of 333Ah = 200Ah’s on average.
Equivalent using GELs means you would need 60%DOD / 18%DOD = 3.33 times more storage to achieve the same cycle life. So 200Ah x 3.33 = 666Ah’s with a DOD limited to only 18%.
660Ah’s means you would need 2V 660Ah x 24 batteries in series to achieve 48V 660A’s. At 36.7Kg each x 24 = 880KG’s + the amount of copper required to do all the 24 series connections.
The battery GEL cells are 147mm long x 208mm wide x 535mm tall each.
Arranged as a 6 x 4 grid, would mean they would take up 0.832m x 0.882m x 0.535m = 0.4m3 @ 900Kgs.
According to the manufacturers spec sheet the 24 series connections must all be tested as well as the temperature every 6 months otherwise you run the risk of getting the battery bank out of balance and essentially killing a cell prematurely due to cell attenuation.
The manufacturers spec sheet does not stipulate the warranty terms and conditions however after calling the supplier they stated over the phone that it’s only 3 years.
So there you have it depicting this all in an easy to understand format below;
DCS LiFePO4 (LFP) cells are specifically engineered for long term cyclic applications (such as off grid systems) and have no memory effects or capacity looses associated with deep discharges (deep cycles). Hence our company name Deep Cycle Systems.
In fact the cyclic service life of our cell chemistry is so long that there is no real advantage is babying the batteries, they are so robust they are best enjoyed and frequently deep cycled. Yes please go ahead and abuse them – that’s exactly what we designed them for! No really we are not joking.
Your household will have its own minimum power usage, unique to your home, used to run the essential household items – fridge/freezer, lights, standby appliances, charging devices, water pumps. This is known as your base load. The typical sized system in our example has a base load of 2.25kWh/day. This means that over a 24 hour period this home is drawing 2250W / 24 hours = 94Watts per hr.
So lets break down the other household appliances and see what we can run solely off the 16kWh battery bank, with no additional power from the panels.
Heating/Cooling – This is one of the most important considerations in a home, due to the number of different types available. We recommend a 3 ~ 6kW centrally ducted inverter based system (heat pump), which can heat & cool a modern well designed home up to 250m2 in floor space. You need to pay close attention to the COP (coefficient of performance) of the heat pump compressor. The ratio of work or useful output to the amount of work or energy input.
How does a Heat Pump work?
There will always be surplus solar available during the summer months, so it’s more important to ensure a higher COP under the heating operation (during the winter months) compared with the COP under cooling mode (during the summer months).
The typical COP for a 6kW centrally ducted system that we recommend for our customers today has a average Heating COP of 5.2:1 and Cooling COP of 3.2:1.
This means that for every 1KW of energy input you get around 3.2Kw of cooling output or 5.2kW of heating output. Which means this 6KW heat pump is drawing 6000W / 5.2 (winter/heating) = 1.153kW. If you run it for 4 hours at maximum output, this is a 4.615kWh power consumption in total.
Turn on the entertainment system. 42inch LED TV with Bose sound system, 200w. On for 4 hours so 0.8KWh
Now lets say you want to cook dinner. So you turn on the stovetop to boil some pasta for 20mins.
Typical single cooktop on high, 2000W = 2KWh / 20mins is 0.66KWh to boil pasta.
Now you are going to turn on another stove top to cook some pasta sauce, simmer for an hour on medium = 1KWh.
After dinner you load the dishes into the dishwasher. Dishwasher cycle runs for 1.5 hours, and on average will use 2KWh per 90min cycle.
Does this really need to be turned on at night? Not really, so it can wait until daylight hours. Load dishwasher and wait until morning once the sun is out to turn it on.
Now you want a cup of tea. Kettle goes on, probably twice. Kettle 2000W for 3mins, so uses 0.1KWh per boil = 0.2kWh.
LED lighting we can allow 30W of lighting for 16hours = 0.48kWh.
On demand 1500W water pump will come on for 10mins throughout the evening 1500W/10mins = 0.15kWh.
So our energy totals, on top of our base load are:
4.615 + 0.8 + 1.66 + 0.2 +0.48 + 0.15 + = 7.9KWh, on top of the 2.25KWh base load, of which we can say 16 hours is running from our battery reserve (the other 8 hours will be running during sunlight hours directly off the solar panels), 16hrs x 94W/hr = 1.5kWh. So our total over night loads are 7.9kWh (usage) + (1.5kWh base load) = 9.4kWh.
So 9.4kWh out of our 16kWh battery bank, still leaves us with 6.6KWh in our battery bank, which is exactly a 60% DOD (with 40% capacity still reaming).
Achieving a daily average 60% DOD is optimal for the DCS LFP batteries, anything less or shallower than that is only further improving the overall service life. Remember the DCS cell chemistry is engineered and specifically designed for deep cycling, regular discharges down as low as 70-80% is not hurting the cells in any shape way or form.
Looking at the power usage of our typical customer below the average %DOD over night is only around 30%DOD;
Once you get a better understanding on your unique power usage you can do regulator DOD’s down to 40% or more such as the below customer;
We can clearly see here the customer above has managed a 40% depth of discharge (DOD) on the batteries. This is within the optimal amount for maximised lifespan of the batteries, and is what we as the manufacturer of the batteries, and as Off Grid System designers would recommend. Averaging a 40% DOD will easily provide a 15 year service life.
If you considered only doing a 30% DOD on the batteries you won’t necessary exceed that 15 years service life by a great deal, because remember cell ageing effects come into play whether you are using the batteries or not. If you really wanted to ensure you obtained the absolute maximum lifespan from the battery investment and wanted to configure the system for 20% DOD’s with the potential to exceed a 20 year service life, the best thing you can do is install the batteries in a climate controlled environment. For example sealing and well insulating a garage or small shed (where the batteries are installed) and keeping this room at a continuous 22 ~ 25 Degrees C ambient (by means of a heat pump) all year round will allow the maximum life span to be obtained.
Hot Water Service (HWS) – This is also one of the most important considerations in a home, due to the number of different types available. In our opinion with the efficiency and performance of the latest generation of PV solar panels as of 2018 the most economical and reliable form of hot water heating is actually a 125L or 160L electric hot water storage tank using a 1.8kW heating element. The water is reheated every day directly from the PV solar panels. The water tank is confined to a simple timer between the hours of 9am – 3pm. On average it takes around 3 hours to reheat a 160L water tank, so 3hrs x 1.8kW = 5.4kWh. A brand new 125L tank will only set you back around $565. A brand new 160L tank will only cost $735. Simple and reliable and replacement elements only cost around $50, for 10 years you won’t have to think about your HWS.
The example below shows how a customers 160L / 1.8kW water tank comes on at 9am and by midday it’s fully reheated. You’ll also note that the batteries SOC% is already 100%SOC by 9am from the overnight power usage. The batteries have already fully charged from 70% to 100% in 3hours from 5am till 9am. So the water tank is actually being reheated directly from the solar panels the batteries are no longer supplying any power to the house loads.
9-10am HWS comes on.
11am-12pm both dishwasher and washing machines are on and the HWS is still reheating.
What’s also important to see is that whilst all the appliances are running during the day the battery SOC% remains at 100%SOC. So essentially all these appliances are running directly from the solar panels. You have so much power to use during the day you can run just about anything you like you don’t have to think about it. You can charge at up to 8.2kW which is the output limit of the PV inverter. However you can supply loads well in excess of the PV inverter’s maximum output limit. From the batteries alone you can run 11.25kW of power output for up to 30 minutes (limited by the 7.5kW SP PRO) OR as long as the sun is shining you can run the combined power output of PV Inverter + Battery Inverter so 8.2kW + 11.25kW = 19.45kW. Although it’s possible we still recommend to keep loads under 15kW which is the continuous output of the 2 x DCS PV series batteries just in case there are mild overcast conditions which can be difficult to spot with the human eye.
Days of Autonomy!?
Let’s consider a term thrown around in the off grid world a lot. Days of Autonomy. This basically means the number of days your system can run without a recharge from your solar panels. We think that Days of Autonomy is pretty much just an excuse for a poorly designed system, and here’s why.
Even on the cloudiest, rainy, middle of winter day, a 12KW solar array, using quality solar panels will still be able to peak at about a quarter of its output 12/4 = 3kW.
From 10am until 2pm peak is around 3kW x 4 hours = 12kWh.
And then the shoulder yield of approx 730am-10am, and 2pm-430pm is another 5 hours at about one eighth of its output 12/8 = 1.5kW x 5 = 7.5kWh.
Totaling 19.5kWh on even the most cloudy of days.
Please note if you are in the southern parts of Australia the same numbers will apply as we will offset the lower PV yield with a larger system array size.
We know from our example above that an average off grid household will use around 9.4kWh during a winters evening.
So by around midday the solar array – even on an overcast day will have replenished this deficit (fully charged the batteries), and covered the new days load. But because the system was put together using only the highest quality components, there is no need to worry about the time of year or weather conditions. Just get on with your life and enjoy not being under the stranglehold of these volatile electricity companies.
Ok, I want to go ahead with a DCS battery and Selectronic SP PRO system. What sort of after sales support can I expect? What if there’s a problem?
We understand that it’s a big commitment investing in a system like this, and we are with you every step of the way. Our after sales support is second to none. After all, our family business relies on our customers being 100% satisfied to succeed.
We have spent years developing and manufacturing our batteries. It’s not only a business, but a way of life for us at DCS. We know and understand every aspect of the system and how it can work best for you. Our batteries have an expected service life of at least 15 years. And most of all because we have spent so much time developing the batteries we have complete faith in their performance and engineering and we have a warranty to reflect that.
All DCS PV series batteries are supported by a true 10 year warranty. At the 10 year mark DCS batteries are warrantied to be at least 80% nominal capacity.
Not only are our batteries backed by a 10 year warranty, they have an expected service life of at least 15 years, are rebuildable, and if there is a problem you will deal with us directly here in Australia.