Off-grid solar systems are very different compared to their grid-tied counterparts, presenting unique challenges that demand careful consideration.
While grid-tied systems can almost always fall back on the grid if the solar or batteries malfunction, off-grid systems stand alone, calling for thorough deliberation before you take the leap.
With the help of an expert in the field, we’ll guide you through the key considerations that will help you make an informed decision about buying an off-grid solar system.
12 Tips for Off-Grid Solar Systems
Glen Morris needs no introduction to many in the solar industry. He is one of the leading authorities in off-grid solar energy systems in Australia right now.
Presently, Glen is General Manager at Smart Energy Labs, an off-grid living laboratory at Mount Toolebewong in the Yarra Valley, set up to do product testing and training courses for solar, batteries, and everything off-grid.
We asked him to put together his top 12 tips to consider when buying off-grid solar. Bear in mind, if you’re serious about going off-grid, the following is merely scratching the surface.
Over to you Glen…
Tip #1. Keeping The Upfront Cost Manageable
An off-grid renewable energy system is like pre-purchasing your next ten years of electricity, hence there is a considerable up-front cost. That cost is directly proportional to how much energy you require the system to supply. Keeping the demand as low as possible is key. By choosing appliances with high energy efficiency ratings, you can reduce your overall energy demand, and avoid a larger, more expensive system.
Tip #2. Passive Solar Design Is The First Step
Consider the passive solar design of your dwelling as the first step in saving money. The passive solar design maximizes natural heating and cooling opportunities through smart placement of windows, insulation, and thermal mass. By harnessing the sun’s power effectively, you can minimize your reliance on active heating and cooling systems, reducing your energy consumption and increasing the efficiency of your off-grid system.
Passive solar design basic principles. Image: yourhome.gov.au
Tip #3. Choose An Experienced Off-Grid Solar System Installer
When it comes to off-grid installations, selecting the right installer is paramount. It’s always best to choose an experienced off-grid installer. Assess their expertise by asking them to see examples of their previous work. Even better, try to speak firsthand to their previous customers, as well as the usual avenues of Google searches and review websites.
Tip #4. Supply Detailed Appliance Information And Load Profile
To ensure your off-grid system is designed accurately, provide your system designer with an anticipated load profile — a comprehensive list of appliances, their power ratings, and their usage patterns over a 24-hour period. This load profile is crucial for sizing your system appropriately and optimizing its performance based on your specific energy needs throughout the day. Be honest and conservative in your estimate.
A simple daily load profile like this one is easy to make with an Excel spreadsheet.
Tip #5. Get Design Sign Off From The Installer/Designer
Before finalizing your off-grid system design, obtain a sign-off from your designer on the daily energy supply estimate for the worst month of the year, and a load profile showcasing appliance power ratings and usage patterns over 24 hours. This estimate gives you a clear understanding of your system’s performance in conditions it has been designed to operate under.
Tip #6. You’ll Need A Backup Generator (Yes, Fossil Fuel!)
Consider investing in a reliable auto-start backup generator for electricity during extended low solar input or unexpected events. This backup option ensures that you have a backup plan and can continue enjoying an uninterrupted power supply when needed. It can even form part of the system design for low solar months.
Tip #7. Don’t Use A Hybrid Inverter
While hybrid inverters are popular for grid-tied or grid-connected setups, they may not be the most suitable choice for off-grid applications. The primary reason lies in their low surge ratings, which means they may not be able to handle sudden spikes in power demand that can occur in off-grid scenarios. Additionally, hybrid inverters may lack the auto generator start function.
Left: Sungrow SH5 hybrid inverter, and right: Seltronic SP PRO off-grid inverter. Both will function off-grid, but the dedicated off-grid inverter with the high surge rating is better suited. Image: Sungrow and Seltronic
Tip #8. Oversize the PV Array To Optimize Battery Size
Oversizing the solar array can be a smart strategy if your energy demands are largely daytime usage. You can reduce the required battery size by generating surplus electricity during peak sunlight hours. This approach helps optimize your system’s performance and can save costs.
Tip #9. Choose A Battery Suited To Your Local Climate
Lithium-ion batteries have largely replaced lead-acid for off-grid due to falling prices and much greater usable capacity. However, it’s important to consider the restricted charge rates of lithium-ion batteries in temperatures below 5ºC. Ensure that the battery technology you choose aligns with your climate as well as your energy requirements.
Tip #10. Comply With Battery Standards And Regulations
You must comply with battery standard AS/NZS 5139, which outlines restrictions on battery installation locations in habitable rooms. Typically, a separate building or garage is a suitable location for battery installation to ensure that you meet safety and regulatory requirements.
An off-grid system in a purpose-built shed – lithium-ion batteries, inverter/charger, solar inverters. Image: Off-Grid Energy Australia
Tip #11. Be Prepared To Adapt And Live By The Weather
When living off-grid, weather conditions influence your energy consumption significantly. Focus on energy efficiency to maximize your available power during low solar input. Embrace seasonal appliance selection, like using electric cooking in summer and wood or gas options in winter, to align with solar energy availability. This smart approach optimizes your energy usage and allows you to fully utilize your off-grid system throughout the year.
Tip #12. Seasonal Energy Use and Surplus Generation
For temperate climates, often the lowest dip in solar production occurs mid-winter, which aligns with higher energy use (longer nights and indoor activities) thus off-grid PV-designed systems will have significant surplus energy in summer months. This allows for seasonal changes in energy use. This surplus energy can be used for various purposes, such as water heating, pumping water for seasonal storage tanks or dams, or even cryptocurrency mining!
Will crypto mining with summer excess solar pay off your system? Image: Bitcoin Magazine
Is Off-Grid Solar Really For You?
So, after hearing some insights and expert advice from solar off-grid guru Glen Morris, it’s clear that thoughtful planning is crucial. The off-grid solar system is a completely different beast than a grid-tied system. We’ve only just scratched the surface, so it may be the start of a long journey if you choose to take it.
One more thing that may be a stumbling block before you even get started – Glen says as a ready reckoner, be prepared to fork out a system build price of $2,000 to $4,000 per kWh of daily energy demand!
If that’s in your budget and you’d like quotes from up to 3 highly-vetted local companies for a proper off-grid system, click here.
About Kim Wainwright
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Good article and thank you Kim. Provides a reality check regarding the costs of having an off grid system. Even though I was entertaining having a battery storage for my existing pvc / inverter grid tied system. Having an induction cooktop and require a waterpump to run water in the house etc etc.
I got cold feet when reading another of your articles regarding the low surge ratings of the various hybrid inverters, which Glen brings up here. I believe that this low surge capacity is problematic for anyone considering having battery storage with ample draw down current to meet the long evenings and nights during the winter months and of course cloudy weather duing the day.
I was going to be off grid back in 2005 had designed a system using solar trackers for the expensive pvc (1200 watts) the latest MPPT inverter and some bank of 1.2 volt to 24 volt
german lead acid batteries. Until I enquired how long I could depend on these high quality batteries would last… And the electricitan who has installed several off grid systems along the WA regional areas for telcos etc..Said “in the trade we say anything over 5 years is a bonus ! My dream crashed.
Pointing out the likely hood of DOD being greater than 20% and high variation of temperatures ie not constant 25 C
I disagree with the ‘buying 10 years’ thing we read everywhere, not just here in Kim’s post. There’s at least three factors I can immediately see that are at odds with buying for a long term like 10 years.
I buy tech all the time, I think we can agree that solar is tech, and the number one rule is that it will be cheaper and better next year. Your laptop, your phone, your car. You probably didn’t plan a 10 year investment in any of these and if you did you probably realised a few years in that changes in circumstances and advancements in the tech meant they became problematic well before year 10. 10 years may as well be a thousand years in tech.
Another factor to consider is your family situation changing over the next 10 years, i.e. will you have kids, will your kids be teenagers, will your teenagers have moved out? Some of these events were planned, some were inevitable and some were their choices not yours. These all play in to your energy requirements. Both the overall total and the time of use.
We also have to factor in the changes to the cost of energy in general. If you’re looking at energy generation as an alternative to buying energy you will probably assume that it’s always going up, and the numbers on the bill almost certainly will go up, but these aren’t lone factors. The biggest factor here is purchasing power, can you imagine someone in the 80’s or 90’s building the infrastructure you are, or any infrastructure like a home off-grid power plant? There just wasn’t the left over cash in the family budget to do so (notable exceptions excepted). Look at the boomers, they’re shivering under blankets because that’s how they were brought up.
Buy the minimum viable product that will serve you now and for the duration of it’s usefulness. So, this means the 10 year investment advice you read is correct with the one notable exception being that 10 year number. Too much changes over 10 years. Perhap aim for 3 with a hope of 5…
Drew, I disagree about your claim that next year’s tech will be better and cheaper. The reality is next year’s tech will probably be more expensive thanks to inflation etc. And while it may be more advanced technologically speaking, odds are it’ll be gimmick packed rather than reliable bare bones, meaning you’re paying for things you neither need nor want.
You give cars, phones, and computers as examples. But is it really worthwhile to pay extra for RAM, keyboards, mice, fans etc, with RGB lighting for instance? And if the lighting dies will the tech still work? (I think the answer is yes but it’s still a gimmick, and not helpful to epileptics, ADHD types etc). A basic game capable PC can last 10+ years.
What of cars? Most cars use electric windows which are expensive to repair when compared to the ‘old’ lever wind your window down option. They include tablet type screens, may include voice control, use keyless entry, various cameras, and assorted ‘smart’ technology. Some customers want all of that, some would prefer none of that but still have to pay for it, and most are somewhere in between.
As for phones, rotary phones worked but people spend thousands on cellphones these days only to update them a couple of years later. For those who don’t want cellphones, or at very most basic talk and text, this is practically incomprehensible.
By contrast solar technology is less gimmick packed, more bare bones, for now. What you install today should be working fine in 20+ years, albeit minor efficiency loss. Yes you’ll need to replace your battery after 10 or so years, maybe you’ll tweak things slightly, but to suggest buying the bare minimum and updating every 3-5 years is an unwise and expensive option unless you know your situation will change regularly.
George, I appreciate your perspective and I did try to cover the price on the sticker vs purchasing power to try to cover the concerns about inflation that you have. Inflation is a tide more so than an impacting wave, it mostly increases income and expenditure equally (although with some lag). Sure, it does hit like that wave now and then (some would say right now) and when local inflation exceeds foreign inflation it impacts our largely import/export economy significantly. In future spending it’s not significant enough to matter in my estimate.
Regarding your tech comparisons though, an i7 from 2013 lacks the instruction sets to play modern games, same for gpu of either brand. If you bought the i5 or i3 every 2-3 you’d have been in a better position over the period. If you used your iPhone 5S like the phone in your iPhone 12 right now you’d need to charge it 5 times a day and the 4k videos would be a stuttering mess. As for cars, safety advancements are so rapid that they have to keep rewriting the test, an ANCAP 5 star car from 2013 would likely not get 1 star on today’s test. A 2023 Kia is probably safer than a 2013 Mercedes at 1/8th the price. My background is IT so I can only say that PC stat for certain, I have a passing interest in the other topics but off the top of my head I think they’re correct. Happy to stand corrected. All of this detail aside, renewables is a fast advancing area right now (not just in the lab or in the news) with the cost effective panel choice jumping from ~300 to ~400, 90+ inverter efficiency even from budget Chinese brands, and lifepo4 batteries in base model units.
Again, I appreciate the reply and enjoy the debate.
Drew,
I disagree. In my opinion, the key to happy off-grid living (“normal” living, not hermit-in-the-woods living) is to install as much PV as your roof and budget allow. That goes a long way to alleviate having to always micro-manage consumption, which grows tiresome if the whole family isn’t into it as much as you are. Plan to produce enough except for a very few days in the middle of winter, then use the genny to get you through those.
Everyone will have a different definition of what’s an acceptable style of living, so this obviously reflects ours.
dave
Dave, I assume your comment is in response to the minimum viable product part of my comment. The minimum viable product is in agreement with buying as much PV as your roof and budget allow. The keyword is ‘viable’. When you set your requirement as not living as a Hobbit, then the minimum may well be all of your roof, all of your budget, all of your out-buildings roofs, and some debt to extend your budget. Minimum viable doesn’t mean tiny and not fit for purpose.
What are the regulations about off grid now we have to use smart inverters? Must we still use an internet enabled, externally controllable inverter?
If you are not connected to the grid – the smart inverter regulations do not apply.
Great set of tips, as you’d expect from Glen. His YT clips are good value too.
I designed my tree-change build around central E-shaped masonry, with wood heater/cooker in one niche, and woodbox under, HWS over in the other. The raised tank is heated by an in-flue heat exchanger, via convection recirculation. A 10 p.m. deep winter room temperature of 16.4 degC with no heating can mean slow water heating, unless you open a window when firing, due to insulation and double glazing. A narrow porch cuts off sun into N-facing windows in summer. Honeycomb blinds might be added for winter nights.
That generator is essential. Batteries, if sufficient, are likely to be half the system cost. An occasional few litres of diesel is infinitely cheaper, and will be biodiesel when all oilwells are corked in a decade or two. (Ya ain’t seen nuthin yet!) The generator does not need to handle peak load, only average, as the batteries do the rest.
I’ll have to find out whether a wooden framed, cement-sheet clad battery enclosure is compliant for LiFePO₄ batteries. The workshop is separated from the dwelling by a full-height firewall, and lacks the vehicular traffic found in the garage, so much better for batteries & inverters, I figure. (i’d love LTO batteries, but can’t afford enough of them for full off-grid with miniscule genset operation.)
While the Selectronic battery inverter is ideal wrt surge capability, I know that a pair of Victron Multiplus IIs will start a good sized compressor, or run a welder. They’ll need a few MPPTs to handle half of 20 kW of PV array, as they only charge at 3.5 kW each. A pair of PV inverters can handle the other half, better serving an EVSE & the HWS.
Looked after, good LiFePO₄ batteries can give 6000 cycles. For a 24 carat geek, a pair of 13.4 kWh EVE cell banks with good BMS & balancer could be better than a manufacturer’s warranty, especially with protective upper and lower cell voltage limits set in the BMS, supported by MPPT settings.
Great post. Offgrid energy systyems are DEFINITELY different and considerably more complexity than grid or hybrid connected energy systems. Essently off grid energy systems are mini power houses. There is an unwritten saying about offgrid energy systems; “The load is the tail that wags the dog” when determining the sizing of a solar energy system. Regarding the load there two components to the load – the average daily energy use and the peak surge power requirements. Regarding the peak and or surge power requirement it is worth understanding that some types are appliances are not well suited for offgrid energy systems, in particular large 2 pole (3000RPM) electric motors – particularly single phase as well as induction cookers. These appliances/tools/pumps will require larger peak power inverter charger units and bigger battery banks. The other issue I see in offgrid energy systems is system with no back-up power supply (typically generator) Given our dynamic weather patterns expienced around Australia, it is not unreasonable to experience several days of low to very low insolation (solar/sunshine) thus a generator becomes critical for reliable solar energy systems. Finally do take the time to assess the expandability of your Solar Energy System – ensure the batteries can be added too and the battery inverter can be added too. Provided a reasonable design has been completed and the installation is compliant with CEC requirements, modern solar energy systems off the grid are generally reliable – particularly Australian Made equipment and installations carried out by electrical contractor’s with more than 5 years experience installing and maintaining solar energy systems.
I’d be interested to understand how having some capacity from a generator affects the pricing. i.e. what’s the difference in total cost between having to run a generator 1% of the time vs 5% or 10% of the time?
Craig, if it costs $14k (installed) for an extra Powerwall, and $2k – $3k for a little 3 kW manual start genset, then you’re more than $10k in front, and the interest might pay for all the fuel you use – _if_ you have jammed a big roof with all the panels that can fit, and usage is modest. Off-grid may still necessitate two batteries if you’re not keen on running the genset regularly in winter, but it can avoid a third battery. OK, a freezer full of food, and the habit of going away for a few days in winter, might necessitate an auto-start genset with a larger fuel tank. The economics of that is a different equation, veering to the subjective. (But “Eat the ice-cream first.” is my motto.)
As I see it, the genset does not need to power peak loads, just catch up with the average over as many hours as the fuel tank allows. (It’s not a good idea to refill while the engine is hot, so a double run needs a safety break.)
The equation also changes if you have a wood heater with a cooktop, such as the “Heat & Cook” I picked up at Bunnings. It even has an oven. Then you might not need to run the induction cooktop. (I’d _forget_ about slow & inefficient resistive ceramic cooktops when off-grid.) An in-flue water heating jacket obviates the need for solar water heating in winter – another economics variable. And do you pay for firewood?
But if you’re set on LTO batteries, not just LiFePO₄, then _anything_ else is cheaper. ($24k for 15 kWh, anyone?) They are though supposed to be good for 22,000 cycles. But will we all just go with Na-Ion in a few years? Mid-term economics attracts me most – long enough for payback, short enough to minimise being run over by technology advances. YMMV 😉
Hi Eric, yes, there are no absolute right answers to the question of how much generator usage versus renewable generation should you consider when designing an off-grid system.
Having lived off-grid for the past 30 years, here’s a few pros and cons of generators:
Pros: second source of on-demand power; can reduce peak demand sizing requirements for inverter; can reduce battery storage capacity and shorten days of autonomy requirements; relatively cheap power compared to inverter + battery
Cons: probably runs on fossil fuel; on-going cost of fuel needs to be considered; replacement due to wear and tear (<1,000hrs for small petrol gensets; <5,000-10,000hrs for diesel); maintenance cost for diesel gensets can be very high when parts fail; reliability of autostart function; need to maintain and store adequate fuel supply; noise; fumes; vibration; housing of generator; and ease of access for replacment (particularly heavy diesel gensets)
Glen Morris,
“Cons: probably runs on fossil fuel; on-going cost of fuel needs to be considered…”
The ongoing availability of petroleum fuels need to be considered. It seems Australia’s fuel import vulnerabilities look increasingly precarious.
http://crudeoilpeak.info/another-3-year-warning-on-australias-fuel-imports-vulnerability
http://crudeoilpeak.info/peak-oil-in-south-east-asia-and-india-part-1-production-and-consumption-update-2022
Saudi Arabia has already passed crude oil + condensate peak production (~12.0 Mb/d briefly in 2020) and seems to be now in a gradual production decline, and Russia has probably too (~11.3 Mb/d in 2019).
The only major potential growth remaining for US crude oil production is in the Permian Basin, but the oil rig count, an early predictor of future production, suggests otherwise.
https://www.reuters.com/business/energy/us-drillers-cut-oil-gas-rigs-second-week-row-baker-hughes-2023-07-21/
Most other oil producing countries are in decline (post-peak). There are very few oil producing countries currently at pre-peak.
The era of cheap, abundant crude oil and petroleum fuels has ended.
Hi Glem,
I can confirm the maintenance requirements of gensets. After 59 years off-grid out on the farm, we have a small stack of worn out Honda motors in the corner of the shed. (For decades, the genset has been all we’ve had.) The third alternator is still going, but I’ve had to put a new 20 uF motor run capacitor in it. The output voltage had fallen to 190 Vac, but a new cap brought the ferro-resonant regulation back into whack.
We get well over 5,000 hrs out of a Honda motor, by changing the oil twice as frequently as recommended, and stopping it by cutting fuel. My father was adamant that using the kill switch left condensed petrol on the cylinder walls, washing the oil off on standing. Running with a dry piston immediately after each start is then supposed to wear more than a couple of hours of oiled running. It sounded marginal to me, but I’ve run the current motor around 3,000 hrs, and it had done at least as much before I took it over.
(I have put in a new sparkplug in the 4,000 hrs, though, and cleaned the airfilter.)
Yes, I was a lot younger when building the little generator shed behind the outhouse laundry & WC. It nicely solved the noise issue. As for fuel supply, I can still swing a 20 L jerrycan into the back of the ute with one hand, but would not want to rely on that through my 70s.
Once the solar goes on, we’ll not only save the petrol emissions, but also those from the gas fridge. (Used to be kero, and gas lamps.) But for my 2 sq. km. of forest to absorb that and many tonnes more, I’d be in even more of a hurry to get it done. (At nearly 70, the pre-sale reno here in town is taking longer than desired. Nearly done, though. Going solar out there will be a lot more fun, especially as the reno is on top of a 3-year owner-build on the farm.)
Thanks again for the good hints, especially for a solar first-timer who likes an optimal solution.
Good article. Our 2018 build was off-grid from day 0. Initially 10kw of PV, one Victron Quattro 10kw inverter /charger, Victron mppt and 33kwh of LiFePO4 plus 10kva genny. We later upgraded to a second Quattro and added 13kw of PV to reduce genny hours in the depth of winter and accommodate a Tesla.
During winter we may have surplus to get the car to 80% charge over several days, where in summer we have massive surpluses even running aircon frequently.
Victron gear has been perfect and their Web portal useful. It even provides a PV energy forecast customised to our configuration and local weather.
I created automation to manage EV charging so as to intelligently prioritise charge rate of the EV and house battery.
All in all, we live in luxury without any compromise due to being off-grid. In fact, the grid here is unreliable so that is an issue we bypassed.
Dave, what do you use to manage EV charging (and HWS?) vs battery charging priority, just Victron’s DVCC and a smart EVSE, home assistant, or other? (I’m not wild about Node Red, so hope that’s not the answer. 😉
Many thanks for your generation & usage data point. I have room for 10 kW flat, 10 kW North facing & 40 deg elevated for a winter grab, plus 3 kW West facing, also 40 deg elevated for late afternoon aircon without battery drain. Your experience suggests it’ll probably do the job. The plan is to begin with 26 kWh of LiFePO₄, then add another 13 kWh in a DIY garden tractor. (Could take some time to get moving, but can serve as battery before then.)
I have been planning two 5 kVA Multiplus IIs & two (Fronius?) PV inverters, as the latter provide a more direct power path to the EVSE & HWS. A pair of 10 kW Quattros & no PV inverters, instead, would necessitate more MPPTs, but might be easier to manage via DVCC, I guess. The extra loss ought to be minimal, though, as DVCC can float variable power across the the DC bus without battery charge/discharge being involved. There won’t be any need for delta-f throttling taking things to 53 Hz, either.
Do you auto-shutdown one Quattro at night in winter? It could save a wander to the garage to manually start my 3.2 kW Honda genset. (I don’t plan to go to anything auto-start unless there’s a freezer, and I go away.)
I’ve installed VenusOS on a RPi4, to familiarise. Do you run the extra management on the (Cerbo?)GX controller or an additional host?
Erik,
All our PV panels are on a flat roof sloped at 5 degrees. The winds here are such that angling the panels was not advised and instead they now nestle below the parapet and are protected. I lose maybe 10-15% from this non-optimal angle. Once a year I spend 10 minutes cleaning the panels.
For the EV, I have a Tesla wall connector and Node Red, which gets info from the Victron mqtt API to determine how to charge the car. Also, of course, the Tesla API. I’ve found Node Red is the best tool for this, based on my skills and interests. I use OpenHab to provide a GUI to control charging, exterior lights, irrigation, etc.
My EV charging logic in Node Red is simple. Two modes– manual or automated. Both protect from depleting the house battery. Manual mode just sets a desired EV charging current. Auto mode ensures the battery is being charged, going more to less power as the SOC improves during the day. At 85% house SOC, the Tesla charging is maxed. Otherwise, the Tesla charge current will vary every 15 seconds from 2A to 32A based on incoming solar power and house consumption. The goal is to ensure the house battery always gets enough power to charge through the day.
I don’t power off one of the Quattros at night, though I might consider that. I’m unsure if it is worth the risk and bother to save 60W X 10 hours.
I love having two big 10KVA Quattros and was lucky enough to make use of the new Victron SmartSolar MPPT RS 450/100. These are huge (the /200 is huger) and I have two of them and an older MPPT.
I have a Colour Control GX that runs the VenusOS. I didn’t put Node Red on there as there’s really no benefit vs running it on a Pi or my Mac. Better, I think, to have it send data to my mqtt server and from there to Node Red.
Great to see some content from Solar Quotes aimed directly at us off-gridders – and so soon after my post suggesting just that. Yegads! It’s almost as if we’re being noticed!
For anyone contemplating a move out beyond the traffic and the noise, Glen’s point about passive solar design deserves close consideration, and it goes well beyond careful window placement and deciduous trees. I’m building a new earth-sheltered house in the Yarra Valley which will avoid, or at least minimise, the need for artificial heating and cooling throughout the year. A think soil cover over your roof is worth a bunch of PV panels and batteries, and there are no fuel requirements, malfunctions or warranty issues..As hard as it may be to imagine T shirts indoors while I sit here shivering in my steel shed, I’ve heard from many users confirming that this is indeed real. And a bonus is the extra safety margin through the bush fire season.
Hi Craig, it’s possible to model and give performance and cost estimates for various senarios such as increasing the energy supplied from a generator v’s batteries and solar. Software like SolarPlus (*my company) can model both on and off-grid system designs.
Apart from cost though you need to consider reliability of supply. A PV/battery system is far more reliable than an auto start generator. There are so many reasons that the generator won’t start: low fuel, low starter battery, poor maintenance etc…
However, for designs that may include regular high and sustained peak demands such as morning electric cooking, scheduling a generator to run at these times can help reduce battery storage sizing and inverter maximum power rating.
As I’m replying to my own comment, it just HAS to get a “like” from me. However, you’ve printed “think soil cover” rather than “thick soil cover”. No doubt most people woul read it in the way intended, but I want to put you on notice that I’m coming for you now!
To reduce inverter and battery costs, I have been working in two off-grid projects for the same house.
The first project is thermal energy. Thermal energy is hot water and air conditioning. This is the portion using most of the energy.
The second project is electricity for home appliances such as refrigerator, induction stove, oven, dishwasher, blender, water distiller, washer, heat pump dryer, and lights.
Using DC electricity saves money three ways:
1- There is no inverter required during daylight hours for thermal energy. This saves around 10% in lost energy from the solar panels since there is no conversion from DC to AC. This implies less solar panels as well.
All inverters lose energy in converting from one type of electricity to the other type. This is why inverters run hot.
2- Batteries for an air conditioner unit can be skipped all together if the weather at night is temperate and low in humidity. This saves money in batteries.
There are air conditioners that use direct current, DC, directly from solar panels, and if required, they can, also, work off from alternating current, AC.
3- The third way having two systems saves money is by using a smaller inverter, smaller battery bank, and smaller gauge cables for the system supplying electricity for house appliances using alternating current.
The thermal system, also, uses a DC hot water element for hot water limited to 750 watts when using DC.
The DC hot water resistive element is variable in its energy usage. Therefore, it will take less than 750 watts. It is self limited to 10-amperes.
This allows making hot water over a longer period of time and requiring less solar panels (the same solar panels used, also, for the air con unit).
The air con unit is setup to work with up to 10-amperes of DC; however, steady state operation usually requires less than 5-amperes.
The thermal portion will work for both the air con unit and the hot water element with 7-solar panels of 300 watts.
The hot water heating element will not work with more than 360 volts DC, and the air con unit will not work with more than 380 watts DC.
Ideally these seven solar panels can be installed in one or two mini two-axis solar trackers from Eco-worthy.
The solar trackers extend solar harvesting in the morning and in the evening, and they provide a maximum level of harvesting throughout the day.
A two axis solar tracker is less than AUD$ 800 from Eco worthy.
If you have a large house and / or a large family using a lot of hot water, you can dedicate seven 300 watt solar panels for hot water, and you can install another 6-solar panels for the air con unit.
In any case, this is cheaper than sizing up a system that uses an inverter, batteries, and solar panels for both thermal energy and AC appliances.
As I mentioned before the air con unit can work both from DC and AC, and the resistive heating element can, also, work with both types of current.
If night usage is required from the air con unit, my suggestion is to purchase a DC only air con unit using a solar charger and batteries. This will still be cheaper than a whole house system with an inverter and a large battery bank.
Great for when solar is really expensive, – but it isn’t anymore! It is very cheap to throw more solar at something these days. Standardising on 240V cuts a lot of costs – tradies are loathe to touch anything ‘non-standard’.
Having said that, if you are knowledgeable – technician-level plus, and/or in the industry, then go for it, as you’ll be doing the fixing!
Hot water thermostats *die* if fed DC direct (are you saying give them DC?)
Otherwise stick with: lots solar, *lots* insulated walls, roof *and floor* (boy I could tell you about that), and put it all in the sun.
PS I’ve been doing off-grid on and off for over 20 years)
Your picture of ‘hybrid’ inverters shows a Selectronic, and infers it has a low surge rating!
Erm. . .nothing could be further from the truth. It is probably *the* most robust off-grid inverter readily available! It was first designed as a full off-grid, generator-capable inverter in the 1990s, and was adapted to accept grid about 1999. It was doing its grid-battery interactive thing for more than 10 years before the term ‘hybrid’ was even thought of.
I’ve owned a few models of them in the last 20 years.
the caption explained Selectronic was the go for off grid – but point taken and image updated