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Off Grid Garage Using Roof Top Solar + Portable Solar Generator?

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Off Grid Garage Using Roof Top Solar + Portable Solar Generator?

Ok. Has anyone taken a part of their house off grid? My double garage is separate from my main residence, has one power point and one light switch.

I also have an electric car that I charge mostly during solar hours, as I do have a small 1.8KW array currently installed ( yeah yeah, was in 2010, circumstances changed in 2014, no longer able to afford the $10k plus to increase),  but I've built a half wall to split the garage in half, and my workshop side has no easily accessible power!


Soooo...I was wondering if it would be worth installing a small array ( one roof side gets sun 10+ hrs daily), an inverter for both a power point and car charger ( solaredge does one), and then charge a solar generator for powering my workshop and dragging around the yard for other projects ( yes, it will need a 2000w minimal pure sine discharge rate...still cheaper than increasing my current rooftop array, and can take camping as well as home backup)?


Or, alternatives?


Oh, I should add that my electricity usage is minimal, in fact, with the government rebates for this year re cost of living, I'm in credit. The biggest electricity use is my car, but that rebate is temporary, I go camping, and I live on a quarter acre block, so drag builders extention cords everywhere...and even my 50m one doesn't reach my back boundry. So a solar generator would get substantial use.



Bunnings Team Member
Bunnings Team Member

Re: Off Grid Garage Using Roof Top Solar + Portable Solar Generator?

Hello @sara22au 


I recommend going with installing the smaller array and the solar generator. The advantages are numerous aside from the fact that you can use your tools all over your property where normal extension cables won't reach. You can have the power tools going for an extended period of time in the workshop without having to worry about adding to your power bill. 


The best part of course is that there will be minimal disturbance to your workshop as the only electrical items that will need to be installed are the ones relating to your solar array.


Let me call on our experienced members @Dave-1, @Nailbag, @Jewelleryrescue and @TedBear for their recommendations.


If you need further assistance, please let us know.




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Becoming a Leader

Re: Off Grid Garage Using Roof Top Solar + Portable Solar Generator?

Hi @sara22au you have one hell of a project on your hands and one requiring very specialised advice. It's not my area of expertise, though I am well across portable generator requirements. 2,000W won't provide even a stand domestic GPO which is 2,400W. At the very least your will require a 3,000w Pure Sinewave inverter. Your lengthy extension leads are also your big enemy. The longer the lead, the more "voltage drop" incurs. In other words the longer the garden hose the less pressure you will have at the sprinkler. Low voltage (less than 240V) can damage items connected to them, in particular anything with a motor. 20-25m max heavy duty leads not extended is recommended. So, I would be Googling business specialising in the area. Sparkies might appear to be the right solution, but they aren't. Just like specialist doctors have their field for expertise.


Regards, Nailbag



Kind of a Big Deal

Re: Off Grid Garage Using Roof Top Solar + Portable Solar Generator?

Hi @sara22au , I agree that this is an interesting proposal, that will require some research - especially questioning suppliers and consulting their websites to make a sensible assessment.  Unfortunately, I haven't done this either, so can't advise you from direct experience, only from my background in electronics.

Some things to consider: - can you charge the vehicle from a DC source?  If so, is it worth getting an inverter? Does you solar generator not have an inverter built in (ie have a 250V AC outlet)?

If so, you can get the 250v from your solar generator when required in your workshop as well as using outside where required, as you propose to do.   1.8Kw will be enough to supply many tools, as you have probably already assessed. It is the delivery capacity of the battery in the generator that will be the real limitation of power that you have available.   A solar array will charge the solar the generator directly (I would have thought, since that is usually their job) so a small array should do it, if you are only drawing power via the solar generator occasionally and choose an array size having assessed the charging needs of the car.




Kind of a Big Deal

Re: Off Grid Garage Using Roof Top Solar + Portable Solar Generator?

Hi @sara22au 


Just doing some  quick sums  re  your needs as follows:


Needs  - A car will require between 50 to 70 Kwatts to fully recharge if  dead  flat just as a  guide.  Model dependant re battery size

SO that means a 10 kW solar panel system will take approx 5 to 7 hours to fully charge the car  on a sunny day. But the car will also be rarly fully  discharged so a half full car  battery will require less time.  You have the option of a  Solar genorator which is  just a  big battery with multi inputs and outputs.  Or  charge a  100AH battery To keep weight down lithium.  Your battery can  be 12 or 24V  (24v more  efficient  )and  matching 12  or 24 volt inverter  must be 3000W for power tools usually  pure sine wave works best for some power items.  Power tools  have a  large startup  power drain hence the 3000w capacity.


The  latest solar Tech uses micro inverters(Enphase micro inverters ) which create 240v from  each solar panel ( Superior   to string inverters which will shut down if one panel not performing.  Think old xmas tree lights one bulb is out they all out/) which  can go directly to a controller  which will a car  charger can connect too which  will also supply your shed with 240V   This  array off 10kw  watt panels not portable too many big  panels.


Further  reading re our  solar  future the wise  will take note.


It is critical you install systems  that can  take future battery additions as solar battery prices drop.


The  goal for solar is to use the sun off your roof  to power your house fisrt then charge your batteries for night use. 


Battery prices set to be rebated by Gov  I hope battery prices halve ASAP


It is no longer the goal to run a  solar  farm on your roof  as  solar tariffs  electricity companies pay us  has  just dropped from 7cents  per kw to 5cents a Kw in my area NSW   and the more  people put solar on the roof the further the price will drop/.


In  fact look  up google  SUN TAX  power providers are going to very soon  charge solar  setups 1.2cents per KW we place on the grid!!

You heard me they will charge us to dump power onto the grid. How  wrong is  that.   This  solar tax as it is known  will operate 10am to 4pm as a  loose guide ie the suns peak /


So the best way to use your solar setup in the future is to on a  timer  charge your  house batteries to  power up your car, air con hot water service during those  hours to power your house not the grid as they will  take your peak days  power and  charge you for it  then if you turn your kettle on  they will sell  your own power back to you at full cost/





Home Improvement Guru

Re: Off Grid Garage Using Roof Top Solar + Portable Solar Generator?

Morning @sara22au 

Whoops, missed this question 😕 

I dont have solar as yet, considered it but keep disguarding it as I am generally not home during peak generating times, and I dont think the battery storage is cost effective for me as yet. 


I am thinking for the outlay of what you are proposing and the amount of panels you will need to generate for your use it would be far better to add to your existing array and install power out to your garage, either a suspended powerline or a burried one.  You will need to factor in a voltage drop on long extension cabels as @Nailbag mentions. A portable generator would potentially be a solution for those jobs at the edge of your property requiring use of heavy duty tools.


That way your excess will all be able to charge the car or be used in your workshop as needed. Plus your household will benifit with a large capacity system.




Getting Established

Re: Off Grid Garage Using Roof Top Solar + Portable Solar Generator?

Hi Sara22au. I think your aim is definitely doable. The main thing is to calculate your intended loads correctly so you can meet your goals with some additional spare capacity. We live in rural area of SEQ and are totally off grid. We have 2 main systems 1 was on our shed and was diy.  We learned as we went. Great support from a couple of local companies who helped us on the journey. The other system on the new house was professionally designed and built and installed. Cost a bit of money but now there’s no power bills which is very nice. If you want some recommendations feel free to shoot me a dm. All the best. 

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