Hey, I've done something similar in the UK. 'Kind of' Off Grid, I do have access to the grid, but do my upmost not to use it for anything other than charging my batteries when I get negative rates from my Energy provider and loads that are just too big for my inverter.
I built my own battery using
EVE LF280K LifePo4 cells and a
Seplos Mason DIY kit. The rest of my install is all Victron equipment. It's expensive, but it's reliable, and there's lots of support on the
Victron Community Forums. Also I'm a data geek and Victron's system monitoring capabilities are second too non. It's been up and running now for 10 months and I've no complaints, although if I were to do it again I would likely install an
EG4® 18kPV-12LV All-In-One Hybrid Inverter. The Victron equipment is good, but it's very very expensive, especially if you want to be able o run some high loads.
The first thing I would do though is change your energy supplier, those rates are terrible. I'm on Octopus Agile currently and again have no complaints. Rates are lower outside on-peak hours and you sometimes get plunge pricing, where you are actually paid to use electricity. I'm in the process of upping my battery charging capacity to exploit it as much as possible.
The second would be an energy audit. You need to know how much energy you use on average each day and what your highest loads are.
If you have a smart meter you can use your energy supplier’s app/website to give you an idea of your daily usage, but you will need a monitoring device to measure your loads. I used this:
Shelly EM (You’ll need the 120A clamp). There are other cheaper alternatives out there, but I wanted to be able to consume the data and use the built in relay for IOT projects down the line. You need to know how much energy you use on average each day and what your highest loads are for several reasons. Solar requirements, battery capacity and inverter size.
Solar Requirements
There are lots of detailed tools you can use to calculate your daily sun insolation (How many hours of direct sunlight on average per day) which
will help you calculate your solar requirements, but here’s a basic example to illustrate. A 4KW solar array in the peak of summer under
ideal conditions (your roof points directly south, has a 35 degree angle and has no shade whatsoever) will on average generate 16.36KW of electricity (4.09 * 4KW). However in December with a 4KW array you will only generate on average 3.76KW a day. Not great if your daily usage is say 12KW. You’re only going to generate enough to cover your daily requirements for 6 of the 12 months. And the months with the greatest shortfall are those when you are likely going to require the most energy. There are ways around that however. If you have a big enough battery bank you can store more on the days when the sun hours exceed the average to be used on low yield days. And you can also use an off peak energy tariff such as Octopus Agile or Octopus Go/Intelligent recharge your battery overnight on a low or negative rate to be used during the day.
Here's a handy calculator that will allow you to see your solar irradiance figures:
Irradiance Calculator Ultimately though you will want to fill as much of your available roof space as possible with the most powerful panels you can afford or justify buying.
Battery Capacity
Once you know your daily energy requirements, and hopefully your solar array size, you can calculate what size battery you will require. The bigger the battery the more energy you can capture and store from your solar array, and the less reliant you are on the grid. My battery has a total capacity of 33.8KWH, however I only use 80% of that as I keep my battery above 20% State of Charge (SOC) to aid longevity. So I’ve 27.04KWH to play with. Although that is contentious, some use 10-90%, others 0-100%. I may soon move to 10-90% myself as degradation from ageing is likely to kill the cells long before charging cycles will. My aim when I designed the system was to have enough battery capacity for around 3 days usage from fully charged with no solar or grid input whatsoever. That way in the winter months I could ride out those days where next to no energy is generated from solar and capture and store everything on those rare sunny days here up north in winter. I have a 12KW array, which is 3 x the typical install size, and even I'm starting to realise I may need to charge from the grid at some point over winter.
Inverter
Once you know your peak loads and your solar array capacity you can size your inverter. I chose a
Victron Multiplus 48/5000 in the end. However it’s only capable of around 4.2KW continuous and 9KW peak (for around 60 seconds), and my shower is 9KW, and I also have a couple of other loads exceed that. There's a few ways you can approach inverter sizing in relation to your highest loads. You can buy an inverter capable of delivering the loads, which can be expensive. You can reduce your highest loads to match your inverter capacity, which may not always be possible (like in my case). You can use an inverter that can power assist, i.e. provide the maximum amount of electricity possible from your inverter and supplement that from the grid, although this will require you to give notice to your Distribution Network Operator
(DNO). Or as I have done, separate your higher and lower loads into two consumer units, so the higher draws energy from the grid, and the lower from your inverter. I added a changeover switches on both my high and low consumer units so I can switch them both back and forth between the grid and my inverter/battery. This especially comes in handy during my energy providers plunge pricing days when I get paid to use electricity and go absolutely nuts switching everything in the house on ?
Take the above with a pinch of salt. It's just a brain dump of how I approached my install, and ultimately like many here I'm just a noob DIYer. However i'm sure if I've led you down the wrong path others will soon be along to put you straight. This forum is a great resource, and I'm not sure whether I would have managed to complete my build without it. I'd also highly recommend you check out Andy & Will's Youtube channels,
@OffGridGarageAustralia and
@WillProwse.
Any questions do not hesitate to ask.
