Hi guys, great forum, thank you for all your input, I’m learning so much.
We are looking to go 75-80% off grid. We’re currently using around 45kw/day. I would really appreciate any advice on the two quotes we’ve received. The specs for each are quite different in terms of battery power (3 x 4.8kwh LIFEPO vs 2 x 5kwh Greenrich); inverter (5kw Sunsynk vs 8.8kw Sunsynk); and panels (16 x 420w Canadian vs 16 x 455w Trina). I’m all at sea here, any guidance would be so appreciated to help me make a decision. The costing is very similar. Which one would you go for and why? Which system would produce the most power?
Canadian vs Trina… toss a coin. Both good options.
Greenrich? Never heard of her. Google says it’s your standard slap some cells and a BMS into a box. Not enough info to tell you which battery. They both seem like “beige box” solutions. Toss a coin… or buy a brand name like Pylontech of FreedomWON instead.
A 5kW inverter can offset 25kWh on average per day, just using solar during the day time. In that sense the 8kW is the better option, if you want to use most of your energy directly instead of storing for later. I think the 8kW is better matched with the PV you have available.
Thanks, that’s helpful. My main issue is actually working out the trade-off. So an 8kw inverter is better than a 5kw, but the 5kw inverter comes with 14.4kwh battery power, while the 8kw inverter comes with only 10kwh battery power. Which combination is more powerful?
It depends on whether you plan to use the battery at night, or if the battery is more for backup and you want to use the PV directly to cover loads during the daytime.
The sunsynk inverter’s topology will make it more efficient to use the energy directly for loads rather than sending it into the battery and taking it out again.
If you intend running off the grid most of the time, and dig into the battery deeply every night, take the bigger battery and the smaller inverter.
Edit: I represent a competitor, so I use the info I know about sunsynk though I am not fully up to date with the hardware. I know what topology is used. For someone who is going to store two thirds of the energy in the battery for later use, I would recommend something more off-grid focused, putting the PV on dedicated MPPTs and swapping in a Victron Multiplus instead
If for residential, forget about 80% off-grid and most powerful as concepts. You are either trying to lessen dependence on Eskom because you need to/can and/or trying to hedge against tariff increases. The saving money part is a long, complicated calculation. To lessen dependence on eskom is probably easier to solve.
you should know more than your basic energy use per day. Which inverter will cover your realistic peak loads better with a bit of room to spare (5KW or 8KW)? Which battery will be able to cover those same peak loads?
When do you use the bulk energy (day light hours or night), and what do those loads look like size wise? If most day use, then battery probably less important. If mostly night time then battery more important. Will you split your loads so that you have the option to limit battery use when there is load shedding/bad weather? If no, then both inverter and battery size will be influenced.
Considering that they represent very big line items on a quote I would be careful to try cut costs too much on batteries by going for what looks to be the lowest cost option (this is about whether the battery will work 100% correctly with your system and whether 5 years from now there will be support around if needed).
I have a 10kWh battery and use about ~4-5kWh during night time till it can start charging the next day. If it is raining or cloudy then that can be delayed. I would say I have below average consumption compared to others.
Something to remember is that you can only use up to ~80% of your battery. So for my 10kWh that means I only have 8kWh usable capacity.
If I assume 12h daylight (which is correct twice a year ) that means I use around 0.4kWh during the evenings (5kWh / 12h) and I have capacity to use 0.6kWh (8kWh / 12h)
If you can do a similar calc. (adjust to fit your usage)
45kW in 24h - lets assume you do use less power at night when everyone is sleeping.
So 15kW for 12h night time and 30kW for 12 hours daytime.
Then 15kWh battery for night time would be better than 10kWh (for 80% off-grid usage and 80% battery capacity). If you use 10kWh during night time then a 10kWh battery will give you a better match.
For daytime you need an inverter that can charge your batteries and also give you the power so that is for the full 45kW over 12h or average 3kWh (the 5kW Sunsync should be able to give you that)
For the PV Panels you should be able to get 380W for the 445W panels and around 350W from the 420W panels. (Marketing value vs actual real world)
This will give you 6kW or 5.6kW of PV and you can assume around 5h production which will give you 30kW or 28kW per day from the sun.
Differently put:
5kva inverter = 4kw (it is a lot) continuously and make everything fit into that i.e. lifestyle changes and scheduling.
10kwh bank = to match inverter, offset evening use, as per Plonkster’s post.
5-6kw array = to cater best one can for non-optimal weather. Too small, you cannot recharge, too big you seldom use it, balance.
After 1 year of data/learning one’s system’s optimal sweet spots, one can double up on everything, if the data says so, and the budget allows it.
My views stem from one can do the math, all of it is true, that is until one puts the panels up and discover, this, that, or the other, or the wife refuses XYZ, weather patterns change, or Eksom LS gets even worse … real life gets interesting.
If I can throw my 6,000,000 Zim Dollar in the pot.
Take a step back, a deep breath, this load shedding spell will also pass, you don’t need a system tomorrow, rather bargain on a month or 2 from now, in the end you’ll save money because you’ll have more info and data to work with.
Buy yourself a energy meter to put on your DB, Efergy is popular, let it run for at least a month, maybe even 2 while you do further research. As others said already you need to see what times of day you use the most electricity, day time or night time and you also have to figure out your average load and peak loads, the energy meter will be able to tell you all of this over time.
As the energy meter readings come in you will start to see where you are wasting, where you can save. Examples, spending R1000 on LED bulbs for the entire house is much cheaper than having to spend R30000 on a extra 5 kWh of battery power to run all your old bulbs threw the night. R1000 per geyser timer is much cheaper than spending R20000 extra on more panels and inverter power to run that geyser continuously. Lifestyle changes come in here as well, first make lifestyle changes to lower your electricity usage and only then spec your solar system.
If you and your family isn’t willing to make lifestyle changes, then solar won’t work for you, then you will be one of those guys around the braai in a years time who will tell everyone solar systems is BS, they don’t work because you installed one for X amount but you save nothing on your electricity bill.
Once you have energy meter readings then you’ll be able to determine much better whether a 5 or 8 kW inverter will suit your needs best. After you know what size inverter then you size your solar array according to your inverter size and only after that you size your battery based on how much electricity you use threw the night plus some extra for rainy days.
