I found comparing grid power costs to my own PV power costs was silly. Instead of spending a lot of money on a backup generator for emergencies I have my PV/battery system that requires almost no maintenance. And for the years I lived in an RV my PV panel /battery energy system was priceless. A friend told me that PV panels simply didn't pay for themselves. I replied that he wouldn't say that in the dead of winter at a campsite in the national forest. ANY money I put into the system just made my life better, and it saved me over $1000 a month in rent. So the RV and the PV/battery system entirely paid for itself in the first 2 years, ALL of it. So it's entirely a situational thing, as you mentioned.

Nice video Dave. One thing you also need to consider is your best and worst solar days combined with worst and best home usage - not just average for the seasons. For example, if you have many days in the summer where your solar is pumping but your house load is light, that energy can't all get saved with your battery system - you will hit max state of charge. At which case you still have to give back to the grid (at your lower feed-in rate). But if you then have rainy days where you need more power than the battery could have banked, you have to get that from the grid at your higher consumption rate. If it turns out you have an overall surplus, that's not a big deal. But you really need to look at your daily worst cases to size the battery - not just average within the seasons. Otherwise your calculations are giving you a best case, and you'll be 'clipped' by your battery state of charge in reality and not achieve that. Seems super easy to have many days where your solar provides more than 10kWh surplus over your home usage (which would be your 0-100% battery SOC for a 10kWh battery) - and that extra energy can't be banked by the battery and goes back to your current grid feed in/out pricing. And conversely, on a rainy but high consumption day, you won't get your battery charged to last through the night - so need power from the grid. If you do a day to day analysis, you'd probably see that both these scenarios happen fairly often, and you have to either go with a bigger battery - or just factor in the grid in/out cost for those daily over / under consumption scenarios. And also, when sizing the battery, you also want to consider how far you want to dip down. Battery life is extended if you aren't cycling 0-100%, so you generally want to oversize capacity to account for that as well. I think in your case a battery system is a tough call. You probably won't reclaim your expenditure if you figure a 10 year life on the batteries. Unless you have some incentives in your area to help with the price. If you have time-of-use billing, or zero credit for feed-in, then a different story.

We have a Tesla system, Solarroof and Powerwalls. We got it to do 2 things. First, ensure we had power all the time. We have 3-5 power shutoffs per year some lasting upwards of 18 hours, and since we work from home, no power means no work and associated billings. Second, to reduce our power costs. The system has done very well at both. The system has pretty much removed our electrical power bill. We used to pay upwards of $600 USD/mo. in the summer. Now we usually only pay the minimal connection fee amount, about $12/mo. And as far as backup goes, we have not lost power, even when the neighborhood is out. We usually just get a message in the app that says the grid is down. And we verify this by looking out the windows and see the lights are out at in the neighborhood. We usually don't even see our lights flicker.

I have lived off grid for quite a while and I have learned that the word battery can mean several different methods, some are electrical in nature however the larger ones are usually water, air, and even larger ones are large tank batteries for sweet crude oil, I like the idea of heat storage, as far as the electrical devices that I use most are one off which I have repurposed from other devices and redesign their power supplies to a softer mode to the lightest power usage needed, as an example instead of using one Pelletier device at 12 volts I will connect to in series and run them using the load control on the solar charge controller.

Absolutely LOVE the intelligent ‘walkthrough’ of your “Shall I buy a battery” question. Don’t beat yourself up about your ‘wacky’ system, nor your decisions. Score highly for making decisions around sensible reasoning. I have the same question over here in the UK, but I have different sums to do, as my government decided to PAY ME to generate electricity, whether I use it or not !! They pay something called a FIT payment. They did this ages ago, and their payments from my (maximum domestic micro generation system allowed) 4kW system covers ALL my utility bills. This is very different to the offer down under, as you describe. So, what’s my problem ? I have a couple of puzzles I’d love to answer. 1) how can I show I am using my generated power 1st, before my electricity meter charges me for any electricity? An electrician came over to fix a ‘fault to earth’ problem on one panel string, and he found something unusual by clipping current meters onto various cables in my supply cabinet. I wondered if the electricity meter - (which shows the statement RED on it’s screen for Reverse Energy Detected, when the solar is driving power back up the grid) is then charging me for some proportion of the electricity I’m generating ! In other words, my power is going into the grid and then I’m being charged for it via the meter as I use it ! I can’t see why this is a daft idea, and I can’t see what gadget to design to prove what’ happening. If I have a current coils on the solar generation output, on the grid supply and on the house supply from the grid’s meter; can I watch current/voltage waveforms (Raspberry Pi-type project) to see where power is going? If the solar is winning, I should see it’s power output being partially sent to the grid (reversed through the meter) and partially consumed by the house (via the meter) But how can I tell if the meter is registering input power to the house? That would be a naughty thing, and great fun to prove. Does anyone see what I mean? I’m quite content to be branded a) paranoid and b) bonkers, but it’s bugging me. The government is generously giving me X for generating, and the electricity company takes a cut Y by billing me for the same electricity ! 2) Is it worth grabbing unused power in a battery system? Typical answers may include, “why the hell do you care? The government is paying your utility bills, anyway!” Well, I’m a degreed electrical techie, and it would be fun to power the house when the solar was not. Lastly, I have daily data (manually logged - good grief!) since to system was installed. If you’d like a copy, let me know. Like you, I have 1/2 my solar panels NOT oriented optimally. Here, 52N, I need South facing panels, and 1/2 are N facing. I can’t tinker with this, as the FIT scheme requires a ‘licensed installation’ which I can’t change. (Not unreasonably) Any-road-up, great video. Matt Lee (old computer and electrical hack - BBC micro era !)

Wow... about time this made sense. I've been off-grid for 4 years now and I paid $2000 usd for a 10kw lifepo4 24v battery plus $800 usd for a hybrid inverter. Best purchase so far!

Nice analysis, thanks! I live off more or less 8 kWh usable, off grid (14 kWh SiO2 total). I like when the batteries go full, then the charge controllers will lower the input for float stage. Then I can turn on more loads such as boiling water or cooking. The charge controllers will instantly adjust and pull the exact quantity of required power, you can see the stats of the load by looking at the difference of the input before/after! Going off grid requires a lot of optimization and compromises, let's call it degrowth.

These hybrid inverters are "whole house" too as they can measure the energy in and out of the total house and make decisions based on that to for example charge or discharge their battery. A transfer switch like you showed could also be handy

Lithium Iron Phosphate is way to go to have a grid/house battery. And i would buy 12~15kWh, a bit overhead will have less stress on your batteries and better live span, in my opinion.

You could take a small 5kwh battery to power the house if your electric car is on its way and install a system that takes the energy from your parked car. Then you would have a 60+ kwh battery at no additional cost other then the setup. (Hyunday Ioniq 5 has a 58 kwh battery with bi-directional output of max 3.6 kwatts)

Even though the feed-in tariff is a pittance, if you factor it into the calculations it reduces the yearly saving to ~$1170. Because you're no longer selling the excess energy to the grid and instead storing it in a battery, then you need to subtract that loss of revenue from the savings made on your electricity bill. I still think the battery system is a good way to go, as feed-in tariffs only seem to be going down, so I don't think you can rely on it for long term investments like this.

I noticed that a fair share of energy that I used to pull from the grid was down to pulling energy at the wrong instant (clouds) or the solar not providing sufficient power. So now with the battery system I can bridge those cloud gaps and boost the solar system on high power loads. So it's not just night and day that matters.

You forgot to factor in the rampant inflation over the next decade.

At 1.49€/kWh from the grid and 0.086€ to the grid, pretty much every battery becomes economically viable where I live.

Power in my neighborhood used to go out once every 2 months or when it's stormed. I got tired of looking out of my window doing one of these blackouts and seeing the next door neighborhood have power. So I went out and bought a few power stations. The following year the power company buried the power cables in my city. Now the power only goes out twice a year. However I'm still glad I bought my power station because over half my power usage is now from solar power.

Having a battery bank with solar panels is a no brainer. I have 4 server rack batteries that store 20k Kilowatt hours. Cost me $9500 U.S dollars. I'm 100% grid independent. BEST money I have ever spent.

Not sure what Heat Pump water heaters you have down under, but I replaced my 50 gallon (190 Liter) electric resistive heater with a heat pump model in April. According to my records I'm using a smidgen less than 1/4 the electricity to heat water. Bonus is that it pulls moisture out of the garage, and keeps it a bit cooler out there as well. Best case scenario for me. The heater sits in the garage, and I'm in the Southeast US, so it gets HOT out there. Plenty of heat to pull from the air and pump into the water. Highly recommend!

The viability of batery storage lies in self-sufficiency - if the grid goes don;t for whatever reason, you still can fill up those batteries with your solar panel.

I'm so happy, that we have yearly accumulation of solar production in our country. Whatever you produce during the year gets fed into the grid (minus what you can use urself at the moment) and that MWh then transfers to the next year. So if you size your solar panels right, so the yearly total production is equal or higher than your yearly consumption, you're pretty much golden and you have almost free electricity. Grid is really the best kind of battery there is.

Here in South Australia we have all been (forcibly with no options) moved off flat rate charges - so we now pay off peak, shoulder and peak. All properties get/got a smart meter when solar is installed so easy for the suppliers to do this. Expect this will come to NSW over the next year? This will significantly increase your bills. There is so much BS re the grid - solar power distributed across the network actually lowers grid cost, and improves reliability. Current best feed in I have been able to get is 7.5cents - which is straight forward theft, maybe a class action against the AEMO? Tesla 13.5Kw battery has cost me $11,529.00 (actual cost). Went to this solution because of install options and location. This is currently working as part of the Tesla virtual power plant - which I can leave at any time, but does give additional rebates and extends battery warranty if you stay on the plan. Waiting to see what real costs are.

Dave, with the Victron gear (a Multiplus II for example) you can AC couple your Enphase system and at the same time can hook up your string. The Multiplus II is inverter and charger, so you can charge your battery via AC. With regular MPPT solar controllers you can feed your string to the battery via DC, so you have the best of both worlds. The Multiplus can also act as a grid tie inverter and sell the excess solar power generated with the DC side. I have one and during the morning it charges the battery and power the loads directly from solar, and sell the excess power to the grid on the afternoon, at night it it power your loads until the battery reach a SOC that you set.

If the size of the battery is just 1 average day then often you won't have enough energy if there's under average weather. To really eliminate most of the sell/buy electricity from the grid you must have a battery capable of smoothing/averaging the production of multiple days. I guess there's an optimal level using a big enough battery to have an effect without costing too much. You could simulate the effect by just doing the analysis on a day by day instead of a 3 months level.

This was helpful good sir. Thank you. This is an upvote from me.

Hi Dave, I do a slightly different system. Rather than export, I import limit. I have 8 truck batteries feeding a couple of inverters that feed lighting and general supplies to the house. The system swiches through an ATS switch so at 8am we go off grid and run on the batteries. 8pm switch back to grid where Leccy is then at off peak level and that what I do to charge the batteries is to start recharging through midnight to 6am. As long as you have loads of battery capacity recharging is minimal. Have cut my import cost by 35 to 40%

With rising power prices, the sums are moving towards batteries..... we picked up a Powerwall in Jan 2021 with the proceeds of a couple of Covid-cancelled holidays, so a reasonable investment.... getting power bills sub $100 is pretty cool. The daily supply charges are a killer, especially in winter when you don't produce much grid excess (or any) to pay for them.

Great Video, thanks. But I think u missed to mention, that every kwh you store in your battery, you wont export to the grid. Therefore you "loose" an income of about ~400$ per year, isnt it? Here in Germany our winters are quite bad for PV, which leads to a situation, where in some days, the battery has to be charged from the grid, to prevent deep discharge. Maybe that isnt relevant in your country?

Where we live, Northern San Diego County, the power grid is not that reliable and we've had frequent outages. Some as long as 34 hours and being without power for that long is a real PIA. After looking at our options, this was several years ago, we went with a solar/battery system from Tesla. We chose this over getting a gas/diesel/propane generate since there is little to no maintenance, other than periodic cleaning of the solar panels, transfer to battery is quick and it's hands-off. Since we've installed the system we have not needed to pay for electricity, other than the fixed admin costs. Paying for itself was never a selection criteria. Looking at the outage data since the system was installed, we've had 44 outages, for a total of 7 days, with the longest being 34 hours.

Dave, your situation mimics mine here in Si Valley CA w/ a newer and older PV, annual consumption and overall needs. Excellent discussion, highlighting some basic considerations. Well done, thanks!

To calculate the real number you will need to do a continuous test. There is a Domoticz script that will add a virtual battery. I have had this script running since 26 august so not too long. However since then it would have stopped about 263 kWh from flowing into the grid. With a price of 0.3 euro per kWh that would be about 79 euro. However until some point next year we can freely export power and take that number off of our used numbers ("Salderen"). At that point we can only do that to 50% so Theoretically right now there was 0 gained or lost. Next year it would be 40 euro lost during this same time. (Not exactly we would have to calculate the payback for return power after the 50%.) But even at 80 euro a month that seems not worth it. At least not right now. There is an elephant in the room though. It is no longer 0.3 euro kWh it is going closer to like 0.7 euro soon. Which all of the sudden makes it 184 euro per month. Perhaps those prices are interesting. But how long will that last? So if these prices keep up we would be doing 92 euro a month in potential recuperated costs next year. With those prices it would still take 10 years to get a return on investment. Which likely means... knowing lithium, that there is no real return on investment as the thing will die before that. Extra information: I set the script to 12.5 kWh battery capacity and during this last month the battery "overflowed" for 92.917 kWh so that power would get exported to the grid because the battery would have been full. Also it couldn't supply 83.404 kWh which had to be imported because the battery was empty. (58.3828 euro in import costs and 8.3625 euro for the returned. Meaning with this system it would still cost 50 euro a month.) Then lastly I set the maximum power the inverter can give to 5.8 kW and it only went over that number twice which would have taken 0.012 kWh from the grid.

Did I miss something in the video? On long summer days you generate way more than your battery can store and you are only using a fraction of it during the short night. The next day starts with a pre filled battery already. So you are going to export the excess most of the time. In winter it's hardly possible to fill up the battery to store enough for the longer night. Especially if you got a heat pump that needs the most energy during these cold days. I created a battery simulator from my hourly data on my sold/bought values of my main meter for the last >400 days and came to the conclusion that no matter what size of battery I buy at this time, I get ROI dates of around 15 years. As soon as I get

people need to consider their options depending on how many phases their property uses. This changes the hybrid system installation or our household power circuits.

It's worth doing in California, where lovely PG&E thinks it's fine to go days without power a few times per year.

Excellent video, very interesting. I live alone in a small off-grid house, and I have 2 kW solar panels connected to 9.6 kWh batteries (8 x 12 V 100 Ah lead acid deep cycle). This is more than enough during spring and summer. My use averages around 3.5 kWh/day. But during fall and winter, I have to be very careful about my energy use. I turn off the fridge, which is the biggest consumer, and instead lead outside cold air via a duct into the fridge. Frozen items are put outside. I run a gas powered generator sometimes in the winter to top up the batteries. I've spent a lot of time trying to come up with cost effective energy storage. My first idea was to make my own led acid batteries by buying the lead keel off of a second hand sail boat. However this is very toxic and dirty work. My second idea was to build my own LiFePo battery bank from individual cells and a balancer circuit. I've also looked into DIY super capacitors. Although there are videos online about various methods, they all look too good to be true. Instead of focusing on the weak link (the batteries), I've decided to just throw a lot of overcapacity of solar panels at the problem. A week of rainy over cast skies is normally a big headache for my energy system, but if I had several fold more panels it wouldn't be a problem anymore, because they would give enough power even at bad conditions. And unlike batteries they virtually never wear out. So I'm looking to purchase around 6 kW of panels to install. But right now with the European energy crisis they are hard to find at bargain prices. My energy system: www.bjornmoren.com/Solar-power-for-homes.html Different ways of storing energy: www.bjornmoren.com/Optimizing-energy-storage.html

Have you considered building the battery yourself? Good quality EVE LiFePo cells can be purchased pretty affordably nowadays and you can pretty easily build a 10KWH system for under 2000 bucks. Just add a BMS and a hybrid inverter and you're good to go. Also look into server rack batteries, very affordable too.

With one person I know, there was one requirement that made even very expensive backup power a requirement- they had a whole year of food in their deep freezer. The system proved its worth after a grid outage for 10 days(!) following a huge severe weather event, but a combination of solar power plus some quickly added tractor batteries to hold over a cloudy day, kept the freezer working through it all. A backup generator could have worked too, but sometimes I find seldom-used complex mechanical things end up not working when you need them most. Also, during that event, generators were unobtanium because everyone else wanted them too.

Excellent presentation!!! My power literally never goes out, I'm lucky to live in a sub division directly beside the 4 reactor Darlington Nuclear Plant so we even get generator backup from the plant LOL.

The 1 day power storage is impractical in the extreme and can not be considered an "off grid" solution. At least around my parts. Around my area, a week or 2 of constant rain and heavy clouds is normal. We are using around 8kwh per day on average, and an actual longest blackout was for around a week (a tractor vs an underground cable incident). Basically, "off grid" would require an enormous redundancy in both - power production AND storage. Like an x10 redundancy. Assuming a 15% efficiency (North Europe) my 8kwh consumption would require a 100kw solar cell setup(double daily use to compensate for weather) and at least a 50 kwh of storage (blackouts are frequent and sometimes last days). That will never pay for itself. The most practical solution for me (and most europeans north of Italy) is getting a gas generator for emergencies.

This is fab - I've recently done my own maths and it's just on the other side of the "not yet" line for me (town house so roof a bit small and high up, leading to expensive install price and lower possible generation capacity). I could go without solar and make use of the cheap night rate of power, but I'd still need around a decade to make that break even. But the good news is that's down from about 17 years only a couple of years ago, so I live in hope it'll happen very shortly 😀

In Washington State, USA, we have "net-metering" system where the grid is essentially your battery. A separate meter tracks your PV system production and keeps a balance; anything you consume is taken away from your existing balance and you are billed for the excess. The two drawbacks are that your balance resets to zero in the spring, and the utility will remotely disconnect your PV system from the grid when they work on the power lines. We had a subsidy that expired a few years ago where the state paid electricity production ~50 cents/kWh for systems manufactured locally. This was great as our fixed-rate costs are about 10-11 cents/kWh! Other states have/had similar incentives, but the laws vary in every state with some promoting PV systems and others stifling them (go USA!).

I have batteries, Tesla powerwalls to be specific. The biggest reason I got that is because the grid here is really bad. I am in Texas and in addition to the 3 days without power in February 2021, I have seen so many more outages than I had when I lived in Arizona. So, for me it is about not being able to trust the grid so trying to account for power outages and keep solar generating power during those outages.

So long as I can control my backfeed to the grid, I'm good with almost any battery solution, as I can disconnect from the grid whenever desired. I'm planning to do a 9KW home system when the new US incentives kick in next January, which includes battery incentives. I only plan to feed the grid when I'm paid well to do so, and I hope something like Tesla's "Virtual Power Plant" becomes an industry standard.

Shouldn't you aim for at least 20kwh if you want to pull 15kwh out each day so you don't have to deep cycle the cells?

Try Victron ESS System.. Quatro or Multiplus II, AC coupled with your existing enphase system . Use DC strings to charge directly a "low" voltage 48V DIY Battery (i.e. 14 KWh ~ US$ 2500 with a descent BMS ..) using external Solar Charge Controller.. Include a raspberry PI, with Venus OS as "GX" Control Center, visible and configurable from anywhere in the world... Works like a charm..

Yes. Even Dave and I don't agree on many things, one thing we both agree is that fossil fuels needed to be retired early for our kids. It's actually funny as the current price surging situation it looks like if you have a smart meter and has a TOU tariff, installing a battery alone to charge at night and output power during the day with dirty coal power is economically feasible in Australia.

I am not sure if using average production/consumption figures gives you the actual pontential savings. I mean on sunny day you might charge your battery quickly and have to sell rest of the power to grid and on a overcast day you might actually have to buy some power from the grid. I assume that you have saved your actual daily production/consumption data so you could run a "simulation" with that and see how much would a battery actually saved in the last year for instance.

Cool video. One nice thing about my Tesla powerwall system is that they're part of the Virtual Power Plant program. So when there is a grid event coming they act as a distributed grid stabilization force and whenever my system participates in those we get 2$ per kwh. So far this year it has been several hundred dollars. Pretty nifty little unforeseen benefit that might reduce the payoff time substantially for my system. I believe they pioneered the VPP program in Australia a few years ago by having a local utility subsidize the installation cost in exchange for future participation. I just like the idea that I'm helping the grid be more resilient.

Nice Video, Dave. But you forgot the payback from the exported solar. Over the year this would be close to $500. So actual budget for your battery storage is roughly $11k. Cheers

HP41 - that's nice, or rather awesome! Where I live the electricity price swings wildly right now, the price is changing every hour based on trade done the day before. It's wilder than the stock market in 1929.

definitely swap out the gas water heater, I recently switched to a heatpump water heater and I can't recommend it enough. we (3 person household) saved ~70usd / month over the old resistance heater. A trap for young players though, make sure the model you buy allows you complete control over the mode it runs in (all heatpump water heaters have a resistance heater backup and many will use them for fast water temperature recovery even when you think it's in heatpump only mode). If you can space out the major uses of hot water, like showers you can turn down the setpoint on the heater I was able to set mine at 112f (~44c) from the default 120f (~49c). Heatpumps are a lot more efficient the lower the temperature differential is.

Great video Dave. You mentioned you aren’t on a time-of-use plan. Have you looked at that to see if it would save you anything? Or is it hard to know without the hourly usage data?

10kWh is sweet spot for most residential houses. Problem is if you started without hybrid inverter, then you need to buy more power electronic or replace inverters you have. Then if you do investment to battery it is good to have islanding option. You can also take a look on Solax, but for you take look on Victron, you can play with it a lot, it also accept some string inverter on island output. With Victron you can choose battery you want and easily replace and expand it in future.

I recently moved house and took my battery with me. I upgraded from the Sungrow SH5K-20 which was a manual emergency power switch to a Sungrow SH5K-30 which is fully automatic change over. The installers just selected the emergency power circuit to connect it to. Also had a Catchpower Smart Relay installed to control the HWS load. I also adjusted the run times on the pool filter system Most days I am running @ >90% self sufficient with a 10kWh (7kWh daily charge) Chem Resu battery. Granted this is spring so no Heating/Cooling as yet. Yesterday it was 97.56% self sufficient and that was a slightly cloudy day. East - West setup due to roof layout. I plan to get additional panels installed. In all of that I think the cheaper battery systems can be economically viable at this time. I was fortunate enough to get $3k from the Qld Govt when I purchased my first system with a battery.

Hi Dave. You should look in to Victron Energy Quattro. It will work as the ones you call “AC battery” but you can choose what battery you will like to use.

Sounds to me that the first move should be getting rid of the gas boiler and use an electric boiler or solar water heater as a big thermal battery. Hopefully in the meantime battery prices will go down (or electricity will go up like here in Europe) and then it will be an easier ROI. In the meantime hopefully EV bidirectional chargers will become interesting and then you could even use your EV as battery storage

As people are at work during the day, it is unlikely that a solar system can return on the investment to an e-car owner in the same way as someone that can charge their vehicle directly from their own solar system during the day. Also three phase homes won't be able to capitalise on the whole of house power style battery and will have to lose air conditioning and heating. Also historical anecdotes surrounding blackouts can be dismissed as speculation considering the added load on the grid that is expected by the e-vehicle and holus bolus dumping of gas alternatives. Adding 5-50kW/hrs a day to charge every electric vehicle per house (for a single vehicle) will add strain on the grid that has not been taken into account by ideologues of e-vehicles.

"brown stuff hits the fan" - nice, I'm going to start using that :)

I was so confused for a minute. I always forget that not everyone has the same summer/winter/spring/autumn.

You'll probably increase the battery life if you go with a bigger pack that you only use maybe 80% of its capacity.

I like the idea of standardizing on "Group 31" sized LiFePO4 batteries since there are many brands supporting this standard, so you can easily replace them in the future. An example is Renogy 12V, 100 AH: these are around $3750 USD for 10 KWH. An issue is that not all batteries can be put in series. I would rather trust parallel only, but there are 24V, 50 AH commonly available in this size as well. Strictly for emergency backup, there are RV inverters that will charge the batteries with "shore power"- basically turns your batteries into a UPS (plus you can add a cheap MPPT if you have solar). This is good for some applications: I want to keep a sump pump powered on during storm outages, otherwise my basement floods.

Interesting that you mentioned Greenbank. A lot of their stuff is showing as 'out of stock'. But their warranty looks good and the cells they use are CATL - good cells

Two words: Demand Tariffs. With demand tariffs being applied to residential customers now, and if you don't have gas (which is also rising in price) then batteries are probably going to be as "worth it" as solar panels used to be 10 or 15 years ago. And they will only get more "worth it" as the retailers increase their demand tariffs. (Presently around 10 to 15c/kWh/day)

Almost regardless of financial viability, I do think that for a moderately efficient PV array, say 6+kW real peak production, a battery should be mandatory. I'm running almost independent (the setup doesn't allow grid independence and the battery "only" has a ~3.3kW inverter) for around 7 to 8 months a year, and with some "intelligence", a bit of capacity can even be used for grid stabilisation.

5 or six hours. That's crazy. I just went through 8 days haha. Very informed breakdown. Great video.

I’m excited to see this happen

Thanks for the video. What I'm missing in all these videos is security. What if a war started in your garden and prices go up like crazy (what happened in Europe now), what if there is a risk the grid can go down for days (what can happen in Europe now), what if it's no longer possible to get a fixed rate for energy (what happened in Europe now). We pay 0.60 Euro/c per kWh and more at the moment. We have a shortage of gas. We pay for a fire insurance for the house, why don't we insure for energy by installing batteries and generators in case the grid goes down? We have an inflation of 10% and more. It's better to invest in renewable energy than to leave the money in the bank. My advice is currently to install as many solar panels as possible with a very big battery and a generator that can run the house for days off the grid.

Installed a LG Panel, Fronius inverter and Tesla powerwall 2 plus backup in 2018 for ~ 21K. It serves as well and our household is low in consumption. If no room heater (Winter) is used at night we are left with around 50 - 60% battery capacity in the morning. The battery is set to preserve 15%. We are able to run the air con at night off the Tesla for up to 2 hrs, just to cool bedrooms (Summer) before sleep. Is is worth it, yes.

If you use any hot water in the summer you can probably save some gas with a thermal solar panel for that. And it should still help at least pre-heat the water before feeding it to an heat pump during a mild winter.

Dave, check out Goodwe GW5000S-BP it's a whole of house AC coupled battery inverter, allows you to use any combination of solar with most LV 48V batteries. It can even support 3-phase with solar inverters on different phase (like me). Goodwe is huge with the like of GE rebranding them. Note the Tesla only has a backup circuit if the grid goes down.

7c pkwh is good here in the UK I get 0.05p pkwh, I have 2x tesla powerwalls and a 10kw pv system mainly because its all there was back in 2018 when my system was installed my system dosnt have the ability to run if the power fails as it wasn't available yet, but after 4 years my system has half paid for itself the biggest saver for my has been able to charge the battery off the cheaper night power 7.5p pkwh and run the house off it in the day when it's 31p pkwh

There is a house for sale in Melbourne that mention one word "Solar" but failed to mention the two batteries in one of the garage pictures. At least they showed the dream garage.

You are correct in that the financials are entirely customer specific. I get 45.7 cents/KwHr for what I export (in the ACT) and pay 22 cents/KwHr for what I consume. I've never paid a power bill since I had the solar installed. For me investing in a battery makes absolutely no sense at all.

Dave, about your math, there is simple way to check it: 1. 10 kWh battery has 8 kWh cycle capacity (20-100%) and about 2000 cycles lifespan. That is 16.000 kWh of power delivered from the battery during its life. *2. If price of such battery pack is $4.800, then cost of single kWh just from the battery is $0,30*

I bought batteries from two Nissan leafs and made my own pack. I have about 50kwh storage, It was totally worth it. Around 6k with 4kwh transformer inverter and bms, etc I don’t think off the shelf ones are worth it though But the reward isn’t in savings, the reward is I can run off grid indefinitely

Reportedly, some Goodwe Hybrid inverters may be able to charge using not only their solar input, but also from the output of other inverters in the house, as they use a simple nullying algorithm that just tries to zero the current entering/exiting the house. I can't check it but some forums say that.

Nice video I'm always learning something new from you thank you very much

You need to factor in 15 -20% conversion losses for charging/ discharging storage batteries.

According to my calculation, you need something like a 40KW battery to be grid independent. 1407 sold + 1783 used means your daily consumption in winter was 3190 / 89 = 35.84KWh per day, and you need to factor in the excess use over what you can charge which is 1783-1407 = 376 / 89 = 4.22 . 4.22+35.84 = 40.06KWh battery. $24,000 bucks for the cheapest stack.

I'm doing pretty much the same thing in France. I will use Solis 6kW hybrid inverter, and Pylontech batteries. All high voltage batteries are proprietary, they speak a secret protocol on CAN, and are married to one or two inverter brands, which is not acceptable. So it had to be 48V. Among 48V batteries, Pylontech is the cheapest that is still of acceptable quality, uses open protocol, and is somewhat user-serviceable. BYB is expensive, cells are not replaceable.

I would choose Ni Fe batteries over any type of lithium battery as they have a very long life and are more rugged - the energy density is lower but it is not so critical for home solar installation !! - go for Ni Fe Dave !!!

The backup capacity of batteries makes it worth it regardless of the marginal finances. It’s not even just at night, but during the day when the house will cut over to running of solar if the mains is down.

The late John Seymour once quoted "Do not work for those who plunder and do not buy the goods and services of those who plunder"

Like the looks of the proposed business putting solar awnings over parked electric cars in workplaces, where the car gets charged during the day and you can dismiss the Duck curve at night. The size of reserve batteries need not be as large as they are now if Vehicle to Home or Carpark in the Grid is making use of the big Fusion Reactor in the Sky. Most impressed with the demo Home setup so far. EVs and Electrification in general is changing so fast it's not a good idea to choose one for your Commuter until, as you say, it's also LFP.

I have two systems very7 close to Dave's and I have 15kW of LiFePo4 batteries on it. I do run all summer off grid because I refuse to sell energy back to the grid for a pittance! I'll see this winter how well it goes but right now I have ~14,650 watts of PV built up over the last 15 years. Hey Dave, that looks like an HP71B calculator from the 80's - ask me how I know!

I already have a huge 85kWh battery just sitting there most of the time. If only the HVDC plug were bidirectional and someone made a compact system that could take solar, grid and battery input power and deliver power to the home and charge the battery it would be golden. Run it all on an internal HVDC bus. You'd only need a PFC (AC grid input to bus), a couple of HVDC converters (one solar to bus, one bus to battery with charging current control), an inverter (bus to grid) and some HVDC switches. A microcontroller reading voltages and currents can run the show.

Did I miss how you accounted for the different rate for generated vs. purchased electricity? The question needing answered is if it is more cost effective to store your electricity or sell it at the 7cent/kwh rate.

You can use you house as a thermal battery, if it's a hot and sunny day, crack down your air conditioning to as low as it can go until the sun goes down. If your institution is good enough you should be able to be cool all night.

It really depends on so many parameters you didn't (and probably can't take) into account - so its all kind of a milkmaid bill in the end. You can't predict daily solar power, charge cycles, energy consumption - its all an average attempt and a prognose of the future behavior. It will pay off in good conditions and won't in the worse ones. But you have good chance that it will in the end!

Where I live you can generally expect to lose power for at least an hour yearly. Generally we have 2-3 mini "blackouts" that last a few minutes every year. The record for me was just 2 years ago where a monster storm took out power to virtually the entire city (500,000 people, over a million in the area) for DAYS. Some were without for a week. I was without for about 3 days. In general if you are producing more than consuming and can afford it I'd suggest a battery backup "just in case".

Have you looked at alternate energy storage systems? Like a big ol' flywheel? Or a gravity or thermal system? I wonder what kind of free space you have on your property you have for such things. Personally, I like the concept of a flywheel. I doubt it would wear out anywhere near as fast as an electro-chemical battery. You may have to do maintenance on certain parts periodically though. Parts like the bearing. But if it's made right, it should be simple to yank the bearing out and replace it. Lubricant may need changing too. I hear there are magnet bearings for flywheels too, but I suspect those wear out too, because force and motion is still being applied to them constantly. I haven't really looked into them too closely, so I don't know enough to give useful details.

you are really lucky. Here in Germany the relation between the best and worst month in solar production is greater than 7!

Another thing worth looking at if your installing a battery is the ability for the system to be included as part of a virtual power plant rather than just directly feeding into the grid. in this case, the company aggregates the capacity and uses a % of your capacity within agreed limits, this means they can sell onto the market at the standard generators rate or higher on spot market and pay you a higher feed in rate.

The calculator at 4:40 gets my approval.

I never thought about it, but the seasons are totally different on the other side of the globe.

i've been thinking and looking around for the battery (and hot water tank) storage options for months now. Our house is from 1960 and my gramps planned ambivalent back then. 2 "and a half" apartments for living. Diesel based heater (modernized) for the house heating only, so only running in winter. large underground tank outside. 2x fresh water gas direct heater for shower/bathtub. + added a few years ago 3phase electricshower +back then 1960 also gas stove in kitchen. +back then 1960 also wood fired stove (with water tank) in washing room basement. Small electric tank (around 5 Liter) heaters under the kitchen sinks. No central water heating/tank for drinking water. And we have solar (electric only) for about over 20 years now, peaking at 5.7kW. Roof got new/better insulated before solar got installed. Now the problem is to use PV-solar for warm water, "hotwater" panels would be better, combined with a large hot water tank/pump in the basement which does not exist yet. Then new plumbing over 3 stories and 3x heat exchangers in the bathrooms, instead of the 2x old gas +1x electric heaters. Combined with an input into the diesel heater (which can be used for drinking water, 2 loops standard) .. then adding also more solar-PV panels and a heat-pump (in combo with the hot water roof collector) to stock up energy during day into hot water tank. With all that (above 30k euro investment with luck and lots of optional problems, noise and dirt), we might be able to reduce consumed fuel during winter time. On the other hand central water heating+pumps would need to run all year round. And there would still not be enough power overhead to charge the EV for the daily work round 80km, charging every 3 days (

It's not as simple as it looks. Allow for losses when storing and drawing from the battery. The capacity will also be needed at least double, and even then sometimes in the summer it will happen that the battery will be full. But the most important omission is the own consumption of the entire system, which is normally around 200-300 W. Here it depends on the installed power of the solar panels, but for routine installations it pays to completely disconnect the battery in winter.

At least your going for the lesser of two evils, and appreciate its not all rosy. Fascinating that you can charge your ev with your solar panels alone.

Here in the UK 1 kWh or 1 Unit is now costs A$ 1 or 56p (UK). A battery storage (Li-ion) 24kWh will be paid back in 6 years with 15% annual energy inflation.

I’ve got a 8KWH Tesla Roof solar panels plus three Tesla l. I live in South Floridas hurricane alley, so power can go down for days at a time after a storm and I decided that whole house backup was a good solution for me. Tesla installed a soft start for my 60000 BTU Central AC unit, so with careful AC. management we can keep the house cool if needed.

If you can get Amber Electric as your retailer and a smart meter. You will pay off your battery a lot sooner! You can sell at a higher price and pick when to use your own battery instead of the grid. When it’s cheaper to just charge from grid. Just off your phone. They charge a monthly subscription fee and then buy and sell at the wholesale rate. Ideal for those with a battery.

Looking at this from the USA where average electricity cost is around 14 cents per KWh, battery storage seems like a definite nogo.