This discussion relates to replacing the grid with a viable RE solution:
The nub of RE is that it’s still limited wrt power compared to the power available via the grid.
To minimise the inconvenience of these systems one has a choice: To either throw the kitchen sink at the problem by radically oversizing your system to cater for most situations (and then hope for the best)
Or to do an exhaustive analysis of your power utilization in your home. By doing this one can install far more efficient appliances to achieve the exact same result. This then mitigates the size of the RE system that needs to be installed.
Most that have been here a very long time, did that. Used to joke, solar costs X, to lower that cost will cost Y ito new appliances, appliances you will have to replace in any event in due course.
Then habit changes to fit the sun, as the sun does not fit us.
What I recently deduced in Cpt after THIS winter … you can go as oversized as you want, but it won’t help in some cases. Cheaper to just consider a diesel gennie than “going Bos” on a big system. Note: Cpt view that…
Where that “spot” is, that I don’t know yet. Depends on the extreme weather cases.
Back of my mind: If the diesel gennie could maybe run on 100% biodiesel … but that is an effort for another day.
Whatever the solution, I think it has to be tailored to the situation.
So I am referring to my neck of the woods.
In KZN, sure, Winter production doesn’t match Summer production, but I can count on cloudless skies for the entirety of Winter. That means moderate production every day of Winter, day in, day out.
In other words, my danger of running out of power because of poor weather is not in Winter, it is in Summer.
It is Summer that is mostly feast, but can be famine for a week.
I noticed I can count on about 5% of my peak production in inclement weather in a previous system I oversee.
In my retirement installation, my panels will be as flat as I am comfortable with; hopefully, I can increase this minimum production to closer to 10%.
That means the Winter production will be even less, and Summer will be a glut, but it doesn’t matter.
That is because I will massively oversize the system so that 10% of production can support me indefinitely. So running at 40% production in Winter will be a piece of cake.
It seems massively wasteful in Summer, but here is the twist. I want to pair this with about 22kW of irrigation pumps from the river. I figure in Summer; I won’t waste that massive power surplus when the sun shines and the land is dry. Then, when it rains in Summer for a week, I won’t need to irrigate, so I’ll be back down to a sub 2kW average domestic load, which my 10% production will cover.
So, is it actually massively oversizing the system when I can tailor my loads to use massive production?
As the play Defending the Caveman highlighted the male gender of our species is not prone to dialectical thinking. This is a method of reasoning and analysis that involves examining and reconciling opposing or contradictory ideas or perspectives.
The RE buyer uses his ‘gut feel’ to decide which system he reckons is the best. Once the fairly heavy financial transaction is concluded he can’t allow himself to have doubts about his choice so he seeks to justify his decision by looking for any supportive argument/fact/hearsay ‘evidence’ to prove that he made the best decision.
And those that don’t get RE go through similar mental exercises to justify why they didn’t.
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Yeah, this “buy then justify your purchase”, I have seen my arse good and well.
Now I tell selected people my idea and then sit back and listen to their replies. Each person has an angle, idea, view, and purpose that they can add making the final buy the most thorough thought out purchase one can make.
Having said that, still saw my arse a time or two.
So I learned to buy so that I could easily sell it if I still got into a corner, telling the prospective buyer exactly why I was selling, where I ran nose first into a “wall”.
Reputation and happy buyer at the end of the day … at least, I have never had complaints.
Keep your options open … say I.
Today, I struggle to justify adding to my system … the sums just don’t make sense to ME.
I’m happy, and I don’t have to justify anything anymore to anyone.
My core focus has always been to work from home with no LS woes, and to not charge batts using Eskom … “accidentally” I solved LS stages 6 and up … and an ROI to smile about.
You need a lot of experience to be able to keep your options open… (Whew!)
One often has to break things to make improvements which costs. And then there’s no guarantee it will all be hunky dory…
Now, I meant too small inverter, sell it, get a bigger one.
MPPT is too big/small for the array, swap/upgrade it.
In my experience, it is a rare person who gets into solar and gets it right straight off the bat.
Who has bought the right gear at the right capacity, in the right proportion, from the outset?
(Nevermind that the word “right” is totally subjective and means different things to different people).
I can’t think of many ( or really any) that haven’t paid school fees, and pretty substantial ones at that.
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For sure! My understanding is that intelligent engineers try to have a grasp of what to expect before they place their orders. One has to at least try to measure the success or failure of a project by some means. Hectic thinking (and writing it down) is required to define what your aspirations are so that you have the means of assessing the result…
Therein lies the rub.
We, the people, aren’t engineers, we are:
Domestic users, who are primarily driven by economic and lifestyle challenges, stretching our budgets whilst reacting to a host of information and misinformation presented by the equally ill-informed. We are “boer-maak 'n plan” people who can’t afford engineers.
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The concept of oversizing is not conventional in the RE world.
I experienced this with my first PV solar water system. The supplier provides you with solar power estimates for various locations so that you can order the correct number of panels. They are conservative in this I believe because they don’t want their systems to overcook themselves and fail. For me however I’m happy to have oversized my system to cope with cloudy conditions reasonably well.
I thrive on challenging conventions.
I agree with the notion that most people’s “toe in the water” system makes them want more.
Here is the conventional “Now I need a bigger system” system:
The system is expanded in an attempt to meet requirements, and that initial undersize North facing array is added to.
Obviously, the user just needs a bigger version of the same, right?
Wrong.
It is soon realized that a power glut in the middle of the day:
a) Requires bigger MPPTs (extra-overhead cost)
b) Once the batteries are charged, the excess power is wasted.
The user can’t have that so bigger batteries are purchased, but batteries are expensive and an overhead.
Can you really buy enough batteries for a long stretch of bad weather?
No, you can afford an extra day or two of batteries, and it’s back to ESKOM. So all you have bought is two extra days, that are needed maybe 5 times a year, before you concede defeat - bloody expensive batteries.
That’s about where most users are… and roads I have also travelled.
Then, I did things a bit differently. I went with more panels instead of more batteries.
I went with E-W arrays combined on the same MPPTs, resulting in cheaper overheads, a more extended solar day, less power potential, but more usable power and less battery reliance.
It was an unconventional choice, but I am confident it was correct after a few years.
I did things unconventionally, but how far can you push something? Judge for yourself.
I know by quoting the size of this battery bank versus the power production of the panels in this system, I will meet disbelief and naysaying conventioneers.
But I’ll do it anyway.
I have produced over 15MWh this year alone and never lost power to my Mum’s granny flat in the last three years. (Yes, “M” is for Mega).
Now, here’s the kicker:
The system has run on the batteries reclaimed from a golf cart for the same three years. (4 x T1275 150A Trojans).
Call it what you like, but that bank is not oversized.
(Favourable non-technical arrangements allow me to do this, but they don’t belong here).
I reference this because I have detailed above my future system will be oversized to the degree that there will be sufficient domestic power during lousy weather whilst I introduce a mechanism for not wasting the power glut on sunny days. That is a future intention and as yet unrealized, so it can be dismissed as fiction.
However, this is an existing system with a track record that utilizes the same principle. You can tell by the energy production figures. I am walking the talk.
One needs to think of the problem a bit differently.
If the situation changes from “How do I make enough power for my house and family?”
To the problem of “What do I do with all the extra power that my house and family don’t need at times?”.
It becomes a much nicer problem to have and much easier to solve.
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We can do that?
I’m asking because I recall a visit to Rudyard Kipling’s house in Sussex. It was one of the first electrified houses in the country. A river runs through the property, this turns a genie, the gennie charges batteries, and the batteries power lights for a few hours.
These days the whole system is in place, but they can’t dip the wheel that drives the gennie into the water. The banks of the river still belong to the property, but the water and the energy produced by its flow belong to MAF (Ministry of Agriculture and Fisheries). So the National Trust (who now own the house) have to apply for permission to use the kinetic energy in the river, and will then get a permit for X hours.
I will be in ZA, which is closer to being the Wild West, than the Western World in terms of what is possible.
A few years ago a guy who lives in Livingstone posted a solar PV question. I suggested that he use the Victoria Falls as a head of pressure for a mini hydro. He responded saying that the authorities there were quite sticky about such installations… 
I’m guessing Bob was not his uncle, then.
Same is true for Electric cars. Well, any new car really, but more so with electric cars.
Once you spent the money, at least for the first 6 months, you will mentally jump through every hoop to explain why it was the best decision ever. That is why “new car satisfaction” studies don’t ask people who had the car for less than 6 months.
For electric cars, the divide is even sharper. The person who bought it (that is me!) will harp a LOT on how good the thing is. The person who didn’t will repeatedly tell you it won’t work because load shedding, it costs too much and only the rich can really afford them and you need more money for the solar system to charge them oh and did you see what the wallboxes cost and children mining cobalt in Africa and batteries on garbage dumps, risk of fire, higher carbon footprint that is never repaid, political involvement, muh communism, China can switch your car off remotely, I hate the quiet, etc etc…
The mental exercises you see in the anti-EV crowd definitely takes the cake on this one! But yea, I do occasionally see anti-renewable people too. They are usually American.
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Amen.
The more I ponder one’s options (and having implement some of them) the more I realize the situations you are going to be confronted with are not what was expected. You start out with a challenge in your head but it often doesn’t turn out like that.
So I think you need to keep flexibility in mind wrt your installation. You aren’t going to be able to predict the future but you will be able to respond better if you haven’t got a dedicated solution that only address a particular issue.
This is a bit vague I confess but it’s one of those life experience things…