SolarPi experiment 2: Finally something that works
blog.rfox.eu
blog.rfox.eu
I've spent last few years trying to build out my solar shed mainly to have auxilary power to charge weed whacker, leaf blower, power lights, power a camera, etc. Just basic 12v power.
The number one lesson is to 4x your power needs. 4x your watts and 4x your battery amp hours. Don't cheap out on charge controllers.
There's never enough sun light to fully charge your batteries and your panels are never at the right angle to maximize sunlight. Especially in less solar friendly areas like Michigan.
Lead acid is fine if you over compensate with panels. Lead acid will last longer in the cold than LiFEP04. Die hards will say you cant charge LiFEP04 in winter but I do. I accept the fact that my batteries will degrade faster. When you can build your own packs, its a lot easier to find which single set of cells went out and cheaper to replace. Its a risk I accept.
If you are starting out, get a 200 Ah/hr LiFEP04 battery and 400 watts solar. Its a very good starting point for 12v and gives room for expandability.
Avoid foldables. Avoid Harbor Freight. Avoid Jackery Solar Panels. You need Quality Panels.
If you wanna learn more, check out Will Prowse https://www.youtube.com/@WillProwse
Contrary to popular belief, LFP is not immune to thermal runaway. While LFP batteries do release less heat than Nickel based cathode chemistries, they can still cause a building to burn down when you have 200Ah or more.
I think an issue in Michigan could be depleting your lead acid batteries and then freezing too, no?
But should be fine if they get some occasional trickle charging and no real draw (gotta clear the snow off the panels here and there over winter)
lots of marine-use lifepo4s have heaters on board and they're not a lot more expensive, and it's not too hard to diy something to an existing pack, either -- although of course it constitutes yet another draw.
Can you explain? I bought the solarpanel seen in the article and also have their Explorer 240 portable power station. So far I used it only slightly and it seems to work. Any specific things I have to keep an eye on with Jackery stuff?
Why?
I'm just starting out with solar power and I got a 100W panel set (4 x 25W with a charge controller) and 35Ah battery from HF just to try it out and so far it seems fine.
every. last. thing. ~25-30 things between myself and my family & friends. all of us have had the same results.
sure, they'll often replace the thing free of charge, but that just addresses the money - my time is valuable, too, and going back and forth to HF all the time just got really old.
no more.
I had one of these back home to power my hydroponics system, using a 20W solar panel. It worked "well" until there were cloudy days that the charge controller couldn't simply provide enough output to charge the battery. We used a normal car battery for that.
After a few days the battery was dead because it wasn't being charged, so we decided to scrape it and run our hydroponics connected to the grid instead.
If you're feeling adventurous, there is a MPPT chip that you can use for your electronics projects (though the only time I tried it I managed to burn the chip and couldn't find it anywhere in local stores, buying from AliExpress would take months to arrive) is the LT3652, though it's rated for 2A only. I believe you can find bulkier chips for higher PV wattage.
EDIT: > The number one lesson is to 4x your power needs. 4x your watts and 4x your battery amp hours. Don't cheap out on charge controllers.
I have installed a PV system on my home back in 2019 and the rule of thumb we found out as well is, if you're building a PV system for a house and use inverters, you should also not go cheap on inverters (i.e. go for cheap chinese brands).
We have a Fronius inverter and it works wonders, much better than the other cheap brands and it has a lot of interfaces you can use it to retrieve data from.
Another useful thing, if you buy an inverter rated for, say, 2kWp, you can safely overdesign your system to provide at least 20% (I don't remember the exact percentage) more power than the peak wattage your inverter supports. Reason for this is that because you can't predict clouds and bad weather, having a few extra panels will compensate the performance loss and will make sure you're always running at peak performance. It will also help a lot during off-peak hours. Of course, the extra panels won't magically bring you to peak performance if you have a very cloudy, dark day. But if you have some clouds, you can get a very big performance hit and you can compensate that by having more panels than your inverter is designed for.
So, for example, if the inverter is designed for 2kW, you can build your system to produce 2.4kW.
Another suggestion is to split your arrays in as many strings as your inverter suggests. They will operate like if they were independent systems, so if you have cloud covering one string, bringing its output power down, it won't affect the other string (assuming the cloud is only covering one of the strings). If they were under the same string, any shade on any of the solar panels would severely affect the output of that string.
Instead, I acquired two large 140W panels that had been removed from an old installation for the princely sum of $20 (USD).
After struggling with trying to find connectors that I could pair with the MC3 connectors (remember, these panels came off an old installation), I bought a dozen MC4 and just cut off the old MC3 connectors...MC4 is the way to go these days.
Next came the surprise at finding out about "MPPT" - in all my years looking at solar panels on roofs, I never knew they were so finicky about voltage vs current curves...real MPPT charge controllers start at $70 for a Victron 15Amp and I decided to try my luck with Chinese sellers on AliExpress...turns out the charger was a PWM fake sold as a MPPT charge controller.
Anyway, I also needed a battery since the charger doesn't work without a battery source. That's another saga but short story - I built my own 3S battery pack out of 18650s.
You may be aware and this is 100% redundant but lifepo4 is a safer chemistry and small cells are becoming more affordable by the day. If there’s no risk of those 18650s overheating it’s fine I guess.
2. Modules to charge LeadAcid are so cheap, they don't even make them. This specified PS-battery hsa a 13.5V to 13.8V "standby" voltage, meaning that 13.65V from the Solar Panel is all you need to have a UPS. Connect the 13.65V source from the Solar-panels to the + and - leads of the 12V battery, and volia. You get 13.65V when solar is available, and 12V from the battery when the solar cuts off. The end. Isn't that easy?
3. Grid-tie should be similarly easy, though I don't have too much experience with it myself. IMO, buy a professional AC->DC converter, probably at 19V or some other suitable voltage and then get a DC-DC buck converter to go from 19V to 14.35V, and then a diode (0.7V dropoff) to hook up to your batteries in parallel. You'll also need a diode in your Solar-panels cause you don't want your Grid-tie system "charging your solar panels" (that'd probably create a fire and/or damage them...).
Hobbyists should NOT deal with main-power themselves, but there's a gross-many number of AC-to-DC converters available from $10 to $40.
4. Don't battery balance. Just buy bigger batteries. If 12Ah isn't enough, buy a 20Ah battery. If 20Ah isn't enough, buy a 33Ah battery, etc. etc. The limit is whatever you're comfortable with (the bigger batteries give more current which can be more dangerous)
But sizing 12V 20Ah (ie: 240 Wh), and now 0.3C is 72W or 6A of safe charging (less than 0.3C).
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See #4: just buy a bigger battery if you need a bigger battery. Bigger battery provides more power and energy proportionally for the chemistry.
And a 12V 20Ah lead-acid is just $40 on Amazon.
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I guess your overall point is that "Trickle-charge" isn't enough for Solar? Which is something I admit I didn't think about earlier (trickle-charge just doesn't send as much current to the battery due to the lower voltage). But I guess there's a "simplicity of circuit" advantage of trickle-charging. A more complex state-of-charge circuit (likely a microcontroller keeping tabs on the battery) is needed to safely send 0.3C down to the Lead Acid.
EDIT: On the other hand, having your "charge controller" just be like, two power diodes, is a gross benefit to simplicity. Its something you can do with Lead-Acid that's fully impossible with LiFePo (and is why LiFePo4 needs expensive charge controllers to work). For hobbyist purposes, there's something to be said about using simpler technologies, even if their specs are worse (and I'm not entirely sure if Lead-Acid has worse specs than LiFePo4 in this use case).
Lead-acid can charge at 0.3C but only when empty until 50% or so. In the absorption phase, current drops (dramatically).
Also lead-acid means 50% usable capacity for longevity so the 12v 12Ah lithium is 12v 24Ah lead-acid (minimum). Which also means you can never charge with 0.3C. And even then is longevity of lifepo4 so much better it’s not funny.
Please spend the extra money on lifepo4, save yourself some headaches.
That's not a concern, is it? We're talking about battery backup, meaning the "expected use case" is that the Lead-Acid battery is sitting at near 100% capacity for almost its entire life, without significant amounts of discharge. Sure, you've got to discharge when the sun goes down but I don't expect a properly-sized battery to be deeply discharged (especially when we're aiming for multiple days worth of "worst-case" power, like multiple days of clouds/rain to reduce our power-collection).
Lets just be dumb with napkin math for a second: 12-hours of charge, 12-hours of discharge on a "typical" day, with a 3-day / 72-hour period of worst-case charge. Where does this leave us?
12-hours of typical discharge / 72-hours of worst-case discharge == DoD of 100% to 83% on your typical day-to-day basis.
Hardly anything that considers a "deep discharge". And if we really need deep-discharges, most Lead-Acids can survive something on the order of 300x to 500x deep discharges right? So its not like the 5 to 10 times a year where you need all 72-hours of battery are significantly hampering your lifespan?
> And even then is longevity of lifepo4 so much better it’s not funny.
Measured in deep cycle-counts (ie: cell phones or laptop usage), sure. (like 3000 cycles on LiFePo4 vs 500 on Lead Acid). But years of sitting on a float-charge, I don't think its that much better than Lead-Acid.
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That being said, LiFePo4 is a "superior" battery for sure, and its much cheaper than I remember. But Lead Acid remains significantly lower-priced than LiFePo4 as far as I can tell (2-to-1 or less)
I think you have a point about Lead-Acid charging slower when its near full (and keeping it full is key to keeping Lead-Acid long-lasting). So I admit to not recognizing that (LiFePo4 also charges slower when near full, its just that it charges like 3x to 4x faster than Lead Acid so its less of a concern)
> Please spend the extra money on lifepo4, save yourself some headaches.
We're at the hobbyist level where the original post decided that MPPT solar charge controllers weren't needed (at least, in an earlier version of this project)
Clearly no one here is talking about the strictly most optimal design, but are instead talking about simpler and cheaper solutions.
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Simplicity here is key. LiFePo4 does _NOT_ like topping charges or staying at 100% charge for long periods of time. Lead Acid however, prefers 100% charge and UPS use Lead Acids for this reason.
LiFePo4, in UPS/Standby like systems, need to stop charging, and wait for the battery to be used before engaging in a new charge cycle.
Lead-Acid on the other hand, can just have a constant voltage applied (ex: 13.5V or so) and you can just hold that indefinitely, for incredibly simple standby circuits.
The systems I worked on used multiple deep discharge, cold weather hardened lead acid batteries.
Deep discharge batteries have an important distinction from automotive batteries. They tolerate significantly more deep discharge cycles but can't produce as many amps. If you're just trickling a more or less steady amount of power into some electronics, you don't need massive amounts of cranking amps that an auto battery provide.
Solar PV and battery tech have definitely improved quite a bit since then, so were I now building these same installations, I might do something entirely different. But "back in the day" your advice of "buy another battery" was more or less exactly how we handled charge rate limitations.
Pretty much the only reason to buy lead acid for a solar generator that faces daily partial discharge is because you can't afford sufficient LifePO4 capacity in the short term but don't care that you'll pay more long term.
Which for a hobbyist: simplicity is everything. As far as I know, Lead-Acid still is very popular in UPS, which is basically what this SolarPi is.
> (i.e. cycles * usable capacity / $)
That's not really how UPS systems work. UPS systems sit at 100% state of charge for years at a time getting constantly fed power.
As far as I'm aware: LiFePo4 still doesn't like being stored at 100% charge, like any other Lithium chemistry.
No, SolarPi is a solar powered server. The application here is a "solar generator" type setup that has no grid connection and is very different from a UPS style setup.
A 3W Rasp. Pi with 12V 20Ah lead-acid backup with a 500 cycle lifespan should last 1500 days at a minimum. Because it takes 3+ days for a discharge cycle to occur, so that's easily 4+ years of worst-case durability.
And I'm willing to bet that if you design the solar panel CORRECTLY, you ain't gonna be doing full discharges every 3 days (IE: enough solar panels to have 99%+ uptime, meaning you've overbuilt solar panels to handle the worst case scenarios and try to stay at 100% power as much as possible).
> No, SolarPi is a solar powered server. The application here is a "solar generator" type setup that has no grid connection and is very different from a UPS style setup.
If you're hoping for 90% or 99% uptime, this solar application is going to look closer-and-closer like a UPS. 90% means you're down at most 36-days of the year (pretty crap reliability, all else considered).
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> Grid backup
Also, the SolarPi guy is looking into Grid-backup systems. So yes, we're back to UPS
While you can get 500 "deep" (50% usage) cycles out of a lead acid battery that is specifically designed for that, you'll have lost almost half your capacity by the end. You also ignore the extra wear from partial recharges which will be pretty common since the top 20% capacity charges so slowly
You have to buy 2x as much lead acid capacity, it lasts less than half as long and you get worse charging efficiency. The only time lead acid makes sense is when you need a lot of capacity but that capacity is only used infrequently and you have plenty of time to recharge between usage events. That is not the use case here.
> If you're hoping for 90% or 99% uptime, this solar application is going to look closer-and-closer like a UPS.
No, it is still a solar generator with a solar generator usage cycle. You still have the paired problems of reduced lead acid charging efficiency at the top 20% combined with extra battery wear for every day that you don't get the batteries topped up despite that efficiency. In order to reduce this, you have to have enough extra batteries that they can soak in your solar output even when in the slower charging of the top 20% while also having enough solar capability to get back up to 100% on partially sunny days. These issues significantly hamper the viability of lead acid for solar generators and are why LifePO4 has completely dominated Lead Acid in that market.
> Also, the SolarPi guy is looking into Grid-backup systems. So yes, we're back to UPS
The goal here is to switch to grid only when the battery runs out. That is the opposite of a UPS and is still a solar generator.
When your battery wears out, recycle the old Lead Acid battery and buy a new one. Its not that big of a deal. The battery I spec'd out is a 15lb battery (~7 kg). Heavier than LiFePo4 for sure, but no one is going to have issues moving, replacing, or buying new batteries.
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Anyway, I recognize that LiFePo4 is superior durability by a long shot. Thousands of cycles instead of hundreds, yes. My overall point however, is that "hundreds of cycles" is still years in this use case, and I don't think you've challenged the math too much from that perspective.
Obviously, I'd prefer to keep on the cheaper-side of Lead-Acid batteries. But the more expensive Trojan AES batteries or "Gel" batteries have far better durability (rather than the cheapest AGMs that I've been talking about)
I'm talking 1400 cycles at 100% DoD without any precharge or low-charge penalties for Trojan AES (though this is a very new battery only coming out this year). Trojan is working on making Lead Acid competitive vs Lithium Ion and have the cream-of-the-crop Lead Acid chemistries.
But even "Gel" (more expensive than AGMs) type Lead Acids have specifications for 100% DoD cycles, 300 to 500 depending on brand.
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Anyway, this has gone on for many posts. But here's my arguments to finalize.
1. Float-charging "feature" for Lead Acid grossly simplifies circuit design. You possibly don't need a charge controller at all anymore (feasible design with just diodes), although if you want decent charge speeds you'll need to build your own charge controller. (though this seems doable with uCs and/or OpAmps to make CC-CV circuits).
2. Very low explosion risk, so this is appropriate for hobbyists (unlike Li-ion which even LiFePo4 have had some worrying fires). So DYI controllers for LiFePo4 is an issue of trusting the battery-controller and the brand you buy, details I don't have to worry about with Lead Acid.
3. Lead Acid has less durability, "hundreds" depending on brand (and yes, I'm talking about 100% DoD specs, not 50% specs like you wanna talk about). By my estimation, this provides years of service though this obviously depends on various assumptions.
4. Lead Acid's linear voltage is an advantage when determining DoD when building your own controllers (ex: 13V OCV means you're likely full, and 11.6V OCV means you're likely empty, and 12.3V means you're at 50%). LiFePo4 has "constant voltage", which is better for efficiency and power but it makes state-of-charge far more difficult to perform if you're building your own charge circuitry.
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LiFePo4 is a "superior" battery from a durability perspective. But no one seems to want to float-charge this thing for extended periods of time, and I certainly don't want to have an explosion risk while I test that out.
And "downsides" (like Lead Acid's linear voltage drop, leading to lower efficiencies) are advantages with regards to circuit simplicity and circuit design. A *simpler* design is more suited for hobbyists, even if its got worse technical specs than a more sophisticated chemistry.
You still seem to be missing the use case here, which still does not involve any extended periods of floating.
You seem fixated on building your own UPS with your own controller. Go for it, lead acid sounds like it might be the right choice for you.
However, for a solar generator like this one, LifePO4 is the cost effective solution.
Fancy VLRA batteries like the Trojan do suffer fewer deficiencies around DoD and partial charging, but they cost just about as much per capacity as LifePO4 and still offer significantly fewer cycles.
So, sure, if you don't care about lifetime costs/cycles, leave battery charged most of the time, or want to build your own charge controller, then lead acid could be a better choice.
However, for a solar generator, LifePO4 is better in almost every way.
Lead-acid is really, really not recommend anymore for solar.
In a solar project like this, the battery will never stay at 100% for long.
They get water topped up every few months and fizzed every couple of years.
Speed of charge is not everything.
It seems like some serious chemists are at work there.
By Wh of capacity may be but certainly not by Wh cycled out of the battery, LFP has many thousands of cycle life.
"LFP 12v 100AH batteries for $290": let's say 5000 thousand full cycles, 121005000 = 6000 kWh out of the battery (with still 80% capacity left), that's $290/6000 = $0.048/kWh.
It's entirely plausible for remote autonomous systems to be discharged deeply during a rainy period of several days.
And how often is that going to be, pray tell?
Lead-Acid has hundreds of deep-discharges available. And these deep-discharges in the use case suggested (ie: 12V 20Ah Lead-Acid backing up a 3W Rasp. Pi) take 80-hours to happen with zero-sunlight at all.
So... how many multi-day periods per year do you expect to happen where you deeply-discharge such a battery over 80-hours? Even at 100-times per year (aka: every 3 days you have a full deep-discharge), with a 500-deep discharge lifespan battery, we're looking at 5+ years of durability. Worst-case scenario.
So lead acid is okay at lower temps and with only occasional deep discharges.
Also, they are heavy. Not a problem in fixed install or vehicle but pain if need to move.
> Lead acid battery can only use 50% of rated capacity.
That's definitely wrong. Lead Acids lose durability when you deeply-discharge them, but all Lead-Acids have *hundreds* of deep-discharge cycles supported.
The question is one of frequency. Li-ion is great because it has high-durability through deep-discharge cycles. But is this the use case of a UPS or Solar Backup? I argue no, it isn't.
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The key advantages of Lead Acid are its cheapness and simplicity. If you can overlook its size and weight (okay, 15lbs is heavy if you're used to Li-ion... but is it really a *problem*? I argue no), and also know that deep-discharges would be rare (ie: UPS style "backup battery" usage), then LeadAcid suddenly rises to #1 choice due to gross simplicity you can have when designing circuits.
As I described earlier: two diodes and a constant 13.5V source are pretty much all you need to create a minimally viable Lead-Acid battery backup solution. None of this "LiFePo4 charge controller" crap or CC-CV charging circuits (Lead Acid _prefers CC-CV especially if you want to charge it in 20 hours or less, but it doesn't _need_ CC-CV circuits)
A long-term trickle charger over days (~72-hours of charge) of use is perhaps a non-obvious usecase. But that's called "Always plugged in UPS" and is IMO, the kind of use-case that's best suited for "SolarPi".
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You might laugh at "hundreds" of deep discharge cycles or counter with the "thousands" that LiFePo4 can support. But seriously, think about it.
A 240 W-hr battery (12V and 20Amp-hours) hooked up to a 3W Rasp. Pi will give you 80-HOURS of life per cycle, that's over 3 days.
Assuming ~500 Deep Cycles of durability (which is in-line with Lead Acid specs), that's 1500 days of worst-case deep-cycles, or 4 YEARS of life.
And that's deep-cycling every 3 days, then fully charging on the 4th day instantly (it takes 20 hours to charge Lead-Acid in practice), so really you're looking at closer to 2000+ or 5+ years of worst-case life from something like the PS-12200.
Do you _really_ need the thousands of deep cycle charges? The damn chemistry is going to fail for other reasons (temperature / humidity issues) after 5 to 10 years, rather than from the cycles. Especially in a UPS situation where you've got oversized Solar Panels keeping the Lead-Acid at near-100% charge for most of its life.
Years ago I worked on environmental monitoring systems for snow and ice management. One of the things I did was help spec out solar systems for remote installations in Alaska and Canada.
The basic issue was "How much sun will there be in a typical summer?" combined with "How much power can we store in our batteries?" and "How much power can we draw from the lead acid batteries without them freezing?" (who knew that a discharged battery freezes at a lower temperature than a charged one? I sure didn't).
It's a pretty straightforward process, actually. The company I worked for had a pretty detailed spreadsheet to help with bids, but essentially you: 1. look up the insolation data for the install site in one of the databases with that info (like https://nsrdb.nrel.gov/) 2. compute rate of loss over time for your installation (power consumption +_self-discharge) 3. look at the battery datasheets to determine how much you can discharge the battery at any given time based on anticipated temperature ranges 4. work out what your tolerances are for temperature and insolation variability
Usually there would be a couple of options that were in the cost sweet spot where you had a bit more solar and bit less battery or vice versa. Some of these sites were up around the arctic circle, so battery was pretty important in those cases, since you're looking at months without appreciable sun combined with low temperatures.
This wasn't even the major part of my job, but it was a small company and I wore a lot of hats.
The challenge is more difficult than it seems. A raspberry pi 4b does ~3.4 watt idle so that’s 84 watt-hour per day. This may not sound like a lot, but for battery-powered devices it quite a bit. Microcontrollers can run months on that amount of energy, but they aren’t as convenient as the Pi.
The 12v 12ah battery used, contains 144 watt hour. Only enough to cover less than two full days with little to no sunlight.
The 50 watt panel is already small, but the non-mppt controller makes it even more inefficient. With good sunlight, the panel can easily run the pi and charge the battery during daytime.
The “real” challenge is to keep the Pi online during days of overcast weather. A 150 watt panel may only do 4-8 watt under those circumstances and that’s not enough.
But I always love these projects none the less.
* Beaglebone Black uses slightly less power and is slower than Rasp. Pi. Lower power is a big benefit however.
* Beaglebone has the "Programmable Realtime Unit" (a microcontroller-like hard-realtime subsystem with GPIO pins).
* These PRU subsystems can probably (???) be utilized for the battery-state-of-charge and possibly even provide a software-control for mppt solar chargers. Theoretically of course, but... I have to imagine that a Cortex M4 has enough MHz to handle these kinds of calculations.
* If not, the Beaglebone Black has a built in ADC that could be used as the basis of power calculations. Worst case, add in a proper uC to handle power / build my own MPTT / Battery charger.
I'd like to know if this also happens with these SBCs, or if they even have any aggressive power saving features that can be employed.
But in any case, servers cannot sleep. Only clients can. Maybe the software architecture of this SolarPi should be rethought.
Or maybe perpetual power needs to be more carefully figured out here so that the Pi can truly function as a server.
You probably have no idea how philosophical this sounds.
Just some random guy that I'm connected to via his frustrations
Edit: Just wanted to add the relevant quote: "My only regret is that you can’t power the raspberry from frustration, because my levels are lately spiking so high, that I am continually wondering why isn’t reality bending around my hate."
But then when that thing breaks you can't fix it with the knowledge and spare parts you have on hand.
I don't know about his controller but these cheap controllers will power the USBs even on low battery. They will kill the battery (he even mentions this bellow).
The right way to have USB output is to connect a car charger to the 12V output of the controller and then connect your load to that charger. That 12V output is cut when the battery is low and reconnected after it is charged. These voltages can be set in the controller. This way the battery will never discharge so much that the controller doesn't even recognize the type of battery (6V, 12V)
One for main house. Another for the pump house. A temporary garage setup and one for a studio.
A good way to learn to manage your own power generation and setting up systems.
I've long wanted to do a sort of small scale migration to solar. Offset the load from my home server with a few solar panels and source any excess power needed from the grid while also charging the batteries/providing power from solar when the sun is up. I could probably engineer something myself but doing things right on high power circuits is not worth the effort/risk. Any suggestions?
As long as your solar capacity production is not often more than your usage at the same time, batteries won’t be of any particular use … they have to be fairly large to have any great utility in your home anyway, battery backup and solar production are orthogonal goals until you are producing a lot of power.
If you do want battery backups on a small scale, just get a UPS the same as you would without solar.
The ve.direct cable is for doing more complex things. https://www.victronenergy.com/upload/documents/Datasheet-Sma...
Not sure what rPi version the author is using, i think i remember i was using the original one ? It was 700mhz by default i think i clocked down to 200mhz and 50mhz. Granted, it was mostly unusable (bye bye openssh) at 50 mhz.
Just because there's "light" doesn't mean the panel will produce power. The sun has to shine BRIGHTLY.
This is why solar power in Berlin or London is a waste of resources, because the sun doesn't shine BRIGHTLY there.
In your specific case you had to over provision your solar installation compared to , for example, Egypt.