Jump to content

Cost of solar generation


Recommended Posts

  • Replies 52
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

ROI is typically the single most important factor when considering going solar - even though being Loadshedding resilient and producing clean energy are close seconds and thirds. The screenshot g

So, on a good day, like yesterday, I generated 17kWh on the DC side, from my panels. I have 12*320 = 3,840W worth of mono panels. I had maybe another 1kWh I could've used, as the panels idled a little

Current SA EV prices are ludicrous - we got ours 2nd hand for R193K with 35K on clock - so then it's ok. Future EV pricing will be in line with ICE in a few years. We had to replace the other car anyw

Posted Images

On 2020/09/14 at 6:08 AM, MongooseMan said:

Just checking, are all Cape Town people with approved solar installations charged according to this table whether they feed-in or not? Or is that only for feed-in customers?

elec.png.9f0c0bb126ab4020ae5e7ff47190f47a.png

Source: http://resource.capetown.gov.za/documentcentre/Documents/Financial documents/Electricity Consumptive Tariffs.pdf

@Tariq, I can't see the R160/R120 on there, am I looking in the wrong place?

 

The CoCT Residential SSEG tariff shown is only for customers who feed-in - if you are not feeding in, you pay the same Energy Charge but a reduced Service charge of R171 VAT incl. pm. on Home User Tariff. 

Link to post
Share on other sites

ROI is typically the single most important factor when considering going solar - even though being Loadshedding resilient and producing clean energy are close seconds and thirds.

The screenshot gives our savings on a 5.6kWp (320W modules) - 10KVA (Axpert inverters) - 13.5kWh (Solar MD Li-Ion Battery) for the past 3.5 years. Cost of system R200K. Annual solar savings: R25K+

What it doesn't show, is that we have further estimated savings of R25,000-R30,000 per year in avoided petrol purchases and vehicle maintenance as the system is also powering our Nissan Leaf EV. We use the electric vehicle for school runs, daily shopping and the odd meetings/outings and are able to have it on the solar powered plug for 3-4hours per day.

Standalone the solar system will pay for itself in 6-8 years but adding the car doubled the ROI of the solar system.

Screen Shot 2020-09-17 at 08.03.45.png

Link to post
Share on other sites
49 minutes ago, PeterP said:

Standalone the solar system will pay for itself in 6-8 years but adding the car doubled the ROI of the solar system.

Quite impressive on just the standalone system by adding the vehicle charging it seems like improving the ROI-efficiency, that makes good sense. 

This makes me wonder, Is solar seen as an asset by Mr. Tax and does it depreciate in value like a car?

Link to post
Share on other sites
3 hours ago, MongooseMan said:

I think that makes the whole ROI argument a bit weaker

Unless if the car is used for business you could probably recover the cost of charging the car by claiming per KWH or docking costs instead of the normal fuel expenses. Then still have the depreciation like with normal vehicles. That gives business owners alternative options when purchasing new vehicles, making even solar installations slightly more attractive.

Link to post
Share on other sites
4 hours ago, MongooseMan said:

Eish, I think that makes the whole ROI argument a bit weaker, in my opinion (if you factor in buying that car in place of a normal one).

 

Current SA EV prices are ludicrous - we got ours 2nd hand for R193K with 35K on clock - so then it's ok. Future EV pricing will be in line with ICE in a few years. We had to replace the other car anyway, so for us it made sense.

Link to post
Share on other sites
7 hours ago, PeterP said:

Current SA EV prices are ludicrous - we got ours 2nd hand for R193K with 35K on clock - so then it's ok. Future EV pricing will be in line with ICE in a few years. We had to replace the other car anyway, so for us it made sense.

In my house we generally have two cars. The one is the long distance holiday car, generally dad's car. It is bigger, more comfortable, and it has an internal combustion engine because it needs to drive deep into Namibia.

The other one is a small little hatch that does maybe 6000km a year. We bought the last one 5 years ago at 85k. Right now we're kinda sorta thinking of maybe replacing it, and the budget is 150k (ish).

An EV would be perfect for this second car. But for the difference in price I can buy a heck of a lot of fuel and do a lot of maintenance... and get some interest on the difference.

An EV is perfect for the man who lives in the suburbs and works in the CBD. He drives every day, and the mileage is perfect for even a small EV. He will likely get his money back rather soon. However, COVID19 has taught us that we can work from home and completely skip all that nonsense...

Link to post
Share on other sites

A small diversion - apologies if off topic. Something else that I have not found many people take into account: Batteries are consumable items. Power from a battery is not free, the battery has to be replaced eventually. 

Taking an optimistic view for lead acid batteries. A battery with a 50% dod cycle life of 2000 cycles will cost you around R2/kWh excluding the cost of putting power into the battery. Thats simply the total amount of energy you will pull from the battery over its life, set off against the typical cost of the battery. I am guessing this scales fairly well for LiFe batteries - higher cost, higher cycle life. 

From the figures above it looks like there is some battery use in there but the cost does not seem to be taken into account. 

Link to post
Share on other sites
1 hour ago, RobM said:

Taking an optimistic view for lead acid batteries. A battery with a 50% dod cycle life of 2000 cycles will cost you around R2/kWh excluding the cost of putting power into the battery.

The batteries make up for a big portion of the cost when installing solar, that’s if you also need backup after dusk. The cost of putting power into those batteries with PV are relatively cheap if you take into consideration the lifetime of the PV panels that will do most of the work over many years and possibly outlive any inverter and batteries. 

Batteries can almost be compared to a generator using fuel, to a inverter using batteries. The difficult part is to re-coup as much as possible of that battery cost over the shortest possible time. In my opinion it is a real work of art to put a system together that is efficient with the bare minimum.

Link to post
Share on other sites
20 hours ago, RobM said:

Taking an optimistic view for lead acid batteries. A battery with a 50% dod cycle life of 2000 cycles will cost you around R2/kWh excluding the cost of putting power into the battery. Thats simply the total amount of energy you will pull from the battery over its life, set off against the typical cost of the battery. I am guessing this scales fairly well for LiFe batteries - higher cost, higher cycle life. 

 

Just did the calcs for Pylontech US3000 - energy cost drops to about R1.3/kWh so Li-Ion more cost effective in the long run if you have the cash up front. 

Link to post
Share on other sites
40 minutes ago, RobM said:

Just did the calcs for Pylontech US3000 - energy cost drops to about R1.3/kWh so Li-Ion more cost effective in the long run if you have the cash up front. 

Not sure how to R1.3/kWh.

Think they rate it for 6000 cycles with 60% capacity remaining at 80% DoD, you can assume linear degradation of capacity for simplicity. And DC to AC conversion has about 10% loss. So:

6,000 * [(1 - 0.6)/2] * 0.8 * 3.5 * (1 - 0.1) = 12,096 kWh usable on the AC side. The battery costs about R23.5k, so R1.94 per kWh. Pretty much in line with CoCT tarrifs.

Batteries are only useful up to the point where they make your system viable (the inverter would be able to function normally) or if you are completely off-grid. Unless Eskom increases rates by most than the investment return you would earn elsewhere.

If you have spare cash, I think this is more effectively invested in stuff like a heat pump for your geyser (when you don't have solar power it still saves money), LED lights, more energy efficient appliances, etc.

Edited by jykenmynie
Link to post
Share on other sites
4 hours ago, jykenmynie said:

Think they rate it for 6000 cycles with 60% capacity remaining at 80% DoD, you can assume linear degradation of capacity for simplicity. And DC to AC conversion has about 10% loss. So:

6,000 * [(1 - 0.6)/2] * 0.8 * 3.5 * (1 - 0.1) = 12,096 kWh usable on the AC side. The battery costs about R23.5k, so R1.94 per kWh.

I will agree R1.94 per KWh is close enough as this is based on what could be used from a fully charged battery. There is however a added advantage that is sometimes not considered when using a battery, the battery also functions as a backup during the day for various loads especially when running off-grid with PV this pv complimenting the battery, although a 3.5KWH pylontech can deliver about <2.9KWh during a full cycle which might occur in the evenings. The system could also allow you to draw a additional in my case >6KWh everyday day (permitting weather) while the battery is being fully charged by about 14H00 and not actually registering cycles. 

My daily average generation is between R12.00 and R18.00 (based on my municipal cost of R2.20/KWh) Thats with 1 x pylon 3.5 and 6 x 330W panels. The batteries basically make it possible to have some savings, without the battery I don’t think it would be possible.

 

Link to post
Share on other sites
4 hours ago, Plaashaas said:

You cant bring into account degradation of the battery but over the same period exclude Eskom tariff increases. (On average 11%p.a over the last 10 years)

Oh but I can. As I said, I assumed that Eskom’s increases are on par with the interest you would earn on the money you would have spent on a battery. It is just easier that way. Mathematically you can express it as 12,096kWh x (1.10)^5 (assuming you will use the battery for 10 years, at which point it is out of warranty, so 5 years is the mid point) x (1.10)^-5 (discounting it for 5 years at an annual effectively interest rate of 10%, if you are able to earn 10% return elsewhere) so the 5 doesn’t matter, neither does the 10%. It just gets back to 1 as the adjustment factor. What you should rather ask yourself is, how much can you earn on your investments (probably not 10%) in which case you do gain a bit. However, you’d also need to be confident in Eskom’s future increases and that it’ll keep on being that high, for this calc to tip in favour of the battery.

It is also quite likely that you reach 10 years without even reaching 6k cycles, for example, at which point the battery is out of warranty and might just break for a different reason.

Link to post
Share on other sites
1 hour ago, Gerrie said:

The system could also allow you to draw a additional in my case >6KWh everyday day (permitting weather) while the battery is being fully charged by about 14H00 and not actually registering cycles.

Sorry for the double post, but I’m on my phone so difficult to quote and type stuff in one post.

The battery would still register those little discharges and charges as cycles whenever it needs to smooth the availability of the PV. But I did note that batteries are useful up until it makes your solar viable, or you are off-grid (or your backup needs are immense). However, grid-tied, it isn’t financially as beneficial as panels or in fact many over energy saving options.

Edited by jykenmynie
Link to post
Share on other sites
On 2020/09/08 at 9:11 PM, Gerrie said:

I’ve been wondering how much generation in Rand per day vs. Total cost of solar installation. Can it be compared or calculated in some sort of ratio. My own 4KW system generated this over a 24Hr period.

I ran my 3.5KWH pylon tech down to 12% SOC last night, so:

Last nights battery use = 2.9KWH 

Today sunlight use = 5.3KWH (mixing pv & battery)

Battery again fully charged at 14H00

Total = 8.2KWH/day @ R2,20 = R18.04 for today on a R55K system.

Anyone with similar or better cost ratio? Is R18.04 saving per day worth the R55K spent.

I think it is a can of worms trying to calculate that.

I get 15kWh or R33 per day on average but on a R140k system using almost all the available pv power it can generate. This is a 4.8kW inverter with 3.8kW PV and 7kWh batteries.

Some questions and how others might differ: How do you install a 4kW system on R55k only?  Most will cost more. If you add more solar panels you can generate more Kwh per day to better the ROI, but then you also have to use the power generated. Many systems have batteries charged by midday and then you lose the rest of the sun power you could have used.

 

Link to post
Share on other sites
1 hour ago, Plaashaas said:

You can bet on it! 

You could, but I'd rather not allow for it in my ROI calculations and be pleasantly surprised if they do and my ROI is better than expected (or payback period is shorter than expected). However, as an actuary I am inclined to add prudence in most of my calculations, which seems to be a pragmatic way to deal with uncertainty.

Link to post
Share on other sites
2 hours ago, Pietpower said:

I get 15kWh or R33 per day on average but on a R140k system using almost all the available pv power it can generate. This is a 4.8kW inverter with 3.8kW PV and 7kWh batteries.

So, on a good day, like yesterday, I generated 17kWh on the DC side, from my panels. I have 12*320 = 3,840W worth of mono panels. I had maybe another 1kWh I could've used, as the panels idled a little from 16:00 to 18:00 (and my panels are west facing, so I still have some power then). But I think I am pretty much maxed out on 18kWh. So the investment in my panels was about R60k, MPPTs and installation included. CoCT rates on the electricity used after 600kWh for the month, is R2.53 per kWh. So I calculate my ROI on that since my panels keep me out of that range (it is an overestimate on my ROI, but I use it as a "best case" calculation).

Therefore, I can save R45.54 * 90% per day on the AC side, on the best day. So I'll rate that down by 50% (prudently) for bad PV days, but also four out of the three weeks days where I probably won't get to utilise all the available PV. After a year of monitoring my system, I'll have better data to do an actual calculation.

That puts me on about R20.5 per day of savings, or R7,485 per year. Again, assuming Eskom increases in line with investment return earn on the R60k outlay elsewhere (prudently), I shall pay back my investment in about 8 years. BUT WAIT! You say. What about the inverter and the batteries? To me, backup power was a luxury purchase that requires to ROI but my convenience in having power. So it is excluded from my calculations. With an inverter and batteries thrown into the mix, my payback period (as I went Victron and spent R22.5k + R4.5k on the inverter and Venus GX as well as about R45k on the batteries) would be much longer than I expect my batteries to last. But that was never part of my justification for the panels or the purchase of backup power to begin with.

Link to post
Share on other sites
2 hours ago, Pietpower said:

How do you install a 4kW system on R55k only?  Most will cost more.

I know it wont be possible for most people to install at this price but it can be done as I done my own installation that meant no labour cost, no markup on materials and no brand names except the pylon battery that I recently installed removing the old gel batteries. Roof mountings and channels for pv were made by myself with products from central support systems. I bought a clone and did not know it at the time fortunately it performs pretty well.

4KW clone inverter - R8000, 6x330W panels - R12600, 4x120AH gel batteries - R8400, (batteries were replaced) with Pylontech3.5-R19900, brackets, wire, auto-change over with DB upgrade and COC by myself R6000. 

2 hours ago, Pietpower said:

If you add more solar panels you can generate more Kwh per day to better the ROI

 

I would like to add more but the benefit will be to little as I don’t really need more PV panels as the six panels can carry my daytime loads and still have the pylon charged by late afternoon, which means very little wasted PV. 

Link to post
Share on other sites
13 hours ago, Pietpower said:

I get 15kWh or R33 per day on average but on a R140k system using almost all the available pv power it can generate. This is a 4.8kW inverter with 3.8kW PV and 7kWh batteries.

Thank you to you guys for sharing these PV generation figures it gives a nice indication of two different 3.8KW arrays. Pietpower’s 15KWh generation is pretty close to Jykenmynie’s 17kWh generation for the same array size. The only other way to get more generation might be to install a solar tracker to get a better curve during the day, that’s if it was really required and if you have the loads to go with it.

My own array size is only 1890W and the best generation was 8.2KWh for a 24hr cycle like mentioned in my first post, this is measured with a digital KWh meter on the inverter ac output and I have another KWh meter on the Inverter ac input so that I can monitor if Eskom was also used to feed or charge the inverter. 

I think I will add 2 more panels at a later stage but than I will also have to tell my wife we also need another battery, so I think it’s safer to rather just keep quiet for now. 🤫

 

 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...