# The future of solar power

1. May 19, 2017

### NTL2009

AFAIK, no utility pays a homeowner more (per kWh) for excess power than they charge that homeowner for consumption. It's a wash.

2. May 19, 2017

### gleem

Suppose I normally use 40 kwhr per day my meter reads 10000 kwhr. at the beginning of the day. I use 25kWhrs. during the daytime when my panels produce 60 kwhrs. during this period. producing 35kwhrs of excess energy. At the end of the day my meter reads 9965kWhrs. I produced enough electricity myself so no charge for electricity that day plus I sent to the utility for their use 35KkWhrs for which they credit my account via the meter. At least that's the way I understand it and the reason people spend big bucks to put in these panels. and then there's the tax breaks on top of it.

3. May 19, 2017

### Staff: Mentor

The German government did that for a while (and continues to do so for old installations), now the rates are lower.
Various governments do that for wind energy, this plus the equivalent for solar power can make electricity market prices negative - it makes sense to "sell" electricity and pay for it if the government pays you more than that. An odd situation.
Everything is heavily subsidized. Directly, and indirectly - because you still need the grid with your solar panels (even more than before: you now use it in both directions!), but now you pay less for it. Which means others have to pay more for it.

4. May 19, 2017

### gleem

I do not know in fact that they pay the total cost per kwhr. because it includes the charge for generation and the charge for transmission which for me are about equal. If the meter reads less than the previous day then they know your sold them power and they might credit your account for the generation charge only and not the total charge. So everything is copacetic.

5. May 19, 2017

### Staff: Mentor

That's not what I meant. Let's ignore taxes for now:

Producing 1 kWh typically costs something like 4 cent in big power plants. The distribution, logistics and so on cost about the same, so you pay 8 cents per kWh in total. That is the system with big power plants only.
Now you install a small solar panel on your roof. On some days you don't need to buy electricity. You don't pay the 4 cent/kWh for the production naturally, but you also don't pay the 4 cent/kWh used to maintain the grid. But the grid still has to be maintained, because you want to be able to use it at any time. To get the same money to operate the grid, the electricity price has to rise. The effect from your local solar panel is tiny, of course, but summed over all residential solar power it can matter. While you save 8 cent/kWh, summed over all customers we only save 4 cent/kWh.

It gets worse. Electricity demand is quite predictable and follows daily and weekly cycles. Production from solar panels is not that predictable, and has a different pattern every day. The grid operators have to match production to demand, which means regulating down some power plants. Power plants that are idle still cost money but suddenly no money flows in when the sun shines.. What does the power plant operator do to recover these losses? Increase the price per kWh. Your electricity company guarantees that you get power even if the sun doesn't shine - the power plants will have to stay as long as we don't have a better storage solution.

A production/demand pattern that changes frequently can also mean the transmission lines need more capacity, increasing distribution costs. And handing down these costs to the customers, of course.

For you as customer solar power can be worth the investment - you save 8 cent per kWh, and even more if we add taxes. You might even get subsidies if you produce more power than you need, to increase the use of solar power for you even more. That is the calculation you see solar power proponents make. The overall economic use is much smaller: It is the difference between running or not running an existing power plant, something like 1-2 cent per kWh. And I don't see how solar panels are supposed to get that cheap - installation costs alone are at this price level.
If it helps to reduce emissions from coal and gas power plants, I think it is worth the investment, but we wouldn't need solar power to do that.
A reliable method to store electricity would improve things a lot.

6. May 19, 2017

### NTL2009

Yes, yes, yes, I understand how the numbers 'work'. But you are looking at the micro-level, and I'm looking at the macro-level. At the macro level, physics and economics and common sense say residential rooftop solar makes no sense, compared to large industrial scale installations. At the micro-level, Congress (with few if any physicists or engineers) has warped the market.

Please read the excellent post above from mfb. I'd summarize that by saying - the utility is currently paying residential solar generators retail cost for something they normally buy at wholesale, and everyone else on the grid is going to pay extra for that. That is not reasonable and it is not sustainable.

Anyone who really wants to promote solar for environmental reasons (or any other reasons I guess) should be against residential installations and in favor of large scale installations. If someone just wants what they can get from the government and their fellow taxpayers, well, I think that's outside the realm of a physics forum.

7. May 20, 2017

### Physics_Kid

a lot of panels, inverter(s), step up xfmer. as the efficiency of panels get better the number of panels needed will go down. i dont know what the quantum limit is, thats the real stickler.

8. May 20, 2017

### nikkkom

Residential solar is less economically efficient - well known "economies of scale" reasons apply here. The cost of installation, for example. The same worker can install maybe 20-50 times more panels in the same time span when he is installing them at the solar farm, not on a smallish roof.

This will be somewhat alleviated when integrated solar roofing becomes mainstream. If you need to build a roof anyway, then ordering a solar roof only costs more than ordinary roof, but the same workers do about the same amount of work and it takes about the same amount of time.

9. May 20, 2017

### NTL2009

Getting back to your earlier post, here are my thoughts... Using the large roof of schools, big-box stores, etc does not require any additional transmission lines, storage facilities (no more than residential), or significant power disruption either. Here's some numbers:

I mentioned the large school install near us. 440 KW, 1760 panels. So lets put that in perspective. When converted to 120 V, that would be 3667 Amps. A typical NA home has 200 Amp capacity wiring, so we could think about one of these buildings as needing the same wiring capacity as about 18 homes (or 9 homes if that is 200 Amps capacity per each branch of two phases, I'm not sure on that). Off hand, I would think any big building would have that much wiring capacity (large A/C systems). Since the panels offset usage first, we never exceed the panel power amperage, it is always subtractive. We would have full panel amperage on the wiring only if the building was shut down to zero. As long as the panel peak power does not exceed the wiring capacity of the building, no upgrades to any of the distribution system is required. In fact, the panels reduce loading on the distribution system, on average.

You might be picturing solar farms that are the size of present thermal power plants, ~ 1 GW. But there is no need for that. We don't need to have solar distant from homes, as there is no smoke or other need for separation. Better to distribute 2000 large roofs of 1/2 MW each distributed throughout the area consuming it.

There is talk of large solar farms in the desert, and those would need large transmission lines. I haven't seen the numbers, but offhand, I wouldn't think that added % of sunshine would offset the cost of transmission lines, when smaller, distributed local installations would need little/no infrastructure changes.

10. May 20, 2017

### nitsuj

This whole thread has pointed out the higher cost of solar to traditional. http://energyrates.ca/ontario/green-energy-ontario/

Another point is personally owning the electricity / installation. A very attractive feature that makes economic sense...sometimes (smelting, pulp) making your own coal / hydro plant makes economic sense. "Soon" it will "make sense" even for jane doe consumer.

Who on earth thinks that paying to get electricity from here to there, a profit margin, supporting billions in infrastructure, at the mercy of market pricing is better economically than simply owning your own power generation equipment and having it on your own property?

Last edited: May 20, 2017
11. May 20, 2017

### nitsuj

This would vary greatly from jurisdiction, Some places the homeowner could install and hook up the panels, others may require the permission of neighbors to even have them in the first place. Some may ban (Texas?) their use all together.

12. May 20, 2017

### nikkkom

I suspect large installations are significantly cheaper per kW. When you plan and install 1 km^2 of PV, there are significant economies of scale.

13. May 20, 2017

### gleem

This has to do with homeowners associations (in Texas) who you agree to abide by their rules which can vary anywhere from forcing you to garage your car every night to regulating your landscape and color of your house. We lived in one that required approval of the architecture of the house before building it. The advantage I guess is that you have the same taste as your neighbor.

And as far as the unsightliness? is concerned Tesla is manufacturing roof tiles with the solar electric capabilities.

14. May 20, 2017

### nitsuj

With Texas I was leaning on their ban of Tesla dealerships...not sure of any details. For all I know Texas is big on solar for electricity (fine with there being a solar industry there.

15. May 20, 2017

### mheslep

16. May 20, 2017

### mheslep

You have not made the case from running entirely off "your own power equipment", but rather for using your own installation part time, and then when it doesnt work, and often it won't, receiving the benefit of a trillion dollars worth of reliable electric grid almost for free.

17. May 20, 2017

### mheslep

Many things begin with a single step, like getting lost the forest.

18. May 20, 2017

### NTL2009

Hello - from your fellow Earthling!

We have so many examples where it is worthwhile to purchase the end product rather than DIY. Electricity is a fantastic example of that.

Even with the present situation where you get to use the grid for zero, or near zero cost, solar PV has a pretty long payback (and subsidies don't really count, that is still a cost, it is just someone else paying for it). With all the uncertainties, I'd rather get what I need at ~ $0.11/kWh. As @mheslep pointed out, it isn't as 'simple' as you say ("simply owning your own power generation equipment and having it on your own property"). You are still very reliant on that big, old, bad, profit seeking utility and their billions of infrastructure. If you really want to disconnect from the electrical grid, be my guest. But please let me know how much it will cost for batteries and inverters to store enough kWh to get you through a cloudy, snowy Canadian winter, or how people would do it with large A/C needs? The economy of solar PV you see is because we have a grid available for you to use at night, in bad weather, and to pull from anytime your instantaneous power demand exceeds your system capacity. The grid is your storage system, and you are getting it almost for free. You deride it, but I bet you won't give it up! 19. May 20, 2017 ### nitsuj lol the grid is free, Who's still reliant on "still very reliant on that big, old, bad, profit seeking utility"? What's more in my province ultimately the populace owns the infrastructure, well apparently just a controlling share at this point...they sold 60% to those big bad stakeholders. teeheee hee the infrustrure was failing apart, repair greatly increasing the cost...of electricity, hmmm... 20. May 20, 2017 ### NTL2009 ? You didn't answer the question. What would it cost you to disconnect from the grid? 21. May 20, 2017 ### gleem It sound like people with solar panels should feel guilty for not paying their fair share of the transmission cost. How is that different from a person who has a second home which is used for 4-5 months and turns off the power when not in use. In the US 15 million residences are occupied part time. I don't get it. One user putting power on the grid is the same as one user reducing his pull from the grid by the same amount. The fluctuations of demand from the grid from solar at least currently is small the great fluctuations occur in the morning as household and commerce awake and at night when they wind down. Except as new solar installations come on line the solar effect on fluctuations should be predicable but new solar usually comes on line in very small negligible capacities. As new solar comes on line so do new houses without solar which increase the demand on the grid which must be accommodated. I can't see where solar is particularly bad for the power companies. 22. May 20, 2017 ### nitsuj That's a good question, I'll try and measure-calculate it. It'll take me some research and stuff but will do it as I'm interested to know myself. I have played with measurements from a single solar panel, I can't remember exactly but think it farmed maybe 0.10$ over a day (not straight /kwh cost, our billing includes fixed recurring costs). So maybe 30 panels , lets add a 1/3 for bad weather, so 40 panels for 90$(assumed cost of current elec use -$3*30days) of electricity. $5000 just for the panels (40*$100+$tuff). then there's the batts... super rough guess is$10k per person per 15yrs. looking for to getting it from a measurement perspective.

1kwh for 0.08 - 0.16\$ is SO CHEAP, it'll be bad lol

Last edited: May 20, 2017
23. May 20, 2017

### NTL2009

No, it is very different.

Take the simple case where a solar home nets to zero, they have a very low bill (connection fees vary), but they used the grid for most of the day. If they are able to net to zero, they had an excess around noon (so used the grid to absorb the excess), and then they used the grid to pull what they need for ~ 18 hours/day. Yet they pay almost nothing. Their solar system would not function w/o the grid, they ought to pay for it's use, the same as anyone.

If I reduce my consumption through efficiency, I'm using the grid less, and it's reasonable for me to pay a lower share of its support.

24. May 20, 2017

### Staff: Mentor

I don't say people should feel guilty, but keeping it in mind is certainly not a bad idea.
As long as it replaces coal or oil, I think it is a great thing, and I happily pay for it.
That house won't suddenly need power if it is cloudy, and the owners use electricity and pay elsewhere for the grid infrastructure.
The daily cycles are highly predictable, and changes occur over a timescale of about an hour. The overall fluctuations from solar power can be faster and they are less predictable. They are small today, sure, but the fraction of solar power is small as well.

25. May 21, 2017