8 ms·

I think researchers underestimated how much solar simply “makes sense” to the average person. Once the price is reasonable enough, people are very easily able t

I think researchers underestimated how much solar simply “makes sense” to the average person. Once the price is reasonable enough, people are very easily able to latch onto the idea of using what they already know and feel - the sun’s heat. Whenever I mention the solar panels in my parents house, the first question is always about the price. When I tell them they will break even in a few years, their next question is always about where to get it. There is never any skepticism about the technology, the safety, the long term impact (as you would have if someone was setting up a nuclear or gas power plant). They simply “get it”

koolba 6y ago
Where are we at in 2021 for pay off period? Does it vary by region?
- alexktz 6y ago
  I'm getting 8kw installed on my roof next month and the pay off is somewhere between 10-12 years. That's with NC's electricity costs being cheap at ~11c per kWh - in other areas this will drastically change.
- zdragnar 6y ago
  My area has a payoff roughly in line with the lifetime of the panels themselves, or half that if you believe the local companies absurd projections of future energy prices.
- gwicks56 6y ago
  In Australia, after a $2500 .gov subsidy, mine will pay for themselves in 4.5 years. LG Panels with 25 Year output guarantee. 6.6kw System. Financially speaking it's a complete no brainer. One thing I did notice when I was living in the USA though, was how expensive it was over there compared to Australia. Installation costs are 3x the price, I have no idea why. My system before the subsidy was $11k, and that was for top of the line panels and inverter. Cheap panels would have been around $7k Electricity costs are ~ $0.2 per kwh, AUD
  - epistasis 6y ago
    Most of the difference is in business practices, in customer acquisition. Basically all the advertising and salespeople to push solar. Lack of uniform building codes, and highly disparate permitting processes also raise costs in the US. Utilities are also hugely inconsistent throughout the US, not varying city-to-city like permitting processes, but there are thousands of different utilities in the US each with different policies. And perhaps the biggest problem is utility policies that either eliminate or make feasible solar for homes. After a utility makes solar possible by allowing favorable interconnection policies, companies rush in attempting to take advantage of the new market. But when utility executives get enough lobbying power to make solar economically infeasible through unreasonable fees, it kills existing solar installers. So the only solar companies that survive are those with large reach across lots of geographies that also have massive marketing arms that can do big customer acquisition when there's a sudden window of favorable solar interconnection policy.
  - tda 6y ago
    I paid €3900 for 22 panels, 7.2kw system here in the Netherlands. I did install it myself (but the whole package was delivered and the electric connections done by the supplier), and the panels and inverter are cheap Chinese brands. As I didn't situate them ideally and they lose efficiency as the heat up quite drastically I expect to generate between 4500 and 5000kwh. That should save me about €800 a year so this is a pretty solid business case. So to me the US prices seem even more ridiculous
  - fatcow 6y ago
    Very interesting -- currently in WA and quite interested too. What size house you're referring to?
  - sgerenser 6y ago
    In the U.S. it varies by region, but mid-quality panels are usually quoted at $2.50 to $3.00 per watt installed (before subsidies). Tesla Solar is advertising $2.00/watt nationwide but there are some questions about their responsiveness in actually getting anything installed in a timely manner. Outside of CA most people are only paying $0.10-$0.13/KWh making payback rough unless you have a large state or local subsidy on top of the federal 26% tax credit.
- eigen 6y ago
  definitely varies by region according to cost from local utility and solar efficacy. - SoCal Edison is $0.23 / kWh. https://www.sce.com/residential/rates/Standard-Residential-Rate-Plan https://www.sce.com/residential/rates/Standard-Residential-R... - Entergy Arkansas is $0.074 / kWh. https://cdn.entergy-arkansas.com/userfiles/content/price/tariffs/eal_rs.pdf https://cdn.entergy-arkansas.com/userfiles/content/price/tar...
- ezzaf 6y ago
  Hugely. A few of the main factors that will determine your payoff time: - Subsidies. - Cost of labour. How much do you need to pay to install the panels? - Your energy usage patterns. If you use a lot of energy when the sun is shining, your panels will pay themselves off faster. - Cost of transmission of energy. How much does it cost to get the energy from the generator to you. - Cost of energy. How much it costs to generate energy where you are. - Location. Proximity to the equator, annual sunshine hours, shading, panel angle.
- supermatt 6y ago
  To install on your roof - 7-8 years in lithuania. There is a ~20% subsidy for up to 10kW systems. Alternatively, pending a change in the law, there are solar fields where you can purchase panels (also eligible for subsidy) and pay an annual maintenance fee. In this case it is around 6-7 yrs.
  - dzhiurgis 6y ago
    Annual fees on those farms make no sense... We've got a quote for €6k - €2.5k subsidy for 8KW system. We use a ton of power - which is a main factor how quickly you get your money back.
    - supermatt 6y ago
      What doesn’t make sense about it? We were planning to get 18kW system installed on roof, but to get sign off from power grid we would need to upgrade our power lines at great expense (we are end of line rural), so I am wondering about using solar farm for additional capacity (when it’s available). Interested in your thoughts.
      - dzhiurgis 6y ago
        18-25 €/kw = €200 per year times 25 years = 5k€ of 8k€ install is 62.5% of your system cost... This actually buys you some off the shelve batteries (5kwh so far IIRC) which might alleviate your line capacity issue (not sure tho). Plus they reserve right to set it whatever they want it and you have no practical way to sell your investment...
        supermatt 6y ago
        Yeah, batteries won’t cut it really - need to store thousands of kWh for winter. I’ll have to look into the terms some more - afaik nothing is finalised yet, awaiting change in law. Thanks for input!
        dzhiurgis 6y ago
- gandalfian 6y ago
  The key is do you use lots of electricity during summer days when the panel are producing? If so a 5-10% return even with loss of capital is possible. If you don't consume the electricity yourself then it's not really economic. Obviously closer to the equator and higher your electricity prices the better it gets.
- neilwilson 6y ago
  In the UK it takes a while: "The price of a typical solar panel system is about £4,800. It can take anywhere between 15 and 26 years to recoup this costs, for a typical home – depending on where you live" https://www.moneysavingexpert.com/utilities/free-solar-panels/ https://www.moneysavingexpert.com/utilities/free-solar-panel...
conradev 6y ago
My favorite part of PV is that you can scale it to fit any power generating capacity, from a residential roof all the way up to a 50MW farm. It’s fairly linear, too, in terms of land usage and cost, which makes it easy to understand.
- epistasis 6y ago
  Yes, this is really the crucial thing about solar. It scales, in all directions, from small to large. Production capacity is scaling too, though just barely at the edge of what we need. I really wish that governments would commit hard to decarbonization of the hydrogen market (including ammonia for fertilizer), through solar/wind + elctrolyzers. The only thing stopping further scaling of production capacity is the demand side of things. Having an extra 50-100 GW of solar production to decarbonize industry would really speed the climate transition. But until there's the guaranteed market for it, the market is going to develop very slowly until green hydrogen is cheaper than natural gas as an input. Germany pushed solar along when it wasn't cheap, greatly accelerating the fall off solar prices. All governments should push industrial chemical process decarbonization together.
- ezzaf 6y ago
  50MW is a small scale solar generator these days. Bhadla Solar Park is 2.2GW, and there are plans being tossed around to go even larger. For example 10GW in northern Australia (Sun Cable).
- Gibbon1 6y ago
  The other thing to is the massive redundancy with solar. Friend mine worked on installing a giant GE Gas Turbine for a power plant. They fired it up and it threw its blades. And it was down for 9 months. Doesn't really happen with solar.
  - pfdietz 6y ago
    This means PV can be installed with some level of sloppiness and inattention to detail that would be ruinous on a large integrated power plant, like a nuclear power plant. I bet this also reduces labor costs by reducing the level of training and expertise required.
dane-pgp 6y ago
> I tell them they will break even in a few years Then why don't more companies offer to become your electricity provider and install the solar panels for free? They could say "We promise that your energy bills will be cheaper this year than last year (as long as you don't use more energy), and within a few years you'll own the panels and can switch to a different electricity provider."
- eightysixfour 6y ago
  Pretty sure there are companies that do this. My parents received an offer like this, structured like a lease with a small buyout at the end.
  - shaklee3 6y ago
    Solarcity does this
- artificialLimbs 6y ago
  This would be more palatable than "We're going to install these panels after you buy then and provide x warranty". I've had 3 solar companies come give us prices on our house. If the company folds/disappears then the warranty doesn't mean squat and if there is any breakage after that happens, we're likely to end up in the red.
- xavriley 6y ago
  One reason is issues with property ownership. In the U.K. a company could do this but if the original customers were to see the house, they’d have no legal means of compelling the new owners to take up the arrangement. At least that’s what I understand.
  - bostik 6y ago
    The plural of anecdote is not data, but I can provide some figures. There is currently a push in London to get households install solar panels, and I expressed interest in getting a set installed to our house. Sadly, the finances don't add up. Our house is not exactly small, and optimistically you could fit 10 PV panels on the roof. At least according to the quote I received, but having scouted installations in the nearby places, 8 might be more realistic. (Shape of the roof is a factor.) Assuming energy prices overall grow as they have over the past decade, it would take 12-15 years to break even on the installation cost. That's with 10 panels. With 8, add a couple of years. And assume there will be no additional maintenance or replacement costs to consider. So, at least in the UK: unless you are wealthy enough to have a large house with a sufficiently large roof, PV installations are not yet financially viable. It should be better in the rural regions where houses tend to be larger. With more installation surface area available, the marginal cost of each PV panel goes down and the marginal benefit of its energy production goes up. Hence, in the UK, for a single-family dwelling, a roof with space for 14 panels should be enough to make the installation viable. A house with that much roof surface, at least near us, starts from approximately £700k.
jollybean 6y ago
I don't think we misunderstood that part. When people can make or save money easily, then it will sell, if they can't it won't. So the 'tipping point' was always going to be when it became practical to industry, then business, then consumers etc.. We're still not quite there yet as it will 'really happen' when homeowners can go to Home Depot, pick up what they need and have it up and working same day. When that happens, it will Solar Armageddon, the good kind.
chrismcb 6y ago
Unless you live in the sunbelt, it will take more than a few years to recoup. Factor in replacing the inventor every 7 years, it becomes questionable, it also depends on your storage solution or local buy back program. Add an electric car to the mix and it becomes feasible. But I think it still needs to become cheaper.
- rhodozelia 6y ago
  Any source for inverter life span only 7 years ?
  - monkeydreams 6y ago
    It depends greatly on your setup but, unless you are running some crazy, completely off-grid, system with cheap batteries and cheap inverter, you can expect an inverter to last you longer than this. Most are rated for 10-15 years, with some rated for 25 year lifecycle. As with many things, quality costs, but not all costly inverters are quality, so do your research before you buy.
  - xnyan 6y ago
    The warranty for most residential solar inverters is around 10 years, though often prorated towards the end of that timeframe. 7 years does not sound crazy, though with good cooling and and decent quality it's probably a tad low.
ivanhoe 6y ago
> There is never any skepticism about the technology, the safety, the long term impact (as you would have if someone was setting up a nuclear or gas power plant). They simply “get it” This is also a bad thing, because there are some real issues with PV panels too: leaking toxic materials, recycling problems, environmental side-effects because you need to mine for rare earths and critical metals, etc. It's far from being as simple and as clean as many people imagine, and not taking into consideration all this might cost us all a lot of damage to nature and wildlife in future. I don't want to get into nuclear vs. solar energy flame wars here, primarily because I don't feel that I have enough information and knowledge to be able to perceive all the possible side-effects of each type of energy - but the fact that world is so deeply biased one way for solar, the other way fro nuclear energy definitely will not help the best judgment on this very important topic.
- Tade0 6y ago
  Correction: Crystalline silicon solar cells, the most popular type today, require no rare earths. The most expensive and rare element in them is silver - used for the reflective layer underneath.
  - ivanhoe 6y ago
    yes, if you don't count in the inverter and charger controller units and the batteries used as part of a common setup... I've got a degree in electrical engineering, but as I've said, I really don't feel competent enough to go into any discussion on a degree of actual threat, if any, as looking into all the side-effects of some tech is really complex task far above my pay grade and it's super easy to overlook something and jump to wrong conclusions. I just wanted to point out that this popular black & white bias between solar and nuclear is not as simple as people think of it.
    - pfdietz 6y ago
      How are rare earth elements used in any of those? I think you're just repeating a propaganda lie about PV.
    - 6y ago
xyzzy21 6y ago
If and only if you own the land (or enough land) to put solar collection on!! That's NOT MOST PEOPLE. And not that many "average people".
- solraph 6y ago
  Depends on where you live. Sure, if you an apartment heavy area like Singapore, then no - but based on some very quick googling, it looks like globally around 60% to 80% of the population live in detached or semi-detached houses, where they own the roof, so there's your free space. Even when people rent, I can see having solar panels simply becoming factored into the rent equation. If the renter can expect to save $100 off their monthly power bill, then the landlord can easily ask for an additional $80 in rent, which means they make more profit over the owned lifetime of the property.

koolba 6y ago

Where are we at in 2021 for pay off period? Does it vary by region?

alexktz 6y ago
I'm getting 8kw installed on my roof next month and the pay off is somewhere between 10-12 years. That's with NC's electricity costs being cheap at ~11c per kWh - in other areas this will drastically change.
zdragnar 6y ago
My area has a payoff roughly in line with the lifetime of the panels themselves, or half that if you believe the local companies absurd projections of future energy prices.
gwicks56 6y ago
In Australia, after a $2500 .gov subsidy, mine will pay for themselves in 4.5 years. LG Panels with 25 Year output guarantee. 6.6kw System. Financially speaking it's a complete no brainer. One thing I did notice when I was living in the USA though, was how expensive it was over there compared to Australia. Installation costs are 3x the price, I have no idea why. My system before the subsidy was $11k, and that was for top of the line panels and inverter. Cheap panels would have been around $7k Electricity costs are ~ $0.2 per kwh, AUD
- epistasis 6y ago
  Most of the difference is in business practices, in customer acquisition. Basically all the advertising and salespeople to push solar. Lack of uniform building codes, and highly disparate permitting processes also raise costs in the US. Utilities are also hugely inconsistent throughout the US, not varying city-to-city like permitting processes, but there are thousands of different utilities in the US each with different policies. And perhaps the biggest problem is utility policies that either eliminate or make feasible solar for homes. After a utility makes solar possible by allowing favorable interconnection policies, companies rush in attempting to take advantage of the new market. But when utility executives get enough lobbying power to make solar economically infeasible through unreasonable fees, it kills existing solar installers. So the only solar companies that survive are those with large reach across lots of geographies that also have massive marketing arms that can do big customer acquisition when there's a sudden window of favorable solar interconnection policy.
- tda 6y ago
  I paid €3900 for 22 panels, 7.2kw system here in the Netherlands. I did install it myself (but the whole package was delivered and the electric connections done by the supplier), and the panels and inverter are cheap Chinese brands. As I didn't situate them ideally and they lose efficiency as the heat up quite drastically I expect to generate between 4500 and 5000kwh. That should save me about €800 a year so this is a pretty solid business case. So to me the US prices seem even more ridiculous
- fatcow 6y ago
  Very interesting -- currently in WA and quite interested too. What size house you're referring to?
- sgerenser 6y ago
  In the U.S. it varies by region, but mid-quality panels are usually quoted at $2.50 to $3.00 per watt installed (before subsidies). Tesla Solar is advertising $2.00/watt nationwide but there are some questions about their responsiveness in actually getting anything installed in a timely manner. Outside of CA most people are only paying $0.10-$0.13/KWh making payback rough unless you have a large state or local subsidy on top of the federal 26% tax credit.
eigen 6y ago
definitely varies by region according to cost from local utility and solar efficacy. - SoCal Edison is $0.23 / kWh. https://www.sce.com/residential/rates/Standard-Residential-Rate-Plan https://www.sce.com/residential/rates/Standard-Residential-R... - Entergy Arkansas is $0.074 / kWh. https://cdn.entergy-arkansas.com/userfiles/content/price/tariffs/eal_rs.pdf https://cdn.entergy-arkansas.com/userfiles/content/price/tar...
ezzaf 6y ago
Hugely. A few of the main factors that will determine your payoff time: - Subsidies. - Cost of labour. How much do you need to pay to install the panels? - Your energy usage patterns. If you use a lot of energy when the sun is shining, your panels will pay themselves off faster. - Cost of transmission of energy. How much does it cost to get the energy from the generator to you. - Cost of energy. How much it costs to generate energy where you are. - Location. Proximity to the equator, annual sunshine hours, shading, panel angle.
supermatt 6y ago
To install on your roof - 7-8 years in lithuania. There is a ~20% subsidy for up to 10kW systems. Alternatively, pending a change in the law, there are solar fields where you can purchase panels (also eligible for subsidy) and pay an annual maintenance fee. In this case it is around 6-7 yrs.
- dzhiurgis 6y ago
  Annual fees on those farms make no sense... We've got a quote for €6k - €2.5k subsidy for 8KW system. We use a ton of power - which is a main factor how quickly you get your money back.
  - supermatt 6y ago
    What doesn’t make sense about it? We were planning to get 18kW system installed on roof, but to get sign off from power grid we would need to upgrade our power lines at great expense (we are end of line rural), so I am wondering about using solar farm for additional capacity (when it’s available). Interested in your thoughts.
    - dzhiurgis 6y ago
      18-25 €/kw = €200 per year times 25 years = 5k€ of 8k€ install is 62.5% of your system cost... This actually buys you some off the shelve batteries (5kwh so far IIRC) which might alleviate your line capacity issue (not sure tho). Plus they reserve right to set it whatever they want it and you have no practical way to sell your investment...
      - supermatt 6y ago
        Yeah, batteries won’t cut it really - need to store thousands of kWh for winter. I’ll have to look into the terms some more - afaik nothing is finalised yet, awaiting change in law. Thanks for input!
        dzhiurgis 6y ago
gandalfian 6y ago
The key is do you use lots of electricity during summer days when the panel are producing? If so a 5-10% return even with loss of capital is possible. If you don't consume the electricity yourself then it's not really economic. Obviously closer to the equator and higher your electricity prices the better it gets.
neilwilson 6y ago
In the UK it takes a while: "The price of a typical solar panel system is about £4,800. It can take anywhere between 15 and 26 years to recoup this costs, for a typical home – depending on where you live" https://www.moneysavingexpert.com/utilities/free-solar-panels/ https://www.moneysavingexpert.com/utilities/free-solar-panel...

conradev 6y ago

My favorite part of PV is that you can scale it to fit any power generating capacity, from a residential roof all the way up to a 50MW farm. It’s fairly linear, too, in terms of land usage and cost, which makes it easy to understand.

epistasis 6y ago
Yes, this is really the crucial thing about solar. It scales, in all directions, from small to large. Production capacity is scaling too, though just barely at the edge of what we need. I really wish that governments would commit hard to decarbonization of the hydrogen market (including ammonia for fertilizer), through solar/wind + elctrolyzers. The only thing stopping further scaling of production capacity is the demand side of things. Having an extra 50-100 GW of solar production to decarbonize industry would really speed the climate transition. But until there's the guaranteed market for it, the market is going to develop very slowly until green hydrogen is cheaper than natural gas as an input. Germany pushed solar along when it wasn't cheap, greatly accelerating the fall off solar prices. All governments should push industrial chemical process decarbonization together.
ezzaf 6y ago
50MW is a small scale solar generator these days. Bhadla Solar Park is 2.2GW, and there are plans being tossed around to go even larger. For example 10GW in northern Australia (Sun Cable).
Gibbon1 6y ago
The other thing to is the massive redundancy with solar. Friend mine worked on installing a giant GE Gas Turbine for a power plant. They fired it up and it threw its blades. And it was down for 9 months. Doesn't really happen with solar.
- pfdietz 6y ago
  This means PV can be installed with some level of sloppiness and inattention to detail that would be ruinous on a large integrated power plant, like a nuclear power plant. I bet this also reduces labor costs by reducing the level of training and expertise required.

dane-pgp 6y ago

> I tell them they will break even in a few years Then why don't more companies offer to become your electricity provider and install the solar panels for free? They could say "We promise that your energy bills will be cheaper this year than last year (as long as you don't use more energy), and within a few years you'll own the panels and can switch to a different electricity provider."

eightysixfour 6y ago
Pretty sure there are companies that do this. My parents received an offer like this, structured like a lease with a small buyout at the end.
- shaklee3 6y ago
  Solarcity does this
artificialLimbs 6y ago
This would be more palatable than "We're going to install these panels after you buy then and provide x warranty". I've had 3 solar companies come give us prices on our house. If the company folds/disappears then the warranty doesn't mean squat and if there is any breakage after that happens, we're likely to end up in the red.
xavriley 6y ago
One reason is issues with property ownership. In the U.K. a company could do this but if the original customers were to see the house, they’d have no legal means of compelling the new owners to take up the arrangement. At least that’s what I understand.
- bostik 6y ago
  The plural of anecdote is not data, but I can provide some figures. There is currently a push in London to get households install solar panels, and I expressed interest in getting a set installed to our house. Sadly, the finances don't add up. Our house is not exactly small, and optimistically you could fit 10 PV panels on the roof. At least according to the quote I received, but having scouted installations in the nearby places, 8 might be more realistic. (Shape of the roof is a factor.) Assuming energy prices overall grow as they have over the past decade, it would take 12-15 years to break even on the installation cost. That's with 10 panels. With 8, add a couple of years. And assume there will be no additional maintenance or replacement costs to consider. So, at least in the UK: unless you are wealthy enough to have a large house with a sufficiently large roof, PV installations are not yet financially viable. It should be better in the rural regions where houses tend to be larger. With more installation surface area available, the marginal cost of each PV panel goes down and the marginal benefit of its energy production goes up. Hence, in the UK, for a single-family dwelling, a roof with space for 14 panels should be enough to make the installation viable. A house with that much roof surface, at least near us, starts from approximately £700k.

jollybean 6y ago

I don't think we misunderstood that part. When people can make or save money easily, then it will sell, if they can't it won't. So the 'tipping point' was always going to be when it became practical to industry, then business, then consumers etc.. We're still not quite there yet as it will 'really happen' when homeowners can go to Home Depot, pick up what they need and have it up and working same day. When that happens, it will Solar Armageddon, the good kind.

chrismcb 6y ago

Unless you live in the sunbelt, it will take more than a few years to recoup. Factor in replacing the inventor every 7 years, it becomes questionable, it also depends on your storage solution or local buy back program. Add an electric car to the mix and it becomes feasible. But I think it still needs to become cheaper.

rhodozelia 6y ago
Any source for inverter life span only 7 years ?
- monkeydreams 6y ago
  It depends greatly on your setup but, unless you are running some crazy, completely off-grid, system with cheap batteries and cheap inverter, you can expect an inverter to last you longer than this. Most are rated for 10-15 years, with some rated for 25 year lifecycle. As with many things, quality costs, but not all costly inverters are quality, so do your research before you buy.
- xnyan 6y ago
  The warranty for most residential solar inverters is around 10 years, though often prorated towards the end of that timeframe. 7 years does not sound crazy, though with good cooling and and decent quality it's probably a tad low.

ivanhoe 6y ago

> There is never any skepticism about the technology, the safety, the long term impact (as you would have if someone was setting up a nuclear or gas power plant). They simply “get it” This is also a bad thing, because there are some real issues with PV panels too: leaking toxic materials, recycling problems, environmental side-effects because you need to mine for rare earths and critical metals, etc. It's far from being as simple and as clean as many people imagine, and not taking into consideration all this might cost us all a lot of damage to nature and wildlife in future. I don't want to get into nuclear vs. solar energy flame wars here, primarily because I don't feel that I have enough information and knowledge to be able to perceive all the possible side-effects of each type of energy - but the fact that world is so deeply biased one way for solar, the other way fro nuclear energy definitely will not help the best judgment on this very important topic.

Tade0 6y ago
Correction: Crystalline silicon solar cells, the most popular type today, require no rare earths. The most expensive and rare element in them is silver - used for the reflective layer underneath.
- ivanhoe 6y ago
  yes, if you don't count in the inverter and charger controller units and the batteries used as part of a common setup... I've got a degree in electrical engineering, but as I've said, I really don't feel competent enough to go into any discussion on a degree of actual threat, if any, as looking into all the side-effects of some tech is really complex task far above my pay grade and it's super easy to overlook something and jump to wrong conclusions. I just wanted to point out that this popular black & white bias between solar and nuclear is not as simple as people think of it.
  - pfdietz 6y ago
    How are rare earth elements used in any of those? I think you're just repeating a propaganda lie about PV.
  - 6y ago

xyzzy21 6y ago

If and only if you own the land (or enough land) to put solar collection on!! That's NOT MOST PEOPLE. And not that many "average people".

solraph 6y ago
Depends on where you live. Sure, if you an apartment heavy area like Singapore, then no - but based on some very quick googling, it looks like globally around 60% to 80% of the population live in detached or semi-detached houses, where they own the roof, so there's your free space. Even when people rent, I can see having solar panels simply becoming factored into the rent equation. If the renter can expect to save $100 off their monthly power bill, then the landlord can easily ask for an additional $80 in rent, which means they make more profit over the owned lifetime of the property.