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> The biggest challenge with going to half renewables is overgeneration. The state receives power from a number of sources that simply can't be shut down—combin

> The biggest challenge with going to half renewables is overgeneration. The state receives power from a number of sources that simply can't be shut down—combined heat and power systems and nuclear plants, for example. Layered on top of that are renewable sources like solar that generate power whether you want them to or not. What? The biggest problem is the cost of storage, not the fact that the underlying technology is not yet efficient enough to compete with non-renewables cost wise? Can someone please summarize and explain this article to me? I saw no data, and there was no serious discussion of the underlying technology or economics of solar power.

mtgx 11y ago
Indeed. The biggest "problem" right now is storage, but anyone saying it's too big of a problem that won't be overcome soon would be as foolish as saying solar can't take off 6 years ago...which is apparently what the International Energy Agency did say then, and its estimates were overshot by 9x. > At that point the International Energy Agency (IEA) was still predicting that solar power would struggle to reach 20 gigawatts by now. Few could have foretold that it would in fact explode to 180 gigawatts. http://www.telegraph.co.uk/finance/economics/11958916/Paris-climate-deal-to-ignite-a-90-trillion-energy-revolution.html http://www.telegraph.co.uk/finance/economics/11958916/Paris-... Battery storage for solar power plants and even homes is going to explode over the next 5 years.
jws 11y ago
"Overgeneration" is not a problem with photovoltaic panels. You simply open circuit the panel and let it sit. In my own off grid solar installation I routinely fill my batteries, and after doing any high power tasks, like vacuum the rugs, the panels just go idle. To a grid connected system it means you can't sell your power during the solar peaks, but it also means that you have enough capacity to sell more power during the edges of the solar periods. Certainly any business which invests in long lived capital equipment would like to operate it at 100% capacity all the time, but most industries realize this doesn't happen. Solar will adjust. For off grid people "excess" capacity means getting by better on partly cloudy days. I'll probably double my capacity next spring for just this reason.
- toomuchtodo 11y ago
  Could you dump excess energy into a hot water heater? Preheat with thermal on the roof and with excess solar PV power, and then the final temperature lift with propane or natural gas?
  - ChuckMcM 11y ago
    Yes, you can do that. One of the more interesting strategies if you have the space for it is to pump water with excess energy. Pump water from a lower reservoir to a higher reservoir, you can later recover that energy by draining the water through a micro-hydro system. One challenge though is capacity, you would probably want essentially two olympic sized pools, one above the other as your storage unit. PG&E in California does this one a fairly large scale in the Bay Area. Pumping water into the Helms Creek reservoir (https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant)
    - AnimalMuppet 11y ago
      And if you can afford having two olympic swimming pools, you can probably also afford the solar installation. ;-)
    - logfromblammo 11y ago
      Pumped storage is not practical for a typical home. A 1000kg mass, raised 1m off the ground, stores about as much potential energy as a single AA (LR6) battery. The only other energy storage technology that is economically competitive with rechargeable batteries [in 2015] is compressed air. A pressure vessel approximately the same mass and volume as a lead-acid battery bank can store about the same amount of energy. It also has a longer useful lifespan and lower maintenance requirements. But the additional equipment required to connect it to your house power system is more complex and expensive. Rather than stacking two giant swimming pools, you would likely be better off burying a giant concrete sphere wrapped in Spectra/Dyneema/UHMW-PE fiber in your yard, and using a thermo-pneumatic engine to fill or drain the energy reservoir.
Natanael_L 11y ago
The idea is that it isn't profitable to focus on building out a network of renewable energy supply when you'll take a short-medium term loss on shutting down what it is replacing. Regarding storage, that doesn't entirely come into play until the big power plants are scaled down enough that your total available supply is less than the usage, which is not the case on most places most of the time. The risk is that you try to rely on renewables when renewable energy supply is at a minimum and load is at a high, and it exceeds your margin. That's when you need to tap into stored energy. Again, you can usually plan against that.
IkmoIkmo 11y ago
So I'm not sure how familiar you are but solar and wind are intermittent energy sources. Particularly solar peaks around noon while usage peaks in the morning and evening, and around noon when everyone is at work, usage is relatively low. So you've got an issue, you generate a bunch of energy that's not being used, so it's thrown away. That means the effective cost of an average kwh of solar electricity goes up a lot because you're not just paying for when you're using it, you're also paying (not really, but in a way when you average it) for electricity that's generated and then wasted. i.e. if I build a machine that produces energy for $1 per unit on average, but half my units are generated when I'm not there (and wasted), my actual average cost per unit of energy is $2. The $1 may be competitive with non-renewables, but because half is wasted, the actual $2 price is not. But of course you don't have to waste it, you can store it, but then you need large amounts of storage and that's not easy or cheap. Take the Tesla powerwall for example, roughly has the capacity to run 1 clothes washer + dryer cycle, and it costs $3k (and doesn't last forever, either). Paying for battery storage for everyone (for when renewables are a big part of total energy production), would put the cost in my hypothetical example somewhere between $1 and $2. For the actual data (rather than my silly numbers above) you're better off using google, there are a ton of studies that look at the kwh premium when running storage in different contexts. A quick back of envelope calculation for example for home-consumer storage prices... the above powerwall, $3k, lifetime of around 3500 cycles, at 7 kwh capacity, you're talking about the ability to store and use about 24.5k kwh of electricity at a cost of $3k before the device dies, or 12c per kwh. Now 12c per kwh is roughly the average price of a kwh in the US, so a powerwall essentially doubles the cost of of any unit of electricity you want store (the excess power solar generates around noon which can become very significant if we increase renewables a lot). Doubling in price for those kwh is massive, on average it makes little economic sense. In Hawaii, it makes total sense because prices of electricity are much higher. But this is a consumer solution, utility scale is cheaper, and some things can be much, much cheaper (like pumped hydro, way cheaper than a powerwall in general, and way way cheaper if you've got the natural resources like Norway does to build cheap pumped hydro capacity). So why not turn off the power plants (e.g. coal/natgas) when solar production is high at noon? Because these plants can take 24-48 hours to startup, they provide base power and you can't just shut them on and off. So yeah, storage is essential and it's not quite there yet. Battery tech has always lagged behind, and now we need it at a massive scale.
lumberjack 11y ago
The quote is talking about a problem the utility companies are facing with the adoption of personal PVs. Right now, the way your electricity bill is structured is heavily biased towards consumption. The service charge is a small part of the overall bill. What happens if 50% of the costumers have PVs is that the utilities will lose a lot of revenue but they will still have exactly the same amount of costs because they are not able to turn down their plants during the day and the PV people will still consume the same amount of peak grid energy during the night. So there is two ways to fix this. One of them is for the plants to downsize their constant power generation methods like coal fired boilers and get a bunch of gas peaker plants. The other one is to increase the service charge on your electricity bill.
- jws 11y ago
  This gets into the other billing problem with domestic solar. In rough numbers, half of your electric bill is for energy, the other half is to pay for all the grid and capacity. Billing is purely on energy consumption. The effect of this is that low electric users get subsidized by high electric users. When someone installs a domestic solar system they reduce their payments, but they still depend on the grid infrastructure. The system reaches its ultimate perversion when a grid tied domestic user achieves a negative bill. Not only have they been paid for their energy, they have been paid for the utility having a grid. You can solve this economic distortion by a couple of ways: • split billing into a grid-tie fee and an energy consumption charge: This accurately covers the solar houses, but it also raises the bills of the poor and cuts those of the wealthy (generally larger consumers). • only pay domestic solar producers half what you charge for power: This works out asymptotically for a huge producer where the grid portion vanishes, but it doesn't work for people reducing their consumption but maintaining a grid tie or selling a little bit. • put a surcharge on each watt of solar capacity: This works out accurately, but feels abusive. 1 watt of solar panel is going to make about 100 wHr of power a month. If grid-tie privilege includes a surcharge to cover the grid portion of 100wHr then this 1 watt solar panel user will end up paying the same for the grid as he did before. If a domestic solar installation is a net producer, it will end up getting paid for the energy and the grid fees will cancel. Even before we get to a point where the power company may say "no thank you" to a domestic user that wants to sell power at 1pm on a sunny day, we still need to straighten out the billing. The current system ends up with the utilities (and by extension all grid users) subsidizing solar installations by forgiving their grid costs. I'm in favor of that now, but in a future where our carbon emissions are under control the distortions will need to be smoothed out.

mtgx 11y ago

Indeed. The biggest "problem" right now is storage, but anyone saying it's too big of a problem that won't be overcome soon would be as foolish as saying solar can't take off 6 years ago...which is apparently what the International Energy Agency did say then, and its estimates were overshot by 9x. > At that point the International Energy Agency (IEA) was still predicting that solar power would struggle to reach 20 gigawatts by now. Few could have foretold that it would in fact explode to 180 gigawatts. http://www.telegraph.co.uk/finance/economics/11958916/Paris-climate-deal-to-ignite-a-90-trillion-energy-revolution.html http://www.telegraph.co.uk/finance/economics/11958916/Paris-... Battery storage for solar power plants and even homes is going to explode over the next 5 years.

jws 11y ago

"Overgeneration" is not a problem with photovoltaic panels. You simply open circuit the panel and let it sit. In my own off grid solar installation I routinely fill my batteries, and after doing any high power tasks, like vacuum the rugs, the panels just go idle. To a grid connected system it means you can't sell your power during the solar peaks, but it also means that you have enough capacity to sell more power during the edges of the solar periods. Certainly any business which invests in long lived capital equipment would like to operate it at 100% capacity all the time, but most industries realize this doesn't happen. Solar will adjust. For off grid people "excess" capacity means getting by better on partly cloudy days. I'll probably double my capacity next spring for just this reason.

toomuchtodo 11y ago
Could you dump excess energy into a hot water heater? Preheat with thermal on the roof and with excess solar PV power, and then the final temperature lift with propane or natural gas?
- ChuckMcM 11y ago
  Yes, you can do that. One of the more interesting strategies if you have the space for it is to pump water with excess energy. Pump water from a lower reservoir to a higher reservoir, you can later recover that energy by draining the water through a micro-hydro system. One challenge though is capacity, you would probably want essentially two olympic sized pools, one above the other as your storage unit. PG&E in California does this one a fairly large scale in the Bay Area. Pumping water into the Helms Creek reservoir (https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant https://en.wikipedia.org/wiki/Helms_Pumped_Storage_Plant)
  - AnimalMuppet 11y ago
    And if you can afford having two olympic swimming pools, you can probably also afford the solar installation. ;-)
  - logfromblammo 11y ago
    Pumped storage is not practical for a typical home. A 1000kg mass, raised 1m off the ground, stores about as much potential energy as a single AA (LR6) battery. The only other energy storage technology that is economically competitive with rechargeable batteries [in 2015] is compressed air. A pressure vessel approximately the same mass and volume as a lead-acid battery bank can store about the same amount of energy. It also has a longer useful lifespan and lower maintenance requirements. But the additional equipment required to connect it to your house power system is more complex and expensive. Rather than stacking two giant swimming pools, you would likely be better off burying a giant concrete sphere wrapped in Spectra/Dyneema/UHMW-PE fiber in your yard, and using a thermo-pneumatic engine to fill or drain the energy reservoir.

Natanael_L 11y ago

The idea is that it isn't profitable to focus on building out a network of renewable energy supply when you'll take a short-medium term loss on shutting down what it is replacing. Regarding storage, that doesn't entirely come into play until the big power plants are scaled down enough that your total available supply is less than the usage, which is not the case on most places most of the time. The risk is that you try to rely on renewables when renewable energy supply is at a minimum and load is at a high, and it exceeds your margin. That's when you need to tap into stored energy. Again, you can usually plan against that.

IkmoIkmo 11y ago

So I'm not sure how familiar you are but solar and wind are intermittent energy sources. Particularly solar peaks around noon while usage peaks in the morning and evening, and around noon when everyone is at work, usage is relatively low. So you've got an issue, you generate a bunch of energy that's not being used, so it's thrown away. That means the effective cost of an average kwh of solar electricity goes up a lot because you're not just paying for when you're using it, you're also paying (not really, but in a way when you average it) for electricity that's generated and then wasted. i.e. if I build a machine that produces energy for $1 per unit on average, but half my units are generated when I'm not there (and wasted), my actual average cost per unit of energy is $2. The $1 may be competitive with non-renewables, but because half is wasted, the actual $2 price is not. But of course you don't have to waste it, you can store it, but then you need large amounts of storage and that's not easy or cheap. Take the Tesla powerwall for example, roughly has the capacity to run 1 clothes washer + dryer cycle, and it costs $3k (and doesn't last forever, either). Paying for battery storage for everyone (for when renewables are a big part of total energy production), would put the cost in my hypothetical example somewhere between $1 and $2. For the actual data (rather than my silly numbers above) you're better off using google, there are a ton of studies that look at the kwh premium when running storage in different contexts. A quick back of envelope calculation for example for home-consumer storage prices... the above powerwall, $3k, lifetime of around 3500 cycles, at 7 kwh capacity, you're talking about the ability to store and use about 24.5k kwh of electricity at a cost of $3k before the device dies, or 12c per kwh. Now 12c per kwh is roughly the average price of a kwh in the US, so a powerwall essentially doubles the cost of of any unit of electricity you want store (the excess power solar generates around noon which can become very significant if we increase renewables a lot). Doubling in price for those kwh is massive, on average it makes little economic sense. In Hawaii, it makes total sense because prices of electricity are much higher. But this is a consumer solution, utility scale is cheaper, and some things can be much, much cheaper (like pumped hydro, way cheaper than a powerwall in general, and way way cheaper if you've got the natural resources like Norway does to build cheap pumped hydro capacity). So why not turn off the power plants (e.g. coal/natgas) when solar production is high at noon? Because these plants can take 24-48 hours to startup, they provide base power and you can't just shut them on and off. So yeah, storage is essential and it's not quite there yet. Battery tech has always lagged behind, and now we need it at a massive scale.

lumberjack 11y ago

The quote is talking about a problem the utility companies are facing with the adoption of personal PVs. Right now, the way your electricity bill is structured is heavily biased towards consumption. The service charge is a small part of the overall bill. What happens if 50% of the costumers have PVs is that the utilities will lose a lot of revenue but they will still have exactly the same amount of costs because they are not able to turn down their plants during the day and the PV people will still consume the same amount of peak grid energy during the night. So there is two ways to fix this. One of them is for the plants to downsize their constant power generation methods like coal fired boilers and get a bunch of gas peaker plants. The other one is to increase the service charge on your electricity bill.

jws 11y ago
This gets into the other billing problem with domestic solar. In rough numbers, half of your electric bill is for energy, the other half is to pay for all the grid and capacity. Billing is purely on energy consumption. The effect of this is that low electric users get subsidized by high electric users. When someone installs a domestic solar system they reduce their payments, but they still depend on the grid infrastructure. The system reaches its ultimate perversion when a grid tied domestic user achieves a negative bill. Not only have they been paid for their energy, they have been paid for the utility having a grid. You can solve this economic distortion by a couple of ways: • split billing into a grid-tie fee and an energy consumption charge: This accurately covers the solar houses, but it also raises the bills of the poor and cuts those of the wealthy (generally larger consumers). • only pay domestic solar producers half what you charge for power: This works out asymptotically for a huge producer where the grid portion vanishes, but it doesn't work for people reducing their consumption but maintaining a grid tie or selling a little bit. • put a surcharge on each watt of solar capacity: This works out accurately, but feels abusive. 1 watt of solar panel is going to make about 100 wHr of power a month. If grid-tie privilege includes a surcharge to cover the grid portion of 100wHr then this 1 watt solar panel user will end up paying the same for the grid as he did before. If a domestic solar installation is a net producer, it will end up getting paid for the energy and the grid fees will cancel. Even before we get to a point where the power company may say "no thank you" to a domestic user that wants to sell power at 1pm on a sunny day, we still need to straighten out the billing. The current system ends up with the utilities (and by extension all grid users) subsidizing solar installations by forgiving their grid costs. I'm in favor of that now, but in a future where our carbon emissions are under control the distortions will need to be smoothed out.