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By Geoffrey Styles on Feb 12, 2014 with 22 responses

Can Solar Fill the Hydropower Gap During California’s Drought?

Solar Is Growing, But Hydro Remains Much Bigger

A tweet this morning sent me on a fact-checking expedition into state-level  electricity statistics. The subject was a San Jose Mercury article with the unwieldy title, “Drought threatens California’s hydroelectricity supply, but solar makes up the gap.” The article’s quote from the head of the California Energy Commission implied that solar power additions were sufficient to make up for any shortfall in hydro, historically one of the state’s biggest energy sources.

My gut reaction was to be skeptical: Solar has been growing rapidly, especially in California, but even with nearly 3,000 MW of photovoltaic (PV) and solar thermal generation in place, it’s still well short of the scale of California’s 10,000 MW of hydropower dams, especially when you consider that the latter aren’t constrained to operate only in daylight hours. However, I also know better than to respond to a claim like this without checking the data on how much energy these installations actually deliver.

The Comparison Has Shifted In the Last Year

My first look at the Energy Information Administration’s annual generation data seemed to confirm my suspicions. In 2012 California’s hydropower facilities produced 26.8 million megawatt-hours (MWh), while grid-connected solar generated just 1.4 million MWh. However, when I looked at more recent monthly data, the mismatch was much smaller, due to solar’s strong growth in the Golden State. For example, in October 2013 California solar power generated 435 MWh, or nearly 24% of hydro’s 1.8 million MWh.

The potential drought benefits of solar stand out even more sharply when we compare the growth in solar generation to the change in output from hydro. On a January-November basis — December 2013 data isn’t yet available — solar electricity in the state increased by 1.5 million MWh, compared to the same period in 2012, while hydropower fell by nearly 1.8 million MWh. That added solar power won’t provide grid operators the same flexibility as the lost hydropower, because of its cyclical nature, but it is clearly now growing at a rate and scale that makes it a serious contributor.

The Benefits of Installing Solar Where It’s Sunny

I’d be remiss if I didn’t point out that solar in California is still nowhere near the scale of the state’s biggest electricity source, natural gas generation, which in that same 11-month period produced over 93 million MWh, or 56% of the state’s non-imported electricity supply. It’s mainly gas that is filling the roughly 18 million MWh shortfall left by the early retirement of Southern California Edison’s San Onofre Nuclear Generating Station last summer, and if the state’s drought worsens, gas will be the main backup for further declines in hydropower.

Yet solar’s growing contribution to the state’s energy mix provides a clear demonstration that while generous state and federal policies can make installing PV economically attractive nearly anywhere, it’s abundant sunshine like California’s that makes it a useful energy source, especially when drought conditions reduce the output of other, water-dependent energy supplies.

  1. By Forrest on February 13, 2014 at 2:27 pm

    Interesting, the solar energy progress in that part of country. The future of solar appears to be very positive. Hopefully, they won’t break the treasury trying to force rapid adaption of this developing energy sector. It’s better for the industry and country to have steady state progress than race to implement. Going a bit slower, with better plans, equipment, and technology is more attractive and reflects better on solar as compared to race ahead per some easy money no risk government investment. Good to support the budding development of this technology, but not good to attempt to push poor solutions to game the easy money. Better to let the energy markets do some of the decision making. Biggest problem of solar and wind is energy storage and with out such solution to rely on back up generators that are more expensive and pollute more. Uncontrollable Intermittent power not that valuable. California may be able to produce more dependable solar, unlike wind turbines that infamously quit on highest peak loads of summer. I just read an interesting article on concentrated solar power achieving 40% efficiency. It appears to be a thermal device and can store energy easier to level load electric production. That technology sure would be attractive. It may be a mistake to waste natural gas per stationary power plants. It is best utilized per transportation sector, household, and business use. Coal and nuclear still should be in the mix as our coal reserves are huge and nuclear will continue the best large energy source for future. Example, the news on successful fusion reaction under laboratory control.

    • By Forrest on February 14, 2014 at 2:32 pm

      Thursday, a ribbon cutting celebration of new concentrated solar power plant at Ivanpah solar electric generation station. What I posted above of pushing the technology per rapid deployment a waste of taxpayer money…applies here. Some of the points of interest: The plant costs 4x more than traditional gas power plant, but produces less power, and requires much more land and produces electricity at 2x the cost. They spent $15,700 per home equivalent for the 140,000 home power or $2.2 billion for the station. A five mile square land mass loaded with 350,000 mirrors directed to towers to power steam turbines.

      I think the post from the editors corner of this site is spot on. Were distorting true cost of green power per tax credits, federal loan guarantees, state tax incentives, accelerated deprecation, etc.. How about an honest cost engineering evaluation of the process? Lets not get into the commercial phase of energy production until the pilot phase is cost effective. BTW I think too many are emotional invested in solar or wind and can’t be objective. When the math doesn’t add up they always hype the earth destroying CO2 gases floating about. I read an article that claimed the simple wood stove and pellet stove has accomplished more at cost saving to consumers than the combined solar and wind energy per the environmental improvement. Guess it’s not sexy enough to those on the hunt for change?

      • By JonathanMaddox on April 29, 2014 at 1:21 am

        > Lets not get into the commercial phase of energy production until the pilot phase is cost effective.

        Sure-fire way to ensure nothing new ever competes with incumbent technologies. Mass deployment can reduce costs dramatically, so modest subsidies have realised enormous benefits.

        • By Forrest on April 29, 2014 at 7:04 am

          Industrial engineering studies can account for future mass production efficiencies to compare costs. They could have built a large pilot plant, instead a $2 billion commercial utility class power plant. The cost vs production is way out of whack for wasting taxpayer money. This would have been easily understood by businessmen whom had responsibilities of investor’s money. It’s a fun project to not be accountable for cost. Much to talk about and impressive to see. Probably a win for political ambitions and public can be hood winked into easy talk of investing in future. Per economic terms, their is limited quantity of precious capital within economy. Capitalist economies are very efficient in allocating precious resources to best ROI. IOWs making money work harder and creating an efficient economy. Central control government decision making is horrible inefficient. Their motivations opposite and not cost responsible. They easily spend other peoples money to earn popularity. The public thinks federal spending is magic and with deficit spending unlimited.

          • By JonathanMaddox on April 29, 2014 at 9:19 am

            I wasn’t speaking to US federal government largesse, but to directed subsidies in general and to subsidies for deployment of wind and solar PV in numerous countries of which the US is only one. Thanks to those subsidies, new-build onshore wind now has a lower LCOE than that of any new-build dispatchable power station. Solar PV isn’t there yet due to its modest hours of operation, but it does generate plenty of power in times of peak demand in sunny climes, beating the peaking generators of just a decade ago out of sight. It’s entirely conceivable that solar PV *will* reach the point where its LCOE is lower than that of traditional generation, thanks simply to mass deployment with modest subsidies.

            The US federal government is quite capable of judicious directed investment into R&D, pilot programs and directed mass-market subsidies when it chooses. It’s also capable of enormous boondoggles such as laser missile shields and requiring the use of vast quantities of over-proof corn whiskey (not to mention then-nonexistent cellulosic ethanol) in internal combustion engines. Ivanpah may not have represented the best possible bang for the taxpayer’s buck, but it sure beat Range Fuels, Solyndra, or your average foreign war.

            • By Forrest on April 29, 2014 at 11:20 am

              Use of federal tax funds can dovetail with expensive R&D efforts. Same with regulations per stabilizing market share, or to calm the waters a bit for increase success. Corn whiskey one of the few successful alternative fuels within the market. Cellulosic ethanol just getting started, but has evolved from pilot, commercial, to production stages. Range fuel, apparently not within that zone. There are two competing or complementary processes that hold most value for future. Enzyme process and solvent process from MIT and UW-Madison. Two or three companies within production mode this year utilizing the enzyme process. Enzyme development companies claim they are targeting 100 gallon ethanol per ton biomass in near future. Conversion efficiency catching up to corn. The solvent process is a cheaper and quicker process with higher yield if process can be industrial controlled. The grass plants of which corn is one hold the most value for biomass production. Target is 20t per acre per year.
              The LCOE term was a new one for me, per my cost studies. They claim “In other words, it’s like averaging the up-front costs across production over a long period of time.” My comment…because of high investment cost, low utilization, the proponents of wind energy have invented a new measure that awards itself maximum rating. First the critical investment cost or time value of money is regimented to simple division of useful life. Wouldn’t we all like that trick when paying mortgages. Then there is the entry “Investment tax credit 30%” that completely obliterates a fair apples to apples comparison of cost of energy. The apples to apples cost numbers average citizens think of when reading wind energy is on par with coal or natural gas.

            • By JonathanMaddox on April 29, 2014 at 7:04 pm

              LCOE *includes* the cost of finance so your mortgage quip is quite out of place. It’s a calculation of the unsubsidised cost of power from newly built electricity generation, which means it *is* an apples-to-apples comparison, but obviously it doesn’t factor in the incumbent price advantage of older and long-amortised power stations. Also of course wind technology has improved quite dramatically in the past 15 years. New-build wind, unsubsidised, really does produce cheaper power than new-build coal or gas.

              You’re right that the LCOE metric makes intermittent renewables look good, which is why you find advocates quoting it a lot, but the calculation certainly wasn’t invented for that purpose. It may have been *renamed* to include distributed generation, however. LCOE used more commonly to be known as “busbar cost” and you would see phrases like “constant dollar levelized plant busbar generating cost” in cost analyses for nuclear power stations long before wind was remotely competitive. The word “busbar” doesn’t literally apply to smaller distributed facilities like wind turbines and rooftop solar panels, so the LCOE term has come into wider use along with these technologies.

              LCOE doesn’t include any sort of penalty for electricity being generated when there isn’t any demand for it or for there being insufficient power at times of peak demand, but then it never did that for baseload generators either which were operated at full capacity day and night regardless of actual demand. Meeting peaks and finding things to do with generation in excess of demand has always been considered separately. Peaking generators get an LCOE metric too. Storage facilities, not so much, but quite a few still got built :-)

              I realise that cellulosic ethanol exists now, but it simply *didn’t* exist beyond pilot scale when the US federal government first mandated its consumption circa 2008.

            • By Forrest on April 30, 2014 at 8:00 am

              The LCOE has many variants. The business models for grid and commercial published by NREL have cost of debt calcs and ROI inputs. The residential calcs for solar proponent web sites did not. I reviewed three spread sheets with increasing complexity for LCOE evaluations and no cost of money or ROI concerns. The basic enhancement of this investment model is to level cost over life expectancy of turbine. This make expensive purchases shine brighter if low fuel costs. It’s not the ultimate exact accounting tool, just another way of looking at investment. It would be wrong to us LCOE analysis cost as a general claim. The example given for utility investment based on 30 year lifespan. The input 20 cents per kwh sales price. Wow, I’ll generate power for that price. The real LCOE cost is 16.4 cents per kWh. The $51 million dollar investment receives a nice ROI of 15% thanks to investment tax credit of $15 million and fed and state tax savings of $20 million. The biggest reason for increasing competitiveness of wind energy is the dirt cheap cost of money, hefty credits, tax savings (investors offset high earning otherwise pay high tax rates) and outrageous sales price of environmental power. The real open market prices of uncontrollable power at 50% of baseline power. Don’t discount the hefty tax savings of lousy investments. This is not a good barometer of national encouragement; Just the opposite. Read the editor’s corner article on this web site upon the frustration of a bio fuel business owner completely frustrated on the U.S. making all competing alternative power generators uncompetitive per government regulations, subsidies, tax saving, tax credits, etc. This insider claims wind energy is 6x higher than promoted. Interestingly enough, just read another CO2 comparison of PV vs the pellet stove. The lowly pellet stove outperformed the PV system 3x yet receives no easy government money incentives.

            • By JonathanMaddox on April 30, 2014 at 11:17 pm

              Your assessment indicates that you’re reading very different references from the ones I’m looking at.

              I don’t see the sale price of power as an input to these LCOE calculations by the Energy Information Administration


              Or these ones by the OECD


              Or these ones by the European Commission


              It’s a metric of gross cost (though the EIA does have another column for LCOE net of subsidy, which I found curious). Retail and wholesale electricity sale prices don’t enter into the calculation.

  2. By Russ Finley on February 15, 2014 at 2:40 pm

    As you note, it is natural gas that is primarily taking over for nuclear and hydro. Solar can make a significant contribution but only in sunny places …and in a grid that has enough natural gas or hydro peaking power plants to take over when the sun does not shine.

    I’ve said this before …solar is best viewed as a component of a hybrid natural gas/solar power plant, where solar reduces fuel bills when there is enough sun. Solar reduces fuel costs but increases the cost of the total gas/solar hybrid system. In the chart below, note the relatively small role the NREL expected for solar photo voltaic to play in their 80% renewable electricity study. Note in the next chart the thin yellow line representing solar.

    I bring that up only to counter all of the misinformation out there suggesting that solar and wind are capable of doing it all. They both have a long way to go before reaching their limits of usefulness, but that limit is well short of providing the majority of our total energy needs. People should understand this and give some thought as to what power sources they want to fill in where wind and solar can’t.

  3. By Wayne Lusvardi on February 16, 2014 at 12:10 pm

    This writer completely omits the emerging “Duck Chart” problem in California caused by gradually shifting from natural gas to solar power for daytime baseload power. The Duck Chart is a visual depiction of the energy usage profile during day hours. As solar kicks in early in the morning conventional energy usage dips and then about 4 pm as the sun sets conventional energy has to ramp up to take over. The visual picture looks like the tail of a duck in the early morning, like the belly of a duck in the afternoon, and at the end of the day it looks like the beak of a duck (or like an elongated “U”). The problem is that by 2015, the California grid operator will have to start dumping solar power that was paid due to green energy mandates and switching fast to gas power. The natural gas powered plants will have to sit idle all day waiting for this 3 hour window from 4 pm to 7 pm when it will have to resume supplying the grid. This results in very high prices for gas power from 4 pm to 7 pm because nat gas becomes in high demand during a very short period of time. So solar has free fuel cost during the day but the cost savings is merely shifted to very high natural gas prices at the end of each day. With the installation of smart meters this means customers will have to change their lifestyles (no watching Monday Night football unless you can afford it, no late night soccer practice under the lights that will be prohibitively expensive, no turning on electric gadgets until after 7 pm and sometimes until 10 pm, convalescent homes will have to turn off TV sets, etc). For 3 to 5 hours per day California will become like Cuba or North Korea for at least those households which can’t afford the electricity price shocks. Wealthy households won’t feel the price shock. This is going to create a 4 hour mini-energy crisis every day especially during the shoulder months of Feb-March and Oct-Dec. So California’s grid operator is trying to create what is called an “Energy Imbalancing Market” (a misnamed term which sounds like the grid operator is trying to imbalance the market. A better name would be energy rebalancing market). This is a maneuver to try to find cheap, clean hydropower from federal owned dams along the Columbia River or from the Colorado River. This creates another problem of grid congestion. So many megawatts of power have to be shipped to California in such a short time window that if the gird is congested (say due to cold weather or an unplanned outage) then California could be in for some very politically explosive reaction to such high electricity bills. Moreover, what if some of the out of state hydropower suppliers don’t want to sell their power to California from 4 to 7 pm EVERY day? Or prolonged drought precludes spilling water to spin hydroelectric turbines? California’s new green power system is muddling through and it is uncertain if it will work despite the tremendous expertise of the California grid operator. So puffing up solar power investments sounds great but California’s green power system is being cobbled together on the fly.

    • By Geoffrey Styles on February 18, 2014 at 10:36 am

      I’m aware of the “duck curve” and share some of your concerns, though it’s a stretch to compare the situation in CA to Cuba or N. Korea. Germany is a more apt comparison, and I hope CA regulators (and voters) are paying close attention to developments there. The clear lesson is that when you achieve high renewable penetration through subsidies that are transferred outside the normal power market–in their case through surcharges on consumer but not industry electricity bills–you drastically alter the functioning of the market and impair the economics of any generation with fuel costs, no matter how essential it is to the reliability of the grid. Forcing CCGT plants to run as peakers will, as you note, result in higher full costs which, if not recovered in the power market, will result in loss of capacity that can come back to bite when wind and solar output hits cyclical or seasonal lows.

    • By jdeely on February 18, 2014 at 11:51 am

      The “duck curve you mention is definitely going to be an issue. These peak hours are definitely the a tough problem that needs to be solved.

      However, not sure if that automatically translates into “very high prices” when gas plants kick-in. Remember, the amount of overall gas used in CA should decline dramatically when solar reaches penetrations described in duck curve problem. So the price of natural gas in CA may be cheaper. However, as Geoffrey mentions below using CCGT plants as peakers may result in higher costs from the plants themselves. It will interesting to see how this tradeoff will work.

  4. By Forrest on February 17, 2014 at 9:27 am

    The last graphic Russ had attached depicts a problem with electric generation. Notice the fat arrow of energy in to power plant generators and the small path of electric out. So, electric power is high value energy, hard to produce, and should be utilized only upon those processes/devices that are constrained to electric power, i.e. lights, coffee makers, and computers. The grid is a very polluting energy source per the low efficiency of energy conversion. So, this would infer an improvement to our energy efficiency in which will lessen environmental harm is to quit using electric for heat as this function is better preformed by other means. Instead, switch to natural gas,
    propane, and biofuel. Change the clothes dryer, hot water heater, and stove to
    natural gas or propane. Change the home heating to biofuel. This would be an improvement to our cost of energy and environment.
    Notice on Russ’s graphic the arrows going into business, industry, and households
    are almost the same size as the arrows going out. This depicts good energy
    conversion efficiency. The electric power is almost completely efficient (less
    line loss), but we must acknowledge the waste is just a dislocation upon power
    plant operation as the grid is really an inefficient energy source, hard to
    balance, require idling capacity, requires expensive distribution, and upkeep.
    Appears, the pipelines and biofuels suffers little of this.
    Also, the graphic depicts how efficient heat generation is as compared to
    electric and transportation. In fact heat is so easy to produce most of it is
    just waste product from electric production and transportation. So, we have a
    huge disconnect between waste heat and valuable heat. This appears to be of immediate concern, a free energy source, and directly impacting pollution. Wouldn’t
    capturing waste heat be a more productive use for our investments as compared
    to costly changes of wind and solar? Wouldn’t the grid imbalance diminish by
    diverting the morning and evening consumption of energy required for heating to
    other sources? We can even power our A.C. compressor per natural gas or propane
    at a very efficient rate as the waste heat can be captured for free hot water
    per engine exhaust, cooling water, and waste heat of condenser. Same for home
    generation of electric power where upon the waste heat utilized for hot water
    and home heating needs. We need to always produce electric where there is a
    need for heat as it’s usually a waste product. Solar and wind probably would be
    easier to accommodate as this inside out grid production of power is more
    flexible, rigorous, and suffers little start up loss.

    • By Geoffrey Styles on February 18, 2014 at 10:16 am

      The phenomenon you’re describing at is the basis for CHP, or combined heat and power generation and applications. Thermal efficiencies of CHP are very high, in some cases over 80%, compared to 50s for CCGT and 30s for coal and older thermal plants. However, the environmental tradeoffs for some of the switching you’re suggesting aren’t as straightforward, especially re biofuels. At this point we have only crop-based biofuel in any meaningful quantity, and those compete with both petroleum liquid fuels and with food production and prices. If there’s only a couple billion gallons a year of biodiesel available, what’s its best use? Displacing petroleum diesel and heating oil, or displacing electric heating, especially if the local power grid has ample low-emission generation from hydro, nuclear, etc.?

      • By Forrest on February 18, 2014 at 1:58 pm

        Honda’s CHP system advertised 94%peak when using all the thermal. These simple single cylinder generators are not that complicated and stand on mature tested technology. They could be mass produced with ensuing drop in cost. Maybe the water heater producers will add a CHP lineup?

        The environmental trade offs of substituting electrical energy with more efficient NG home energy seems an easy choice, as the home efficiency beats the grid generation of power mightily in current condition. Gas stoves about 100% efficient for heat, in winter as compared to coal plants 30s efficiency and I can cook with the stove when electric is down. The electric stove use correlates well with electric spike in morning and evening. Gas water heaters and dryers are more efficient by far as compared to grid power, and in the process save environmental CO2, save consumers $. They should be marketed per easy pickings environment improvements.

        Maybe I should have written biomass instead of biofuel? We have enormous reserves of biomass. Much of it wasted upon decay and contributes to CO2 load. Our western and Canadian pine forests have been stricken. They are contributing massively to global warming gases, for example. Pelletizing densifies biomass resulting in standardizing BTU / pound i.e. bark about the same as oak wood. Switch grass per pound about the same as oak wood once produced into pellets. The main difference is ash content. Michigan State University is working on biomass energy with the production concept of pelletizing for use either upon cellulosic ethanol processes or pellet fuel for thermal. It’s easier to store, transport, and create a market exchange with pellets. Also, the next generation of pellet stove in the works, resulting in almost zero particulates and higher efficiency’s, 70-80s. Biomass is extremely environmentally friendly and best choice for the easy task of producing low grade heat. Why waste precious electricity on such an easy task. Natural gas best saved for more demanding tasks as well. Teaming up a CHP water heater, pellet heater, and home solar seem to be a powerful trio. Consumers may balance load with PLC programmer much like industry does. These process controllers not that expensive anymore. Water, heat, electric, may work in harmony with homeowner habits, and solar production. Maybe we have a smart phone ap for that?

  5. By jdeely on February 18, 2014 at 11:45 am


    Good article. Here are a couple of additional items to consider.

    1) I don’t believe the EIA is a good source for solar data- or any distributed energy for that matter. They collected the data you use in comments above by using form EIA-923 –

    If you look at the instructions in this form you will see the following:

    “The Form EIA-923 is a mandatory report for all electric power plants and CHP plants that meet the following criteria: 1) have a total generator nameplate capacity (sum for generators at a single site) of 1megawatt (MW) or greater;

    Many of the grid-connected solar systems are smaller than 1MW and are therefore not reported.

    So for example, in your October 2013 example you mention that solar generated 435,000 MWh (by the way you have a typo- forgot thousands). The CAISO data for October shows 580,000 MHh for October and CAISO does not include all CA (no LADWP, SMUD etc). I have seen 20% as a number for area not covered by CAISO. So in reality all grid- connected solar for October in CA might be closer to 700,000 MWH. These are small numbers in the bigger scheme of things but moving forward they will be more important.

    2) You didn’t really mention behind the meter(mostly rooftop) solar – Estimates are that this resource is now at about 2,000 MW and growing fast.

    This summer there will be at least 6,000 MW of Solar in CA. (4,000 grid and 2,000 rooftop)

    • By Geoffrey Styles on February 19, 2014 at 12:35 pm

      Thanks for spotting that typo. Consistency of solar data is something that needs to be addressed as the technology grows. However, I’m not sure I would have counted rooftop solar in this discussion, because it functions more like a demand-side measure here; it’s not a dispatchable source for the grid to fill the gap from hydro.

      • By jdeely on February 19, 2014 at 6:12 pm

        “However, I’m not sure I would have counted rooftop solar in this discussion.”

        Sorry, I must have misinterpreted what you meant by “hydropower gap”. When you said:
        “In 2012 California’s hydropower facilities produced 26.8 million megawatt-hours (MWh), while grid-connected solar generated just 1.4 million MWh.”
        I thought you were emphasizing the total amount of carbon-free electricity from Hydro that would need to be replaced in order for gap to be filled or as you said very nicely “how much energy these installations actually deliver.”

        In 2014, CA will actually deliver about 10M megawatt hours(MWh) from grid solar (via CAISO) and an estimated 4M from behind the meter solar for a total of 14M. So solar is already “in the ballpark” with hydro.

        Eventually(within 10 years) the behind the meter will generate the equivalent of what hydro did in 2012(>26M). That’s why I think it is important to count it.

      • By JonathanMaddox on April 29, 2014 at 1:31 am

        The flexibility and dispatchability of hydroelectricity are unaffected if the head of water can be conserved by reduced demand at what would otherwise be peak hours of generation. Hydro can still be dispatched at full capacity for the hours of the “duck head”.

  6. By TimC on February 18, 2014 at 1:24 pm

    Good breakdown, Geoffrey. I’ve been hearing more and more about the “power to gas” (P2G) energy storage vector. This approach uses off-peak renewable electric power (solar, wind) to generate compressed H2 or CH4, which can then be injected into existing natural gas pipelines. There are already a number of projects underway in Europe, and some analysts are predicting this will break big in the US over the next couple of decades. Efficiency is not great, but P2G leverages existing infrastructure to integrate renewable and NG power generation in a way that meets renewable energy mandates with moderate capital costs. Do you know if California is exploring this approach to solar energy storage?

    • By Geoffrey Styles on February 19, 2014 at 12:32 pm

      My understanding is that California’s initial energy storage mandate for utilities is technology-neutral. That’s much better than pushing any one technology like P2G.

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