AndyH said:
RegGuheert said:
If you need to store the energy for a month or more, then it seems likely that H2 will be more resource efficient than batteries.
And you
get the Kewpie doll. Glad you grok that we need BOTH kinds of music...er storage...here - country AND western...
Saying that H2 fuel-cell technology is more resource-efficient for long-term energy storage than batteries does not imply that we need H2 fuel-cell technology for long-term storage. That is a non-sequitur fallacy equivalent to saying "If A is better than B, then we need A". That reasoning ignores C, D, E, F, etc.
So the question becomes "Do we need energy storage (long- or short-term) if it means converting 2/3 of the electricity produced directly to heat?"
Like all technology applications, you need to work within a scenario to determine if it makes sense or not for that scenario. Since I'm most familiar with my own personal energy scenario, let's take a look at that an see if that kind of energy storage would make sense. (And, no, I'm not going to try to say that our energy consumption is typical, even for this area.)
Here is the current situation:
Annual electricity consumption: ~19.2 MWh (All household erergy needs, including space heating, plus most transportation.)
Annual electricity production: ~18.3 MWh
Current energy storage type: Net metering
Energy storage capacity: As much as I need for up to 12 months
Energy storage efficiency: ~98% (I'll allow for some losses within the wiring on our side of the meter.)
Annual gasoline consumption: 250 gallons
Annual Propane Consumption: 100 gallons (Cooking only)
Other: There is a lot of energy embodied in many of our possessions. That is important, but let's start without them for this post.
Notes:
- Heat is provided by a modern (~2008) Heat pump with a HSPF rating of 8.2. (Annual heating COP of ~2.5, but much lower in very cold months.)
- House was built in 1995. Insulation is fairly typical for this area. Certainly it is not anywhere close to German Passivhaus!
- Hot water is provided by a heat-pump water heater that sits next to the air handler for the home heat pump. (That room needs to be cold for food preservation, so that's not a big issue in the wintertime.
- Most transportation is handled by the LEAF.
I think we all know that net metering is not *really* storage and that our PV system does not *really* meet practically of our electricity needs, since it does not provide any of the electricity that we need at night nor does it provide all of the electricity that we use during four-to-five months of the year. Even during the daytime, our home sometimes consumes electricity from the power grid. Unfortunately, while I have production information on an every-five-minutes basis, I have very poor consumption data due to the fact that my utility does not report meter readings which are lower than the most recent high-water mark. In other words, I can only see my consumption in the months when we consume the most electricity.
Here is a table showing monthly production, consumption, net monthly and net yearly energy usage (currently provided by net metering):
Code:
Month Prod. Cons. Month Year Units
---------------------------------------------------------------
January 1000 2600 -1600 1100 kWh
February 1300 3000 -1700 -600 kWh
March 1500 1800 -300 -900 kWh
April 1700 1000 700 700 kWh
May 2000 1000 1000 1700 kWh
June 2000 1200 800 2500 kWh
July 1900 1400 500 3000 kWh
August 1800 1200 600 3600 kWh
September 1600 1000 600 4200 kWh
October 1300 1000 300 4500 kWh
November 1200 1800 -600 3900 kWh
December 1000 2200 -1200 2700 kWh
---------------------------------------------------------------
Totals 18300 19200 -900 4500 kWh
The bottom line is that net metering "stores" over 4 MWh for months and provides an additional ~1 MWh of energy for consumption.
Scenario: Net metering disappears and grid electricity simultaneously becomes either not available or not affordable. In other words, I need to move ALL electricity off-grid.
Question 1: In that scenario, would a storage solution which converted 1/6 of the energy to heat upon storage and 1/2 of the energy to heat upon conversion back to electricity make sense as a part of the solution? If so, how much storage of that type would be needed (in kWh)?
Question 2: In that scenario, would a storage solution which converted 1/20 of the energy to heat upon storage and 1/20 of the energy to heat upon conversion back to electricity make sense as a part of the solution? This later storage solution is cheaper (in both resources and money) than the other previous solution storage, but becomes more expensive if you need to store the energy for more than two weeks. If so, how much storage of that type would be needed (in kWh)?
Assumptions:
- Burning fossil fuels to provide heat or hot water is not allowed.
- Let's look only at current electricity consumption for now, not gasoline or propane.
- PV generation is reliable and still available for consumption, even if/when it is not used.
- Consumption needs remain the same, except in the area of space heating, which may be addressed by insulation or non-electrical solutions.
- The EV can be used for household electricity storage needs.
Approach 1: Build more generation and use only short-term storage (<1 week) to meet my energy needs. That approach would require approximately tripling the area of the PV array and adding batteries for short-term storage. The cost would be about $40,000 for the PV and over $60,000 for batteries. (I used 200 kWh at $300/kWh.)
Approach 1 Total: ~$100,000
Approach 2: Insulate to cut heat loss by half. That approach would require doubling the area of the PV array and adding batteries for short-term storage. The cost would be $20,000 for new windows and insulation, $20,000 for more PV and $30,000 for batteries (I used 100 kWh at $300/kWh).
Approach 2 Total: ~$70,000
Approach 3: Build more PV and use a long-term storage solution. Long-term storage electrical efficiency is about 1/3, but I would be able to get back another 1/2 of what I put in as heat (what is needed in wintertime). The heat pump COP drops down to 1.0 in very cold temperatures, so waste heat would be just as valuable during those few days, but less valuable on warmer days. If we say that waste heat can cover about 1/2 of the shortfall, then that leaves about 2.25 MWh of electricity needed (after conversions), or about 7.5 MWh of extra electricity production (instead of the 4.5 MWh extra currently produced). Plus another 1 MWh is needed for the original shortfall. The cost would then be ~$5000 for additional PV, $30,000 for batteries (I used 100 kWh at $300/kWh) and $60,000 (I'm guessing) for an electrolyzer (a small one: ~500W), compressor (also small), storage tanks and co-generation fuel cell with electrical output power of 5 kW plus BOM.
Approach 3 Total: ~$95,000
Approach 4: Insulate to cut heat loss in half AND use a long-term storage solution. In this case, I doubt that additional PV would be required and battery storage would likely be cut in half. The cost would be $20,000 for new windows and insulation, $15,000 for batteries (I used 50 kWh at $300/kWh) and $40,000 (I'm guessing) for an electrolyzer (a small one: ~500W), compressor (also small), storage tanks and co-generation fuel cell with electrical output power of 3 kW plus BOM.
Approach 4 Total: $75,000
Some conclusions:
- I like net metering!
- With net metering, PV is less expensive than insulation for wintertime loads, giving little incentive to insulate. The PV *does* reduce the fossil-fuel load in the middle of winter, but not as much as more insulation would. But PV reduces the year-round fossil-fuel load more than more insulation would.
- Without net metering, insulating the house is the cheapest solution.
- Even with additional insulation, dealing with heating in the wintertime is a costly endeavor. More PV and batteries are comparable in cost to hydrogen storage in cost, but they offer massive benefits over the hydrogen solution if the PV is still connected to the grid. In Approach 2 an additional 10 MWh of energy is available to the grid from the additional PV. The question would then become "What to do with all that extra energy in the summertime around here?" Hydrolyze water is probably the best answer, since I think the peak loads occur in the wintertime (though I could be wrong).
- In my scenario, renewable generation is not limited by resources, meaning that approaches 1 and 2 are both realizable. But this is not generally true, which indicates that, in particular, approach 4 would be preferred in the primary case in which renewable resources are extremely limited.
- In areas where the wintertime load is not dominant (like CA), I doubt hydrogen would look as attractive. In fact, when loads peak during the summertime, then I think PV and batteries is much more attractive. Batteries can efficiently time-shift renewable energy within the shorter timeframes needed for those cases.
- But there are much colder places than here, so in those cases, I think the hydrogen solution would have a leg up, for the opposite reasons.
The bottom line is that while PV has matured to a nice level (and is still improving), BOTH batteries AND fuel cells have a way to go before they can replace what we have been doing. But I do see that any solution using just PV and/or wind and batteries in my climate is going to eventually have unused capacity during at least a portion of the year. If that extra production can be stored through electrolysis, then there is a role for hydrogen. I doubt hydrogen will become "too cheap to meter", but its cost should come down.
