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Lorrainelovesplants
Joined: 13 Oct 2006
Posts: 6521
Location: Dordogne
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Lorrainelovesplants
Joined: 13 Oct 2006
Posts: 6521
Location: Dordogne
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Slim
Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)
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 Posted: Tue Jul 25, 17 3:21 pm Post subject: |
 
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| Quote: |
A kWp is the kilowatt �peak� of a system. This is a standardised test for panels across all manufacturers to ensure that the values listed are capable of comparison. The test conditions for module performance are generally rated under Standard Test Conditions (STC) : irradiance of 1,000 W/m2, a module temperature at 250C and a solar spectrum of AM 1.5. This spectrum can be found here, but is unlikely to be of any interest to anyone outside the industry. Suffice to say that it is a standardised test.
When the solar PV panels are working they will over an hour convert the suns irradiance into energy, which is measured in kilowatt hours (kWh). A PV system with a kWp of 3kW which is working at its maximum capacity (kWp) for one hour will produce 3kWh. |
https://www.evoenergy.co.uk/blog/18514/what-is-a-kwp-and-how-does-it-relate-to-kw-and-kwh/
To put it in a relatable manner, I have a 3.3 kwp system on my garage. It has never produced more than about 2.5 kw at any given time. I'm on the grid, so it's a bit different than what you're trying to figure.
Over the course of a day my system has produced between 3 kwh (a very rainy yesterday) to just under 22 kwh on a clear cool day in June.
Your 9 kw figure for hot water seems awfully high to me. Is that a tankless on-demand water heater? I think you'd want a tank to store heat (and therefore require longer time with less power, as a standard water heater only draws like 5 or so kw, or better yet a heat pump hybrid hot water heater. (or even more likely a gas water heater, as I think that's the most common for off-grid applications)
Electric water heat makes the most sense when you're on the grid.... |
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Lorrainelovesplants
Joined: 13 Oct 2006
Posts: 6521
Location: Dordogne
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Slim
Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)
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Slim
Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)
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| Posted: Tue Jul 25, 17 3:44 pm Post subject: |
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We'd probably be able to provide better advice if we knew more about the motivations, and limitations, etc...
Is a grid tie-in impossible? (I don't know UK net metering laws, but over here I think it's preferable to be tied-in to the grid, personally)
Is this more of a philosophical quest to produce all of one's own power?
Is it about living somewhere that would be mostly inaccessible and therefore prohibitively expensive to be tied-in to the grid?
Over here there are plenty of off-grid folks that power most of their lives through propane. (lamps, refrigerator, etc....) That's not really the same as someone who's trying to reduce their carbon footprint.
If trying to go 100% solar with no grid back up, I would shift as much heating (living space and water) to gas combustion as possible, simply because it's impractical to attempt to store that much energy in batteries for long dark winter months.
I am on the grid with a good net-metering system, so I use the grid as my "battery". Right now we've got over $100 in credit from the power we've sold back to the utility, and we'll use that to make up for whatever electric we use in the winter months that we don't directly off-set with our generation in those months. |
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Lorrainelovesplants
Joined: 13 Oct 2006
Posts: 6521
Location: Dordogne
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| Posted: Tue Jul 25, 17 3:59 pm Post subject: |
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So, all theoretical. Im doing a book and HAVE to include some stuff on self sufficiency.
Some of the stuff Im quite happy with. Some, Im very unfamiliar with.
So, rainwater harvesting, sand filtering UV treatment - yes - I understand it, I get it and can recommend it.
We dont have mains gas here (like a lot of Cornwall) so we have 2 heating & hot water systems that run independently.
The first is LPG bulk tank to a combi boiler and 8 rads. This gives HW and heat. Its quite expensive, but can be timed efficiently. We actually only use it in the mid winter.
The other system is a solid fuel woodburner with a back boiler which heats our main room, gives us loads of HW and also runs 5 rads. This is the system we use the most as our firewood is free.
I have to look at solar PV and discuss the options in the book.
I have to look at solar hot water (which I think everyone should do), and when we move imminently to France we will be doing.
Ive looked a little at ground source heat - Im not really up to speed on this, but it sounds good. I'd like to know more.
Ive just had a chat with John, who is more technical than me. He explained about solar electric, the inverters, the batteries etc.
I think my advice to anyone contemplating living off grid in a wood or on an island or whatever would be to forget solar, apart from running 12 volt lighting, possibly to power a pump for water, and to use an old fashioned range for cooking & heating, make the most of passive heat collecting windows (we have them in our garden room), and either having a borehole or filtering & treating rainwater. |
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Lorrainelovesplants
Joined: 13 Oct 2006
Posts: 6521
Location: Dordogne
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Slim
Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)
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| Posted: Tue Jul 25, 17 4:37 pm Post subject: |
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Just as a BTW, solar thermal hot water is no longer as cost effective as solar pv panels plus heat pump water heaters, and solar pv plust heat pump setups will likely get even more cost effective as the price of solar panels continues to fall. https://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-really-really-dead
The above example will likely give you some stuff to think about as you write....
OK, here I'm about to get rambly, but read on if you're interested:
I'm curious about your book and its aims. I try to blend greater self-sufficiency with greater community sufficiency, and feeding my excess solar electric production back into the grid off-sets the higher cost peak electrical demand for my municipal utility is part of that, as I see it. If I truly wanted to be self-sufficient, I could also purchase a tesla powerwall (or 2) which could theoretically store a normal day's power usage (or more) for me and have a grid disconnect wired up so that I can isolate my home from the grid in the case of an outage, but as I stated above, I'd prefer to not have that expense and help lower everyone's rates by supplying power approximately when our utility most needs it and has to purchase power from the wholesale market at a greater cost than they normally produce it (sunny summer days).
As it is, I'm having heat-pump water heaters installed for my apartment and my for my tenant's apartment (duplex). That will allow us to ditch the gas service for the tenant's apt, and reduce our own gas usage.
That would necessitate at least a second(third?) powerwall if I was trying to be completely off-grid, and possibly a third(fourth? - can't be bothered with that math right now).
I'm keeping an eye closer on the tesla solar roofs, as I don't have much other property space for more panels, and have a 100+ year old roof that will likely need replacing at some point. If that were the case, I would immediately yank out the gas heater that heats my apartment, put in a mini-split heat pump, and a couple resistance baseboard heaters as back-up/supplemental heating for the coldest months, and subsequently be supplying, or at least off-setting all of my power usage, and likely all of my tenant's power usage.
I see the above as self-sufficiency, and going carbon neutral (though my municipal power company is already 100% renewable electric). It may not yield as high a return as a traditional stock market investment, but I would be covering all of our heating, hot water, and normal domestic electrical needs, as well as a necessary roof replacement, and that would essentially be free after the needed loans are paid back (with no utility/heating costs from then on). It would likely be enough power to include all utilities in the higher rent from the tenant (and thereby pay back the solar loan faster) and likely would have enough power left over to provide for an electric bike so that I could ditch my car.
So, that's my grand on-grid self-sufficiency vision. Is that less self-sufficient than being off-grid? Clearly self-sufficiency can mean a lot of things, but if you're not looking to towards the future with a grid-tied setup like this, than aren't you just re-hashing what everyone else has said about off-grid living for decades? (i.e., thermal battery, passive solar gain, etc....) |
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Slim
Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)
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Slim
Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)
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Lorrainelovesplants
Joined: 13 Oct 2006
Posts: 6521
Location: Dordogne
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| Posted: Tue Jul 25, 17 6:25 pm Post subject: |
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The whole self sufficiency thing has been a large part of our lives.
We have always been thrifty, but wanted to live a simpler life, which isnt always easy when you have a mortgage, 2 kids and need transport in a county that really (really) doesnt do public transport).
We have a house with 1.2 acres, so whatever we did had to be pretty intensive as any number of livestock is really a non starter.
This site helped me loads when we started out, and Ive learned loads, and made some nice (and really supportive) friends.
We used recycled water to wash our apples and equipment when we made cider, tried to get community funded solar panels for our holding (just when the FITS thing collapsed here and the community interest company decided it wasnt feasible), installed the 2 heating systems to reduce our reliance on LPG. Replaced all our lights (inside & out) with LED's.
We downsized to one car, produced a lot of our own meat, eggs, alcohol, apple juice, fruit, veg and nuts. Ditched the tumble drier in favour of polytunnel drying in summer & pulley over the woodburner in winter.
As a FE teacher Ive run loads of courses on the stuff we do and other people want to learn. Its great that people care and want to make a difference.
We really do live very self sufficiently. Im proud of it. Im extra proud of my lovely son, who is at Manchester Uni doing Geography and wants to work in flood control and possibly drought prevention. He sings from the same book as me.
I was delightfully surprised and emotional when in 2014 I was awarded Cornwall Sustainability Awards Best Individual , and then at the start of this year I was asked to write a book on sustainable and profitable smallholding. And thats kind of where we are at the mo.
Apart from packing like crazy as we leave this house in less than 3 weeks! |
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Slim
Joined: 05 Mar 2006
Posts: 6612
Location: New England (In the US of A)
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dpack
Joined: 02 Jul 2005
Posts: 46207
Location: yes
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| Posted: Tue Jul 25, 17 7:03 pm Post subject: |
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| Lorrainelovesplants wrote: |
DPack - can I just confirm I understand the first bit of explanation you did in this thread -
Unfortunately most appliances and power tools rely on mains voltage � 240V AC (alternating current). Sadly PV is always DC (direct current) and storing power in batteries is always DC. So this necessitates the use of a transformer or inverter to convert the load and lose a some power (can be up to 50%) whilst doing so.
is this correct? |
yep, is the simple answer, why follows.
inverters convert between dc and ac and transformers convert ac voltage to a different voltage, they sometimes come in the same box eg 12 car battery to 240v ac
a power supply unit (charger ) might just convert dc to a different voltage eg 12v to 6v as in a car lighter charger for a phone
or might convert 240v ac to whatever v dc to charge the battery for something like a drill or a toothbrush.
motors are ac (either single or 3 phase, unless you have a semi industrial power supply dont worry about 3 phase stuff) or dc , whichever they are they will only work with the correct type of leccy (ac or dc) at the correct voltage for that design of motor
most uk stuff will require 240v ac to make it work either directly or by powering it's charger/power supply unit.
some stuff has a multi input power supply for mains 240ac or car 12v dc (and sometimes 110v ac )as the power source.
a few things can accept a different input which is another layer of complication
american kit is usually 110v ac so plugging it into EU 240ac supplies gets rather exciting
a rather neat trick is to check the specifications of a bit of kit as quite a few things have internal power supply units that plug into 240v ac but the working parts use a different voltage and perhaps use it as dc (pooters for instance) this does give some scope for avoiding inverters and going direct from a dc supply to the inside of the machine.
tis best to know what you are doing with this type of "make it work somehow" as out of service and on fire is easy to do 
unless you want to become a mad max style electrical engineer it is best to get off the shelf kit that will provide 240v ac (110 in the us ) and either stores it domestically before turning it into ac or uses the grid as a storage facility.
the first costs more to install, the second costs more to run ( see 2p to 14 p as above ).
off grid you need storage for PV or wind but a constant flow of water could be considered to be it's own storage battery. a dam might be required( think small mill pond rather than hoover)
water is good so long as you have gravity and water,
it can be a lot (or a bit ) of water moving slowly or a bit (or a lot )moving fast.
various kit is available to suit what you have
archimedes screws and paddle wheels for low speed/pressure ie a stream on fairly flat land,
turbines for high speed/pressure ie a stream and a mountain.
water require quite a bit of engineering, dams ,races or pipes etc etc as well as the moving bits/generator unit.
again it can be mad maxed but that would be beyond most folk.
with water there is still the issue of converting what is produced to what is needed in terms of voltage and ac or dc
water isn't cheap unless you mad max it via scrapheap challenge, a pit and tarp up the hill etc etc |
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dpack
Joined: 02 Jul 2005
Posts: 46207
Location: yes
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