Sizing off-grid systems in Ireland
Siddhartha
I live in Dublin, Ireland. I am designing a off-grid photovoltaic
system for a remote home. While going through the solar insolation
data for Dublin, I found that there is a big difference in the
insolation level between summer and winter months. The worst month is
December and the solar insolation is for that month is only 0.465 KWh/
m2 (source: ISPRA website). The highest insolation month is June and
the corresponding solar insolation is 4770 KWh/m2 (source: ISPRA
website). generally the off-grid photovoltaic array is sized based on
worst month insolation. But if I size based on december month, it will
generate 10 times more energy in the month of June.
Please let me know how to optimize the sizing, so that it will give
sufficient energy to the load all round the year. Please also let me
know whether off-grid photovoltaic system is a economically viable
source of energy or not.
Regards.
Sid
Eeyore
Siddhartha wrote:
> Hi,
>
> I live in Dublin, Ireland. I am designing a off-grid photovoltaic
> system for a remote home. While going through the solar insolation
> data for Dublin, I found that there is a big difference in the
> insolation level between summer and winter months. The worst month is
> December and the solar insolation is for that month is only 0.465 KWh/
> m2 (source: ISPRA website).
That's horribly low.
> The highest insolation month is June and
> the corresponding solar insolation is 4770 KWh/m2 (source: ISPRA
> website). generally the off-grid photovoltaic array is sized based on
> worst month insolation. But if I size based on december month, it will
> generate 10 times more energy in the month of June.
Yes.
> Please let me know how to optimize the sizing, so that it will give
> sufficient energy to the load all round the year. Please also let me
> know whether off-grid photovoltaic system is a economically viable
> source of energy or not.
You need to size it to supply enough energy to feed the required loads
even under minimum insolation conditions. You have discovered the achilles
heel of PV solar in northern climes.
Graham
Ron Rosenfeld
<siddha...@gmail.com> wrote:
>Hi,
>
>I live in Dublin, Ireland. I am designing a off-grid photovoltaic
>system for a remote home. While going through the solar insolation
>data for Dublin, I found that there is a big difference in the
>insolation level between summer and winter months. The worst month is
>December and the solar insolation is for that month is only 0.465 KWh/
>m2 (source: ISPRA website). The highest insolation month is June and
>the corresponding solar insolation is 4770 KWh/m2 (source: ISPRA
>website). generally the off-grid photovoltaic array is sized based on
>worst month insolation. But if I size based on december month, it will
>generate 10 times more energy in the month of June.
>
>Please let me know how to optimize the sizing, so that it will give
>sufficient energy to the load all round the year.
1. Minimize your electrical usage by all the energy saving methods you can
think of. CFL's; energy efficient appliances; etc.
2. There is no way around the fact that, if you are going to use the
property in December, you are going to have to have a system that will
provide the necessary amount of energy in December. If you only have 0.5
kWh/m2/day during December, and you are using 5kWh/day, you will need at
least 10kW of panels (actually more once you figure in losses and
efficiency issues).
3. You could consider other sources of electricity for this property --
e.g. wind, micro-hydro, fossil-fuel generator, etc.
>Please also let me
>know whether off-grid photovoltaic system is a economically viable
>source of energy or not.
You'll have to tell us what you mean by "economically viable". Certainly,
you can compare the cost of grid-extension vs the cost of doing your own
system. Add in the "cost of money" and you can see which one is less
expensive.
HOMER, a free program from www.nrel.gov/homer can compare the costs of
various systems, including all of the above and more, vs the cost of grid
extension.
--ron
Eeyore
Ron Rosenfeld wrote:
> Siddhartha wrote:
> >
> >I live in Dublin, Ireland. I am designing a off-grid photovoltaic
> >system for a remote home. While going through the solar insolation
> >data for Dublin, I found that there is a big difference in the
> >insolation level between summer and winter months. The worst month is
> >December and the solar insolation is for that month is only 0.465 KWh/
> >m2 (source: ISPRA website). The highest insolation month is June and
> >the corresponding solar insolation is 4770 KWh/m2 (source: ISPRA
> >website). generally the off-grid photovoltaic array is sized based on
> >worst month insolation. But if I size based on december month, it will
> >generate 10 times more energy in the month of June.
> >
> >Please let me know how to optimize the sizing, so that it will give
> >sufficient energy to the load all round the year.
>
> 1. Minimize your electrical usage by all the energy saving methods you can
> think of. CFL's; energy efficient appliances; etc.
>
> 2. There is no way around the fact that, if you are going to use the
> property in December, you are going to have to have a system that will
> provide the necessary amount of energy in December. If you only have 0.5
> kWh/m2/day during December, and you are using 5kWh/day, you will need at
> least 10kW of panels (actually more once you figure in losses and
> efficiency issues).
And don't forget the cloudy days. I'll bet that figure is an average of
something like 900Wh one day and 100 Wh the next day.
> 3. You could consider other sources of electricity for this property --
> e.g. wind, micro-hydro, fossil-fuel generator, etc.
Wind's an obvious, esp if near the coast.
> >Please also let me
> >know whether off-grid photovoltaic system is a economically viable
> >source of energy or not.
>
> You'll have to tell us what you mean by "economically viable". Certainly,
> you can compare the cost of grid-extension vs the cost of doing your own
> system. Add in the "cost of money" and you can see which one is less
> expensive.
Viable would seem to me to depend on how deep the pockets are. As it doesn't
seem to be a new build from the OP's post, the hope of needing only 5kWh/day
seems remote. A multifuel stove (coal + wood) for space and water heating
would seem to be an essential.
Graham
Ron Rosenfeld
<rabbitsfriend...@hotmail.com> wrote:
>> 2. There is no way around the fact that, if you are going to use the
>> property in December, you are going to have to have a system that will
>> provide the necessary amount of energy in December. If you only have 0.5
>> kWh/m2/day during December, and you are using 5kWh/day, you will need at
>> least 10kW of panels (actually more once you figure in losses and
>> efficiency issues).
>
>And don't forget the cloudy days. I'll bet that figure is an average of
>something like 900Wh one day and 100 Wh the next day.
Once I looked more closely at the data, I realized that the value the OP
was quoting probably referred to irradiance on a horizontal surface.
Insolation values, at least from the tables I've seen, do include cloudy
days. They take an average for the time period -- usually over ten or more
years.
Using the NREL database, and the lat/long of Dublin, for the month of
December the variability seems to be from about 25-900 Wh, with 3-4 day
stretches close to the lower level.
The values given for insolation, at least in the NREL database, are for a
horizontal surface. At Dublin's latitutde, with a panel tilted at the
angle of the latitude, the incident radiation on the solar panel is much
higher in December than is the global solar insolation (flat panel).
Running the simulations through HOMER, I find the following for December
(entire month) in Dublin:
Global Solar insolation (horizontal surface):
16 kWh/m^2 for Dec (0.500 kWh/m^2/day)
With Panel tilted at latitude + 15°; with azimuth of true solar south:
Incident Solar: 37 kWh/m^2 for Dec (1.203 kWh/m^2/day)
Again, assuming a 5kWh/day energy use:
If we derate the panel to 80% to account for for such factors as soiling of
the panels, wiring losses, shading, snow cover, aging, and so on; figure
inverter efficiency of 90%, and include an appropriately sized battery bank
(11 days of autonomy, in this case); it seems we could "get by" with 6kWp
of solar panels.
Using a set of more basic spreadsheets supplied by BP solar, along with
their insolation maps, I come up with similar results, so that number is
probably correct, given the conditions described.
In the US, you could probably have such a system installed for about
$60,000(USD).
I don't know what the OP's energy use will be, or what installation costs
will be around Dublin. But the costs should scale fairly directly with the
energy use, if he sticks with a pure PV system.
It seems to me that $60K USD is pretty expensive for 5kWh/day.
If he is using say 20kWh/day, and has good wind resource in the winter,
some kind of hybrid system might be preferable. And he might be better
off, in that instance, with a different tilt on his panels (e.g. latitude -
15°). He might also be able to get by with a relatively smaller battery
bank.
--ron
spaco
The "0.465 KWh/m^2" seems to mean that during December, the average
DAILY insolation is 465 watt hours on a one meter square surface.
But isn't there a missing decimal point on the second number? Shouldn't
it be "4.770 KWh/m^2"?
Next, is that total insolation or is it the photovoltaic energy
gathering capability of some modern panels?
I'll bet that your data is for total insolation, and bears only a 1/7th
or 1/8 resemblance to what you'd get from photovoltaic sources.
If I am wrong, I am willing to learn,
Pete Stanaitis
------------------------
Ron Rosenfeld
wrote:
>I don't understand your figures.
>The "0.465 KWh/m^2" seems to mean that during December, the average
>DAILY insolation is 465 watt hours on a one meter square surface.
Provided that surface is horizontal on the earth's surface (see below)
>
>
>But isn't there a missing decimal point on the second number? Shouldn't
>it be "4.770 KWh/m^2"?
Undoubtedly.
>Next, is that total insolation or is it the photovoltaic energy
>gathering capability of some modern panels?
>
>I'll bet that your data is for total insolation, and bears only a 1/7th
>or 1/8 resemblance to what you'd get from photovoltaic sources.
>
>If I am wrong, I am willing to learn,
Here's one way to look at the information:
1. From another source (NREL), I see similar figures and they are for the
daily radiation on a *horizontal* surface
Dec: 0.500 kWh/m2/day
Jun: 4.350 kWh/m2/day
For a surface tilted at the Dublin latitude, the irradiation on that tilted
surface would be:
Dec: 1.174 kWh/m2/day
Jun: 3.797 kWh/m2/day
Panels are usually rated based on standard test conditions (meaning a
radiation of 1 kW/m2, a cell temperature of 25°C, and no wind). So a panel
array rated at 1kW would produce, under STC, during December near Dublin,
angled at 53° from the horizontal, and with an azimuth of due south, 1.174
kWh/day.
Its physical size would depend on its efficiency, so a panel with a rating
of 1kW, and an efficiency of 13%, would use an area of approximately 7.7m2.
If it had a lower efficiency but the same 1kW rating, it would be a
physically larger panel, but should still produce the same.
In the real world, the STC rating needs to be adjusted to account for
environmental factors such factors as temperature (difference from STC
temps), soiling of the panels, wiring losses, shading, snow cover, aging,
and so on. 20% should be an appropriate derating factor here, although
specific local conditions, and temperatures, might cause that to vary.
--ron
Eeyore
Ron Rosenfeld wrote:
> Eeyore wrote:
>
> >> 2. There is no way around the fact that, if you are going to use the
> >> property in December, you are going to have to have a system that will
> >> provide the necessary amount of energy in December. If you only have 0.5
> >> kWh/m2/day during December, and you are using 5kWh/day, you will need at
> >> least 10kW of panels (actually more once you figure in losses and
> >> efficiency issues).
> >
> >And don't forget the cloudy days. I'll bet that figure is an average of
> >something like 900Wh one day and 100 Wh the next day.
>
> Once I looked more closely at the data, I realized that the value the OP
> was quoting probably referred to irradiance on a horizontal surface.
>
> Insolation values, at least from the tables I've seen, do include cloudy
> days. They take an average for the time period -- usually over ten or more
> years.
>
> Using the NREL database, and the lat/long of Dublin, for the month of
> December the variability seems to be from about 25-900 Wh, with 3-4 day
> stretches close to the lower level.
Sounds quite likely.
> The values given for insolation, at least in the NREL database, are for a
> horizontal surface. At Dublin's latitutde, with a panel tilted at the
> angle of the latitude, the incident radiation on the solar panel is much
> higher in December than is the global solar insolation (flat panel).
>
> Running the simulations through HOMER, I find the following for December
> (entire month) in Dublin:
>
> Global Solar insolation (horizontal surface):
> 16 kWh/m^2 for Dec (0.500 kWh/m^2/day)
>
> With Panel tilted at latitude + 15°; with azimuth of true solar south:
> Incident Solar: 37 kWh/m^2 for Dec (1.203 kWh/m^2/day)
OK.
> Again, assuming a 5kWh/day energy use:
Which is VERY low for winter.
> If we derate the panel to 80% to account for for such factors as soiling of
> the panels, wiring losses, shading, snow cover, aging, and so on; figure
> inverter efficiency of 90%, and include an appropriately sized battery bank
> (11 days of autonomy, in this case); it seems we could "get by" with 6kWp
> of solar panels.
>
> Using a set of more basic spreadsheets supplied by BP solar, along with
> their insolation maps, I come up with similar results, so that number is
> probably correct, given the conditions described.
>
> In the US, you could probably have such a system installed for about
> $60,000(USD).
>
> I don't know what the OP's energy use will be, or what installation costs
> will be around Dublin. But the costs should scale fairly directly with the
> energy use, if he sticks with a pure PV system.
>
> It seems to me that $60K USD is pretty expensive for 5kWh/day.
I couldn't agree more.
> If he is using say 20kWh/day, and has good wind resource in the winter,
> some kind of hybrid system might be preferable. And he might be better
> off, in that instance, with a different tilt on his panels (e.g. latitude -
> 15°). He might also be able to get by with a relatively smaller battery
> bank.
Depending on location, wind turbine 'backup' would very sensible. Indeed the
turbine might end up being the primary source of power.
For space heating he's got to be thinking heat pump or a good old multifuel
stove with back water heater.
Graham
Ron Rosenfeld
<rabbitsfriend...@hotmail.com> wrote:
>For space heating he's got to be thinking heat pump or a good old multifuel
>stove with back water heater.
Is wood practical in that part of the world? I've seen some neat, outdoor,
wood boilers that work well (if you've got the energy to keep them supplied
with wood). One fellow I know has a lot of trees that he's slowly clearing
(as they need to be), so has a good source. He uses a propane heater for
backup. The system is hydronic.
Do you have any information on the electric consumption of a heat pump
system vs a propane boiler? I much prefer hydronic heat to FHA.
--ron
Eeyore
Ron Rosenfeld wrote:
> Eeyore wrote:
>
> >For space heating he's got to be thinking heat pump or a good old multifuel
> >stove with back water heater.
>
> Is wood practical in that part of the world?
Absolutely. I converted a friend of mine to one and he got free offcuts from a
local joinery. Kept his home warm as toast for the cost of picking the stuff up.
They burn coal too.
> I've seen some neat, outdoor,
> wood boilers that work well (if you've got the energy to keep them supplied
> with wood). One fellow I know has a lot of trees that he's slowly clearing
> (as they need to be), so has a good source.
Never known anyone in the UK with an outdoor bolier/furnace/stove.
> He uses a propane heater for backup. The system is hydronic.
I'm not familiar with the term hydronic. Ah I see. It's the norm here. Hence my
mention of the 'back boiler' for a stove.
> Do you have any information on the electric consumption of a heat pump
> system vs a propane boiler? I much prefer hydronic heat to FHA.
Well the heat pump has a huge efficiency gain (forget what they call it now).
Propane's expensive here too.
Graham
Ron Rosenfeld
<rabbitsfriend...@hotmail.com> wrote:
>> He uses a propane heater for backup. The system is hydronic.
>
>I'm not familiar with the term hydronic. Ah I see. It's the norm here. Hence my
>mention of the 'back boiler' for a stove.
When we've been looking at recently built homes, it seems most in this area
use forced hot air. I suppose that makes it simpler if you are also doing
air conditioning, but the one time I lived in a home with FHA heating,
neither I nor my wife liked it at all. Our current dwellings have hydronic
systems.
>
>
>> Do you have any information on the electric consumption of a heat pump
>> system vs a propane boiler? I much prefer hydronic heat to FHA.
>
>Well the heat pump has a huge efficiency gain (forget what they call it now).
>Propane's expensive here too.
I know the heat pump is supposed to be very efficient, compared with other
heating methods. But since I'm off-grid and have to generate my own
electricity, that's the first important number for me. I've not been able
to locate any good data for that.
If I have to generate more electricity to use less propane, my cost
considerations will be different than it might be for those on-grid.
--ron
Siddhartha
> On Sun, 07 Sep 2008 13:47:57 +0100, Eeyore
>
I think based on the given climatic conditions in Dublin, the best way
would be to put a pv-wind hyrid off-grid system. Both wind turbine and
pv system can compliment each other and will give the best output.
Please let me know what should be the nergy ratio of the wind-pv hyrid
system? Should I design for 50:50 wind-pv hybrid or something else.
How to size a perfect wind-pv hybrid system?
- Sid
Ron Rosenfeld
<siddha...@gmail.com> wrote:
>I think based on the given climatic conditions in Dublin, the best way
>would be to put a pv-wind hyrid off-grid system. Both wind turbine and
>pv system can compliment each other and will give the best output.
>Please let me know what should be the nergy ratio of the wind-pv hyrid
>system? Should I design for 50:50 wind-pv hybrid or something else.
Probably something else. Actually, given the information you have
provided, it is completely unknown.
>How to size a perfect wind-pv hybrid system?
What do you mean by "perfect".
If you mean "most economical but will supply all, or most of, my power",
that will depend on a number of factors including energy usage, solar
resource, wind resource, cost of components and installation. You may also
need to factor in the cost of a backup generator, and the cost of its fuel.
I guess from your response that you have not yet looked at the HOMER
program to which I referred you in my first response. It has all the
detail you will need to properly size a system, EXCEPT for your cost of the
components and installation. It also does not have the wind resource for
your location.
Those you will have to obtain yourself, and then provide those inputs to
the program.
--ron
bea...@gmail.com
Now that you have enough BS to grow your veggies for a year you might
want to take a serious look at what you are asking.
Step One - Work out your daily load.
Step Two - Size a system to meet the daily load.
Step Three - Cost resulting system.
Step Four - Do your nut about the cost and rant to anybody that will
listen about the thieving bastards that are trying to rip you off.
Step Five - Compare cost of system with cost of grid connection.
Step Six - Rant some more.
Step Seven - Repeat steps one, two and three, adjusting your loads in
step one to reduce the load.
Learn the difference between "Wants" and "Needs". Do steps 1 - 2 - 3
with only the things you "Need" to stay alive. Then you can add the
things you would like to have if possible in your budget.
Eeyore
Siddhartha wrote:
> I think based on the given climatic conditions in Dublin, the best way
> would be to put a pv-wind hyrid off-grid system. Both wind turbine and
> pv system can compliment each other and will give the best output.
> Please let me know what should be the nergy ratio of the wind-pv hyrid
> system? Should I design for 50:50 wind-pv hybrid or something else.
> How to size a perfect wind-pv hybrid system?
Why don't you just go LEARN something about it instead of expecting everyone to do it
for you ?
Then you might realise how STUPID an idea it is.
YOU WILL NEED A STOVE to keep warm in winter.
Graham