I have an interest in solar power and have an i2c temperature and barometer sensor.
What do people think of the following specification for an arduino project? Feasible/unfeasible/ never going to do anything useful
Hardware inputs
calibrated temperature and barometer pressure
uncalibrated linear solar panel voltage and linear solar panel current at mpp
calibrated local time and calender date
Fixed inputs
Latitude and longitude
solar panel orientation (compass and elevation)
CPU
A 328 arduino
Desired outputs
The expectation (+-40%) of "hours of sunlight" remaining today (now to midnight)
The expectation (+-60%) of "hours of sunlight" tomorrow (midnight to midnight)
If it is sunny now but the temperature is changing and the barometer falling rapidly, then the expectation of hours of sun remaining today is going to be a lot less than the hours of daylight remaining.
If the barometer is doing nothing much but the calender says December, then both expectations are less than the hours of daylight by some fraction which is known from historic stats of December weather.
Has anyone done something like this before on arduino?
Do you think that it is feasible? Do you think that it would be useful? Where do you think I should look for relevant weather stats?
If your weather is variable (as in the UK and Ireland) I don't think local meteorological data will provide a useful basis for forecasting even one day ahead.
You would be better to write a screen scraper to pick up reliable met-office forecasts. In my experience the UK Met Office has good forecasts for up to 5 days ahead but I don't think even that pretends to forecast percentage cloud cover. And Met Office forecasts depend on "awesome" computer power.
This isn't a proper forecast from thousands of boat and sattelite data collectors from the Atlantic to the Baltic going through a supercomputer. This is arduino automation of the local decision from looking at one local barometer for
A) "looks like a nice day for solar panels. switch everything on and use up batteries"
vs
B) "barometer has been falling over the past few hours, expect poor weather, switch off discretionary loads and store solar power when possible, expecting not much sun over the next day or so"
And it being standalone, there is nothing to stop it from recieving a count of the fraction of yellow pixels in a proper weather forecast obtained online, and using that instead if available.
When it is sometimes wrong, it will either empty the batteries the day before a murky horrid day or fill them up and be miserly the day before a lovely sunny day. The worst consequence of incorrect barometer decision would be that the extra functions of my solar don't help the next day. The normal part of the grid tied solar is not looking at this arduino anyhow.
I had assumed that you were thinking along those lines and my earlier comment about the poor ability to make a useful forecast without a supercomputer was made in that context.
My sense is that your "forecast" won't be any better than not having that forecast whereas using a "proper" Met Office forecast might be a little better than no forecast.
I use solar panels to reduce the use of a diesel generator. They allow me to run my generator for a shorter period at the end of a sunny day. My battery system is sufficient to deal with my needs regardless of the amount of solar energy that is available on any particular day.
How about monitoring the output of the panels and using them when the output is above some threshold. You could buy a smaller solar panel that you monitor in real time for output then you would only turn on the larger array when the smaller one is above some threshold.
Robin2:
Why not just use all the power thay can produce rather than take the trouble to monitor them just for the purpose of not using some of their power?
...R
The grid tied pv does use all the power which they can produce, and that is the default condition. ..give away free kWh to a commercial electric company who'll sell it to my neighbour for 14p/kWh. My other thing can choose to divert power into batteries instead, which I tend to use at night time. If the batteries are full then most power goes out to national grid, so "sunny weather forecast" implies that I may as well use up as much as possible, as I'll get it back for free tomorrow. "barometer low and falling" implies that I should only use battery power tonight where it is most useful to me, as I expect less than typical tomorrow.
ad2049q:
The grid tied pv does use all the power which they can produce, and that is the default condition. ..give away free kWh to a commercial electric company who'll sell it to my neighbour for 14p/kWh. My other thing can choose to divert power into batteries instead, which I tend to use at night time. If the batteries are full then most power goes out to national grid, so "sunny weather forecast" implies that I may as well use up as much as possible, as I'll get it back for free tomorrow. "barometer low and falling" implies that I should only use battery power tonight where it is most useful to me, as I expect less than typical tomorrow.
In no particular order...
If you can put some of that electrical energy in a bucket I wll pay 100p/kWh for it (and consider it good value).
I thought the Grid paid for surplus power?
Are you saying that there are electrical applications that you don't use if you have to buy power from the grid for them?
I think a more logical approach would be to use the batteries if they are "full" and then if there is insufficient sun to recharge them tomorrow, don't use them again until they are full. That way your usage is based on actual rather than predicted sunshine.
How much energy are you storing in and withdrawing from the batteries? 1 kWhr per charge or more?
wwbrown:
You could buy a smaller solar panel that you monitor in real time for output then you would only turn on the larger array when the smaller one is above some threshold.
wade
My "smaller solar panel" is 2V little thing recycled from a scrap garden lamp, whose circuits were pulled out and replaced with one 220 Ohm resistor. It gets to about 1.5 Volts in direct sun implying 6mA.
Sunny now but barometer is 980 and falling implies a bit less expectation of hours of sunlight over the next day than sunny now and barometer doing nothing much. So I'd change my decision thresholds to aim to fill batteries now while it is sunny rather than aim to empty them by dawn.