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Maximum Power Point Tracking for Solar Applications (and tomatoes!)

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thedatastream

Wed Aug 08 2007, 01:13PM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

For anyone interested in this subject, I found a good paper describing several different ways of implementing MPPT systems

http://energy.ece.uiuc.edu/chapman/papers/EC%202006%20in%20press.pdf

I'm going to be implementing a MPPT scheme for a solar powered battery charger I'm working on and this paper was the best of the ones I've found. I'm going to use a small micro and probably implement a hill climbing / P+O control method.

James

Sulaiman

Wed Aug 08 2007, 01:31PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Seems a logical choice. (hill climbing / P+O)

Will the solar panel also be steerable for max power?

thedatastream

Wed Aug 08 2007, 03:08PM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

No, it's going to be stuck to my 45Âº angled, south facing greenhouse window (I want to keep it as simple as possible). This will charge the SLA battery that is going to power my irrigation system for my tomatoes

yum!

I would quite like to make a heliostat out of an old satellite dish, some mirrors and a few other bits. You can then use the Solar Positioning Algorithm to point it in the correct direction. However that's a real "blue sky" project (pun intended)

Sulaiman

Wed Aug 08 2007, 03:37PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Just a brief straying off topic - please excuse.....
I too planted tomatoes this year! 3 plants each of 5 varieties
being planted outside they've had PLENTY irrigation with this year's weather - what happened to global warming?

Back on topic -
one of the many (pick any very large number) projects I want to do is
a solar powered VRLA 12V 7 AH battery charger for my shed/workshop.
Which PIC are you using / could you share circuit and code once working?

thedatastream

Wed Aug 08 2007, 07:37PM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

Excellent stuff, can't beat homegrown tomatoes!

What varieties have you planted? We've got 4 Moneymaker, 2 cherry and 1 plum plants all in the greenhouse. and the moneymakers are starting to come in nicely now. They've got big due to the lack of sun and have only just started going red but they are very nice! Besides I've changed topic so that tomatoes are a perfectly acceptable side discussion

I was intending to use a 6V, 4Ah Yuasa SLA battery being charged by a Texas Instruments BQ2031 battery charger evaluation board. This will be run from a 17V 3W solar panel and I was going to use an Atmel ATtiny26L AVR to be the supervisor and MPPT controller.

The BQ2031 charger regulates the voltage and the micro adjusts the charging current using a PWM output, integrated to DC and fed in through a resistor to the current sense node.

The main watering controller will be an ATmega16 (lots of GPIO + 7 ADCs for soil moisture sensors) with a DS1305 RTC to tell it when to water - 5am is supposed to be the optimum watering time cos you don't want the roots sitting in water all night.

I'll post the C source code and the cicuit once it's complete

James

Sulaiman

Wed Aug 08 2007, 10:35PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Wow! That's a high-tech setup for tomato growing
(sure you are not using hydroponics, aluminium foil and indoor lighting?)

As for the battery charger I don't think I'll copy you as I'm just getting into Microchip PIC programming in assembly
and I don't want to learn another architecture and especially not C for now,
this will just remain on my project wish list I think.

I'm growing
Gardeners Delight - a lovely cherry tomato that I grew last year which made me want to try others this year
also Alicante , Tigerella , Marmande and San Marzano

Last year I relied only on rain and a heavy rain after a dry spell caused the tomatoes to split
so I can see the benefit of controlled irrigation - this year I shall not let the soil dry out.
When I water the garden it is almost always in the morning rather than the evening, mainly to reduce slug damage.
I predict lots of sunshine in August and September so we should have plenty of ripe tomatoes.

I'd learn C++ or even LISP or Pascal if you come up with a microcontroller that can hunt down and destroy slugs!

thedatastream

Thu Aug 09 2007, 06:52AM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

I think our cherrys are Gardeners Delight too, I look forward to them coming on.

The splitting problem (due to uneven watering) is the problem we had last year due to someone (i.e. me) negelecting their watering duties!

I'm going to be making some raised beds for vegetables sometime this year and I was contemplating putting an electric fence made of copper foil around the beds run from a solar panel / SLA / micro arrangement. I think I'll wait and see how well the slugs destroy my first crop before I take that one any further!

Electroholic

Thu Aug 09 2007, 10:29PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

this is one of the best MPPTs around.

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