Solar organic garden

Re: Solar organic garden

Icarus/Tony is correct... For any practical use of solar panels for green house "grow" lighting of plants--it will be pretty much cost prohibitive...

But, we can always give it a shot.

First, we need to make some assumptions.

1. Lights--the most efficient lamps for "grow-lights" are not full spectrum but HP Sodium in conjunction with natural lighting... So, lets assume 100 watt HID lamp for supplemental lighting a 3'x3' area for 12 hours per day.

100 watts * 12 hours = 1.2 kWhr per day.

Now--lets also assume that you are doing this to get an early start on the season rather than trying to raise plants in the dead of winter.

From this link, we will figure out how much in solar panels you will need in February to start your seedlings (as you head into summer, you will get more sun).

Assume that you will be using batteries and an 120 VAC inverter, plus charge controller... Use a derating factor of 0.52 (based on losses of listed components):

A 1kW fixed mount solar array in Vancouver BC, will produced an average of 36 kWhrs in a month, or, on average 1.2 kWhr per day. (lucky guess).

So, for this system, you will need a 1,000 watt solar array, and for a battery bank:

(1,200 watts / 12 volts) * 3 days of no sun * 1/50% max discharge = 600 amp*hours at 12 volt.

Of course, we can play with the solar panels (tilt them up in winter and down in summer to get more power). But--we have the bare bones of a system here...

5x 205 watt panels for $4,600
1X 80 AMP Outback charge controller $580
Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC $259
12x Crown 225 Amp-Hour 6 Volt deep cycle battery 6 Volt Golf Car Battery $1,329
Wiring, timer, frame, concrete, fuses, panel ~$500 (place holder)

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Total (excluding shipping, taxes and duties)= $7,268

Note: Batteries will last approximately 3-7 years before replacement is needed.

At least this gets you into the ball park (soccer pitch?) for approximate cost of a system to power a 3'x3' seedling bed.

And just for fun... What would a system that ran for three months using a gas genset to power 100 watts of lights look like (and pump the CO2 and waste heat from the generator into the greenhouse for better growing conditions):

1x Honda eu1000i (900 watt) $700
Roughly 5kWhrs per gallon of gas. 4x 12 hour days of runtime per gallon (should power 200 watts of lights or 3'x6' bed).

90 days / 4 days per gallon * $4.50 per gallon = $101 worth of fuel...

For less than $1,000 USD, you can build and run a twice as large "fossil fueled" bedding green house with a brand new generator every year (even at $9.00 per gallon gas prices--sorry for the US gallons and pricing--I don't know your fuel/parts costs up there in BC).

Of course, the two solutions are not equivalent... The solar one would work 9 months out of the year--the fossil fueled one I sized for 3-6 months of the year. And I know that you would not want to go with a gasoline genset to run your green house--but many parts of the world do exactly this.

Just trying to scope the problem out here... The devil is in the details.

But, truly, if you only want the grow lamps for a limited time of the year (early spring), and you have utility power available (i.e., home garden)--the "greenest" way is utility power... And look at Solar Grid tie for your home. Solar PV is best used when you have a 9-12 month of the year load--which grid tie with net metering is the best solution... And use solar thermal design for your green house to warm up the soil (if needed in your area).

-Bill