Solar requirements - hydroponic grow lights

[Marleyuk]

Afternoon all,

I run a small hydroponic farm and I’m interested in exploring the potential for solar to provide some of, if not all of the power required to generate my grow lights.

The lights I use are 28w LED’s that run for 18 hours per day.

I currently have 60 of these lights, and would be really interested in understanding what kind of solar setup would be required to provide sufficient power to keep these off the main grid.

Thanks

Ian

 

[binky]

28x60 = 1.68kW. What about pumps, filters etc, lights aren't your only electric demand. 

What I would suggest as a 'starter for 10', is installing an East-West array (assuming a suitable roof space) to spread energy production over the day, get an earlier start in the morning and later finish at night, but avoiding having a big peak of electric mid-day. With the FiT being so low, energy saving is the key to a good installation for you. Previously, when the FiT was far higher, we used to target that, with energy saving as a bonus, and use the money to cover the bills.  Don't expect to generate everything you use, to do that would require a much larger array to cover the winter months and possibly the installation of battery storage, which is expensive stuff, dearer than the panels.

 

[Marleyuk]

Thanks for the reply.

There would also be 6 * 30w water pumps running for roughly 20 minutes per day. 

No additional lighting is required but I do have a small water heater, although this isn’t used very regularly, and finally 2 * 30w fans.

With regards to the solar panels, if for example we had 4kw worth of panels, what would the usual power generation be through summer months compared to winter? I.e would 4kw panels generate at roughly 50% (2kw?!). I’m trying to work out if I went heavy on panels could I offset the poorer performing seasons?

Thanks,

Ian

 

[Rob.]

What is it you're growing? 

 

[Marleyuk]

Edible flowers - mainly pansies

 

[Blue Duck]

With a name like Marley and a question about hydroponics it's easy to make assumptions but....

http://uk.businessinsider.com/local-roots-hydroponic-shipping-container-farm-spacex-2017-12

 

[Marleyuk]

With a name like Marley and a question about hydroponics it's easy to make assumptions but....

http://uk.businessinsider.com/local-roots-hydroponic-shipping-container-farm-spacex-2017-12

it’s a good Irish name but I see how you can come to alternative conclusions!

 

[Marleyuk]

The article you have linked to is very similar farm concept to mine (although slightly smaller) but this doesn’t expand much of the solar generation aspect?

 

[binky]

a 4 kw array will generate around 4000kWh per year and around 15-30 kWh per day for about half the year (weather dependent of course). A recent 4kW array I fitted just before xmas is doing about 10kWh per day currently, when the sun is out. Depending on your roof spave and connections to the national grid a slightly larger split array might work better for you given the steady base load that you have. You could also fit a Solic 200 to divert surplus energy to your water heater, assuming it has a storage tank. Expect to pay around £6-7k for the 4kW system, using all German parts. I normally fit Q-Cell panels and SMA inverters. If you need to build a ground array, a simple wooden frame that you can build yourself is cheaper than off the shelf frames.

you can have a look at other peoples systems here https://www.sunnyportal.com/templates/publicpagesplantlist.aspx

 

[Marleyuk]

Thanks Binky.

Given the amount of energy it’s producing, would you recommend a battery to harness the surplus energy? 

 

[binky]

Hmmm, be careful with batteries, given your long hours it may work for you. I need to do some seriuos reading up on batteries, the oleder units just didn't pay for them selves, so, being the sort of fella that I am, I've never sold or fitted any. What you have to watch is the number of charge cycles which varies with the chemical composition of the battery. Now, this has improved a lot over the last fey years to around 10,000 charge cycles for a battery maker called Sonnen (German). 

Easy calculation:- number of charge cycles x kw of batteries x electric tariff. so say you pay 15p per kwh and had a 6kW battery, then that is offering £9k (max)saving over its life span. But a 6kW battey can be around £5k fitted, so that's only a £4k saving max. However your system is only likely to charge and discharge once a day, so if you divide £4k by the max daily saving (6kWh x 15p) its going to take 12 years to get your money back. Inflation will reduce that time as energy costs rise, but batteries work better for systems where the load can increase notably several times a day, eg put washing machine on a for a few hours, drain battery, charge it up again and then say cook dinner to flatten it again. That sort of cycle would retun 6 years to pay for itself. Also, given that you are a business you may well be on a higher user tariff like 10 or 11p per kWh, so it reduces the financial benefits further.  To me batteries are a nicety for those with surplus cash who hate paying any money to electric companies!

 

[Marleyuk]

Hmmm, be careful with batteries, given your long hours it may work for you. I need to do some seriuos reading up on batteries, the oleder units just didn't pay for them selves, so, being the sort of fella that I am, I've never sold or fitted any. What you have to watch is the number of charge cycles which varies with the chemical composition of the battery. Now, this has improved a lot over the last fey years to around 10,000 charge cycles for a battery maker called Sonnen (German). 

Easy calculation:- number of charge cycles x kw of batteries x electric tariff. so say you pay 15p per kwh and had a 6kW battery, then that is offering £9k (max)saving over its life span. But a 6kW battey can be around £5k fitted, so that's only a £4k saving max. However your system is only likely to charge and discharge once a day, so if you divide £4k by the max daily saving (6kWh x 15p) its going to take 12 years to get your money back. Inflation will reduce that time as energy costs rise, but batteries work better for systems where the load can increase notably several times a day, eg put washing machine on a for a few hours, drain battery, charge it up again and then say cook dinner to flatten it again. That sort of cycle would retun 6 years to pay for itself. Also, given that you are a business you may well be on a higher user tariff like 10 or 11p per kWh, so it reduces the financial benefits further.  To me batteries are a nicety for those with surplus cash who hate paying any money to electric companies!

Thank you very much for coming back so comprehensively on the above post - I was meant to come back on it sooner but I’ve been pretty manic trying to master grow cycles for various produce types.

I suppose going against the traditional approach, I’m less focused on the cost benefit and more the environment - albeit if it’s considerably more expensive that would be a problem!

Have you had much experience with solar trackers - and if so, is the energy yield notably more beneficial for the additional cost?

 

[binky]

Too much money. It's easier and cheaper to arrange split fixed array to give wider energy spread. East-West works very well for reducing electric bought, as it starts earlier in the morning, finishes later at night, and gives more even spread of energy over the day. Some of these that I've installed only lose about 5% against due South. 

Nothing environmentally friendly about batteries - all those rare metals and chemicals...