RHI payments on Solar Drying

[Woodworks]

I can't see how solar could be much use at this time of year. I don't know the in and outs of solar thermal but a quick search suggest that down here in December the amount of energy per m2 from the sun peeks at 0.65kWh. Looking at the biomass kilns they are using 180 kWh 24-7 So with 100% efficient panels you could meet the kins needs briefly in the middle of the day with 276m2 of panels!

 

This is where I plucked the numbers from Solar Irradiance Calculator - Useful Sun power tool

[arboriculturist]

I can't see how solar could be much use at this time of year. I don't know the in and outs of solar thermal but a quick search suggest that down here in December the amount of energy per m2 from the sun peeks at 0.65kWh. Looking at the biomass kilns they are using 180 kWh 24-7 So with 100% efficient panels you could meet the kins needs briefly in the middle of the day with 276m2 of panels!

 

This is where I plucked the numbers from Solar Irradiance Calculator - Useful Sun power tool

 

Agreed, as December one of the worst months.

 

You will generate an average of approx 1.95 kWh per day (24 hr period) per m3 of panel in the UK. (Based on average Solar thermal efficiency of 75%)

 

So a 2.5Kw panel can generate 4.88 Kw per day.

 

Anyone care to comment?

[renewablejohn]

I can't see how solar could be much use at this time of year. I don't know the in and outs of solar thermal but a quick search suggest that down here in December the amount of energy per m2 from the sun peeks at 0.65kWh. Looking at the biomass kilns they are using 180 kWh 24-7 So with 100% efficient panels you could meet the kins needs briefly in the middle of the day with 276m2 of panels!

 

This is where I plucked the numbers from Solar Irradiance Calculator - Useful Sun power tool

 

Thats like comparing the energy requirements of a stewpot on an open fire to that of a slow cooker. What you must remember is the kilns you referred to are not designed to kiln dry wood efficiently only to screw the current RHI system with the most inefficient kiln they can get away with, I am very surprised ofgem have allowed such kilns when on the domestic tariff you have to have a minimum insulation requirement.

[renewablejohn]

How many panels should I be looking at for a 20ft hi-cube container - thinking around 12?

 

Not entirely sure how they are rated per panel.

 

Cant answer that as it will depend on the amount of insulation and your heat recovery system. Certainly on my system 12 x 30 tube panels would be more than adequate.

[skyhuck]

Thats like comparing the energy requirements of a stewpot on an open fire to that of a slow cooker. What you must remember is the kilns you referred to are not designed to kiln dry wood efficiently only to screw the current RHI system with the most inefficient kiln they can get away with, I am very surprised ofgem have allowed such kilns when on the domestic tariff you have to have a minimum insulation requirement.

 

Yes your home is assessed but that is because the system is not metered but based on the heating requirements of your home, you may be asked to improve insulation, but not always.

[farmer rod]

Agreed, as December one of the worst months.

 

You will generate an average of approx 1.95 kWh per day (24 hr period) per m3 of panel in the UK. (Based on average Solar thermal efficiency of 75%)

 

So a 2.5Kw panel can generate 4.88 Kw per day.

 

Anyone care to comment?

 

for clarity a 2.5kW panel would generate 4.88 kWh per day

[arboriculturist]

Cant answer that as it will depend on the amount of insulation and your heat recovery system. Certainly on my system 12 x 30 tube panels would be more than adequate.

 

It is a standard insulated container, with 300mm of additional insulated cladding in addition.

 

15 x 30 panels.

 

H stat. to control vent fans when internal reaches pre-determined RH level

 

Looking at 10-14 days to lower MC from 50-60 to 20-25.

 

Do you think that is achievable?

[renewablejohn]

It is a standard insulated container, with 300mm of additional insulated cladding in addition.

 

15 x 30 panels.

 

H stat. to control vent fans when internal reaches pre-determined RH level

 

Looking at 10-14 days to lower MC from 50-60 to 20-25.

 

Do you think that is achievable?

 

10-14 days to bring the moisture down from 50-60 to 20-25 is easy to achieve but your design needs to follow commercial kiln technology of high temperature making the most of the 6 bar capability of solar tubes rather than the low temperature of the typical biomass boiler kiln discussed previously on the forum. Also there is no point in having a high temperature kiln if you then just vent that heat to the atmosphere so a heat recovery system is vital.

[openspaceman]

for clarity a 2.5kW panel would generate 4.88 kWh per day

 

 

That clarifies the difference between units of power and units of energy but if my experience with PV panels is anything similar to the proposed solar thermal tube panels then energy output on a dull December day will be less than 5% of that on a sunny mid summer day.

 

We got 18 tonnes of 60% moisture content wood into our container, to reduce this to 25% requires the removal of 8400kg of water. To do this at perfect efficiency in 14 days requires a thermal input of 384kWh per day but this assumes air entering the system leaves it at the same temperature but more saturated. In practice you need a higher temperature to not only reduce the RH of the air in the system but to increase the water movement from the wood.

Edited November 30, 2014 by openspaceman

[renewablejohn]

I used this as my guide for adopting a high temperature kiln

 

http://www.firewoodkiln.com/pdf/fplrn254.pdf