Use SolarView (solarview.niwa.co.nz) to access information on the solar radiatio

Question

Use SolarView (solarview.niwa.co.nz) to access information on the solar radiation for 730 Cumberland St, North Dunedin, Dunedin 9016 in Dunedin, New Zealand. Use this data to calculate:

• The total heat energy you can extract per year assuming a 60% efficient 2.5 m2 evacuated tube solar hot water system with a hot water storage tank.

• The percentage of hot water demand this is able to meet for a typical household in Dunedin. (A standard household in Dunedin uses about 14,000 kWh/year of energy and about 20% of this is for hot water).

• The difference in energy recovered on a summer and a winter day. Explain what difficulties this difference may cause.

Explanation / Answer

from the solarview data for solar radiation for 730 Cumberland St, North Dunedin, Dunedin 9016 in Dunedin, New Zealand

1. CUmulative solar power per unit area for all months of the year is

(4.77 + 4.35 + 3.83 + 2.84 + 1.97 + 1.74 + 2.12 + 2.76 + 3.73 + 4.41 + 4.61 + 4.64) = 41.77 kWh/m^2 year

per dfay average = 3.48 kWh/m^2

given area, A = 2.5 m^2

so, Energy, E =3.48*2.5 = 8.702 kWh per day

for 60 percent efficientcy

E' = 5.22125 kWh energy can be extracted

2. energy used for hot water per day = 0.2*14000/365 = 7.671 kWh

energy from solar energy = 5.22125 kWh

percentage energy requirement = 5.22125*100/7.671 = 68.0627 percent

3. energy recieved in summer day = 4.77 kWh/m^2

energy reieved in winter day = 1.74 kWh/m^2

this causes problems as in winters very less amount ofg eater can be heate4d to meed requirements where as in summers more than 100 percent of the requirement of the water heat is met. this inconsistency makes solar water heaters useless inwinters and hence impacting their feasibhility

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