[Urban Solar Water Heating]
Product Information, Economics, Power Output, Individual Possibilities, National Benefits, The Future, Manufacturers
The initial concept of solar water heating was discussed as part of the Passive-Solar section in the introductory guide. Using the data from the sections on Module Inclination and Data Acquisition an assumption can now be made on the effectiveness of a solar flat plate collector in an urban environment. For the given results we will examine how much energy the sun’s heat can displace, using the formulas illustrated in the beginner’s guide.To reduce the power requirements for water heating it may be viable to consider solar water heating. The solar water heating installation would generally comprise a roof-mounted solar collector that would heat the water, which would then be pumped through a second coil in the storage cylinder to pre-heat the water. A typical solar water heating installation would have 0.75m² of collector panel per person in the household, normally with a minimum area of approx 3m² for the most cost effective system. In order to calculate the potential we first needed to select a suitable collector and obtain the relevant product data regarding its performance.
A
high efficiency flat plate collector manufactured by AES was chosen, manufactured
at Findhorn, near
Abosrber area=2.75 m2Collector
‘U’ value= 5 W/m2K
Collector Absorptance (a)= 0.95
Transmissivity of cover (t)= 0.85
Collector Efficiency= 0.84
Cylinder Capacity= 140 litres
Installed
Cost= £ 1950 (+Vat)= £ 2291 = £833 m2
(http://www.unlimited-power.co.uk)
From this information the daily power supplied by the solar water collector can be calculated and also the water temperature of the hot water cylinder.
Q(supply) = Power supplied,
Water Temp (Tc)=277°K (4°C)(273°K = 0°C)
(assumes initial daily water temperature of 4°C – temperature of cold mains water)
AES flat plate collector / valves / pumps £1350
1 cylinder £40
Additional pipe work / fittings / fixtures £10
Installation £500
Annual Maintenance £50
Total Installed Cost =£ 1950 (+Vat)= £ 2291
These calculations are to provide an approximation to the expected costs and performance from a solar water system installed in a Scottish urban environment. The calculations make the approximation that the solar panel is facing south. Modules facing any other direction will receive less power.
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Using the
irradiance figures from the Pyranometer and the calculations as explained in
the Beginners Guide, the estimated power
output of the solar collector can be demonstrated. The
average daily energy produced from the solar collector panel during the winter
months is 2.73 kWh per 2.75 m2. (0.99kWh per m2) The total energy
produced over a period of 50 days (during four month period) by the 2.75m2 flat
plate collector was 137kWh. From this we can conclude that over the course of
a year the panel could hope to produce; = (365/50) x 136.5 = 996.45
kWh The
AES panel would have produce around 1000kWh in a year – using the winter irradiance
values. Remember the figures used for calculations were from December to
March, summer irradiation levels would be greater due to the increased levels
of sunshine during the summer months. From this increase it would be expected
that more water could be heated due to increased irradiation levels – however
households tend to use less hot water during the summer when solar collectors
can supply most energy.
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The increase
in average daily irradiance can be seen from the graph below. Using the yearly
average we can approximate how much energy is likely to be saved by a solar
collector in a year – assuming 2.73kWh/m2 falls every day.
The
average daily power output of the collector (2.75m2) should be 2.73 kWh
x 2.75m2 = 7.51 kWh per day on the collector. This figure assumes
that all the heat from the sun is useful and is directly transferred to the
cylinder; it is ignoring any losses that may occur – pre-heat losses. This figure
must be altered to take into account such losses and is usually altered by the
solar fraction, which is the ratio of the useful solar output to the total load,
which is equal to the proportion of the hot water energy load that the system
supplies. For our example we will assume that the Solar Fraction is 55%. 1 Using
this figure we can calculate the average daily energy output of the collector 0.55
x 7.51kWh = 4.1305 kWh on flat plate collector daily.
2
Typically one household would have a 2.75m2 kW installation this would require a 10m2 PV array area. Taking the assumed figure from Data Acquisition = 110W/m2 This would result in an electricity production of; = 4.13 (kWh) x 365 (days)= 1507.63 kWh /year
Cost of gas = 1.2pence per kWh
Saving per annum= 1507.63 x 0.012= £18.09 per 2.75m2
Assume
that every household in
To
date, there has been a negligible uptake of solar water heating in the new-build
sector. This is despite the fact that the installation of solar water heating
systems at the new-build stage is the most cost-effective approach to utilising
solar energy in houses. House builders generally have a resistance to new investments
that increase the costs of building houses. The present low levels of
public awareness and the effectiveness of solar water heating in the
There
are many different types of flat plate collectors but there are few manufacturers
in
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List of possible
contacts;
Home, Beginners Guides, Urban, Passive ,Passive solar, Data Acquisition, Urban PV, Module Inclination
