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Grid Connect Sizing
The limiting factors for a grid connected solar PV
system are usually the maximum available sunny area for the siting of a
PV array combined with the budget available! Since all energy can be
used (surplus going to the grid if necessary) and all needs met
(shortfall coming from the grid as required) sizing based on critical
load patterns is not necessary. Instead, comparison of potential energy
generation (kWh) can be made with energy usage - found on one’s
electricity bill (1 unit = 1 kWh).
In common with off-grid systems - energy conservation
and efficiency is a pre-requisite step to obtaining energy
self-sufficiency. Once electricity requirements have been reduced
through efficiency, it is much easier (and cheaper) to meet those
requirements through on-site PV generation.
-
For most
of the UK there are on average approx. 4-5 peak sun hours in summer
going down to an average of 1 hour in winter.
-
For well
sited grid connected PV arrays - 1kWp will produce ~ 800kWh (units)
per year.
-
Installed
cost for 1kWp PV system is approx. £5-6,000.00.
 If mounting a PV array on a roof then the first step is
to determine how many and which type of PV module fits into the
available roof space.
It is important to avoid any areas that are
shaded by obstructions such as chimneys, other parts of the building or
trees & aerials. (at any time of the year).
The
Solar Horizon Estimator is a useful tool in assessing this.
A margin should be allowed around the PV array to reduce
wind loadings and to enable access.
Once the PV array area has been determined, then the
number of modules is matched to inverters and mounting frame dimensions,
to decide upon the most cost effective and efficient system.
Measuring Power Consumption
Before deciding to invest in a renewable energy
system it is vital to first of all find out how much and where energy is
being used and then conserve any energy that might be being wasted. For
appliances that switch on & off automatically (eg. fridges & freezers)
measurement over time is necessary.
Many appliances use energy when you think they are
switched off eg. televisions on Standby or washing machines, computers &
chargers left switched on at the wall. It is not uncommon to find that
some appliances (eg. TV’s) use more energy over a 24hr period when
switched off (but left plugged in) than when being used. To check for
these ‘Phantom’ loads consumption meters can be used to detect where
electricity is being wasted and offending items switched off at the wall
when not in use.
The efficiency of different appliances can be
compared to ensure power is used sensibly and inefficient ones replaced
where necessary. This investigation is invaluable to either reduce
electricity bills or to make off-grid electricity systems more
successful.
A watt saved is a watt that doesn’t need to be
generated!
After a renewable energy system is installed it is
just as important to monitor consumption. Consumption can then be
compared with production to ensure self-sufficiency.
Energy Monitors
Powermeter
 This is a plug-in meter that measures the energy
consumption of an individual appliance.
Simply plugs in between the
appliance and a socket to give power & cumulative energy consumed.
Especially useful to measure energy consumption of items such as
fridges.
Electrisave
 Monitors the total energy consumption of a household or building
allowing wastage to be eliminated. Displays electricity consumption,
cost & associated CO2 emissions, together with temperature & humidity.
Audible alarm can be set for excess consumption. Uses a clip on wireless
transmitter sensor and portable LCD display with a range of 30m. Extra
sensors needed for 2 or 3 phase supplies
See Also:
Grid Connect Accessories for other electricity consumption
(kWh) meters.
Output
 Performance can vary according to geographical area and orientation.
In order to estimate approximate yearly output:
(1)
Find the peak power (kWp) of the array to be installed,
(2)
Identify your location on the solar radiation map and it’s annual energy
production (kWh/kWp).
(3)
Identify the Correction Factor for required orientation.
Total Annual Energy Production =
(1) x
(2) x (3)
Approx. annual energy production in kWh for
a 1kWp PV system.
South facing, unshaded & 35º tilt
| Tilt
Angle ( º ) |
Average Irradiation Correction
Factor For Different Tilt & Orientation (Azimuth)
|
|
Orientation
from South ( Azimuth Angle in º ) |
|
0
(South) |
10 |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90
(East/West) |
| 0-10 |
90.1% |
90.1% |
90% |
89.7% |
89.3% |
88.9% |
88.4% |
87.9% |
87.3% |
86.6% |
| 11-20 |
96.5% |
96.3% |
95.7% |
95% |
93.7% |
92.4% |
90.7% |
88.8% |
86.8% |
84.8% |
| 21-30 |
99.2% |
99% |
98.3% |
97.1% |
95.5% |
93.4% |
91% |
88.3% |
85.4% |
82.5% |
| 31-40 |
100% |
99.7% |
98.8% |
97.4% |
95.4% |
92.9% |
90% |
86.7% |
83.2% |
79.4% |
| 41-50 |
99% |
98.7% |
97.7% |
96.1% |
94% |
91.4% |
88.2% |
84.6% |
80.9% |
76.8% |
| 51-60 |
94.2% |
93.9% |
93% |
91.4% |
89.1% |
86.2% |
82.8% |
79% |
75% |
70.7% |
| 61-70 |
88.5% |
88.3% |
87.3% |
86% |
83.6% |
80.9% |
77.5% |
73.8% |
69.8% |
65.7% |
| 71-80 |
81.1% |
80.9% |
80.5% |
78.8% |
77.3% |
73.8% |
71.2% |
67.8% |
64.1% |
60.1% |
| 81-90 |
72.3% |
72.1% |
71.6% |
70.5% |
68.9% |
66.7% |
64.1% |
61% |
57.6% |
54.3% |
A
useful tool for estimating monthly output using sunlight data for
anywhere in Europe and Africa is available
here.
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